What *are* the core components of the Internet? Well, there are many ways to slice the pie. In this context, we'll talk about four "core areas" and the components of each.

Core areas:

1. Devices: the hardware that generates physical signals, interprets them, and sends them along the right transmission medium to get to their destination.
2. Transmission media: the means by which signals are sent from one place to another.
3. Software: the internal instructions used by computers to do their job correctly.
4. Protocols: the standard "language" for messages from one device to another for requesting services and replying to the requests. Protocols are not discussed (directly) in this module, but are touched on in several others, including:
   • NG01d: The OSI Seven-Layer Network Model
   • NG04c: Domain Names and IP Addresses
   • NG07c: Internet Standards
   • NG10c: Wide Area Connection Options

In order to understand how the components fit together, some background concepts are helpful.

Background Concepts

Packets

The information transmitted over the Internet is put into packets, which are rather like envelopes or shipping boxes. This concept is discussed in module NG03c; for more detail, read the Linktionary and WhatIs entries.

Bandwidth

The amount of data that can be transmitted in a given time period is known as bandwidth. Why width? Picture a pipe carrying water. The wider the pipe, the more water can be carried in a given amount of time. Bandwidth is measured in bits per second (bps) and its multiples. (Baud is an engineering term that is roughly equivalent to bps, but is not widely used now - it was more common between 1970 and 1990). Multiples of bps:

• Kbps :: kilobits (per second) :: 1 Kbps = 1024 bps
• Mbps :: megabits (per second) :: 1 Mbps = 1000 Kbps
• Gbps :: gigabits (per second) :: 1 Gbps = 1000 Mbps
• Tbps :: terabits (per second) :: 1 Tbps = 1000 Gbps

Service Providers

Most functions of the Internet are carried out by private companies that offer services of different types.

• ISP: Internet Service Providers connect individual and small business users to the Internet by purchasing bandwidth from regional or national network service providers. In southeast Michigan, there are many small ISPs like Provide.net, Michigan Bizserve, Netmeg.org, and others. Larger areas are served by AOL, AT&T, Comcast, TDS, MSN, Earthlink, and others.
• NSP: Network Service Providers connect ISPs to their regional, national, or international networks. NSPs in the United States are private companies link AT&T, Sprint, MCI, Cable and Wireless, and others. In some other parts of the world, NSPs are government owned.

Devices are the hardware that generates physical signals, interprets them, and sends them along the right transmission medium to get to their destination. Let's look at two types of networking devices: those likely to be in the building you're in (or close to it) and those likely to be handling long-distance transmission. There's no hard-and-fast distinction between these two - just a general clustering.

Network adapter

If you use your computer for any kind of networking, whether local-area (LAN) or Internet, your computer has a network adapter.

The network adapter is the electronic device (OSI Layer 1) that allows a computer to attach to a network. Its job is to translate messages (OSI Layer 2) from the computer's internal memory and communication busses to whatever type of network it's designed for. The most common networks now are ethernet for hard-wired communication, and WiFi for wireless communication.

Each network adapter has a Media Access Control (MAC) address, which is a long number that uniquely identifies the adapter on the network.

Switch

A networking "switch" is a general term for any device (OSI Layers 1 and 2) that takes input from several sources and sends output to the desired destination. There are several kinds of switches, including:

• Telephone switch: with the original telephone "switchboard" a human operator connected one phone to another by plugging wires into sockets. Newer ones did the same job automatically, without a human.
• Data switching is done in several different kinds of devices, including:
  • Hub
  • Router
  • Bridge
  • Gateway

See: http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci213079,00.html

Hub

A network hub is a device (OSI Layer 1) from which multiple connections fan out to other devices. The term is taken from the hub at the center of of a wheel. The idea is similar to airports which are hubs for an airline, as Detroit Metro is a hub for Northwest Airlines and Atlanta is a hub for Delta.

Since a network hub is the center of a group of devices, it is also a kind of switch. Signals coming from each device attached to the hub are switched to another device on the hub. The other devices may be close by or distant.

If your computer is connected to a local area network, it's very likely the cable from your computer leads to a hub where all the other computers close to you are also plugged in - for example, all the computers in a classroom would be connected to one or two hub devices.

