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

Network Devices 43
Table 3.2
Types of DSL
Type of DSL Bandwidth Distance Limitations
Asymmetric digital subscriber Downstream: 1.544 to 6.1 Mbps Speeds decrease over distance.
line (ADSL) Upstream: 16 to 640 Kbps 1.544 Mbps at 18,000 ft.,
2.048 Mbps at 16,000 ft.,
6.312 Mbps at 12,000 ft., and
8.448 Mbps at 9,000 ft.
Consumer digital subscriber Downstream: 1 Mbps 18,000 ft.
line (CDSL)
Upstream: Under 1 Mbps
DSL Lite or G.Lite 1.544 to 6 Mbps 18,000 ft.
ISDN digital subscriber line 128 Kbps 18,000 ft.
(IDSL)
High digital subscriber line Varies depending on twisted- 12,000 ft.
(HDSL)
pair lines. 1.544 Mbps duplex
on two twisted-pair lines or
2.048 Mbps duplex on three
twisted-pair lines
Symmetric digital subscriber 1.544 Mbps 12,000 ft.
line (SDSL)
Very high digital subscriber Downstream: 12.9 to 52.8 Mbps Speeds decrease over distance.
line (VDSL) Upstream: 1.5 to 2.3 Mbps 4,500 ft. at 12.96 Mbps,
3,000 ft. at 25.82 Mbps, and
1,000 ft. at 51.84 Mbps
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ISDN Channels An ISDN transmission circuit consists of a logical grouping
of data channels which carry voice and data. Each ISDN connection consists
of two channels, a B channel and a D channel, each with their own function
and bandwidth constraints. The bearer channels (B channels) transfer data
and offer a bandwidth of 64 Kbps per each channel, and the data channel
(D channel) handles signaling at 16 or 64 Kbps so that the B channel
doesn’t have to do it. This includes the session setup and teardown using a
communications language known as Digital Subscriber Signalling System
No. 1 (DSS1). The bandwidth available for the D channel is dependent
upon the type of service – basic rate interfaces (BRIs) usually require 16 Kbps
and primary rate interfaces (PRIs) use 64 Kbps. Typically, ISDN service contains
two B channels and a single D channel. H channels are used to specify
a number of B channels. The following list shows the implementations:
■ H0 384 Kbps (six B channels)
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H10 1472 Kbps (23 B channels)
H11 1536 Kbps (24 B channels)
H12 1920 Kbps (30 B channels) – Europe