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Page 102 - Part 2 Voice Over IP How Do I?
Examples
Calculation for G729 without Header compression on a PPP link:
((4 + 20 + 8 + 12 + 20)* 50 * 8) = 64 * 50 * 8 = 25600
Calculation for G729 with
Header compression on a PPP link:
((4 + 7 + 20)* 50 * 8) = 31 * 50 * 8 = 12400
The table below provides a quick reference for these calculations.
Compression Type Payload (bytes) Bandwidth bits per sec (single call)
LAN PPP without
IPHC
PPP with
IPHC
729 20 29600 25600 12400
711 160 85600 81600 68400
723 24 20592 17952 9240
The table shows there is a significant reduction in bandwidth requirements when
running IPHC. Use the table to determine the bandwidth that will be used for
each VoIP call. The number of VoIP calls that can occupy a link is directly related
to the bandwidth /speed oO that the link. As General rule 75/80 % of the WAN
bandwidth should be used for VoIP traffic; use the VPN line to restrict the number
of calls the IPNC will allow to occupy the link.
Note: IPHC implementation on the IPNC is such that for speeds above
1024Kbps IPHC compression is not applied to either non-voice or voice
streams. In this way the effect of latency on the speech quality is reduced.
Page 102 - How Do I? INDeX IPNC Cassette Administration Manual
Part 2 Voice Over IP 38DHB0002UKDD – Issue 7 (22/11/02)