Network
A computer network allows separate
computers to share resources within the boundaries of the network. Those resources
may be shared files or databases, programs, e-mail access, printers, telephony
application processors, FAX capability, or high speed internet access. Resources
may be shared individually by each computer (peer-to-peer networks) or may be
controlled by a central computer or server (client-server
network.)
Each PC is connected to the network by a
Network Interface Card (NIC). Elements of the network may be connected by cable,
the internet, dedicated data circuits, or by wireless network devices.
Selection of network type depends upon speed, distance, cost, and security
issues.
Peer-to-Peer
Network
A peer-to-peer network allows two or more
Personal Computers (PCs) to pool resources. Individual resources like disk
drives, CD-ROM drives, and printers can be made accessible from every PC. Each PC
may act like a “client” and request resources from another PC or act like a
“server” and provide resources to another PC. Devices like printer servers,
telephony application processors, and high speed internet access can also be
accessed via the network.
Network Operating Software (NOS), usually
contained in the PC operating system, allows each PC to determine which resources
will be available to other users. Specific hard & floppy disk drives,
directories and files, printers, and other resources can be attached or detached
from the network via software.
Client-Server
Networks
In a Client-Server network, files are
stored on a centralized high speed file server. Network access speeds are usually
higher than speed on a peer-to-peer network. Nearly all services such printing,
internet access, and e-mail are routed through the server, allowing them to be
tracked. Client PCs are subordinate to the Server and have their capabilities,
settings, and access to resources set by programming on the server. A
Client-Server network centralizes administration and simplifies administration on
large networks.
Network
Printing
Network printing uses a small print server
(or a print server card built into the printer) connected directly to the network.
Printers can be used on a peer-to-peer network without having to turn on the PC
with the printer attached. Printing is faster and less cumbersome. Printer servers
may be used on either peer-to-peer or client-server
networks.
10/BaseT and
100BaseTX
10BaseT and 100BaseTX are the two most
common standards for networking speed. 10BaseT was the first standard for
unshielded twisted pair (UTP) cable for networks. It operated at a speed of 10
Mbps (10 million bits per second) and used two twisted pairs of wire. 100Base TX
operates at a speed of 100 Mbps (10 time faster than 10BaseT) and uses four
twisted pairs of wire. New standards of 350 Mbps and 1000 Mbps have been approved
and are now being implemented. Installation costs for the new standards are
higher.
10/100
Autosensing
Auto sensing refers to network devices like
hubs, switches, and network adapters which automatically sense which speed the
network is using and adjust to the proper speed. Current equipment is primarily
designed for 10/100 speed. New auto sensing equipment will eventually be marketed
for the higher speed networks.
CAT 3 and CAT
5
CAT 3 and CAT 5 are common standards which
define the cable used for networks. CAT 3 was designed for 10BaseT networks
which operate at 10 Mbps. CAT 5 was designed for 100BaseTX networks. In addition
to electronic and physical specifications for the cable, the standards define
specifications for patch panels, jack inserts, patch cords, network adapter jacks,
and installation practices. Also defined are a CAT 5e + (155 Mbps) and CAT 6 (250
Mbps). CAT 6 has recently been approved and the equipment and testers are not yet
fully available.
Full Duplex and Half
Duplex
Full Duplex devices send and receive data
simultaneously - a full duplex switch sending and receiving data at 100 Mbps is
actually transferring data at 200 Mbps. A Half Duplex device can only send or
receive - not both - at one time. Switches are usually full duplex devices and
have greater throughput of data. Hubs are half duplex devices and are more limited
in throughput. Full Duplex devices are more expensive than half duplex
devices.
Wireless
Networking
In wireless networking, cables are replaced
by wireless transmitters and receivers and may be either full duplex or half
duplex. Wireless devices may be difficult to integrate into a wired network and
there may be some security and coverage issues that need to be resolved. Wireless
networking is probably more useful for a very small
network.
Hubs and
Switches
Hubs and Switches are devices which connect
computers in a network and help transfer data across the network. Hubs are either
10 Mbps or 100 Mbps and are usually half duplex. Computers on a hub share the
total bandwidth available to the hub. If you have a 10 Mbps 5 port hub, each of
the five connected PCs has available only 2 Mbps of
bandwidth.
Switches use dedicated bandwidth for each
port. A 10 Mbps 5 port switch will provide each device with a full 10 Mbps data
speed. In addition, since switches are usually full duplex, the actual data
throughput may be as high as 20 Mbps. Switches are more expensive than hubs, but
increased performance probably justifies the difference in
cost.
Routers
Routers provide two valuable network
functions: They act as traffic cops for network traffic making sure data gets to
the right place and they provide and interface or gateway to other networks and
the internet. Routers have programmable software which keeps track of devices on
the network and guides data packets to the correct device. They also keep track of
incoming and outgoing data from external networks (a company wide area network or
the internet) and routes the data to the correct network PC. They may have
additional software to provide protection to network computers (a firewall) and
enhanced IP addressing via DHCP (see below).
IP
Addresses
Using Internet Protocol (IP), each computer
and each networking device is assigned an identifying number referred to as an IP
address. This address is in the form of XXX.XXX.XXX.XXX and must be unique for
every device on the network.
Static IP addresses may be assigned to each
network device. These numbers are permanent and the network administrator must
keep track of all IP addresses to make sure there are no duplicates and addresses
are assigned to proper devices.
For networks with large numbers of
computers and with people constantly logging in and out a better method of
assigning IP addresses was needed. Dynamic Host Configuration Protocol (DHCP)
actually “leases,” or temporarily assigns, IP addresses as computers log on to the
network. The address belongs to the computer for the duration of the session but
goes back to the pool of available addresses as soon as the computer logs out. The
process is completely automatic and does not require the record keeping
characteristic of static IP addresses. Use of DHCP by routers simplifies set up of
an internet sharing network.
|
