Multiprotocol Encapsulation over ATM Adaptation Layer 5 (RFC1483)
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2019-Feb-10
Internet Society Requests For Comment (RFCs)
This memo describes two encapsulations methods for carrying network interconnect traffic over ATM AAL5. [STANDARDS-TRACK]
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.
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
Heinanen [Page 1]
RFC 1483 Multiprotocol over AAL5 July 1993
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 prevail in private ATM networks. LLC Encapsulation, on the other hand, may be desirable when it is not practical for one reason or another to have a separate VC for each...