Wide Area Network (WAN)

Types and Characteristics of WANs

What is a WAN?

There are two prevailing definitions of a Wide Area Network (WAN). The book definition of a WAN is a network that spans large geographical locations, usually to interconnect multiple Local Area Networks (LANs). The practical definition of a WAN is a network that traverses a public network or commercial carrier, using one of several WAN technologies

What are its Main Components?

The main components for a WAN are routers, switches and modems. These components are described below in the hardware section.

CPE - Devices on the subscriber premises are called customer premises equipment (CPE).
The subscriber owns the CPE or leases the CPE from the service provider. A copper or fiber cable connects the CPE to the service provider's nearest exchange or central office. This cabling is often called the local loop, or "last-mile".

DTE/DCE - Devices that put data on the local loop are called data circuit-terminating equipment, or data communications equipment (DCE). The customer devices that pass the data to the DCE are called data terminal equipment (DTE). The DCE primarily provides an interface for the DTE into the communication link on the WAN cloud.

Hardware

In a WAN you will need various types of hardware components for it to function. The typical items of hardware that you will need in a WAN are:

Router - An electronic device that connects a local area network (LAN) to a wide area network (WAN) and handles the task of routing messages between the two networks. Operates at layer 3, and makes decisions using IP addresses.

Switch - A switch is a network device that selects a path or circuit for sending a unit of data to its next destination. Operates at layer 2, and uses MAC addresses to send data to correct destination.

Modem - Short for modulator/demodulator, a modem enables a computer to communicate with other computers over telephone lines. Operates at layer 1, where signals are converted from digital to analogue and vice versa for transmission and receiving.

Wan Standards

WANs operate within the OSI model using layer 1 and layer 2 levels. The data link layer and the physical layer. The physical layer protocols describe how to provide electrical, mechanical and functional connections to the services provided by the ISP. The data link layer defines how data is encapsulated for transmission to remote sites.

Encapsulation

Encapsulation is the wrapping of data in a particular protocol header. Remember that WANs operate at the physical layer and the data link layer of the osi model and that higher layer protocols such as IP are encapsulated when sent across the WAN link. Serial interfaces support a wide range of WAN encapsulation types, which must be manually specified. These types include SDLC, PPP, Frame delay etc. Regardless of WAN encapsulation used it must be identical on both sides of the point to point link.

Packet and Circuit Switching

Circuit switching and packet switching are both used in high-capacity networks.
The majority of switched networks today get data across the network
through packet switching.

Circuit-switching is more reliable than packet-switching. Circuit switching is old and expensive, packet switching is more modern.

General Routing Issues

What is a Routing Protocol?

A routing protocol is a protocol that specifies how routers communicate and exchange information on a network. Each router has prior knowledge of its immediate neighbours and knows the structure of the network topology. The routers know this because the routing protocol shares this information.

Protocol

RIP (Routing Information Protocol) was one of the most commonly uses protocols on internal networks. Routers use RIP to dynamically adapt changes to the network connections and communicate information about which networks routers can reach and the distance between them. RIP is sometimes said to stand for Rest in Pieces in reference to the reputation that RIP has for breaking unexpectedly and rendering a network unable to function.

Routing Algorithms

Distance Vector

This type of routing protocol requires that each router simply inform its neighbours of its routing table. The distance vector protocol is also known as the bellman-ford algorithm.

Link State

This type of routing protocol requires that each router maintain a partial map of the network. The link state algorithm is also know as Dijkstra's algorithm.

IGRP

IGRP is a type of distance vector routing protocol invented by cisco used to exchange routing data in a autonomous system. Distance vector protocols measure distances and compare routes. Routers that use distance vector must send all or a portion of their routing table in a routing update message at regular intervals to each neighbour router.

Addressing and Routing

What does routing mean?

Routing is the process of deciding how to move packets from one network to another.
The directions also known as routes can be learned by a router using a routing protocol then the information is passed from router to router along the route of the destination.

