In the previous article we introduced the concept of a LAN and then dwelt in detail about the Connection Media, which is one of the important components of the LAN Hardware. In this we would focus on LAN Interfaces, Hubs and Switches, which are the other important components of the LAN hardware one by one.

LAN Interfaces

Once the cabling is laid there needs to be an interface that would allow it to connect it to the computers where all the information, data and applications are resident. Typically the physical connection to the LAN is made through a Network Interface Card (NIC). This card also is sometimes called a Media Access Control (MAC) card. The MAC card is installed in the computer much the same way as a video graphics adapter card or a CD-ROM controller card. Some computers come with built-in network cards. A laptop computer can access a LAN with a PCMCIA LAN card or even through a parallel port adapter, which allows the computer to talk on the network through the computer’s printer port.

Again, the functionality remains the same whether the computers use a parallel port adapter, a PCMCIA card, or a standard LAN card. The network card, in whatever form, provides a path for the data to travel from the computer to the LAN cabling. There are two most popular types of network interface cards used today in local area networks, and a few more new technologies are gaining popularity. The primary differences between them are in the way they “package” and transmit the data to the cable and the speed at which they transmit.

Ethernet/802.3

The Ethernet or 802.3 network is probably the most commonly used network interface card. Ethernet networking was first developed by the DEC (Digital Equipment Corporation). The Institute of Electrical and Electronic Engineers (IEEE) in the IEEE 802.3 standard defined a variation of DEC’s Ethernet technology. The Ethernet card can transmit 10 or 100 million bits (a bit is a binary 1 or 0) per second on the LAN cable. Ethernet uses either a bus or a star topology.

Since a predominant number of installations these days are done using Twisted Pair cable as the connection media and considering the constraints of space we will limit our focus to star topology. The star topology uses twisted pair cable. In this topology, each computer has its own twisted pair cable that connects the Ethernet card to a connection port on a hub or concentrator or switch, as shown in the Figure. Inside the hub is the equivalent of the single cable that connects to all the hub ports. The advantage of using a star topology is that if any one cable that runs to a computer is damaged, the other computers can still communicate over the LAN. The only real disadvantage is that you must run a separate cable for each workstation. Many LAN designers feel that the benefits of the twisted pair star far outweigh the disadvantages and the twisted pair hub approach to Ethernet networking is very widely used.

Token Ring

Token Ring was developed by IBM and is found mainly in mainframe or IBM AS/400 environments. Token Ring comes in two different versions - the 4Mbps and the 16Mbps version.
As with Ethernet, Token Ring has an IEEE equivalent in the 802.5 standard, but they differ slightly in the way they package data into frames for transmission onto the network. The IBM Token Ring uses twisted pair cables and is set up in a star topology with each computer connected to a hub or concentrator. The 802.5 Token Ring also operates over twisted pair cables and can be in a star topology or an actual ring where each computer is connected to the next and the last computer is connected back to the first to close the ring, as shown in the Figure.

Unlike Ethernet, the communications over the Token Ring network are moderated by means of an electronic token-hence the name. Each computer on the network must wait to transmit data until it receives the token. Using this method, there is no possibility of data collisions created when two computers “talk” at the same time.

Active Components ( Hubs and Switches)

There is some additional hardware that you can use in local area networking, some of which we mentioned earlier. This includes the hubs that are used in the twisted pair Ethernet LAN. The hub is the device to which all the twisted pair LAN computers are connected. These hubs come in a variety of makes and models, and selecting one can be based largely on price. However, as with the servers, you probably don’t want the cheapest one in your LAN. A good rule is to eliminate the cheapest and the most expensive models and what’s left will probably serve the average LAN pretty well.

A variation on the hub concept is the switch. A switch has ports just as the hub does, but the switch is smarter than a hub. The switch learns all the addresses (the unique network identifying numbers that are on each network interface card) of all the computers on the LAN. The switch knows what address can be found on each of its ports. When you issue a login or connect request to a server, the switch sees the request and connects the calling port directly to the called port.

This is similar to the phone company’s switching. The advantage is that the connect request doesn’t have to circulate around the network looking for the right address. The switch knows which port the server is on and connects you directly.

Because the switch is handling all the connections, fewer transmission problems occur, and more time is spent sending data instead of collision messages. Switches were first used for Ethernet networks, but now there are switches for Token Ring LANs as well. If you are supporting the heavy-duty applications, such as Computer Aided Design and Software Engineering packages on your LAN, or if your LAN is simply very busy with several users, you may be a candidate for a switch. If users are complaining that it takes forever to send and receive data and that the collision lights on your equipment are constantly flickering, you may need a switched LAN.

There is a lot of leeway in the day-to-day operations of the local area network. Every little connector and cable need not be the same type or engineered down to the micrometer. Every workstation need not be set up exactly the same in terms of operating system and hardware performance. Establishing solid maintenance schedules and backup routines will go a long way in keeping your network running smoothly and efficiently

The author Paul Devkumar Ranjan is with Bangalore Labs, which is into Internet Infrastructure management. For obtaining Part-I of this article series on setting up a LAN network as well as queries, please mail: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it \n This e-mail address is being protected from spam bots, you need JavaScript enabled to view it "

Issue BG3 June01

Related Items:

---

Be first to comment this article

Only registered users can write comments.
Please login or register.