16.9 Trunk Considerations

This topic describes the important considerations for when you configure CCD trunks.

  • One SAF SIP trunk and one SAF H.323 trunk can be configured for CCD.
  • If both are configured, load sharing occurs.
  • With globalized call routing, PSTN numbers are to be dialed in +E.164 format.
    1. TEHO calls received via SAF are assumed to have + in called number.
    2. Hosted directory number is in globalized format with + prefix.
  • H.323 trunks do not send + (+ is stripped).
    1. Requires incoming called-party prefix to be configured at H.323 trunk (prefix +).
    2. Otherwise, received TEHO call cannot be routed out to PSTN.
      • Difficult to troubleshoot when H.323 and SIP trunks are configured for SAF.
      • Half of the calls work (SIP), and half of the calls fail (H.323).

As mentioned earlier, you can configure one SAF-enabled SIP trunk or one SAF-enabled H.323 trunk in Cisco Unified Communications Manager and in Cisco IOS Software. If both types of trunk are used by the advertising SAF client and both are used at the requesting SAF client, then all routes are learned twice—once per protocol. When placing a call to such a route, load sharing occurs, which means that half of the calls are set up using SIP and half of the calls are signaled by H.323.

H.323 trunks, however, do not send the + sign. When a call is received (or placed) through an H.323 trunk and the called number includes a +, the + sign is stripped. The + sign is not stripped on SIP trunks.

When you rely on the + to be received through the H.323 trunk, you must configure incoming called-party settings at the H.323 trunk. Consequently, the + is prefixed before the received called-party number is matched in the call-routing table without the +.

If you have a SIP trunk and an H.323 trunk, and you do not prefix the + at the H.323 trunk, due to the load-sharing algorithm, every second call would fail (H.323) while the other half of the calls would work (SIP). These kinds of errors seem inconsistent and are difficult to troubleshoot.

Note

When you expect to receive VoIP calls to internal directory numbers and to globalized (PSTN) numbers, make sure that your incoming called-party settings prefix only the + to the called numbers where it is required. You can either refer to the ISDN type of number or use global transformations to control which called-party numbers you can modify.