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RFC 3423 - XACCT's Common Reliable Accounting for Network Elemen


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Network Working Group                                           K. Zhang
Request for Comments: 3423                                      E. Elkin
Category: Informational                               XACCT Technologies
                                                           November 2002

     XACCT's Common Reliable Accounting for Network Element (CRANE)
                   Protocol Specification Version 1.0

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document defines the Common Reliable Accounting for Network
   Element (CRANE) protocol that enables efficient and reliable delivery
   of any data, mainly accounting data from Network Elements to any
   systems, such as mediation systems and Business Support Systems
   (BSS)/ Operations Support Systems (OSS).  The protocol is developed
   to address the critical needs for exporting high volume of accounting
   data from NE's with efficient use of network, storage, and processing
   resources.

   This document specifies the architecture of the protocol and the
   message format, which MUST be supported by all CRANE protocol
   implementations.

Table of Contents

   1  Introduction...................................................2
      1.1  Specification of Requirements.............................3
      1.2  Terminology...............................................3
   2  Protocol Overview..............................................5
      2.1  CRANE Architecture........................................6
      2.2  CRANE over TCP............................................7
      2.3  Alternate servers.........................................7
      2.4  Templates.................................................9
      2.5  Template Transmission and Negotiation....................10
      2.6  Changing Templates.......................................11
      2.7  Flow Control.............................................12
      2.8  The CRANE Client Query Messages..........................13

      2.9  CRANE Sessions...........................................13
   3  CRANE Message Format..........................................14
   4  CRANE Messages................................................16
      4.1  Flow Start (START).......................................16
      4.2  Flow Start Acknowledge (START ACK).......................16
      4.3  Flow Stop (STOP).........................................17
      4.4  Flow Stop Acknowledge (STOP ACK).........................17
      4.5  Connect (CONNECT)........................................18
      4.6  Template Data (TMPL DATA)................................18
      4.7  Template Data Acknowledge (TMPL DATA ACK)................23
      4.8  Final Template Data (FINAL TMPL DATA)....................25
      4.9  Final Template Data Acknowledge (FINAL TMPL DATA ACK)....26
      4.10  Get Sessions (GET SESS).................................26
      4.11  Get Sessions Response (GET SESS RSP)....................27
      4.12  Get Templates (GET TMPL)................................30
      4.13  Get Templates Response(GET TMPL RSP)....................30
      4.14  Start Negotiation (START NEGOTIATE).....................33
      4.15  Start Negotiation Acknowledge (START NEGOTIATE ACK).....34
      4.16  Data (DATA).............................................34
      4.17  Data Acknowledge (DATA ACK).............................36
      4.18  Error (ERROR)...........................................37
      4.19  Status Request (STATUS REQ).............................38
      4.20  Status Response (STATUS RSP)............................38
   5  Protocol Version Negotiation..................................39
   6  Security Considerations.......................................42
   7  References....................................................43
   8  Acknowledgments...............................................43
   9  Authors' Addresses............................................44
   10 Full Copyright Statement......................................45

1  Introduction

   Network Elements are often required to export usage information to
   mediation and business support systems (BSS) to facilitate
   accounting.  Though there are several existing mechanisms for usage
   information export, they are becoming inadequate to support the
   evolving business requirements from service providers.

   For example, some of the export mechanisms are legacies of the Telco
   world.  Typically usage information is stored in Network Elements as
   Log files (e.g., CDR files), and exported to external systems in
   batches.  These are reliable methods, however, they do not meet the
   real-time and high-performance requirements of today's rapidly
   evolving data networks.

   RADIUS [1] is a widely deployed protocol that may be used for
   exporting usage information.  However, it can only handle a few
   outstanding requests and is not extensible due to its limited command

   and attribute address space.  RADIUS also does not support
   unsolicited messages from a server to a client.  A detailed analysis
   of limitations of RADIUS can be found in [3].

   DIAMETER [2] is a new AAA protocol that retains the basic RADIUS
   model, and eliminates several drawbacks in RADIUS.  The current
   DIAMETER protocol and its extensions focus on Internet and wireless
   network access, and their support to accounting is closely associated
   with authentication/authorization events.  DIAMETER is intended to
   solve many problems in the AAA area; by doing so, it does not
   adequately address some critical issues such as efficiency and
   performance in an accounting protocol.

   There are also SNMP based mechanisms that generally require a large
   amount of processing and bandwidth resources.

   Based on the above analysis, a critical need for a reliable, fast,
   efficient and flexible accounting protocol exists.  The XACCT's CRANE
   protocol is designed to address these critical requirements.

   This document defines the CRANE protocol that enables efficient and
   reliable delivery of any data, mainly accounting data from Network
   Elements to any systems, such as mediation systems and BSS/OSS.  The
   protocol is developed to address the critical needs for exporting
   high volume of accounting data from NE's with efficient use of
   network, storage, and processing resources.

   This document specifies the architecture of the protocol and the
   message format, which MUST be supported by all CRANE protocol
   implementations.

1.1 Specification of Requirements

   In this document, the keywords "MUST", "MUST NOT", "SHOULD", "SHOULD
   NOT", and "MAY" are to be interpreted as described in BCP 14 [5].
   These keywords are not case sensitive in this document.

1.2 Terminology

   CRANE Protocol

      CRANE stands for Common Reliable Accounting for Network Element.
      The CRANE Protocol maybe referred as CRANE, or the Protocol in
      this document.  The CRANE Protocol is used at the interface(s)
      between a CRANE client and one or multiple CRANE servers for the
      purpose of delivering accounting data.

   Client or CRANE Client

      A CRANE Client is an implementation on the data producing side of
      the CRANE protocol.  It is typically integrated with the network
      element's software, enabling it to collect and send out accounting
      data to a mediation/billing system using the protocol defined
      herein.

   Server or CRANE Server

      A CRANE Server is an implementation on the data receiving side of
      the CRANE protocol.  It is typically part of a Business Support
      System (BSS) (e.g., Billing, Market Analysis, Fraud detection,
      etc.), or a mediation system.  There could be more than one CRANE
      server connected to one CRANE client to improve robustness of the
      usage information export system.

   CRANE Session

      A CRANE Session is a logical connection between a CRANE client and
      one or multiple CRANE servers for the purpose of delivering
      accounting data.  Multiple sessions MAY be maintained concurrently
      in a CRANE client or a CRANE server; they are distinguished by
      Session IDs.

   Server Priority

      A CRANE server is assigned with a Priority value.  Accounting data
      is always delivered to the perceived operating CRANE server (from
      the CRANE client point of view) with the highest Priority value
      (the primary server) within a CRANE Session.

