    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.

    Cohen                                                          [Page iv]

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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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       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>"

    Cohen                                                           [Page 3]

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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.

    Cohen                                                           [Page 4]

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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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          #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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          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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             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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          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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             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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                           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.

    Cohen                                                          [Page 30]