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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

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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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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:

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

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

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

  • 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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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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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>"


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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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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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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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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.


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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.


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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.


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      (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.



      (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.


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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.)


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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


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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.


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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.


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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).


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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


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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.


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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


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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


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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


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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


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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.


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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.


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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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