   Message

      A Message is encoded according to rules specified by the CRANE
      protocol and transmitted across the interface between a CRANE
      client and a CRANE server.  It contains a common CRANE header and
      optionally control or user data payload.

   Data Record

      A Data Record is a collection of information gathered by the
      Network Element for various purposes, e.g., accounting.  The
      structure of a Data Record is defined by a Template.

   Template

      A Template defines the structure of any types of Data Record, and
      specifies the data type, meaning, and location of the fields in
      the record.

   Data Sequence Number (DSN)

      An accounting Data Record level sequence number, which is attached
      to all data messages to facilitate reliable and in-sequence
      delivery.

2  Protocol Overview

   The CRANE protocol is designed to deliver accounting data reliably,
   efficiently, and quickly.  Due to the nature of accounting data,
   large records often need to be transmitted; thus supporting
   fragmentation of large records is required.  Furthermore, the value
   associated with accounting data is high; to prevent data loss, quick
   detection of unresponsive CRANE servers is also required for added
   robustness.

   The CRANE protocol can be viewed as an application that uses the data
   transport service provided by lower layer protocols.  It relies on a
   transport layer protocol to deliver reliable, in-sequence data
   packets.

   UDP is a simple connectionless transport layer protocol that has
   advantages of being fast and agile, but it provides no reliability
   and lacks flow control mechanisms.  Hence, The CRANE protocol must
   not use UDP as the transport layer protocol to avoid the risk of
   adversely impacting the networks it is being run over.

   TCP and SCTP [4] are two transport layer protocols that fulfill the
   reliability requirement of CRANE.  Either one of them MAY be used to
   transport CRANE messages.  TCP meets some of the requirements, but
   not all (e.g., quick detection of server failure, the fact that TCP
   is stream oriented and not record oriented).  Therefore, SCTP [4] is
   the preferred way to transmit CRANE messages.

2.1 CRANE Architecture

   The CRANE protocol is an application running over a reliable
   transport layer protocol.  The transport layer protocol is
   responsible for delivering CRANE messages between CRANE clients and
   CRANE servers.  It MUST support the following capabilities:

   1. Reliable, in-sequence message delivery.
   2. Connection oriented.
   3. Delivery of messages with a length of up to 2^32 octets (i.e., the
      transport layer has to support fragmentation of messages when
      running over IP).

   The transport layer MAY support:

   1. Authentication.
   2. Bundling of multiple messages into a single datagram.

   Possible transport layer protocols MAY be TCP or SCTP [4].  TCP
   supports the minimal requirements for CRANE, but lacks some desirable
   capabilities that are available in SCTP, these include:

   1. Session level authentication.
   2. Message based data delivery (as opposed to stream based).
   3. Fast connection failure detection.

   Reliable delivery of accounting data is achieved through both the
   transport layer level and the CRANE protocol level.  The transport
   layer acknowledgments are used to ensure quick detection of lost data
   packets and unresponsive servers, while the CRANE protocol
   acknowledges CRANE messages after they have been processed and the
   accounting information has been placed in persistent storage.

   Being a reliable protocol for delivering accounting data, traffic
   flowing from a CRANE client to a CRANE server is mostly accounting
   data.  There are also bi-directional control message exchanges,
   though they only comprise of small portion of the traffic.

   The following diagram illustrates the CRANE protocol architecture:

       +----------------+             +----------------+
       |    CRANE       |             |     CRANE      |+
       |    User        |             |     User       ||+
       +----------------+             +----------------+||
       |    CRANE       | ==========> |     CRANE      |+|
       |    Client      | <---------- |     Server     ||+
       +----------------+             +----------------+||
       |  Transport     |             |   Transport    |+|
       |    Layer       | <---------> |     Layer      ||+
       +----------------+             +----------------+||
       |    Lower       |             |     Lower      |+|
       |    Layers      | <---------> |     Layers     ||+
       +----------------+             +----------------+||
                                       +----------------+|
                                        +----------------+

2.2 CRANE over TCP

   TCP can be used as a transport layer for the CRANE protocol.  CRANE
   running over TCP MUST conform to the following rules:

   1. The CRANE client MUST accept TCP connections over a specific TCP
      port.
   2. The CRANE server MUST connect to the CRANE client, and SHOULD be
      responsible for reestablishing a connection in case of a failure.
   3. CRANE messages are written as a stream of bytes into a TCP
      connection, the size of a CRANE message is specified by the
      Message Length field in the CRANE message header.

2.3 Alternate servers

   For purposes of improved reliability and robustness, redundant CRANE
   server configuration MAY be employed.  The CRANE protocol supports
   delivering accounting data to alternate CRANE servers, which may be
   part of a mediation system or a BSS.

   A CRANE session may comprise of one or more CRANE servers.  The CRANE
   client is responsible for configuring network addresses of all CRANE
   servers belonging to the session.  A Server Priority is assigned to
   each CRANE server.  The Server Priority reflects the CRANE client's
   preference regarding which CRANE server should receive accounting
   data.  The assignment of the Server Priority should consider factors
   such as geographical distance, communication cost, and CRANE server
   loading, etc.  It is also possible for several CRANE servers to have
   the same priority.  In this case, the CRANE client could randomly
   choose one of them as the primary server to deliver accounting data.

   Additional features such as load balancing may be implemented in a
   multi-server environment.  The process of configuring CRANE client is
   carried out using the NE's configuration system and is outside the
   scope of this document.

   A CRANE client MUST deliver accounting data to its perceived
   operating CRANE server with the highest priority; if this CRANE
   server is deemed unreachable, the CRANE client MUST deliver the
   accounting data to the next highest priority CRANE server that is
   perceived to be operating.  If no perceived operating CRANE servers
   are available, accounting data MUST be queued in the CRANE client
   until any CRANE server is available or the client's queue space runs
   out.  An alarm should be generated to inform the CRANE user of the
   queue overflow condition.

   Accounting data delivery SHOULD revert to the higher priority server
   when it is perceived to be operating again.

   The CRANE protocol does not specify how a CRANE client should
   redirect accounting data to other CRANE servers, which is considered
   an implementation issue.  But all the supporting mechanisms are
   provided by the protocol to work in a multiple-server environment
   (e.g., the template negotiation process, and configuration
   procedures, etc.).  The transport layer (together with some other
   means) is responsible for monitoring server's responsiveness and
   notifying CRANE protocol for any failures.  The client may choose to
   transition to an alternate server.

   Implementation Note:

      The transition to an alternate CRANE server is an implementation
      issue and should occur under the following conditions:

      A) Transport layer notifies the CRANE client that the
      corresponding port of the CRANE server is unresponsive.

