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Case Study: Configuring an H.323 Gateway

In this case study, the router at the Leeds office is configured as an H.323 gateway. It will use three of the CallManagers in the New York office for internal company traffic. Users dial an 8 plus the complete number (minus international code) to call another office, and 9 to dial an outside number. All PSTN traffic, including emergency calls, will be routed out the E1 interface of the gateway. The emergency number for Leeds, England is 999. Dial peers will be created for the emergency number so that users will not have to wait for the interdigit timeout to expire. When the gateway is operating in SRST mode, only calls to the U.S. offices are allowed. Router configuration that does not directly pertain to the gateway configuration is beyond the scope of this example.

Figure 3-7 shows the networks at the New York and Leeds offices. Example 3-4 shows the Leeds gateway configuration.

Figure 3-7. New York and Leeds Networks

In addition, you will need to configure the CallManager publisher in New York to use this router as a gateway.

Example 3-4. Configuring an H.323 Gateway

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!Create a voice class for the H.225 timeout
voice class h323 1
 h225 timeout tcp establish 3
!
!Create a voice class for codec negotiation
voice class codec 2
 codec preference 1 g729r8
 codec preference 2 g729br8
 codec preference 3 g711ulaw
!
!Create VoIP dial peers for the CallManagers
!"8" is the interoffice code
dial-peer voice 81 voip
 destination-pattern 8T
 preference 1
 no vad
 voice-class h323 1
 voice-class codec 2
 dtmf-relay h245-alphanumeric
 session target ipv4:10.1.10.10
!
dial-peer voice 82 voip
 destination-pattern 8T
 preference 2
 no vad
 voice-class h323 1
 voice-class codec 2
 dtmf-relay h245-alphanumeric
 session target ipv4:10.1.10.11
!
dial-peer voice 83 voip
 destination-pattern 8T
 preference 3
 no vad
 voice-class h323 1
 voice-class codec 2
 dtmf-relay h245-alphanumeric
 session target ipv4:10.1.10.13
!
!Create a default incoming VoIP dial peer
dial-peer voice 1 voip
 incoming called-number .
 codec g711ulaw
 no vad
 ip qos dscp ef media
 ip qos dscp cs3 signaling
!
!Create a POTS dial peer for general external numbers
dial-peer voice 9 pots
 destination-pattern 9T
 port 0/0:15
!
!Create POTS dial peers for emergency numbers
!This dial peer is for outside code of "9" plus emergency number "999"
dial-peer voice 9999 pots
 destination-pattern 9999
 port 0/0:15
!
!This dial peer is for emergency number "999" without the outside code
dial-peer voice 999 pots
 destination-pattern 999
 port 0/0:15
!
!Create a default incoming POTS dial peer
dial-peer voice 2 pots
 incoming called-number .
 direct-inward-dial
 port 0/0:23
!
!Create a POTS dial peer for intracompany traffic to the U.S. in case

the WAN link fails
!The prefix of "001" is for international access to U.S. sites
dial-peer voice 800 pots
 destination-pattern 8T
 preference 2
 prefix 001
 port 0/0:15
!
!Enable SRST on the gateway
call-manager-fallback
 ip source-address 10.40.25.1 port 2000
 max-ephones 100
 max-dn 200

Review Questions

1	List at least four benefits of using H.323 as a gateway protocol.
2	When you are configuring an H.323 gateway on a CallManager, what information do you enter for Device Name ?
3	Name four types of DTMF Relay that H.323 uses.
4	What commands must you enter for a Cisco gateway to use H.323 Fast Start?
5	Briefly describe toll bypass.
6	If you configure conflicting commands globally under the voice service voip configuration mode, and under the dial peer using voice class , which commands will the router use?
7	How do you prevent active calls from being terminated when the CallManager becomes unreachable?