IP Address's

Every machine connected to the internet is assigned an IP address. An example of an IP address would be 192.168.0.1. IP addresses are displayed in decimal format to make it easier for humans to understand but computers communicate in binary form. The four numbers that separate an IP address are called Octets. Each position consists of eight bits. When added to together you get 32 bit address. The purpose of each octet in an IP address is to create classes of IP addresses that can be assigned within a network. There are three main classes that we deal with Class A, B and C. The octets of an IP address are split into two parts Network and Host. In a class A address the first octet is the network portion, this determines which network the computer belongs to, the last octets of the address are the hosts that belong to the network.

Sub netting

Sub netting allows you to create multiple networks within a class A, B or C address. The subnet address is the address used by your LAN. In a Class C network address you would have a subnet mask of 255.255.255.0. A subnet mask identifies which portion is network and which is host. For example 192.168.6.15 the first octet three octets are the Network address and the last octet being the host(Workstation). It is important to subnet a network because gateways need to forward packets to other LANS. By giving each NIC on the gateway an IP address and a Subnet mask it allows the gateways to route packets from LAN to LAN. Once the packet arrives at its destination, the gateway then uses the bits of the subnet portion of the IP address to decide which LAN to send the packets.

Circuit Switched Leased Lines

A circuit switched network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. Here are some terminologies associated with a Circuit switched network.

Frame relay is a telecommunication service designed for cost-efficient data transmission between local area networks (LANs)

Basic rate interference is a service used by small business for internet connectivity. An ISDN BRI provides two 64 Kbps digital channels to the user.
Primary rate interface (PRI) is a telecommunications standard for carrying voice and data transmissions between two locations
All data and voice channels are ISDN and operate at 64kbit/s

Packet Switching

http://www.raduniversity.com/networks/2004/PacketSwitching/main.htm - _Toc80455261

Packet switching refers to protocols in which messages are broken up into small packets before they are sent. Each packet is then transmitted over the Internet. At the destination the packets are reassembled into the original message. Packet switching main difference from Circuit Switching is that that the communication lines are not dedicated to passing messages from the source to the destination. In Packet Switching, different messages can use the same network resources within the same time period.

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

Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and protocolwhich encodes data into small fixed-sized cells.

ISDN is used to carry voice, data, video and images across a telephone network. ISDN stands for integrated services Digital Network. Isdn also provides users with a 128kbps bandwidth. This is done through frame relay. Frame relay complements and provides a service between ISDN, which offers bandwidth at 128 Kbps and Asynchronous Transfer Mode which operates in somewhat similar fashion to frame relay but at speeds from 155.520 Mbps or 622.080 Mbps. Frame relay is based on the older X.25 packet switching technology and is used to transmit analogue signals such as telephone conversations.

PSDN stands for packet switched data network and is a data communication network. Packet switched networks do not establish a physical communication signal like the public telephone does (circuit switched network) Packets are sent on a fixed length basis and assigned with a source and a destination address. The packets then rely on the routers to read the address and route the packets through the network.

Mobile and Broadband Services

Digital Subscriber line(DSL) is mainly used to bring high bandwidth connections to homes and small business's over a copper wire telephone line. This is can only be achieved if you stay within the range of the telephone exchange. DSL offers download rates of up to 6mbps allowing continuous transmission of video, audio and 3D effects. DSL is set to replace ISDN and compete with the cable modem in providing multimedia to homes. DSL works by connecting your telephone line to the telephone office over copper wires that are twisted together.

Asymmetric Digital Subscribers Line is most commonly used for home users. It provides a high download speed but a lower upload speed. Using ADSL, up to 6.1 megabits per second of data can be sent downstream and up to 640 Kbps upstream.

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

Symmetric Digital Subscriber Line is a digital subcriber line which runs over one pair of copper wires. The main difference between ADSL and SDSL is the difference in upload and download speeds. SDSL allows the same upstream data rate and downstream data rate as ADSL upstream can be very slow.