      B) Total size of unacknowledged accounting records has exceeded a
      threshold (configurable) for certain duration (configurable).

      C) A STOP message is received from the active server.

      D) A lower priority server is the active one and a higher priority
      server has recovered.

2.4 Templates

   The CRANE protocol enables efficient delivery of accounting data.
   This is achieved by negotiating a set of Data Templates for a CRANE
   session before actual accounting data is delivered.   A data template
   defines the structure of a DATA message payload by describing the
   data type, meaning, and location of the fields in the payload.  By
   agreeing on session templates, CRANE servers understand how to
   process DATA messages received from a CRANE client.  As a result, a
   CRANE client only needs to deliver actual accounting data without
   attaching any descriptors of the data; this reduces the amount of
   bytes sent over communication links.

   A template is an ordered list of keys.  A key is the specification of
   a field in the template.  It specifies an accounting item that a
   network element MAY collect and export.  The specification MUST
   consist of the description and the data type of the accounting item.
   (e.g., 'Number of Sent Bytes'  can be a key that is an unsigned
   integer of 32 bit long).  A CRANE client typically defines keys.

   The CRANE protocol supports usage of several templates concurrently
   (for different accounting records).  Keys contained in a template
   could be enabled or disabled.  An enabled key implies that the
   outgoing data record will contain the data item specified by the key.
   A disabled key implies that the outgoing record will omit the
   specified data item.  The enabling/disabling mechanism further
   reduces bandwidth requirement; it could also reduce processing in
   network elements, as only needed data items are produced.

   In a CRANE session, all the CRANE servers and the CRANE client MUST
   use the same set of templates and associated enable/disable status.
   The templates' configuration and connectivity to an end application
   MUST be the same in all servers.  The CRANE client MUST publish the
   relevant templates to all CRANE servers in a session through user
   configuration, before it starts to send data according to the
   templates.

   The complete set of templates residing in a CRANE client MUST bear a
   configuration ID that identifies the template set.  Each data record
   is delivered with the Template ID and the Configuration ID, so that
   the correct template can be referenced.  A server, when receiving a
   record with an older Configuration ID, MAY handle the record
   gracefully by keeping some template history.  The transport layer
   should ensure that a server would not get messages with future
   configuration IDs.

2.5 Template Transmission and Negotiation

   As stated before, all CRANE servers MUST use the same set of
   templates in a CRANE session.  In case that servers do not share the
   same set of templates (the templates are considered different if
   different keys are enabled or disabled), a negotiation process
   between the client and the server would ultimately determine one set
   of templates that is accepted and used by all the CRANE servers in a
   session.

   After a CRANE session is established and the server sent a START
   message indicating that it is ready to take part in the session, the
   client MUST deliver the set of templates that it intends to use by
   sending a TMPL DATA message to the server.  The CRANE server MUST
   acknowledge the reception of the set of templates.

   Templates are negotiable between a CRANE client and CRANE servers.  A
   CRANE server may propose changes to the templates received from a
   CRANE client (e.g., enabling some keys and disabling others), or it
   can acknowledge the templates as is.  In the case that a template or
   a key is not recognized by the server (e.g., they might be added to
   the client after the server configuration has completed), the server
   MAY choose to disable each unknown key or unknown templates in order
   to avoid unnecessary traffic.  A template is disabled when all the
   keys are disabled.  If changes were received from the CRANE servers,
   the client will send the changed template set to all connected
   servers (using FINAL_TMPL_DATA message).  It is the client's
   responsibility to decide what would be the final set of templates
   used by a session.  At this time, each CRANE server MUST accept and
   acknowledge the templates without changing anything (to avoid
   deadlock and loop conditions).  Each CRANE server is given a single
   chance to propose any changes during the negotiation process.

   The template negotiation process is outlined as follows:

   A) CRANE client sends a TMPL DATA message with a set of templates.

   B) CRANE server either responds with the TMPL DATA ACK message with
   changes in the template set (process continues in step C) or responds
   with FINAL TMPL DATA ACK message if no changes are needed (process
   continues in step E).

   C) CRANE client receives proposed changes, incorporates them if
   possible and then sends a FINAL TMPL DATA message containing the new
   set of templates to all servers (in order to deploy the change).

   D) CRANE server receives the FINAL TMPL DATA message containing the
   new set of templates and MUST send a FINAL TMPL DATA ACK message to

   acknowledge the reception of the templates.  No changes are allowed
   at this stage and the templates, which the client sent, are going to
   be used.

   E) CRANE client receives a FINAL TMPL DATA ACK message from the
   server and can assume that the server knows which templates to use.

   All these stages take place only when there are multiple CRANE
   servers with differences in the template set (e.g., not all key
   states are identical).  If all CRANE servers within a session share
   the same configuration exactly, all servers will respond with FINAL
   TMPL DATA ACK and the ping-pong between the client and the servers
   will end immediately.  This is the common case, but in case some
   other CRANE servers have a different configuration, the protocol
   offers the way to maintain consistency among CRANE servers.

   Implementation Note:

      TMPL DATA messages SHOULD be sent only after all DATA messages
      with the previous configuration have been acknowledged.  This
      ensures the server to transition properly to the new
      configuration.

2.6 Changing Templates

   Though TMPL DATA messages allow for deploying and publicizing
   template, a need to configure the template set still exists.  Each of
   the CRANE servers in a CRANE session may change the template set,
   which is typically requested by an end-user through User Interface.
   If the end-users need to know what templates are available and the
   current template set status, they may issue the GET TMPL message.

   The following steps are performed in order to change the templates:

   A) The server MUST retrieve from CRANE client the template set that
   requires change by issuing GET TMPL message.  The server can issue a
   GET TMPL even if it has not yet issued a START message.

   B) After received a GET TMPL message, the client sends back a GET
   TMPL RSP message with the requested data.

   C) The server makes the necessary changes to the templates and sends
   back a START NEGOTIATION message.  This message triggers the CRANE
   client to inquire about changes made by the CRANE server.

   D) After received a START NEGOTIATE message, the client MUST respond
   with START NEGOTIATE ACK message followed by a TMPL DATA message.
   From this point on, the template negotiation process starts.

2.7 Flow Control

   After templates have been deployed, DATA messages start to arrive at
   the primary CRANE server (the operational one with the highest
   priority within the CRANE session).  Each DATA message contains a
   Data Sequence Number (DSN).  The primary CRANE server MUST accept the
   data as long as it is in-sequence.  Out-of-sequence DATA messages
   should be discarded.

   The CRANE server detects the start of accounting data when it
   receives the first DATA message either after startup or after a
   server transition.  The first DATA message MUST have the 'S' bit
   ('DSN Synchronize' bit) set by the CRANE client.  Upon reception of
   the message with initial DSN, the server MUST accept all in-sequence
   DATA messages.  The DSN MUST be incremented by 1 for each new DATA
   message originated from the client.

