Table Of Contents

Codec Handling

Contents

Prerequisites for Codec Handling

Restrictions for Codecs

Configuring Codec Restriction and Packetization Time

Packetization Time

Codec Restriction

Configuring Codecs

Configuring a CAC Policy to Use a Codec List

Examples of Configuring Codec Restriction

Example of Configuring Codecs

Example of Configuring a CAC Policy to Use a Codec List

Codec Handling

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A compressor-decompressor (codec) is a device or program that performs a transformation on a data stream or signal. Cisco Unified Border Element (SP Edition) is hard-coded with a set of recognized codecs (see Table 18-1 to Table 18-5), 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 Cisco Unified Border Element (SP Edition).

This enhancement allows you to restrict which codec(s) a particular call can use and to configure a minimum permissible packetization period for each permitted codec.

Cisco Unified Border Element (SP Edition) supports passthrough codecs that are passed through the SBC without transcoding. See Table 18-4 for a list of passthrough codecs by type.

H.323 only supports PCMA, PCMU, G.722, G.723, G.728, G.729, GSM, telephone-event, H.261, H.263, H.264, and T.38 codecs. Therefore in a SIP to H.323 call, if SIP codecs are sent to H.323 that H.323 cannot support, then these codecs are not passed through and the call may fail accordingly.

Cisco Unified Border Element (SP Edition) supports codec transcoding for SIP to SIP calls only. 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 PCMU into one encoded as G.726-32. For more information on transcoding, see the Implementing SBC Transcoding chapter.

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Note For Cisco IOS XE Release 2.4 and later, this feature is supported in the unified model.

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For a complete description of 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 Codec Handling

Release	Modification
Cisco IOS XE Release 2.4	This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers along with support for the unified model.
Cisco IOS XE Release 2.4.2	The SBC uses the packetization time, p-time, attribute in the SDP offer or answer configured in a codec list.
Cisco IOS XE Release 2.5	Support for H.323 calls, and H.323 video codecs H.261, H.263, and H.264 were added. Support for passthrough codecs without transcoding was added.

Contents

This module contains the following sections:

•Prerequisites for Codec Handling

•Restrictions for Codecs

•Configuring Codec Restriction and Packetization Time

•Examples of Configuring Codec Restriction

Prerequisites for Codec Handling

The following prerequisites are required before you can restrict codecs:

•Before implementing Codec Handling, Cisco Unified Border Element (SP Edition) must already be configured. See the procedures described in Chapter 2, "Configuring Cisco Unified Border Element (SP Edition)."

•All signaling border element (SBE) and data border element (DBE) configurations required to make simple calls must already be configured.

Restrictions for Codecs

Review the following restrictions for codecs:

•For H.323 calls, SIP to H.323 and H.323 to SIP calls, both the callee and caller must use the same codec because any calls requiring transcoding will fail the call setup.

•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, Cisco Unified Border Element (SP Edition) 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.

•If a codec whitelist has not been configured, all recognized codecs (see Table 18-1 to Table 18-5) 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 could set a bandwidth limit of 0 to achieve the same result.

•Codec lists are not applied to media-bypass calls (those in which Cisco Unified Border Element (SP Edition) 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 18-1 - Table 18-5.

•A single codec can only be added to each list 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, then the greater of all the packetization periods configured for each codec in the list is applied to the stream.

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Note The bandwidths listed in the tables below are the bandwidths without the transport layer overheads. Therefore, the actual bandwidths reserved by Cisco Unified Border Element (SP Edition) are higher than the listed values.

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Table 18-1 Sample-Based Audio Codecs with Packetization Time 10 ms 

Payload Type	Codec Name	Clock Rate (Hz)	Sample Size (bits)	Channels
0	PCMU (also known as G.711)	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

Table 18-2 Non-Sample-Based Audio Codecs 

Payload Type	Codec Name	Packetization Time (ms)	Allocated Bandwidth (bps)
3	GSM	10	13200
7	LPC	10	5600
9	G722	10	64000
13	CN	10	400
18	G729	10	8000
18	G.729A	10	8000
18	G729A	10	8000
4	G723	30	6400
12	QCELP	—	13300
14	MPA	N/A	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 18-3 Video Codecs 

Payload Type	Codec Name	Packetization Time (ms)	Allocated Bandwidth (bps)
25	CelB	—	524228
26	JPEG	—	524228
28	nv	—	524228
31	H261	—	524228
32	MPV	—	524228
33	MP2T	—	524228
34	H263	—	524228
NA	H264		21000000
—	BMPEG	—	524228
—	BT656	—	170000000
—	DV	—	1500000000
—	H263-1998	—	524228
—	H263-2000	—	524228
—	MP1S	—	1600000
—	MP2P	—	524228
—	MP4V-ES	—	524228
—	raw	N/A	1500000000
—	SMPTE292M	N/A	1500000000

The following table lists the supported passthrough codecs without transcoding.

