Computer Networks

Coordonator: Mr. Dr. Z. Pólkowski Dobrica Adrian

• Definition & Caracteristics• ArcNet • Token Ring• Ethernet• FDDI

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A network is a group of two or more computer systems linked together. There are many types of computer networks, including the following:

• local-area networks (LANs): The computers are geographically close together (that is, in the same building).

• wide-area networks (WANs): The computers are farther apart and are connected by telephone lines or radio waves.

• campus-area networks (CANs): The computers are within a limited geographic area, such as a campus or military base.

• metropolitan-area networks MANs): A data network designed for a town or city.

• home-area networks (HANs): A network contained within a user's home that connects a person's digital devices.

http://www.webopedia.com/TERM/N/network.html

Definition & Caracteristics

http://www.webopedia.com/TERM/N/network.html

ARCnet

• In September 1977, the world's first commercially available local area network was first put into service at Chase Manhattan Bank, New York, as a beta-site. 

• Short for Attached Resource Computer network, ARCnet was developed by Datapoint Corporation in San Antonio, Texas. It was defined as a group of nodes that communicates to one another over a geographically-limited area usually within one building or a campus of buildings. 

• It was the simplest, and least expensive type of local-area network. It used a token-ring architecture, supported data rates of 2.5 Mbps, and connected up to 255 computers. A special advantage of ARCnet is that it permitted various types of transmission media to be mixed on the same network: twisted-pair wire (Max. extension 150 meters), coaxial cable (650 m.) and fibre optic cable (2.000 m.) 

• The ARCNET Trade Association (ATA) is no longer a structured organization of ARCNET users and manufacturers but instead has become a virtual organization carrying out its original mission by providing information and standards for users of ARCNET technology.

http://www.alrcnet.com/http://www.old-computers.com/history/detail.asp?n=23&t=3

History

• To start off, ARCnet is not a standardized network. All information provided here is gathered through the years by different people and by just making mistakes, so if you have other experiences don't be surprised, but share them with us.

• This way we can all learn from it.• ARCnet (Attached Resource Computer NETwork) was originally developed

by Datapoint Corporation in 1968, way before OSI and the like. The original purpose was a harddisk interface, later it became popular as a local area network.

• All distaces are rough estametes. The actual calculation should be done like this: an active device provides 24 Volt output, and needs atleast 5 Volt on the receving pins.

http://ckp.made-it.com/arcnet.html

How ARCnet works

Token Ring

• Token ring local area network (LAN) technology is a protocol which resides at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that travels around the ring. Token-possession grants the possessor permission to transmit on the medium. Token ring frames travel completely around the loop.

• The Token Ring protocol is the second most widely-used protocol on local area networks after Ethernet.

• The IBM Token Ring protocol led to a standard version, specified as IEEE

802.5. Both protocols are used and are very similar. The most common

local area network alternative to Ethernet is a network technology

developed by IBM, called token ring. Where Ethernet relies on the random

gaps between transmissions to regulate access to the medium, token ring

implements a strict, orderly access method. A token-ring network arranges

nodes in a logical ring, as shown below. The nodes forward frames in one

Direction around the ring, removing a frame when it has circled the ring

once.http://searchnetworking.techtarget.com/definition/Token-Ring

http://en.wikipedia.org/wiki/Token_ring

Definition

Unlike Ethernet, Token Ring uses a ring topology whereby the data is sent from one machine to the next and so on around the ring until it ends up back where it started. It also uses a token passing protocol which means that a machine can only use the network when it has control of the Token, this ensures that there are no collisions because only one machine can use the network at any given time. Token Ring networks are now very rare because the cost and flexibility of Ethernet came to dominate the marke. When the first Token Ring computer comes online, the network generates a token. The token is a predetermined formation of bits (a stream of data) that permits a computer to put data on the cables. The token travels around the ring polling each computer until one of the computers signals that it wants to transmit data and takes control of the token. A computer cannot transmit unless it has possession of the token; while the token is in use by a computer, no other computer can transmit data. After the computer captures the token, it sends a data frame out on the network.

