© 2006 Cisco Systems, Inc. All rights reserved. GWGK v2.04-1 Advanced Gateway Features Implementing Fax and Modem Support on Cisco IOS Gateways. - презентация

1 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Advanced Gateway Features Implementing Fax and Modem Support on Cisco IOS Gateways

2 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Transporting Modulated Data over IP Networks Fax and modem traffic consists of digital data modulated into high-frequency tones. In contrast to voice, packet loss is much more critical for fax and modem communications. VoIP compression algorithms are designed for voice, not for fax or modem data frequencies. Methods to transmit fax and modem over IP networks: –Terminating and transmitting the data on the gateway (fax relay) –Sending the data in-band into the RTP stream (fax pass-through) –Receiving and converting faxes to files using T.37 (store-and-forward)

3 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Analog Data Analog data tunnelled through 64 kbps VoIP G kbps Encoding IP Network G kbps Decoding Analog Data End-to-End Connection Understanding Fax and Modem Pass- Through: Pass-Through Topology

4 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Works only when the configured codec is G.711 or clear-channel VAD and echo cancellation needs to be disabled Supported under the following call-control protocols: –H.323 –SIP –Media Gateway Control Protocol (MGCP) Understanding Fax and Modem Pass- Through: Fax Pass-Through Considerations

5 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Works only when the configured codec is G.711 or clear-channel VAD and echo cancellation need to be disabled Modem pass-through over VoIP performs these functions: –Repressing processing –Issuing redundant packets –Providing static jitter buffers –Differentiating modem signals from voice and fax signals –Reliably maintaining a modem connection across the packet network Understanding Fax and Modem Pass-Through: Modem Pass-Through Considerations

6 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Analog Data DSP demodulates DSP modulates Analog Data IP Network TCP transmission of data packets Connection 1Connection 2Connection 3 Understanding Fax and Modem Pass-Through: Pass-Through Topology

7 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Understanding Fax and Modem Relay: Fax Relay Considerations T.38 fax relay includes these features: Fax relay packet loss concealment MGCP-based fax (T.38) and DTMF relay SIP T.38 fax relay T.38 fax relay for T.37/T.38 fax gateway T.38 fax relay for VoIP H.323

8 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Understanding Fax and Modem Relay: Modem Relay Considerations Modem relay includes these features: Modem tone detection and signaling Relay switchover Controlled redundancy Packet size Clock slip buffer management

9 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Gateway Signaling Protocols with Fax and Modem Pass-Through and Relay Fax and modem pass-through: IP Network G3 Fax initiates the call G3 Fax Gateway T.30 VoIP call CED tone Call control issues NSE NSE NSE accept VoIP call Change codec

10 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Gateway Signaling Protocols with Fax and Modem Pass-Through and Relay (Cont.) H.323 T.38 relay: IP Network G3 Fax initiates the call G3 Fax T.38 Gateway T.30 VoIP call Mode Request ACK Mode Request CED Tone DIS Message Close VoIP and Open T.38 Channels T.38 UDP packets

11 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Gateway Signaling Protocols with Fax and Modem Pass-Through and Relay (Cont.) SIP T.38 Relay: IP Network G3 Fax initiates the call G3 Fax T.38 Gateway T.30 VoIP Call 200 OK INVITE (T.38 in SDP) CED Tone DIS Message ACK T.38 UDP Packets

12 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Gateway Signaling Protocols with Fax and Modem Pass-Through and Relay (Cont.) MGCP T.38 fax relay provides two modes of implementation: Gateway-controlled mode –Gateways negotiate fax relay transmission by exchanging data in SDP messages. –Allows the use of MGCP-based T.38 fax without necessity to upgrade call agent software. Call agent-controlled mode: –Call agents instruct gateways to process fax traffic. –Call agent can instruct gateways to revert to gateway-controlled mode if it cant handle fax control.

