The operation of LAN and WAN hardware and protocols€¦ · Web viewThe operation of LAN and WAN...

The operation of LAN and WAN hardware and protocols

The operation of LAN and WAN hardware and protocols The operation of LAN and WAN hardware and protocols


Page 2 of 44 29th August 2017

http://www.open.edu/openlearncreate/course/view.php?id=2784







Contents 1 Introduction to Wide Area Networks 2 Digital Subscriber Line 3 Cable 4 Fibre optic 5 Wireless 6 Municipal WiFi 7 Worldwide Interoperability for Microwave

Access 8 Cellular wireless 9 Sending data across the LAN 10 Sending data to the WAN 11 Point-to-Point Protocol over Ethernet 12 Activity 13 End of course quiz 14 Acknowledgements





1 Introduction to Wide Area Networks At home, your Local Area Network (LAN) might

connect together devices over a distance measured in

tens of metres. At work or school, the LAN might

connect devices over hundreds of metres. A Wide

Area Network (WAN) operates over a much larger

area, as they interconnect LANs to allow them to

exchange data.

Figure 1

For example, in the diagram above a large business

network needs to provide a connection to a remote

branch office, and to employees who work from home

(telecommuters) and who are travelling (remote

users). This connection is provided by a WAN. WANs





are operated by a service provider, and businesses

pay them a fee in order to gain access.

WAN service providers are businesses that provide

WAN services using a variety of technologies,

including the telephone network, cable and satellite.

The WAN allows employees to connect to the

business network in order to carry out work related

tasks – the connection is not primarily for accessing

the Internet.

Why doesn’t the company set up its own WAN to save

money? Traditionally, due to the distance that WANs

operate over, setting one up would cost a substantial

amount of money as the business would need to

purchase the necessary cabling, fibre and satellite

systems. Setting up a WAN would therefore prove to

be extremely expensive and time-consuming, so most

businesses prefer to rent WAN services from an

established service provider.

Consider your home network, which probably provides

you with access to the Internet. You too are paying for

WAN services as your Internet Service Provider (ISP)

is a business that specialises in connecting

households to the Internet. They have invested a

considerable amount of money in creating a suitable





WAN infrastructure that allows thousands of domestic

users (who pay a fee) to connect.

ActivityDo you know who your ISP is? How much do they charge for

Internet access?

Domestic networks are primarily connected to an ISP

for Internet access, unlike business WANs. Because

there are a great many different reasons for creating a

WAN, there are many different types of WAN

technology available. Most commonly a business

WAN needs to support its employees and remote

offices, and it will have a different set of requirements

to a home user requiring just Internet access.

Traditionally, businesses and home users have used

different types of WAN technology to provide

connectivity.

As the need to access the Internet has become more

widespread, broadband technology has been

introduced to provide connections for home, school

and small business users. This technology utilises a

wide band of frequencies, transmitted over a single

transmission media (coaxial, UTP, fibre, wireless), to





provide an Internet service that is always on and has

a high data rate.

Broadband provides the connection between a home,

school or small business and the ISP. Once within the

ISP, different WAN technology will be used to transfer

the data around the ISP network and between other

ISPs.

However, it is becoming increasingly common for even

large businesses to connect to the Internet to provide

connection between their LANs, as opposed to using

more traditional WAN solutions. Thus, many

businesses are also using broadband connectivity to

provide WAN connectivity.

There are four main types of broadband WAN

connectivity available via UK ISPs:

1.Digital Subscriber Line (DSL)

2.cable

3.fibre optic

4.wireless.





2 Digital Subscriber Line DSL technology is an always-on connection

technology that uses existing twisted-pair telephone

lines to transport high bandwidth data and provide IP

services to subscribers.

Multiple DSL subscriber lines are multiplexed into a

single, high-capacity link using a DSL access

multiplexer (DSLAM) which is installed in the local

telephone exchange by the service provider. The

digital multiplexed output can then be transported

through the service provider’s network by whichever

WAN technology they have chosen to implement.

Figure 2

The diagram above shows a home office worker

connecting to their ISP using DSL. This provides them

with a connection to the Internet and to the business

WAN of their employer.





