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The late-to-early media interworking feature is supported for Session Initiation Protocol (SIP) calls. In order to interwork between a late media caller and an early media callee, Cisco Unified Border Element (SP Edition) sends an invite to the callee that includes a Session Description Protocol (SDP) offer of media. Two implementations of late-to-early media interworking are available:
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 Late-to-Early Media Interworking
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The customizable offer for late-to-early media interworking feature was introduced on the Cisco IOS XR. |
The restrictions for late-to-early media interworking are:
This section includes the following topics:
Early Media is the ability of two user agents to communicate before a call is actually established. Early Media can flow when the caller makes a media proposal on the initial call setup request and the callee responds to the offer before the call is connected. Cisco Unified Border Element (SP Edition) provides interoperability between SIP devices that do not provide SDP on their INVITEs and SIP devices that require SDP on INVITEs they receive. This occurs when:
The normal negotiation for media is for the caller to include an SDP offer on the initial INVITE and for the callee to accept with a 200 response. However, the following might occur:
In order to interwork between a late media caller and an early media callee, Cisco Unified Border Element (SP Edition) sends an invite to the callee that includes an SDP offer of media. Cisco Unified Border Element (SP Edition) then sends appropriate messages between the caller and callee, depending on the responses from each.
Cisco Unified Border Element (SP Edition) supports this interworking on a per-adjacency basis. You can configure each adjacency to require late-to-early media interworking for calls made to that adjacency and/or for calls made from that adjacency.
By default, SBC generates the SDP with a single media description that specifies codecs common to both the caller and callee’s codec whitelists.
The Customizable Offer for Late-to-Early Media Interworking feature provides customized SDPs with one or more media descriptions. You configure the media descriptions in named profiles (SDP media profiles) and associate the profiles to signals by including the profile name in a CAC policy.
To enable a customized offer for late-to-early media interworking:
When a call requires late-to-early interworking, if the CAC policy entry for that call contains a valid SDP media profile name, then SBC generates a customized SDP. In the absence of such an association, SBC generates the default SDP. In the customized case, SBC inserts the media description lines in the media profile in the SDP when it generates the INVITE. Each entry in the media profile includes a sequence number, which controls the ordering of the lines in the generated SDP.
A section of SDP is configured as an entry in the SDP Media profile. An entry can have one or many media description lines. The format of an SDP Media profile is:
If more than one media description is created in the same profile, all of the entries are used to generate the same output SDP, in ascending order by entry number.
The media_description argument must be enclosed in quotes ('' ''). The value inside the quotes must be syntactically valid SDP as defined in RFC 2327. The following rules apply:
The Cisco command line interface handles the contents of media_description as a string value. It does not check the syntax of the configured information. If the syntax is incorrect, outbound offers by the SBC are rejected.
This section describes the following configuration scenarios for Late-to-Early Media Interworking:
This task shows how to configure late-to-early media interworking per adjacency.
Note The caller and callee commands have been used in this procedure. In some scenarios, the branch command can be used as an alternative to the caller and callee command pair. The branch command has been introduced in Release 3.5.0. See the “Configuring Directed Nonlimiting CAC Policies” section for information about this command.
4. adjacency sip adjacency-name
8. authentication nonce timeout value
17. media-late-to-early-iw {incoming | outgoing}
Before performing this task, configure late-to-early media interworking per adjacency.
4. sip sdp-media-profile profile-name
6. media-line index " media_description "
7. (Optional) Repeat the previous step with a different index to add more media lines to this entry.
9. (Optional) Repeat Steps 6 through 9 with a different entry-num in Step 6 to add another entry to this profile.
12. cac-policy-set policy-set-id
15. sip sdp-media-profile profile-name
17. show sbc sbc-name sbe sip sdp-media-profile profile-name
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Enters the submode for configuring the method profile. Use the service-name argument to define the name of the service. |
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sip sdp-media-profile profile-name |
Configures an SDP media profile for a customized offer. Enter into SIP SDP media profile configuration mode. |
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Enters the submode for adding a section of media description to the profile. A section, or entry, can contain one or more media description lines. |
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media-line index “ media_description ” Router(config-sbc-sbe-sip-sdp-media-ele)# |
Adds a media description line to the entry. Quotation marks must surround the media description. See “Rules for Media Lines in SDP Media Profiles” section. |
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(Optional) Repeat the previous step with a different index to add more media lines to this entry. Router(config-sbc-sbe-sip-sdp-media-ele)# |
Adds additional media descriptions to the entry. The index controls the ordering of the media descriptions. |
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(Optional) Repeat Steps 5 through 8 with a different entry-num in Step 5 . Router(config-sbc-sbe-sip-sdp-media)# entry 2 Router(config-sbc-sbe-sip-sdp-media-ele)# Router(config-sbc-sbe-sip-sdp-media-ele)# |
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Enters the submode to make a change to a previously configured CAC policy set. Changes are not permitted to the active policy set. |
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Enters the submode to make a change to a previously configured admission control table. |
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Enters the submode to modify an entry in an admission control table. |
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sip sdp-media-profile profile-name Router(config-sbc-sbe-cacpolicy-cactable-entry)#sip sdp-media-profile profile1 |
Associates an SDP media profile with an admission control table entry. |
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show sbc sbc-name sbe sip sdp-media-profile profile-name |
Shows the contents of the profile. It is important to check the contents of the profile to make sure it is syntactically valid SDP as defined in RFC 2327. The command line interface does not check the syntax of the media_description arguments. |
This section includes the following examples:
The following example shows a configuration of the Late-to-Early Media Interworking feature.
Note The caller and callee commands have been used in this procedure. In some scenarios, the branch command can be used as an alternative to the caller and callee command pair. The branch command has been introduced in Release 3.5.0. See the “Configuring Directed Nonlimiting CAC Policies” section for information about this command.
The following example configures a customized media description and assigns it to a CAC policy.
Use the commands listed in Table 49-1 to verify operation.
The following example shows adjacencies.
The following command lists a summary of the CAC policy tables associated with the given policy set:
The following example shows a list of SDP media profiles configured under an SBC service:
The following example shows the contents of a named SDP media profile: