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How Fat is Your Pipe?
Deciphering Internet and Wide Area Networking
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In simplest terms, today’s globe spanning computer networks, including the Internet, are little more than very long electrical circuits between computers. Unfortunately, understanding the technology that goes into each circuit is far from simple. This month’s Technology Corner will help decode the jargon of our connected world. From a function perspective, the most basic part of a network is the circuit that connects a person’s local device to a distant device. For example, when you make a phone call, your telephone is creating a circuit between your local phone and the phone of the person you are calling. These circuits are created with a vast array of technologies from regular wires to fiber optics and microwaves. Leaving the actual devices aside, the stuff between the two devices used to exchange information is commonly referred to as pipe while the actual circuit is called a network connection or tunnel. Network connections are classified by the distance between the end points: for example, local area (LAN), metropolitan area (MAN), or wide area (WAN). These names do more than tell how the distance between connected devices; they also reveal the complexity and type of tunnel information travels through. The type of tunnel dictates many factors including the reliability, performance, and security of the connection. Short tunnels, LANs, are more reliable, have better performance, and offer greater security than long tunnels like WANs. More complex connections loose fidelity because they rely on equipment outside of the users control. Specifically, all the wire and connecting equipment in a LAN connection is located on premises and to at least some degree controlled by the user while MAN tunnels use equipment owned by the user’s network provider and WAN tunnels use equipment from any number of third parties. The Internet is a WAN since Internet connections are travel over public circuits known as the Internet backbone. A big part of networking magic is the ability to build connections that span networking equipment owned by different people. This magic comes from a specialized piece of equipment, commonly known as a router. Routers determine the path, or route, of each information tunnel. An individual connection will typically use between 2 and 16 different routers. The connection between each router is known as a hop; so the network distance between two devices is counted in hops. Each hop in a network connection is a link in your information chain. The strength of link is measured mainly by the amount of data that can be transferred across it. A link’s data transfer capacity, or its bandwidth, is usually measured in terms of how much data moves over the link in a period of time. Lets consider a typical 1.5 Megabit file. That file would take 26 seconds on a typical modem at 56 kbs (kilobits per second). The same file requires 1 second on a 1.5 Mbs (megabits per second) T1 WAN link and just 0.15 seconds a 10 Mbs LAN connection. Links with lots of bandwidth are known as either “broadband” or “fat” while limited bandwidth links are titled “narrowband” or “small.” Bandwidth is not the only measure of a link’s capacity. Since most network links are shared by many connections, even fat pipes can become congested. The amount of data traveling on a link is called traffic. When the amount of traffic nears the bandwidth of a link, it will reduce its bandwidth to meet demand or may stop making connections. Users experience this type of overload as either very slow or unreliable connections. Since a network connection hops in sequence over each information link, the usable bandwidth of the entire tunnel is limited by the smallest link. That link becomes the bottleneck in any information exchange. Generally, the smallest link in the chain is the pipe from the user’s LAN to the Internet. When someone asks, “how fat is your pipe?” they usually want to know the bandwidth of your connection to the Internet. Of all the links in a connection tunnel, Internet connections are the most confusing. The industry jargon for this link is “the last mile” because it is the typically the a relatively short distance between the user’s office and Internet service provider’s (ISP) router. Even though the distance is short, someone must still run a set of wires (aka a local loop) between the office and the router sitting in the ISPs switching room (aka point of presence or POP). Luckily, local phone service monopolies already have many wires running from office and homes to their POP. Generally, an ISP will piggyback on this infrastructure to link users to their router and establish an Internet connection. The type of connection they use depends on the type of equipment available. For example, an analog modem turns traditional phone lines into a temporary Internet connection, an ASDL modem turns the same line into a permanent (known as tied) high-speed connection , or you can lease a traditional T1 voice circuit to carry data traffic. Some wireless technologies are emerging that may eliminate last mile issues, but they are not fully matured. The table below lists the most common connection types. In a future Technology Corner, we will build upon this networking primer to cover advanced topics like virtual private networks (VPN) and Internet telephony (aka Voice over IP or VoIP). Until then, stay connected! |
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Table 1: Bandwidth by Pipe
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Originally appeared in Midrange Enterprise,
Sept 2000. Used with permission.