DSL provides high-speed connections over the copper

wires installed for the domestic public switched

telephone network (PSTN) or ‘plain old telephone

service’ (POTS). The existing phone system only uses

frequencies between 0 and 4 KHz, but DSL can use

the additional bandwidth available between 4 KHz and

1 MHz for high-speed data services.

DSL divides the 4 KHz to 1 MHz bandwidth into

different transmit (upstream) and receive

(downstream) channels, which it uses to connect the

home to the ISP. The diagram below shows a DSL

system with more downstream channels than

upstream channels, meaning that it can support

higher download than upload speeds. This is referred

to as asynchronous DSL (ADSL), and is ideal for

home users connecting to the Internet, as the majority

download rather than upload content.

Figure 3

Another form of DSL provides equal upload and

download speeds, and is referred to as symmetric





DSL (SDSL). SDSL is popular with businesses which

chose to create WAN connections between their sites

using the Internet as opposed to more traditional WAN

solutions.

There are many varieties of DSL, including some that

support data rates exceeding 100 Mbps. Regardless

of the variety used, the data rates are dependent on

the actual length of the physical cabling between the

user and the local telephone exchange. For

satisfactory ADSL service, the cabling must be less

than 5.5 km.

ISPs provide home users with a router capable of

connecting to a telephone system line socket. The

home router will use an internal modem to create the

required upstream and downstream channels,

allowing its WAN port to communicate with the

DSLAM at the local telephone exchange over the

phone line (local loop):

Figure 4

There is a gap called a guard band between the

telephone voice signal and the modulated DSL signal, Page 11 of 44 29th August 2017




which is intended to prevent interference. However,

most DSL connections still utilise a filter, connected

into the telephone socket, to prevent the DSL signal

being picked up by the telephone.

A filter is also used at the exchange to separate the

telephone signal, which is fed to the telephone

exchange, and the DSL signal, which is sent to the

DSLAM and then towards the ISP WAN for

connection to the Internet.

In the UK, all ISPs must be able to install their DSLAM

equipment within a local exchange, allowing them to

offer their services to domestic customers connected

via the copper cabling installed and owned by

BT/Openreach.





3 Cable Cable television systems were introduced in the USA

in the late 1940s as a means of distributing television

programs received by a single antenna to users in

remote areas with poor reception. Cable systems

have now grown in popularity as a means of

distributing a wide number of television channels to

users within cities without the need for individual

homes to have external antenna systems.

Figure 5

Modern cable systems can provide two-way

communication between homes and the cable system

operators, and now offer advanced

telecommunications services, such as a telephone

service and high-speed Internet access, alongside the

usual digital cable television.

Cable system providers traditionally used coaxial cable

to connect devices throughout their network. Because

of the increase in demand for bandwidth by the Page 13 of 44 29th August 2017




service now available to home users, most cable

providers use fibre optic cabling within the trunks

used to connect together their network and only utilise

coaxial cable to provide the link from their local

junction box (normally a green, steel street cabinet) to

the household. This is called a hybrid fibre-coaxial

(HFC) system.

Figure 6

Home users are normally provided with a cable

modem which connects to the coaxial cable used to

deliver the television, telephone and Internet services.

The cable modem provides suitable output for the





devices required – TV to the television, voice services

to the telephone, and data to the home router.

Typical cable modems use Ethernet to provide the

connection to the home router WAN port. Thus, home

routers designed for DSL and cable systems are not

compatible, as their WAN ports are designed to

support different signals.

Although cable providers generally offer a higher

speed Internet service than DSL, the speed depends

on the number of local customers, and as the number

of users increases, the data rate decreases. Cable

customers must use the ISP services of the cable

provider as cable operators are not required to open

up their network to competitors.





4 Fibre optic Fibre optic transmission media consists of a glass core

surrounded by a slightly less optically dense cladding

material. Pulses of light, representing binary digits, are

transmitted into the fibre using laser or LEDs and

propagate along its length due to refraction at the

core/cladding interface.

Fibre optic provides extremely high data rates over

great distances, and fibre optic cables are used to

provide telecommunication links between continents

using cables laid across the seabed. Because many

WAN connections need high data rate links between

service providers based in different countries, fibre

optics are commonly used.