13 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Understanding Store-and-Forward Fax On-ramp receives faxes that are delivered as attachments. Off-ramp sends standard messages that are delivered as faxes PSTN

14 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v fax protocol protocol Router(config-dial-peer)# Specifies the protocol used for a fax on the dial peer fax rate [2400|4800|7200|9600|12000|14400|disable|voice] router(config-dial-peer)# Identifies if fax relay is used and which data rate is used Configuring Fax Pass-Through and Relay with Dial Peers Configure fax settings: fax nsf word router(config-dial-peer)# Specifies non-standard fax facilities, country, and vendor

15 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v fax-relay ecm disable Router(config-dial-peer)# Disables ECM for fax relay fax-relay sg3-to-g3 [system] router(config-dial-peer)# Allows SG3 fax machines to operate at G3 speeds using fax relay Configuring Fax Pass-Through and Relay with Dial Peers (Cont.) Configure advanced relay fax settings:

16 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v dial-peer voice 550 voip destination-pattern 550 session target ipv4: incoming called-number 200 fax rate disable fax protocol pass-through g711ulaw Example: H.323 Fax Pass-Through Configuration IP Network G3 Fax T.38 Gateway

17 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v voice service voip fax protocol t38 ! dial-peer voice voip destination-pattern session target ipv4: fax-relay sg3-to-g3 fax rate ! dial-peer voice voip destination-pattern session target ipv4: fax protocol cisco Example: H.323 Fax Relay Configuration IP Network G3 Fax T.38 Gateway Cisco fax used for the special dial peer Uses fax protocol configuration from voice service VoIP

18 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v no ccm-manager fax protocol cisco Router(config)# Disables the Cisco fax relay protocol mgcp fax rate [2400|4800|7200|9600|12000|14400|voice] router(config)# Defines the maximum MGCP T.38 fax pass-through transmission speed Configuring Fax Pass-Through and Relay with MGCP Gateways Configure fax settings: mgcp fax t38 parameter router(config)# Specifies MGCP T.38 fax pass-through parameters

19 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v mgcp timer nse t38 period Router(config)# Defines the timeout period for awaiting NSE responses from the dial peer mgcp fax-relay sg3-to-g3 router(config)# Allows SG3 fax machines to operate at G3 speeds in fax relay mode Configuring Fax Pass-Through and Relay with MGCP Gateways (Cont.) Configuring fax settings (Cont.): mgcp package-capability rtp-package router(config)# Defines the MGCP package capability as RTP

20 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Example: MGCP T.38 Fax Configuration IP Network G3 Fax T.38 Gateway ccm-manager mgcp no ccm-manager fax protocol cisco ! mgcp mgcp call-agent service-type mgcp version 0.1 mgcp package-capability fxr-package mgcp fax rate no mgcp fax t38 inhibit ! mgcp profile default

21 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Cisco Unified CallManager Interaction and Restriction Cisco Unified CallManager-controlled T.38 fax relay is not supported for MGCP gateways. Solutions to implement T.38 in a Cisco Unified CallManager: –H.323 or SIP: Use dial peers directly on the incoming gateway –MGCP or complex dial plans on Cisco Unified CallManager: Forward fax calls back to the gateway using H.323, loop them out and back to a T1/E1 interface, and use dial peers.

22 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Example: Cisco Unified CallManager, MGCP, and T.38 Fax T1 T1/E1 Loop MGCP H.323 PSTN H.323 T.38 Fax Server

23 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Summary Fax and modem traffic is digital traffic translated into analogue signals and therefore not ideal to be digitalized. For fax and modem pass-through data is encoded into RTP packets. For fax and modem relay, data streams are terminated and transferred using a different transfer type. Store-and-Forward fax uses messages to transfer faxes. T.38 pass-through and relay use special protocol enhancements on H.323, SIP, and MGCP. There are several commands used to configure fax features on H.323 and SIP gateways.

24 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v Summary (Cont.) To allow fax support, some additional MGCP commands need to be configured manually on the gateway. To support T.38 within a Cisco Unified CallManager environment using MGCP, it is necessary to use at least two additional H.323-controlled T1/E1 interfaces on the gateway.

25 © 2006 Cisco Systems, Inc. All rights reserved. GWGK v