implementing sbc transcoding and codec restriction

Implementing SBC Transcoding and Codec Restriction

Transcoding is the process of translating a media stream encoded using one codec into a media stream encoded using another codec. For example, translating a media stream encoded as Pulse Code Modulation u-law (PCMU) into one encoded as G.726-32.

The primary reason for transcoding configurations is to configure the capabilities of external media transcoding devices when these devices cannot be discovered automatically. In-band auto-discovery of transcoder capabilities is currently not supported. Therefore, this step must be done when configuring all connections to all current remote transcoding devices.

Note Transcoding configurations can be skipped altogether if the described reason does not apply.

Media gateways are allowed to connect whether or not configuration has been supplied for them. To help avoid configuration errors, the signaling border element (SBE) logs a warning if an incoming connection is received from a media gateway that is not a data border element (DBE) and does not have transcoding configured.

Note For a complete description of commands used in this chapter, refer to the SBC Transcoding Commands on Cisco IOS XR Software module of Cisco IOS XR Software Session Border Controller Command Reference. To locate documentation for other commands that appear in this chapter, use the command reference master index, or search online.

Feature History for Implementing SBC Transcoding and Codec Restriction

Release Modification

Release 3.3.0 This feature was introduced on the Cisco XR 12000 Series Router.

Release 3.4.0 No modification.

Release 3.4.1 Restricting Codecs feature was supported.





SBC-353Cisco IOS XR Session Border Controller Configuration Guide

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Implementing SBC Transcoding and Codec RestrictionContents

Contents• Prerequisites for Implementing SBC Transcoding and Codec Restriction, page SBC-354

• Restrictions for Codecs, page SBC-354

• Information About SBC Transcoding, page SBC-357

• Information About Codec Restriction, page SBC-359

• How to Implement SBC Transcoding, page SBC-359

• How to Implement Codec Restriction, page SBC-362

• Configuration Example for Transcoding, page SBC-366

• Configuration Examples for a Codec Restriction, page SBC-366

• Additional References, page SBC-368

Prerequisites for Implementing SBC Transcoding and Codec Restriction

The following prerequisites are required to implement SBC transcoding:

• You must be in a user group associated with a task group that includes the proper task IDs for SBC commands being used. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of Cisco IOS XR System Security Configuration Guide.

• You must install and activate the package installation envelope (PIE) for the SBC software.

For detailed information about PIE installation, refer to the Upgrading and Managing Cisco IOS XR Software module in Cisco IOS XR Getting Started Guide.

• The SBC must already be created. See the procedures described in the SBC Configuration Prerequisites module.

• Transcoding must be configured before you can restrict codecs.

• All SBE and DBE configurations required to make simple calls must already be configured. Transcoding configurations follow these configurations.

Restrictions for Codecs• The media packet forwarder on the DBE polices the bandwidth consumed by each media stream, but

it cannot police the type of codecs or the packetization periods.

• Unrecognized codecs cannot be configured as members of the codec whitelist.

• Active calls are not released if there is a change in the codec whitelist during the call.

• If a codec whitelist is configured, SBC removes any unlisted codecs from the call setup flow and media gate allocation.

• Multiple codec whitelists can be configured on a call admission control (CAC) policy basis. For example, the list of codecs allowed for calls from “SipAdj1” can be different than the list of codecs allowed for calls from “SipAdj2”.


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Implementing SBC Transcoding and Codec RestrictionRestrictions for Codecs

• If a codec whitelist has not been configured, all recognized codecs (see Table 32 – Table 35) are allowed for all calls.

• You must use the textual value of the codec description that appears on the session description protocol (SDP) to configure the codec whitelist, for example “PCMU” or “telephone-event”.

• Disallowing all codecs is not supported. However, you can set a bandwidth limit of zero to achieve the same result.

• Codec lists are not applied to media-bypass calls (those in which the SBC does not reserve media resources).

• The format of the codec name is the same as the string used to represent it in SDP, for example PCMU or VDVI. All recognized codec names are listed in Table 32 – Table 35.

• A single codec can be added to each list only once, with a single packetization period.