[http://searchnetworking.techtarget.com/sDefinition/0],,sid7_gci558545,00.html

HDSL High bit-rate Digital Subscriber Line, one of the earliest forms of DSL, is used for wideband digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that provides equal bandwidth in both directions.

IDSL is a system in which data is transmitted at 128 Kbps on a regular copper telephone line from a user to a destination using digital transmission.

The Local Loop enables operators to connect directly to the consumer via copper local loops and then add their own equipment to offer broadband and other services. This process involves operators accessing local exchange buildings to connect to a network of copper lines which connect them to homes and businesses. BT is an Example of a Local Exchange. The local loop connecting the telephone exchange to most subscribers is capable of carrying frequencies well beyond the 3.4 kHz upper limit.

Benefits of using DSL

DSL can provide virtually instantaneous transmission of voice, data and video over ordinary copper phone lines. A DSL connection can eliminate delays when waiting to download information and graphics from the Internet. It provides users with a cost effective high speed Internet connection. Another benefit is that a DSL connection is always on-line (like a LAN connection) with no waiting time for dialling or connecting.

There are now more than 10 million broadband connections in the UK. By December 2005 there were 9.792 million broadband connections in the UK and the average broadband take up rate during the three months to December was more than 70,000 per week.

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Types of Network Topology

Network topology refers to the physical layout of the network i.e. the locations of the computers and how the cable is run between them. To select the right topology for how the network will be used is very important. Each topology has its own strength and weaknesses.

The choice of a topology for installing a computer network depends upon a combination of factors such as, reliability, performance of the system, number of nodes and geographical distribution of the system.

The main 2 types are

Bus Topology & Peer to Peer Topology

Peer to Peer topology consists of Star topology and Ring topology.

Bus Topology

It is often used when network installation is small, simple or temporary. On a typical bus network the cable is just 1 or more wires with no active electronics to amplify the signal or pass it along from computer to computer. This makes the bus a passive topology. When 1 computer send a signal up the wire all the computers receive the information but only one with the address that matches accepts the information, the rest disregard the message.

Advantages:

1) Easy to use and to understand.

2) Requires least amount of cable to connect the computers together. It is therefore less expensive than other cabling arrangements.

3) It is easy to extend a bus; two cables can be joined into 1 longer cable with a BNC, Barrel connector making a longer cable and allowing more computers to join the network.

Disadvantages:

1) Heavy network traffic can slow a bus considerably as only 1 computer can send a message at a time.

2) It is difficult to troubleshoot the bus. A cable break or loose connector causes reflection and stops all the activity.

Star Topology

In this kind of topology all the cables run from the computers to the central location where they are all connected by a device called hub or switch. Each computer on a star network communicates with a central device that resends the message either to each computer or only to the destination computer, e.g. if it is a hub then it will send to all and if it is a switch then it will send to only destination computer.When network expansion is expected and when the greater reliability is needed, star topology is the best.

Advantages:

1) It is easy to modify and add new computers without disturbing the rest of the network.

2) The center of the star network is a good place to diagnose the faults.

3) Single computer failure does not necessarily bring down the whole star network.

Disadvantages:

1) If the central device fails the whole network fails to operate.

2) Star networking is expensive because all network cables must be pulled to one central point, requires more cable than other network topologies.

Ring Topology

In this type each computer is connected to the next computer with the last one connected to the first. Each retransmits what it receives from the previous computer. The message flows around the ring in one direction. The ring network does not subject to signal loss problem as a bus network experiences. There is no termination because there is no end to the ring.

Advantages:

1) Each node has equal access.

2) Capable of high speed data transfer.

Disadvantages:

1) Failure of one computer on the ring can affect the whole network.

2) Difficult to troubleshoot the network.

Topologies remain an essential part of network design speculation. But understanding these can help you to get the deeper knowledge of the elements like hub, switch etc.

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Computer Network Topology

More and more computer networks use wireless methods to move data from one system to another, however many networks still use some type of cabling (Copper or Fiber Optic) to connect systems. The way that cable and hardware, or wireless signals connect to one another to form a network is known as the Network Topology. Historical network topologies include Bus, Ring, and Star, while modern topologies include Hybrid, Mesh, Point-to-Multipoint, and Point-to-Point.

