RFC 1483 (rfc1483) - Page 1 of 16

Multiprotocol Encapsulation over ATM Adaptation Layer 5

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Network Working Group                                      Juha Heinanen
Reguest for Comments: 1483                               Telecom Finland
                                                               July 1993

            Multiprotocol Encapsulation over ATM Adaptation Layer 5

Status of this Memo

   This RFC specifies an IAB standards track protocol for the Internet
   community, and requests discussion and suggestions for improvements.
   Please refer to the current edition of the "IAB Official Protocol
   Standards" for the standardization state and status of this protocol.
   Distribution of this memo is unlimited.


   This memo describes two encapsulations methods for carrying network
   interconnect traffic over ATM AAL5.  The first method allows
   multiplexing of multiple protocols over a single ATM virtual circuit
   whereas the second method assumes that each protocol is carried over
   a separate ATM virtual circuit.

1.  Introduction

   Asynchronous Transfer Mode (ATM) based networks are of increasing
   interest for both local and wide area applications.  This memo
   describes two different methods for carrying connectionless network
   interconnect traffic, routed and bridged Protocol Data Units (PDUs),
   over an ATM network.  The first method allows multiplexing of
   multiple protocols over a single ATM virtual circuit.  The protocol
   of a carried PDU is identified by prefixing the PDU by an IEEE 802.2
   Logical Link Control (LLC) header.  This method is in the following
   called "LLC Encapsulation" and a subset of it has been earlier
   defined for SMDS [1].  The second method does higher-layer protocol
   multiplexing implicitly by ATM Virtual Circuits (VCs).  It is in the
   following called "VC Based Multiplexing".

   ATM is a cell based transfer mode that requires variable length user
   information to be segmented and reassembled to/from short, fixed
   length cells.  This memo doesn't specify a new Segmentation And
   Reassembly (SAR) method for bridged and routed PDUs.  Instead, the
   PDUs are carried in the Payload field of Common Part Convergence
   Sublayer (CPCS) PDU of ATM Adaptation Layer type 5 (AAL5) [2].

   Note that this memo only describes how routed and bridged PDUs are
   carried directly over the CPCS of AAL5, i.e., when the Service
   Specific Convergence Sublayer (SSCS) of AAL5 is empty.  If Frame


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