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RFC 741 - Specifications for the Network Voice Protocol (NVP)


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NWG/RFC 741                                           DC 22 Nov 77 42444

                         SPECIFICATIONS FOR THE

                      NETWORK VOICE PROTOCOL (NVP)

                                  and

         Appendix 1:  The Definition of Tables-Set-#1 (for LPC)

              Appendix 2:  Implementation Recommendations

   NSC NOTE 68

   (Revision of NSC Notes 26, 40, and 43)

   Danny Cohen, ISI

   January 29, 1976
NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

                                CONTENTS

   PREFACE                                                           iii

   ACKNOWLEDGMENTS                                                    iv

   INTRODUCTION                                                        2

   THE CONTROL PROTOCOL                                                2
      Summary of the CONTROL Messages                                  3
      Definition of the CONTROL Messages                               4
      Definition of the <WHAT> and <HOW>
         Negotiation Tables                                            8
      On RENEGOTIATION                                                10
      The Header of Data Messages                                     10

   THE LPC DATA PROTOCOL                                              13

   EXAMPLES FOR THE CONTROL PROTOCOL                                  15

   APPENDIX 1:  THE DEFINITION OF TABLES-SET-#1                       18
      General Comments                                                20
      Comments on the PITCH Table                                     20
      Comments on the GAIN Table                                      21
      Comments on the INDEX7 Table                                    21
      Comments on the INDEX6 Table                                    21
      Comments on the INDEX5 Table                                    21
      The PITCH Table                                                 22
      The GAIN Table                                                  24
      The INDEX7 Table                                                25
      The INDEX6 Table                                                26
      The INDEX5 Table                                                27

   APPENDIX 2:  IMPLEMENTATION RECOMMENDATIONS                        28

   REFERENCES                                                         30

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Specifications for the Network Voice Protocol (NVP)

                                PREFACE

   The major objective  of ARPA's  Network  Secure  Communications (NSC)
   project  is to develop  and demonstrate  the feasibility  of  secure,
   high-quality, low-bandwidth, real-time, full-duplex (two-way) digital
   voice communications  over  packet-switched  computer  communications
   networks.   This kind  of  communication  is  a  very  high  priority
   military  goal for all levels  of  command  and  control  activities.
   ARPA's  NSC projrct will supply digitized speech which can be secured
   by existing  encryption  devices.  The major goal of this research is
   to demonstrate  a digital  high-quality,  low-bandwidth, secure voice
   handling  capability  as part of the general military requirement for
   worldwide  secure voice communication.  The development at ISI of the
   Network  Voice Protocol  described herein is an important part of the
   total effort.

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Specifications for the Network Voice Protocol (NVP)

                            ACKNOWLEDGMENTS

   The Network Voice Protocol (NVP), implemented first in December 1973,
   and has been in use since then for local and transnet real-time voice
   communication over the ARPANET at the following sites:

      o    Information  Sciences  Institute,  for LPC and CVSD,  with  a
           PDP-11/45 and an SPS-41.

      o    Lincoln  Laboratory,  for LPC and CVSD,  with a TX2  and  the
           Lincoln FDP, and with a PDP-11/45 and the LDVT.

      o    Culler-Harrison,  Inc.,  for LPC,  with  the  Culler-Harrison
           MP32A and AP-90.

      o    Stanford Research Institute, for LPC, with a PDP-11/40 and an
           SPS-41.

   The NVP's success  in bridging  the  differences  between  the  above
   systems  is due mainly  to the cooperation  of  many  people  in  the
   ARPA-NSC  community,  including Jim Forgie (Lincoln Laboratory), Mike
   McCammon  (Culler-Harrison),  Steve Casner  (ISI)  and Paul  Raveling
   (ISI),  who participated  heavily  in the definition  of the  control
   protocol;   and   John   Markel   (Speech   Communications   Research
   Laboratory),  John Makhoul  (Bolt Beranek  & Newman,  Inc.) and Randy
   Cole (ISI),  who participated in the definition of the data protocol.
   Many other people  have contributed  to the NVP-based effort, in both
   software and hardware support.

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Specifications for the Network Voice Protocol (NVP)

                            1.  INTRODUCTION

   Currently,  computer  communication  networks  are designed  for data
   transfer.   Since there  is  a  growing  need  for  communication  of
   real-time interactive voice over computer networks, new communication
   discipline  must be developed.   The current HOST-to-HOST protocol of
   the ARPANET,  which was designed  (and optimized)  for data transfer,
   was found  unsuitable  for  real-time  network  voice  communication.
   Therefore   this  Network  Voice  Protocol  (NVP)  was  designed  and
   implemented.

   Important design objectives of the NVP are:

      - Recovery  of loss of any message  without  catastrophic effects.
        Therefore  all answers have to be unambiguous, in the sense that
        it must be clear to which inquiry a reply refers.

      - Design  such that no system  can tie up the resources of another
        system unnecessarily.

      - Avoidance of end-to-end retransmission.

      - Separation of control signals from data traffic.

      - Separation of vocoding-dependent parts from vocoding-independent
        parts.

      - Adaptation to the dynamic network performance.

      - Optimal  performance,  i.e.  guaranteed  required bandwidth, and
        minimized maximum delay.

      - Independence from lower level protocols.

   The protocol consists of two parts:

      (1) The control protocol,

      (2) The data protocol.

   Control messages are sent as controlled (TYPE 0/0) messages, and data
   messages  may be sent as either controlled (TYPE 0/0) or uncontrolled
   (TYPE  0/3)   messages   (see  BBN  Report  1822  for  definition  of
   MESSAGE-TYPE).

   Throughout this document a "word" means a "16-bit quantity".