   A CRANE server MUST acknowledge the reception and correct processing
   of DATA messages by sending DATA ACK messages.  The DATA ACK MUST
   contain the DSN of the last processed in-sequence DATA message.  If
   the CRANE server receives an Out Of Sequence DATA message, it MUST
   also send a DATA ACK message.  It will trigger an immediate
   retransmission of unacknowledged records.

   The CRANE client is responsible for delivering all the records.  In
   the case of a redundant server configuration, there could be a
   scenario when one server does not receive all the records but another
   redundant CRANE server for the same mediation system receives the
   rest of the records.  For example, server #1 could receive records
   3042-3095 and then 3123-..., with server #2 receiving records 3096-
   3122.  It is the sender's responsibility to deliver all the records,
   in-sequence, but not necessarily to the same server.

   The billing/mediation system eventually receives all the records,
   possibly through more than one CRANE server.  The CRANE client MUST
   convey all the records it received to the billing/mediation system.
    This MAY result in duplicate records in the billing/mediation
   system.  In this case, the DSN MUST be used to remove duplicates.  To
   aid the process of duplicate removal, whenever a record is re-sent to
   another server, its 'Duplicate' bit MUST be set to suggest that this
   record might be a duplicate.

   Implementation Note:

      When the amount of unacknowledged records reaches a threshold, a
      timer should be started.  When the timer expires, all the
      unacknowledged records should be transmitted to an alternate

      server with 'D' bit set in the DATA message; if alternate servers
      are not available, the records should be retransmitted.

      The CRANE flow control also supports redundant server
      configuration.  A server MUST send a START message in order to
      move to the 'ready' state.  In the 'ready' state, the server can
      receive and process CRANE messages.  To leave the 'ready' state
      and stop the message flows from the client, the server should send
      a STOP message to the client.

2.8 The CRANE Client Query Messages

   A CRANE server may query a CRANE client's status by sending query
   messages after it has established a session with the client.  A CRANE
   client that is connected to the server MUST respond with response
   messages.  All the Query Messages MUST be initiated by a CRANE
   server.  The CRANE protocol defines three such Query Message pairs,
   they are:

   Get Session (GET SESS)
   Get Session Response (GET SESS RSP)

   Get Template (GET TMPL)
   Get Template Response (GET TMPL RSP)

   Status Request (STATUS REQ)
   Status Response (STATUS RSP)

   All the query messages incorporate a Request ID field for tagging
   purposes and matching requests and responses.  This field contains a
   16 bit counter incremented with every request and is set by the
   initiator of the request.  Along with the CRANE server's IP address
   and port number, this constitutes a unique identifier for a request.
   This value MUST be copied to Request ID field in the response message
   in order to associate a specific response with a request.

   The CRANE client SHOULD collect and send out meta-data about the data
   collected (counters, statistics, etc.).  This is done by creating
   status templates, which are treated like any other template, with the
   exception that these templates are marked with a /'Status' bit.
   Status templates are used with the set of STATUS REQ and STATUS RSP
   messages.  A server MAY issue a STATUS REQ to a CRANE client and
   receive a STATUS RSP message with the requested data.

2.9 CRANE Sessions

   A CRANE client MAY deliver accounting data to different
   mediation/billing systems by establishing different CRANE sessions.

   Each session MAY consist of several CRANE servers in a redundant
   configuration.  The session ID imbedded in all the CRANE messages
   enables the correct association of CRANE sessions with CRANE users.
   All the CRANE processes (e.g., template negotiation, configuration,
   flow control, etc.) should be carried out in the same way in a multi
   session scenario.

   Each session has its set of templates (these may be the same
   templates, but the keys could be enabled or disabled differently).
    The sessions are configured in the NE, each with a different session
   name with associated Session IDs.  The session ID is carried in each
   message to associate the message with a specific session.

   A CRANE server MAY take part in different sessions.  When configuring
   a server, it needs to know the sessions in which it participates.
   The server can issue a GET SESS message to receive a list of relevant
   sessions.

3  CRANE Message Format

   A summary of the CRANE protocol message format is shown below.  A
   CRANE message consists of an 8 octet message header; it is followed
   by a variable length message payload that is aligned to 32 bit
   boundary.  Some of the messages do not have the CRANE Message Payload
   part.  The fields are in network byte order and transmitted from left
   to right.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |Message ID(MID)|  Session ID   | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                    CRANE Message Payload                      ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Version: 8 bit unsigned integer

      The Version field indicates the supported CRANE protocol
      implementation.  This field MUST be set to 1 to indicate the CRANE
      protocol Version 1.0.  CRANE protocol Version 1.0 only supports
      Ipv4 addressing; however, it can be used to transfer information
      related to Ipv6 flows.

   Message ID (MID): 8 bit unsigned integer

      The Message ID field identifies the type of the message.  The
      message IDs defined by CRANE Version 1 are:

      Message Name               Short Name         Message ID
      ---------------------      ---------------    ------------
      Reserved                                         0x00

      Flow Start                  START                0x01
      Flow Start Acknowledge      START ACK            0x02
      Flow Stop                   STOP                 0x03
      Flow Stop Acknowledge       STOP ACK             0x04
      Connect                     CONNECT              0x05

      Template Data               TMPL DATA            0x10
      Template Data Acknowledge   TMPL DATA ACK        0x11
      Final Template Data         FINAL TMPL DATA      0x12
      Final Template Data Ack.    FINAL TMPL DATA ACK  0x13
      Get Sessions                GET SESS             0x14
      Get Sessions Response       GET SESS RSP         0x15
      Get Template                GET TMPL             0x16
      Get Template Response       GET TMPL RSP         0x17
      Start Negotiation           START NEGOTIATE      0x18
      Start Negotiation Ack.      START NEGOTIATE ACK  0x19

      Data                        DATA                 0x20
      Data Acknowledge            DATA ACK             0x21
      Error                       ERROR                0x23

      Status Request              STATUS REQ           0x30
      Status Response             STATUS RSP           0x31

   Session ID: 8 bit unsigned char

      The Session ID field identifies the session with which the message
      is associated.  The session ID is ignored in the case of GET SESS
      and GET SESS RSP messages.  More details about session can be
      found in Section 2.9.

   Message Flags: 8 bit unsigned char

      The Message Flags field can be used to identify options associated
      with the message.  For CRANE Version 1.0, all the flags are
      reserved; unless otherwise specified, the flags are set to zero on
      transmit and are ignored on receipt.

