Toshiba IP edge General Description Manual page 135

When sharing voice and data on the same network segment, the data will cause some jitter in voice
communications, especially on slower segments.
jitter assuming a worst case data packet size of 1500 bytes (Maximum Transmission Unit (MTU) =
1500) based on a segment's bandwidth. This also requires that the routers connecting the segment
through the WAN support Diffserv.
A router that doesn't support Diffserv may stack multiple data packets together increasing
Note
the jitter perhaps indefinitely. And the voice quality will be indeterminate.
Table 14
No. of
B-Channels
of WAN
2
4
6
8
24
Class definition categories are shown in
Table 16 shows the amount of bandwidth required for setting up and tearing down calls
independent of the amount of voice traffic.
So the amount of bandwidth that is required on a segment to support a specific number of calls is
the sum of the number of channels multiplied by the bandwidth for the selected CODEC and
interval, plus the bandwidth required for the selected number of busy hour call attempts. And the
jitter is determined by the bandwidth of the WAN segment.
Example: If you want to support 4 calls using the G.711 CODEC with a 20 msec. interval, this
requires 4 x 88 kbps = 352 kbps of bandwidth. In addition, to support 1000 busy hour call
attempts, 6 kbps must be added for a total of 358 kbps. If only voice is going to be carried on the
segment, then a 384 kbps segment (6 B-channels) is sufficient.
If voice and data are going to be mixed on the segment, then at least 25% (89.5 kbps) should be
added, or more, based on the amount of data traffic desired. In this case, a total of 447 kbps will be
required which would best be supported by a 512 kbps segment (8 B-channels). This would result
in an expected jitter of 20 ms in the voice traffic.
When using the MEGACO+ protocol with IP telephones, keep alive packets are exchanged
between the IPU and the phones. This traffic amounts to 3 kbps per phone.
IPedge General Description
IPedge Net IP Jitter on Mixed Voice and Data WAN
Bandwidth
transmit max.
(kbps)
128
256
384
512
1536
Table
Table 15 IPedge Net IP Class Definitions
Class
Excellent
Good
Fair
Poor
Table 16 IPedge Net IP Bandwidth Required for Call Setup
Traffic Rate
1
(BHCA )
1000
2000
4000
6000
1. BHC = Busy Hour Call Attempts
03/16
IPedge Net and IP Telephone Bandwidth Requirements
Table 14 shows calculations of the amount of
Time to
Expected
Jitter (ms)
MTU (ms)
93.75 100
46.88 50
23.44 30
15.63 20
1.00 1
15.
Delay (ms) Jitter (ms)
< 20 < 10
< 50 < 20
< 100 < 50
< 200 < 100
Required
Bandwidth
6
12
23
36
Appendix – Specifications
Class
Poor
Fair
Fair
Good
Excellent
121