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Specifications for the Network Voice Protocol (NVP)

                        2.  THE CONTROL PROTOCOL

   Throughout  this document the 12-bit MESSAGE-ID (see BBN Report 1822)
   is referred to as LINK (its 8 MSBs) and SUB-LINK (its 4 LSBs).

   The control  protocol starts with an initial connection phase on link
   377 and continues on other links assigned at run time.

   Four links are used for each voice communication:

      Link L    will be used for control, from CALLER to ANSWERER.
      Link K    will be used for control, from ANSWERER to CALLER.
      Link L+1  will be used for data,    from CALLER to ANSWERER.
      Link K+1  will be used for data,    from ANSWERER to CALLER.

   Both  L and K should be between 340 and 375 (octal). L and K need not
   differ.

   The first message  (CALLER  to ANSWERER)  on link 377 indicates which
   user wants to talk to whom and specifies K. As a response (on K), the
   ANSWERER either refuses the call or accepts it and assigns L.

   The CALLER  then calls  again  (this  time on link L).  The  ANSWERER
   initiates  a negotiation  session  to verify the compatibility of the
   two parties.

   The negotiation  consists  of suggestions  put forth by  one  of  the
   parties,  which are either  accepted  or rejected by the other party.
   The suggesting  party in the negotiation  is called  the  NEGOTIATION
   MASTER.  The other party is called the NEGOTIATION SLAVE. Usually the
   ANSWERER  is the negotiation  master,  unless agreed otherwise by the
   method described later.

   If the negotiation  fails,  either  party may terminate  the call  by
   sending  a "GOODBYE".  If the negotiation  is successfully ended, the
   ANSWERER  rings bells to draw human attention  and sends "RINGING" to
   the CALLER. When the call is answered (by a human), a "READY" is sent
   to the CALLER  and the data starts flowing (on L+1 and K+1). However,
   a "READY" can be sent without a preceeding "RINGING".

   This bell ringing  occurs  only after the  initial  call  (not  after
   renegotiation).

   The assignment  of L and  K  cannot  be  changed  after  the  initial
   connection phase.

   Only one control message can be sent in a network-message. Extra bits
   needed to fill the network-message are ignored.

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Specifications for the Network Voice Protocol (NVP)

   The length  of control  messages  should never exceed a single-packet
   (i.e., 1,007 data bits).

   Control  messages  not recognized by their receiver should be ignored
   and should  not cause any error condition  resuting in termination of
   the  connection.  These  messages  may  result  from  differences  in
   implementation level between systems.

   SUMMARY OF THE CONTROL MESSAGES

      #1   "1,<WHO>,<WHOM>,K"

      #2   "2,<CODE>" or only "2"

      #3   "3,<WHAT>,<N>,<HOW(1),...HOW(N)>"

      #4   "4,<WHAT>,<HOW>"

      #5   "5,<WHAT>,<HOW>" or only "5,<WHAT>"

      #6   "6,L" or only "6"

      #7   "7"

      #8   "8"

      #9   "9"

      #10  "10,<ID>"

      #11  "11,<ID>"

      #12  "12,<IM>"

      #13  "13,<YM>,<OK>"

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Specifications for the Network Voice Protocol (NVP)

   DEFINITION OF THE CONTROL MESSAGES

      #1  CALLING (on 377 and L)

         This  call is issued first on link 377 and later on link L. Its
         format  is "1,<WHO>,<WHOM>,K", where <WHO> and <WHOM> are words
         which identify  respectively  the calling  party and the  party
         that is being  called, and K is as defined above. The format of
         the <WHO> and <WHOM> is:

            (HHIIIIIIXXXXXXXX)

         where  HH are 2 bits identifying  the HOST,  followed by 6 bits
         identifying  the  IMP,  followed  by  8  bits  identifying  the
         extension   (needed   because   there  may  be  more  than  one
         communication unit on the same HOST).

         The system  which sends this message  is defined as the CALLER,
         and the other system is defined as the ANSWERER.

      #2  GOODBYE (TERMINATION, on L or K)

         This message has the purpose of terminating calls at any stage.

         ICP can be terminated  (on  K)  either  negatively  by  sending
         either   a  single  word  "2"  ("GOODBYE")  or  the  two  words
         "2,<CODE>",  or positively  by sending  the two words "6,L", as
         described later.

         After the initial  connection phase, calls can be terminated by
         either  the  CALLER  (on  L)  or  the  ANSWERER  (on  K).  This
         termination  has two words:  "2,<CODE>",  where <CODE>  is  the
         reason for the termination, as specified here:

            0.  Other than the following.

            1.  I am busy.

            2.  I am not authorized to talk with you.

            3.  Request of my user.

            4.  We believe you are down.

            5.  Systems incompatibility (NEGOTIATION failure).

            6.  We have problems.

            7.  I am in a conference now.

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Specifications for the Network Voice Protocol (NVP)

            8.  You made a protocol error.

      #3  NEGOTIATION INQUIRY (on L or K)

         Sent by the NEGOTIATION  MASTER for compatibility verification.
         The format is:

         "3,<WHAT>,<LIST-LENGTH>,<HOW-LIST>", meaning

         "CAN-YOU-DO,<WHAT>,<LIST-LENGTH>,<HOW-LIST>".

         The <HOW-LIST>  is a list of pointers  into agreed-upon tables,
         as shown below.

      #4  POSITIVE NEGOTIATION RESPONSE (on L or K)

         Sent by the NEGOTIATION  SLAVE in  response  to  a  NEGOTIATION
         INQUIRY. The format is:

         "4,<WHAT>,<HOW>", meaning: "I-CAN-DO,<WHAT>,<HOW>".

