Information Technology Reference
In-Depth Information
Ta b l e 6 - 2
WA N C o m p a r i s o n
Key
To p i c
WAN Technology
Bandwidth
Reliability
Latency
Cost
ISDN
Low
Medium
Medium
Low
DSL
Low/medium
Low
Medium
Low
Cable
Low/Medium
Low
Medium
Low
Wireless
Low/Medium
Low
Medium
Medium
Frame Relay
Low/Medium
Medium
Low
Medium
TDM
Medium
High
Low
Medium
Metro Ethernet
Medium/high
High
Low
Medium
SONET/SDH
High
High
Low
High
MPLS
High
High
Low
High
Dark fiber
High
High
Low
High
DWDM
High
High
Low
High
The follow ing sections offer more details about each WA N technology covered in Ta ble 6-2.
ISDN
Integrated Services Digital Network (ISDN) is an all-digital phone line connection that was
standardized in the early 1980s. ISDN allows both voice and data to be transmitted over
the digital phone line instead of the analog signals used in dialup connections. ISDN pro-
vides greater bandwidth and lower latency compared to dialup analog technology. ISDN
comes in two service types: Basic Rate Interface (BRI) and Primary Rate Interface (PRI).
ISDN BRI Service
ISDN BRI consists of two B channels and one D channel (2B+D). Both of the BRI B chan-
nels operate at 64 kbps and carry user data. The D channel handles the signaling and con-
trol information and operates at 16 kbps. Another 48 kbps is used for framing and
synchronization, for a total bit rate of 192 kbps.
ISDN PRI Service
ISDN PRI service offers 23 B channels and 1 D channel (23B+D) in both North America
and Japan. Each channel (including the D channel) operates at 64 kbps, for a total bit rate
of 1.544 Mbps, including overhead. In other parts of the world, such as Europe and
Australia, the ISDN PRI service provides 30 B channels and 1 64-kbps D channel.
