Page 98 - DLIS408_INFORMATION_TECHNOLOGY-APPLICATIONSL SCIENCES

Unit 8: Network Media

leased lines. At each end of the leased line, a router connects to the LAN on one side and a hub Notes
within the WAN on the other. Leased lines can be very expensive. Instead of using leased lines,
WANs can also be built using less costly circuit switching or packet switching methods. Network
protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet
over SONET/SDH, MPLS, ATM and Frame relay are often used by service providers to deliver the
links that are used in WANs. X.25 was an important early WAN protocol, and is often considered
to be the “grandfather” of Frame Relay as many of the underlying protocols and functions of X.25
are still in use today (with upgrades) by Frame Relay.
Academic research into wide area networks can be broken down into three areas: mathematical
models, network emulation and network simulation.
Performance improvements are sometimes delivered via wide area file services or WAN
optimization.

Connection Technology Options
Several options are available for WAN connectivity:

Option: Description Advant- Disadvan- Band- Sample
ages tages width protocols
range used
Leased Point-to-Point connection Most Expensive PPP,
line between two computers or secure HDLC,
Local Area Networks (LANs) SDLC,
HNAS
Circuit A dedicated circuit path is Less Call Set- 28 - 144 PPP,
switching created between end points. Expensive up kbit/s ISDN
Best example is dialup
connections
Packet Devices transport packets via a Shared X.25
switching shared single point-to-point or media Frame-
point-to-multipoint link across across link Relay
a carrier internetwork. Variable
length packets are transmitted
over Permanent Virtual Circuits
(PVC) or Switched Virtual
Circuits (SVC)
Cell relay Similar to packet switching, but Best for Overhead ATM
uses fixed length cells instead of simulta- can be
variable length packets. Data is neous use consider-
divided into fixed-length cells of voice able
and then transported across and data
virtual circuits

Transmission rates usually range from 1200 bit/s to 24 Mbit/s, although some connections such as
ATM and Leased lines can reach speeds greater than 156 Mbit/s. typical communication links used
in WANs are telephone lines, microwave links & satellite channels.
Recently with the proliferation of low cost of Internet connectivity many companies and organi-
zations have turned to VPN to interconnect their networks, creating a WAN in that way. Companies
such as Cisco, New Edge Networks and Check Point offer solutions to create VPN networks.
8.3.1 Advantages and Disadvantages of Wide Area Network

Advantages

1. Broader reception area.
2. More recievable connections available
3. Portablility (if you use a laptop)
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