Datasheet

Book VII
Chapter 1
Wide-Area
Networking Basics
811
Connection Types
✦ V.35: The OSI physical layer ITU partially balanced standard that sup-
ports high-speed data rates up to 2.048 Mbps (but used mostly for
56kbps and 64kbps communications).
V.35 is a standard for synchronous serial interfaces that has become
obsolete in favor of EIA/TIA-449, but it continues to be used and remains
popular today. V.35 eliminates line noise by separately twisting the indi-
vidual wires carrying data and clock information.
Connection Types
Various connection types are available when designing a WAN connection.
Each type provides advantages and disadvantages that must be understood
prior to implementation. Defining an organization’s WAN traffic flow
requirements is crucial to the success of the WAN design.
The four common types of WAN connections available are as follows:
✦ Dedicated leased line connection: An individual, point-to-point serial
connection that uses a permanently established link to provide guar-
anteed bandwidth between remote networks. These dedicated circuits
provide up to 44.736-Mbps speeds over a public carrier’s T-1 or T-3 lines.
These types of high-speed connections are “always on” and have the advantage
of minimum overhead compared to other connection types. Also, this persis-
tent connection does not require continuous setup and tear down between
communication phases. The disadvantage of dedicated leased lines is cost (fac-
tored by distance between links and the amount of bandwidth assigned to the
single link), because they are more expensive that other connection types.
✦ Circuit-switched connection: The most popular type of WAN connection in
which a physical circuit is established “as needed” between two endpoints
for the duration of the connection. This type of connection requires call
setup of the link to occur before any communications may begin. The physi-
cal lines remain unavailable for other users until the connection is dropped.
The two types of serial circuit-switched connections are
• Asynchronous plain old telephone system (POTS) dialup
• Synchronous Integrated Services Digital Network (ISDN)
✦ Packet-switched connection: A point-to-point virtual circuit connection
established using a public carrier’s network, allowing multiple customers to
share carrier resources. The sharing of packet-switched connections between
customers remains transparent to the end user. Packet-switched connections
provide high bandwidth and reduced cost compared to dedicated leased
lines, but are more expensive than ISDN and dialup connections.
Frame Relay and X.25 are known as packet-switched technologies.
48_489628-bk07ch01.indd 81148_489628-bk07ch01.indd 811 3/1/10 10:15 PM3/1/10 10:15 PM