Table 18-4 Passthrough Codecs without Transcoding 

Codec Name	Codec Type	Packetization Time (ms)	Allocated Bandwidth (bps)
PCMA (also known as G.711)	sample-based audio	10	64000
PCMU (also known as G.711)	sample-based audio	10	64000
G726-16	audio	10	NA
G726-24	audio	10	NA
G726-32	audio	10	NA
G728	audio	10	NA
G729 A	non-sample-based audio	10	8000
G729 B	non-sample-based audio	10	8000
G723-53	non-sample-based audio	30	6400
G723-63	non-sample-based audio	30	6400
GSM/GSM-FR	non-sample-based audio	10	13200
GSM-EFR	non-sample-based audio	20	12400
GSM-HR	non-sample-based audio	20	5600
AMR	non-sample-based audio	10	12500
EVRC	non-sample-based audio	10	8550
G722	non-sample-based audio	10	64000
iLBC	non-sample-based audio	20	15200
H.261	video	NA	524228
H.263	video	NA	524228

Table 18-5 Other Codecs 

Codec Name	Packetization Time (ms)	Allocated Bandwidth (bps)
telephone-event	20	1600
tone	20	1600
RED	20	1
parityfec	20	1
T140	100	80
pointer	20	1600
H224	20	6560
T38	N/A	15500
X-NSE	20	1600

Configuring Codec Restriction and Packetization Time

Packetization Time

The packetization time (p-time) is the time period a codec is applied to a media stream to build a single digital packet. When a call travels between two end points, both the codec and the p-time for that codec is negotiated. The SBC acts on the p-time attribute in the SDP based on the configuration in the codec list.

SBC adds the ptime attribute to an SDP offer or answer, when one is configured explicitly in a codec whitelist. The exception is if a minimum packetization time is configured as part of SBC policy. This configuration causes SBC to insert a=ptime lines into forwarded offers or answers.

SBC ensures that media clipping does not occur as a result of overestimating the ptime (and hence underestimating the bandwidth requirement).

If ptime is signaled explicitly on the offer and answer, it uses the lower of the two values to calculate the bandwidth allowance for both directions of media.

Codec Restriction

You first configure the codecs and then apply them as explained in the following sections:

•Configuring Codecs

•Configuring a CAC Policy to Use a Codec List

Configuring Codecs

To restrict which codec(s) 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 codec(s) to the list.

SUMMARY STEPS

1. configure terminal

2. sbc service-name

3. sbe

4. codec list name

5. description text

6. codec codec-name [packetization-period packetization-period]

7. end

8. show sbc service-name sbe codec-list list-name

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: Router# configure terminal	Enables global configuration mode.
Step 2	sbc service-name Example: Router(config)# sbc mysbc	Enters the submode of an SBC service.
Step 3	sbe Example: Router(config-sbc)# sbe	Configures the submode of the SBE entity within a SBC service.
Step 4	codec list name Example: Router(config-sbc-sbe)#sbc mysbc sbe codec list my_codecs	Creates a codec list.
Step 5	description text Example: Router(config-sbc-sbe-codec-list)# description Legitimate codes	Adds a description for the specified codec list using a readable text string format. The no form of this command removes the description. This description is displayed when the show command is used for this codec list. It is also included for each codec list when a summary of all codec lists is displayed.
Step 6	codec codec-name [packetization-period packetization-period] Example: Router(config-sbc-sbe-codec-list)# codec PCMU packetization-period 20	Adds a codec to a codec list, and sets a minimum packetization period (optional) for the codec. The no form of this command (without the packetization period) removes the named codec from the codec list. Note If the no form of this command includes the packetization period, only the packetization period for the codec is removed.
Step 7	end Example: Router(config-sbc-sbe-codec-list)# end	Exits codec-list mode and enters Privileged EXEC mode.
Step 8	show sbc service-name sbe codec-list list-name Example: Router# show sbc mysbc sbe codec-list my_codecs	Displays detailed information about the codec lists configured on the SBE. If the list name is omitted, for example, my_codecs, then details are displayed for all codec lists on the SBE.

