An IRM (Internal Resource Manager) function within Lotus Sametime Unified Telephony's UCE (Universal Call Engine) integrates bandwidth management with call processing in order to provide robust call handling, such as the rerouting of a call via the PSTN (Public Switched Telephone Network) when there is insufficient bandwidth in the enterprise network to carry the call, based on bandwidth availability.
The IRM can limit the calls over a bandwidth-limited link based on
Number of Calls:
the concurrent calls per link are simply counted, and when the limit is reached, no new calls are admitted.
the Lotus Sametime Unified Telephony calculates the used bandwidth based on the negotiated codecs in the SDP.
If both are defined then the limit will be enforced as soon as one is crossed.
In case of bandwidth-based policies, Open Scape Voice's behavior for new calls will be as follows:
- The IRM calculates the required bandwidth based on the most bandwidth-consuming codec(s) in the SDP offer. It then adds the required bandwidth to the currently used bandwidth and compares it to the limit provisioned for the applicable policy. If the limit is not reached, the required bandwidth is reserved and the call is allowed to proceed. Otherwise the call is terminated.
- Once the offered SDP is answered, the IRM calculates the actual bandwidth used by the call based on the negotiated codec in the SDP answer. The Lotus Sametime Unified Telephony then updates the resource reservation with the actual bandwidth used by the call.
- When the call is disconnected, the IRM releases reserved resources used by the call.
When an initial offer without session description
(SDP) is received, a "dummy reservation" for the most bandwidth-consuming voice
codec allowed for that link is attempted. If this fails, the call is dropped immediately.
Otherwise the call proceeds and when the first 200 OK with SDP offer arrives from the callee, IRM releases the "dummy reservation" and tries to reserve the actually required media resources. This may fail if the SDP tries to include a media type other than voice
(e.g. video) and the required resources are not available. In this case a 606 Not Acceptable is sent to the caller and the call is dropped. Otherwise the 200 OK is forwarded to the caller.
Dropping answered calls can be prevented by setting the Allow Answered Calls
flag in the related CAC policy, but this may result in overbooking the CAC policies' resources.
How to Perform RM (Resource Management) SettingsParent topic: CAC (Call Admission Control)