4.8 URI Call Routing

his topic describes how URI calls are routed.

Calls to URIs are routed differently, depending on their type.

  • Numeric versus non-numeric depends on the Dial String Interpretation SIP profile parameter setting:
    1. Always treat all dial strings as URI addresses.
    2. The phone number consists of characters 0–9, A–D, *, #, and + (others treated as URI addresses).
    3. The phone number consists of characters 0–9, *, #, and + (others treated as URI addresses).
  • If numeric, local versus remote
    1. A URI is considered to be local if the host portion matches one of the following:
      • IP address of any cluster member
      • Cluster Fully Qualified Domain Name enterprise parameter
      • Organization Top Level Domain enterprise parameter

The URI call-routing process is rather complex and depends on several conditions. The first thing that is checked is whether the user portion of the called URI is numeric. The SIP profile Dial String Interpretation parameter specifies when a called URI is considered to be numeric.

The service parameter can be set to one of the following options:

  • Always treat all dial strings as URI addresses.
  • The phone number consists of the characters 0–9, A–D, *, #, and + (others are treated as URI addresses).
  • The phone number consists of the characters 0–9, *, #, and + (others are treated as URI addresses).

In the call-routing flow, if a URI is considered to be numeric, then further processing differs for local versus remote URIs. A pattern is considered to be local when one of the following conditions applies:

  • The host portion of the URI matches the IP address of a cluster member.
  • The host portion of the URI matches the CFQDN.
  • The host portion of the URI matches the OTLD.
Note

The CFQDN and the OTLD are enterprise parameters.

The figure illustrates the complete URI call-routing process.

Procedure

Non-Numeric URI Call-Routing Process

When a SIP call is placed to a URI and the user portion of the called URI is not a number, then Cisco Unified Communications Manager will route the call as follows:

  1. The full URI is looked up in the URI routing table, which contains all locally configured directory URIs (URIs that are applied to directory numbers at the Directory Number Configuration page or via an end user). If a match is found, then the call is sent to the corresponding phone line.

Note

This lookup follows the CSS and partition logic. Like directory numbers, a partition can be assigned to a directory URI. There is no separate CSS for URI routing. The CSS that is used for numeric call routing is also applicable to URI routing.

SIP route patterns and ILS-learned URIs are ignored at this stage.

  1. If no match is found, then the full URI is looked up against the ILS-learned URIs.

Note

The lookup against the ILS-learned URIs always considers all ILS-learned URIs. ILS-learned URIs do not have an assigned partition, and the CSS and partition logic does not apply to lookups against ILS-learned URIs.

  1. If the full URI matches an ILS-learned URI, then the associated route string is matched against all accessible SIP route patterns. If no matching SIP route pattern is found, then the host part of the originally called URI is looked up against all accessible SIP route patterns.

  1. If the full URI does not match an ILS-learned URI, then the host part of the originally called URI is looked up against all accessible SIP route patterns.

Note

A partition can be assigned to a SIP route pattern. When a route string or the host part of a called URI is matched against the SIP route patterns, the CSS and partition logic applies. SIP route patterns in partitions that are not included in the CSSs of the calling devices are ignored.

  1. If a matching SIP route pattern is found, then the call is routed using the matched SIP route pattern. If no matching SIP route pattern is found, then the call fails.

    In summary, the non-numeric URI call-routing process depends on the CSS and partitions (when looking up locally configured full URIs and SIP route patterns), but the priorities also depend on the type of lookup. The full URI is first searched in local URI entries. ILS-learned patterns are searched next (without involving any CSS and partitions), and SIP route patterns are searched with the lowest priority.

Procedure

Numeric URI Call-Routing Process

When a SIP call is placed to a URI, and the user portion of the called URI is a number, then Cisco Unified Communications Manager routes the call based on the rules for numeric URI call routing. The rules for numeric URI call routing include the following steps:

  1. If the host portion of the called URI is the IP address of a cluster member or matches the CFQDN, then the user portion of the URI is looked up in the accessible partitions of the numbered call-routing table. If a match is found, then the call is routed to the matched entry. If no match is found, then the call fails.

  1. If the host portion of the called URI matches the OTLD, then the user portion of the URI is looked up in the accessible partitions of the numbered call-routing table. If a match is found, then the call is routed to the matched entry.

  1. The host portion of the called URI is looked up against the accessible SIP route patterns. If a match is found, then the call is routed using the matched SIP route pattern. If no matching SIP route pattern is found, then the call fails.

Note

All three described lookups follow the CSS and partition logic.

Calls placed to directory URIs are sent to a remote SIP call control system as follows:

  • The called host portion or the ILS route string matches a SIP route pattern configured by one of the following methods:
    1. Domain routing with a pattern, which is the destination host portion specified as FQDN
    2. IP address routing with a pattern, which is the destination host portion specified as IP address
  • The SIP route pattern refers directly to a SIP trunk or ends up at a SIP trunk through the route list and route group configuration.
  • The SIP trunk refers to one or more destinations by IP address or FQDN or to a target DNS SRV entry.
  • The same SIP trunk can be used for numeric and non-numeric calls.

When the URI call-routing process finds a match of the called host portion of a URI or of the ILS route string of the called host portion of a URI or of the ILS route string in a SIP route pattern, then the call is sent to a remote SIP call control system.

The SIP route pattern can be configured as an IP address or, more likely, as an FQDN. When you configure a SIP route pattern as an IP address, you must set the Pattern Usage to IP Address Routing. When you configure a SIP route pattern as an FQDN, you must choose Pattern Usage Domain Routing.

You can configure a SIP route pattern to refer directly to a SIP trunk, or you can use the route list and route group construct. You must use the route list and route group construct when multiple SIP trunks should be used for load-sharing or backup purposes.

Each SIP trunk refers to one or more destinations by IP address or FQDN. In the case of an FQDN, the FQDN is not only a domain (as in the case of a SIP route pattern), but is also the FQDN of a host, specifically the host of the remote call control server. You can configure more than one destination per SIP trunk. If the remote call control system is a Cisco Unified Communications Manager cluster, you must configure all members of the remote cluster that can control the interconnecting SIP trunk. If you omit a remote server, your cluster will not accept incoming calls from that unknown host.

Alternatively, a SIP trunk can be configured to use DNS name resolution by requesting the SIP server SRVs of the specified SIP service name. To enable DNS SRV at SIP trunks, check the Destination Address Is an SRVcheck box and enter the target SIP service name in the Destination Address field. When you check theDestination Address Is an SRV check box, you can specify one destination address only. Redundancy is provided by the DNS server in this case.

You can use the same SIP trunk for numeric and non-numeric calls.

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