   Message Length: 32 bit unsigned integer

      The Message Length field is the total length of the CRANE message
      in octet including the header.

4  CRANE Messages

   This section defines CRANE mandatory messages.  They MUST be
   supported by any CRANE protocol implementation.

4.1 Flow Start (START)

   Description

      The Flow Start message is sent from a CRANE server to a CRANE
      client to indicate that the CRANE server is ready to receive CRANE
      messages.

     Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x01     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2 Flow Start Acknowledge (START ACK)

   Description

      The Flow Start Acknowledge message is sent by a CRANE client to
      acknowledge the reception of a START message from a specific CRANE
      server.  It is sent only to that server to indicate that the
      client considers it ready to receive CRANE messages.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x02     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Client Boot Time                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Client Boot Time: 32 bit unsigned integer

      The Client Boot Time field is the timestamp of the last client
      startup in seconds from 1970.  This field can be combined with the
      DSN and the client's IP address to serve as a system wide unique
      record identifier.

4.3 Flow Stop (STOP)

   Description

      The Flow Stop message is sent from a CRANE server to a CRANE
      client to instruct it to stop sending data (to that server).  The
      STOP message does not disconnect the server; it only stops the
      CRANE client from sending "DATA" messages.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x03     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.4 Flow Stop Acknowledge (STOP ACK)

   Description

      The Flow Stop Acknowledgement message acknowledges the STOP
      message issued by a CRANE server.

   Message Format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Version      |  MID=0x04     | Session ID    | Message Flags |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Message Length                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.5 Connect (CONNECT)

   Description

      The CONNECT message is sent from a CRANE server to a CRANE client
      to identify itself.  The message MUST be the first message sent
      over a transport layer connection between the server and the
      client.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x05     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Server Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Server Port          |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Server Address: 32 bit unsigned integer

      The Server Address field is the server's IP address (IPV4).

   Server Port: 16 bit unsigned integer

      The Server Port field is the server's port number for the
      transport layer (the port number specified here doesn't
      necessarily have to match the port number used by the transport
      layer)

4.6 Template Data (TMPL DATA)

   Description

      A CRANE client sends the Template Data message to a CRANE server
      after a START or a START NEGOTIATE message was received from the
      server.  The message MUST contain all the templates that are going
      to be used for the session.  It SHOULD also include the template
      for the status records (See section 2.8)

      The receiving CRANE server MUST acknowledge the message by sending
      either a TMPL DATA ACK (if template changes are needed) or a FINAL
      TMPL DATA ACK message.  For more information, see section 2.5.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x10     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Config ID   |  Flags      |E|       Number of Templates     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       Template Block                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       ...       ...                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       Template Block                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Configuration ID (Config. ID): 8 bit unsigned char

      The Configuration ID field identifies the version number
      associated with a template set.  Changes to any of the templates
      would result in a new template version, and the version number
      would be incremented by one.  An implementation SHOULD handle
      rollovers of the version number.

   Flags: 8 bit unsigned char

      The Flags field identifies any options associated to the message.

      The flag defined by the CRANE Version 1 is:

      The 'E' bit indicates the transmission order of the "DATA"
      messages.  If the field is set to 1, data is in big endian format;
      otherwise, little endian format is used.

   Number of Templates: 16 bit unsigned integer

      The Number of Templates field is the number of Templates (a
      template is described by a Template Block) specified by the
      message.

   Template Block

      The Template Block field is of variable length and aligned to 32
      bit boundary.  It is the specification of a template.

   Template Block Format:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Template ID            |         Number of Keys        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Template Flags         |T|      Description Length       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Template Block Length                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                         Description                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                          Key Block                            ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       ...       ...                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                          Key Block                            ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Template ID: 16 bit unsigned integer

      The Template ID field identifies a specific template.

   Number of Keys: 16 bit unsigned integer

      The Number of Keys field is the number of keys included in the
      template.

   Template Flags: 16 bit unsigned integer

      The Template Flags field is composed of flags that indicate
      different attributes of the template.  In CRANE Version 1.0, only
      the 'T' bit is defined, other bits in the field SHOULD be set to
      zero by the sender and ignored by the receiver.

      The 'T' bit ('Status' bit) indicates that the template is a status
      template that is used by the STATUS RSP message only.  See section
      2.8 for more details.

   Description Length: 16 bit unsigned integer

      The Description Length field is the length of the Description
      field.  If no description is supplied, the length MUST be 0.

   Template Block Length: 32 bit unsigned integer

      The Template Block Length is the length of the template block in
      octets.

   Description: Variable length unsigned char

      The Description field contains the text description of the
      template (e.g., "Aggregated by interface and ToS bits").  It is a
      variable length field of up to 64Kb long, and padded with 0 to the
      next 32 bit boundary.

   Key Block

      A key Block contains the specification of a key within a template.

   Key Block Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Key ID                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Key Type ID          |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Key Attribute Vector                   |K|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Key ID: 32 bit unsigned integer

      The Key ID field identifies the key within a template.  See
      section 2.4 for more details.

   Key Type ID: 16 bit unsigned integer

      The Key Type ID field specifies the data type of the key.

           The fixed length data types are defined as following:

               Data Type             Data Type ID
           ---------------------    --------------
            Boolean (1)                 0x0001
            Unsigned Integer8           0x0002
            Signed Integer8             0x0003
            Unsigned Integer16          0x0004
            Signed Integer16            0x0005
            Unsigned Integer32          0x0006
            Signed Integer32            0x0007
            Unsigned Integer64          0x0008
            Signed Integer64            0x0009

            Float (2)                   0x000a
            Double (2)                  0x000b

            IP address (Ipv4)           0x0010
            IP address (Ipv6)           0x0011
            Time_SEC  (3)               0x0012
            Time_MSEC_64(4)             0x0013
            Time_USEC_64 (5)            0x0014
            Time_MSEC_32 (6)            0x0015
            Time_USEC_32 (7)            0x0016

           The variable length data types are defined as following:

            String (8)                  0x400c
            Null Terminated String      0x400d
            UTF-8 String                0x400e
            UTF-16 String               0x400f
            Arbitrary Data (BLOB) (9)   0x4015

           (1) Boolean is represented as a single octet holding 0 for a
           value of FALSE and 1 for a value of TRUE.

           (2) Float and Double are single and double precision floating
           point numbers that comply with the IEEE-754 standard.

           (3) Time_SEC is a 32 bit value, most significant octet first
           - seconds since 00:00:00 GMT, January 1, 1970.

           (4) Time_MSEC_64 is a 64 bit value, most significant octet
           first - milliseconds since 00:00:00 GMT, January 1, 1970.

           (5) Time_USEC_64 is a 64 bit value, most significant octet
           first - microseconds since 00:00:00 GMT, January 1, 1970.