As service providers need to use a common,

standardised interface to exchange data, their fibre

networks use either Synchronous Optical Networking

(SONET) or Synchronous Digital Hierarchy (SDH)

standards. These standards define how data is

transferred over high data rate circuits stretching over

thousands of kilometres.





Figure 7

A newer fibre optic technique used for long distance

communications is dense wavelength division

multiplexing (DWDM), shown above. This allows a

single fibre to support multiple channels (around 80,

only 4 shown) by using different wavelengths (i.e

colours) of light, with each channel supporting a data

rate of 10 Gbps.

DWDM fibre optic technology is now used in all the

submarine cables laid between the continents.

Some home users are also able to benefit from the

high data rates available from fibre optic through a

number of changes to the existing network. For

example, fibre to the home (FTTH) is replacing the

copper cabling that used to provide the ‘local loop’

connection between households and service

providers, and offers data rates of approximately 1

Gbps. Another upgrade involves the use of fibre to the

cabinet (FTTC), where fibre optic is run from the Page 17 of 44 29th August 2017




service provider to the local street cabinet, which is

then connected to individual properties using copper

cabling.

Because FTTC still utilises copper, the data rate

decreases as the distance between the cabinet and

the household increases. By around 1500 m the data

rate will have dropped to 15 Mbps in a fibre/DSL

system. Cable FTTC uses coaxial cable to the home,

which supports higher data rates of between 50–150

Mbps.

Although both cable and DSL operators have started

to offer FTTH/FTTC, it is expensive and time-

consuming to roll out, so availability is currently

limited.





5 Wireless The use of radio frequencies to support broadband

access for home and small business users has been

limited by the low transmission range typically

associated with the available wireless technology.

However, new developments in broadband wireless

technology are available that provide improved

connectivity:

municipal WiFi

Worldwide Interoperability for Microwave

Access (WiMAX)

cellular.





6 Municipal WiFi Many cities (such as London) have begun setting up

municipal WiFi networks utilising the same range

technology that is used within homes. Most of these

networks are provided to allow the emergency

services to access data services when attending an

incident, but often allow residents to access the

network for Internet connectivity too.

Figure 8

Most municipal wireless networks utilise a mesh

topology, as shown in the figure above. In this

topology the access points are all interconnected

wirelessly and several access points provide coverage

for the same area. The use of a wireless mesh

reduces the amount of cabling required to implement

it and the overlapping coverage is able to maintain

service even if several access points fail.





Note that the access points connect to a wired router

(backhaul node), which provides connectivity to a

service provider for Internet access.

Because subscribers to municipal WiFi are connecting

to access points that may be located quite a distance

from their home, they require WiFi modems with

improved receivers and directional antenna to

optimise the weak signal that they receive.

Some UK based ISPs offer a form of municipal WiFi by

allowing their customers to access the Internet by

connecting to other subscriber’s home routers via

WiFi wherever they happen to be in the UK.





7 Worldwide Interoperability for Microwave Access

WiMAX operates in a similar manner to WiFi, but

provides a higher data rate over a much wider

coverage area to more customers.

The WiMAX standard (802.16) provides data rates up

to 70 Mbps, and operates over a range of frequency

bands from 2 to 6 GHz.

WiMAX uses a network of towers, similar to those

used for cellular telephones, which provide a

broadband connection to customers within 50km. The

towers themselves provide point-to-point wireless

connectivity to the service provider’s premises, where

it is routed to the Internet. WiMAX is thus able to

provide coverage to rural areas beyond the range of

DSL and cable broadband services.

Figure 9





WiMAX, as shown above, can provide both point-to-

point links between towers and full mobile cellular type

access to subscribers, and is likely to supersede

municipal WiFi as the preferred wireless broadband

technology. WiMAX customers connect to the service

using a variety of WiMAX capable devices, such as

home routers, or mobile devices with integrated

WiMAX technology.





8 Cellular wireless Cellular or mobile telephony provides telephone

services using wireless technology, allowing users to

place calls from a wide range of handsets (smart

phones, laptops, tablets) to a network of fixed base

stations (or cell towers). The base stations are

connected to the cellular service provider’s network

either by point-to-point or wired links, allowing calls to

be placed to other cellular users and telephones

within the PSTN.

