Networks have been around for quite some time. And as with most things, they keep changing, becoming faster and hopefully better. While one can never escape legacy networking, the majority of today's networks follow standard architectures, topologies, and protocols, which you'll learn about in this chapter. While we will spend a brief amount of time on the history of networking, we will concentrate the majority of our effort learning about concepts relevant to today's networking.
Upon successfully completing this lesson, you should:
Networking Essentials Plus: Pages 10-48
The network adapter as a commodity was first made by the 3Com Corporation. With the introduction of the EtherLink ISA Ethernet adapter, 3Com provided a relatively cheap mechanism for connecting the first PCs. IBM then entered the picture, weighing into the networking world in the mid-1980s. IBM's foray into the networking world was called Token Ring and was based on a different approach to networking. Whereas it is possible for Ethernet devices to talk at the same time (and their messages to collide, requiring them to repeat them), Token Ring circulates an electronic token around the network and devices are only allowed to "speak" when they have the token. In this way, there is never a collision of transmissions on the network. This simplicity means in theory that network communications are never slowed with retransmissions, allowing for superior throughput. This approach has merit and would later be integrated into Ethernet equipment; however, Token Ring suffered from a variety of technical and market problems.
First, Token Ring equipment was proprietary to IBM and was much more expensive than the standards-based Ethernet. That extra expense didn't provide speed superiority over Ethernet. Because of collisions and retransmissions, the maximum throughput of 10Mb/s Ethernet is considered to be 40% (or 4Mb/s). IBM's Token Ring only ran at 4Mb/s. In retrospect it seems clear that Token Ring did not offset its expense and proprietary nature with functional technical superiority; however, IBM carried great influence into the early 1990s and Token Ring was adopted by many large, high-profile institutions that had always depended on IBM for computer expertise. But by the mid-1990s, these same institutions found themselves establishing gradual replacement of their Token Ring equipment. By 1999, Token Ring held less than 10% of the network hardware market and continued to be much more expensive than Ethernet while improving at a more gradual pace.
If there was any question about Ethernet's lead over Token Ring, it disappeared with the introduction of Ethernet over unshielded twisted-pair (UTP) wiring. Approved as a standard in 1990, the new technology didn't suffer from the network fragility that Token Ring suffered. UTP wiring was also less expensive and less bulky than shielded twisted-pair wire that Token Ring required and the connectors were simpler. Finally, the 10BaseT specification allowed Ethernet to run over Level 3 UTP which was already in the wall of some offices to provide connections for the telephone system.
In the early 1990s, a company called Kalpana made three improvements to the way that Ethernet was delivered that would continue to be implemented through subsequent iterations of Ethernet.
When Kalpana introduced the EPS-700 in 1990, it was the first device that could transmit multiple conversations simultaneously through a concentrating device: the first Ethernet switch. Kalpana demonstrated their switches at conventions simultaneously transmitting two video streams through a five-port switch to underscore the availability of full bandwidth across multiple ports on the switch.
Kalpana also introduced full-duplex Ethernet on its switches in 1993. Full-duplex Ethernet is enabled by the separate transmit and receive pairs in the 10BaseT standard. Coaxial-based Ethernet could never support full-duplex operation since all transmissions occurred on the same cable. By leveraging the difference in wiring, Kalpana was able to double the potential bandwidth between the switch and the computer's Ethernet adapter.
Finally, Kalpana introduced the concept of the Etherchannel which is basically multiplexing Ethernet over multiple connections between switches. A two-wire Etherchannel with full-duplex operation could provide a theoretical bandwidth of 40Mbps between two Kalpana switches.
Kalpana was eventually acquired by Cisco Systems.
Topology: Refers to the layout of a network and how computers are connected to one another.
Protocol: Refers to standards. In terms of networking, protocols provide rules and standards by which hardware and software must be designed to properly interact with one another. Protocols allow hardware and software manufacturers to design networking equipment that works across brands. Protocols require these manufacturer's products to follow a set of rules, or a protocol.
Probably the most common type of network, a LAN, or Local Area Network, is comprised of a collection of devices (mainly computers) that are connected to one another electrically. This means these devices can receive each other's electrical signals over common collection of wires, cables, or even wirelessly. Computers in a LAN are usually physically connected to the network at all times (although they might not be turned-on all the time).
A WAN, or Wide Area Network, is a collection of LANs connected together, allowing computers separated by large distances to still exchange data. While WANs do share much of the same networking hardware used by LANs, there is a difference between the two. WANs have some unique hardware and protocols that are tailored to exchanging of large amounts of data at high speeds over long distances.
A MAN, or Metropolitan Area Network, falls somewhere between a LAN and WAN, and is defined in geographical terms. A MAN may cover a city, group of buildings, or less commonly a larger area. In today's world, MANs mainly serve as community networks that provide shared services, such as a wireless internet connection, to the local community or educational institution.
While the distinction between LAN, MAN, and WAN is useful in understanding the purpose of such networks, one cannot distinguish between them by solely looking at the technology that is being used to create one or the other. LANs, MANs, or WANs use similar technology and concepts, and the distinction mainly exists in how they are used.
An emerging type of network is the PAN, or Personal Area Network. A PAN is a wireless connection between devices that are relatively close together for the purpose of eliminating wiring. For example, a PAN could be used to allow a computer to use a printer without needing to physically plug-in a printer cable from one device to the other. Or a PAN could allow a user to listen to a portable music player without a cable between the player and the headphones. The PAN is differentiated from a wireless LAN because the maximum distance between devices in a PAN is only a few meters whereas in a wireless LAN devices may be over a hundred meters apart. Bluetooth technology is becoming the most common PAN technology, allowing cables between devices, such as a mouse, keyboard, or printer, to be replaced wirelessly. Today, there are a wide range of Bluetooth enabled devices available, including mice, keyboards, printers, headphones, and more. However, adoption of Bluetooth is not as widespread as other wireless networking technologies.
Indeed, one of the most well known networks in the world may be one you use every day, the Internet. While the Internet is a very complicated network, it is nothing more then a collection of millions of computers and other devices, connected via a complex set of network connections. When connected together, these devices can share information between one another. When you access a web page for example, you are merely accessing a computer somewhere in the world that is hosting that web site. And thanks to standardized networking protocols, the Internet allows us to access millions of resources in mere seconds. Protocols ensure these computers are following the same set of rules, allowing them to work together.
While wireless networking technologies will be discussed in more detail in a later lesson, it is important to understand how rapidly these technologies are affecting the networking arena. Today, many LANs, MANs, and PANs are going wireless. For example WLANs, or Wireless Local Area Networks, are becoming more common in places from coffee shops to our home to our businesses and schools. A WLAN has the same purpose of a LAN; however, computers are connected to one another by wireless networking rather then cords. Aside from this, WLANs use the same protocols of a regular LAN. In many of these environments neither wired or wireless is the standard, but rather a mix of the two methods. Although less common then WLANs, MANs are also going wireless. Many cities are piloting projects to implement wireless community networks, providing access to shared services, such as an internet connection, anywhere in the city, wirelessly.
Most commonly, a network inside a school building would be considered a LAN. However, many school districts link the many LANs at different schools together to create WANs, allowing the sharing of information as well as centralized administration. Schools are also increasingly adopting wireless technologies, allowing network access almost anywhere, with the proper security precautions of course.