Historical Topologies

Bus: A bus topology uses a single bus cable that connects all of the computers in a line, and data goes out on the entire bus. To prevent data from reflecting at the ends of the cable and creating unnecessary traffic a bus topology needs terminators at each end of the cable.

Ring: A ring topology is similar to a bus topology except that it connects all computers with a central ring cable, so there are no ends to the bus and it does not require termination. The data flows in a circle from one computer to the next in the same direction.

*If a cable is broken at any point in a bus or ring topology the entire network stops working. The broken ends in a bus topology creates reflection of data between the still connected computers because the termination point is no longer connected to the network. A broken cable in a ring topology breaks the circuit and stops the flow of data.

Star: A star topology uses a central connection point for all computers on a network, which offers fault tolerance not available with bus or ring topologies. If any one connection is broken in a star topology the other systems on the network are not affected and are still able to send and receive data.

Modern Topologies

Hybrid: A hybrid topology combines the features of the bus and ring topologies with the star topology by shrinking the actual bus or ring into a small box called a hub which serves the purpose of the central connection point or star. Star-bus and star-ring topologies physically look like star topologies however the actual electronic schematics act like a bus or ring. Any topology that combines a physical topology with an electronic signalling topology is known as a Hybrid Topology.

Mesh: A mesh topology connects every system to every other system in a network via two or more routes, sometimes requiring particular routes to traverse through another system in the mesh network. A partially meshed topology includes at least two systems with redundant connections, and every computer does not need to connect to every other computer. In a fully meshed topology every computer connects directly to every other computer. A meshed topology is very robust and if a single connection is broken the systems are not affected, however because of the complexity of connecting cables to and from every computer in a network the mesh topology is not practical for cabled networks and will usually only be seen in wireless networks.

Point-to-Multipoint: A point-to-multipoint topology includes a single computer system that is used a common source through which all of the other systems on the network converse. Similar to the star topology in that there is a central point, the difference is in the device that exists in the center of the network. The center of the star topology is little more than a path for the data to travel to the various systems, whereas the center of a point-to-multipoint topology includes an actual hub, router, or switch which controls the data flow to the various other systems in the network. The point-to-multipoint topology is sometimes referred to as a Tree Topology and is known as an Infrastructure Network.

Point-to-Point: A point-to-point topology includes two computers directly connected together with no need for a central hub, router, or switch. Point-to-point topologies are found in both wired and wireless networks. They are known as Ad-hoc or Peer to Peer networks.

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What is Peer-To-Peer File Sharing (P2P)?

Peer to peer file sharing systems, otherwise known as P2P, connect people directly together on the internet. Some systems are true networked systems, in that there is a central server which acts as a central point to which all traffic is directed then distributed to the clients.

An excellent example of this is the original Napster. When someone wanted to download a particular track, they would enter it into a request box, much as with P2P software, then Napster would inform them what sites had the track or movie, then facilitate the download between two computers. Computer A would pass to Napster who would pass to computer B. In other words, if your joined Napster, you allowed the music files on your hard drive to be copied to Napster's central server, then on to another of Napster's customer's hard drive. OpenNap was another, which copied Napster's way of making money through file exchange.

However, this central server is what destroyed Napster, at least for a while. Once the central server could be identified as the single source of this file exchange, it was forced to close. And once the server closed, the whole system broke down. The Napster team eventually tugged their forelocks and began to operate using payment per track systems which developed to the Napster you now know, which is owned by software company Roxio.

Peer to peer file sharing took over Napster's original role, but extended it from simply sharing music tracks. P2P provides an opportunity for new artists to have their work heard without the high costs of cutting disks or CDs and trying to promote them through other media. The beauty of P2P is that no moguls can take it over and dictate who and who cannot have their original music heard.

