Network Topology

Network Topologies

LANs and WANs- Geographical coverage

LANs

-A single geographical location, such as office building, school, etc.

-Typically High speed and cheaper.

WANs

-Spans more than one geographical location often connecting separate LANs.

-Slower.

-Costly hardware, routers, dedicated leased lines and complicated implementation procedures.

Topology- Physical and logical network layout

-Physical- actual layout of the computer cable and other network devices.

-Logical- the way in which the network appears to the devices that use it.

Common topologies: Bus, ring, star, mesh and wireless.

Bus topology

-Uses a trunk or backbone to which all of the computers on the network connect.

-System connect to this backbone using T connectors or taps.

-coaxial cablings (10Base-2, 10Base-5) were popular years ago.

Bus Topology

Advantages	Disadvantages
Cheap and easy to implements	Network disruption when computers are added or remove
Required less cable	A break in the cable will prevent all systems from accessing thee network
Does not use any specialized network equipment	Difficult to troubleshoot

Ring Topology

-Logical ring

- Meaning that data travels in circular fashion from one computer to another on the network.

-Typically FDDI, SONET or Token Ring technology are used to implement a ring network.

-Ring networks are most commonly wired in a star configuration.

Token ring has multi-station access  unit (MSAU), equivalent to hub or switch. MSAU performs the token circulation internally.

Advantages	Disadvantages
Cable faults are easily located, making troubleshooting easier	Expansion to the network can cause network distruption
Ring networks are moderately easy to install	A single break in the cable can distrup entire network

Star Topology

-All computers/ devices connect to a central device called hub or switch.

-Each device requires a single cable.

-Point-to-point connection between the device and hub.

-Most widely implement.

-Hub is the single point of failure.

Advantages	Disadvantages
Easily expanded without disruption to the network	Requires more cable
Cable failure affect only a single user	A central connecting device allows for a single point of failure
Easily to troubleshoot and isolate problem	More difficult to implement

Mesh Topology

-Each computer connects to every other.

-High level of redundancy.

-Rarely used.

         -Wiring is very complicated.

         -Cabling cost is high.

         -Troubleshooting a failed cable is tricky.

         -A variation hybrid mesh- create point to point connection between                                 in WAN implementation.

Advantages	Disadvantages
Provides redundant paths between Devices.	Requires more cable than the other LAN topologies
The network can be expanded without disruption to current uses.	Complicated implementation

Wireless networking

-Do not require physical cabling.

-Particularly useful for remote access for laptops users.

-Eliminate cable faults and cable breaks.

-Signal interference and security issues.

Advantages	Disadvantages
Allows for wireless remote access	Potential security issues associted with wireless transmissions
Network can be expanded without disruption to current users	Limited speed in comparison to other network topologies.

IEEE and Networking standards

-Institute of Electrical and Electronic

Engineers (IEEE) developed a series of

networking standards.

– Networking technologies developed by

manufacturers are Compatible.

– Cabling, networking devices and protocols are

  all interchangeable under the banner of a

             specific IEEE.

802.3 IEEE standard

-Defines characteristics for Ethernet networks.

-New additions,

   – 802.3u for Fast Ethernet

   – 802.3z for Gigabit Ethernet, referred to as 802.3x.

   – … …

   – 802.3ac 10gbits/s, expe. 2009

   – … …

-Speed: Original 10Mbps, Fast Ethernet 100Mbps, Gigabit Ethernet

1000Mbps

-Topology: bus or star.

-Media: Coaxial and twisted pair cabling, also fiber optic cable.

-Access method: CSMA/CD

802.5 IEEE standard

-Specifies the characteristics for Token Ring

Networks.

-Introduced by IBM in the mid 80s, network

topology of choice until the rise of the popularity

of Ethernet.

-Speed: 4 to 16Mbps

-Topology: logical ring and most often a physical

star. Logical ring is often created in the

Multistation Access Unit (MSAU)

-Media: twisted pair cabling.

-Access method: token passing.