114
C
HAPTER
5: E
STABLISHING
ATM C
HANNELS
(see “Update Protocol Timer Resolution” on page 212 in the
Management Guide).
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 signalling channels.
The SAAL provides a reliable transmission service to the signalling layer
above it, since 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 a response to a message is
not received within an expected time interval.
Table 30 shows the SSCOP PDU set according to type.
Table 30
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
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Страница 234: ...234 APPENDIX B PROTOCOLS AND INTERFACES...
Страница 238: ...238 APPENDIX C COREBUILDER 7000 FAMILY ATM SWITCH SPECIFICATIONS...
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