RFC 1483 (rfc1483) - Page 2 of 16
Multiprotocol Encapsulation over ATM Adaptation Layer 5
Alternative Format: Original Text Document
RFC 1483 Multiprotocol over AAL5 July 1993
Relay Service Specific Convergence Sublayer (FR-SSCS), as defined in
I.36x.1 [3], is used over the CPCS of AAL5, then routed and bridged
PDUs are carried using the NLPID multiplexing method described in RFC
1294 [4]. 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 carried protocol. This is the case, for
example, if the ATM network only supports (semi) Permanent Virtual
Circuits (PVCs) or if charging depends heavily on the number of
simultaneous VCs.
When two ATM stations wish to exchange connectionless network
interconnect traffic, selection of the multiplexing method is done
either by manual configuration (in case of PVCs) or by B-ISDN
signalling procedures (in case of Switched VCs). The details of B-
ISDN signalling are still under study in CCITT [5]. It can, however,
be assumed that B-ISDN signalling messages include a "Low layer
compatibility" information element, which will allow negotiation of
AAL5 and the carried (encapsulation) protocol.
3. AAL5 Frame Format
No matter which multiplexing method is selected, routed and bridged
PDUs shall be encapsulated within the Payload field of AAL5 CPCS-PDU.
The format of the AAL5 CPCS-PDU is given below:
Heinanen