Figure 10

Cellular providers also support connectivity for data

services such as email and web surfing, and cellular

wireless has become an increasingly popular way of

accessing Internet based services for mobile users.

Because of the comprehensive cellular coverage of all

but the most remote areas of the UK, it can also be





used to provide Internet WAN services for domestic

subscribers using cellular-capable home routers.

The data rate, wireless frequencies and coverage

areas available via cellular WANs depend on the

technology utilised. This is referred to as

‘generations’, with each passing generation providing

an improved service when compared to its successor.

Common cellular industry terms include:

3G wireless, or third generation cellular

access, is a range of technologies

supporting wireless Internet access. 3G

systems can support data rates of

between 7.2 and 42 Mbps, depending on

the actual technology.

4G/Long Term Evolution (LTE), or

fourth generation cellular access, can

support a theoretical maximum data rate

of 150 Mbps.

The data rate actually achieved via cellular WAN is

extremely variable as there are many factors that can

significantly reduce the rate from the theoretical

maximum, such as distance from the cell tower,

movement and electromagnetic interference.





9 Sending data across the LAN Your home network provides access to both the

devices you have installed within your house, and to

the Internet via the WAN connection provided by your

ISP. Before considering how data is sent to and from

the WAN, we will examine how devices within the

home network exchange data.

Consider the home network shown below, where PC1

is sending a file to a printer connected to the network:

Figure 11

Both PC1 and the printer are using IP addresses

within the private range of addresses in IP network

19.168.0.0/24. The printer is listening on a registered

port of 9100 and the PC has selected registered port

1024 to identify its TCP session with the printer. Both

devices are fitted with an Ethernet NIC card, which

have manufacturer assigned MAC addresses.

PC1 first performs a check on the planned source and

destination addresses to see which IP networks they

are within:





Figure 12

PC1 uses its own subnet mask (/24 – 255.255.255.0)

to determine the IP network that it is within. The mask

identifies the first three octets of the IP address as

belonging to the IP network address: 192.168.0. It

then simply adds a ‘0’ to the end to complete the

address: 192.168.0.0. PC1 then uses the same

subnet mask to see which IP network the destination

address is within and achieves the same result,

192.168.0.0.

PC1 recognises that the source and destination IP

addresses are within the same IP network, so there is

no requirement to forward them to a default gateway

(the home router) for delivery to a different IP network.

PC1 encapsulates the print information into a

succession of TCP segments, which are then

encapsulated in appropriately addressed IP packets.

The source address identifies PC1 (192.168.0.101)

and the destination address identifies the printer

(192.168.0.102):





Figure 13

The packet needs to be encapsulated within an

Ethernet frame by the NIC on PC1. This appears to be

straightforward until you consider the destination MAC

address field. How does PC1 learn the MAC address

burnt into another device’s NIC?

Figure 14

At this point, PC1 is unable to identify the correct MAC

address to place in the destination field of the frame,

so the frame cannot be transmitted to the printer.

Consequently PC1 initiates a broadcast communication to all the devices in its IP subnet using

the Address Resolution Protocol (ARP), requesting





information about the MAC address associated with

the device using IP address 192.168.0.102:

Figure 15

Note the destination address used by the ARP is

FF:FF:FF:FF:FF:FF – this is a broadcast address,

which is flooded by the Ethernet switch from all its

ports (apart from the one the address was received

on). Thus, all the devices within the LAN receive the

ARP query, but only the printer responds as the query

contains its IP address. It returns an ARP response,

identifying its assigned MAC address:

Figure 16

PC1 uses the MAC address received in the ARP

response to complete the destination MAC address

field in the frame it is using to send data to the printer:





Figure 17

Because ARP uses a broadcast destination address it

can have a large impact on the operation of Ethernet

switches, which are required to flood multiple copies

of it from all their ports. To ease this burden, PC1

creates a local table called an ARP cache in which it

stores all the IP address/MAC address pairings it has

learnt. As a result, subsequent frames created by PC1

addressed to the printer will use the ARP cache to find

the required destination address instead of using

ARP.

The entries in the ARP cache have a lifetime

associated with them, which is constantly updated

while the device is sending frames using the entries.

Once the device stops sending frames the entries will

timeout and be removed from the cache. This

prevents the cache becoming full of outdated MAC

address information.





