Client/Server Versus Peer Networks
Although every computer on a LAN is connected to every other computer, they do not
necessarily
all communicate with each other. There are two basic types of LANs, based on the communication patterns between the machinesclient/server networks and peer-to-peer networks.
Client/Server Networks
On a
client/server
network, every computer has a distinct role, that of either a client or a server. A
server
is designed to share its resources among the client computers on the network. Typically, servers are located in secured areas, such as locked closets or data centers (server rooms), because they hold an organization's most
valuable
data and do not have to be accessed by operators on a continuous basis. The rest of the computers on the network function as
clients
(see Figure 18.1).
A dedicated server computer typically has faster processors, more memory, and more storage space than a client because it might have to service dozens or even hundreds of users at the same time.
High-performance servers typically use from two to eight processors (and that's not counting dual-
core
CPUs), have several gigabytes of memory installed, use the 64-bit version of the PCI expansion slot for server-optimized network interface cards, and have redundant power
supplies
. The server runs a special network operating systemsuch as Windows Server, Linux, Unix, or Novell NetWarethat is designed solely to facilitate the sharing of its resources. These resources can reside on a single server or on a
group
of servers. When more than one server is used, each server can "specialize" in a particular task (file server, print server, fax server, email server, and so on) or provide redundancy (duplicate servers) in case of server failure. For very demanding computing
tasks
, several servers can act as a single unit through the use of parallel processing.
A client computer typically communicates only with servers, not with other clients. A client system is a standard PC that is running an operating system such as Windows XP. These versions of Windows contain the client software that enables the client computers to access the resources that servers share. Older operating systems, such as Windows 3.x and DOS, require add-on network client software to join a network.
Peer-to-Peer Network
By contrast, on a peer-to-peer network, every computer is equal and can communicate with any other computer on the network to which it has been granted access rights (see Figure 18.2). Essentially, every computer on a peer-to-peer network can function as both a server and a client; any computer on a peer-to-peer network is
considered
a server if it shares a printer, a folder, a drive, or some other resource with the rest of the network. This is why you might hear about client and server activities, even when the discussion is about a peer-to-peer network. Peer-to-peer networks can be as small as two computers or as large as hundreds of systems. Although there is no theoretical limit to the
size
of a peer-to-peer network, performance
drops
significantly and security becomes a major
headache
on peer-based networks with more than 10 computers. Also, Microsoft imposes a 10-station limit on computers running Windows 2000 Professional or Windows XP Professional that are sharing resources with other systems. For these reasons, I recommend that you switch to a client/server network when your network climbs above 10
stations
.
Peer-to-peer networks are more common in small offices or within a single department of a larger organization. The advantage of a peer-to-peer network is that you don't have to
dedicate
a computer to function as a file server. Instead, every computer can share its resources with any other. The potential disadvantages to a peer-to-peer network are that typically less security and less control exist because users normally administer their own systems, whereas client/server networks have the advantage of centralized administration.
Comparing Client/Server and Peer-to-Peer Networks
Client/server LANs offer enhanced security for shared resources, greater performance, increased backup efficiency for network-based data, and the potential for the use of redundant power supplies and RAID drive arrays. Client/server LANs also have a much greater cost to purchase and maintain. Table 18.1
compares
client/server and peer-to-peer server networking.
Table 18.1. Comparing Client/Server and Peer-to-Peer Networking
|
Item
|
Client/Server
|
Peer-to-Peer
|
|
Access control
|
Via user/group lists of permissions; a
user
has access to only the resources granted, different users can be given different levels of access
|
Via password lists by resource; each resource requires a separate password, all-or-nothing access, no centralized user list
|
|
Security
|
High; access is controlled by user or by group identity
|
Low; knowing the password gives anybody access to a shared resource
|
|
Performance
|
High; the server is dedicated and doesn't handle other tasks
|
Low; servers often act as workstations
|
|
Hardware cost
|
High; specialized high-performance server hardware with redundancy features
|
Low; any workstation can become a server by sharing resources
|
|
Software cost
|
Higher; license fees per user are part of the cost of the server OS
|
Lower; client software is included with OS
|
|
Backup
|
Centralized on the server; managed network administrator, backup by device and media only required at server
|
Decentralized; managed by users, backup devices and media required at each workstation
|
|
Redundancy
|
Yes; duplicate power supplies, hot-swappable drive arrays, and even redundant servers are common; network OS normally is capable of using redundant devices automatically
|
No true redundancy among peer "servers" or clients; failures require manual intervention to correct, with a high possibility of data loss
|
|
