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790 WIDEAREA ANDMETROPOLITANAREANETWORKSnecessary legally to protect the service user’s interests, but
it is important to remember that failure of the provider to
deliver service typically means that the user has failed to
meet a business requirement as well. Consequently it is
in both the customer’s and provider’s best interests if the
penalty clause is never invoked.CONCLUSION
The boundaries between local area, metropolitan area,
and wide area networks have become less clear over time,
due to the increasing variety of implementation choices
available to network designers. For MANs and WANs in
particular, classifying equipment, services, and manage-
ment responsibilities by architectural category (access,
edge, and core) may help to distinguish among options
so that choices can be made in alignment with the busi-
ness priorities of each designer’s organization. Flexibility
to accommodate change and growth, reliable service de-
livery, and optimal cost/performance ratios are the major
characteristics typically desired for every network design.
The tension between network users wishing to maximize
cost-effectiveness and service providers trying to maxi-
mize profit continues to work with technological develop-
ments to create opportunity for new business approaches.
The primary challenge always seems to lie in balancing ex-
pensive, long-term infrastructure investments with new
technologies and services that meet changing application
requirements.GLOSSARY
Circuit A complete connection between a source and
destination for the purposes of transferring informa-
tion, i.e., for communication.
Circuit switching Aconnection-orientedapproach to
networking where the entire path from source to des-
tination is determined and sufficient resources are al-
located along the path to carry the traffic before any
traffic can flow.
Local area network (LAN) A network covering a single
office, building, or campus that is built and operated
as a private network, by an individual or organization,
for his/her/its own use.
Metropolitan area network (MAN) A network cover-
ing distances up to tens of miles, often within or sur-
rounding a major city, with public ones built and op-
erated by service providers who offer network services
to subscribers for a fee.
Packet A portion of a message to be carried from a
source to a destination.
Packet switching A connectionless networking ap-
proach where each packet is routed through the net-
work independently.
Private network A network built, owned, and operated
by a single individual or organization for his/her/its
own use.
Public network A network built to offer resources or
services to a set of subscribers who are typically inde-
pendent from each other and from the owner of the
network. Most people think of the Internet as the only
truly “public” network.Routing Determining where a packet should go next to
get it closer to its intended destination, i.e., deciding
what is the next hop along the path.
Service provider (SP) Builder and/or operator of a net-
work for the purpose of selling capacity or services to
subscribers for a fee.
Service user Subscriber to the offerings of a public net-
work.
Switching Placing a packet on the appropriate trans-
port mechanism to get it to the network device repre-
senting the next hop.
Wide area network (WAN) A network covering dis-
tances up to hundreds or thousands of miles, such as
between cities, across or between countries, or across
oceans, where public facilities are built and operated
by service providers who offer network capacity or ser-
vices to subscribers for a fee while private ones are built
by organizations for their own use.CROSS REFERENCES
SeeCircuit, Message, and Packet Switching; Conducted
Communications Media; Local Area Networks; Propagation
Characteristics of Wireless Channels; Public Networks.FURTHER READING
ATM Forum (2002). ATM service categories: The bene-
fits to the user. Retrieved September 17, 2002, from
http://www.atmforum.com/aboutatm/6.html
Cisco Systems, Inc. (2001). Fundamentals of DWDM
technology. Retrieved September 17, 2002, from http://
http://www.cisco.com / univercd / cc / td / doc / product / mels /
cm1500/ dwdm/dwdmovr.htm
Cisco Systems, Inc. (2002). Switched multimegabit data
service. Retrieved September 17, 2002, from http://
http://www.cisco.com/univercd/ cc /td /doc /cisintwk /itodoc/
smds.htm
Defense Information Systems Agency (n.d.). ANSI T1
standards related to TMN. Retrieved September
17, 2002, from http://www-comm.itsi.disa.mil/tmn/
tmnt1.html
DSL Life (n.d.) DSL tutorial. Retrieved September 17,
2002, from http://www.dsllife.com/dsltut.htm
Frame Relay Forum (2002). Retrieved September 17,
2002, from http://www.frforum.com
H.323 Forum (2002). Retrieved September 17, 2002, from
http://www.h323forum.org
Horak, R. (n.d.) T-carrier basics. Retrieved September
17, 2002, from http://www.commweb.com/techcenters/
main/experts/3783/COM20010726S0011
Welcome to get IEEE 802 (n.d.). Retrieved September 17,
2002, from http://standards.ieee.org/getieee802/
International Engineering Consortium (2002). Ca-
ble modems. Retrieved September 17, 2002, from
http://www.iec.org/online/tutorials/cablemod
International Engineering Consortium (n.d.). Various
other tutorials. Retrieved September 17, 2002, from
http://www.iec.org/online/tutorials
International Telecommunication Union, Telecommuni-
cation Standardization Sector (n.d.) Retrieved Sept-
ember 17, 2002, from http://www.itu.int/ITU-T/