           (6) Time_MSEC_32 is a 32 bit value, most significant octet
           first - milliseconds since 00:00:00 GMT, January 1, 1970.

           (7) Time_USEC_32 is a 32 bit value, most significant octet
           first - microseconds since 00:00:00 GMT, January 1, 1970.

           (8) String is prefixed by a 32 bit length field that
           indicates the length of the string, and followed by ASCII
           codes of the string characters.  This representation MUST
           only be used for encoding data records in a "DATA" message.

           (9) The arbitrary data is prefixed by a 32 bit length field
           and followed by the data in binary format.

   Key Attribute Vector: 32 bit unsigned integer

      The Key Attribute Vector field indicates different attributes of
      the key.  In CRANE Version 1, only the 'K' bit is defined, other
      bits in the field SHOULD be set to zero by the sender and ignored
      by the receiver.

      The 'K' bit ('Disabled bit') is set to 1 when the key is disabled
      in this template.

4.7 Template Data Acknowledge (TMPL DATA ACK)

   Description

      The Template Data Acknowledge message is sent from a CRANE server
      to a CRANE client after a TMPL DATA message has been received.  It
      proposes changes of the templates and/or key status changes
      (enable/disable) for the templates.

      If a CRANE server wishes to acknowledge reception of TMPL DATA
      without changes, it MUST respond with the FINAL TMPL DATA ACK
      message.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x11     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Config. ID |    Reserved   |   Number of Template Changes  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                    Template Change Block                      ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       ...       ...                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                    Template Change Block                      ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Configuration ID (Config. ID): 8 bit unsigned char

      See Section 4.6.  The value MUST be identical to the Config.  ID
      field of the acknowledged TMPL DATA message.

   Number of Template Changes: 16 bit unsigned integer

      The Number of Template Changes field is the number of changed
      Templates (a changed template is described by a Template Change
      Block) specified by the message.

   Template Change Block

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Template ID            |        Number of Keys         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                          Key Block                            ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       ...       ...                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                          Key Block                            ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Template ID: 16 bit unsigned integer

      See Section 4.6.

   Number of Keys: 16 bit unsigned integer

      See Section 4.6.

   Key Block

      See Section 4.6, only relevant keys are described.

4.8 Final Template Data (FINAL TMPL DATA)

      Description

      The Final Template Data message is sent by a CRANE client to all
      the CRANE servers in a session, to convey the finalize templates.
      It is similar to the TMPL DATA message, with the only difference
      that a server must accept the templates in this message.

   Message Format

      Identical to the TMPL DATA (see section 4.6)

   Message ID (MID)

      0x12      Final Template Data

4.9 Final Template Data Acknowledge (FINAL TMPL DATA ACK)

   Description

      The CRANE server acknowledges reception of the TMPL DATA or FINAL
      TMPL DATA by sending a Final Template Data Acknowledge message.
      It does not carry any changes to the templates.  Unlike TMPL DATA
      ACK messages, a FINAL TMPL DATA ACK message indicates the
      acceptance of the templates for the session.  A server MAY respond
      with this message to a TMPL DATA (if it does not want any changes
      in the templates).  A server MUST respond with this message to a
      FINAL TMPL DATA.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x13     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Config. ID  |                     Reserved                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Configuration ID: 8 bit unsigned char

      See Section 4.6.  This field MUST copy the configuration ID from
      the acknowledged message.

4.10    Get Sessions (GET SESS)

   Description

      The Get Sessions message is sent by a CRANE server to a CRANE
      client to query what are the sessions it should participate.  This
      is typically done just before a UI configuration of the CRANE
      client's templates.  As each session has its own set of templates,
      there is a need to know the server's participation of all the
      sessions.

      The Session ID field in the CRANE message header MUST be ignored
      by the receiver.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x14     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Request ID          |        Reserved               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Request ID: 16 bit unsigned integer

      The Request ID field identifies the specific request issued by the
      server.  The same Request ID MUST be placed in the responding
      message in order to associate it with the request.

4.11    Get Sessions Response (GET SESS RSP)

   Description

      The Get Sessions Response message is sent by a CRANE client to a
      CRANE server as a reply to a GET SESS request.  The message MUST
      contain all the information related to any session with which the
      requesting server is associated.

      The Session ID field in the common message header MUST be ignored
      by the receiver.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      --+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x15     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Request ID          |       Number of Sessions      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Vendor String Length       |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
      |                                                               |
      ~                       Vendor String                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                         Session Block                         ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       ...       ...                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                         Session Block                         ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Request ID: 16 bit unsigned integer

      See Section 4.10.

   Number of Sessions: 16 bit unsigned integer

      The Number of Sessions field is the number of session blocks in
      the message.

   Vendor String Length: 16 bit unsigned integer

      The Vendor String Length field is the length of Vendor String
      field in octet.  The field limits vendor strings to 64Kb long.  If
      no such string is supplied, the length MUST be set to 0.

   Vendor String: Variable length unsigned char

      The Vendor String field is a variable length field.  It identifies
      the vendor that created the session.  It MUST be padded with 0 to
      the next 32 bit boundary.  The information differentiates similar
      templates from different vendors.  The actual format of the
      information is application specific and outside the scope of this
      document.

   Session Block

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Session ID    |   Reserved    |      Session Name Length      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Session Description Length   |             Reserved          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                          Session Name                         ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       Session Description                     ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Session ID: 8 bit unsigned char

      See Section 3.

   Session Name Length: 16 bit unsigned integer

      The Session Name Length field is the length of the Session Name
      field.  The field limits the session name strings to 64 Kb long.
      As a name is mandatory to differentiate between sessions, this
      field MUST NOT be 0.

   Session Description Length: 16 bit unsigned integer

      The Session Description Length field is the length of a session
      description.  The field limits the session description to 64Kb
      long.  If no such Description is supplied, the length MUST be set
      to 0.

   Session Name: Variable length unsigned char

      The Session Name field is the name for a session, which MAY be
      displayed to end-users.  It MUST be padded with 0 to the next 32
      bit boundary.  Session Name MUST be unique within a CRANE client.
      This field is mandatory and MUST be a part of any Session Block.

   Session Description: Variable length unsigned char

      The Session Description field is the text description of a
      session; it could be displayed to end-users.  It MUST be padded
      with 0 to the next 32 bit boundary.

4.12    Get Templates (GET TMPL)

   Description

      The Get Templates message is sent by a CRANE server to a CRANE
      client to query templates in a session.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x16     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Request ID          |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Request ID: 16 bit unsigned integer

      See Section 4.10.

