RFC 1483 (rfc1483) - Page 3 of 16
Multiprotocol Encapsulation over ATM Adaptation Layer 5
Alternative Format: Original Text Document
RFC 1483 Multiprotocol over AAL5 July 1993
AAL5 CPCS-PDU Format
+-------------------------------+
| . |
| . |
| CPCS-PDU Payload |
| up to 2^16 - 1 octets) |
| . |
| . |
+-------------------------------+
| PAD ( 0 - 47 octets) |
+-------------------------------+ -------
| CPCS-UU (1 octet ) |
+-------------------------------+
| CPI (1 octet ) |
+-------------------------------+CPCS-PDU Trailer
| Length (2 octets) |
+-------------------------------|
| CRC (4 octets) |
+-------------------------------+ -------
The Payload field contains user information up to 2^16 - 1 octets.
The PAD field pads the CPCS-PDU to fit exactly into the ATM cells
such that the last 48 octet cell payload created by the SAR sublayer
will have the CPCS-PDU Trailer right justified in the cell.
The CPCS-UU (User-to-User indication) field is used to transparently
transfer CPCS user to user information. The field has no function
under the multiprotocol ATM encapsulation described in this memo and
can be set to any value.
The CPI (Common Part Indicator) field alings the CPCS-PDU trailer to
64 bits. Possible additional functions are for further study in
CCITT. When only the 64 bit alignment function is used, this field
shall be codes as 0x00.
The Length field indicates the length, in octets, of the Payload
field. The maximum value for the Length field is 65535 octets. A
Length field coded as 0x00 is used for the abort function.
The CRC field protects the entire CPCS-PDU except the CRC field
itself.
4. LLC Encapsulation
LLC Encapsulation is needed when several protocols are carried over
the same VC. In order to allow the receiver to properly process the
incoming AAL5 CPCS-PDU, the Payload Field must contain information
Heinanen
