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comp.dcom.lans.token-ring FAQ

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Archive-name: LANs/token-ring-faq
Posting-Frequency: monthly
Last-modified: 1999/07/08
Version: 990708
Copyright: (c) 1999 James Messer
Maintainer: James Messer <>

See reader questions & answers on this topic! - Help others by sharing your knowledge
            comp.dcom.lans.token-ring Frequently Asked Questions

       This document is provided as is without any express or implied
  warranties. While every effort has been taken to ensure the accuracy of
      the information contained in this article, the authors assume no
 responsibility for errors or omissions, or for damages resulting from the
   use of the information contained herein. The contents of this article
     reflect my opinions only and not necessarily those of my employer.

FAQ Table of Contents

1.0 FAQ Administration

[1.1] What is this FAQ?
[1.2] Who maintains this FAQ?
[1.3] Where can this FAQ be found?
[1.4] Who provides information to the FAQ?
[1.5] Can I use this FAQ on my web page?
[1.6] Copyright Information

2.0 Introduction to Token Ring

[2.1] What is token ring?
[2.2] How do Ethernet and token ring networks compare?
[2.3] Where are the IEEE specifications?

3.0 General Token Ring Information

[3.1] How does token ring work?
[3.2] What is used to convert between Ethernet and Token Ring?

4.0 Token Ring Physical Layer

[4.1] What physical devices are required for a token ring network?
[4.2] What types of cables are used for token ring?
[4.3] What pin assignments are used in token ring cabling?
[4.4] What is the difference between a MAU, a CAU, and a LAM?
[4.5] Can two token ring stations be directly attached?
[4.6] What is the maximum distance between token ring stations?
[4.7] What is the formula for computing adjusted ring length (ARL)?
[4.8] Why is ring length important?
[4.9] At what speeds does token ring run?
[4.10] How many stations are supported by a single token ring network?
[4.11] What is High Speed Token Ring?

5.0 Token Ring Data Link Layer

[5.1] What is a token?
[5.2] What are MAC frames?
[5.3] What are LLC frames?
[5.4] What are Locally Administered Addresses (LAAs)?
[5.5] What are functional addresses?
[5.6] What is an Active Monitor and Standby Monitor?
[5.7] What is early token release?
[5.8] What is transparent bridging?
[5.9] What is spanning tree bridging?
[5.10] What is source route bridging?
[5.11] What is token ring switching?
[5.12] What is the process for inserting into a ring?
[5.13] How do you troubleshoot the insertion process?

6.0 Token Ring Errors and Troubleshooting

[6.1] What are isolating and non-isolating errors?
[6.2] What is the claim process?
[6.3] What is a beacon frame?
[6.4] What is promiscuous mode?
[6.5] What software is available to monitor a token ring network?

7.0 Other Information

[7.1] What token ring books are available?
[7.2] What certifications are available regarding token ring networks?
[7.3] What companies make token ring adapter cards and MAUs?

1.0 FAQ Administration

 [1.1] What is this FAQ?

       This FAQ will attempt to explain and decipher the intricacies of
       token ring networking and answer some of the most common questions
       relating to token ring networks. Although it contains technical
       information, this FAQ is best used as an introduction to token ring
       networking. See section [7.1] for token ring book and publication

 [1.2] Who maintains this FAQ?

       This FAQ is maintained by James Messer <>.
       Questions, comments, corrections, and contributions are encouraged!

 [1.3] Where can this FAQ be found?

       This FAQ will be posted to the comp.dcom.lans.token-ring newsgroup
       on the first of each month. An archive of the FAQ can be found at:

       A HTTP version of this FAQ can be found at:

 [1.4] Who provides information to the FAQ?

       In many cases, the FAQ questions and answers are summarized from the
       comp.dcom.lans.token-ring newsgroup. Other submissions to the FAQ
       were contributed by:
       Lawrence L. Baldwin <>
       Kris Carlier <>
       David Holbrook
       Neil Jarvis <>
       Bernie Keenan <>
       John Kristoff <>
       Mark R. Kuijper <>
       Richard F. Masoner <>
       Michele Mastroianni <>

       Send any corrections or FAQ additions to

       Our thanks to all who have provided information to the FAQ! Keep
       those submissions coming!

 [1.5] Can I use this FAQ on my web page?

       Since this FAQ changes almost daily, a copy of the FAQ on your web
       page would be out of date in a very short time. Please don't do
       this! A more appropriate method would be to set a hyperlink to the
       URL found in the secondary header of this FAQ. Please send an e-mail
       to if you plan on adding a link to this FAQ
       to your web page. I reserve the right to restrict the use of this

 [1.6] Copyright Information

       Copyright (c) 1999 by James Messer, all rights reserved.

       This FAQ may be posted to any USENET newsgroup, on-line service, or
       BBS as long as it is posted in its entirety, includes this copyright
       statement, and includes written permission from

2.0 Introduction to Token Ring

 [2.1] What is token ring?

