Survivable Remote Site Telephony

Secondary Dialtone, Alias forwarding, octo-line support,

This blog will continue the SRST conversation that we have been having over the last six blogs. During normal operation, most implementations of Cisco Unified Communications Manager (CUCM) provide a secondary (stutter) dial tone after the access code of 9 is dialed. The 911 route pattern must be configured to provide an outside dial tone in addition to all the other route patterns beginning with a 9. Every route pattern in CUCM beginning with a 9 must be provisioned to provide outside dial tone or else the secondary dial tone will be received after CUCM’s digit analysis only includes route patterns with the provide outside dial tone option. Cisco IP phones in SRST mode will not receive a secondary dialtone unless the following command is provisioned in call-manager-fallback (SRST) configuration mode (assuming the use of 9 as an access code):

secondary-dialtone 9

SRST supports up to 8 (octo) virtual lines per physical directory number (DN) in SRST 4.3. Octo line support is configured with the following call-manager-fallback configuration command (assuming 144 directory numbers):

Max-dn 144 octo-line

Small organizations with tight budgets may decide to use a SRST Cisco router that does not support the number of phones at the site. As an example, let’s assume that www.Highpoint.com has a regional sales office in San Jose, California with 50 users but the 2811 router in use only supports 36 phones. Highpoint configures one device pool containing 36 phones in a device pool that includes an SRST reference, but the other 14 phone are put into a device pool that does not include an SRST reference. During a CUCM outage, anyone calling the 14 phones without a SRST reference will receive reorder tone by default. Call-forward busy and call-forward no answer conditions can be configured in SRST configuration mode for a single phone number or a range of directory numbers. In our example site, we will route all calls in the range of 1517 to 1530 to the operator at extension 1500. The following configuration will achieve this goal:

Alias 1 1517 to 1530 preference 1 cfw 1500 timeout 20

The preference option is used to ensure that extensions 1517 to 1530 will work if these DNs are registered in the SRST gateway. All ephone-dn registrations use preference 0 by default which is the highest priority in dial peer hunting. In the next blog, we will continue our in depth configuration coverage of SRST.

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