Single Number Voice/Fax Routing
When feature F-1450 is configured, using the same dialing number, the
IMG will be able to switch the SIP call from a voice endpoint to a fax
endpoint device. A SIP user first dials a number and the call comes into
the IMG. The IMG then routes the call through an outgoing channel group
to a configured voice endpoint such as a SIP voice gateway. Within this
call, the user then sends a fax and the IMG detects the fax tone. The
IMG then disconnects the outgoing side of the call from the initial voice
external gateway and reconnects it to the fax external gateway. The call
is now connected to the fax device, and the fax is thus sent to the proper
destination. Because the call is always routed to a voice endpoint, the
call remains at the voice endpoint if no fax tones are detected. The call
doesn’t switch to the fax endpoint. For more information see below.
Call Flow Diagram

- Call comes into IMG which is routed to a SIP Voice Endpoint (SIP
external gateway) and a voice session is established.
- The Incoming or A-Leg initiates a fax by sending a Fax Tone.
- The IMG detects the fax tone and disconnects the B-leg from the
SIP Voice endpoint.
- IMG then switches the call to a SIP fax endpoint.
- A fax session is then established and data is sent to the fax endpoint.
- When fax completes the incoming or A-leg disconnects the call.
- The IMG then disconnects the B-leg from fax endpoint.
Call Trace
To view a Call Trace displaying the feature see Single
Number Voice/Fax Routing Call Trace.
Configuration
Below are instructions on how to configure the IMG to allow it to switch
the outgoing call to a fax endpoint. In the procedure below the incoming
side and outgoing side will be using the SIP protocol although the incoming
side can be any protocol supported on the IMG (H.323, CAS, SS7, ISDN and
SIP).
Logical Node
Physical Node
IP Network
IP Address (Configure Interface)
IP Bearer Spans
TDM Spans
Signaling - SIP
SIP SGP
Create a SIP gateway for the incoming side.
- Right Click on IMG EMS and select New
External Network Elements. There is no configuration
needed within this object. The External Network Elements object is
a parent object for external network entities such as gateways, gatekeepers,
DNS Servers, and any other external network entities. Refer to External Network Elements for
more information on this object.
- Right Click on External Network elements just created and
select New External Gateways.
There is no configuration needed within this object. The External
Gateways object is a parent object to the external gateway object.
Multiple external gateway objects are configured under the External
Gateways object. Refer to External
Gateways for more information.
- Right Click on External Gateways object and select New External Gateway. Enter
a Name, IP address, and change the Gateway Signaling Protocol to SIP.
This is the gateway being created for the incoming side. Refer to
External Gateway for more information on this object.
Note:
The incoming side can be any protocol supported on the IMG. This procedure
will use SIP as the incoming protocol
Create two outgoing SIP gateways. One for Fax and one for Voice.
- Right Click on External Gateways object again and select
New External Gateway.
Enter a Name for the Voice endpoint. In this procedure Voice_Gateway_Out
was selected. Enter an IP address, and change the Gateway Signaling
Protocol to SIP. This is the gateway being created for the voice endpoint
on the outgoing side. Refer to External Gateway for more information
on this object.
- Right Click on External Gateways object again and select
New External Gateway.
Enter a Name for the Fax endpoint. In this procedure Fax_Gateway_Out
was selected. Enter an IP address, and change the Gateway Signaling
Protocol to SIP. This is the gateway being created for the fax endpoint
on the outgoing side. Refer to External Gateway for more information
on this object.
Create IP Bearer Profile and configure Single Number Voice/Fax
Routing
- Right click on the Profiles object and select New
IP Bearer Profile. Enter a name in the IP Bearer Profile Name
field that identifies the profile being created.
- In the Single-Number Fax
field select Enable. By selecting Enable, a second field labeled Single-Number
Fax Server can now be modified. Select from drop down menu the external
gateway for the fax endpoint. See screen capture below.

