INSTALLATION - CONFIGURATION CALL SERVER : VOICE ON IP
Ed. 048/20 Réf. 3EH 21000 BSAA
- Gateway Bandwidth / QoS: for each ARS input to a remote H.323 gateway, a bandwidth must be
reserved for the Voice over IP to the remote H.323 gateway. The number of simultaneous commu-
nications that can be held depends on this value:
E.g. if the total bandwidth corresponding to the data rate to a remote gateway is 256 Kbps and the
mean traffic level is 50%, it is wise to define a bandwidth of 128 Kbps for Voice over IP.
Remark concerning the quality of service - QoS
If we take our example, site A can make H.323 calls to sites B and C. One assumes that the bandwidths
reserved for Voice over IP at the LAN/WAN gateways of each site are:
- bandwidth reserved for VoIP on site A: 1024 Kbps (20 calls or more)
- bandwidth reserved for VoIP on site B: 128 Kbps (5 simultaneous calls)
- bandwidth reserved for VoIP on site C: 64 Kbps (2 simultaneous calls)
In this configuration one sees that it is possible to make 7 simultaneous calls from site A to the remote
H.323 gateways: 5 to site B and 2 to site C.
7 DSPs can therefore be assigned in the "VoIP access" pool for site A (7 being the number of DSPs nee-
ded to call sites B and C simultaneously).
However, let us assume that there is no ongoing communication between sites A and C, and that 5
calls are established between A and B. The total number of VoIP network access DSPs consumed in
PBX A is 5: therefore 2 DSPs remain available to establish two other calls to site B.
Yet in this example we exceed the bandwidth reserved for Voice over IP at the LAN/WAN gateway of
site B: the quality of service is no longer guaranteed.
To avoid downgrading the VoIP service, the system uses the "Gateway Bandwidth" field of the ARS table
associated with the input to the remote H.323 gateway of site B, which will be configured at 128 Kbps
(5 calls), as quality indicator (QoS): although there are still 2 DSPs available, the PBX will refuse a 6th
call to site B.
Nota : This service is not available if an external gatekeeper is used.
Bandwidth Number of simultaneous commu-
nications possible
None No communication possible De-
fault value
55.6 Kbps 1
64 Kbps 2
128 Kbps 5
256 Kbps 10
512 Kbps 20
≥ 1024 Kbps > 20
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