      #5  NEGATIVE NEGOTIATION RESPONSE (on L or K)

         Sent by the NEGOTIATION  SLAVE in  response  to  a  NEGOTIATION
         INQUIRY. The format is either:

         "5,<WHAT>,0", meaning "I-CAN'T-DO-<WHAT>-IN-ANY-OF-THESE-WAYS",

         or:  "5,<WHAT>,N",  meaning  inability  to accept  any  of  the
         options  offered  in the INQUIRY, but using "N" as a suggestion
         to  the  ANSWERER   about  another  possibility.  Examples  are
         presented later in this report.

      #6  READY (on L or K)

         Sent by either  party to indicate readiness to accept data. Its
         format  is "6,L"  in the reply  to the initial  call,  and  "6"
         thereafter.

      #7  NOT READY (on L or K)

         Sent by either party to indicate unreadiness to accept data. It
         is always a single word: "7".

      #8  INQUIRY (on L or K)

         Sent by either  party to inquire about the status of the other.
         It is always  a single  word: "8". It is answered by #6, #7, or
         #9.

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Specifications for the Network Voice Protocol (NVP)

      #9  RINGING (on K)

         Sent  by  the  ANSWERER   after  the  negotiations   have  been
         successfully  terminated  and human  permission  is  needed  to
         proceed  further. The ringing will continue for 10 seconds, and
         then stop,  UNLESS  a #8 is received.  This message is always a
         single word: "9".

      #10  ECHO REQUEST (on L or K)

         Sent by whichever  party is interested in measuring the network
         delays.  Its only purpose  is to  be  echoed  immediately.  The
         format  is "10,<ID>",  where <ID> is any word used to  identify
         the ECHO.

      #11  ECHO (on L or K)

         Sent in response  to ECHO REQUEST.  The  format  is  "11,<ID>",
         where <ID> is the word specified  by #10. The implementation of
         this feature  is not compulsory,  and no connection  should  be
         terminated due to lack of response to ECHO-REQUEST.

      #12  RENEGOTIATION REQUEST (on L or K)

         Can be sent by either party at ANY stage after LINKS are agreed
         upon.  This message consists of the two words "12,<IM>". If the
         word <IM> (for I  MASTER)  is  non-zero,  the  sender  of  this
         message  requests  to be the NEGOTIATION MASTER. If it is zero,
         the receiver of this message is requested to be the NEGOTIATION
         MASTER. Renegotiation is described later.

      #13  RENEGOTIATION APPROVAL (on L or K)

         This message  may be  sent  by  either  party  in  response  to
         RENEGOTIATION   REQUEST.   It  consists   of  the  three  words
         "13,<YM>,<OK>".  If  <OK>  is  non-zero,  this  is  a  positive
         acknowledgment  (approval).  If it is zero,  this is a negative
         acknowledgment  (i.e., refusal). <YM> is set to be equal to the
         <IM> of #12, for identification purposes.

      Messages #7, #8, and #9 are always a single word. Messages #1, #3,
      #4, and #5 are several words long. Messages #2 and #6 are either a
      single word or two words long. #10, #11 and #12 are always 2 words
      long.  Message  #13 is always 3 words long. Message #1 is always 4
      words long.

      Message  #1 is sent only by the CALLER, #3 only by the NEGOTIATION
      MASTER, and #4 and #5 only by the NEGOTIATION SLAVE. Message #9 is

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Specifications for the Network Voice Protocol (NVP)

      sent only by the ANSWERER.  All the other  control messages may be
      sent by either party.

      The last <HOW> which was both suggested  by the NEGOTIATION MASTER
      (in #3)  and accepted  by the NEGOTIATION  SLAVE  (in #4) for each
      <WHAT> is assumed to be in use.

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Specifications for the Network Voice Protocol (NVP)

   DEFINITION OF THE <WHAT> AND <HOW> NEGOTIATION TABLES:

      <WHAT>                          <HOW>

      1. VOCODING                   * 1. LPC
                                    + 2. CVSD
                                      3. RELP
                                      4. DELCO

      2. SAMPLE PERIOD

         (in microseconds)            N. N (*150) (+62)

      3. VERSION

                                    * 1. V1 (see definition below)
                                    + 2. V2 (see definition below)

      4. MAX MSG LENGTH (in bits)

         NVP header included          N. N (*976 and +976)
         (32 bits) but not HOST/IMP
         leader and not HOST/IMP padding

      5. If LPC:

         Degree                       N. For N coefficients (*10)

         If CVSD:

         Time Constant
         (in milliseconds)            N. N (+50)

      6. Samples per Parcel           N. N (*128) (+224)

      7. If LPC:

         Acoustic Coding            * 1. SIMPLE (see below)
                                      2. OPTIMIZED

      8. If LPC:

         Info Coding                * 1. SIMPLE (see below)
                                      2. OPTIMIZED

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Specifications for the Network Voice Protocol (NVP)

      9. If LPC:

         Pre-emphasis                 N. N (*58, for
         1 - mu x [Z**-1]               mu = 58/64 = 0.90625)
         N = 64 x mu

      10. If LPC:

         Table-set                    N. N (*1)
                                         See definition of Set #1
                                         in Appendix 1

      (* indicates recommended options for LPC)
      (+ indicates recommended options for CVSD)

      No parameter  (<WHAT>) should be inquired about by the NEGOTIATION
      MASTER  if some option (<HOW>) for it has been previously accepted
      by the NEGOTIATION  SLAVE implicitly in the "VERSION". The purpose
      of this restriction  is  to  avoid  a  possible  conflict  between
      individual parameters and the VERSION-option.