• For each codec on a list, CAC restricts the signaled packetization period for any stream using that codec to be greater than or equal to the packetization period configured along with the codec in the list. If a stream uses more than one codec in the list, the greatest of all the packetization periods configured for each codec in the list is applied to the stream.

Note The bandwidths listed in the tables below are the bandwidths without the transport layer overheads. Therefore, the actual bandwidths reserved by the SBC are higher than the listed values.

Table 32 Sample-Based Audio Codecs with Packetization Time 10 ms

Payload Type Codec Name Clock Rate (Hz) Sample Size (bits) Channels

0 PCMU 8000 8 1

5 DVI4 8000 4 1

6 DVI4 16000 4 1

8 PCMA 8000 8 1

10 L16 44100 16 2

11 L16 44100 16 1

15 G728 8000 2 1

16 DVI4 11025 4 1

17 DVI4 22050 4 1

— G726-40 8000 5 1

2 G726-32 8000 4 1

— G726-24 8000 3 1

— G726-16 8000 2 1

— L8 8000 8 1

— DAT12 8000 12 2

— L20 44100 10 2

— L24 44100 24 2


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Implementing SBC Transcoding and Codec RestrictionRestrictions for Codecs

Table 33 Non-Sample-Based Audio Codecs

Payload Type Codec Name Packetization Time (ms) Allocated Bandwidth (bits/s)

3 GSM 10 13200

7 LPC 10 5600

9 G722 10 64000

13 CN 10 400

18 G729 10 8000

4 G723 30 6400

12 QCELP — 13300

14 MPA — 131072

— G729D 10 6400

— G729E 10 11800

— GSM-EFR 10 12400

— VDVI 10 25000

— AMR 10 12500

— AMR-WB 10 24420

— dsr-es201108 10 4800

— EVRC 10 8550

— EVRC0 10 8550

— mpa-robust 10 327680

— G7221 10 32000

— MP4A-LATM 10 131072

— SMV 10 8550

— SMV0 10 8550

— G729AB 10 8000

Table 34 Video Codecs


25 CelB — 524228

26 JPEG — 524228

28 nv — 524228

31 H261 — 524228

32 MPV — 524228

33 MP2T — 524228

34 H263 — 524228

— BMPEG — 524228

— BT656 — 170000000


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Implementing SBC Transcoding and Codec RestrictionInformation About SBC Transcoding

Information About SBC TranscodingTranscoding requires specialized digital signal processor (DSP) hardware, which is not available within SBC itself. A Cisco MGX 8880 device is used to provide transcoding function for one or more SBCs.

SBC automatically brings the transcoding device into use for any call requiring transcoding between these codecs, as long as the call admission control (CAC) policy configuration does not preclude the transcoder service from being supplied for the call. When a call that requires transcoding is set up, the signaling border element (SBE) goes through the following steps:

1. Receives an initial Signaling request from the calling endpoint. This triggers SBE to perform initial call setup on the incoming and outgoing DBEs. Then, SBE forwards the request to the called endpoint.

2. Receives a response from the called endpoint that indicates that none of the codecs in the initial request are acceptable. This triggers SBE to bring a transcoder into the call, which is inserted in the media path between the incoming and outgoing DBEs. A new request is sent to the called endpoint, indicating the new codec type generated by the transcoder.

— DV — 1500000000

— H263-1998 — 524228

— H263-2000 — 524228

— MP1S — 1600000

— MP2P — 524228

— MP4V-ES — 524228

— raw — 1500000000

— SMPTE292M — 1500000000

Table 35 Other Codecs

Codec Name Packetization Time (ms) Allocated Bandwidth (bits/s)

telephone-event 20 1600

tone 20 1600

RED 20 1

parityfec 20 1

t140 100 80

pointer 20 1600

H224 20 6560

T.38 — 15500

X-NSE 20 1600

Table 34 Video Codecs (continued)



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Implementing SBC Transcoding and Codec RestrictionInformation About SBC Transcoding

3. SBE may have to iterate through the list of codecs the transcoder supports until it finds one that is acceptable to the called endpoint. When this is done, the call is connected and media transmission begins.

