Lane Topologies

Each PC on the network must have access to the network cabling structure so that there is a manageable and systematic flow of information between the file server and workstations. The LAN adapter board produces and regulates this flow. It is the electrical design of the actual LAN card that determines what kind of cable topology it requires.

 

The physical layout of the LAN, or the way the workstations are connected to each other, is called the LAN topology, or architecture.

There are three basic LAN topologies in general use today; the Linear Bus, the Star and the Ring. Some vendors use hybrid topologies combining elements from two of the three basic topologies. Each of three basic topologies has distinct characteristics.

Ring Topology

A ring topology is one in which all stations are linked to form a continues loop. A single channel connects all the computers and there is no central computer in this topology. Data may flow around the ring only one direction. A coded electric signal called a token passes around the ring from station to station. The data transfer rate ranges from 4 MHz Bits per second to 100 MHz bits per second. Depending on the channel selected for transmission.

Advantages of Ring Topology:

1. It provides for deterministic response and access to the LAN.

2. Often has an extensive fault-tolerant feature to ensure proper operation.

Disadvantages of Ring Topology:

1. It is possible that a failed or powered off MAU may cause the LAN to fail.

2. If the central ring is served, the ring will fail.

Star Topologies:

The Hub is installed in a central wiring closet, with all the cables extending out to the network nodes. The advantage of having a central wiring location is that it’s easier to maintain and troubleshoot large networks. All of the network cables come to the central hub. This way, it is especially easy to detect and fix cable problems. You can easily move a workstation in a star topology by changing the connection to the hub at the central wiring closet.

Advantages of Star Topology:

1. Each user has direct access to the shared controller.

2. If a PC workstation fails, the rest of the LAN is unaffected.

3. If a cable is cut or damaged, only the workstation attached to it is cut off from the network.

4. Using media diagnostic tools such as a Time Domain Reflectometer (TDK) is more time consuming and detailed.

Disadvantages of Star Topology:

1. If the shared controller fails, the entire network fails.

2. The number of ports on the controller device limits the total number of PC workstations supported.

3. The more PCs sharing the controller, the slower the aggregate response time.

4. The specialized dedicated controller devices are very expensive.

5. The cabling can be difficult to relocate if a PC is moved another office.

6. Because each PC has its own dedicated cable to the central controller device, the installation can be costly and difficult.

Distributed Star Topology:

The distributed star topology is a hybrid topology. It begins like a linear bus but at interval along the bus a junction box or hub may be attached. From the hub to the workstation it resembles a star type of topology. It is possible to install sub hubs for the purpose of further branching. The distributed star topology is usually combined with the token bus access method. This method allows for a deterministic response to the LAN.

Advantages of Distributed Star Topology:

1. It is usually accompanied by a deterministic access scheme.

2. By using hubs, it is possible to have a large network of cable.

Disadvantages of Star Topology:

1. In order to increase cable or the number of workstations, expensive hubs must be purchased.

2. The more PCs on the LAN, the less time each PC may use the cable.

3. The number of hubs increases the possible number of failure points.

4. It is more time consuming than a linear bus.

5. Each workstation requires its own individual cable.

Tree Topology

Tree topology is the hierarchical bus topology or generalization of bus topology. The node where one or more cables start for branching is called head end, the branches could have more branches for developing complex tree networks. Data travels from every station before reaching the destination.

Bus Topology

Bus network is the most simple and inexpensive of all the networks. A bus has no central controller, and so each network component must be equipped to handle interface problems. The network vendor generally supplies these hardware/software interface elements for specific types of equipments. The data transfer rate is between 1MBPS to 50 MBPS depending on the channel used, with certain limitations.

Advantages of Bus Topology:

1. The linear bus is the most popular topology.

2. It is easy and inexpensive to install.

3. It is very easy to add workstations.

4. It is a very well proven architecture.

5. If a PC fails or is powered down, the LAN is unaffected.

6. A PC booting onto the network has no effect in the LAN.

Disadvantages of Bus Topology:

1. If a piece of the trunk cable is cut or damaged, the entire segment will go down.