This command can be used to help save network bandwidth for a remote
For calls to phones that are not in the same Cisco Unified CME system
(such as VoIP calls), the codec is negotiated based on the protocol that is
used for the call (such as H.323). The Cisco Unified CME system plays no part
in the negotiation.
The G.722-64K codec is supported on some varieties of phone models.
Check your phone documentation to make sure the phone supports the G.722-64K
The telephone’s firmware version must support the specified codec. If
a codec is specified by using this command and a phone does not support the
preferred codec, then the phone will use the global codec as specified by using
codec command in telephony-service
configuration mode or if the global codec is not supported, G.711 micro-law.
For calls to other phones in the same Cisco Unified CME system, an IP
phone that is configured to use G.729 will always have its calls set up to use
G.729. If the phone participates in a call on a line that is shared with a
phone that is configured for G.729 or is paged together with another phone that
is configured for G.729, it must use G.729.
When you use the
codec command without the
dspfarm-assist keyword, you affect only calls
between two phones on the Cisco Unified CME router (such as between an IP phone
and another IP phone or between an IP phone and a FXS analog phone). The
command has no effect on a call directed through a VoIP dial peer unless you
When you use the
g729r8 keyword to select the G.729r8 codec
for the RTP segment between the IP phone and the Cisco Unified CME router and
you also use the
dspfarm-assist keyword, the router attempts
to use DSP-farm resources in the following way: If the IP phone is in a VoIP
call (H.323 or SIP) or a Cisco Unified CME conference in which the codec must
be set to G.711, the router uses configured DSP-farm resources to attempt to
return the segment between the phone and the Cisco Unified CME router to G.729.
Adequate DSP resources must be appropriately configured separately.
dspfarm-assist keyword is configured for a
phone and a DSP resource is not available when needed for transcoding, a phone
registered to the local Cisco Unified CME router will use G.711 instead of
G.729r8. This is not true for non-SCCP call legs; if no DSP resource is
available for the transcoding required for a conference, for example, the
conference will not be created.
It is recommended that the
dspfarm-assist keyword be used sparingly and
only when absolutely required for bandwidth savings or when you know the phone
will have few calls that require a G.711 codec.
You should consider your options carefully when deciding to use the
dspfarm-assist keyword with the
codec command. The benefit is that it allows
calls to use the G.729r8 codec on the call leg between the IP phone and the
Cisco Unified CME router, which saves network bandwidth. The disadvantage is
that for situations requiring G.711 codecs, such as conferencing and Cisco
Unity Express, DSP resources that can be scarce will be used to transcode the
call, and delay will be introduced while voice is shuttled to and from the DSP.
In addition, the overuse of this feature can mask configuration errors in the
codec selection mechanisms involving dial peers and codec lists.
For information about configuring DSP-farm resources, see the
Unified CME Administrator Guide .
dspfarm-assist keyword is ignored if the SCCP
endpoint type is ATA, VG224, or VG248.
This command can also be configured in ephone-template configuration
mode. If you use an ephone template to apply a command to a phone and you also
use the same command in ephone configuration mode for the same phone, the value
that you set in ephone configuration mode has priority.