Specifications

Appendix – Specifications
Strata Net IP and IPT Bandwidth Requirements
Strata CIX General Description 08/14 211
When sharing voice and data on the same network segment, the data will cause some jitter in voice
communications, especially on slower segments. Table 53 shows calculations of the amount of
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.
Note A router that doesn’t support Diffserv may stack multiple data packets together increasing
the jitter perhaps indefinitely. And the voice quality will be indeterminate.
Class definition categories are shown in Table 54.
Table 55 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 IPT telephones, keep alive packets are exchanged
between the IPU and the phones. This traffic amounts to 3 kbps per phone.
Table 53 Strata Net IP Jitter on Mixed Voice and Data WAN
No. of
B-Channels
of WAN
Bandwidth
(kbps)
Time to
transmit max.
MTU (ms)
Expected
Jitter (ms)
Class
2 128 93.75 100 Poor
4 256 46.88 50 Fair
6 384 23.44 30 Fair
8 512 15.63 20 Good
24 1536 1.00 1 Excellent
Table 54 Strata Net IP Class Definitions
Class Delay (ms) Jitter (ms)
Excellent < 20 < 10
Good < 50 < 20
Fair < 100 < 50
Poor < 200 < 100
Table 55 Strata Net IP Bandwidth Required for Call Setup
Traffic Rate
(BHCA
1
)
1. BHC = Busy Hour Call Attempts
Required
Bandwidth
1000 6
2000 12
4000 23
6000 36