         Version 1 (V1) is defined as:

            1-1    LPC
            2-150  150 microseconds sampling
            3-1    V1
            5-10   10 coefficients
            6-128  128 samples per parcel
            7-1    SIMPLE acoustic coding
            8-1    SIMPLE information coding
            9-58   mu = 58/64 = 0.90625
            10-1   Tables set #1

         Version 2 (V2) is defined as:

            1-2    CVSD
            2-62   62 microseconds sampling (16 KHz sampling)
            3-2    V2
            5-50   50 msec time constant
            6-192  192 samples per parcel

         Note that this defines  every negotiated  parameter, except MAX
         MSG LENGTH.

         SIMPLE and OPTIMIZED codings will be described below in Section
         3.

         All the negotiation  is managed  by the NEGOTIATION MASTER, who
         decides  how much negotiation is needed, and what to do in case

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Specifications for the Network Voice Protocol (NVP)

         some discrepancy (incompatibility) is discovered: either to try
         alternative options or to abort the connection. Upon completion
         of successful  negotiation, the NEGOTIATION MASTER sends either
         #9 (RINGING)  only  if it is the ANSWERER  and if  this  is  an
         initial  connection,  else it sends  #6  (READY-FOR-DATA),  and
         probably  inquires  with #8 about the readiness  of  the  other
         party.  The inquiries  (#8) before the successful completion of
         the negotiation are ignored. However, these inquiries after the
         first RINGING  (#9)  and before the first READY (#6) are needed
         to keep the ANSWERER ringing.

         Note that the negotiation process can be shortened by using the
         VERSION option, as shown in the examples that follow.

   ON RENEGOTIATION

      At any stage after links  are  agreed  upon,  either  party  might
      request  a RENEGOTIATION.  If the request is approved by the other
      party, either party might become the NEGOTIATION MASTER, depending
      on the type of renegotiation  request.  When renegotiation starts,
      no previously  negotiated  agreements  (except LINK numbers) hold,
      and all items have to be  renegotiated  from  scratch.  Note  that
      renegotiation  may entirely  replace  the  negotiation  phase  and
      allows the CALLER to be the NEGOTIATION MASTER.

      Upon issuance  (or reception)  of RENEGOTIATION  REQUEST, all data
      messages   are  ignored  until  the  positive  indication  of  the
      successful completion of the renegotiation (#6).

      After the completion  of renegotiation,  the frame-count  (see the
      section on MESSAGE-HEADER) may be reset to zero.

   THE HEADER OF DATA MESSAGES

      Data messages  are the messages  which contain vocoded speech. The
      first 32 bits of each data message  is the  MESSAGE-HEADER,  which
      carries sequence and timing information as described below.

      For each vocoding  scheme a "FRAME" is defined as the transmission
      interval  (as agreed  upon at the negotiation  stage in <WHAT#6>).
      Since this interval  is defined  by the  number  of  samples,  its
      duration  can be found by multiplying the sampling period <WHAT#2>
      by the interval  length  (in samples) <WHAT#6>. For example, in V1
      the sampling  period  is 150  microseconds  and  the  transmission
      interval is 128 samples, which yields:

         128*150 microseconds = 19.2 milliseconds.

      The data describing  a FRAME is called a PARCEL. Each parcel has a

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Specifications for the Network Voice Protocol (NVP)

      serial  number.  The first parcel  created after the completion of
      the negotiation  (or every RENEGOTIATION)  has the  serial  number
      zero. Each message contains an integral number of parcels.

      The serial number of the first parcel in the message is put in the
      first   16  bits  of  the  message  and  is  referred  to  as  the
      MESSAGE-TIME-STAMP. Note that this time stamp is synchronized with
      the data stream.  Note also that these  16 bits are  actually  the
      third  word  of  the  message,  following  the  2  words  used  as
      IMP-to-HOST leader (see BBN Report 1822).

      The next bit in the header is the WE-SKIPPED-PARCELS bit, which is
      described  later.  The next 7 bits tell how many parcels there are
      in  the  message;   this  number  is  called  the  COUNT,  or  the
      PARCEL-COUNT.

      Note that if message  number  N has the time stamp  T(N)  and  the
      count  C(N),  then  T(N+1)  must  be  greater  than  or  equal  to
      T(N)+C(N). Usually T(N+1) = T(N)+C(N), unless the XMTR decided not
      to send some parcels  due to silence.  If this  happens  then  the
      WE-SKIPPED-PARCELS  bit is set to ONE,  else it is  set  to  ZERO.
      Hence, if T(N+1) is found by the RCVR to be greater than T(N)+C(N)
      and the WE-SKIPPED-PARCELS is zero, some message must be lost.

      Note that by definition  the time stamps on messages monotonically
      increase, except for wrap-around.

      The message  header  structure  is illustrated  by  the  following
      diagram:

       WORD 1           WORD 2           WORD 3          WORD 4
!................!................!................!................!...
!P000TTTTHHIIIIII!LLLLLLLLZZZZZZZZ!TTTTTTTTTTTTTTTT!WCCCCCCCSSSSSSSS!DDD
!................!................!................!^...............!...
!<--HOST/IMP-OR-IMP/HOST-LEADER-->!<--TIME-STAMP-->!^<COUNT><-SAVE->!<-D
                                                    ^
                                           WE-SKIPPED-PARCELS

         P = PRIORITY (one bit = 1)
         T = MESSAGE TYPE (4 bits = 0011)
         L = link ("L" OR "K", 8 bits, greater than 337 octal)
         D = data bits (from here to the end of the message)

         ZZZZZZZZ = 8 ZERO bits
         HHIIIIII = HOST (8 bits, destination or source)
         CCCCCCC = parcel COUNT (7 bits)
         SSSSSSSS = 8 bits saved for future applications
         TTTTTTTTTTTTTTTT = TIME STAMP (16 bits)

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Specifications for the Network Voice Protocol (NVP)

         The first parcel  sent by either party after the NEGOTIATION or
         RENEGOTIATION should have the serial number set to zero.