If your home computer is connected by cable TV, the cable company has located a hub in your neighborhood. These hubs typically handle 8 devices - cable "boxes" in nearby homes. Since all the neighboring boxes are connected to the same hub, they are all part of a local area network; they can communicate with one another and see each other's files unless network file-sharing is turned off. (Just thought you'd like to know. ;-)

See: http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci212294,00.html

Router

When your email message goes from your computer to a friend's, it needs to be directed along the right set of routes. A network router is a device with software (OSI Layer 3) that considers the possible routes a particular message packet might take getting to its destination.

Its job is like a travel agent who considers several options for your flight to New York or Los Angeles, based on time, seat availability, and cost. The "Internet Protocol" (IP) is the most widely used system for routing messages, both locally and around the world.

See: http://searchsmallbizit.techtarget.com/sDefinition/0,,sid44_gci212924,00.html

Bridges and Gateways

The Internet has been described as "A network of networks of networks...". Some of these networks operate with the same protocol, others with different protocols.

• A bridge is a device that allows messages to be sent from one network to another that uses the same protocol - for example, from one ethernet network to another on a local area network. See: http://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci211705,00.html
  
• A gateway is a device that allows messages to pass to networks with different protocols - for example from an ethernet network to a fiber optic (FDDI protocol) network. Gateways can be used for firewall protection, caching frequently-used pages, and logging usage. See: http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci212176,00.html
  

Point of Presence

Internet service providers need to have one or more places where their customers can connect locally. Especially the wide-area service providers like AOL need to provide thousands of local numbers all around the country where subscribers can make a local phone call and connect by modem to the system. These places, often rented from long-distance telephone companies, are their points of presence (POPs) in many communities.

See: http://searchenterprisevoice.techtarget.com/sDefinition/0,,sid66_gci212802,00.html

Internet Exchange, Network Access Points, and Metropolitan Area Exchanges

When the National Science Foundation opened its NSFnet to commercial use forming what we now call "The Internet", regional and national network service providers (NSPs - originally long-distance telephone carriers such as MCI, AT&T, and Sprint) were invited to carry Internet data packets on their networks - for a fee, of course. In order to make that work, there had to be a way for the NSPs (also known in this context as peers) to exchange packets and information about rates and availability of bandwidth. Exchange of these packets between peers is sometimes called Internet Exchange or IX.

Originally envisioned as places where transmission peers could access the NSFnet in the early 1990s, Network Access Points (NAPs) and Metropolitan Area Exchanges (MAEs®) have become major interchanges between long-distance transmission networks owned by different transmission service providers, like MCI, SBC, AT&T, Verizon, and others.

See: http://searchwebservices.techtarget.com/sDefinition/0,,sid26_gci214106,00.html

Routing Arbiter and Routing Servers

While NAPs and MAEs exchange Internet data packets between NSPs, there also needs to be a way for NSPs to exchange information about their rates and bandwidth availability.

See: http://www.linktionary.com/r/routing_registries.html

When NSFnet was privatized to become The Internet in the early 1990s, NSF contracted with Merit Network of Ann Arbor to provide an database of routing availability and rate information to enable the private NSP peers to exchange this information. This was known as the Routing Arbiter, and served from 1992 to 1998.

See: http://www.ra.net/

As the Internet became more self-supporting and new ways were developed for private companies to exchange routing information, services of the Routing Arbiter were decentralized and distributed to the NAPs and MAEs in the form of routing servers. You can think of routing servers as a kind of travel agent for Internet packets, providing information about the fastest and most economical routes to get them to their destination. Routing servers don't actually switch packets: instead, they provide information to the routers that actually switch the packets from one network to another.

See: http://www.linktionary.com/r/routing_registries.html

Transmission media are the means by which signals are sent from one place to another. Some require a physical connection - wires or cables; and some don't - they're wireless.

Categories of cable

Most networked data travels over cables of various kinds. There are several categories:

• Metal (usually copper) cable usually involves two wires running between the devices at either end. One may be used to transmit in one direction while the other transmits data back; or one may be used to transmit data while the other is used to control the transmission process. Transmitting signals over wires usually generates radio-frequency signals, as the wires become an antenna. These signals can interfere with transmission of signals on nearby wires, as well as with normal raid and TV reception, so it is essential to prevent transmission wires from inadvertently becoming antennas. This gives rise to the two major types of data cabling:
  • twisted pair
  • coaxial
• Optical fiber cable

See: http://www.linktionary.com/c/cabling.html

Twisted-pair cable

Radio frequency interference problems can be reduced by taking the two transmission wires and twisting them together. Several categories of twisted-pair cable are in use, mainly for telephone and ethernet cabling. These are classified according to their bandwidth and signal quality, beginning with Cat-1 and the low (slow) end. Cat-5 is commonly used to transmit ethernet signals up to 10 Mbps.