Figure 17 shows where the transcoder sits in the network, and the path taken by the media in a transcoded call.

Figure 17 Transcoding Configuration

Note Although Figure 17 shows two data border elements (DBEs), transcoding is possible with a single DBE. With a single DBE, the media flows through the DBE twice, once on its way from the sending endpoint to the transcoder and a second time as it flows from the transcoder to the receiving endpoint.

For SBC to program the transcoder, it must be registered. The transcoding device acts as an H.248 media gateway, so it needs to be configured with the IP address and port of the SBE or SBC to connect to. The SBE or SBC acts as an H.248 media gateway controller. (See the documentation for the transcoder device for notes on how to do this. The documentation for the Cisco MGX 8880 is found at http://www.cisco.com/en/US/products/hw/gatecont/ps3869/products_configuration_guide_book09186a0080535937.html.)

In addition, the SBE must have the following specific configurations:

• An H.248 control address and port must be configured by using the control address h248 command. By default, this is on port 2944, and it is the address and port to which the transcoder must connect.

• An explicit media gateway needs to be configured by using the media-gateway command. The explicit media gateway must have its list of supported codecs defined so that the SBC knows which codecs the transcoder can translate between, and it must be identified as a transcoder by using the codecs and transcoder commands.

• The show services sbc sbe media-gateway-associations command is used to check that the transcoder has correctly registered with the SBE. If this has happened, the transcoder should appear in the list of known media gateways with an active association.

SBE

G.729

G.729G.711G.711 Media path

DBE

V

DBE

V

Telephone

Telephone

1580

12

H.248 ControlAssociations

TranscoderTranscoder


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http://www.cisco.com/en/US/products/hw/gatecont/ps3869/products_configuration_guide_book09186a0080535937.html

Implementing SBC Transcoding and Codec RestrictionInformation About Codec Restriction

Information About Codec RestrictionA compressor-decompressor (codec) is a device or program that performs a transformation on a data stream or signal. The SBC is hardcoded with a set of recognized codecs (see Table 32 – Table 35), including all commonly used voice and video codecs. The default behavior is to allow all recognized codecs on all calls. Any other codec present in call signaling is removed by the SBC.

The Codec Restriction feature allows you to restrict which codecs a particular call can use and to configure a minimum permissible packetization period for each permitted codec.

How to Implement SBC TranscodingThis section contains the following procedure on how to implement SBC transcoding:

• Configuring Transcoding, page SBC-359

In this configuration area, you supply a configuration for a list of remote media gateways. By default, media gateways are allowed to connect whether or not configuration has been supplied for them. To help avoid configuration errors, the SBE logs a warning if an incoming connection is received from a media gateway that is not a DBE and does not have transcoding configured.

The following basic steps for implementing transcoding are listed:

1. Configure the IP address, port, and transport protocol for an H.248 media gateway controller on SBC. This step may not be required if the media gateway controller has already been configured.

2. Configure the media gateway IP address.

3. Configure the codecs to be transcoded (for example, between G.711ulaw and G.729A).

4. Specify the media gateway as a transcoder.

5. Activate SBE.

Configuring TranscodingPerform this task to configure transcoding for SBC.

SUMMARY STEPS

1. configure

2. sbc service-name

3. service-location preferred-active {node-id} [preferred standby node-id]

4. sbe

5. control address h248 [ipv4 ipv4_IP_address]

6. control address h248 [port port-number]

7. control address h248 [transport [tcp | udp]]

8. media-gateway {ipv4 ipv4_IP_address}

9. codecs {codec-list}

10. transcoder

11. exit


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Implementing SBC Transcoding and Codec RestrictionHow to Implement SBC Transcoding

12. activate

13. endorcommit

DETAILED STEPS

Command or Action Purpose

Step 1 configure

Example:RP/0/0/CPU0:router# configure

Enters global configuration mode.

Step 2 sbc service-name

Example:RP/0/0/CPU0:router(config)# sbc mysbcRP/0/0/CPU0:router(config-sbc)#

Enters the configuration mode of an SBC service.

• Use the service-name argument to define the name of the service.