http://www.datacottage.com/nch/troperation.htm#.VRbaWi7AqOV

How Token Ring works

http://en.wikipedia.org/wiki/Token_ring

• Initially (in 1985) token ring ran at 4 Mbit/s, but in 1989 IBM introduced the first 16 Mbit/s token ring products and the 802.5 standard was extended to support this. In 1981,Apollo Computer introduced their proprietary 12 Mbit/s Apollo token ring (ATR) and Proteon introduced their 10 Mbit/s ProNet-10 token ring network in 1984. However, IBM token ring was not compatible with ATR or ProNet-10.• Token ring LAN speeds of 4 Mbit/s and 16 Mbit/s were standardized by the IEEE 802.5 working group. An increase to 100 Mbit/s was standardized and marketed during the wane of token ring's existence while a 1000 Mbit/s speed was actually approved in 2001, but no products were ever brought to market.IBM slowly adopted 100 Mbit/s as the reasoning was that the reduction of collisions allowed better bandwidth.

Token Ring speeds

Ethernet

Information

http://en.wikipedia.org/wiki/Ethernet

• Ethernet is a family of computer networking technologies for local area networks (LANs) and metropolitan area networks (MANs). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3 and has since been refined to support higher bit rates and longer link distances.

• Over time, Ethernet has largely replaced competing wired LAN technologies such as token ring,FDDI, and ARCNET. The primary alternative for contemporary LANs is not a wired standard, but instead a wireless LAN standardized as IEEE 802.11 and also known as Wi-Fi.

• The term 'Ethernet' refers specifically to a set of standards for connecting computers in order they can share information over a common wire or network. Strictly speaking, ethernet systems should comply to the International Standard ISO/IEC 8802-3 or IEEE 802.3.

• As in all systems, there are reasons to use an ethernet network, but also difficulties that must be overcome. The main advantages of ethernet are:

• The ability to carry several hundred times more information on a single cable than would be carried on a typical serial cable. Whereas DMX512 operates at 250kb/s, Ethernet operates at 100 Mb/s - 400 times faster.

• The ability to connect multiple devices in a single network, regardless of the information interchange relationship between the devices. Ethernet allows all devices in the network to communicate.

• A reduction in the amount of cable required. Economic factors will drive the demand for this technology.

http://www.webopedia.com/TERM/E/Ethernet.html

Ethernet is standardized in IEEE 802.3 IEEE standard series. These standards allow data transmission through multiple physical media, such as:

• coaxial cables• twisted pair cables• fiber optic cables

How to send data

http://en.wikipedia.org/wiki/Ethernet

Clasification

Source: http://www.webopedia.com/TERM/E/Ethernet.html

Fast Ethernet Tehnology

Gigabit Ethernet Tehnology

FDDI

Definition

• FDDI (Fiber Distributed Data Interface) is a set of ANSI and ISO standards for data transmission on fiber optic lines in a local area network (LAN) that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users. FDDI is frequently used on the backbone for a wide area network (WAN).

http://searchnetworking.techtarget.com/definition/FDDI

• An FDDI network contains two token rings, one for possible backup in case the primary ring fails. The primary ring offers up to 100 Mbpscapacity. If the secondary ring is not needed for backup, it can also carry data, extending capacity to 200 Mbps. The single ring can extend the maximum distance; a dual ring can extend 100 km (62 miles).

Information

http://searchnetworking.techtarget.com/definition/FDDI

Source: http://www.cisco.com/c/en/us/td/docs/internetworking/technology/handbook/ito_doc/FDDI.html#wp1020549

Therefore a break in the cable will result in the secondary ring being used. There are two network cards which are: 1.Dual attachment stations (DAS) used for servers and concentrators are attached to both rings and a router or switch can link an FDDI network to a local area network (LAN). Normally FDDI is used to link LANs together since it covers long distances. Characteristics Summary:•Topology - Double ring. •Cable - Fiber. •Speed - 100Mbps. •Maximum segment length - 2000 meters. •Media access - Token passing. •Maximum nodes on the network - 500. TroubleshootingPlastic fiber is only useful to 50 meters. Multimode glass is good to 2 kilometers. A tool called an Optical time domain reflectometer (OTDR) may be used to debug this network.