Configuring a CAC Policy to Use a Codec List

SUMMARY STEPS

1. configure terminal

2. sbc service-name

3. sbe

4. cac-policy-set policy-set-id

5. first-cac-scope scope-name

6. first-cac-table table-name

7. cac-table table-name

8. table-type {policy-set | limit {list of limit tables}}

9. entry entry-id

10. cac-scope {list of scope options}

11. action [next-table goto-table-name | cac-complete]

12. codec-restrict-to-list list-name

13. complete

14. end

15. show sbc service-name sbe cac-policy-set id table name entry entry

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: Router# configure terminal	Enables global configuration mode.
Step 2	sbc service-name Example: Router(config)# sbc mysbc	Enters the submode of an SBC service.
Step 3	sbe Example: Router(config-sbc)# sbe	Configures the submode of the SBE entity within a SBC service.
Step 4	cac-policy-set policy-set-id Example: Router(config-sbc-sbe)# cac-policy-set 1	Enters the submode of CAC policy.
Step 5	first-cac-scope scope-name Example: Router(config-sbc-sbe-cacpolicy)# first-cac-scope global	Configures the scope at which to begin defining limits when performing the admission control stage of policy. Note The first-cac-scope definition is only relevant if the table type configured by the first-cac-table command is a Limit table. In that case, the scope of the first-cac-table is determined by first-cac-scope. If the first-cac-table is a Policy Set table, the first-cac-scope is ignored and defaults to global. The scope-name argument configures the scope at which limits should be initially defined. Possible values are: •adj-group •call •category •dst-account •dst-adj-group •dst-adjacency •dst-number •global •src-account •src-adj-group •src-adjacency •src-number Features can be enabled or disabled per adjacency group through CAC configuration the same way this is done per individual adjacencies.
Step 6	first-cac-table table-name Example: Router(config-sbc-sbe-cacpolicy)# first-cac-table first_policy_table	Configures the name of the first policy table to process when performing the admission control stage of policy.
Step 7	cac-table table-name Example: Router(config-sbc-sbe-cacpolicy)# cac-table first_policy_table	Enters the mode for configuration of an admission control table (creating one if necessary) within the context of an SBE policy set.
Step 8	table-type {policy-set | limit {list of limit tables}} Example: Router(config-sbc-sbe-cacpolicy-cactable)# table-type policy-set	Configures the table type of a CAC table within the context of an SBE policy set. The list of limit tables argument controls the syntax of the match-value fields of the entries in the table. Possible available Limit tables are: •account—Compare the name of the account. •adj-group—Compare the name of the adjacency group. •adjacency—Compare the name of the adjacency. •all—No comparison type. All events match this type. •call-priority—Compare with call priority. •category—Compare the number analysis assigned category. •dst-account—Compare the name of the destination account. •dst-adj-group—Compare the name of the destination adjacency group. •dst-adjacency—Compare the name of the destination adjacency. •dst-prefix—Compare the beginning of the dialed digit string. •event-type—Compare with CAC policy event types. •src-account—Compare the name of the source account. •src-adj-group—Compare the name of the source adjacency group. •src-adjacency—Compare the name of the source adjacency. •src-prefix—Compare the beginning of the calling number string. Note For Limit tables, the event or message or call matches only a single entry. Features can be enabled or disabled per adjacency group through CAC configuration the same way this is done per individual adjacencies. The adj-group table type matches on either source or destination adjacency group. When the policy-set keyword is specified, use the cac-scope command to configure the scope within each entry at which limits are applied in a CAC Policy Set table. Note For Policy Set tables, the event or call or message is applied to all entries in this table.
Step 9	entry entry-id Example: Router(config-sbc-sbe-cacpolicy-cactable)# entry 1	Enters the mode to create or modify an entry in an admission control table..
Step 10	cac-scope {list of scope options} Example: Router(config-sbc-sbe-cacpolicy-cactable-entry) # cac-scope call	Configures the scope within each entry at which limits are applied in a Policy Set table. Only per call scope can be configured when using the codec-restrict-to-list command. list of scope options specifies one of the following strings used to match events: adj-group—Events that are from members of the same adjacency group. call—Scope limits are per single call. category—Events that have same category. dst-account—Events that are sent to the same account. dst-adj-group—Events that are sent to the same adjacency group. dst-adjacency—Events that are sent to the same adjacency. dst-number—Events that have same destination. global—Scope limits are global src-account—Events that are from the same account. src-adj-group—Events that are from the same adjacency group. src-adjacency—Events that are from the same adjacency. src-number—Events that have the same source number. sub-category—The limits specified at this scope apply to all events sent to or received from members of the same subscriber category. sub-category-pfx—The limits specified at this scope apply to all events sent to or received from members of the same subscriber category prefix. subscriber—The limits specified at this scope apply to all events sent to or received from individual subscribers (a device that is registered with a Registrar server).
Step 11	action [next-table goto-table-name | cac-complete] Example: Router(config-sbc-sbe-cacpolicy-cactable-entry) # action cac-complete	Configures the action to perform after this entry in an admission control table. Possible actions are: •Identify the next CAC table to process using the next-table keyword and the goto-table-name argument. •Stop processing for this scope using the cac-complete keyword.
Step 12	codec-restrict-to-list list-name Example: Router(config-sbc-sbe-cacpolicy-cactable-entry) # 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. If a codec list is empty, all codecs recognized by the SBE are allowed. The no form of this command, or not setting this command, allows any recognized codecs to be used without restrictions. Note This command replaces any codec list that was set up by an earlier CAC entry. To clear all restrictions from an earlier CAC entry, you must configure a codec-restrict-to-list list-name, where list-name is the name of a list containing no codecs.
Step 13	complete Example: Router(config-sbc-sbe-cacpolicy)# complete	Completes the cac-policy.
Step 14	end Example: Router(config-sbc-sbe-cacpolicy)# end	Exits the cac-policy-set configuration mode and enters Privileged EXEC mode.
Step 15	show sbc service-name sbe cac-policy-set id table name entry entry Example: Router# show 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.

