Biomedical Engineering Reference
In-Depth Information
A file server is a server configured to allow workstation clients on the network to use the disk storage
on the server for collaborative work, to facilitate archiving, and to provide additional disk storage. File
servers typically contain large, high-speed hard drives and comprehensive data management
software. Print servers provide buffering and queuing for networked printers.
Web servers provide HTML pages or files to a Web client. A mail server hosts the e-mail system for
users on the network, providing processing and storage for e-mail messages. Terminal servers
connect several terminals, including dial-up modems, to a single LAN connection. A terminal server
has a single network interface and several ports for terminal connections, allowing several terminals
to be connected to the network by a single LAN cable.
Remote access servers, also known as communications servers, provide access to users seeking to
use a network remotely, especially while traveling away from the main office. A remote access server
is typically configured with a firewall and a router to provide security and to limit the remote access
to a specific subset of the network. For example, a remote access server may allow access to e-mail
and non-confidential files. In this way, if a hacker manages to somehow gain access to the network
through the remote access server, he won't be able to destroy or steal confidential data. A remote
access server is typically configured with one or more telephone modems so that remote users can
call in to the network and read their e-mail and access files from any location with telephone access.
Bridges
A bridge connects two or more network segments and forwards packets between them, amplifying
the signal to compensate for the loss associated with splitting a signal across multiple segments. So-
called dumb bridges are protocol-specific and are designed to connect networks running the same
protocol. These devices simply accept data packets from one segment of a network and forward them
on to the other segments. They have no built-in intelligence.
In addition to these bridges, several varieties of bridge design provide processing, enabling data
sharing between otherwise incompatible networks. For example, encapsulating bridges encapsulate
network data with header information so they are compatible with devices in the destination network.
A translating bridge goes one step further and actually translates the data from the source network
so that the protocol is compatible with that of the destination network. A filtering bridge, also called a
multi-port bridge, directs data from the source network to a specific segment of the destination
network, thereby reducing unnecessary traffic on some segments of the network. In addition, there
are numerous bridge designs that combine filtering, routing, and security functions.
Routers
A router directs data to the portion of a network meant to receive it rather than broadcasting data to
every node of a network. Instead of merely passing information like a dumb bridge, routers monitor
network activity and change traffic patterns if necessary to maintain efficiency or throughput.
Intelligent routers dynamically reconfigure the communications path to improve availability and
reliability.
Routers are rarely used alone but are combined with other devices. For example, routers are located
at every gateway and are often included as part of a network switch. Routers are also commonly
combined with a network bridge in the form of a brouter. In contrast to switches, routers are typically
used at the edges of a network, where intelligence is needed to determine the best path for data.
Switches
A switch is a device that selects a circuit for sending data through a network. A switch, which tends
to be simpler, faster, and less expensive than a router, lacks information about the network that a
router may use in determining the best circuit or path to use to move data from one part of a