       Token ring is the IEEE 802.5 standard that connects computers
       together in a closed ring. Devices on the ring cannot transmit data
       until permission is received from the network in the form of an
       electronic 'token'.
 [2.2] How do Ethernet and token ring networks compare?

       Token Ring is single access, meaning there is only one token. Thus,
       at any given time only one station is able to use the LAN. Ethernet
       is a shared access medium, where all stations have equal access to
       the network at the same time.

 [2.3] Where are the IEEE specifications?
       The IEEE specifications can be purchased from the IEEE at:

       Information on all IEEE standards can be found at:

       For more information on the 802.5 standards, see The official IEEE
       802.5 web site at:

3.0 General Token Ring Information

 [3.1] How does token ring work?

       A token ring network uses a special frame called a token that
       rotates around the ring when no stations are actively sending
       information. When a station wants to transmit on the ring, it must
       capture this token frame. The owner of the token is the only station
       that can transmit on the ring, unlike the Ethernet topology where
       any station can transmit at any time. Once a station captures the
       token, it changes the token into a frame format so data can be sent.

       As the data traverses the ring, it passes through each station on
       the way to the destination station. Each station receives the frame
       and regenerates and repeats the frame onto the ring. As each station
       repeats the frame, it performs error checks on the information
       within the frame. If an error is found, a special bit in the frame
       called the Error Detection bit is set so other stations will not
       report the same error.

       Once the data arrives at the destination station, the frame is
       copied to the destination's token ring card buffer memory. The
       destination station repeats the frame onto the ring, changing two
       series of bits on the frame. These bits, called the Address
       Recognized Indicator (ARI) and the Frame Copied Indicator (FCI),
       determines if the destination station had seen the frame and has had
       ample buffer space available to copy the frame into memory. If the
       frame is not copied into memory, it is the responsibility of the
       sending station to retransmit the frame.

       The frame continues around the ring, arriving back at the source
       station who recognizes the sending address as it's own. The frame is
       then stripped from the ring, and the source station sends a free
       token downstream.

 [3.2] What is used to convert between Ethernet and Token Ring?

       There is no 'converter' that allows an Ethernet network and Token
       Ring network to communicate between each other. A conversion process
       must occur between the two topologies, since they both use different
       signaling types, frame structures, and frame sizes.

       There are two methods to accomplish this 'conversion'; bridging, and


       Bridging is a method of communicating between devices at OSI layer
       2, the data link layer. A bridge connects two networks together and
       acts as a traffic director. If traffic is destined to the other
       network, the bridge allows the traffic to pass. If the traffic is
       local to a single network, the bridge does not pass the traffic
       unnecessarily to the other connected network.

       The bridge makes this determination based on the Media Access
       Control (MAC) address of the workstations on the network. The bridge
       keeps an updated list of everyone active on the network, and uses
       this list to direct traffic from one network to another.

       This method of operation makes the network appear as a single
       logical network, since the only separation of traffic from one
       network to another is done at the MAC address level.

       There are many bridge manufacturers and bridge types on the market.
       The newest version of this bridging technology is called a DLC
       Switch or LAN Switch. These switches have a much higher port density
       than the older two or three port bridges, allowing for much more
       flexibility and network segmentation.


       The second method of 'converting' from Ethernet to Token Ring is
       called routing. Routing occurs at OSI layer 3, and separates
       physical networks into separate logical networks. This
       differentiates routing from bridging, since bridging maintains a
       single logical network.

       In a routed network, the sending workstation determines if outgoing
       traffic is local or remote. If the traffic belongs to another
       network, the originating station sends the frame directly to the
       router for further processing.

       Upon receiving the frame from the source workstation, the router
       examines the frame for the destination address. The router maintains
       a routing table which is used to determine the final destination of
       the data packet through the router.

       Routing is the most common method of connecting Ethernet networks to
       Token Ring networks in most organizations. Most network operating
       systems have routing capabilities built into the servers. By placing
       a token ring and Ethernet card into a Novell NetWare 3.x/4.x or
       Windows NT v4.x server, the two topologies can communicate between
       each other.

       One caveat; some protocols are not routeable. A good example is
       Microsoft's NetBEUI, which has no OSI layer 3 network address and
       therefore cannot be routed. Protocols which cannot be routed must be
       bridged between physical networks.

4.0 Token Ring Physical Layer

 [4.1] What physical devices are required for a token ring network?

       Token ring connectivity requires three separate physical entities; a
       Multistation Access Unit (MAU), a token ring lobe cable, and a token
       ring adapter card.

       A Multistation Access Unit (MAU or MSAU) is a hub-like device that
       connects to all token ring stations. Although the token ring
       stations are attached to the MAU in a physical star configuration, a
       true ring is maintained inside the MAU.