- Within the Fax Mode field, select the Fax Mode to be used. This
field has to be configured to something other than Disable.
- Within the Fax Bypass Codec field select the Bypass Codec to be
used.
- Within the Modem Behavior field, select Disabled
from drop down menu.
- Create a second IP Bearer Profile that will be associated
with the incoming side. In this procedure it is labeled Gateway_Inc.
Refer to IP Bearer
Profile for more information on this object.
Note: The new parameters
are applicable only when the IP Bearer profile is used by an outgoing
Channel Group. The GCEMS can allow the IP Bearer profile with these new
parameters enabled to be associated to an incoming Channel Group. But
these parameters wouldn’t be applicable.
Create Outgoing Channel Group
Create an outgoing channel group. The outgoing channel group has to
be a SIP channel group.
- Right Click on IMG EMS and select New
Routing Configuration. A Routing Configuration Pane will appear.
See Routing Configuration for
more information on this object.
- Right Click on Routing Configuration and select New
Channel Groups. A Channel groups container object is created.
This object will allow multiple channel groups to be created beneath
it. See Channel Groups for more information
on this object.
- Right Click on the Channel Groups Object and select New
Channel Group. A Channel Group Object will appear. Enter a
name for this channel group and set the Signaling Type to SIP. The
outgoing channel group in this example will be a SIP Channel Group
and be named ChannelGrp_Out.
- Set the Outgoing IP Profile field to the IP Bearer Profile created
earlier with the Single Number Voice routing configured. See screen
capture below.

See Channel Group
for more information on configuring a channel group.
Create IP Network Element communicating with Outgoing Channel Group
Right Click on the outgoing channel group created and select
New IP Network Element. Select
from drop down menu, the Gateway for the voice endpoint on the outgoing
side. See Below

Create Incoming channel group
Create an incoming channel group. The channel group being created in
this procedure is an SIP channel group. The incoming channel group can
be any protocol supported on the IMG.
Right Click on the Channel Groups Object again and select New Channel Group. A Channel Group
Object will appear. Enter a name for this channel group. The Incoming
Channel Group in this example will be a SIP Channel Group and be named
ChannelGrp_Inc. See Channel Group for
more information on configuring a channel group.
Create IP Network Element communicating with Incoming Channel Group
Right Click on the incoming channel group created and select
New IP Network Element. Select
from drop down menu, the Gateway on the incoming side. See Below.

The feature is now configured.
Additional Information
- With the Single Number Voice/Fax option enabled, when the IMG detects
the fax tone from the A side, it will disconnect the B side of the
call from the current endpoint (voice), then it will reconnect to
a new endpoint (fax) as specified in the configuration.
- The IMG will use the same dialing number when connecting to the
voice endpoint and when switching to the fax endpoint.
- The IMG will handle the Single Number Voice/Fax option in one direction
only.
The IMG will detect the fax tone from the
A side and switch the endpoints on the B side.
If the IMG detects the fax tone from the
B side, it will not perform the Single Number Voice/Fax functionality
by switching the endpoints on the A side.
The IMG doesn’t differentiate between the
fax tones (thus which side initiates the fax). If the endpoint on the
B side initiates the fax (sending CNG), and the endpoint on the A side
sends back the CED/V.21, the IMG will handle it as a usual and perform
the Single Number Voice/Fax option. In this case, the IMG will disconnect
and switch the endpoints on the B side (failing the fax). It is the user’s
responsibility to have the setup properly for the feature.
- The Single Number Voice/Fax option is applicable only for SIP endpoints
on the B side. That is, both the voice and fax endpoints on the B
side will be SIP endpoints.
- The endpoint on the A side can be of any protocol, including SIP.
- The Single Number Voice/Fax option is enabled by new parameters
in the IP Bearer Profile configuration: a flag to enable/disable the
option, and an external gateway that identifies the fax endpoint.
- The Single Number Voice/Fax option is applied by assigning the
IP Bearer Profile to an Outgoing Channel Group of the voice endpoint.
- If the IP Bearer profile with the Single Number Voice/Fax option
enabled is assigned to an Incoming Channel Group, then the option
will not be applied to the A side. That is, if a fax tone is receive
from the B side, the A side will not switch to another endpoint. The
A side will perform the current fax functionality, which is to send
a RE-INVITE to the same endpoint as needed (e.g. to change session
to T.38 mode).
- The parameter Fax Mode in the IP Bearer profile determines how
the IMG makes the SIP call to switch to the fax endpoint. See Below:
When Fax Mode is set to Enable Relay (T.38),
the IMG sends the RE-INVITE to the fax endpoint for a T.38 session.
When Fax Mode is set to Enable Bypass, the
IMG sends the RE-INVITE to the fax endpoint for a G.711 session.
When Fax Mode is set to Relay Fallback to
Bypass, the IMG sends the RE-INVITE to the fax endpoint for a T.38 session.
And if the RE-INVITE is rejected, the IMG sends another RE-INVITE for
a G.711 session.
If the call to the fax endpoint on
the B side fails, the IMG will terminate the call.
If the RE-INVITE to the fax endpoint
to change the session to fax mode fails, the IMG will leave it to
the fax endpoints to release the call.
The IP Bearer Profile being created
for the feature can be used on the incoming side as well. The Single
Number Voice/Fax fields will be ignored when IP Bearer Profile is
used on the incoming side.