The difference between Peer to peer and Napster is that there is no central server with P2P. Every user of the software is connected directly to every other user. If you download music using a peer to peer system, you can be downloading from the hard drive of your next door neighbor, or somebody on the other side of the world. You will never know, unless you opt for a higher grade system. There is no central server to be shut down since you are in direct contact, so it cannot be stopped, even if made illegal.

P2P file sharing software is mainly sourced from the Gnutella design, and most companies that offer such services look very much the same. However, some have extended this to offer the bells and whistles that set them apart, such as faster downloads and the ability to converse with those you are connected to. There are other benefits to be gained from these subscription sites such as connections to other P2P movie and games download sites.

If you do not have burning software such as Nero, you can also download the software required to burn the files to CD or DVD directly from the software websites you are subscribing to.

The major players in the free peer to peer networks are Gnutella and Bittorrent. They work differently but both provide high quality downloads. If you want to take it a step forward, the subscription download programs, where you make a single life payment, can provide more functionality and interactivity as well as faster download speeds. Beware of free trials since these tend to come with adware and spyware, and the reason they are free, to my mind, is that the software companies are either using their own spyware, or receiving a payment for including it in the free package.

You can't complain about what get free, but you can about what you pay for, which is why free software is not always the best option. The same, however, can be said of some regular or life subscription sites. Before you pay try the contact numbers. If you get no reply, either from email or phone, then don't go near them.

All in all, assuming that you keep legal with copyright, peer to peer file sharing networks are the best way to listen to new music from up and coming artists, and to see movies made by new producers, directors and actors. It is also a great way to get some old games that you have never played before. I should also warn you not to download the current charts!

Peter writes on many aspects of electronic file transfer systems including audio-visual file formats and codecs. His main business involves the the legal downloading of movies, games and music and you can get information on how to back-up DVDs and games and on the difference between the free and subscription download sites on his website [http://www.online-free-movies.com] and [http://www.legalandfree.com]

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What is a Computer Network

In the simplest of terms, a computer network is a collection of computers interconnected with each other, thus forming a network. One of the greatest advantages of computer networks is that they allow users to access and share large amounts of information without having to store that information and use up personal disk space on personal computers.

Computer networks are generally classified by the hardware and software that is employed to establish the network with. For example, there are Ethernet networks, optical fiber networks, and wireless LAN networks to mention some of the most common types of computer networks. Networks are supported by one of two ways, and sometimes a combination of the two. The two ways are hard wired or wireless service.

Hard Wired Service

Of the two means of establishing and accessing a computer network hard wired service is the oldest, and often the most dependable. Below are the three most common wired technologies available in today's networking market. Twisted-pair wire is the most common means of telecommunications, which includes computer networking.

Coaxial cable is extensively used for office buildings, work-sites, as well as television systems. The advantage of coaxial cable is in its transmission speed. Cable can transmit over 500 million bits per second and is highly dependable.

Optical fiber, or fiber-optic, is a relatively new type of hard-wire system. Fiber-optics doesn't use electricity to transmit information like the previous two do. Instead it uses light and can transmit in the trillions of bits per second. Moreover, electromagnetic radiation, like from the sun's solar flares, does not interrupt fiber-optic transmissions like other services are susceptible to.

Wireless Services

Terrestrial microwave use a transmitter/receiver system of antennas to transmit information. However, the transmission distance, although very secure, is limited to about thirty miles. This network service is used extensively by local police departments.

Communication satellites use microwave radio signals to transmit information. These satellites orbit the earth and as they do they receive and send signals of communications. However, the signals to and from these satellites can be affected by such things as the sun's solar flare activities.

Cellular and PCS transmission systems utilize a combination of communications technologies such as relay antenna and even satellites. However, they use is restricted by geographic locations, dependent on where the antenna might be located.

Wireless LANs is perhaps the most popular means for computer network communications. It utilizes both a high-frequency and low-frequency technology, similar to that of digital communications. For computer networks, wireless LANs is generally the choice because it can handle communications between multiple devices more easily and with minimal interruptions.

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