Wide Area Network (WAN)

Types and Characteristics of WANs				the network portion, this determines which
What is a WAN?				network the computer belongs to, the last octets
There are two prevailing definitions of a Wide				of the address are the hosts that belong to the
Area Network (WAN). The book definition of a				network.
WAN is a network that spans large geographical				Sub netting
locations, usually to interconnect multiple Local				Sub netting allows you to create multiple
Area Networks (LANs). The practical definition of				networks within a class A, B or C address. The
a WAN is a network that traverses a public				subnet address is the address used by your LAN.
network or commercial carrier, using one of				In a Class C network address you would have a
several WAN technologies				subnet mask of 255.255.255.0. A subnet mask
What are its Main Components?				identifies which portion is network and which is
The main components for a WAN are routers,				host. For example 192.168.6.15 the first octet
switches and modems. These components are				three octets are the Network address and the
described below in the hardware section.				last octet being the host(Workstation). It is
CPE - Devices on the subscriber premises are				important to subnet a network because
called customer premises equipment (CPE).				gateways need to forward packets to other
The subscriber owns the CPE or leases the CPE				LANS. By giving each NIC on the gateway an IP
from the service provider. A copper or fiber cable				address and a Subnet mask it allows the
connects the CPE to the service provider's				gateways to route packets from LAN to LAN.
nearest exchange or central office. This cabling is				Once the packet arrives at its destination, the
often called the local loop, or "last-mile".				gateway then uses the bits of the subnet portion
DTE/DCE - Devices that put data on the local				of the IP address to decide which LAN to send
loop are called data circuit-terminating equipment,				the packets.
or data communications equipment (DCE). The				Circuit Switched Leased Lines
customer devices that pass the data to the DCE				A circuit switched network is one that establishes
are called data terminal equipment (DTE). The				a dedicated circuit (or channel) between nodes
DCE primarily provides an interface for the DTE				and terminals before the users may communicate.
into the communication link on the WAN cloud.				Here are some terminologies associated with a
Hardware				Circuit switched network.
In a WAN you will need various types of				Frame relay is a telecommunication service
hardware components for it to function. The				designed for cost-efficient data transmission
typical items of hardware that you will need in a				between local area networks (LANs)
WAN are:				Basic rate interference is a service used by small
Router - An electronic device that connects a				business for internet connectivity. An ISDN BRI
local area network (LAN) to a wide area network				provides two 64 Kbps digital channels to the user.
(WAN) and handles the task of routing messages				Primary rate interface (PRI) is a
between the two networks. Operates at layer 3,				telecommunications standard for carrying voice
and makes decisions using IP addresses.				and data transmissions between two locations
Switch - A switch is a network device that				All data and voice channels are ISDN and operate
selects a path or circuit for sending a unit of data				at 64kbit/s
to its next destination. Operates at layer 2, and				Packet Switching - _Toc80455261
uses MAC addresses to send data to correct				Packet switching refers to protocols in which
destination.				messages are broken up into small packets
Modem - Short for modulator/demodulator, a				before they are sent. Each packet is then
modem enables a computer to communicate with				transmitted over the Internet. At the destination
other computers over telephone lines. Operates				the packets are reassembled into the original
at layer 1, where signals are converted from				message. Packet switching main difference from
digital to analogue and vice versa for transmission				Circuit Switching is that that the communication
and receiving.				lines are not dedicated to passing messages from
Wan Standards				the source to the destination. In Packet Switching,
WANs operate within the OSI model using layer 1				different messages can use the same network
and layer 2 levels. The data link layer and the				resources within the same time period.
physical layer. The physical layer protocols				Asynchronous Transfer Mode (ATM) is a cell
describe how to provide electrical, mechanical and				relay, packet switching network and protocolwhich
functional connections to the services provided by				encodes data into small fixed-sized cells.
the ISP. The data link layer defines how data is				ISDN is used to carry voice, data, video and
encapsulated for transmission to remote sites.				images across a telephone network. ISDN stands
Encapsulation				for integrated services Digital Network. Isdn also
Encapsulation is the wrapping of data in a				provides users with a 128kbps bandwidth. This is
particular protocol header. Remember that WANs				done through frame relay. Frame relay
operate at the physical layer and the data link				complements and provides a service between
layer of the osi model and that higher layer				ISDN, which offers bandwidth at 128 Kbps and
protocols such as IP are encapsulated when sent				Asynchronous Transfer Mode which operates in
across the WAN link. Serial interfaces support a				somewhat similar fashion to frame relay but at
wide range of WAN encapsulation types, which				speeds from 155.520 Mbps or 622.080 Mbps.
must be manually specified. These types include				Frame relay is based on the older X.25 packet
SDLC, PPP, Frame delay etc. Regardless of WAN				switching technology and is used to transmit
encapsulation used it must be identical on both				analogue signals such as telephone conversations.
sides of the point to point link.				PSDN stands for packet switched data network
Packet and Circuit Switching				and is a data communication network. Packet
