Syngress - Eleventh Hour Network+ Exam N10-004 Study Guide (11 ...

WAN Protocols and Properties 109
In Europe and Japan, the corresponding carrier types are known as E carriers and
J carriers, respectively.
■
T/E/J Carrier The name T and the number following it denote the type
of line.
■ T1 is a dedicated media connection supporting data rates of 1.544 Mbps.
This speed is derived from 24 individual channels of 64 Kbps.
■ T3 can support data rates of about 43 Mbps, which is created with 672
channels of 64 Kbps.
■ E1 are European based and carry signals at 2 Mbps (32 channels at
64 Kbps, with two channels reserved for signaling and controlling).
■ E3 lines carry data at a rate of about 34.368 Mbps.
■ J lines are used within Japanese carrier systems.
■ T1 channels are sometimes known as digital signal zero (DS0s). In T-carrier
systems, DS0 is a basic digital signaling rate of 64 Kbps, corresponding
to the capacity of one voice or data channel.
■ Twenty-four DS0s (24 × 64 Kbps) equal one DS1. A full T1 is equal to a
DS1; a full T3 is equal to a DS3.
EXAM WARNING
Make sure you are familiar with the speeds of the T- and E-carrier links, as well as the
number of channels that make up a T1. T3 lines are faster than T1 lines because they
have more bandwidth. Use common sense on the exam when determining which has a
higher capacity. A T3 has a higher capacity than an E3, a T3 has a higher capacity than an
E1, and so on. You may be asked to determine which line you would recommend based on
the needs of the client, so be able to respond by knowing which technologies offer which
benefits.
ISDN ISDN is unique, in that it is call initiated and call terminated, so you
only pay for what you use. ISDN uses telephone number-like entities called
service profile identifiers (SPIDs) to dial from peer-to-peer to bring up the line
when traffic has to be sent across it. Because of inactivity, the call is ended
and so is the billing for that usage. There are two key access interfaces related
to ISDN: basic rate interface (BRI) and primary rate interface (PRI).
■ BRI B channel service operates at 64 Kbps and is used for data; BRI D
channel service operates at 16 Kbps and is used for signaling.
■ ISDN supports data transfer rates of 64 Kbps per channel, and most ISDN
circuits used today are configured as two channels to provide 128 Kbps
of throughput.
■ BRI consists of two 64 Kbps B channels and one D channel for transmitting
control information. BRI ISDN has a maximum speed of
128 Kbps.
■ PRI consists of 23 B channels and one D channel (in North America) or
30 B channels and one D channel (in Europe). The B channel is used for
control.
■