         During  silence  periods,  the XMTR might  send a  "6"  or  "7"
         message  periodically.  If it does not do so,  the  RCVR  might
         interrogate  the livelihood of the XMTR by sending periodically
         "8" ("ARE-YOU-THERE?") or #10 (ECHO-REQUEST) messages.

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Specifications for the Network Voice Protocol (NVP)

                       3.  THE LPC DATA PROTOCOL

   The DATA sent at each transmission interval is called a PARCEL.

   Network messages always contain an integral number of PARCELs.

   There are two independent  issues  in the coding.  One is, obviously,
   the acoustic  coding,  i.e., which parameters have to be transmitted.
   SIMPLE  acoustic  coding  is sending  all  the  parameters  at  every
   transmission interval. OPTIMIZED acoustic coding sends only as little
   as acoustically  needed.  DELCO is an example  of OPTIMIZED  acoustic
   coding.

   In this document  only the format  of the SIMPLE  acoustic  coding is
   defined.

   All the transmitted  parameters are sent as pointers into agreed-upon
   tables.  These tables  are  defined  as  two  lists  of  values.  The
   transmitter table {X(J)} is used in the following way: The value V is
   coded  as the code  J if X(J-1) < V =< X(J). The receiver table {R(J)
   is used to retrieve  the value R(J) if the code J was received. X(-1)
   is implicitly  defined  as minus-infinity,  and X(Jmax) is explicitly
   defined as plus-infinity.

   For each parameter, {X(J)} and {R(J)} may be defined independently.

   The second  coding  issue is the information  coding  technique.  The
   SIMPLE  (information-wise)  way of sending  the information is to use
   binary   coding  for  the  codes  representing  the  parameters.  The
   OPTIMIZED  way is to compute  distributions for each parameter and to
   define the appropriate coding. It is very probable that the PITCH and
   GAIN will be decoded  absolutely in the first PARCEL of each message,
   and incrementally thereafter.

   At present, only the SIMPLE (information-wise) coding is used.

   The details  of the LPC data protocol  and its Tables-Set-#1  can  be
   found in Appendix 1.

Cohen                                                          [Page 13]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   Following  is the definition  for the  format  of  the  SIMPLE-SIMPLE
   coding, according to Tables-Set-#1:

   For each parcel:

      PITCH              6 bits  (PITCH=0 for UNVOICED)

      GAIN               5 bits

      I(1)               7 bits

      I(2)               7 bits

      I(3)               6 bits

      I(4)               6 bits

      I(5)               5 bits

      I(6)               5 bits

      I(7)               5 bits

      I(8)               5 bits

      I(9)               5 bits

      I(10)              5 bits

   where  each of the I(j)  is an index  for  inverse  sine  coding.  If
   K(j)=arcsin(Theta(j))  and N bits are assigned  for its transmission,
   then I(j)=(Theta(j)/Pi)*2**N.

   Hence  at  each  transmission   interval   (128  samples   times  150
   microseconds)  67 bits are sent, which results in a data rate of 3490
   bps.  Since this bandwidth  is well within  the capabilities  of  the
   network,  SIMPLE-SIMPLE  coding  is used,  which requires  the  least
   computation  by the hosts.  Note that this data rate is a peak  rate,
   without the use of silence.

Cohen                                                          [Page 14]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

                 4.  EXAMPLES FOR THE CONTROL PROTOCOL

   Here is an example for a connection:

      (377)  C: 1,<WHO>,<WHOM>,340    Please talk to me on 340/341.

      (340)  A: 2,1                   I refuse, since I'm busy.

   Another example:

      (377)  C: 1,<WHO>,<WHOM>,360    Please talk to me on 360/361.

      (360)  A: 6,350                 OK.  You talk to me on 350/351.

      (350)  C: 1,<WHO>,<WHOM>        I want to talk to you.

      (360)  A: 3,1,1,2               Can you do CVSD?  (ANSWERER tries
                                      to be the NEGOTIATION MASTER)

      (350)  C: 12,1                  I want to be it.

      (360)  A: 13,1                  That's OK with me.

      (350)  C: 3,1,1,2               Can you do CVSD?

      (360)  A: 5,1,1                 No, but I can do LPC.

      (350)  C: 3,1,1,3               Can you do RELP?

      (360)  A: 5,1,1                 No, but I can do LPC.

      (350)  C: 3,1,1,1               How about LPC?

      (360)  A: 4,1,1                 LPC is fine with me.

      (350)  C: 3,2,1,150             Can you use 150 microseconds
                                      sampling?

      (360)  A: 4,2,150               I can use 150 microseconds.

      (350)  C: 3,4,3,976,1040,2016   Can you use 976, 1040, or 2016
                                      bits/msg?

      (360)  A: 4,4,976               I can use 976.

      (350)  C: 3,5,1,10              Can you send 10 coefficients?

      (360)  A: 4,5,10                I can send 10.

Cohen                                                          [Page 15]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

      (350)  C: 3,6,1,64              Can you use a 64 sample
                                      transmission?

      (360)  A: 4,6,64                I can use 64.

      (350)  C: 3,7,2,1,2             SIMPLE or OPTIMIZED acoustic
                                      coding?

      (360)  A: 4,7,2                 OPTIMIZED!

      (350)  C: 3,8,1,1               Can you do SIMPLE info coding?

      (360)  A: 4,8,1                 I can do SIMPLE.

      (350)  C: 3,9,1,58              mu = 0.90625?

      (360)  A: 4,9,58                Fine with me.

      (350)  C: 3,10,1                Table set #1?

      (360)  A: 4,10,1                Of course!

      (350)  C: 6                     I am ready.  (Note:  No "RINGING"
                                      sent)

      (350)  C: 8                     And you?

