Ethernet- | CSMA-CD | Topology | Cabling System | High speed Networking LAN

Ethernet is one of the most popular standards for connecting PCs to form a Local Area Network (LAN). Most ethernet systems are able to operate at upto 10 megabits per seconds (mbps), and newer systems are designed for 100 mbps speed. Ethernet defines both the types of network cable to be employed, and the signal levels and frequencies used.

Ethernet is the most widely used and installed LAN technology. Now specified in a standard, IEEE 8019.3, Ethernet was originally developed by Xerox and then developed further by Xerox, DEC, and Intel.

Installation:

An Ethernet LAN installation typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds upto 10Mbps.

The Access method used By Ethernet is CSMA/CD. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.

Topology

Early ethernet systems used a thick (about half a inch) coaxial cable which was tapped at intervals to send smaller cables to each computer. A popular development was the use of 'thin' cables looped to each computer in the system (Example of Ring Topology). A problem with this approach was that if the cable was broken at any point (and it often has to be, to allow computers to be moved) the whole system stopped working. The modern replacement or alternative for 'thin' ethernet is UTP (unscreened twisted pair). The network cable is a twisted pair of wires, connected using phone-type plugs and sockets. UTP systems require a hub, into which all the cables are connected.

In practice, the cable is still a chain between computers like the earlier thin wire, but the hub is able to deal with a cable being disconnected by re-routing internally. This makes the system more reliable, and tidier, in use.

Peer System

Ethernet is a peer system, i.e., all computers on the system have equal (networking) status. There is no 'master' unit which is responsible for deciding whose turn it is to transmit. Some means has to be found to ensure that two units do not try to transmit at the same time. The scheme adopted is called CSMA-CD, carrier sense, multiple access with collision detection. Carrier sense multiple access means that if it wants to transmit, a computer must check that no other unit is doing so. if the line is free, it starts transmission immediately, otherwise it waits before trying again.

Access Method (CSMA-CD):

Ethernet uses the CSMA/CD access method to share network media. The CSMA/CD protocol can be broken down as follows:

1. CS (Carrier Sense) Before trnasmitting, listen for a signal; if none is found, it is okay to transmit.
2. MA (Multiple Access) All computers share the same cable and signalling techniques.
3. CD (Collission Detection) Detect collisions, wait, and retransmit.

Ethernet Cabling Systems
There are 4 commonly used Ethernet cabling systems, which are listed below:

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Cable	description
10Base5	Also Known as RG-8 or Thicknet coaxial cable: carries signals up to 500 meters (1640 feet) at 50 ohms
10Base2	Also known as RG-58 or Thinnet coaxial cable; carries signals upto 185 meters (607 feet) at 50 ohms.
10BaseT	Also known as twisted-pair; the most popular of all Ethernet Topologies, categories include 3.5, and 6 (UTP, or unshielded twisted pair) cable at up to 100Mbps speeds; carries signals up to 100 meters (330 feet)
100BaseT	Also Known as twisted-pair: uses category 5 for speeds upto 100Mbps and category 6 for speed upto 155 Mbps; carries signals up to 100 meters(330 ft)

High-Speed Networking
High speed networking designs are motivated by the limitations of existing network topologies. The basic concept has been to simply increase the data rate of the network. For example, 10-Mbit/sec Ethernet was improved tenfold with the standardization of Fast Ethernet (100 Mbits/sec). For technical reasons, increasing the data rate reduces the maximum station-to-station distance, so alternative schemes such as FDDI (Fiber Distributed Data Interface) are often employed as a backbone technology when long distance and high data rate are required, such as in campus environments. Fast Ethernet can fulfill backbone requirements as long as the network is usually within the confines of a single building.

The typical strategy is to connect servers to backbone, where they can take advantage of the higher throughput. For example, a server connected to a 100-Mbit/sec backbone can simultaneously handle ten clients operating at 10 Mbits/sec with ease.