       Unlike an Ethernet hub, a MAU consists of physical or electronic
       relays which keep each station in a loopback state until a voltage
       is sent from the station to the MAU. Since this voltage does not
       affect data communications, it is referred to as a 'phantom'
       voltage. Once this phantom voltage is received by the MAU, a relay
       is activated that inserts the token ring station onto the ring.

       MAUs are connected together with Ring In/Ring Out (RI/RO) cables. To
       maintain a true ring, both the RI and the RO ports must be connected
       from one MAU to the other.

       A token ring lobe cable connects the token ring station to the MAU.
       This cable communicates over four wires; two for transmit and two
       for receive. The cable can be Shielded Twisted Pair (STP) or
       Unshielded Twisted Pair (UTP).

       A token ring adapter card is the physical interface that a station
       uses to connect to a token ring network. There are token ring
       adapter cards for almost every computer bus type.

 [4.2] What types of cables are used for token ring?

       There are three major physical token ring cabling systems; Shielded
       Twisted Pair (STP), Unshielded Twisted Pair (UTP), and optic fiber.

 [4.3] What pin assignments are used in token ring cabling?

       An IBM-type Data Connector or Universal Data Connector (IDC or UDC),
       is a hermaphroditic connector (neither male nor female). These
       connectors attach to each other without having a specified male or
       female connector type on each end. These connectors are commonly
       found on IBM Type 1 cabling, a two-pair shielded cable.

       The UDC connector has the following cabling requirements:

       Red    - Receive +
       Green  - Receive -
       Orange - Transmit +
       Black  - Transmit -

       A DB-9 connector uses four wires (two pairs) for token ring

       Pin 1 - Red    - Receive +
       Pin 5 - Black  - Transmit -
       Pin 6 - Green  - Receive -
       Pin 9 - Orange - Transmit +

       A RJ-45 connector is an eight wire twisted pair cable:

       Pin 3 - Blue/White   - Transmit -
       Pin 4 - White/Orange - Receive +
       Pin 5 - Orange/White - Receive -
       Pin 6 - White/Blue   - Transmit +

       RJ-11 connectors are rarely used:

       Pin 2 - Blue/White   - Transmit -
       Pin 3 - White/Orange - Receive +
       Pin 4 - Orange/White - Receive -
       Pin 5 - White/Blue   - Transmit +

 [4.4] What is the difference between a MAU, a CAU, and a LAM?

       A MAU is a 8228 Multistation Access Unit. This unit provides eight
       workstation connectors and 2 MAU ports (also called Ring In/Ring Out

       A CAU is a 8230 Controlled Access Unit (Basically a MAU with
       intelligence). A CAU supports up to four LAMs. The Ring In/Ring Out
       ports of a CAU are copper, but can replaced with fiber connectors.

       A LAM is a Lobe Attachment Module for the 8230. Each LAM supports 20
 [4.5] Can two token ring stations be directly attached?

       Unlike Ethernet stations, token ring stations _cannot_ be directly
       attached with a cross-over cable. Because of the process required
       for inserting into a ring, a loopback process must complete and
       phantom voltage must exist on a wire for a relay to open. A MAU must
       be used to directly connect two workstations.

       However, some token ring switches allow a station to directly
       connect to a _switch_. This Direct Token Ring (DTR) connection is a
       non-standard method of connecting a switch and a workstation onto a
       single ring. This non-standard DTR connectivity does _not_ allow for
       two workstations to be directly connected.

 [4.6] What is the maximum distance between a MAU and a token ring
       station, or between two token ring stations?

       In token ring networking, distance requirements are different from
       vendor to vendor. In general terms, the recommended standard
       distance between stations for Type 1 cabling is approximately 300
       meters, and the recommended standard distance between stations for
       UTP cabling is about 150 meters.

       Token ring distances are computed as the distance between repeaters.
       IN a token ring network, each Network Interface Card (NIC) is a
       repeater. Therefore, the length between stations cannot exceed the
       cable lengths listed above.

       Some manufacturers use 'active' MAUs which can regenerate the token
       ring signal and act as a repeater. In these cases, the distances
       between the token ring workstations and the MAUs can be much larger
       than many 'passive' MAUs. Many active MAUs have other network
       management features such as SNMP capabilities and auto-station
       removal for stations inserting at the incorrect speeds.

 [4.7] What is the formula for computing adjusted ring length (ARL)?

       The adjusted ring length of a token ring network is the sum of all
       cable lengths between wiring closets, minus the shortest cable
       between wiring closets. The ARL is used to determine the total
       length of the ring, and the maximum lobe distances (see section

       This calculation determines the ring length if part of the ring is
       removed for troubleshooting. When a cable is removed from a Ring
       In/Ring Out port, the loop-back creates a much larger ring than
       normal. The ARL calculation defines the largest ring size that can
       occur, based on the shortest cable between wiring closets.

 [4.8] Why is ring length important?

       The design of any network is dependent on limits. In token ring
       networks, ring length is a large factor in the physical design of an
       error-free network. If the ring is too long, timing and attenuation
       issues can create physical-layer errors, disrupting communication
       over the entire ring.