      (360)  A: 6                     I am ready, too.

         .......                      Data is exchanged now,

         .......                      on 351 and 361.

      (350)  C: 10,1234               Echo it, please.

      (360)  A: 11,1234               Here it comes!

         .......

      (360)  A: 10,3333               Now ANSWERER wants to measure

      (350)  C: 11,3333               ...the delays, too.

         .......

      (???)    X: 2,3                 Termination by either user.

Cohen                                                          [Page 16]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   Another example:

      (377)  C: 1,<WHO>,<WHOM>,360    Please talk to me on 360/361.

      (360)  A: 6,340                 Fine.  You send on 340/341.

      (340)  C: 1,<WHO>,<WHOM>        I want to talk to you.

      (360)  A: 3,3,1,1               Can you use V1?

      (340)  C: 4,3,1                 Yes, V1 is OK.

      (360)  A: 3,4,1,1984            Can you use up to 1984 bits/msg?

      (340)  C: 5,4,976               No, but I can use 976.

      (360)  A: 3,4,1,976             Can you use up to 976 bits/msg?

      (340)  C: 4,4,976               I can use 976.

      (360)  A: 9                     Ringing (note how short this
                                      negotiation is!!).

         .......

      (340)  C: 8                     Still there?

      (360)  A: 9                     Still ringing.

         .......

      (340)  C: 8                     Still there?

      (360)  A: 9                     Still ringing.

         .......

      (340)  C: 8                     How about it?

      (360)  A: 9                     Still ringing.

      (340)  C: 2                     Forget it!  (No reason given.)

Cohen                                                          [Page 17]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

                               APPENDIX 1

                           THE DEFINITION OF:

                             TABLES-SET-#1

                                   by

                             John D. Markel

                Speech Communication Research Laboratory

                       Santa Barbara, California

Cohen                                                          [Page 18]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

                             TABLES-SET-#1

   This set includes tables for:

      PITCH -  64 values, PITCH table
      GAIN  -  32 values, GAIN table
      I( 1) - 128 values, INDEX7 table
      I( 2) - 128 values, INDEX7 table
      I( 3) -  64 values, INDEX6 table
      I( 4) -  64 values, INDEX6 table
      I( 5) -  32 values, INDEX5 table
      I( 6) -  32 values, INDEX5 table
      I( 7) -  32 values, INDEX5 table
      I( 8) -  32 values, INDEX5 table
      I( 9) -  32 values, INDEX5 table
      I(10) -  32 values, INDEX5 table

   These tables  are defined  specifically  for a sampling period of 150
   microseconds.

Cohen                                                          [Page 19]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   GENERAL COMMENTS

      The following  tables  are arranged in three columns, {X(j)}, {j},
      and {R(j)}.  Note that the entries in the {X(j)} column are half a
      step off the other columns.  This is to  indicate  that  INTERVALS
      from X-domain (pitch, gain, and the Ks) are mapped into CODES {j},
      which are transmitted  over the network,  to be translated  by the
      receiver   into  the  {R(j)}.   These  intervals  are  defined  as
      OPEN-CLOSE  intervals.  For  example,  the  PITCH  value  (at  the
      transmitter)  of 4131 belongs to the interval "(4024,4131]", hence
      it is coded  as j=6 which  is mapped  by the receiver to the value
      21.  Similarly, the value of 2400 for INDEX7 is found to belong to
      the interval  "(2009,2811]", coded into the CODE 3 and mapped back
      into 2411.

      Note  that  if N bits  are used  by a certain CODE, then there are
      2**N+1  entries  in the X-table,  but only  2**N  entries  in  the
      R-table.

      The  transformation   values   used  for  PITCH,   GAIN,  and  the
      K-parameters  (in the X- and R-tables)  are as defined in NSC Note
      42.

      Values  above  and below  the range of the X-table are mapped into
      the maximum and minimum table indices, respectively.

      Note that R(J) of INDEX5 is identical to R(2J) of INDEX6, and that
      R(J)  of INDEX6  is identical to R(2J) of INDEX7. Therefore, it is
      possible to store only the R-table of INDEX7, without the R-tables
      of INDEX5 and INDEX6.

      In the SPS-41 implementation there is no need to store any R-table
      for the K-parameters.  The transmitted  index can be used directly
      (with the appropriate  scaling)  as an index into the SPS built-in
      TRIG tables.

   COMMENTS ON THE PITCH TABLE

      The level J=0 defines the UNVOICED condition. The receiver maps it
      into the number of samples per frame (here 128).

      This PITCH table differs  significantly  from previous  tables and
      supersedes  the table published  in NSC Note 36.  Details  of  the
      calculation  of the table  can be found  in NSC Note 42. Immediate
      questions should be referred to John Markel.

Cohen                                                          [Page 20]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   COMMENTS ON THE GAIN TABLE

      The level J=0 defines absolute silence.

      This table  is designed  for a maximum  of 12-bit  A/D input,  and
      allows for a dynamic range of 43.5 dB.

      NSC Notes  36, 45, 56 and 58 supply background for the GAIN table.
      Gain is the energy of the pre-emphasized, windowed signal.

      This table  is the NEW GAIN table. NSC Notes 56 and 58 explain the
      reasoning behind the NEW GAIN.

   COMMENTS ON THE INDEX7 TABLE

      Positive values are coded into the range [0-63, decimal]. Negative
      values  are coded into the 7-bits two's complement of the codes of
      their absolute value [65-127, decimal].

      Note that all values -403 < V < 403 are coded as (and mapped into)
      0. Note also that the code -64 (100 octal) is never used.

      In  SPS-41  implementation,  the  R-table  is  not  needed,  since
      TRIG(2J) is the needed value R(J).

