Technical data

17.3 SAP - Job Number Assignment
Before you can work with free channels, the SAPs involved must be
configured with the free layer 2 links.
While the dual-port RAM sizes are limited to 128 bytes for the predefined
S5S5 links, data units of up to 256 bytes can be exchanged using "free
channels". This allows transmission of blocks of data with a maximum
length of 242/256 bytes. The first 8 bytes of these 256 bytes are used for
the header.
B8976060/02 Appendix
17 - 5 Volume 1