ISDN Terms

bandwidth on demand

ISDN cost-control feature defining the bandwidth threshold that must be reached on all links before a Services Router initiates additional ISDN data connections to provide more bandwidth.

Basic Rate Interface (BRI)

ISDN service intended for home and small enterprise applications. ISDN BRI consists of two 64-Kbps B-channels to carry voice or data and one 16-Kbps D-channel for control and signaling.

bearer channel (B-channel)

64-Kbps channel used for voice or data transfer on an ISDN interface.

callback

Alternative feature to dial-in that enables a J-series Services Router to call back the caller from the remote end of a backup ISDN connection. Instead of accepting a call from the remote end of the connection, the router rejects the call, waits a configured period of time, and calls a number configured on the router's dialer interface. See also dial-in.

caller ID

Telephone number of the caller on the remote end of a backup ISDN connection, used to dial in and also to identify the caller. Multiple caller IDs can be configured on an ISDN dialer interface. During dial-in, the router matches the incoming call's caller ID against the caller IDs configured on its dialer interfaces. Each dialer interface accepts calls from only callers whose caller IDs are configured on it.

delta-channel (D-channel)

Circuit-switched channel that carries signaling and control for B-channels. In ISDN Basic Rate Interface (BRI) applications, a D-channel can also support customer packet data traffic at speeds up to 9.6 Kbps.

demand circuit

Network segment whose cost varies with usage, according to a service level agreement with a service provider. Demand circuits limit traffic based on either bandwidth (bites or packets transmitted) or access time. For example, ISDN interfaces can be configured for dial-on-demand routing backup. In OSPF, the demand circuit reduces the amount of OSPF traffic by removing all OSPF protocols when the routing domain is in a steady state.

dial backup

Feature that reestablishes network connectivity through one or more backup ISDN dialer interfaces after a primary interface fails. When the primary interface is reestablished, the ISDN interface is disconnected.

dialer filter

Stateless firewall filter that enables dial-on-demand routing backup when applied to a physical ISDN interface and its dialer interface configured as a passive static route. The passive static route has a lower priority than dynamic routes. If all dynamic routes to an address are lost from the routing table and the router receives a packet for that address, the dialer interface initiates an ISDN backup connection and sends the packet over it. See also dial-on-demand routing backup; floating static route.

dialer interface (dl)

Logical interface for configuring dialing properties and the control interface for a backup ISDN connection.

dial-in

Feature that enables J-series Services Routers to receive calls from the remote end of a backup ISDN connection. The remote end of the ISDN call might be a service provider, a corporate central location, or a customer premises equipment (CPE) branch office. All incoming calls can be verified against caller IDs configured on the router's dialer interface. See also callback.

dial-on-demand routing (DDR) backup

Feature that provides a J-series Services Router with full-time connectivity across an ISDN line.

When routes on a primary serial T1, E1, T3, E3, Fast Ethernet, Gigabit Ethernet, or PPPoE interface are lost, an ISDN dialer interface establishes a backup connection. To save connection time costs, the Services Router drops the ISDN connection after a configured period of inactivity. Services Routers with ISDN interfaces support two types of dial-on-demand routing backup: on-demand routing with a dialer filter and dialer watch. See also dialer filter; dialer watch.

dialer profile

Set of characteristics configured for the ISDN dialer interface. Dialer profiles allow the configuration of physical interfaces to be separated from the logical configuration of dialer interfaces required for ISDN connectivity. This feature also allows physical and logical interfaces to be bound together dynamically on a per-connection basis.

dialer watch

Dial-on-demand routing (DDR) backup feature that provides reliable connectivity without relying on a dialer filter to activate the ISDN interface. The ISDN dialer interface monitors the existence of each route on a watch list. If all routes on the watch list are lost from the routing table, dialer watch initiates the ISDN interface for failover connectivity. See also dial-on-demand routing backup.

floating static route

Route with an administrative distance greater than the administrative distance of the dynamically learned versions of the same route. The static route is used only when the dynamic routes are no longer available. When a floating static route is configured on an interface with a dialer filter, the interface can be used for backup.

Integrated Services Digital Network (ISDN)

Digital communication service provided by telecommunication service providers. It is an all-digital dialup (on-demand) service that carries voice, data, and video transmissions over telephone lines.

Primary Rate Interface (PRI)

ISDN service intended for higher-bandwidth applications than ISDN BRI. ISDN PRI consists of a single D-channel for control and signaling, plus a number of 64-Kbps B-channels—either 23 B-channels on a T1 line or 30 B-channels on an E1 line—to carry network traffic.

service profile identifier (SPID)

Number that specifies the services available to you on the service provider switch and defines the feature set ordered when the ISDN service is provisioned.

terminal endpoint identifier (TEI)

Number that identifies a terminal endpoint, an ISDN-capable device attached to an ISDN network through an ISDN interface on the Services Router. The TEI is a number between 0 and 127. The numbers 0–63 are used for static TEI assignment, 64–126 are used for dynamic assignment, and 127 is used for group assignment.