       In the design of a token ring network, total ring length dictates
       the maximum length of cable between the workstation and the MAU.
       This value, called the lobe length, can be computed with a series of
       tables. These tables are computed for passive MAU networks. Active
       MAUs provide capabilities that deviate greatly from the values in
       these tables. Consult the manufacturer of the active MAUs for values
       that are appropriate for that equipment.

 [4.9] At what speeds does token ring run?

       Token ring runs at speeds of 4 megabits per second (500,000 bytes
       per second) and 16 megabits per second (2,000,000 bytes per second).
       Some token ring switches support a non-standard referred to as
       Direct Token Ring (DTR), or full-duplex token ring. This allows for
       16 megabit speeds in the sending and receiving directions
       simultaneously, for a maximum of 32 megabits per second (4,000,000
       bytes per second).

[4.10] How many stations are supported by a single token ring network?

       Again, this number is dependent on the token ring equipment that is
       used in the network. Current standards list a maximum of 72 stations
       on a UTP ring, and approximately 250 to 260 on a Type 1 network.

[4.11] What is High Speed Token Ring?

       High Speed Token Ring, or HSTR, is a new token ring standard that
       promises to push token ring speeds to 100 Mbps and 1 Gbps. The High
       Speed Token Ring Alliance consists of 3Com, Bay Networks, IBM,
       Madge, Olicom, UNH Interoperability Lab, and Xylan.

       The first HSTR specification will allow for 100 Mbps token ring
       speeds over both Type 1 and UTP copper cabling. Further
       specifications will tackle 100 Mbps token ring over fiber. These
       standards are due for completion in June or July of 1998. Another
       HSTR specification will allow for 1 Gbps HSTR over fiber, and this
       standard is due to be completed at the end of 1998.

       For more information on HSTR, see:

5.0 Token Ring Data Link Layer

 [5.1] What is a token?

       A token frame is a three byte frame that takes this format:

                          | SDEL   | AC     | EDEL   |
                          | 1 byte | 1 byte | 1 byte |

       The Starting Delimiter (SDEL) byte is coded as JK0JK000, where the J
       and K bits are intentional Manchester encoding violations. These
       intentional violations delineate the token from normal traffic data.
       J is the encoding violation of a 1, and K is the encoding violation
       of a 0.

       The Access Control (AC) byte is coded as PPPTMRRR. The priority bits
       (PPP) provide eight levels of priority (000 through 111). The token
       indicator bit (T) of 0 determines that the following information is
       a token, a 1 designates the following information is a frame. The
       Monitor bit (M) is used to prevent frames from constantly circling
       the ring. The Priority Reservations bits (RRR) provide token
       reservation to ring stations.

       The Ending Delimiter (EDEL) byte is coded as JK1JK1IE, where the J
       and K bits are encoding violations and the I and E bits are the
       intermediate frame and error detection bits, respectively. The
       intermediate bit is set to 1 if there are more frames to transmit in
       this set. The error detection bit is set to 1 by a station that
       recognizes a CRC error in the frame so other stations downstream do
       not report the same error.
 [5.2] What are MAC frames?

       A Media Access Control (MAC) frame is used for management of the
       token ring network. MAC frames do not traverse bridges or routers,
       since they carry ring management information for a single specific
       The MAC frame has this format:

             | SD  | AC  | FC  | DA  | SA  |Data | FCS | ED  | FS  |
       Size     1     1     1     6     6    >=0    4     1     2
       in bytes

       Starting Delimiter (SD) - See section [5.1].

       Access Control (AC) - See section [5.1].

       Frame Control (FC) - The frame control field consists of eight bits,
       coded as TT00AAAA. The Frame Type bits (T) indicate the frame type.
       Bits 2 and 3 are reserved, and are always zero. Bits four through
       eight are Attention Codes which provide the token ring adapter of
       incoming MAC information that can be copied to a special Express
       Buffer in the token ring adapter.

       Destination Address (DA) - The Destination Address specifies which
       station is to receive the frame. The Destination Address can be sent
       to a specific station, or a group of stations.

       Source Address (SA) - The Source Address is the MAC address of the
       sending station.

       Data - A MAC frame data field contains token ring management
       information, and a non-MAC (LLC) data field contains user data.

       Frame Check Sequence (FCS) - A 32 bit Cyclical Redundancy Check
       (CRC) is performed on the frame data to provide an integrity check
       of the frame data. As each station copies the frame, the CRC is
       computed and compared with the value in the FCS frame to verify that
       the frame data is correct.

       Ending Delimiter (ED) - See section [5.1].

