Let’s talk about ISDN configuration and the related DDR configuration that causes Cisco IOS software to use the BRI interface. You must understand DDR configuration and concepts for the ISDN configuration topics to make sense. ISDN configuration can be very brief. In spite of the noise surrounding all the protocols and terminology, you can configure just a few ISDN options in a router. However, the DDR configuration to tell the router when to dial and when to tear down the call can become quite involved.
The following table summarize the commands used for congiguration:
| Command | Description | Conf. Mode |
|---|---|---|
| isdn switch-type switch-type | Defines to the router the type of ISDN switch to which the ISDN line is connected at the central office. | Global or interface |
| isdn spid1 spid | Defines the first SPID. | Interface |
| isdn spid2 spid | Defines the second SPID. | Interface |
| isdn caller phone-number [callback] | Defines a valid number for incoming calls when using call screening. | Interface |
| dialer-list dialer-groupprotocol protocol-name{permit | deny | listaccess-list-number |access-group} | Defines the types of traffic that are considered interesting. | Global |
| dialer-group n | Enables a dialer list on this interface. | Interface |
| dialer string string | The dial string used when dialing only one site. | Interface |
| dialer map protocol next-hop-address[name host-name] [spc] [speed 56 | speed 64] [broadcast] [dialstring[:isdn-subaddress]] | The dial string to reach the next hop. The map command is used when dialing more than one site. This also is the name used for authentication. The broadcast option ensures that copies of broadcasts go to this next-hop address. | Interface |
| dialer idle-timeoutseconds [inbound | either] | Defines how long to wait with no interesting traffic before terminating a dial. | Interface |
| dialer fast-idle seconds | If all lines are in use, and new interesting traffic arrives for which another line must be dialed, no dial can occur. fast-idle defines how long to wait to time out the existing dialed lines when this occurs, allowing for a quicker timeout than the normal idle timeout. | Interface |
| controller t1 int-number | Selects the channelized T1 interface to be used as a PRI. | Global |
| pri-group timeslotsrange | Defines which of the DS0 channels will be used in this PRI. | Controller interface subcommand |
| framing sf | esf | Defines the type of framing used on T1-based PRI. | Controller interface subcommand |
| linecode ami | b8zs | Defines the type of encoding on T1-based PRI. | Controller interface subcommand |
| show interfaces brinumber [:B channel] | Includes a reference to the access lists enabled on the interface. | EXEC |
| show controllers brinumber | Shows Layer 1 statistics and status for B and D channels. | EXEC |
| show isdn {active | history | memory | status | timers} | Shows various ISDN status information. | EXEC |
| show interfaces brinumber [[:B channel] | [first] [last]] [accounting] | Displays interface information about the D channel or the B channel(s). | EXEC |
| show dialer interface brinumber | Lists DDR parameters on the BRI interface. Shows whether a number is currently dialed by indicating the current status. Also shows previous attempts to dial and whether they were successful. | EXEC |
| debug isdn q921 | Lists ISDN Layer 2 messages. | EXEC |
| debug isdn q931 | Lists ISDN Layer 3 messages (call setup/teardown). | EXEC |
| debug dialer {events | packets | map} | Lists information when a packet is directed out a dial interface, specifying whether the packet is interesting. | EXEC |
You can configure DDR in several ways, including Legacy DDR and DDR dialer profiles. The main difference between the two is that Legacy DDR associates dial details with a physical interface, whereas DDR dialer profiles disassociate the dial configuration from a physical interface, allowing a great deal of flexibility. The concepts behind Legacy DDR apply to DDR dialer profiles as well, but Legacy DDR configuration is a little less detailed. Legacy DDR is covered first. DDR can be used to cause the router to dial or to receive a dialed call on asynchronous serial interfaces, synchronous serial interfaces, and ISDN BRI and PRI interfaces. All examples in this chapter use ISDN.
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