Step 3 service-location preferred-active node-id [preferred standby node-id]

Example:RP/0/0/CPU0:router(config-sbc)# preferred-active 0/2/CPU0 preferred-standby 0/4/CPU0

Enables a service card to run SBC function as a primary location, and optionally, secondary location.

Step 4 sbe

Example:RP/0/0/CPU0:router(config-sbc)# sbeRP/0/0/CPU0:router(config-sbc-sbe)#

Enters the configuration mode of the signaling border element (SBE) function of the SBC.

Step 5 control address h248 [ipv4 ipv4_IP_address]

Example:RP/0/0/CPU0:router(config-sbc-sbe)# control address h248 ipv4 88.88.133.21

Configures an SBE to use a given IPv4 H.248 control address when acting as a media gateway controller.

• Use the ipv4 keyword to specify the IPv4 H.248 control address.

Step 6 control address h248 [port port-number]

Example:RP/0/0/CPU0:router(config-sbc-sbe)# control address h248 port 2944

Configures an SBE to use a given port for H.248 communications when acting as a media gateway controller.

• Use the port keyword to specify the listening port number. The range is from 1 to 9999. Port 2944 is the default H.248 port. (If using the default port, this step can be skipped.)

Step 7 control address h248 [transport [tcp | udp]]

Example:RP/0/0/CPU0:router(config-sbc-sbe)# control address h248 transport udp

Configures an SBE to use a given transport for H.248 communications when acting as a media gateway controller.

• Use the udp keyword to configure the UDP transport for H.248 signaling.

• Use the tcp keyword to configure the TCP transport for H.248 signaling.


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Implementing SBC Transcoding and Codec RestrictionHow to Implement SBC Transcoding

Step 8 media-gateway {ipv4 ipv4_IP_address}

Example:RP/0/0/CPU0:router(config-sbc-sbe)# media-gateway ipv4 10.0.0.1RP/0/0/CPU0:router(config-sbc-sbe-mg)#

Configures the media gateways on an SBE and enters SBE media gateway configuration mode.

• Use the ipv4 keyword to configure the IPv4 address for the allowed media gateway.

Step 9 codecs {codec-list}

Example:RP/0/0/CPU0:router(config-sbc-sbe-mg)# codecs “m=audio 6000 RTP/AVPR 4,a=rtpmap:0 PCMU/8000”

Configures the codecs supported by the media gateway.

• Use the codec-list argument as a description of the quoted and comma-separated list of the codecs supported.

Step 10 transcoder

Example:RP/0/0/CPU0:router(config-sbc-sbe-mg)# transcoder

Configures the media gateway with transcoder support.

Step 11 exit

Example:RP/0/0/CPU0:router(config-sbc-sbe-mg)# exitRP/0/0/CPU0:router(config-sbc-sbe)#

Exits the current configuration mode.

Step 12 activate

Example:RP/0/0/CPU0:router(config-sbc-sbe)# activate

Initiates the SBC service after all SBE address configuration has been successfully committed.

Step 13 end

or

commit

Example:RP/0/0/CPU0:router(config-sbc-sbe)# end

or

RP/0/0/CPU0:router(config-sbc-sbe)# commit

Saves configuration changes.

• When you issue the end command, the system prompts you to commit changes:

Uncommitted changes found, commit them before exiting(yes/no/cancel)?[cancel]:

– Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

– Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

– Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

• Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.



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Implementing SBC Transcoding and Codec RestrictionHow to Implement Codec Restriction

How to Implement Codec RestrictionYou must configure the codecs and then apply them as described in the following tasks:

• Configuring Codecs, page SBC-362

• Configuring a CAC Policy to Use a Codec List, page SBC-364

Configuring CodecsTo restrict which codecs a particular call can use and to configure a minimum permissible packetization period for each permitted codec, you must configure CAC with a list of codecs, provide a description for the list, and then add any codecs to the list.

Perform this task to configure codecs.