       Frame Status (FS) - The Frame Status field provides information for
       the sending station regarding the status of the frame as it
       circulates the ring. The Frame Status field is coded as AF00AF00.
       The bits of the Frame Status field are duplicated, since this field
       does not fall under the CRC checking of the Frame Check Sequence
       bytes. The Address Recognized Indicator (ARI) is set to 1 by the
       destination station if the destination station recognizes the frame.
       The Frame Copied Indicator (FCI) is set to 1 if the destination
       station was able to copy the frame into the local adapter buffer
 [5.3] What are LLC frames?

       A Logical Link Control (LLC) frame is used to transfer data between

       LLC frames have the same frame structure as MAC frames, except frame
       type bits of 01 are used in the Frame Control (FC) byte.

 [5.4] What are Locally Administered Addresses (LAAs)?

       Token ring addresses are either locally administered or universally
       administered. Locally administered addresses are assigned by a local
       manager and universally administered addresses are assigned by a
       standards organization. Locally administered addresses are
       designated by bit one set to 1 in byte zero of the destination
       address field.
 [5.5] What are functional addresses?

       Functional addresses are assigned by the token ring specification to
       allow for communication to functional devices. Some devices include:

            Device                       Functional Address
            ------                       ------------------
            Active Monitor               C0 00 00 00 00 01
            Ring Parameter Server        C0 00 00 00 00 02
            Ring Error Monitor           C0 00 00 00 00 08
            Configuration Report Server  C0 00 00 00 00 10
            Source Route Bridge          C0 00 00 00 01 00

 [5.6] What is an Active Monitor and Standby Monitor?

       Devices are either active monitors or standby monitors. There can
       only be a single active monitor on a physical token ring. Any
       station on the ring can assume the role of Active Monitor. All other
       stations on the ring are standby monitors.

       The Active Monitor provides many functions on a token ring network:

       * The Active Monitor is responsible for master clocking on the token
       ring network and the lower level management of the token ring

       * The Active Monitor inserts a 24-bit propagation delay to prevent
       the end of a frame from wrapping onto the beginning of the frame.

       * The Active Monitor confirms that a data frame or good token is
       received every 10 milliseconds. This timer sets the maximum possible
       frame size on a token ring network to 4048 bytes on a 4 megabit
       ring, and 17,997 bytes on a 16 megabit ring.

       * The Active Monitor removes circulating frames from the ring. As a
       frame passes the Active Monitor, a special bit called a monitor
       count bit is set. If the monitor count bit is set, the Active
       Monitor assumes the original sender of the frame was unable to
       remove the frame from the ring. The Active Monitor purges this
       frame, and sends a Token Error Soft Error to the Ring Error Monitor.

       If the Active Monitor is removed from the ring or no longer performs
       the Active Monitor functions, one of the Standby Monitors on the
       ring will take over as Active Monitor.

 [5.7] What is early token release?

       In normal token ring operation, a station sending information holds
       the token until the sending data circles the entire ring. After the
       sending station strips the data from the ring, it then issues a free

       With Early Token Release (ETR), a token is released immediately
       after the sending station transmits its frame. This allows for
       improved performance, since there is no delay in the downstream
       neighbor waiting for the token.

       ETR is only available on 16 megabit rings. Stations running ETR can
       coexist with stations not running ETR.

 [5.8] What is transparent bridging?

       Transparent bridging is a method to connect two similar network
       segments to each other at the datalink layer. It is done in a way
       that is transparent to end stations, hence end-stations do not
       participate in the bridging algorithm.

       Transparent bridges are sometimes called (self) learning bridges.
       When they are turned on and receive data packets from a network
       segment they

       1) learn the relation between MAC address and segment/port, and
       2) forward the packet to all (!) other segments/ports.

       The first step in this process is essential to the "learning" aspect
       of the bridge. After some time the bridge has learned that a
       particular MAC address, say MACa, is on a particular segment/port,
       say PORT1. When it receives a packet destined for the MAC address
       MACa (from any port not being PORT1) it will no longer forward the
       packet to all ports (step 2). It knows that MACa is associated with
       PORT1 and will only forward the packet to PORT1.

       Please note that transparent bridging is most often used in a
       Ethernet environment. In a token-ring environment it can be used but
       is not common. In a token-ring environment source route bridging is
       most often used.
 [5.9] What is the spanning tree protocol?

       Spanning tree is a protocol defined in IEEE 802.1q to prevent
       bridges from creating network loops. Using the spanning tree
       protocol, bridges communicate to each other and disable certain
       ports/segments to prevent looping of packets.

       Many implementations of the spanning tree protocol are configured so
       an alternate path is available to network traffic, should the
       original path become disabled.

[5.10] What is source route bridging?

       Source route bridging is a method to connect two similar network
       segments to each other at the datalink layer. It is done in a
       "distributed way" where end-stations participate in the bridging
       algorithm, thus the name _source_ routing. (as compared to
       transparent bridging, refer to 5.9]).

       In a source-route bridging environment a source end-station will
       sent out a "route explorer" frame (broadcast) to find out the route
       to the destination end-station. Source route bridges will forward
       these frames to all segments/ports. The source route bridge will add
       route information (the segment the packet came from) to the frame
       prior to forwarding it. This route information is called the Routing
       Information Field (RIF).