   COMMENTS ON THE INDEX6 TABLE

      Positive values are coded into the range [0-31, decimal]. Negative
      values  are coded into the 6-bits two's complement of the codes of
      their absolute values [33-63, decimal].

      Note that all values -805 < V < 805 are coded as (and mapped into)
      0. Note also that the code -32 (40 octal) is never used.

      In  SPS-41  implementation,  the  R-table  is  not  needed,  since
      TRIG(4J) is the needed value R(J).

   COMMENTS ON THE INDEX5 TABLE

      Positive  numbers  are  coded  into  the  range  [0-15,  decimal].
      Negative  numbers  are coded into the 5-bits  two's complement  of
      their absolute values, i.e., [17-31, decimal].

      Note  that  all values  -1609  < V < 1609 are coded as (and mapped
      into) 0. Note also that the code -16 (20 octal) is never used.

      In  SPS-41  implementation,  the  R-table  is  not  needed,  since
      TRIG(8J) is the needed value R(J).

Cohen                                                          [Page 21]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   THE PITCH TABLE (as of 10-29-74)

      X(J)    J  R(J)           X(J)    J  R(J)          X(J)    J  R(J)

         0                      6002                     10770
              0  128*                  21   33                   42   61
         0                      6168                     11080
              1   18                   22   34                   43   63
      3630                      6338                     11399
              2   19                   23   35                   44   65
      3724                      6515                     11728
              3   19                   24   36                   45   67
      3821                      6696                     12067
              4   20                   25   37                   46   69
      3921                      6883                     12417
              5   20                   26   38                   47   71
      4024                      7075                     12776
              6   21                   27   39                   48   73
      4131                      7274                     13147
              7   22                   28   40                   49   75
      4240                      7478                      13529
              8   22                   29   41                   50   77
      4353                      7689                     13922
              9   23                   30   43                   51   80
      4469                      7905                     14327
             10   24                   31   44                   52   82
      4588                      8129                     14745
             11   24                   32   45                   53   85
      4711                      8359                     15175
             12   25                   33   47                   54   87
      4838                      8596                     15618
             13   26                   34   48                   55   90
      4969                      8840                     16075
             14   27                   35   50                   56   93
      5104                      9092                     16545
             15   27                   36   51                   57   95
      5242                      9351                     17029
             16   28                   37   53                   58   98
      5385                      9618                     17529
             17   29                   38   54                   59  101
      5533                      9894                     18043
             18   30                   39   56                   60  104
      5684                     10177                     18572
             19   31                   40   57                   61  107
      5841                     10469                     19118
             20   32                   41   59                   62  111
      6002                     10770                     19681
                                                                 63  114
                                                         infinity

Cohen                                                          [Page 22]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

      Note:  This table has only 58 different intervals defined, since 5
      values are repeated in the R(j) table.

      * This value is the "Transmission Interval" (measured in  samples)
      as defined in item #6 of the NEGOTIATION.

Cohen                                                          [Page 23]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   THE GAIN TABLE (as of 9-17-75)

      X(J)  J  R(J)          X(J)    J   R(J)

        0                     225
            0     0                 16    245
       20                    266
            1    20                 17    289
       22                    315
            2    24                 18    342
       26                    372
            3    28                 19    404
       30                    439
            4    33                 20    478
       36                    519
            5    39                 21    565
       42                    614
            6    46                 22    667
       50                    725
            7    54                 23    789
       59                    857
            8    64                 24    932
       70                   1013
            9    76                 25   1101
       83                   1197
            10   90                 26   1301
       98                   1415
            11  106                 27   1538
      116                   1672
            12  126                 28   1818
      137                   1976
            13  148                 29   2148
      161                   2335
            14  175                 30   2539
      191                   2760
            15  207                 31   3000
      255                   infinity

Cohen                                                          [Page 24]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   INDEX7 TABLE (as of 9-23-74)

      X(J)    J    R(J)       X(J)    J    R(J)       X(J)    J    R(J)

          0                  15800                   27897
              0       0              21   16151              42   28106
        402                  16500                   28311
              1     804              22   16846              43   28511
       1206                  17190                   28707
              2    1608              23   17531              44   28899
       2009                  17869                   29086
              3    2411              24   18205              45   29269
       2811                  18538                   29448
              4    3212              25   18868              46   29622
       3612                  19195                   29792
              5    4011              26   19520              47   29957
       4410                  19841                   30118
              6    4808              27   20160              48   30274
       5205                  20475                   30425
              7    5602              28   20788              49   30572
       5998                  21097                   30715
              8    6393              29   21403              50   30853
       6787                  21706                   30986
              9    7180              30   22006              51   31114
       7571                  22302                   31238
             10    7962              31   22595              52   31357
       8351                  22884                   31471
             11    8740              32   23170              53   31581
       9127                  23453                   31686
             12    9512              33   23732              54   31786
       9896                  24008                   31881
             13   10279              34   24279              55   31972
      10660                  24548                   32058
             14   11039              35   24812              56   32138
      11417                  25073                   32214
             15   11793              36   25330              57   32286
      12167                  25583                   32352
             16   12540              37   25833              58   32413
      12910                  26078                   32470
             17   13279              38   26320              59   32522
      13646                  26557                   32568
             18   14010              39   26791              60   32610
      14373                  27020                   32647
             19   14733              40   27246              61   32679
      15091                  27467                   32706
             20   15447              41   27684              62   32729
      15800                  27897                   32746
                                                             63   32758
                                                     infinity

Cohen                                                          [Page 25]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   INDEX6 TABLE (as of 9-23-74)

      X(J)    J    R(J)              X(J)    J    R(J)

