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Collaboration, Voice & AV · Intermediate

Call Signaling Marking

Marking SIP, SCCP, H.323 and other call control traffic as CS3 so it gets protected bandwidth without priority queuing.

Definition

Signaling is not delay sensitive like media but must not be dropped, because lost signaling causes delayed dial tone, failed setup or phone unregistration. Cisco endpoints mark signaling CS3 (older designs used AF31), and it is typically placed in a guaranteed CBWFQ class. Signaling should never be placed in the priority queue with media.

Example

A class-map matches dscp cs3 and allocates bandwidth percent 2 for call signaling on the WAN.

Exam tip

Signaling goes in a CBWFQ class with guaranteed bandwidth, not in the LLQ.

Related terms