SUMMARY STEPS

1. configure

2. sbc service-name

3. sbe

4. codec-list {list-name}

5. description {description}

6. codec {codec-name} [packetization-period value]

7. endorcommit

8. show services sbc sbc-name sbe codec-list {list-name}

DETAILED STEPS


Step 1 configure







Step 3 sbe




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Step 4 codec-list {list-name}

Example:RP/0/0/CPU0:router(config-sbc-sbe)# codec-list my_codecsRP/0/0/CPU0:router(config-sbc-sbe-codec-list)#

Create a codec list and enters SBE codec list configuration mode.

• Use the list-name argument to configure the name of the codec list.

Note A codec list can exist despite having no codecs. Deleting all codes from a list does not delete the list.

Step 5 description {description}

Example:RP/0/0/CPU0:router(config-sbc-sbe-codec-list)# description Legitimate codes

Adds a description for the specified codec list using a readable text string format.

It is also included for each codec list when a summary of all codec lists is displayed.

Step 6 codec {codec-name} [packetization-period value]

Example:RP/0/0/CPU0:router(config-sbc-sbe-codec-list)# codec PCMU packetization-period 20

Configures a description of a codec list and sets a minimum packetization period (optional) for the codec.

• Use the codec-name argument to configure the name of a codec. This value must be one of the list of codecs that the SBE is hardcoded to recognize. Otherwise, when you execute this command, the SBE displays an error.

Step 7 end

or

commit

Example:RP/0/0/CPU0:router(config-sbc-sbe-codec-list)#end

or

RP/0/0/CPU0:router(config-sbc-sbe-codec-list)# commit








Step 8 show services sbc sbc-name sbe codec-list {list-name}

Example:RP/0/0/CPU0:router# show services sbc mysbc sbe codec-list my_codecs

Displays detailed information about the codec lists configured on the SBE.

If the list name is omitted, details are displayed for all codec lists on the SBE.



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Configuring a CAC Policy to Use a Codec ListPerform this task to configure a CAC policy to use a codec list.

SUMMARY STEPS

1. configure

2. sbc service-name

3. sbe

4. cac-policy-set {policy-set ID}

5. cac-table {table-name}

6. entry {entry-id}

7. codec-restrict-to-list list-name

8. endorcommit

9. show services sbc sbc-name sbe cac-policy-set set-id [table name {entry entry-id | entries} | tables]

DETAILED STEPS


Step 1 configure







Step 3 sbe



Step 4 cac-policy-set {policy-set ID}

Example:RP/0/0/CPU0:router(config-sbc-sbe)# cac-policy-set 1RP/0/0/CPU0:router(config-sbc-sbe-cacpolicy)#

Configures a specific CAC policy that is set to restrict codecs and enters SBE CAC policy configuration mode.

• Use the policy-set ID argument to define the unique identifier of the policy set.


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Step 5 cac-table {table-name}

Example:RP/0/0/CPU0:router(config-sbc-sbe-cacpolicy)# cac-table MyCacTableRP/0/0/CPU0:router(config-sbc-sbe-cacpolicy-cactable)#

Identifies the CAC table and enters SBE CAC policy CAC table configuration mode.

• Use the table-name argument to identify the name of the admission control table.

Step 6 entry {entry-id}

Example:RP/0/0/CPU0:router(config-sbc-sbe-cacpolicy-cactable)# entry 1RP/0/0/CPU0:router(config-sbc-sbe-cacpolicy-cac-table-ent)#

Identifies the specific table entry and enters SBE CAC policy CAC table entry configuration mode.

• Use the entry-id argument to identify the number of the table entry.

Step 7 codec-restrict-to-list {list-name}

Example:RP/0/0/CPU0:router(config-sbc-sbe-cacpolicy-cac-table-ent)# codec-restrict-to-list my_codecs

Configures CAC to restrict the codecs used in signaling a call to the set of codecs provided in the named list.

Step 8 end

or

commit

Example:RP/0/0/CPU0:router(config-sbc-sbe-cacpolicy-cac-table-ent)# end

or

RP/0/0/CPU0:router(config-sbc-sbe-cacpolicy-cac-table-ent)# commit








Step 9 show services sbc sbc-name sbe cac-policy-set set-id [table name {entry entry-id | entries} | tables]

Example:RP/0/0/CPU0:router(config-sbc-sbe)# show services sbc mysbc sbe cac-policy-set 1 table standard_policy_list entry 1

Displays detailed information for a specific entry in a CAC policy table, including any restricted codecs.



