Subscriber rerouting is a feature that can provide additional reliability for remote subscribers connected to Lotus Sametime Unified Telephony by a WAN link which has restricted bandwidth or less-than-desired reliability.
When a single Lotus Sametime Unified Telephony supports subscribers that are geographically distributed, most subscribers are typically co-located with Lotus Sametime Unified Telephony. However, many subscribers may be located remotely, connected to the main location via a WAN link or network. In that case, subscriber-to-subscriber calls between the locations will typically transit over the WAN link between the sites.
If the WAN link between the sites goes down or is blocked due to bandwidth restrictions, calls to the remote subscriber which normally go over the WAN can be automatically rerouted via the PSTN.
In the example below, subscriber 31002 (in Florida) dials subscriber 21001 (in San Jose). Because the WAN link is down or congested, Lotus Sametime Unified Telephony instead routes the call through the PSTN to the destination. This routing can be accomplished in either of the following modes:
In survivable mode, the survivable branch office proxy or gateway does not retain communication with Lotus Sametime Unified Telephony via the PSTN.
In backup mode, the survivable branch office proxy or gateway can continue to communicate with Lotus Sametime Unified Telephony via a backup link through the PSTN. This option requires appropriate provisioning of the applicable CAC groups.
This feature is also available when the RG 8700 is used as the survivability solution (without the proxy)
This feature is extended to permit its use:
If the calling party is not a subscriber registered on Lotus Sametime Unified Telephony
If the called party is a member of a hunt group arrangement
If the called party is a mobile subscriber or private subscriber
In all possible call forwarding scenarios
The operation of this feature relies on the availability of a survivable proxy at the remote site. The proxy function may be:
provided by a separate box - for example, the Comdasys box.
built into the remote PSTN gateway, as in the case of the RG 8700 or the RG 2700.
SIP signaling to the associated phones passes through the proxy, which is basically transparent during normal operation, but is capable of providing basic SIP-to-SIP softswitch functionality when a WAN outage is detected.
The RG 8700 is not technically a proxy because registrations and signaling do no pass through the RG 8700 and on to Lotus Sametime Unified Telephony. Instead, the phones register with both the RG 8700 and Lotus Sametime Unified Telephony (dual registration), and signal calls to the RG 8700 only in failure mode.
The RG 2700 automatically uses an ISDN trunk to route external calls if the IP network fails. RG 2700 also features other functions for call number administration and for accounting to ensure that VoIP telephony remains operational.
The branch office IP packets are normally routed via RG 2700. If the integrated RG 2700 router fails, another (redundant) router in the branch office LAN can take over. RG 2700 supports the Virtual Router Redundancy Protocol (VRRP) that guarantees high-availability by connecting routers in parallel.
To enable the subscriber rerouting feature, the following hardware configuration and database parameters need to be configured:
The SIP phones in the branch must be configured with the IP address of the proxy, and the proxy must be configured with the IP address of Lotus Sametime Unified Telephony. The phones then register with the proxy, which relays the registration message to Lotus Sametime Unified Telephony after adding a second VIA-header.
When the RG 8700 provides the survivability solution, the phone is configured with the IP address of both Lotus Sametime Unified Telephony and the RG 8700.
In Telephony Control Server Assistant:
Each branch subscriber that is served by the proxy must be identified, by filling in the Associated Endpoint field with the IP address (or name) of the serving proxy. This field must match the address of the proxy or RG 8700 survivable gateway in order for the feature to be activated.
The SIP endpoint definition of the proxy or RG 8700 must always be marked with the Survivable Endpoint attribute.
The SIP endpoint definition of the proxy or RG 8700 must, as applicable have the following additional attributes selected:
Table 1. Selectable attributes (none of them applicable to subscriber endpoints)
|Enhanced Subscriber Rerouting:||Reroute Forwarded Calls:||Reroute Incoming Calls|
|Select this attribute to enable enhanced subscriber routing, which pertains to the ability to reroute forwarded calls and hunt group calls.||Select this attribute to allow subscriber rerouting of incoming calls through the SIP endpoint that are forwarded to a survivable SIP subscriber.||Select this attribute to allow subscriber rerouting of incoming calls through the SIP endpoint (that are not forwarded). This attribute ist not commonly used, and should not be selected for gateway endpoints.|
Neither of these attributes is applicable to subscriber endpoints.
If applicable, hunt groups must have the Enable Rerouting advanced attribute selected.
The DID pool of a branch office must be appropriately provisioned in order to enable the correlation of calls. This correlation is required to support Lotus Sametime Unified Telephony hunt group and call forwarding features when calls are rerouted.
As in the case of Gateway rerouting
, when the feature is enabled, alternate routing is triggered if the remote location fails to respond to the call request, or sends back a 606 response code from the proxy, which typically indicates network congestion.
When rerouting is required, the dialed digits are prefixed by an appropriate access code created specifically for this feature, then sent through translation again, to select the appropriate egress gateway.
The prefix digit strings for international, national, and local rerouting are defined. The system chooses which of these three prefix access codes to use, based on analysis of the fully qualified calling and called party numbers (subscriber IDs) and not based on the dialed digits.
The administrator must provision a subscriber rerouting prefix access code. These access code digits are prepended to the E.164 number of the DN that is being rerouted; in the case of forwarded or hunt group calls, this is not necessarily the called party number.
If the subscriber rerouting prefix access code is not provisioned, the appropriate international, national, or local prefix access code is used in the translation process; however, this is not recommended.
The administrator must set up appropriate entries in the prefix access code table of the caller's numbering plan, to route calls using these prefix digits to the appropriate egress gateways.
In addition, the survivable proxy must be configured to handle the inbound PSTN calls to the isolated subscribers, without the assistance of Lotus Sametime Unified Telephony, to handle the case of a total WAN outage (lack of even signaling connectivity).
Figure 1. Subscriber Rerouting Example
Subscriber Rerouting and Toll and Call Restrictions
A system-wide option Srx/Main/InvokeTRSOnRerouting
determines, whether toll restrictions shall be bypassed (RtpFalse
) or not (RtpTrue
) on the subscriber rerouting call leg. Its default value is RtpFalse
, i.e. Toll and Call restrictions won't be applied.
Parent topic: CAC (Call Admission Control) Rerouting