Table of Contents Link to heading
Overview Link to heading
The path that a message takes from source to destination can be as simple as a single cable connecting one computer to another, or as complex as a collection of networks that literally spans the globe. This network infrastructure provides the stable and reliable channel over which these communications occur.
The network infrastructure contains three categories of network components:
- Devices
- Media
- Services
Devices and media are the physical elements, or hardware, of the network. Hardware is often the visible components of the network platform such as a laptop, PC, switch, router, wireless access point, or the cabling used to connect the devices.
Services include many of the common network applications people use every day, like email hosting services and web hosting services. Processes provide the functionality that directs and moves the messages through the network. Processes are less obvious to us but are critical to the operation of networks.
End Devices or Hosts Link to heading
An end device is either the source or destination of a message transmitted over the network.
Data originates from an end device, flows through the network, and arrives at another end device.
To distinguish one end device from another, each end device is identified by a:
- Host or physical address (MAC address) if they communicate within a network.
- Network address - (IP address) if they communicate across different networks.
When an end device initiates communication, it uses the address of the destination end device to specify where the message should be sent.
Examples Link to heading
- Computers (work stations, laptops, servers connected to a network)
- Network printers
- Voice over Internet Protocol (VoIP) phones
- Cameras on a network (webcams and security cameras)
- Remote monitoring stations for weather observation
- Handheld devices (smart phones, tablets, personal digital assistants (PDAs), and wireless card readers, and barcode scanners)
- TelePresence endpoints
Intermediary Devices Link to heading
connect the individual end devices to the network and can connect multiple individual networks to form an internetwork.
These intermediary devices provide connectivity and ensure that data flows across the network.
Intermediary devices use the destination end device address, in conjunction with information about the network interconnections, to determine the best (shortest) path that messages should take through the network.
Intermediary devices are not all the same. Some work inside the LAN performing switching functions, whilst others help route messages between networks.
Examples Link to heading
| Device Type | Description |
|---|---|
| Network access devices | Connect end users to their network. Examples are hubs, switches, and wireless access points. |
| Internetwork devices | Connect one network to one or more other networks. Routers are the main example. |
| Communication servers | Route services such as IPTV and wireless broadband. |
| Modems | Connect users to servers and networks through telephone or cable. |
| Security devices | Secure the network with devices such as firewalls that analyse traffic exiting and entering networks. |
Functions Link to heading
Intermediary network devices perform some or all of these functions:
- Regenerate and retransmit data signals
- Maintain information about what pathways exist through the network and internetwork
- Notify other devices of errors and communication failures
- Direct data along alternate pathways when there is a link failure
- Classify and direct messages according to Quality of Service (QoS) priorities
- Permit or deny the flow of data, based on security settings
Network Media Link to heading
Communication across a network is carried on a medium which provides the channel over which the message travels from source to destination.
Modern networks primarily use three types of media to interconnect devices and to provide the pathway over which data can be transmitted.
- Copper - data is converted to electrical impulses and thus susceptible
to outside interference.
- Cheap and common for short distances
- E.g. twisted-pair cable usually used as LAN media
- Fibre Optics - data is converted to light pulses* and thus not affected
by outside interference.
- Transmits data at extremely fast speeds
- Good for long distances
- E.g., glass or plastic fibres in a vinyl coating usually used for long runs in a LAN and as a trunk
- Wireless - data is converted to electromagnetic waves.
- Connects local users through the air
- However, wireless networks have decreased throughput compared with wired networks
Considerations Link to heading
Different types of network media have different features and benefits. Not all network media have the same characteristics, nor are they all appropriate for the same purpose.
When choosing network media, administrators must consider the following:
- The distance the media can carry the signal
- The environment in which the media works
- The bandwidth requirements for users
- The cost of installation
- The cost of connectors and compatible equipment
Network Connection Link to heading
Network Interface Card (NIC)
- A LAN adapter that provides the physical connection to the network at the PC or other end device.
- The media that are connecting the PC to the networking device, plug directly into the NIC.
- Each NIC has a unique physical address that identifies it on the LAN.
Physical Port
- A connector or outlet on a networking device where the media is connected to an end device or another networking device.
Interface
- A specialised port on a networking device that connect to individual networks.
- It allows two different networks to communicate.
- Because routers are used to interconnect networks, the NICs on routers are referred to as network interfaces.
- Each interface on a router has a unique physical address and appears as a host on the local network.
Network Topology Link to heading
the arrangement or relationship of the network devices and the interconnections between them.
There are two types of topology diagrams:
- Physical topology diagrams - identify the physical location of intermediary devices and cable installation.
- Logical topology diagrams - identify devices, ports, and addressing scheme.
Physical Topology Link to heading
an arrangement of the nodes and the physical connections between them.
The representation of how the media is used to interconnect the devices is the physical topology.
Logical Topology Link to heading
the way a network transfers data from one host to the next.
This arrangement consists of virtual connections between the nodes of a network independent of their physical layout.