Life of a High Priority VoIP Packet Cont

Re-mark DSCP;

voice gets highest priority (LLQ)

Re-mark DSCP;

voice gets highest priority (LLQ)

DSCP=40

While the packet traversed the service provider network, the DSCP was marked as 46 so that the packet would be immediately dispatched as a member of the service provider real-time class.

But the packet was marked DSCP = 40 by the customer before it entered the service provider network. At the edge of the service provider network, the DSCP is re-marked to "40" to match the classification scheme being used by the enterprise customer.

The packet is dispatched immediately using the LLQ method that always provides absolute priority to voice packets.

Upon arriving at the enterprise network router, the voice packet is sent out the LAN interface toward the switch using FIFO queuing on the LAN interface.

Upon arriving at the Cisco Catalyst 2950 switch, the DSCP-to-CoS mappings are used to recognize the frame as a high-priority voice frame, and the Layer 2 priority is set to CoS = 5. The frame jumps ahead of any nonvoice frame and is immediately dispatched to the PQ.

The packet finally arrives at the receiving IP Phone.

The RTP header is used to ensure that the packet is synchronized correctly with other packets from the same voice flow and that the voice payload is delivered.

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