10 Sending data to the WAN When your home devices forward data towards the

Internet, they use source and destination IP

addresses that sit within different IP networks, so the

data must be forwarded via the default gateway

(home router). Consider the network shown below,

where PC1 wishes to access the WWW server:

Figure 18

PC1 performs a check on the planned source and

destination addresses to see which IP networks they

are within by comparing them with its own subnet

mask:

Figure 19

PC1 recognises that the destination address is on a

different IP network and that it must send packets via

the default gateway it has been configured to use:





192.168.0.1. PC1 encapsulates the webpage request

into a succession of TCP segments, which are then

encapsulated in appropriately addressed IP packets.

The source address identifies PC1 (192.168.0.101)

and the destination address identifies the web server

(211.100.100.1):

Figure 20

Why doesn’t PC1 use the address of the default

gateway (192.168.0.1) as the destination of the

packet? Remember that IP addresses are used to

provide end-to-end connectivity between devices

located on different IP networks – they are not used to

identify any intermediate devices through which the

packet is forwarded. PC1 therefore encapsulates the

packet within an Ethernet frame and uses its

destination MAC address to deliver the frame to the

default gateway.

Once again, PC1 uses ARP to determine the MAC

address being used by the interface with IP address

192.168.0.1:





Figure 21

The ARP query generated by PC1 is sent in a

broadcast frame and delivered to all the devices in the

home LAN. R1 recognises its own IP address within

the ARP query and returns an ARP response

providing its MAC address:

Figure 22

PC1 uses the MAC address it received in the ARP

response to complete the destination MAC address

field in the frame it is using to send data to the default

gateway:





Figure 23

The frame is delivered across the local network to the

gigabit interface of the home router, R1. Because the

destination MAC address of the frame matches the

MAC assigned to the interface, the router accepts the

frame and de-encapsulates it to recover the packet.

The router then tries to match the destination IP

address with an entry within its own routing table so it

can make a forwarding decision:

Figure 24

The image above shows the home router in slightly

more detail, including the routing table which contains

two entries. The devices within the home network are

connected to the router via the G0/0 interface, so

network 192.168.0.0/24 appears directly connected.

The second entry shows a default route, connected to

the external WAN interface G0/1. It may look strange Page 34 of 44 29th August 2017




as it consists of an all zero IP address and subnet

mask. However, this means that it will match all possible destination IP addresses and forward

them from interface G0/1 towards the ISP.

Why is a default route required? Remember, a router

will only forward a packet if it finds a match for its

destination IP address within the local routing table. If

the home router did not use a default route it would

need to have an entry for every possible destination

network within the Internet, and it simply does not

have enough memory to do that.

By using the default route to forward all packets to the

ISP, home users are relying upon the routers within

the service provider’s network having sufficient routing

information to be able to deliver their packets to the

required destination networks.

Once the router has determined that the packet needs

to be forwarded from G0/1, it has three tasks:

switch the packet to interface G0/1

perform Network Address Translation

(NAT) on the source address of the

packet

encapsulate the packet in an appropriately

addressed frame.





Figure 25

The diagram above shows more detail about the

connection between the home router and the ISP. The

G0/1 interface is connected via whichever broadband

technology is being used (DSL, cable or wireless) to a

router within the ISP, which is configured with IP and

MAC addresses.

Referring to the diagram, note that the source IP

address of the packet has been converted by NAT to

87.100.100.10, which is the public IP address that

uniquely identifies the home router within the

Internet.

The packet is then encapsulated within an Ethernet

frame, which uses the MAC address of home router

interface G0/1 as its source and the MAC address of

the ISP router interface as its destination.

Subsequent routers that forward the packet towards

the WWW server will not change the source IP

address, otherwise reply packets would not be able to

locate the home router.





The packet will be encapsulated in a new frame every

time it is forwarded by a router. The frames that are

used may not be Ethernet – it depends on the type of

WAN technology that is utilised by the devices which

forward the packet to its destination.

Another function provided by routers is to limit the

spread of broadcast traffic such as ARP. Imagine

what would happen if ARP could be propagated

across the Internet – every time an ARP was

generated, on any device, it would be sent to every

other device in the world. This is obviously extremely

undesirable and router interfaces create a broadcast

domain – they will examine broadcast traffic, but they

will not forward it onto other networks.