Pusing the bandwidth even further is Gigabit Ethernet, which operates at a data rare of 1,000 Mbits/sec. Its primary purpose is for use in network backbone or as a replacement for existing 100-Mbit/sec switches.

Still,pumping up the bandwidth is not always a complete solution. While Gigabit Ethrnet can improve backbone performance, local network traffic may still suffer from bottlenecks due to the shared nature of the LANs or the collisions caused under heavy traffic loads on Ethernet networks. Switching and Virtual Private Networking can provide a solution.

Related Ethernet Reads:

• Gigabit Ethernet or Fast Ethernet.
• FDDI (Fibre Distributed Data Interface).

Disadvantages of a network

We List below some of the Disadvantages of a networking

• Crashes.  The biggest disadvantage is on a server based network. When the server crashes, work gets disrupted as all network resources and its benefits are lost. Unless proper precautions are taken to ensure regular backups, the lost may result in loss of days and even months of critical data and time.
• Data Security. As all data resources are all pooled together in a  network, it is possible for unauthorised personnel to access classified information if network security is weak or poorly implemented.
• Privacy. A network may also mean loss of privacy as anyone, especially your boss, with the right network privileges may be in a position to read your private e-mail or hook into your private chat session., thus breaching the privacy.
• There are advantages and disadvantages of sharing a program like Microsoft Word. On the plus side it makes easier to keep Microsoft Office updated, because if you want to upgrade the software you need to update only one copy of office, the one which is located on the server. Its easier to configure as well as a network version of an application is less expensive than if you copy a new application on each computer system.
• On the minus side, with so many users using a network to access a Program on the network, the network may get jammed, and the overall performance is poor.

Above were some of the disadvantages of setting up a computer network. But overall, the advantages of a networking are more than the disadvantages.

Related Posts

• Advantages of a Networking
• Network Basics

Advantages of networking

Here are some of the benifits of setting up a network

• Sharing Files : Networks let you share information with other computers on the network. Depending on how you set your network, you an do this in one of two ways. The most direct way is to send a file directly from your computer to your friend's computer. The second way is to send your file to an intermediate resting place, where your friend can pick it up later, kind of like dropping a bag full of ransom money at a phone booth. A third way is to permanently store the file at that intermediate place, where both of you can get at the file whenever you want. One way or the other, the data travels to your friend's computer over the network cable.
• Sharing Resources : This means that you can set up certain computer resources - like a disk drive or a printer - so that all of the computers on the network can access the. For example, the laser printer attached to server computer is a shared resource. That means that anyone on the network can use it. Without the network, the other computer members will have to buy their own laser printers.
• Disk drives can be shared resources too. In fact, a disk drive must be set up as a shared resource in order to share files with other users. Suppose in a Network a Computer number 3 wants to share a file with the computer number-4, and a shared disk drive has been set up at computer number 2. All computer number 3 has to do is to copy its file to the shared drive on number 2 computer and tell the number 4 computer where the file is put. Then when the number 4 comes around, he can copy the file from number 2 to its own computer.
• You can share other resources too, such as  CD-ROM devices (those new dangled devices that store gigabytes of data and are more useful to large clip-art libraries and encyclopedia) or modems (which let you access other computers that aren't on your network).
• A network allows users to share resources with others on the network. This can be hardware related like a printer or a modem, or it can be software related like programs and databases, or work processors. System administrators in a server based network can configure or install new software on network computers remotely.
• Sharing Programs. Sometimes its best to put programs that everybody uses on a shared disk on a computer, rather than keep separate copies of the programs on each person's computer. For example if you have 10 computer users who all uses Microsoft Word, you could either store Ten copies of a Microsoft Word on each computer or you can store a single copy on a central server computer in a network which each user can access. This also allows to just invest on one computer, the server, more than on other computers, resulting in overall lowering of cost of a network.
• Backups. As all data is stored on a server , backing up critical data is a simple process.
• Communication. The biggest benefit however, comes in the form of better communication-electronic mail and groupware applications. Through electronic mail or e-mail, members of a network can send messages and ensure safe delivery of data to other members, even when they are not there. Groupware applications allow users to work collectively on same document.

