Motorola 110502USM001 - Vanguard 60 Router User Manual page 45

Compressing the
RTP/UDP/IP Header
Context Identifier
Vanguard Routing Model
T0100-01, Revision B
If the Vanguard determines that the packet can be compressed, it compresses the
packet's RTP/UDP/IP header as shown in Figure 2-19 and the table:
1st Packet
Voice/Data
RTP/UDP/IP
Packet
header
2nd Packet
Voice/Data
RTP/UDP/IP
Packet
header
3rd Packet
Voice/Data
RTP/UDP/IP
Packet
header
Figure 2-19. Compression Process
Step
1 The RTP/UDP/IP header of the first packet is not compressed. The first
packet will have the full RTP/UDP/IP header and a Context Identifier (CID)
attached to it. The CID is used to uniquely identify the session between the
compressor and decompressor modules. The Vanguard attaches the CID
before sending the packet.
2 For all subsequent packets, the Vanguard compressor module compresses
the 40 byte RTP/UDP/IP header into a 2 or 4 byte compressed header. The
Vanguard compressor module also attaches the CID to the packet.
A unique Context Identifier (CID) is assigned to each flow. The CID contains the
following information:
8-bit or 16-bit CID Number
This is used to uniquely identify a flow or session. If the number of sessions is less
than 255, an 8-bit CID number is used; if the number of sessions is greater than 255,
a 16-bit CID number is used.
RTP/UDP/IP Header Compression
Router A Router B
1
Voice/Data
Compressed RTP/UDP/
Packet
IP Header + CID
2
Voice/Data
Compressed RTP/UDP/
Packet
IP Header + CID
Voice/Data
Compressed RTP/UDP/
Packet
IP Header + CID
Process
2-29
Release 5.4