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RTP/UDP/IP Header Compression
How RTP/UDP/IP Compression and Decompression Occurs
Introduction
Determining if the
Packet can be
Compressed
2-28
This section describes how the Vanguard RTP/UDP/IP compression and
decompression occurs.
When the Vanguard receive a packet, the first step is to determine if the packet can
be compressed. The Vanguard performs this process:
Step
1
The Vanguard examines the packet's RTP/UDP/IP header information and
looks at the following:
• Source IP address
• Destination IP address
• Source UDP port
• Destination UDP port
• SSRC field
These items define a flow. If the packet with a new flow is received, this
flow information will be saved in the compressor list.
2
The Vanguard compares the packet's source and destination UDP ports
against a list of configured UDP port ranges on which header compression
can be applied. If either source or destination ports match the configuration,
the packet is considered for compression. If the packet's source and
destination UDP port:
• Match the configured list, the packet is checked against the negative
cache.
• Does not match the configure list, the packet is forwarded without
compression.
3
The negative cache contains a list of dynamically identified flows that
should not be compressed.
The packet's flow (source IP address, destination IP address, source UDP
port, destination UDP port, and SSRC field) is compared against the
negative cache. If the packet's flow:
• Matches an entry in the negative cache, the packet is forwarded without
compression.
• Does not match an entry in the negative cache, the packet can be
compressed.
Process
Vanguard Routing Model
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