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5.1 | |
Cabling the LAN | |
| 5.1.12 | |
Peer-to-peer |
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By using LAN and WAN technologies, many
computers are interconnected to provide services to their users. To
accomplish this, networked computers take on different roles or
functions in relation to each other. Some types of applications
require computers to function as equal partners. Other types of
applications distribute their work so that one computer functions to
serve a number of others in an unequal relationship. In either case,
two computers typically communicate with each other by using
request/response protocols. One computer issues a request for a
service, and a second computer receives and responds to that request.
The requestor takes on the role of a client, and the responder takes
on the role of a server.
In a peer-to-peer network,
networked computers act as equal partners, or peers. As
peers, each computer can take on the client function or the server
function. In a peer-to-peer network, individual
users control their own resources. The users may decide to share
certain files with other users.
Peer-to-peer networks are relatively easy to install and operate. No additional equipment is necessary beyond a suitable operating system installed on each computer. Since users control their own resources, no dedicated administrators are needed. As networks grow, peer-to-peer relationships become increasingly difficult to coordinate. A peer-to-peer network works well with 10 or fewer computers. Since peer-to-peer networks do not scale well, their efficiency decreases rapidly as the number of computers on the network increases. Also, individual users control access to the resources on their computers, which means security may be difficult to maintain. The client/server model of networking can be used to overcome the limitations of the peer-to-peer network.
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At one time, computer A may make a request for a file from computer B,
which responds by serving the file to computer A. Computer A functions
as client, while B functions as the server. At a later time, computers
A and B can reverse roles. 
The users
may also require passwords before allowing others to access their
resources. Since individual users make these decisions, there is no
central point of control or administration in the network. In
addition, individual users must back up their own systems to be able
to recover from data loss in case of failures. When a computer acts as
a server, the user of that machine may experience reduced performance
as the machine serves the requests made by other systems. 
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