Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Protocols for Communication over a Serial Communication Link

IP.com Disclosure Number: IPCOM000116482D
Original Publication Date: 1995-Sep-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 6 page(s) / 183K

Publishing Venue

IBM

Related People

Fisk, BE: AUTHOR

Abstract

In order to communicate successfully over a serial communications link, even where established computer interfaces are used, computer applications such as those providing point to point communication facilities need to follow certain protocols. The ease of use of the applications can be affected critically by the manner in which the protocol is drawn up, and particularly by its compatibility with other protocols.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 31% of the total text.

Protocols for Communication over a Serial Communication Link

      In order to communicate successfully over a serial
communications link, even where established computer interfaces are
used, computer applications such as those providing point to point
communication facilities need to follow certain protocols.  The ease
of use of the applications can be affected critically by the manner
in which the protocol is drawn up, and particularly by its
compatibility with other protocols.

      The basic protocol described defines the exchange of different
types of packet in order to set up a call between two 'endpoints' on
different ends of a serial communications link, to propagate
information between the two 'endpoints' with a fair degree of data
integrity, and to terminate the call in an orderly fashion.  The
protocol permits a number of such 'endpoint to endpoint' links to be
established and maintained across a single serial link.  The concept
of 'endpoints' is described in (*).

The protocol defines a number of packet types:
  DATA_CONNECT
    a request to set up a new connection
  DATA_ENDPOINT
    information about the identity of the calling or called endpoint
  DATA_ADDRESS
    information about the telephone number of the called or calling
     party
  DATA_ACCEPT
    a packet to indicate acceptance of an incoming call
  DATA_HANGUP
    an indication of the requirement to terminate a call
  DATA_PACKET
    a means of conveying data within an established call

      Depending upon whether a null-modem or a real modem is being
used, the protocol is developed as follows:
  Null-Modem
  Setting up a call:
  1.  A DATA_CONNECT packet is sent by the caller
  2.  A DATA_ENDPOINT packet is sent by the caller
  3.  A DATA_ADDRESS packet is sent by the caller
  4.  A DATA_ENDPOINT packet is sent by the called party
  5.  A DATA_ACCEPT packet is sent by the called party.

      If the called party wishes to reject the call a DATA_HANGUP
packet is sent instead of the DATA_ACCEPT packet.  If, after a
certain period of time, there is no reply or the DATA_ACCEPT packet
does not arrive then it is assumed that the call has failed.

      The call continues with exchange of DATA_PACKETS and can be
terminated by either party by sending a DATA_HANGUP packet.

      In practice all calls are accepted and are rejected by sending
a DATA_HANGUP packet.  This does not affect the protocol.

      It is possible for more than one call to be set up over a
single telephone line.  In this case the protocol is established in a
similar manner.  The only difference is that a call is considered to
be in place until the last parallel call has been terminated with a
DATA_HANGUP packet.

      It should be noted that all packets are prefixed by bytes
OxFOFO.  If other characters are received instead of the expected
'trigger bytes' then an error has occurred and a DATA_HANGUP packet
is sent to term...