       Eventually, the route explorer frame reaches the destination
       end-station INCLUDING THE COMPLETE ROUTE (via the RIF) the packet
       took. The destination end-station then uses this RIF to reply to the
       source end-station directly (i.e. no broadcast). Please note that
       the reply traverses all bridges in reverse order of the route
       explorer frame and INCLUDES THE RIF. When the reply reaches the
       source end-station, the complete network route is known by both the
       source and destination end-stations. Subsequent packets will use
       this route information (i.e. no broadcast).

       It is possible that a network has multiple routes to a destination
       end-station. In this scenario, the source end-station will receive
       more than one reply to the route explorer broadcast. In most cases,
       the source end-station uses the route that was received first.

       In a source-route bridging environment, the end-stations discover
       and store information about the network topology. In a transparent
       bridging environment, the (transparent) bridge discovers and stores
       this information.

[5.11] What is token ring switching?

       From a functional point of view switching is exactly the same as
       bridging. However switches use specially designed hardware called
       Application Specific Integrated Circuits (ASICs) to perform the
       bridging and packet-forwarding functionality (as supposed to
       implementations using a central CPU and special software).
       Consequently, switches are much faster than ancient bridges.

       When you compare token-ring switches to multiport (token-ring)
       bridges in more detail you can find more differences. For example
       switches forward packets directly and at wire-speed from port x to
       port y. However ancient multiport bridges are often implemented
       using a internal token-ring segment. Consequently a packet being
       source-routed from port x to port y makes two (!) hops (from the
       segment attached to port x to the internal ring and from the
       internal ring to the segment attached to port y). Please note that
       there is a maximum on the number of hops a packet is allowed to make
       (8 or 16, don't remember) and that the maximum aggregate throughput
       of the multiport bridge is limited by the capacity of the internal

       Other goodies token-ring switches often offer are support for
       virtual LAN's and full duplex connections.

[5.12] What is the process for inserting into a ring?

       This information is derived from the TMS380 Second-Generation Token
       Ring User's Guide from Texas Instruments published in 1990.

       In order for any token ring adapter to insert successfully into a
       ring, the adapter must successfully complete 5 steps known as the
       phases of insertion. These phases are described as follows:

       Phase 0 - Media Lobe Check,
       Phase 1 - Physical Insertion,
       Phase 2 - Address Verification,
       Phase 3 - Participation in Ring Poll, and
       Phase 4 - Request Initialization.

       Phase 0: Media Lobe Check

       The first step for any token ring device initialization is known as
       the Lobe Media Check. This phase actually tests the transmitter and
       receiver of the adapter and the cable between the adapter and the
       Multistation Access Unit (MAU). A MAU physically wraps the
       connection cable's transmit wire back to its receive wire. The
       effect is that the adapter can transmit media test Media Access
       Control (MAC) frames up the cable to the MAU (where it is wrapped)
       and back to itself. The adapter will send lobe media test MAC frames
       to destination address 00-00-00-00-00-00 (with the source address of
       the adapter) and a Duplication Address Test (DAT) MAC frame
       (containing the address of the adapter as both the source and
       destination) up the cable during this phase. 2047 test MAC frames
       and 1 DAT frame must be successfully transmitted in order to
       complete phase 0. The adapter will only attempt this phase 2 times
       before reporting a failure.

       Phase 1: Physical Insertion

       In phase 1, the adapter attempts to open the relay on the MAU by
       sending a DC current (4.1-7.0 V for current less than 1mA or 3.5-7.0
       V for current of 1-2 mA, in either case known as phantom since it is
       transparent to any signals being transmitted on the same wires) up
       the transmit wire pair. Once the phantom is applied and the relay on
       the MAU opens (hopefully), the adapter waits to see one of the
       following: an Active Monitor Present (AMP) MAC frame, a Standby
       Monitor Present (SMP) MAC frame, or a ring purge MAC frame. Any one
       of these frames indicates that there is an Active Monitor (AM)
       present on the ring, which indicates successful completion of phase
       1. If an AM is not detected within 18 seconds, the adapter initiates
       the monitor contention process. The monitor contention process
       determines a new AM based on the highest address of those contending
       for AM status. Not all stations contend for AM every time contention
       is initiated. If contention is not completed within one second, the
       adapter fails to open. If the adapter becomes AM and initiates a
       purge and the purge process does not complete within one second, the
       adapter fails to open. If the adapter receives a beacon MAC frame or
       a remove station MAC frame, the adapter fails to open.

