Table Of Contents
Restricting Codecs
Contents
Prerequisites for Restricting Codecs
Restrictions for Codecs
How to Configure Codec Restriction
Configuring Codecs
Configuring a CAC Policy to Use a Codec List
Examples of Configuring Codecs
Example of Configuring Codecs Restriction
Example of Configuring a CAC Policy to Use a Codec List
Example of Codec Ordering
Restricting Codecs
A compressor-decompressor (codec) is a device or program that performs a transformation on a data stream or signal. The Session Border Controller (SBC) is hard-coded with a set of recognized codecs (see Table 17-1 to Table 17-4), 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.
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.
Note 
For ACE SBC Release 3.0.0 and later, this feature is supported in the unified model only.
Feature History for Restricting Codecs
Release
|
Modification
|
ACE SBC Release 3.1.00
|
Added support for codec ordering.
|
ACE SBC Release 3.0.00
|
This feature was introduced on the Cisco 7600 series router along with support for the SBC unified model.
|
Contents
This module contains the following sections:
•Prerequisites for Restricting Codecs
•Restrictions for Codecs
•How to Configure Codec Restriction
•Examples of Configuring Codecs
Prerequisites for Restricting Codecs
The following prerequisites are required before you can restrict codecs:
•On the Application Control Engine Module (ACE), you must be an Admin user to enter SBC commands. For more information, see the Application Control Engine Module Administration Guide at http://www.cisco.com/en/US/products/hw/modules/ps2706/products_configuration_guide_book09186a00806838f4.html.
•Before implementing restricting codecs, the SBC must already be created. See the procedures described in Chapter 2, "ACE Configuration Prerequisites for the SBC".
•Transcoding must be configured before you can restrict codecs. See the procedures described in the Implementing SBC Transcoding section.
•All signaling border element (SBE) and data border element (DBE) configurations required to make simple calls must already be configured. Transcoding configurations follow these configurations.
Restrictions for Codecs
Review the following 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.
•If a codec whitelist has not been configured, all recognized codecs (see Table 17-1 to Table 17-4) 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 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 17-1 - Table 17-4.
•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.
•The Codec Ordering feature implicitly orders codecs according to the order in which they are added to the codec list using the codec command. Explicit codec ordering is not available with this feature.
Note The SBC will not order the codecs in SIP messages that are not generated by the SBC.
Note The bandwidths listed in Table 17-1 to Table 17-4 below are the bandwidths without the transport layer overheads. Therefore, the actual bandwidths reserved by the SBC are higher than the listed values.
Table 17-1 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
|
Table 17-2 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 17-3 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
|
—
|
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
|
Table 17-4 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
|
T.38
|
N/A
|
15500
|
X-NSE
|
20
|
1600
|
How to Configure 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
2. sbc service-name
3. sbe
4. codec-list list-name
5. codec
6. description text
7. codec codec-name [packetization-period packetization-period]
8. exit
9. show services sbc service-name sbe codec-list list-name
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
host1/Admin# configure
|
Enables global configuration mode.
|
Step 2
|
sbc service-name
Example:
host1/Admin(config)# sbc mysbc
|
Enters the submode of an SBC service.
|
Step 3
|
sbe
Example:
host1/Admin(config-sbc)# sbe
|
Configures the submode of the SBE entity within a SBC service.
|
Step 4
|
codec-list list-name
Example:
host1/Admin(config-sbc-sbe)#sbc mysbc sbe
codec-list my_codecs
|
Creates a codec list.
|
Step 5
|
codec codec-name
Example:
host1/Admin(config-sbc-sbe-codec-list)# codec
PCMU
|
Adds a codec to a codec list.
|
Step 6
|
description text
Example:
host1/Admin(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 7
|
codec codec-name [packetization-period
packetization-period]
Example:
host1/Admin(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 8
|
exit
Example:
host1/Admin(config-sbc-sbe-codec-list)# exit
|
Exits the codec-list mode to the SBE mode.
