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Implementing Voice Gateways

Implementing Voice Gateways. Lecture 3. Voice Gateways. Any device with one or more TDM PSTN interfaces on them TDM - Time Division Multiplexing (i.e. traditional telephony) PSTN - Public Switched Telephone Network To be really useful, gateways also need an IP interface on them

jacqueline-williamson
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Implementing Voice Gateways

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  1. Implementing Voice Gateways Lecture 3

  2. Voice Gateways • Any device with one or more TDM PSTN interfaces on them • TDM - Time Division Multiplexing (i.e. traditional telephony) • PSTN - Public Switched Telephone Network • To be really useful, gateways also need an IP interface on them • Many vendors, but we will look at Cisco IOS based voice gateways • Both analogue and digital interfaces, we’ll look at the more common ones

  3. Interface Types - Digital • ISDN primary rate circuits • E1 (primarily used in Europe) 2 Mbit/s bearer • 32x 64kbit/s channels. 30 for voice, 1 for signalling (timeslot 16), 1 framing • Common interfaces for ISP dial-in, PBX to carrier trunks, etc. • DSL – ADSL and HDSL • Wireless – 802.11x

  4. Interface Types - Digital • Basic Rate ISDN • 144kbit/s bearer • 2x 64kbit/s channels + 1x 16kbit/s signalling channel • 2B + D • B channels = 64kbit/s voice/data channels • D channel(s) = signalling data channels

  5. Interface Types - Analogue • Only really two types: • FXO interface - plugs into your Service provider (Exchange or company PBX) • FXS interface - plugs into a telephone. e.g. ATAs • Uses analogue signalling, limited to one DDI per line • Signalling is generally more ambiguous and harder to work with than digital signalling

  6. IOS Voice Configuration • For VoIP we need to configure: • voice-port - the voice ‘interface’ • FXS / FXO - e.g. voice-port 1/0/0 • E1/T1 signallingchannel - e.g. voice-port 1/0:D • dial-peer - tells the gateway how to connect voice ports to VoIP call legs • For E1/T1 links we also need to configure the physical bearer controller E1 / controller T1 • interface serial 0:15 (the signalling timeslot for an E1)

  7. FXS / FXO Configuration ! Some useful settings ! voice-port 1/0/0 no comfort-noise ! needs ‘no vad’ on VoIP dial-peer cptone GB timeouts interdigit 3 ! timeout when gathering dialled digits description Analog phone line ! ! Or, if you’re just having a play, the defaults will work: ! voice-port 1/0/1 !

  8. Dial Peers • Basic building block on Cisco voice gateways, the dial-peer • All calls consists of at least two call legs: • Originating device to originating gateway (POTS) • Originating gateway to IP network (VoIP) • ...and/or • IP network to destination gateway • Destination gateway to destination device

  9. (1) Two Analogue Phones – 1 Gateway Voice Gateway Router Configuration File voice-port 1/0/0 ! voice-port 1/0/1 ! ! dial-peer voice 1 pots destination-pattern 5551234 port 1/0/0 ! dial-peer voice 2 pots destination-pattern 5555678 port 1/0/1

  10. (2) Two Analogue phones – 2 Gateways Voice Gateway Router 1 Configuration File voice-port 1/0/0 ! dial-peer voice 1 pots destination-pattern 5551234 port 1/0/0 ! dial-peer voice 10 voip destination-pattern 5555678 session target ipv4:10.5.6.7 codec g711ulaw Voice Gateway Router 2 Configuration File voice-port 1/0/0 ! dial-peer voice 2 pots destination-pattern 5555678 port 1/0/0 ! dial-peer voice 20 voip destination-pattern 5551234 session target ipv4:10.2.3.4 codec g711ulaw