Above were some of the advantages of a network. This is by no means a comprehensive or a complete list, but just enough to give you an idea, on how useful it is to set up a computer network.

• Network Basics
• Disadvantages of a network.

Networking : Basics of computer Network

A network is nothing more than two or more computers conneted together by a cable so that they can exchange information. WIth a computer network, all the computers in the office are hooked together with cables, install a special network adapter card (an electronic circuit card that goes inside your computer-ouch!) in each computer so you'll have a place to plug in the cable, set up and configure special network software to make the network work, and viola, you have a working network,

node : Every computer connected to the network is said to be on the network. The technical term for the computer that is on network is node.

online and offline : When a computer is turned on, using computer on and off button, and is able to access the network the computer is said to be online. On the other hand if a computer is unable to access the network despite connectd to it, is called offline. A computer can be offline for several reasons, it could be unplugged, it could be broken, the cable that connects computer to network is damaged, or there could be wad of gum jammed into the disk drive.

computer network : In general terms a computer network is an interconnection of various computer systems located at the same/different places. The interconnection is done through a communication link also known as the physical layer of the network and the link is such that it is totally transparent to the users of the network. The transparency of the communication link is brought about by the interfacing software known as protocols which enables a user in one location to freely access a computer system/database/process/software in another location.

However, if the computers in the network operate together as a single unit which to user appears as a single computer, albeit physically dispersed, then the complete system is more accurately described as a distributed system. Therefore, although, any interconnected set of computers is often conveniently referred to as "computer network", the use of the term often implies as interconected set of independent computers and not a distributed system. However, it may be useful when considering a distributed system to be able to recognize the particular type of network on which it is based.

Computer networks are collection of computers and intelligent periperal equipment (e.g., automatic teller machines and point-of-sale terminals equiped with microprocessors) that are inteconnected by telephone lines, microwave relays, and other high speed communication links for the purpose of exchanging data and sharing equipment. Networking has been developed on all levels, from local to international, in diverse sectors of society. Examples are networks used by government organizations for rapid retrieval of information form databases at central locations and those used by banks and retail merchants for the transfer of funds or credit verification. If telephone lines adopted for a computer network, each computer in the network must be connected to a telephone line via a ,modem (modulator/demodulator)

Modem  is a device which converts digital pulses from a computer into analog signals to be transmitted over telephone lines and vice versa. When a machine in a network communicates with another computer, both follow a predetermined potocol (i.e set of procedures), according to which data are exchanged.

LAN A local-area network (LAN)  is a communication network consisting of many computers (mostly personal computers and workstations) that are placed within a local area, such as single building or company.

Servers: Since mid-1980's , LANs have become widespread becuse personal computers and workstations are used extensively in offices, enabling individual users to run their specific programs easily and to have their own files at hand on floppy disks. Individual users can also share data or files on LAN as if the data or file reside on their respective computers; computers that are designed or used for this purpose are called servers.

Laser Printers and other peripheral rquipment also can be connected to a network for common use. Coaxial cables or fibre optic cables are popular communication lines because they provide fast data transmission and are easy to install within buildings. In the case of LANs, there are a few different protocols, such as Ethernet and Token Ring, developed by Xerox and IBM, respectively.

