The Separation of Bearer and Signal (SBS) functionality means that SBS trunks do not carry the bearer (audio) portion of a SBS call, and thus do not require Media Processor (VoIP Engine) resources. SBS trunks have different maintenance behavior than regular H.323 IP trunk groups, for example, they can be brought into service as soon as the associated signaling group is in service.

Each SBS signaling trunk group requires an assigned signaling group that is administered on the Signaling Group form.

Communication Manager administrators can define system-wide acceptable limits of round-trip delay and packet loss on the System Parameters Maintenance form, IP page (change signaling-group). If the Bypass if IP thresholds exceeded? field for H.323 signaling groups is set to yes and the IP thresholds are exceeded, the signaling group and its associated IP trunks are placed in maintenance bypass mode. This means that:

• Idle trunks are taken out of service, making them unavailable for new outgoing calls.
• Active trunks are taken out of service after the existing call drops.

Since IP network congestion can be one source of delay in establishing SBS calls, Communication Manager administrators could consider utilizing this bypass mechanism to ensure acceptable SBS feature operation. However, the system-wide packet delay/loss parameters are typically administered to ensure proper voice quality and might be more restrictive than necessary for signaling-only calls. In other words, Bypass could cause SBS trunks to be taken out of service unnecessarily when delays are disruptive to voice quality, but not severe enough to have a noticeable impact on the overall SBS call setup delay. Avaya recommends that you carefully consider the system-wide packet loss and delay settings before implementing Bypass on SBS signaling groups.

Also, the periodic background tests that drive the Bypass capability require Media Processor resources, and if there are none, which is possible because SBS trunks do not require media processor resources, the Bypass test does not execute and no Bypass occurs.