Page 78 of 378 ITG Engineering Guidelines

553-3001-202 Standard 1.00 April 2000

Disable silence suppression at tandem nodes

Silence suppression introduces a different concept of half-duplex or

full-duplex at the voice message layer that results in a kind of statistical

multiplexing of voice messages over the WAN.

When Meridian 1 equipped with an ITG node serves as a tandem switch in a

network where some circuit-switched trunk f acili ties have an exces sively low

audio level, silence suppression, if en abled, will degrade the quality of se rvice

by causing choppiness of speech. Under tandem switching condit ions with

G.723.1
(5.3
kbit/s)
30 20 60 86 27.5 9.6 10.9 17.0
G723.1
(6.3
kbit/s)
30 24 64 90 28.8 10.2 11.5 17.0
T.30/T38
G3 Fax
Modem
(14.4
kbit/s)
16.6 30 7 0 96 46.1 33.6 37.5 50.9
25 30 70 96 30.7 22.4 25.0 33.9
Note 1:
Based on voice multi frame encapsulation for Realtime Transport Protocol per H.323 V2.
Note 2:
The bolded rows contain the default payload/packet size for each codec in the MAT.
Note 3:
T-LAN data rate is the effective Ethern et bandwidth consum ption.
Note 4:
40% voice traffic reduction due to silence s uppression; no suppression for fax.
Note 5:
T-LAN kbit/s for voice traffic = (1-40%)*2 *Ethernet frame bits*8/frame duration in ms
Note 6:
WAN kbit/s for voice traffic = (1-40%)*IP packet bytes*8/frame duration in m s
Note 7:
24 ports per ca rd for all codecs
Note 8:
Overhead (RTP/UDP heade r + IP header) of packet s over the voice payload multif rame is 40
bytes; overhead of Ether net frame over IP packet i s 26 bytes.
Note 9:
The above bandwidth ca lculation does not inc lude an Interframe gap, be cause of the low
probability of occurring in this type of application.

Table 5

Silence suppression enabled, T-LAN Ethernet and WAN IP bandwidth usage per ITG port

(Part 2 of 2)

Codec type
Codec
Multi -
frame
duration
in ms
(payload)
(one way)
Voice/fax
payload
Multi -
frame
in bytes
(one way)
IP voice
packet in
bytes
(one way)
Ethernet
voice
packet in
bytes
(one way)
Bandwidth
use on
T-LAN in
kbit/s
(two way)
Bandwidth
use on
WAN in
kbit/s
(one way)
WAN with
Frame
Relay
overhead
in kbit/s
(one-way)
WAN with
ATM
overhead
in kbit/s
(one-way)