Network Components
The key network components and alternatives are:

• Media: Twisted pair wire, coaxial cable, fibreoptics, Microwave, satellites, cellular radio, point to point transreceivers.
• Processors: Modems, Multiplexers, concentrators, routers, bridges, gateways, Front-end processors, client and server computers.
• Software: Communication software, Network operating system Netware, Slip or PPP, POP, smtp, MSN internet explorer or Netscape Navigator, middleware.
• Channels: Analog/digital, switched/non-switched, circuit/message/packet switching, simplex/duplex, synchronous/ asynchronous, speed and baud rate.
• Topology: Point-to-Point, multidrop, star, ring, mesh, Ethernet
• Architecture: OSI, IEEE, ISDN, PSTN

Frankly, computer networks are a bit of pain to set up. So why bother? Because the benifits of having a network make the pain of setting one up bearable.

Related Posts:

• Advantages of Networking
• Disadvantages of a Network
• Need of Networks

Internet Summary- Internet in a Nutshell (Fact sheet / Cheatsheet)

Following fact sheet provides quick summary about Internet:

• The Internet is a collection of more than 100,000 separate networks.
• ARPANET (the early internet) began as a network with four nodes.
• TCP/IP is the protocol suite for the Internet.
• CSNET provided communication between networks ineligible to join ARPANET.
• NSFNET provided communication between networks throughout the United States.
• Local Internet Service Providers (ISPs) connect individual users to the Internet.
• Regional Internet service providers connect local Internet service providers.
• National service providers (NSPs) are backbone networks created and maintained by specialized companies.
• A protocol is a set of rules that governs data communications; the key elements of a protocol as syntax, semantics and timing.
• Standards are necessary to ensure that products from diffrent manufacturers can work together as expected.
• The ISO, ITU-T, ANSI, IEEE, and EIA are some of the orgaizations involved in standards creation.
• Forums are special-interest groups that quickly evaluate and standardize new technologies.
• Two important forums are Frame Relay Forum and ATM Forum.
• The FCC is a regulatory agency that regulates radio, television, and wire/cable communications.
• A Request For Comment (RFC) is an idea or concept that is precursor to an Internet Standard.
• An RFC is categorized as required, recommended, elective, limited use, or not recommended.
• The Internet Society (ISOC) promotes research and other scholarly activities related to the Internet.
• The Internet Architecture Board (IAB) is the technical advisor to the ISOC.
• The Internet Engineering Task Force (IETF) is a forum of working groups responsible for identifying operational problems and proposing solutions to these problems.
• The Internet Research Task Force (IRTF) is a form of working groups focusing on long-term research topics related to Internet protocols, applications, architecture, topology , and technology.
• The Internet Corporation for Assigned Names and Numbers (ICANN), formerly known as IANA, is responsible for the management of Internet domain names and addresses.
• The Network Information Center (NIC) is responsible for collecting and distributing information about TCP/IP protocols.

Above were Important Facts about Internet, The Cheat sheet showed about The Organisation and people who monitor and administers Internet, as well as about how Internet came into existence and evolved from ARPANET.

Internet Administration-Who Owns It

Nobody owns Internet. The Internet, with its roots primarily in the research domain, has evolved and gained a broader user base with significant commercial activity. Various groups taht coordinate Internet issues have guided this growth and development.

