WAN networking 101: A quick primer

Interconnecting PCs is old hat for most network administrators. But it's sometimes easy to forget the basics.

There are three key factors to consider when setting up WAN connections for your sites: networking hardware, network protocol, and network topology.

Network hardware
The most basic piece of networking hardware is the hub. In a typical twisted-pair Ethernet network, a hub simply retransmits packets across all of its ports.

In more advanced networks, however, there is a switch. In essence, a network switch "learns" which machines, clients or servers or other networking devices are located on each port. Then when a packet is received, the switch can route it down the correct cable to the proper recipient.

Then there is a router, which connects different networks to each other, forwarding each packet on to the next network closer to its destination.

A network bridge is another option for connecting networks. However, a bridge doesn't actually "route" packets toward their proper destinations. Instead, it retransmits packets between networks so that they appear to all of the machines as if they were in one large network.

Network protocols
There are a variety of networking protocols that can be used to connect computers on a network:

TCP/IP (Transmission Control Protocol/Internet Protocol) is the primary protocol used on the Internet, and it's often used in LAN environments to connect clients to servers. With TCP/IP, each computer has a unique address on the network. Routers are used to connect networks with different IP network ranges and to allow those computers to "talk" to one another between networks.

The IPX (Internetwork Packet Exchange) protocol also connects computers across a network. It's most popular in Novell-based networking environments, but Windows NT servers and UNIX machines also support it. IPX, like TCP/IP, is a routable protocol (i.e., machines on different networks can talk to one another through a router device). SPX (Sequenced Packet Exchange) is also associated with Novell networks: It provides packet delivery acknowledgement on top of the normal IPX service.

NetBEUI (NetBIOS Extended User Interface) was developed by IBM for use with LAN Manager, and it was the primary networking protocol in earlier versions of Microsoft Windows NT and Windows for Workgroups. While Windows still supports NetBEUI, it isn't a good choice for enterprises that have to support multiple networks. NetBEUI can't be routed, which means that another protocol must be used for connections between WAN and LAN segments.

Network topologies
There are many methods available for connecting clients, servers, and entire networks.

• Ethernet comes in several varieties including 10 megabit, generally called 10Base-T, 100 megabit (100Base-T), and Gigabit Ethernet (1000Base-T). All of them provide close proximity connections for local area networks.
• ATM (Asynchronous Transfer Mode) is a dedicated line switching technology, capable of speeds in the 155 Mbps to 622 Mbps (megabits per second) range. ATM is an excellent choice for a high performance WAN connection, and it's widely used by the major Internet carriers.
• Frame relay is based on the older X.25 analog packet switching technology, and it offers bandwidth speeds ranging from 56 Kbps to 1.544 Mbps.
• FDDI (Fiber Distributed Data Interface) is a fiber-optic-based LAN technology based on token ring. It's capable of 100 Mbps bandwidth and a range of up to 200 km (124 miles), making it an excellent choice for high-demand campus environments.
• T1 and T3 lines differ only in speed. A T1 line offers 1.544 Mbps of bandwidth, while T3 offers 44.736 Mbps. These lines are most often used by ISPs (Internet Service Providers) and by businesses that need broadband connections to the Internet.
• ISDN (Integrated Services Digital Network) offers home and business users up to 128 Kbps of bandwidth over standard telephone system wiring.
• VPN (Virtual Private Network) requires a dedicated box that's typically integrated into a firewall at each site. A VPN box encrypts packets from its network and passes them across the Internet to the destination network, where the corresponding VPN box then decrypts the packets and sends them along to their recipients. When packets are returned, of course, the process is reversed.

The bottom line
The object of networking any organization's networks is to give users access to the information they need. A connection that provides too little bandwidth can be more costly than a more expensive but more capacious connection, because it practically ensures that users will waste time and lose productivity. The price of a faster connection can be recouped more quickly than some administrators realize.

Of course, each situation is different. But given the wide variety of networking options available today, a network administrator should be able to offer users a combination of performance and price that will make everyone happy and more productive.