Nortel Networks NN43001-563 - Manual (Page 114)

114 ITG engineering guidelines
Codec
type
Codec
Multi -
frame
duration
(ms)
See Not
e
8.
Voice
/fax
paylo
ad
size
(byte
s)
IP
head
er
size
(byte
s)
Ether
net
head
er
size
(byte
s)
Full-d
uplex
Ether
net
Band
width
(bps)
PPP
WAN
Band
width
(bps)
See
Note
9.
Frame
Relay
WAN
bandw
idth
(bps)
ATM
WAN
bandw
idth
(bps)
10 10 40 26 60,800 45,600 46,400 84,800
20 20 40 26 34,400 26,800 27,200 42,400
DSP pro
fileAB/
G.729A
(8kbit/s)
voice
30 30 40 26 25,600 20,533 20,800 28,267
G.723.1
(5.3 kbit/s)
voice
30 20 40 26 22,933 17,867 18,133 26,571
G723.1
(6.3 kbit/s)
30 24 40 26 24,000 18,933 19,200 28,267
16.6 30 40 26 46,265 37,108 37,590 50,600 T.30/T.38
G3 Fax
25 30 40 26 30,720 24,960 24,960 33,900
Based on voice multiframe encapsulation for Realtime Transport Protocol per H.323 V2.
The bolded rows contain the default payload/packet size for each codec in TM 3.1.
TLAN subnet data rate is the effective Ethernet bandwidth consumption.
TLAN subnet kbit/s for voice traffic = 2*Ethernet frame bits*8/frame duration in ms
WAN kbit/s for voice traffic = IP packet bytes*8/frame duration in ms
Overhead (RTP/UDP header + IP header) of packets over the voice payload multiframe is 40
bytes; overhead of Ethernet frame over IP packet is 26 bytes.
An Interframe gap is not included in the above bandwidth calculation, because of the low probability
of occurring in this type of application.
Length of speech captured at each end. By definition, payload is one way.
These values do not include overhead from the network header (IEEE 802.3) that is automatically
added at the TLAN subnet link. To determine the approximate bandwidth used on the TLAN
subnet when including the network header, divide the values in the column "Bandwidth use on
TLAN subnet in kbit/s (two way)" by 2.
Silence Suppression engineering considerations
Silence Suppression/Voice Activity Detection (VAD) results in average
bandwidth savings over time, not in instantaneous bandwidth savings.
For normal conversations, Silence Suppression creates a 40% savings in
average bandwidth used. For example, a single G.729AB voice packet will
still consume 30 Kbps of bandwidth but the average bandwidth used for the
entire call would be approximately 23 Kbps.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.