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Implementing SBC Transcoding and Codec RestrictionConfiguration Example for Transcoding

Configuration Example for TranscodingThis section provides the following configuration example for configuring transcoding on an SBE:

• Configuring Transcoding: Example, page SBC-366

Configuring Transcoding: ExampleThe following example shows how to configure transcoding on an SBE:

configuresbc ABCservice-location preferred-active 0/3/CPU0 sbecontrol address h248 ipv4 88.88.133.2 control address h248 port 2944 control address h248 transport udp media-gateway ipv4 200.200.201.101codecs m=audio 1234 RTP/AVP 0 18,a=rtpmap:0 PCMU/8000,a=rtpmap:18 G729/8000 transcoder exit

activateend

Configuration Examples for a Codec RestrictionThis section provides configuration examples for configuring restrictions on codecs and configuring a CAC policy to use a codec list:

• Configuring Codecs: Example, page SBC-366

• Configuring a CAC Policy to Use a Codec List: Example, page SBC-367

Configuring Codecs: ExampleThis section shows how to configure a codec restriction.

Figure 18 contains three adjacencies (A, B, and C). Any calls involving “A” need to be configured to use only the G729 and PCMU codecs with a minimal preferred packetization period of 10 milliseconds. However, calls between “B” and “C” can use any available codecs.


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Implementing SBC Transcoding and Codec RestrictionConfiguration Examples for a Codec Restriction

Figure 18 Scenario for Configuring Codec Restriction

The following example shows how to create a codec list containing the specified codecs configured with a minimal preferred packetization period:

configuresbc mysbcsbecodec-list allowable_codecsdescription The set of codecs allowed on adjacency AdjAcodec g729 packetization-period 20codec pcmu packetization-period 10end

After configuring codec restriction, you must configure a CAC policy to use the codec list (see “Configuring a CAC Policy to Use a Codec List: Example” section on page SBC-367.)

Configuring a CAC Policy to Use a Codec List: ExampleThe following example shows how to configure a CAC policy to use a codec list:

configuresbc mysbcsbecac-policy-set 1first-cac-table table1first-cac-scope callcac-table table1match-type adjacencyentry 1match AdjAcodec-restrict-to-list allowable_codecsaction cac-completeend

SBC SBC SBC

SBCAdjA

A B C

AdjC

AdjB

2106

11


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Implementing SBC Transcoding and Codec RestrictionAdditional References

Note The codec list CLI commands are entered only at the per-call level in the CAC policy tables. If you configure a codec list at any other level, the CAC policy set does not activate. However, a log is displayed after you commit the configuration and the policy set is marked as “complete”.

Where to Go NextAfter configuring SBC transcoding, you can configure the quality-of-service (QoS) marking. To configure QoS, see the Implementing SBC Quality of Service (Marking) module.

Additional ReferencesThe following sections provide references related to implementing SBC transcoding and codec restriction.

Related Documents

Standards

Related Topic Document Title

Cisco IOS XR master command reference Cisco IOS XR Master Commands List

SBC Transcoding Commands on Cisco IOS XR Software

SBC Media Gateway Controller Commands on Cisco IOS XR Software

SBC Policy Commands on Cisco IOS XR Software

Cisco IOS XR Session Border Controller Command Reference

Initial system bootup and configuration information for a router using the Cisco IOS XR Software

Cisco IOS XR Getting Started Guide

Cisco MGX 8880 documentation http://www.cisco.com/en/US/products/hw/gatecont/ps3869/index.html

Standards Title

No new or modified standards are supported by this feature, and support from existing standards has not been modified by this feature.

—


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MIBs

RFCs

Technical Assistance

MIBs MIBs Link

— To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu:

http://cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

RFCs Title

RFC 2833 RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals

RFC 3261 SIP: Session Initiation Protocol

Description Link

The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/techsupport


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http://www.cisco.com/techsupport



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