As discussed previously, T.38 fax relay is real-time fax transmission where two fax machines communicate with each other as if there were a direct phone line between the two.
Cisco provides two methods for fax relay: A proprietary Cisco method and a method based on the ITU-T T.38 standard. On most platforms, Cisco fax relay is the default if a fax method is not explicitly configured. On the left of the screen capture in the figure, the command enables the T.38 fax relay feature. Fax relay is configured using a few additional commands on gateway dial peers that have already been defined and configured for voice calls. On the right of the screen capture, the highlighted comments declare the type of T.38 configuration enabled: T.38 fax from the voice service voip command in the first and Cisco fax for a specific dial peer in the second configuration.
For additional information on Cisco fax relay, see the Configuring Cisco Fax Relay chapter inCisco IOS Fax Services over IP Configuration Guide Release 12.3(1) at
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide_book09186 a008017cf32.html.
© 2005 Cisco Systems, Inc. All rights reserved. GWGK v1.01-11
T.37 Store-and-Forward Fax Two modes of operation
On-ramp: Receives faxes that are delivered as e-mail attachments
Off-ramp: Sends standard e-mail messages that are delivered as faxes
T.37 store-and-forward fax consists of these two processes:
On-ramp faxing, in which a voice gateway that handles incoming calls from a standard fax machine or the PSTN converts a traditional Group 3 fax into an e-mail message with a Tagged Image File Format (TIFF) attachment. An e-mail server handles the fax e-mail message and attachment while they are traversing the packet network, and they can be stored for later delivery or delivered immediately to a PC or to an off-ramp gateway.
Off-ramp faxing, in which a voice gateway that handles calls going out from the network to a fax machine or the PSTN converts a fax e-mail with a TIFF attachment into a traditional fax format that can be delivered to a standard fax machine or to the PSTN.
On-ramp and off-ramp faxing processes can be combined on a single gateway, or they can occur on separate gateways. Store-and-forward fax uses two different interactive voice response (IVR) applications for on-ramp and off-ramp functionality. The applications are implemented in two Tool Command Language (TCL) scripts that you can download from Cisco.com.
Simple Mail Transfer Protocol (SMTP) facilitates the basic functionality of store-and-forward fax and has additional functionality that provides confirmation of delivery by using existing SMTP mechanisms, such as Extended Simple Mail Transfer Protocol (ESMTP).
Store-and-forward fax requires you to configure gateway dial peers and to specify values for the following types of parameters:
IVR application parameters and IVR security and accounting parameters: These items load the applications on the router and also enable authorization and accounting for the application.
Fax parameters: These items specify the cover sheet and header information that appears on faxes that are generated in the packet network.
Mail Transfer Agent (MTA) parameters: These items define delivery parameters for the
Message disposition notification (MDN) parameters: These items specify the generation of messages to notify e-mail originators when their fax e-mail messages have been
delivered.
Delivery status notification (DSN) parameters: These items instruct the SMTP server to send messages to e-mail originators to inform them of the status of their e-mail messages.
Gateway security and accounting parameters: These items define authentication, authorization, and accounting (AAA) for faxes that enter or exit the packet network.
Note Store-and-forward fax configuration tasks are the same for H.323 and SIP networks. MGCP networks are not supported for store-and-forward fax capabilities.
Fax calls from the PSTN enter the network through an on-ramp gateway, which is sometimes called an originating gateway. Fax calls exit the packet network to the PSTN through an off-ramp gateway, which is sometimes called a terminating gateway. In small networks, on-off-ramp and off-ramp functionality can reside in the same gateway. For store-and-forward fax, each type of gateway is configured for the following two types of dial peers:
The on-ramp gateway is configured with one or more plain old telephone service (POTS) dial peers to handle fax calls inbound to the gateway from the PSTN and with one or more Multimedia Mail over IP (MMoIP) dial peers to direct calls outbound from the gateway to the network.
The off-ramp gateway is configured with one or more MMoIP dial peers to handle fax calls inbound from the IP network and with one or more POTS dial peers to direct calls
outbound through POTS voice ports to the PSTN.
Note The instructions in this lesson assume that your packet network includes separate gateways for on-ramp and off-ramp functions. For smaller networks that use a single router for both on-ramp and off-ramp functionality, follow both the on-ramp and off-ramp instructions on the same router.
© 2005 Cisco Systems, Inc. All rights reserved. GWGK v1.01-12