  11. (3) Each Connected to Their Own Voice Gateway Routers Using the G.729 Codec as 1st choice Voice Gateway Router 1 Configuration File voice class codec 1 codec preference 1 g729r8 codec preference 2 g711ulaw ! voice-port 1/0/0 ! voice-port 1/0/1 ! ! dial-peer voice 1 pots destination-pattern 5551234 port 1/0/0 ! dial-peer voice 2 voip destination-pattern 5555678 voice-class codec 1 session target ipv4:10.5.6.7 Voice Gateway Router 2 Configuration File voice class codec 1 codec preference 1 g729r8 codec preference 2 g711ulaw ! voice-port 1/0/0 ! voice-port 1/0/1 ! ! dial-peer voice 1 pots destination-pattern 5555678 port 1/0/0 ! dial-peer voice 2 voip destination-pattern 5551234 voice-class codec 1 session target ipv4:10.2.3.4

  12. (4) Analogue Phone and an IP Phone Connected over an IP Network Voice Gateway Router 1 Configuration File voice-port 1/0/0 ! dial-peer voice 1 pots destination-pattern 5551234 port 1/0/0 ! dial-peer voice 2 voip destination-pattern 5555678 session target ipv4:10.5.6.7 Voice Gateway Router 2 Configuration File voice-port 1/0/0 ! dial-peer voice 1 pots destination-pattern 5555678 port 1/0/0 ! dial-peer voice 2 voip destination-pattern 5551234 session target ipv4:10.2.3.4

  13. (5) Two IP Phones Connected over a Frame Relay Network Voice Gateway Router 1 Configuration File interface Serial0/0 ip address 10.5.6.6 255.0.0.0 encapsulation frame-relay Voice Gateway Router 2 Configuration File interface Serial0/0 ip address 10.5.6.7 255.0.0.0 encapsulation frame-relay clock rate 2000000 dial-peer voice 1 pots destination-pattern 5551234 port 1/0/0 dial-peer voice 1000 voip preference 1 destination-pattern 5555678 session target ipv4:10.5.6.7 dial-peer voice 1 pots destination-pattern 5555678 port 1/0/0 dial-peer voice 2000 voip preference 1 destination-pattern 5551234 session target ipv4:10.5.6.6

  14. (6)Using the PSTN in the event of an IP network failure

  15. Configuration for Router 1 translation-rule 21 Rule 1 ^2 5552 translation-rule 11 Rule 1 ^5551 1 interface FastEthernet0/0 ip address 10.1.1.2 255.255.255.0 voice-port 1/0/0 translate called 11 dial-peer voice 1 pots destination-pattern 1000 port 1/1/0 dial-peer voice 2000 voip preference 1 destination-pattern 2000 session target ipv4:10.1.1.3 dial-peer voice 20 pots preference 2 destination-pattern 2000 translate-outgoing called 21 port 1/0/0 forward-digits all

  16. Configuration for Router 2 translation-rule 11 Rule 1 ^1 5551 translation-rule 21 Rule 1 ^5552 2 interface Ethernet0/0 ip address 10.1.1.3 255.255.255.0 voice-port 1/1/0 translate called 21 ! dial-peer voice 1 pots destination-pattern 2000 port 1/0/0 ! dial-peer voice 1000 voip preference 1 destination-pattern 1000 session target ipv4:10.1.1.2 ! dial-peer voice 10 pots preference 2 destination-pattern 1000 translate-outgoing called 11 port 1/1/0 forward-digits all

  17. Digit stripping • We want to dial 5554329 #dial-peer voice 3 pots #destination-pattern 555.... #port 2/0/0 • The default behaviour for the router is to strip the first three digits from the number because these are the numbers matched in the dial-peer and send 4329 forward

  18. Digit stripping ctd.. • We want to send all digits to 5554329 #dial-peer voice 3 pots #destination-pattern 555.... #no digit-strip #port 2/0/0

  19. Prefixes • The prefix dial-peer command adds digits to the beginning of the dial string #dial-peer voice 3 pots #destination-pattern 1904678 #prefix 8 #port 1/0/1 • The peer at other end might require a 5 digit number so the number 84678 is forwarded

  20. Number Expansion • People find it easier to just remember the 3 digit extension number e.g.363 ExtDest-PatternNum Expand Command 363 719155363 num-exp 00353 719155363

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