4.13    Get Templates Response (GET TMPL RSP)

   Description

      The Get Templates Response message is sent by a CRANE client to a
      CRANE server as a response to a GET TMPL message.  The message
      SHOULD contain all templates available for the specific session.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x17     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Request ID          |       Number of Templates     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       Template Block                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       ...       ...                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       Template Block                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Request ID: 16 bit unsigned integer

      See Section 4.10.

   Number of Templates: 16 bit unsigned integer

      See Section 4.6.

   Template Block

      Same as the template block defined in the TMPL DATA message (see
      Section 4.6).  However, Extended Key Blocks MUST be used instead
      of Key Blocks.  Extended key Block field provides extensive
      informational data that MAY be displayed to end-users.

   Extended Key Block

      The Extended Key Block field provides comprehensive information
      about a key.

   Extended Key Block Format:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Key ID                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Key Type ID          |        Key Name Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Key Label Length     |        Key Help Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                            Key Name                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                            Key Label                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                            Key Help                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Key Attribute Vector                   |K|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Key ID: 32 bit unsigned integer

      Same as section 4.6.

   Key Type ID: 16 bit unsigned integer

      Same as section 4.6.

   Key Name Length: 16 bit unsigned integer

      The Key Name Length field is the length of the Key Name field.
      The field limits Key Name strings to 64 Kb long.  As a name is
      mandatory to a key, this field MUST NOT be 0.

   Key Label Length: 16 bit unsigned integer

      The Key Label Length field is the length of the Key Label field.
      The field limits Key Label strings to 64 Kb long.  Length of 0
      means that the Label field is to be skipped.

   Key Help Length: 16 bit unsigned integer

      The Key Help Length field is the length of the Key Help field.
      The field limits Key Help strings to 64 Kb long.  Length of 0
      means that the Help field is to be skipped.

   Key Name: Variable length unsigned char

      The Key Name field is the name for the key, which could be
      displayed to end users.  It MUST be padded with 0 to the next 32
      bit boundary.  Key Name MUST be unique (within the template) and
      case sensitive.  This field is mandatory and MUST be a part of any
      Extended Key Block.

   Key Label: Variable length unsigned char

      The Key Label field is a descriptive label, which could be
      displayed to end users concerning this key.  It MUST be padded
      with 0 to the next 32 bit boundary.  This field SHOULD be a part
      of any Extended Key Block.

   Key Help: Variable length unsigned char

      The Key Help field is any Help string that could be displayed to
      end users concerning this key.  It MUST be padded with 0 to the
      next 32 bit boundary.  This field MAY be a part of any Extended
      Key Block.

   Key Attribute Vector: 32 bit unsigned integer

      Same as section 4.6.

4.14    Start Negotiation (START NEGOTIATE)

   Description

      The Start Negotiation message is sent by a CRANE server after the
      configuration process has completed.  The message should initiate
      template negotiation by the client with all CRANE servers in a
      session.  The CRANE server MAY re-send this message up to 3 times
      with repeat interval of 5 seconds unless it is acknowledged by the
      CRANE client.  Otherwise, the CRANE user will be informed.  The
      client should send TMPL DATA message to the servers after
      acknowledged the message.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x18     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.15    Start Negotiation Acknowledge (START NEGOTIATE ACK)

   Description

      The Start Negotiation Acknowledge message MUST be sent by a CRANE
      client to the server to acknowledge the reception of the START
      NEGOTIATE message.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x19     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.16    Data (DATA)

   Description

      The DATA message carries actual data records from a CRANE client
      to a CRANE server.  A data record is a structured collection of
      fields that matches a specific template.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x20     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Template ID            |    Config. ID |  Flags    |D|S|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Data Sequence Number (DSN)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                          Record Data                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Template ID: 16 bit unsigned integer

      See Section 4.6.

     Configuration ID: 8 bit unsigned char

      See Section 4.6.  The Config. ID field can prevent out-of-the-blue
      messages with outdated templates arriving and erroneously
      processed.  A server MAY keep a short history of templates in
      order to cope with this scenario.

   Flags: 8 bit unsigned char

      The Flags field is composed of flag bits that indicate processing
      requirements of the data records.  The CRANE Version 1 defined two
      flags for these purposes.  Unless otherwise specified, the other
      flags are set to zero on transmit and are ignored on receipt.

   The following flags are defined in CRANE Version 1:

      The 'D' bit ('Duplicate' bit): It is set for records that are
      re-sent to an alternate server after a server transition occurs.
      When the same records are sent to different servers, there is a
      possibility that duplicated data exists.  The Status of the 'D'
      bit will help the billing/mediation system to perform
      de-duplication if desired.

      The 'S' bit ('DSN Synchronize' bit): When set, it indicates that
      the record is the first one received by the server after starting
      (or restarting) of data transmission to this server.  The server
      MUST set the initial DSN to the DSN specified in the record.  The
      flag is set to zero by default.

   Data Sequence Number: 32 bit unsigned integer

      The Data Sequence Number field is the record sequence number used
      for preserving data orders and detecting data losses.  The DSN
      MUST be incremented by one for each new record transmitted.  The
      selection of the initial DSN number is implementation specific.

   Record Data: Variable Length unsigned octets

      The Record Data field carries the actual accounting/billing data
      that is structured according to the template identified by the
      Template ID field.

4.17    Data Acknowledge (DATA ACK)

   Description

      The Data Acknowledgement message is sent from a CRANE server to
      acknowledge receipt of records.  It acknowledges the maximal in-
      sequence DSN received.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x21     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Data Sequence Number                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Config. ID  |                  Reserved                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Sequence Number: 32 bit unsigned integer

      See Section 4.16.  It MUST be DSN of the last in-sequence record
      that was received by the server.

   Configuration ID: 8 bit unsigned char

      See Section 4.16.

4.18    Error (ERROR)

   Description

      The Error message MAY be issued by either a CRANE server or
      client.  It indicates an error condition that was detected by the
      sender.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x23     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Timestamp                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Error Code            |      Description Length       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                          Description                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Timestamp: 32 bit unsigned integer

      The Timestamp field is a timestamp in seconds since 00:00:00 GMT,
      January 1, 1970.

   Error Code: 16 bit unsigned integer

      The Error Code field is a code assigned to an error condition.

   The following error codes are defined in CRANE Version 1:

          Error Condition                   Error Code
         -----------                    --------------
          Unknown                           0

   Description Length: 16 bit unsigned integer

      The Description Length field is the length of the Description
      field.  The field limits Description strings to 64 Kb long.
      Length of 0 means that the Description field is to be skipped.

   Description: Variable Length unsigned char

      The Description field is a text description that allows the sender
      to provide more detailed information about the error condition.
      It MUST be padded with 0 to the next 32 bit boundary.

