306 Chapter 8: Fax Services
Figure 8-3 Real-time fax service model.
The Cisco AS5300 access server and Cisco 3600 router families of voice gateways support
both ITU recommendations: T.37 for store and forward fax, and T.38 for real-time fax as of
Cisco IOS Release 12.1(3)XI. The Cisco MC3810 Multiservice Concentrator and Cisco
2600 router families support ITU recommendation T.38 as of Cisco IOS Release 12.1(3)T.
The Cisco AS5300 also requires the recommended VCWare Version 7.16. The proper
VCWare is bundled within Cisco IOS software for the Cisco 3600 series. Real-time fax
works like a VoIP call and requires no extra configuration. Store and forward fax
configuration and testing are the focus of this chapter.
This chapter also documents the never-busy fax solution. This solution uses a Tool
Command Language (TCL) Interactive Voice Response (IVR) script to roll over a T.38 fax
that receives a busy signal into a T.37 fax. This feature is documented in the last section of
the chapter.
Cisco Store and Forward Fax
Store and forward fax enables Cisco AS5300 voice gateways to transmit and receive faxes
across packet-based networks without the timeout restrictions imposed by real-time fax
transport methods. Store and forward fax is an implementation of the RFC 2305 and RFC
2532 proposed standards from the IETF. RFC 2305 proposes a standard aligned with the
T.37 recommendation from the ITU.
ITU-T T.30
Group 3 fax
Gatekeeper (optional)
ITU-T T.30
Group 3 fax
Fax Fax
IP network
Cisco AS5x00
Cisco 36xx
Cisco AS5x00
Cisco 36xx
Cisco Store and Forward Fax 307
With this feature, your access server becomes a multiservice platform, providing both data
and fax communication. Store and forward fax enables you to do the following:
Send and receive faxes to and from Group 3 fax devices.
Receive faxes that will be delivered as e-mail attachments.
Create and send a standard e-mail message that will be delivered as a fax to a standard
Group 3 fax device.
Store and forward fax functionality is facilitated through SMTP. Additional functionality
described in RFC 2532, Extended Facsimile Using Internet Mail, confirms delivery
using existing SMTP mechanisms. Examples of such mechanisms are delivery status
notifications (DSNs) in RFC 1891 and message disposition notifications (MDNs) in RFC
When store and forward fax is configured, the on-ramp gateway receives faxes from
traditional Global Switched Telephone Network (GSTN)-based Group 3 fax devices and
converts them into TIFF file attachments. It then creates a standard MIME e-mail message
and attaches the TIFF file(s) to it. The on-ramp gateway then forwards this fax mail to the
messaging infrastructure of a designated SMTP server, where the fax-mail message is
stored. The messaging infrastructure performs message routing, message storage, and
transport, and can be either custom store-and-forward SMTP software or a standard
Internet mail transport agent (MTA) such as UNIX sendmail or Netscape MailServer.
After the fax mail is stored on the SMTP server, it can be delivered in two ways: as an
e-mail message with an attachment, or as a fax to a standard GSTN-based Group 3 fax
device. In the latter case, the SMTP server mail delivery infrastructure delivers the fax mail
to the Cisco off-ramp gateway. The off-ramp gateway router converts the attached TIFF file
back into standard fax format and transmits the information to a standard GSTN-based
Group 3 fax device. The off-ramp gateway is also responsible for generating DSNs and
MDNs, as appropriate. This simple topology is illustrated in Figure 8-4.
Store and forward fax is used in conjunction with the VoIP software feature for Cisco voice
gateways. The supporting digital signal processor (DSP) technology can be either c542 or
c549. To understand the voice feature card (VFC) and VoIP technology and architecture,
search for these topics on the Cisco web site, www.cisco.com. To learn about VCWare and
DSP technology in particular, see the following web site:
Compatibility issues are addressed at the following link:

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