Computer Networks and Protocol

The OSI Reference Model

By Brandon Bielstein



Since the OSI Model is a reference rather than a standard, it leaves room for standards of many different designs and applications to be made in its image. Based upon OSI Layers One and Two, these standards fill the gaps that exist in both technology and geographical distance allowing digital communication to spreader farther, carry information faster, and cost less.



Ethernet is used to link computers in both small residential and large commercial situations and is the most widely used Network Hardware Standard today. It often delivers internet access from other longer range hardware standards to multiple computers within a home or workplace. Ethernet equipment is relatively small, affordable, and can carry data at high speeds. The original specification called for speeds of 10mbps9, while newer technologies have brought that speed today to lie between 100mbps and 1000mbps. Ethernet is rarely used outside the of local area networks found inside of business or homes due to it's range limitations. Ethernet installations typically can not run for more than a few thousand feet. This leaves other network infrastructures to link computers over great distances. Ethernet most commonly forms what is known as the LAN, or Local Area Network. A LAN is a collection of computers in close proximity that are linked together to form a network. This network may then be linked to other LANs via network infrastructure standards with long distance capabilities.

Originally developed at Xerox's PARC10 facility, the project was predominately conceived and headed by a man named Robert Metcalfe. In 1976, Metcalfe and his team published a paper entitled Ethernet: DIstributed Packet Switching For Local Computer Networks which drew out conceptual specifications for the Ethernet standard. Though the standard defined in his paper was for 3mbps 8bit communication, Ethernet would soon evolve into its more modern-day form when Metcalfe left Xerox to form 3Com. In 1980, he encouraged major companies such as DEC, Intel, and Xerox to participate in a standard he called "DIX" (for DEC, Intel, Xerox). This standard defined Ethernet as having 10mbps speeds and would end up competing directly against the day's largest proprietary systems.

The Ethernet standard demonstrates its flexibility by supporting multiple transmission mediums. The original medium, known as 10BASE-2, utilized BNC11 type coaxial connections and coaxial cabling. This was the standard for many years, transmitting data at a rate of 10mbps. 10BASE-2, however, became increasingly cumbersome, requiring high maintenance. A complete circuit was required for proper operation, meaning that a single failed node or cable break on a large network cause a cease of proper operation. In the early 90s, the newer 10BASE-T standard emerged. 10BASE-T utilizes twisted pair cable, which is similar to copper phone lines but differs in that it carries four twisted pairs instead of one or two. Operating at speeds of either 10mbps, or later 100mbps (100BASE-T), this standard has become and remains the most widely used network standard in the world. In the late 90s, Gigabit Ethernet came into existence, allowing for transfer speeds of up to 1000mbps over the same twisted pair cabling. The Gigabit Ethernet standard is also capable of transmitting over optical cable, though this ability has not gained a following due to the existence of superior high end fiber optic network standards.

While there are numerous other standards operating under the IEEE 802.3 specification, most others are used in niche markets or private deployments for very large network backbones. Ethernet has been and will remain for years the most used standard for the transmission of digital information over short distances.


WI-FI (802.11x)

Wi-Fi is a standard developed to perform nearly the same role as Ethernet does in consumer settings, but without the wires. Taking to the air, Wi-Fi allows a node to lie anywhere within a 100 to 1000 foot range of a Wi-Fi enabled router and have a constant, secure connection to the Local Area Network. Wi-Fi originated with speeds of just 11mbps in the form of IEEE 802.11b, but today can achieve speeds between 54mbps and 108mbps.

In 1991, the original Wi-Fi standard was developed at AT&T by a man named Vic Hayes. It was initially designed to provide wireless communication for cashier systems in retail locations and operated at speeds of 1 or 2mbps. In the late 90s, the IEEE ratified the 802.11b specification, providing wireless ethernet-like connectivity for nodes at speed steps between 1 and 11mbps. The varied speeds allowed a node's hardware to switch to a lower transmission speed when further from the access point12 in order to maintain the connection over a longer distance.

In 2003 and 2004 IEEE 802.11g, a newer standard based on the Wi-Fi specification, emerged. 802.11g provides speeds between 11 and 54mbps while still maintaining backward compatibility with the older 802.11b standard and it's 1 to 11mbps speed range. This means 802.11g is able to offer superior speeds while still capable of reverting to lower speed, long range transmission rates when necessary.

In 2005, an even newer standard began to emerge known as 802.11n. While not officially ratified to date, so called "Pre-N" devices have begun to be sold in the consumer marketplace based upon the 802.11n standard that is still in the ratification process at the IEEE. The 802.11n specification calls for transmission speeds of 108 to 540mbps while still maintaining full support for the 802.11b/g standards speeds between 1 and 54mbps. While in the 802.11g standard the longer range, lower speed backward compatible 802.11b standard was utilized to increase the range and connection stability nodes received when further from the 'g' access point, 802.11n uses previous standards almost exclusively for compatibility with older equipment. This is due to the fact that 802.11n devices are able to communicate at 54 to 108mbps speeds at ranges greater than those offered by 802.11b when operating at 1 to 5mbps. 802.11n is not expected to begin to receive widespread adoption until late 2006 or 2007, both because it has not yet received IEEE certification and it has the current standard's enormous market saturation to attempt to replace.

The issue of range has greatly marred the performance of 802.11 equipment for years. This problem is obvious when it is considered that most 802.11b equipment actually only operates at 5 to 7mbps, and 802.11g equipment at 24 to 36mbps during real- world use. Fortunately, with the improvements brought by the 802.11n and future standards, this problem will begin to fade as the speeds achieved during everyday use close in on the technical maximum speeds offered by emerging standards.


BLUETOOTH (802.15.1)

Bluetooth, IEEE 802.15.1, is a short range wireless network standard originally developed by Ericsson Corporation. Designed to allow nodes to participate in a network using the lowest possible amount of power, Bluetooth supports three power/range levels: 1mW/10cm, 2.5mW/10m, and 100mW/100m. Bluetooth's current maximum transmission rate is 2.1mbps. While this seems very low compared to much older Wi-Fi standards such as 802.11b, Bluetooth is designed to fit a special section of the market, rather than to be a widespread, high-performance technology. Bluetooth is almost always used in a paired or "ad-hoc" type network. In an ad-hoc network, no router exists, but the nodes are simply responsible for negotiating communication among themselves automatically. A paired network is simply an ad-hoc network with only two nodes.

Common Bluetooth devices and applications include mobile phone headsets, PC-to-organizer/PDA synchronization, and other situations in which small devices need low power, short range communication capability. Bluetooth is a staple feature on most of today's newest and smallest portable information and communication devices.

9 mbps; Megabits per second. Equal to roughly one million bits per second.
10 PARC; The Xerox Palo Alto Research Center located in Palo Alto, California.
11 BNC; A type of RF connector used for terminating coaxial cable. The connector was named after its "Bayonet" locking mechanism and its two inventors "Neill" and "Concelman".
12 Access Point; Commonly the term for a wirelessly enabled network router or switch.