4.19    Status Request (STATUS REQ)

   Description

      CRANE servers MAY inquire general operation status of a client by
      sending the Status Request message.  The status information SHOULD
      include a collection of states, counters, accumulators of the data
      collection functions that reside with the client.  The status MAY
      include more information about the CRANE client itself.

      The status reporting mechanism relies on the status template of a
      session.  It is determined similarly as other templates.  Without
      a determined status template, no status information can be
      delivered.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x30     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.20    Status Response (STATUS RSP)

   Description

      The Status Response message contains a status report that MUST be
      compatible with the status template of the session.  It is
      client's response to a STATUS REQ message from a server.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Version      |  MID=0x31     | Session ID    | Message Flags |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Message Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Template ID            |  Reserved     |Config. ID     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Record Length                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                         Record Data                           ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Template ID: 16 bit unsigned integer

      See Section 4.6.

   Configuration ID: 8 bit unsigned integer

      See Section 4.6.  The version is needed here to prevent
      out-of-the-blue messages with outdated templates arriving and
      erroneously processed.  A server MAY keep a short history of
      templates in order to cope with this scenario.

   Record Length: 32 bit unsigned integer

      The Record Length field is the length of the Record Data field in
      octets.

   Record Data: Variable Length unsigned octets

      The Record Data field contains the status data that complies with
      the status template.  For more details see section 2.4

5  Protocol Version Negotiation

   Since the CRANE protocol may evolve in the future and it may run over
   different transport layers, a transport neutral version negotiation
   mechanism running over UDP is defined.  A CRANE server MAY inquire a
   CRANE client about the CRANE protocol version and transport layer
   support by sending a UDP packet on an agreed UDP port.  The client
   MUST respond to this request with a UDP packet carrying the protocol

   version, the transport type and the port number used for the specific
   transport.  The Protocol Version Negotiation is optional for CRANE
   Version 1.

   The CRANE server sends the following message to query the client's
   protocol support.

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Server Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Server Boot Time                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     'C'       |    'R'        |    'A'        |    'N'        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Server Address:

      The Server Address field is the IP address (Ipv4) of the CRANE
      server.

   Server Boot Time

      The Server Boot Time field is the timestamp of the last server
      startup in seconds from 1970.

   'C', 'R', 'A', 'N':

      The 'C', 'R', 'A', 'N' fields are ASCII encoded characters to
      identify the CRANE server.

   The client's reply to a version negotiation request MUST comply with
   the following structure:

   Message Format

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Default Protocol Info                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Additional Protocols Count                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Additional Protocols Info                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              ...   Additional Protocols Info  ...             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Additional Protocols Info                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Default Protocol Info:

      The Default Protocol Info field contains information of the
      default protocol supported by the client.  The field is structured
      as a Protocol Info Block described below.

   Additional Protocols Count: 32 bit unsigned integer

      The Additional Protocols Count field specifies the number of
      additional protocols supported by the client.  In the case that
      only the default protocol is supported, the field MUST be set to
      0.

   Additional Protocols Info:

      The Additional Protocol Info field is an array of Protocol Info
      Blocks (described below) contain information about additional
      protocols supported by the client.

   Protocol Info Block

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Transport Type                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Protocol Version                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Port Number           |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Transport Type: 32 bit unsigned integer

      1 - TCP, 2 - SCTP

   Protocol Version: 32 bit unsigned integer

      Version number of the CRANE protocol supported over the specific
      transport layer, the current version is 1.

   Port Number: 16 bit unsigned integer

      Port number (either SCTP or TCP port) used for the protocol

6  Security Considerations

   The CRANE protocol can be viewed as an application running over a
   reliable transport layer, such as TCP and SCTP.  The CRANE protocol
   is end-to-end in the sense that the CRANE messages are communicated
   between clients and servers identified by the host address and the
   transport protocol port number.  Before any CRANE sessions can be
   initiated, a set of CRANE servers' addresses should be provisioned on
   a CRANE client.  Similarly, a CRANE server maintains a list of CRANE
   clients' address with which it communicates.  The provisioning is
   typically carried out securely using a network management system; in
   this way, the CRANE end-points can be authenticated and authorized.
   As this scheme is static, without additional security protections the
   CRANE protocol is vulnerable to attacks such as address spoofing.

   The CRANE protocol itself does not offer strong security facilities;
   therefore, it cannot ensure confidentiality and integrity of CRANE
   messages.  It is strongly recommended that users of the CRANE
   protocol evaluate their deployment configurations and implement
   appropriate security policies.  For example, if the CRANE protocol is
   deployed over a local area network or a dedicated connection that

   ensure security, no additional security services or procedures may be
   required; however, if CRANE clients and servers are connected through
   the Internet, lower layer security services should be invoked.

   To achieve a strong security protection of communications between
   CRANE clients and servers, lower layer security services are strongly
   recommended.  The lower layer security services are transparent to
   the CRANE protocols.  Security mechanisms may be provided at the IP
   layer using IPSEC [6], or it may be implemented for transport layer
   using TLS [7].  The provisioning of the lower layer security services
   is out of the scope of this document.

7  References

   [1]   Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote
         Authentication Dial In User Service (RADIUS)", RFC 2865, June
         2000.

   [2]   Calhoun, P., "DIAMETER Base Protocol", Work in Progress.

   [3]   Calhoun, P., et. al., "DIAMETER Framework Document", Work in
         Progress.

   [4]   Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
         H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson,
         "Simple Control Transmission Protocol", RFC 2960, October 2000.

   [5]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [6]   Kent, S. and R. Atkinson,  "Security Architecture for the
         Internet Protocol", RFC 2401, November 1998.

   [7]   Dierks,  T. and C. Allen, "The TLS Protocol, Version 1.0", RFC
         2246, January 1999.

8  Acknowledgments

   Special thanks are due to Tal Givoly, Limor Schweitzer for conceiving
   the work, and Nir Pedhatzur, Batya Ferder, and Peter Ludemann from
   XACCT Technologies for accomplishing the first CRANE protocol
   implementation.

   Thanks are also due to Nevil Brownlee for his valuable comments on
   the work, as well as the IETF IPFIX WG.

9  Authors' Addresses

   Kevin Zhang
   10124 Treble Court
   Rockville, MD 20850
   U.S.A.

   Phone +1 301 315 0033
   EMail: kevinzhang@ieee.org

   Eitan Elkin
   XACCT Technologies, Ltd.
   www.xacct.com
   12 Hachilazon St.
   Ramat-Gan, Israel 52522

   Phone +1 972 3 576 4111
   EMail: eitan@xacct.com

10  Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
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   copyrights defined in the Internet Standards process must be
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   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.

 

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