Networking Topologies and Tcp/ip Protocol

Networking Topologies and TCP/IP protocol

Bus Topology

It just doesn't get much simpler than the physical bus topology when it comes to connecting nodes on a Local Area Network (LAN). The most common implementation of a linear bus topology is IEEE 802.3 Ethernet. All devices in a bus topology are connected to a single cable called the bus, backbone, or ether. The transmission medium has a physical beginning and an end. All connections must be terminated with a resistor to keep data transmissions from being mistaken as network traffic. The terminating resistor must match the impedance of the cable.

One advantage of bus topology is that small networks are fairly easy to set up and does not require specialized networking equipment. It is also fairly inexpensive to set up, since it requires the least amount of cable and equipment. Adding or removing nodes is fairly easy, but moving nodes without affecting neighboring nodes can be difficult.

Troubleshooting media problems on a bus networks can be very tedious, since a break in the backbone will bring down the entire LAN. For this reason, bus topology is not considered one of the more robust network topologies, compared with star or mesh. A loose or missing terminating resistor can also bring down a LAN.

Star Topology

In this topology, all nodes are connected to a central device, usually a hub or a switch. Each connected device has a dedicated, point-to-point connection between the device and the hub. The star network topology is by far the most widely implemented topology in use today.

Star topology networks require more cabling than bus, but the tradeoff comes in the form of a more solid network topology. A break in the network media will only affect a single node, since every node has a dedicated connection to the central device; a hub or switch. This also makes the central device a Single Point of Failure (SPOF). Redundant or failover switches are often used to eliminate the SPOF in a star LAN.

Building a star topology is much more expensive and time consuming than the bus network. The increased costs come in the form of cabling and the central device(s). However, star topologies can be easily expanded to accommodate more nodes and troubleshooting is much easier because connectivity problems are simpler to isolate than a bus network.

Mesh Topology

Perhaps the most redundant, fault-tolerant of all network topologies is the mesh LAN. Each node is connected to every other node for a true point-to-point connection between every device on the network. Should one cable fail, network traffic can be rerouted to the destination via an alternate path.

While the mesh topology is by far the most robust of the LAN topologies, the tradeoff is cost, complexity, and difficulty of troubleshooting. Mesh requires the most cabling of any topology. Because of these disadvantages, a true mesh topology is seldom used. Instead, a hybrid mesh, with redundant cabling paths to critical network devices like routers, is sometimes used in the core layer of networks.

Ring Topology

Ring topology is actually a logical ring, which means that while the data travels in a circular pattern from one node to another, the cabling pattern can take on any form. Since each station acts as a repeater, greater distances can be spanned with a ring network than other physical topologies. Ring networks can also offer higher bandwidth with almost no signal degeneration. Fiber-optic media is commonly used in modern ring topology.

An advantage of the ring network is troubleshooting and isolating a break in the media is much easier than other topologies. Some ring technologies have the ability to locate the break for the technician. When a break does occur, the network is effectively down. Many modern rings are built with a redundant or secondary ring to make a more fault-tolerant network. This dual-ring is referred to as Fiber Distributed Data Interface (FDDI).

Comparison of Network Transport Protocols

Ethernet (IEEE 802.3 CSMA/CD) has several advantages over other transport protocols like Token Ring and wireless. First of all, Ethernet hardware and cabling is relatively inexpensive, compared with FDDI or wireless. The simplicity of Ethernet also reduces the expense of maintenance and support. Second, Ethernet allows for various types of networking media such as twisted pair, coaxial, and even fiber. Ethernet also offers more security than wireless, since connectivity requires physical access to the wire.

While wireless is often considered Ethernet, it uses CSMA/CA (Carrier Sensing Media Access/Collision Avoidance). Wireless network security and signal interference has been a real concern for network administrators. Most of these concerns have been addressed, but the reputation of being a largely free and wide-open media still lingers.

Perhaps the greatest advantage of wireless networks is the freedom from physical cabling. Laptop users can finally use their machines as they were intended; away from a desk. Unfortunately, wireless LAN standards (IEEE 802.11) are considerably slower than their wired counterparts. 802.11a wireless is capable of speeds up to 72Mbps; however, it is currently restricted to a throughput of 54Mbps by the FCC.

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