• Internet Society (ISOC). http://www.isoc.org/ The Internet Society is an international, non profit organization formed in 1992 to provide support for the Internet standards process. ISOC accomplishes this through maintaining and supporting other Internet administrative bodies such as IAB, IETF, IRTF, and IANA. ISOC also promotes research and other scholarly activities relating to the Internet.
• Internet Architecture Board (IAB). http://www.iab.org/  The Internet Architecture Board is the technical advisor ISOC. The main purposes of the IAB are to oversee the continuous development of the TCP/IP Protocol Suite and to serve in technical advisory capacity to research members of the Internet community. IAB accomplishes this through its two primary components, the Internet Engineering Task Force (IETF) and the Internet Research Task force (IRTF). Another responsibility of the IAB is the editorial management of the RFCs. IAB is also the external liaison between the Internet and other standards organizations and forums.
• Internet Engineering Task Force (IETF). http://www.ietf.org/ The Internet Engineering Task Force is a forum of working groups managed by the Internet Engineering Steering Group (IESG). IETF is responsible for identifying operational problems and proposing solutions to these problems. IETF also develops and reviews specifications intended as Internet standards. The working groups are collected into areas, and each area concentrates on a specific topic. Currently nine areas have been defined, although this is by no means hard and fast number. The areas are: Applications, Internet Protocols, Routing, Operations, User Services, Network Management, Transport, Internet protocol next generation (IPng), and Security
• Internet Research Task Force (IRTF). http://www.irtf.org/  The Internet Research Task Force (IRTF) is a forum of working groups managed by the Internet Research Steering Group (IRSG). IRTF focuses on long-term research topics related to Internet protocols, applications, architecture, and technology.
• Internet Assigned Numbers Authority (IANA) and Internet Corporation for Assigned Names and Numbers (ICANN). http://www.icann.org/  The Internet Assigned Numbers Authority (IANA), supported by the U.S. government, was responsible for the management of Internet domain names and addresses until October 1998. At that time the Internet Corporation for Assigned Names and Numbers (ICANN), aprivate nonprofit corporation managed by an international board, assumed IANA operations.
• Network Information Center (NIC). The NIC is responsible for collecting and distributing information about TCP/IP protocols.

Above were the main organisations that administers Internet.

Related Posts:

• Internet Introduction and Overview.
• Internet Standards and RFC

Internet Standards, RFC and Maturity Levels

An Internet Standard  is as thoroughly tested specification that is useful to and adhered to by those who work with the Internet. It is a formalized regulation that must be followed. There is a strict procedure by which a specification attains Internet standard status. A specification begins as an Internet draft. An Internet draft is a working document ( a work in progress) with no official status and a six-month lifetime. Upon recommendation from the Internet authorities, a draft may be published as a Request for Comment (RFC). Each RFC is edited, assigned a number, and made available to all interested parties.

RFCs go through maturity levels and are categorized according to their requirement level.

Maturity Levels
An RFC, during its lifetime, falls into one of six maturity levels: proposed standard, draft standard, Internet standard, historic, experimental, and Informational.

• Proposed Standard. A proposed standard is a specification that is stable, well understood, and of sufficient interest to the internet community.  At this level, the specification is usually tested and implemented by several different programs.
• Draft Standard. A proposed standard is elevated to draft standard status after atleast two successful independent and interoperable implementations. Barring difficulties, a draft standard, with modifications if specific problems are encountered, normally becomes an internet standard.
• Internet Standard. A draft standard reaches Internet standard after demonstrations of successful implementation.
• Historic. The Historic RFCs are significant from a historical perspective. They either have been superseded by later specifications or have never passed the necessary maturity levels to become an internet standard.
• Experimental. An RFC classified as experimental describes work related to an experimental situation that does not affect the operation of the internet. Such an RFC should not be implemented in any functional Internet service.
• Informational. An RFC classified as informational contains general, historical, or tutorial information related to the Internet. It is usually written by someone in a non-Internet organization, such as a vendor.

RFC Requirement Levels
RFCs are classified into 5 Requirement Levels: required, recommended, elective, limited use and not recommended.

• Required. An RFC is labeled required if it must be implemented by all Internet systems to achieve minimum conformance. For example, IP and ICMP are required protocols.
• Recommended. An RFC labeled recommended is not required for minimum conformance; it is recommended because of its usefulness. For example, FTP and TELNET are recommended protocols.
• Elective. An RFC labeled elective is not required and not recommended. However, a system can use it for its own benefit.
• Limited Use. An RFC labeled limited use should be used only in limited situations. Most of the experimental RFCs fall under this category.
• Not recommended. An RFC labeled not recommended is inappropriate for general use. Normally a historic (obsolete) RFC may fall under this category.

RFCs can be found at http://www.faqs.org/rfcs

Related Post

• Protocols and standards.
• Birth Of Internet-History and Timeline
• Internet Administration