3Com CoreBuilder 9000, User Manual

Page: 364 / 468

364 C
HAPTER
13: E
STABLISHING
ATM C
HANNELS
Signaling AAL
The signaling described previously takes place in signaling channels kept
separate from the channels used for data transmission. The SAAL
(Signaling AAL) is the adaptation layer used in these signaling channels.
The SAAL provides a reliable transmission service to the signalling layer
above it, because this layer does not possess any error-compensation
mechanisms of its own. This is implemented using SAAL’s service-specific
convergence sub-layer, the SSCOP protocol (Service Specific
Connection-Oriented Protocol).
SSCOP The SSCOP has a message set of 16 messages called PDUs (Protocol Data
Units) together with a set of watchdog timers. The SD and SDP PDUs
carry the signaling protocol described previously. The watchdog timers
allow the system to continue operating when an response to a message is
not received within an expected time interval.
Table 48 shows the SSCOP PDU set according to type.
Table 48
SSCOP PDUs According to Type
Function PDU Description
Establishment BGN Request initialization
BGAK Request Acknowledgment
Release END Disconnect Command
ENDAK Disconnect Acknowledge
Resynchronization RS Resynch Command
RSAK Resynch Acknowledgment
Reject BGREJ Reject initialization request
Assured data transfer SD Sequenced data
SDP Sequenced data with ack request
POLL Sending status with receive status
polling
STAT Receive status
USTAT Unsolicited receive status
Unassured data transfer UD Unnumbered data packets
Management data
transfer MD Unassured transfer of management
data