RFC 741 (rfc741) - Page 2 of 30

Specifications for the Network Voice Protocol (NVP)

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



                        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.




Cohen
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