CCNA Cisco Certified Network Associate Study Guide - FTP Server

44 Chapter 1 � Internetworking
ISDN BRI routers come with either a U interface or what is known as an
S/T interface. The difference between the two is that the U interface is
already a two-wire ISDN convention that can plug right into the ISDN local
loop. The S/T interface is a four-wire interface and needs a Network Termination
type 1 (NT 1) to convert from a four-wire to the two-wire ISDN
specification.
ISDN is covered in depth in Chapter 10.
The U interface has a built-in NT 1 device. If your service provider uses an
NT 1 device, then you need to buy a router that has an S/T interface. Most
Cisco router BRI interfaces are marked with a U or an S/T. When in doubt,
ask Cisco or the salesperson you bought it from.
Primary Rate Interface (PRI) provides T1 speeds (1.544Mbps) in the U.S. and
E1 speeds (2.048) in Europe. PRI is not discussed further in this course.
The ISDN BRI interface uses an RJ-45, category 5, straight-through cable.
It is important to avoid plugging a console cable or other LAN cable into a
BRI interface on a router, because it will probably ruin the interface. Cisco
says it will ruin it, but I have students do it every week and haven’t lost one
yet (I probably shouldn’t have said that…now I will probably lose one
next week).
Console Connections
All Cisco devices are shipped with console cables and connectors, which allow
you to connect to a device and configure, verify, and monitor it. The cable used
to connect between a PC is a rollover cable with RJ-45 connectors.
The pinouts for a rollover cable are as follows:
1–8
2–7
3–6
4–5
5–4