Browse Prior Art Database

Method and Apparatus for Transmission of High Priority Traffic on High-Level Data Link Control-Like or Frame Relay Nets

IP.com Disclosure Number: IPCOM000118361D
Original Publication Date: 1997-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 144K

Publishing Venue

IBM

Related People

Duault, M: AUTHOR [+5]

Abstract

This proposal relates to telecommunications networks and, more particularly, to an improved preempt/resume protocol that allows for the transmission of a mix of low-priority packets (data packets that may be delayed) and high priority packets (voice or video packets that cannot tolerate high delays or delay variations) over low-speed communication media like frame relay networks or High-Level Data Link Control (HDLC) point-to-point links.

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This is the abbreviated version, containing approximately 48% of the total text.

Method and Apparatus for Transmission of High Priority Traffic on
High-Level Data Link Control-Like or Frame Relay Nets

      This proposal relates to telecommunications networks and, more
particularly, to an improved preempt/resume protocol that allows for
the transmission of a mix of low-priority packets (data packets that
may be delayed) and high priority packets (voice or video packets
that cannot tolerate high delays or delay variations) over low-speed
communication media like frame relay networks or High-Level Data Link
Control (HDLC) point-to-point links.

      (*) discloses a mechanism where an incoming real-time packet
is imbedded after the next block of data of the non-real-time packet
being transmitted.  This objective is accomplished by transmitting
each packet along with at least a 1-byte trailer which is used to
indicate the packet type, whether the current block of non real time
data is preempted or whether the current block of non real time data
is resumed.  However, the mechanism described in (*) does not insert
a Frame Check Sequence (FCS) after a block of data (before the
delimiting X'7E' flag).  A FCS is a 16-bit field at the end of the
data packet that implements Cyclic Redundancy Checking used to detect
transmission errors.  When a transmission error is detected, the
frame is discarded.

      The mechanism described in (*) has been defined for high
quality (usually digital) point-to-point links between communicating
nodes (see a) in Fig. 1) for which the error rate is very low.
However, such a mechanism will not work with:
  o  low-speed, low quality links, because the error rate across
      such links will be unacceptable and will lead to unnecessary
      transport of erroneous information across the network.  These
      will themselves eventually lead for retransmissions that will
      exacerbate the problem.
  o  regular HDLC (or HDLC-like) adapters whose mode of operation
      expects to receive and transmit FCS-protected frames.  Such
      adapters will systematically discard any received data for
      which the FCS field has not been appropriately set.
  o  frame relay networks used between the communicating nodes
      (see b) in Fig. 1) with frame relay frame handlers (Data
      Communicating Elements - DCEs) for which the frame relay
      standard imposes the use of an HDLC MAC-layer protocol that
      implement FCS procedures.  These frame relay networks will
      discard all data received for which a properly set FCS field
      is not present.  This will lead to an impossibility to
      communicate between the two nodes across the frame relay
      bearer service network.  Also, the network will declare
      inoperational the link between the transmitting node and
      the network.

      Furthermore, the mechanism proposed in this paper provides a
better data protection against...