Topology, Protocol, Architecture and ATM

HOORAY!!
It's coming to our 4th lesson for telecommunication &networking.
We are going to learn topology, protocol and architecture for this week's lesson.
At the beginning of the lesson, Dr Dayang showed us the definition of topology.


TOPOLOGY


Topology is the study of the arrangement or mapping of the elements such as links and nodes of a network.
Physical topology -The physical layout of devices on a network.It can also be defined as the way that the     devices on a network are arranged and how they communicate with each other

There are 6 types of physical topology:

1)Linear bus

2)Ring 

3)Star

4)Star-wired ring

5)Tree

6)Mesh

Linear bus topology

A linear bus topology consists of a main run of cable with a terminator at each end. All nodes are connected to the linear cable.

Ring topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either “clockwise” or “counterclockwise”). A failure in any cable or device breaks the loop and can take down the entire network.

Star topology

A star topology is designed with each node connected directly to a central network hub or concentrator.

Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer’s network access and not the entire LAN. 

Star wired topology

In the star-wired ring physical topology, the hubs are "intelligent." If the physical ring is somehow broken, each hub is able to close the physical circuit at any point in its internal ring, so that the ring is restored.

Tree topology

A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Mesh Topology

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination.

PROTOCOL

Protocol is a set of rules that governs the communications between computers on a network.

Logical topology are bound to network protocols and describe how data is moved across the network.

Examples of protocol:

1. Ethernet

2. LocalTalk

3.Token Ring

4. FDDI


ETHERNET


Is a common logical bus topology protocol.
Early Ethernet network were half duplex, uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection), a system where each computer listens to the cable before sending anything through the network to avoid collisions.


LOCAL TALK

Is a network protocol that was developed Macintosh computers.

Used a method called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), where a computer signals its intent to transmit before it actually does so.

The disadvantage of local talk is its slow speed (only 230 Kbps).

TOKEN RING

Its access method involves token-passing.

The computers are connected so that the signal travels around the network from one computer to another in a logical ring. 

FDDI

Fiber Distributed Data Interface is a network protocol that is used primarily to interconnect two or more local area networks, often over large distances.

A major advantage of FDDI is speed. It operates over fiber optic cable at 100 Mbps.

ARCHITECTURE

Network architectures are sometimes classified into two broad categories:

1）Peer to peer architecture 

2）Client server architecture

Peer to Peer architecture
In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network.

Client server architecture

Client server architecture allows the network to centralize functions

and applications in one or more dedicated file servers. The file servers become the heart of the

system, providing access to resources and providing security.

ATM (ASYNCHRONOUS TRANSFER MODE)

ATM is a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.