11 Point-to-Point Protocol over Ethernet

So far, you have looked at the network access layer

protocol Ethernet and its role in transporting frames

between devices within networks. It is also important

to note that a wide variety of other network access

protocols are utilised within service provider networks,

some of which include:

High-Level Data Link Control (HDLC)

Point-to-Point Protocol (PPP)

Asynchronous Transfer Mode (ATM)

You will not encounter these protocols within a home

network, but some of the functions of PPP are utilised

to support the connection between a home router and

a service provider.

PPP functions include the ability to assign addresses

to remote devices (in a similar manner to DHCP) and

to authenticate devices attempting to connect to a

network. Authentication is the process in which a user

provides information, such as a username and

password, to identify themselves to the service

provider. Authentication is obviously very important

from a service provider’s point of view, as it allows





them to restrict access to their network to genuine

(paying) subscribers.

Many ISPs use Ethernet framing to connect

households and their own networks, but Ethernet on

its own cannot support authentication. This leads to

the development of Point-to-Point Protocol over

Ethernet (PPPoE), which is a network access protocol

capable of encapsulating PPP frames within Ethernet

frames:

Figure 26

Because the PPP frame is included within the data

payload area, it reduces the room available for

carrying packets. PPPoE allows ISPs providing ADSL

broadband to use the functions of PPP, particularly

authentication, while still providing an Ethernet

service.

Another option for connecting a home router to an ISP

is PPP over ATM (PPPoA), which provides essentially

the same function as PPPoE for service providers

who have implemented ATM routing within their WAN.





The main difference between the two protocols from a

home user’s point of view rests in authentication.

PPPoA requires the home router to be configured with

a username and password in order for it to connect to

the ISP. Any home device that connects to the home

router is then able to access the Internet via the ISP.

PPPoE offers the same service but, additionally, it can

be installed as a client application on individual

devices, allowing them to establish separate,

authenticated sessions with the ISP.





12 ActivityActivity: Understand the devices and protocols used in LAN and WAN networks (Packet Tracer)This module has explored the interaction between devices located

on the LAN as they access WAN services in theory. Try this

activity to see the interaction in action.

You will need:

Lab Book: Understand the Devices and Protocols Used in LAN and WAN Networks

Packet Tracer CASBIT.pkz




http://www.open.edu/openlearncreate/mod/oucontent/olinkremote.php?website=The%20operation%20of%20LAN%20and%20WAN%20hardware%20and%20protocols&targetdoc=CASBIT

https://www.netacad.com/courses/packet-tracer-download/

http://www.open.edu/openlearncreate/mod/oucontent/olinkremote.php?website=The%20operation%20of%20LAN%20and%20WAN%20hardware%20and%20protocols&targetdoc=Lab%20Book:%20Understand%20the%20Devices%20and%20Protocols%20Used%20in%20LAN%20and%20WAN%20Networks

http://www.open.edu/openlearncreate/mod/oucontent/olinkremote.php?website=The%20operation%20of%20LAN%20and%20WAN%20hardware%20and%20protocols&targetdoc=Lab%20Book:%20Understand%20the%20Devices%20and%20Protocols%20Used%20in%20LAN%20and%20WAN%20Networks


13 End of course quizNow it’s time to test what you’ve learned in a quiz.




http://www.open.edu/openlearncreate/mod/oucontent/olinkremote.php?website=The%20operation%20of%20LAN%20and%20WAN%20hardware%20and%20protocols&targetdoc=The%20operation%20of%20LAN%20and%20WAN%20hardware%20and%20protocols%20quiz


14 AcknowledgementsGrateful acknowledgement is made to the following sources:

Figure 1: Cisco

Figure 2: Cisco

Figure 3: Cisco

Figure 4: Birmingham City University (BCU)

Figure 5: Cisco

Figure 6: Cisco

Figure 7: Cisco

Figure 8: Cisco

Figure 9: Cisco

Figure 10: Cisco





















Every effort has been made to contact copyright holders. If any

have been inadvertently overlooked the publishers will be pleased

to make the necessary arrangements at the first opportunity.




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