Coaxial cable

Another common way to prevent radio frequency interference is to put one of the wires "inside" the other. This is usually done by having a small solid wire placed inside a metal mesh tube (separated by insulation, of course). Coax, as it is called, is used for TV cables, which now carry a great deal of Internet data, as well as many other applications.

Fiber optic cable

By far the highest bandwidth transmission medium, fiber optic cables combine multiple strands of very fine glass-like material. Lasers "pump" the data as pulses of light through these strands, the fibers guiding the light so that almost all arrives at the far end. Because they use light to transmit data, optical cabling does not suffer from the radio frequency emission problems of metal cables.

Fiber is used for both medium and long-distance transmission, but is somewhat limited in local use by the fact that the glass-like fibers are delicate and tend to break if they are bent around corners that are too sharp.

Long-range radio

Most long-range data transmission by radio is done in the microwave band, which beams radio waves in a straight line. Their can be done either on the Earth's surface, using towers that beam data along a line of sight, usually spaced about 30 miles / 50 kilometers apart.

Microwave transmission is also used between the Earth's surface and satellites in geosynchronous orbit.

Cellular telephone systems use radio waves or a medium range, 3-5 miles / 5-8 kilometers. Data can be transmitted using cellular systems as well; this is done most commonly in Japan, to some extent in Europe, and less in the United States.

Short-range radio

Short-range radio transmission is becoming an increasingly popular way of connecting to the Internet. Two popular protocols in use are:

• IEEE 802.11 series (including a, b, and g variants), also known as WiFi, popular for setting up wireless connections up to about 100 yards / 100 meters. This is useful for local area networking (LANs).
• Bluetooth, which has a range of 3-5 yards / 3-5 meters, is used to connect small devices together. For example, this text is being typed on a wireless keyboard and mouse, which connect using Bluetooth to a receiver attached to the computer. This could be useful as personal area networks (PANs) develop.

Infrared

Infrared is a form of transmission that uses light waves below the range visible to humans. Since it uses light, transmitting and receiving devices need to be in a line of sight and can easily be blocked from one another.

The most common use of infrared is between remote control devices and home entertainment systems, but they are also used between hand-held computers such as Palm Pilots, and even between buildings up to about 1000 yards / 1 kilometer apart.

Software is the set of internal instructions used by computers to do their job correctly. Some of this we interact with directly as users, but the majority of network software works behind the scenes to keep things running smoothly.

Application software

Application software is the set of programs we purchase computers for. In the networking arena, we use applications like Web browsers, email clients, telnet clients, and FTP clients.

Security software

Security software protects our computers from a host of threats: viruses, trojan horses, adware, and worms. This type of software includes:

• anti-virus and similar scanning programs that check our computers for malicious programs (known as "malware");
• firewall software, that examines what comes in and goes out of our computers over the network to make sure our security and privacy are not compromised;
• encryption and certification software, that "scrambles" our sensitive messages and makes sure we are communicating with the organizations we intend to communicate with.

Stack software

The stack is the "team" of programs that prepare our messages to go out over a network, and interpret incoming messages as they arrive. Though these are largely "behind the scenes", programs that form the "stack" sometimes need to be adjusted by us as users - for example, when we change ISPs.

Protocol handler software

Protocols, the "languages" by which computer devices communicate with one another, are handled by software specially developed for the communication process.

Driver software

Drivers are programs that directly control specific devices - not only networking devices, but video adapters, keyboards, disk drives, and anything else that you can plug into a computer.

The most common network drivers on personal computers are for the network adapters. If your computer has more than one adapter - say, if you have both ethernet and WiFi - you would need two separate drivers.

Server software

A server is a computer with software that waits for requests to come in, asking for some type of service - sending a Web file, delivering email, storing files, linking to the command-line of a computer - there are many kinds of servers on the Internet. The software that responds to these requests is, naturally, known as server software.

Router software

Routers also require software to run them: deciding which route is appropriate for any given packet of information.

Gateway software

Gateways bridge the gap between different kinds of networks, and the software that runs them is highly specialized and attuned to the needs of rapid transfer between one network protocol and another.