Cisco Cisco IOS Software Release 12.2(15)ZJ
SIP Gateway Enhancements
dtmf-relay (Voice over IP)
22
Cisco IOS Release 12.2(15)ZJ
Usage Guidelines
DTMF is the tone generated when you press a button on a touch tone phone. This tone is compressed at
one end of a call; when the tone is decompressed at the other end, it can become distorted, depending on
the codec used. The DTMF relay feature transports DTMF tones generated after call establishment
out-of-band using either a standard H.323 out-of-band method or a proprietary RTP-based mechanism.
For SIP calls, the most appropriate methods to transport DTMF tones are RTP-NTE or SIP-NOTIFY.
one end of a call; when the tone is decompressed at the other end, it can become distorted, depending on
the codec used. The DTMF relay feature transports DTMF tones generated after call establishment
out-of-band using either a standard H.323 out-of-band method or a proprietary RTP-based mechanism.
For SIP calls, the most appropriate methods to transport DTMF tones are RTP-NTE or SIP-NOTIFY.
The SIP-NOTIFY method sends NOTIFY messages bidirectionally between the originating and
terminating gateways for a DTMF event during a call. If multiple DTMF relay mechanisms are enabled
on a SIP dial peer and are negotiated successfully, the SIP-NOTIFY method takes precedence.
terminating gateways for a DTMF event during a call. If multiple DTMF relay mechanisms are enabled
on a SIP dial peer and are negotiated successfully, the SIP-NOTIFY method takes precedence.
SIP NOTIFY messages are advertised in an Invite message to the remote end only if the dtmf-relay
command is set.
command is set.
For SIP, the gateway chooses the format according to the following priority:
1.
sip-notify
2.
rtp-nte
3.
None—DTMF sent in-band
The gateway sends DTMF tones only in the format that you specify if the remote device supports it. If
the H.323 remote device supports multiple formats, the gateway chooses the format according to the
following priority:
the H.323 remote device supports multiple formats, the gateway chooses the format according to the
following priority:
1.
cisco-rtp (highest priority)
2.
h245-signal
3.
h245-alphanumeric
4.
rtp-nte
5.
None—DTMF sent in-band
The principal advantage of the dtmf-relay command is that it sends DTMF tones with greater fidelity
than is possible in-band for most low-bandwidth codecs, such as G.729 and G.723. Without the use of
DTMF relay, calls established with low-bandwidth codecs may have trouble accessing automated
DTMF-based systems, such as voice mail, menu-based Automatic Call Distributor (ACD) systems, and
automated banking systems.
than is possible in-band for most low-bandwidth codecs, such as G.729 and G.723. Without the use of
DTMF relay, calls established with low-bandwidth codecs may have trouble accessing automated
DTMF-based systems, such as voice mail, menu-based Automatic Call Distributor (ACD) systems, and
automated banking systems.
Note
•
The cisco-rtp keyword is a proprietary Cisco implementation and operates only between two
Cisco AS5800 access concentrators that are running Cisco IOS Release 12.0(2)XH or between
Cisco AS5800 access concentrators or Cisco 2600 series or Cisco 3600 series routers that are
running Cisco IOS Release 12.0(2)XH or later releases. Otherwise, the DTMF relay feature does not
function, and the gateway sends DTMF tones in-band.
Cisco AS5800 access concentrators that are running Cisco IOS Release 12.0(2)XH or between
Cisco AS5800 access concentrators or Cisco 2600 series or Cisco 3600 series routers that are
running Cisco IOS Release 12.0(2)XH or later releases. Otherwise, the DTMF relay feature does not
function, and the gateway sends DTMF tones in-band.
•
The cisco-rtp keyword of the dtmf-relay command is supported on Cisco 7200 series routers.
•
The h245-alphanumeric and h245-signal DTMF settings on a Cisco MC3810 multiservice access
concentrator require a high-performance compression module (HCM) and are not supported on a
Cisco MC3810 with a non-HCM voice compression module (VCM).
concentrator require a high-performance compression module (HCM) and are not supported on a
Cisco MC3810 with a non-HCM voice compression module (VCM).
•
The sip-notify keyword is available only if the VoIP dial peer is configured for SIP.