Network Technologies

Ethernet

Of all of the current Local Area Network (LAN) technologies available, Ethernet is the most popular industry standard. This networking standard is defined by the Institute for Electrical Engineers (IEEE) in a standard they created entitled IEEE Standard 802.3. The standard defines the rules for configuring Ethernet as well as the protocol that allow computers to communicate. A protocol is a standard that allows computers to communicate with each other by defining the following: how they identify each other, the form that the data should take in transit, how the information should be reconstructed once it reaches its final destination, and how damaged transmissions are handled. TCP/IP, IPX, AppleTalk, and NetBEUI are all examples of protocols that operate on the Ethernet standard.

Ethernet is typically deployed in two basic topologies called "bus" and "star". A bus topology consists of nodes connected together by a single long cable. The bus topology connections are made by using one of two different types of coax cable. The first is called Thickwire, also known as 10BASE5 and the second is called Thin coax, also know as 10BASE2. An advantage of a bus topology is the easy, low cost expandability because you do not need a hub, but a major disadvantage is that any break in the line will disable the entire line. A star topology links two nodes together on the network. It consists of a central point that each of the nodes is connected to. The advantage here is each connection is independent, so that if a line breaks, only that particular node is affected. The disadvantage is the need for central point equipment. This central point is called a hub or switch. The connections from the hub or switch to the nodes are made using a type of wire called unshielded twisted pair (UTP), commonly known as 10BASE-T. An advantage of this kind of cable over 10BASE5 or 10BASE2 is cost. It is much cheaper as well as easier to work with and install. A major disadvantage to UTP is the maximum cable length of 100 meters. This cable is a 4 wire-pair structure that is very similar to telephone cable in appearance and comes in a variety of grades, with level 1 being the lowest quality and level 6 being the highest, and thus the best. The speed at which data is transmitted over these lines is 10Mbps or 10 mega-bits per second.

Token Ring

Token Ring is a LAN protocol first developed by IBM and later standardized as IEEE 802.5 that was published in 1985. Data access to the network is controlled by a token passing Media Access Control (MAC) protocol. The token is passed from one station to another according to rules. When each station gets the token, it has permission to transmit data. When the data is returned to the sender, the token removes the station from the ring. Token Ring was first released as a 4Mbps data transmission rate and later was improved to 16Mbps.

Token Ring is a logical ring topology, meaning it can be physically configured as a ring or star topology. The passing of the token is just a logical definition of how the technology works. Token Ring can be operated on UTP, Shielded Twisted Pair (STP) also known as Type 1, coaxial cable, and fiber. Typically, a Token Ring network is constructed in a star topology using a device called a Multi-Station Access Unit (MSAU) which uses STP cabling, as the use of UTP will limit the size of a ring to 72 nodes whereas 250 nodes are possible using STP.

A chief advantage of Token Ring is its efficiency. This means that during the communications process, there are no collisions because the token is passed at certain, clearly defined times, thereby reducing the need for retransmissions. A big disadvantage is the fact that a Token Ring network is much more costly to implement than other more popular networks like Ethernet due to the higher hardware and cabling costs. It is also more difficult to install than Ethernet because of the size, weight, and stiffness of the STP cable.

Fiber Distributed Data Interface (FDDI)

Fiber Distributed Data Interface (FDDI) is the oldest 100Mbps LAN type commonly available. It is often used as a backbone technology to interconnect several smaller Ethernet or Token Ring networks and for other high speed reliable network connections. FDDI can combine ring, star, and tree topologies in one network to build very large networks.

FDDI can use four different cable types: Multimode Fiber Optic Cable, Singlemode Fiber Optic Cable, CAT 5 UTP, and IBM Type 1 STP. Each type