SIP DTMF Considerations
The SIP DTMF broadcast adjustment is bare in the afterward situations:
■ When SIP is acclimated to affix a Cisco SRST arrangement to a alien SIP-based IVR or
voice-mail application
■ When SIP is acclimated to affix a Cisco SRST arrangement to a alien SIP PSTN articulation gateway
that goes through the PSTN to a voice-mail or IVR application
304 Authorized Self-Study Guide: Cisco Articulation over IP (CVOICE)
Note The charge to use out-of-band DTMF broadcast about-face is bound to SCCP phones.
SIP phones natively abutment in-band DTMF broadcast as defined in RFC 2833.
SIP usually sends DTMF in-band digits, admitting SCCP supports alone out-of-band digits.
The software-based Media Termination Point (MTP) accessory receives the DTMF out-ofband
tones and generates DTMF in-band tones for the SIP client.
Figure 5-29 illustrates a alarm that begins with media streaming, and the Cisco Unified
Communications Manager software-based MTP accessory has been abreast of the
dynamic DTMF burden type.
In-Band SIP
Out-of-Band SCCP
Out-of-Band Information
SIP Gateway
SCCP Phone
RTP
RTP
MTP
V
Figure 5-29 SIP DTMF Configuration Considerations
The action that makes it accessible to accelerate SCCP out-of-band DTMF tones to SIP networks
is as follows:
1. The SCCP IP buzz user presses buttons on the keypad. Cisco Unified
Communications Manager collects the out-of-band digits from the SCCP IP phone.
2. Cisco Unified Communications Manager passes the out-of-band digits to the MTP
device.
3. The MTP accessory converts the digits to RFC 2833-compliant in-band digits and forwards
them to the SIP client.
Chapter 5: Examining VoIP Gateways and Aperture Control Protocols 305
Note Because the Cisco Unified Communications Manager software-based MTP can
handle no added than 48 media streams in parallel, alone 48 SCCP-to-SIP calls are available
in earlier versions of Cisco Unified CallManager afterwards a accouterments MTP. In that case, it is
necessary to configure the aperture to accelerate DTMF out-of-band. (Cisco Unified Communications
Manager Release 5.0 and afterwards can handle SCCP-to-SIP calls afterwards an MTP.)
As ahead mentioned, SCCP IP phones are able of sending alone out-of-band
DTMF digits. To abutment SCCP devices, basic and absolute SIP gateways can
use Cisco proprietary NOTIFY-based out-of-band DTMF relay. In addition, NOTIFYbased
out-of-band DTMF broadcast can additionally be acclimated by analog phones absorbed to analog
voice ports (known FXS) on the router.
NOTIFY-based out-of-band DTMF broadcast sends letters bidirectionally amid the
originating and absolute gateways for a DTMF accident during a call. If assorted DTMF
relay mechanisms are enabled on a SIP punch associate and are adjourned successfully,
NOTIFY-based out-of-band DTMF broadcast takes precedence.
The basic aperture sends an INVITE bulletin with SIP Call-Info attack information
to announce the use of the NOTIFY-based out-of-band DTMF relay. The absolute gateway
acknowledges the bulletin with an 18x or 200 Acknowledgment message, additionally application the
Call-Info header. Whenever a DTMF accident occurs, the aperture sends a SIP NOTIFY
message for that accident afterwards the SIP Invite and 18x or 200 Acknowledgment letters negotiate
the NOTIFY-based out-of-band DTMF broadcast mechanism. In response, the gateway
expects to accept a 200 OK message.
The NOTIFY-based out-of-band DTMF broadcast apparatus is agnate to the DTMF message
format declared in RFC 2833.