       Phase 2: Address Verification

       This phase is also referred to as the duplicate address test. This
       phase insures that the address of this adapter is unique to the
       local ring. Since token ring allows Locally Administered Addresses
       (LAAs), you could end up with two adapters with the same MAC address
       if this check was not done. The adapter sends out a series of DAT
       MAC frames like the ones used in phase 0. If there is no other
       adapter on the local ring with the same address as the adapter in
       phase 2, then it will receive all of its DAT frames back with the
       ARI (Address Recognized Indicator) and FCI (Frame Copied Indicator)
       bits set to zero. At this time, the adapter would enter phase 3. If
       the adapter in phase 2 receives 2 frames with either the ARI or FCI
       bits set to 1, then it de-inserts from the ring and reports a
       failure to open. If phase 2 does not complete within 18 seconds, the
       adapter reports a failure and de-inserts.

       Phase 3: Participation in Ring Poll.

       This process is where a station learns its upstream neighbor's
       address and informs its downstream neighbor of the inserting
       adapter's address. It is this process which creates a station list
       or ring map. The adapter must wait until it receives an AMP or SMP
       frame with the ARI/FCI bits set to zero. Upon receipt of an AMP or
       SMP frame with the ARI/FCI bits set to zero, the station flips both
       bits (ARI and FCI) to one (if enough resources are available) and
       queues an SMP frame for transmission. If no such frames are received
       within 18 seconds, the adapter reports a failure to open and
       de-inserts from the ring. If the adapter successfully participates
       in a ring poll, it proceeds into the final phase of insertion.

       Phase 4: Request Initialization

       The adapter sends four request initialization MAC frames to the
       functional address of the Ring Parameter Server (RPS). If there is
       no RPS present on the ring, the adapter uses its own default values
       and reports successful completion of the insertion process. If the
       adapter receives one of its four request initialization MAC frames
       back with the ARI/FCI bits set to one, it waits 2 seconds for a
       response. If there is no response, it re-transmits up to four times.
       At this time, if is no response, it reports a request initialization
       failure and de-inserts from the ring.
[5.13] How do you troubleshoot the insertion process?

       Phase 0: Media Lobe Check Troubleshooting

       Failure to complete phase 0 is one of the most common failures when
       trying to configure a token ring network interface card into a PC.
       Most token ring adapters, upon failing, will display some cryptic
       error message like "Adapter failed to open." or "Failed
       initialization.". Always check the cable connected to the adapter
       and where it connects to the hub. In order for an adapter to pass
       phase 0, it must have a closed circuit to test. Either use a wrap
       plug or insure that the adapter is connected to a working MAU. Bad
       cabling causes many adapter problems during the insertion process.
       Things to look for include: "Is the adapter configured to use the
       correct media port, UTP or STP?", "Is the cable run from the adapter
       to the hub complete and correct?", "What exactly is between the
       adapter and the hub, how many punch downs, what kind of cable, how
       is it wired, where does it run, are there phones in the same cable,
       etc.?", and "What kind of media filter are you using?". Keep in mind
       that what will work at 4 Mbps will not always work at 16 Mbps.

       Phase 1: Physical Insertion Troubleshooting

       Many of the problems associated with phase 1 of insertion are the
       same ones accounted for in phase 0, especially bad cabling and bad
       media filters. The error messages at this stage are usually the same
       as those received during phase 0 and are just as cryptic. If the
       cabling checks out, look at the hub. Does the hub indicate
       insertion? Does the hub make a chattering noise when the adapter is
       trying to insert? Are there other stations on the ring? The problem
       could be cabling or a faulty adapter (not supplying consistent
       phantom can cause the relay to chatter). Some simple steps would be
       to move the station to a working location or try a known working
       station at this location. Can the station in question insert if the
       other stations are turned off? It could be that there is a physical
       layer problem (i.e. wiring, line noise, jitter, etc.) on the ring
       which shows up as more stations insert, causing purges and beaconing
       which will kick off a new inserting adapter. If you are sure that
       the cabling is acceptable, you will probably need a protocol
       analysis trace before making any prognosis as to why you can not
       insert. The analyzer should be the immediate upstream neighbor to
       the station trying to insert.

       A normal insertion that completes successfully commonly causes
       several token ring errors on the ring during phase 1. Common errors
       at this time would include burst errors, line errors, token errors,
       ring purges, and lost frame errors, due to the simple act of opening
       the relay. Do not assume that the existence of these errors indicate
       a problematic ring, as these are normal symptoms that occur during
       the insertion process.
       Phase 2: Address Verification Troubleshooting

       The only time you need to worry about this phase is when you are in
       an environment where the user is using LAAs. When users start
       entering LAAs, the chance of duplicate addresses goes up
       dramatically. The most common cause is copying a working adapter
       configuration files (config.sys, autoexec.bat, net.cfg,
       protocol.ini.) between stations. The symptom to look for is when the
       adapter is trying to insert, it will (under most circumstances)
       insert and de-insert twice in rapid succession and then quit trying.
       It will also provide messages such as "Adapter failed to
       initialize." or it might actually say "Failed Duplicate Address
       Test.". Change the LAA or move to another ring and try to reinsert.
       If you can get a trace of the failure to insert, you can look for
       the duplicate address test frames. As in phase 1, insert your
       analyzer directly upstream to the failing adapter.