Examples of Configuring Codec Restriction

This section provides a sample configuration and output for configuring restrictions on codecs and configuring a CAC policy to use a codec list.

Example of Configuring Codecs

The following example shows the commands required to configure codec restriction.

Figure 18-1 contains three adjacencies (A, B, and C). Any calls involving A need to be configured to use only the G729 and PCMU (G.711) codecs with a minimal preferred packetization period of 10 milliseconds. However, calls between B and C can use any available codecs.

To create a codec list containing the specified codecs configured with a minimal preferred packetization period, use the following commands:

Router# configure terminal

Router(config)# sbc mysbc

Router(config-sbc)# sbe

Router(config-sbc-sbe)# codec list allowable_codecs

Router(config-sbc-sbe-codec-list)# description The set of codecs allowed on adjacency AdjA

Router(config-sbc-sbe-codec-list)# codec g729 packetization-period 20

Router(config-sbc-sbe-codec-list)# codec pcmu packetization-period 10

Router(config-sbc-sbe-codec-list)# exit

After configuring codec restriction, you must configure a CAC policy to use the codec list. See "Example of Configuring a CAC Policy to Use a Codec List" section.

Figure 18-1 Example Scenario for Configuring Codec Restriction

Example of Configuring a CAC Policy to Use a Codec List

The following example shows the commands required to configure a CAC policy to use a codec list. To configure a codec list, see "Example of Configuring Codecs" section.

Router# configure terminal

Router(config)# sbc mysbc

Router(config-sbc)# sbe

Router(config-sbc-sbe)# cac-policy-set 1

Router(config-sbc-sbe-cacpolicy)# first-cac-table table1

Router(config-sbc-sbe-cacpolicy)# first-cac-scope call

Router(config-sbc-sbe-cacpolicy)# cac-table table1

Router(config-sbc-sbe-cacpolicy-cactable)# match-type adjacency

Router(config-sbc-sbe-cacpolicy-cactable)# entry 1

Router(config-sbc-sbe-cacpolicy-cactable)# match AdjA

Router(config-sbc-sbe-cacpolicy-cactable)# codec-restrict-to-list allowable_codecs

Router(config-sbc-sbe-cacpolicy-cactable-entry)# action cac-complete

Router(config-sbc-sbe-cacpolicy-cactable-entry)# exit

Router(config-sbc-sbe-cacpolicy)# complete

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Note The codec list command line interface (CLI) commands can only be entered at the per-call level in the CAC policy tables. If you configure a codec list at any other level the CAC policy set will not activate. However, a log is displayed after you complete the configuration and the policy set is marked as "complete".

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