06.01.04 tie29d - © ritva laiho 1

06.01.04 TIE29D - © Ritva Laiho 1

TIE29F – Operation and practice of an Information Network

Part 2: WAN

= Additional information


Choosing a network• Requirement

• What is the network used for?• Which solutions meet the requirements?

• Performance• Does the network meet the required performance• Speed and reliability

• Knowhow• Is the technology to modern? Is necessary training available?• Too many partners?

• Security• Is the solution secure enough?

• Standards• Does the solution meet standards?


Choosing a network

• Costs– Design, purchase, installation and training

• