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This section describes how Cisco Unified Border Element (SP Edition) can be configured to process Session Initiation Protocol (SIP) 3xx responses. 3xx is a class of the response code used in SIP to indicate that further action needs to be taken in order to complete the request. The sender of the request should retry the request, using one or more alternative Uniform Resource Identifiers (URIs), which are presented in the 3xx response.
Note For Cisco IOS XE Release 2.4, this feature is supported in the unified model only.
Cisco Unified Border Element (SP Edition) was formerly known as Integrated Session Border Controller and may be commonly referred to in this document as the session border controller (SBC).
For a complete description of the commands used in this chapter, refer to the Cisco Unified Border Element (SP Edition) Command Reference: Unified Model at:
http://www.cisco.com/en/US/docs/ios/sbc/command/reference/sbcu_book.html.
For information about all Cisco IOS commands, use the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or a Cisco IOS master commands list.
Feature History for SIP 3xx Redirect Responses
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This feature was introduced on the Cisco IOS XR along with support for the unified model. |
This section contains the following subsections:
3xx responses are usually only expected in session-initiating requests, INVITEs. However, the SIP specification does not preclude sending 3xx responses for other request types. A number of alternative URIs are supplied on the 3xx responses in Contact headers.
The 3xx class of responses includes any response code in the range of 300-399 and indicates a redirection of the call. The redirection requires further action to be taken to complete the request. The following 3xx response codes are defined in SIP.
The duration of the validity of the Contact URI can be specified through an Expires header field or an Expires parameter in the Contact header field. Both proxies and UAs may cache this URI for the duration of the expiration time. If there is no explicit expiration time, the address is valid only once for recursing, and must not be cached for future transactions.
If the URI cached from the Contact header field fails, the Request-URI from the redirected request may be tried again only once.
380 Alternative Service. The call was not successful, but alternative services are possible. The alternative services are described in the message body of the response. There are no formats currently defined for this information.
In each case, the request should be retried to one of the supplied alternative URIs. The request can be retried by either the originating UA, or by an intermediate back-to-back user agent (B2BUA) or proxy on behalf of the originating UA (and without notifying it).
Cisco Unified Border Element (SP Edition) is a B2BUA, and, therefore, in some deployments it may be necessary for Cisco Unified Border Element (SP Edition) to retry the request instead of sending a negative response back to the initiator of the request.
The Diversion header enables the called SIP user agent to identify from whom the call was diverted and why it was diverted. The header notifies the original caller:
The diversion header is attached by networking elements that change the final destination of a request.
This section contains the steps for configuring Cisco Unified Border Element (SP Edition) to process SIP 3xx responses.
4. adjacency sip adjacency-name
This section provides two simple configurations for processing SIP 3xx responses.
The following command configures the adjacency “SipToIsp42” to recurse on 300, 301, 302, and 305 INVITE responses.
The following command configures the SBE to perform maximum 4 SIP 3xx redirections per call.