2-30
Vanguard Routing Model
RTP/UDP/IP Header Compression
4-bit Sequence Number
Each packet is numbered sequentially from 0 to 15. The decompressor on the
receiving Vanguard uses the sequence number to determine if packets are received
out of sequence or if there is packet loss. The decompressor recomputes the UDP
checksum of every 16th decompressed packet. This recomputed UDP checksum is
compared against the transmitted UDP checksum. If the UDP checksums match, the
decompressor forwards the decompressed packets. If the UDP checksums do not
match, the decompressor sends a CONTEXT_STATE packet to the compressor.
The CONTEXT_STATE packet contains:
• the CID of the context which needs to be synchronized.
• the sequence number of the last correctly received compressed packet.
When the compressor receives a CONTEXT STATE packet, it sends the next packet
with a full RTP/UDP/IP header. The CONTEXT_STATE packet provides both
synchronization and error recovery.
Configuring RTP/
UDP/IP Header
Compression
To configure the RTP/UDP/IP header compression parameters, access the following
CTP menu:
Configure -> Configure LAN Connection -> LAN Connection Table
For detailed parameter descriptions refer to “LAN Connection Table Record
Parameters” section on page 3-16.
Note
The RTP/UDP/IP header compression parameters only appears for RFC 1294
encapsulation type.