|
Step 9
|
show services sbc service-name sbe codec-list
list-name
Example:
host1/Admin# 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, 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
2. sbc service-name
3. sbe
4. cac-policy-set policy-set
5. cac-table table-id
6. entry entry-id
7. codec-restrict-to-list list-name
8. exit
9. show services sbc service-name sbe cac-policy-set id table name entry entry
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
host1/Admin# configure
|
Enables global configuration mode.
|
Step 2
|
sbc service-name
Example:
host1/Admin(config)# sbc mysbc
|
Enters the submode of an SBC service.
|
Step 3
|
sbe
Example:
host1/Admin(config-sbc)# sbe
|
Configures the submode of the SBE entity within a SBC service.
|
Step 4
|
cac-policy-set policy-set
Example:
host1/Admin(config-sbc-sbe)# cac-policy-set 1
|
Enters the submode of CAC policy.
|
Step 5
|
cac-table table-id
Example:
host1/Admin(config-sbc-sbe-cacpolicy)#
cac-table MyCacTable
|
Identifies the CAC table.
|
Step 6
|
entry entry-id
Example:
host1/Admin(config-sbc-sbe-cacpolicy-
cactable)# entry 1
|
Identifies the specific table entry.
|
Step 7
|
codec-restrict-to-list list-name
Example:
host1/Admin(config-sbc-sbe-cacpolicy-
cactable)# 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 8
|
exit
Example:
host1/Admin(config-sbc-sbe-codec-list)# exit
|
Exits the codec-list mode to the sbe mode.
|
Step 9
|
show services sbc service-name sbe
cac-policy-set id table name entry entry
Example:
host1/Admin(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.
|
Examples of Configuring Codecs
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 Restriction
The following example shows the commands required to configure codec restriction.
Figure 17-1 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.
To create a codec list containing the specified codecs configured with a minimal preferred packetization period, use the following commands:
host1/Admin(config)# sbc mysbc
host1/Admin(config-sbc)# sbe
host1/Admin(config-sbc-sbe)# codec-list allowable_codecs
host1/Admin(config-sbc-sbe-codec-list)# description The set of codecs allowed on adjacency
AdjA
host1/Admin(config-sbc-sbe-codec-list)# codec g729 packetization-period 20
host1/Admin(config-sbc-sbe-codec-list)# codec pcmu packetization-period 10
host1/Admin(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 17-1 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 Restriction" section.
host1/Admin(config)# sbc mysbc
host1/Admin(config-sbc)# sbe
host1/Admin(config-sbc-sbe)# cac-policy-set 1
host1/Admin(config-sbc-sbe-cacpolicy)# first-cac-table table1
host1/Admin(config-sbc-sbe-cacpolicy)# first-cac-scope call
host1/Admin(config-sbc-sbe-cacpolicy)# cac-table table1
host1/Admin(config-sbc-sbe-cacpolicy-cactable)# match-type adjacency
host1/Admin(config-sbc-sbe-cacpolicy-cactable)# entry 1
host1/Admin(config-sbc-sbe-cacpolicy-cactable)# match AdjA
host1/Admin(config-sbc-sbe-cacpolicy-cactable)# codec-restrict-to-list allowable_codecs
host1/Admin(config-sbc-sbe-cacpolicy-cactable-entry)# actionaction cac-complete
host1/Admin(config-sbc-sbe-cacpolicy-cactable-entry)# exit
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".
Example of Codec Ordering
In the example below, codecs are added to the codec list. The show run command is then used to show the list order.
Enter configuration commands, one per line. End with CNTL/Z.
Router/Admin(config)# sbc sbc
Router/Admin(config-sbc)# sbe
Router/Admin(config-sbc-sbe)# codec-list zilu
Router/Admin(config-sbc-sbe-codec-list)# codec PCMU
Router/Admin(config-sbc-sbe-codec-list)# codec AMR
Router/Admin(config-sbc-sbe-codec-list)# codec PCMA
Router/Admin(config-sbc-sbe-codec-list)# codec G729D
Router/Admin(config-sbc-sbe-codec-list)# codec EVRC
Router/Admin(config-sbc-sbe-codec-list)# codec X-NSE
Router/Admin(config-sbc-sbe-codec-list)# codec T38
Router/Admin(config-sbc-sbe-codec-list)# end