       Phase 3: Participation in Ring Poll Troubleshooting
       Some probing is usually required to find out the root of the problem
       at this phase. If you can not insert, time how long it takes for an
       inserting adapter to fail. If the answer is 15-20 seconds, then it
       is probably failing the ring poll. If the answer is less than 15
       seconds, the problem could still be the ring poll failure but more
       information will be required.

       If you get a trace of a ring that is failing the ring poll process,
       you will find a MAC frame issued by the AM called Neighbor
       Notification Incomplete (NNI) or Ring Poll Failure. This frame
       should be issued every 7 seconds in a failing ring just prior to an
       AMP MAC frame. The NNI frame is important because it will contain
       the address of the last station to successfully complete the ring
       poll process. The downstream neighbor from this station is usually
       the culprit and removing the downstream neighbor should cure the
       problem. Exceptions will occur if there is more than one station
       that is not participating in the ring poll process. Another way to
       cure the problem is to have all stations on the ring power down for
       30 seconds (at the same time) and then try to reinsert, however,
       this is only a temporary cure and not a fix since the problem will
       likely reappear. If the failure is proven to be a ring poll failure
       and the problem persists, the customer may need to look at
       contacting the vender of the failing adapter(s) or device(s) and see
       if the vender has a newer driver available.

       Phase 4: Request Initialization Troubleshooting

       Failure at this stage is rare but could point to a failing adapter
       on either the RPS or on the inserting station, a physical layer
       problem on the ring (cabling, jitter, etc.), or some other
       `undocumented' feature of the environment in which the failure
       occurs. The only method to determine a failure at this stage is to
       use an analyzer inserted as the upstream neighbor to the adapter in
       question. An RPS is generally best serviced by bridges or routers
       since they are usually running the server software required to
       perform these services.

6.0 Token Ring Errors and Troubleshooting

 [6.1] What are isolating and non-isolating errors?

       An isolating error can be attributable to a specific station on the
       ring. Non-isolating errors are usually reported by the Active
       Monitor, and cannot be attributed to a specific station.

 [6.2] What is the claim process?

       This is when a the ring elects a new Active Monitor.  It is also
       called the monitor contention process. Election of a new active
       monitor occurs due to one of the following events:

       1. An active or standby monitor detects a loss of signal.

       2. A station attaching to a ring does not detect an active monitor
          (this can happen for 1st station on the ring).

       3. A station's receive-notification timer expires.

       4. A active monitor's ring purge timer expires.

       5. A standby monitor's good_token timer expires (no management
          frames from active monitor detected).

       Once one of these conditions occurs, the ring station(s) go/goes
       into Claim-Token-Transmit mode by broadcasting Claim Token MAC
       frames. The station with the highest MAC address becomes active
 [6.3] What is a beacon frame?

       A beacon frame is sent generated by a station or stations that do
       not detect a receive signal. A station or stations will broadcast
       these beacon MAC frames with the until the receive signal is
       restored. A beacon MAC frame indicates the station's nearest active
       upstream neighbor (NAUN).
 [6.4] What is promiscuous mode?

       Promiscuous mode is used with protocol analysis or network
       management software that allows visibility to all data traversing
       the ring. Not all token ring adapters support promiscuous mode, and
       special drivers and/or configurations are required for using an
       adapter card in promiscuous mode.

 [6.5] What non-commercial software is available to monitor a token ring

       A list of commercial, shareware, and freeware software is available

7.0 Other Information

 [7.1] What token ring books are available?

       The Certified Network Expert (CNX) consortium described in section
       [7.2] has an excellent list of token-ring books. This list is
       designed for the network professional who is studying for the CNX
       certification, and is a very comprehensive list of technical
       publications. This CNX reading list can be found at:

       An updated CNX study library can also be found on

 [7.2] What certifications are available regarding token ring networks?

       A token ring-specific certification is available through the
       Certified Network eXpert (CNX) program. This certification is token
       ring topology specific, and does not emphasize any network operating
       system. Visit for more information on the CNX
       exam. Sylvan Prometric administers the CNX exam, and their web page
       is also keeps a
       CNX resources page at

 [7.3] What companies make token ring adapter cards and MAUs?

       Attachmate (formerly DCA)       <>
       Black Box                       <>
       Cabletron                       <>
       Compaq (formerly Thomas Conrad) <>
       D-Link                          <>
       IBM                             <>
       Intel                           <>
       Kingston                        <>
       Madge                           <>
       NDC                             <>
       Proteon                         <>
       Racore                          <>
       Relia Technologies
       Olicom                          <>
       Sim Ware Technologies / Wiremold Communications
       SMC                             <>
       3Com                            <>
       Unicom                          <>
       Xircom                          <>

                --- End of comp.dcom.lans.token-ring FAQ ---

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