Multiprotocol Encapsulation over ATM Adaptation Layer 5 (RFC1483)
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
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.
Network Working Group Juha Heinanen
Reguest for Comments: 1483 Telecom Finland
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.
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 . 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) .
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
Relay Service Specific Convergence Sublayer (FR-SSCS), as defined in
I.36x.1 , is used over the CPCS of AAL5, then routed and bridged
PDUs are carried using the NLPID multiplexing method described in RFC
1294 . Appendix A (which is for information only) shows the
format of the FR-SSCS-PDU as well as how IP and CLNP PDUs are
encapsulated over FR-SSCS according to RFC 1294.
2. Selection of the Multiplexing Method
It is envisioned that VC Based Multiplexing will be dominant in
environments where dynamic creation of large numbers of ATM VCs is
fast and economical. These conditions are likely to first prevai...