Circuit switching and packet switching are both				switched networks do not establish a physical
used in high-capacity networks.				communication signal like the public telephone does
The majority of switched networks today get				(circuit switched network) Packets are sent on a
data across the networkthrough packet switching.				fixed length basis and assigned with a source and
Circuit-switching is more reliable than				a destination address. The packets then rely on
packet-switching. Circuit switching is old and				the routers to read the address and route the
expensive, packet switching is more modern.				packets through the network.
General Routing Issues				Mobile and Broadband Services
What is a Routing Protocol?				Digital Subscriber line(DSL) is mainly used to bring
A routing protocol is a protocol that specifies how				high bandwidth connections to homes and small
routers communicate and exchange information				business's over a copper wire telephone line. This
on a network. Each router has prior knowledge of				is can only be achieved if you stay within the
its immediate neighbours and knows the structure				range of the telephone exchange. DSL offers
of the network topology. The routers know this				download rates of up to 6mbps allowing
because the routing protocol shares this				continuous transmission of video, audio and 3D
information.				effects. DSL is set to replace ISDN and compete
Protocol				with the cable modem in providing multimedia to
RIP (Routing Information Protocol) was one of the				homes. DSL works by connecting your telephone
most commonly uses protocols on internal				line to the telephone office over copper wires
networks. Routers use RIP to dynamically adapt				that are twisted together.
changes to the network connections and				Asymmetric Digital Subscribers Line is most
communicate information about which networks				commonly used for home users. It provides a
routers can reach and the distance between				high download speed but a lower upload speed.
them. RIP is sometimes said to stand for Rest in				Using ADSL, up to 6.1 megabits per second of
Pieces in reference to the reputation that RIP has				data can be sent downstream and up to 640
for breaking unexpectedly and rendering a				Kbps upstream.
network unable to function.				Symmetric Digital Subscriber Line is a digital
Routing Algorithms				subcriber line which runs over one pair of copper
Distance Vector				wires. The main difference between ADSL and
This type of routing protocol requires that each				SDSL is the difference in upload and download
router simply inform its neighbours of its routing				speeds. SDSL allows the same upstream data
table. The distance vector protocol is also known				rate and downstream data rate as ADSL
as the bellman-ford algorithm.				upstream can be very slow.
Link State				[
This type of routing protocol requires that each				HDSL High bit-rate Digital Subscriber Line, one of
router maintain a partial map of the network. The				the earliest forms of DSL, is used for wideband
link state algorithm is also know as Dijkstra's				digital transmission within a corporate site and
algorithm.				between the telephone company and a customer.
IGRP				The main characteristic of HDSL is that provides
IGRP is a type of distance vector routing protocol				equal bandwidth in both directions.
invented by cisco used to exchange routing data				IDSL is a system in which data is transmitted at
in a autonomous system. Distance vector				128 Kbps on a regular copper telephone line from
protocols measure distances and compare routes.				a user to a destination using digital transmission.
Routers that use distance vector must send all or				The Local Loop enables operators to connect
a portion of their routing table in a routing update				directly to the consumer via copper local loops
message at regular intervals to each neighbour				and then add their own equipment to offer
router.				broadband and other services. This process
Addressing and Routing				involves operators accessing local exchange
What does routing mean?				buildings to connect to a network of copper lines
Routing is the process of deciding how to move				which connect them to homes and businesses. BT
packets from one network to another.				is an Example of a Local Exchange. The local loop
The directions also known as routes can be				connecting the telephone exchange to most
learned by a router using a routing protocol then				subscribers is capable of carrying frequencies well
the information is passed from router to router				beyond the 3.4 kHz upper limit.
along the route of the destination.				Benefits of using DSL
IP Address's				DSL can provide virtually instantaneous
Every machine connected to the internet is				transmission of voice, data and video over
assigned an IP address. An example of an IP				ordinary copper phone lines. A DSL connection can
address would be 192.168.0.1. IP addresses are				eliminate delays when waiting to download
displayed in decimal format to make it easier for				information and graphics from the Internet. It
humans to understand but computers				provides users with a cost effective high speed
communicate in binary form. The four numbers				Internet connection. Another benefit is that a DSL
that separate an IP address are called Octets.				connection is always on-line (like a LAN
Each position consists of eight bits. When added				connection) with no waiting time for dialling or
to together you get 32 bit address. The purpose				connecting.
of each octet in an IP address is to create				There are now more than 10 million broadband
classes of IP addresses that can be assigned				connections in the UK. By December 2005 there
within a network. There are three main classes				were 9.792 million broadband connections in the
that we deal with Class A, B and C. The octets of				UK and the average broadband take up rate
an IP address are split into two parts Network				during the three months to December was more
and Host. In a class A address the first octet is				than 70,000 per week.

TeleComm

Wide Area Network (WAN)