8-8
Configuring Demand Routing for Primary ISDN Modules
Overview of ISDN Connections
ISDN Interfaces: Connecting Equipment to the ISDN
Network
ISDN supports both RJ-11 and RJ-45 connectors. Public carriers typically
install an RJ-45 jack to connect the subscriber’s premises to the local loop.
You can add equipment at four interface points on the subscriber’s side of an
ISDN network:
■ U interface
■ T interface
■ S interface
■ R interface
These interfaces define the mechanical connectors, the electrical signals, and
the protocols used for connections between the ISDN equipment.
U Interface. The U interface provides the connection between the local loop
and NT1. For ISDN BRI, the U interface is one twisted pair. For PRI ISDN, the
U interface is two twisted pairs.
Because public carriers in Europe and Asia provide the NT1, these regions do
not use the U interface. In regions that support the U interface, there can be
only one U interface on the ISDN network.
T Interface. The T interface is used to connect the NT1 to the NT2. This
interface is a four-wire connection, or two twisted pair. Each pair handles the
traffic sent in one direction.
In the United States and Canada, the T interface—along with the NT1 and
NT2—is often built into an ISDN device such as a router. In other regions, the
T interface is the first interface at the subscriber’s premises.
S Interface. The S interface is used to connect the NT2 or the NT1 to the
TE1 or TA. This interface is a four-wire connection, or two twisted pair.
On an ISDN BRI connection, all of the TEs or TAs connected to the S interface
must take turns transmitting traffic. Because the S interface is a shared
medium, the TEs and TAs must be able to detect collisions. PRI ISDN does
not support multiple TEs at the S interface.
The S and T interfaces are often combined as the S/T interface.
To Next Page
Loading...
Need help?
General
