Communications
Computer communication is the process of sharing data, programs and information between two
or more computers.
Communication systems
This is electronic systems that transmit data from one location to another. They can be wired or
wireless, every communication system has four basic elements:
1. Sending & receiving devices – these are computer or specialized communication device.
They send as well as receive messages in the form of data, information, and/or
instructions.
2. Communication channels – this is the actual connecting or transmission medium that
carries the message. The medium can be wire or cable or wireless.
3. Connection devices – these devices act as an interface between the sending and receiving
devices and the communication channel.
4. Data transmission specification – these are rules that coordinate the devices.
Communication channels
This is an essential element of every communication system.
Physical connections - Examples:
 Telephone line – twisted pair cable
 Coaxial cable
 Fiber-optic cable
Wireless connection – examples
 Infrared light waves
 Broadcast radio communication
 Microwave communication – Bluetooth
 Satellite
Computer network
It is a communication system that connects two or more computers so that can exchange
information and share resources.
NIC – network interface card – these are expansion card located in the system that connect the
computer to a network.
NOS – Network Operating system – this OS controls and coordinates the activities of all
computers and other devices on a network.
Network types
1. Local area network (LAN) – networks with nodes that are in close physical proximity,
within the same building.
2. Metropolitan area Network (MAN) – also known as regional network, MANs span
distances up to 100 miles. These networks are frequently used as links between office
buildings that are located throughout the city.
3. Wide area network (WAN) – these are countrywide and world wide networks. Man span
distances greater than 100 miles.
4. WLAN - Wireless Local Area Network
5. SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small
Area Network
6. CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
7. PAN - Personal Area Network
8. DAN - Desk Area Network
Network architectures
Topology – a network can be arranged in several different ways, this arrangement is called the
network topology. There are three types – bus, ring, star.
1. Bus topology
Each device in the network handles its own communication control. There is no host computer.
All communications travel along a common connecting cable called a bus.
2. Ring topology
Each device is connected to two other devices, forming a ring. There is no central file server or
computer. Messages are passed around the ring until they reach the correct destination.
3. Star topology
A number of computers and other devices are linked to a central unit. The central unit is the hub.
All communication pass through this central unit.
Bus
4. Mesh Topology
Ring
Star
Mesh Topology
A mesh topology combines characteristics of bus, ring and star topologies. It consists of groups of starconfigured workstations connected to a linear bus backbone cable and ring networks. Mesh topologies
allow for the expansion of an existing network, and enable companies to configure a network to meet their
needs.
Network hardware:Networking hardware typically refers to equipment facilitating the use of a computer network.
Typically, this includes routers, switches, access points, network interface cards and other related
hardware. This is a comprehensive list of all vendors who produce Network hardware vendors.
A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic
on a LAN by dividing it into two segments.
Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming
traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects
each incoming Ethernet frame - including the source and destination MAC addresses, and
sometimes the frame size - in making individual forwarding decisions.
Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges,
though, support one network boundary, whereas switches usually offer four or more hardware
ports. Switches are sometimes called "multi-port bridges" for this reason.
HUB - is a device for connecting multiple twisted pair or fiber optic Ethernet devices together
and thus making them act as a single network segment.
Routers are small physical devices that join multiple networks together. Technically, a router is
a Layer 3 gateway device, meaning that it connects two or more networks and that the router
operates at the network layer of the OSI model.
Switch:
Definition: A network switch is a small hardware device that joins multiple computers together
within one local area network (LAN). Technically, network switches operate at layer two (Data
Link Layer) of the OSI model.
Network switches appear nearly identical to network hubs, but a switch generally contains more
intelligence (and a slightly higher price tag) than a hub. Unlike hubs, network switches are
capable of inspecting data packets as they are received, determining the source and destination
device of each packet, and forwarding them appropriately. By delivering messages only to the
connected device intended, a network switch conserves network bandwidth and offers generally
Modem:
Definition: Traditional modems used on dialup networks convert data between the analog form
used on telephone lines and the digital form used on computers. Standard dial-up network
modems transmit data at a maximum rate of 56,000 bits per second (56 Kbps). However,
inherent limitations of the public telephone network limit modem data rates to 33.6 Kbps or
lower in practice.