This chapter describes the Integrated Services Digital Network (ISDN) interface on the GlobeTrotter 70 and 72. It includes the following topics:
ISDN Overview
ISDN Hardware
ISDN Overview
Integrated Services Digital Network (ISDN) is a switched digital technology that upgrades an ordinary analog telephone network to an all-digital, end-to-end network. Using ISDN, you can transmit all types of information, such as voice, data, and video. With ISDN, you no longer need to incur the expense of leasing an all-digital line to receive the high-speed benefits of digital technology.
The ISDN interface software allows you to interconnect routers over ISDN. You can set up the interface to act over a dedicated link or to initiate and accept switched-circuit connections, either on demand, automatically from restart, or on command by the operator.
For more extensive information on ISDN, refer to the GlobeTrotter 70 and 72 Getting Started Guide.
ISDN Interface
The ISDN interface is a Basic Rate Interface (BRI) with two 64 Kbps (kilobits per second) bearer (B) channels and one 16 Kbps data (D) channel. The interface uses the B channels for data transmission. It uses the D channel to set up calls.
The ISDN interface establishes connections with a peer router over an ISDN connection. It accepts or initiates connections on command from dial circuits. Once the ISDN interface establishes a connection, it transparently passes data to and from the dial circuit.
Some switches in North America do not provide 64 Kbps service for ISDN data calls; instead, they offer only 56 Kbps service. In this case, the ISDN software automatically falls back to 56 Kbps.
Addressing
To place a call, you specify the name of the destination. To identify yourself to the destination, you specify your own directory number. For ISDN, directory numbers are called network dial addresses, and, for convenience, you give them names called network address names that represent the number.
You can add multiple numbers for each network address name. If you are using two ISDN directory numbers, you need to add both numbers for the same local network address name.
When you configure a dial circuit, you specify the name of the destination router as part of the WAN Manager configuration.
Multiple Numbers to a Destination
If you define multiple numbers for a destination network dial address, the dial circuit attempts to call the first number. If the dial circuit is not able to complete the connection, it cycles through all of the defined numbers until it establishes the connection.
Cost Control Over Demand Circuits
Dial-on-demand circuits always appear to be in the Up state to routing protocols. Most protocols send out periodic routing information that could cause the router to dial out each time it sends routing information over dial-on-demand circuits. To limit periodic routing updates, configure IP to use only static routes and disable the routing protocol (RIP) over the dial circuits. Configure IPX for low-frequency updates or change updates so that the router sends broadcast messages at specified intervals, when there is data to send, or if there is a problem. You should also enable IPX keepalive filtering, which prevents keepalive and serialization packets from continually activating a dial-on-demand link.
Caller ID
Some ISDN switch variants provide a feature called caller ID. Caller ID provides the telephone number of the calling router. The ISDN service uses this number to identify the name of the calling router. This name can identify the remote router if PAP or CHAP is not enabled.
ISDN Hardware
For information on the GlobeTrotter ISDN hardware capabilities, refer to the GlobeTrotter 70 and 72 Getting Started Guide.
Point-to-Point and Multipoint Configurations
In the ISDN configuration in Figure 12-1, both the GlobeTrotter and Router 2 are in a point-to-point configuration, where there is one router on the ISDN line. In this case, the routers can use both B channels.
Figure 12-1 ISDN Point-to-Point Configuration
Figure 12-2 ISDN Multipoint Configuration
Switches Supported
The telephone company's switch variant, or type of switch, determines the capabilities of your ISDN service. It is your primary connection into the ISDN network. The switch variant determines how many ISDN devices you can handle, as well as what different configuration options you can have. Some switch variants support eight different devices, others limit you to two devices. The switch also determines which B channels support voice, video, data, or both. Most telephone companies provide a switch variant from one of the following ISDN switch variants. The GlobeTrotter 70 and 72 support all of the switch variants in Table 12-1.
| Country | Switches |
|---|---|
| North America | USNI1, USNI2 AT&T 5ESS Northern Telecom DMS-100 |
| Europe | European ETSI NET3, France VN3 |
| Japan | INS64 |
| Australia | AUS |
When you call your telephone company, you must ask for the switch variant they use. When you configure the GlobeTrotter, you need to provide the switch variant.
ISDN Interface Restrictions
The following are some ISDN interface restrictions. You cannot