         0                          22595
              0       0                     16   23170
       804                          23732
              1    1608                     17   24279
       2411                         24812
              2    3212                     18   25330
       4011                         25833
              3    4808                     19   26320
       5602                         26791
              4    6393                     20   27246
       7180                         27684
              5    7962                     21   28106
       8740                         28511
              6    9512                     22   28899
      10279                        29269
              7   11039                     23   29622
      11793                        29957
              8   12540                     24   30274
      13279                        30572
              9   14010                     25   30853
      14733                        31114
             10   15447                     26   31357
      16151                        31581
             11   16846                     27   31786
      17531                        31972
             12   18205                     28   32138
      18868                        32286
             13   19520                     29   32413
      20160                        32522
             14   20788                     30   32610
      21403                        32679
             15   22006                     31   32729
      22595                        infinity

Cohen                                                          [Page 26]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

   INDEX5 TABLE (as of 9-23-74)

        X(J)   J    R(J)           X(J)     J    R(J)

          0                       22006
               0       0                    8   23170
       1608                       24279
               1    3212                    9   25330
       4808                       26320
               2    6393                   10   27246
       7962                       28106
               3    9512                   11   28899
      11039                       29622
               4   12540                   12   30274
      14010                       30853
               5   15447                   13   31357
      16846                       31786
               6   18205                   14   32138
      19520                       32413
               7   20788                   15   32610
      22006                       infinity

Cohen                                                          [Page 27]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

                               APPENDIX 2

                     IMPLEMENTATION RECOMMENDATIONS

   (1)   It is recommended  that the priority-bit  be turned  ON in  the
   HOST/IMP header.

   (2)   It is recommended  that in all abbreviations,  "R"  be used for
   Receiver and "X" for Transmitter.

   (3)   The  following  identifiers  and  values  are  recommended  for
   implementations:

      SLNCTH  30          SILENCE-THRESHOLD.

         Used for LONG-SILENCE  definition.  See below.  Measured in the
         same units as GAIN, in its X-table.

      TBS      1.000 sec  TIME-BEGIN-SILENCE.

         LONG-SILENCE is declared if GAIN<SLNCTH for more than TBS.

      TAS      0.500 sec  TIME-AFTER-SILENCE.

         A  delay   introduced   by  the  receiver   after  the  end  of
         LONG-SILENCE, before restarting the playback.

      TES      0.150 sec  TIME-END-SILENCE.

         The amount  of time  the transmitter  backs  up at the end of a
         LONG-SILENCE  in order to ensure  a smooth  transition  back to
         speech.

      TRI      2.000 sec  TIME-RESPONSE-INITIAL.

         Time for waiting  for response for an initial call (#1 and #3).
         The initial call is repeated every TRI until an answer arrives,
         or until TRIGU expires.

      TRIGU   20.000 sec  TIME-RESPONSE-INITIAL-GIVEUP.

         If no response  to an initial  call is  received  within  TRIGU
         after the FIRST initial call, the system gives up, assuming the
         other system is down.

      TRQ      1.000 sec  TIME-RESPONSE-INQUIRY.

         If no response  to an inquiry  (#8) is received within TRQ, the
         inquiry is repeated.

Cohen                                                          [Page 28]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

      TRQGU   10.000 sec  TIME-RESPONSE-INQUIRY-GIVEUP.

         If no response to an inquiry is received  within TRQGU from the
         FIRST inquiry,  the system  gives up, assuming the other system
         is down.

      TBDA     3.000 sec  TIME-BETWEEN-DATA-ARRIVAL.

         If no data arrives  within  TBDA, an INQUIRY (#8) is sent. This
         repeats every TBDA.

      TNR      2.000 sec  TIME-NOT-READY.

         If the other  system  is in the NOT-READY  (#7)  state for more
         than  TNR, an INQUIRY (#8) is sent. This repeats every TNR.

      TNRGU   10.000 sec  TIME-NOT-READY-GIVEUP.

         If the other  system  is in the NOT-READY  (#7)  state for more
         than  TNRGU,  then the system  gives  up,  assuming  the  other
         system is down.

      TBIN     3.000 sec  TIME-BUFFER-IN.

         The input  buffer  size is equivalent  to the time period  TBIN
         (and   its size is  the  DATA-RATE  multiplied  by  the  period
         TBIN).  If the INPUT  QUEUE  ever gets to be longer  than TBIN,
         data is discarded.

      TBOUT    3.000 sec  TIME-BUFFER-OUT.

         The output  buffer  size is equivalent to the time period TBOUT
         (and  its size  is  the  DATA-RATE  multiplied  by  the  period
         TBOUT).  If  the  OUTPUT  QUEUE  ever gets to  be  longer  than
         TBOUT, data is discarded.

Cohen                                                          [Page 29]

NWG/RFC 741                                           DC 22 Nov 77 42444
Specifications for the Network Voice Protocol (NVP)

                               REFERENCES

   Bolt Beranek  & Newman,  Inc.,  Report  No.  1822,  Interface Message
   Processor:  Specifications  for the Interconnection  of a Host and an
   IMP.

   NSC Note 42 (in progress).

   NSC Note 36,  Proposal  for NSC-LPC  Coding/Decoding Tables, by J. D.
   Markel,  Speech  Communications  Research  Laboratory, Inc., July 20,
   1974.

   NSC Note 45,  Everything  You Always Wanted to Know about Gain, by E.
   Randolph Cole, USC/Information Sciences Institute, October 11, 1974.

   NSC Note 56,  Nothing  to Lose, but Lots to Gain, by John Makhoul and
   Lynn Cosell, Bolt Beranek & Newman, Inc., March 10, 1975.

   NSC Note 58,  Gain Again,  by Randy  Cole,  USC/Information  Sciences
   Institute, March 12, 1975.

 

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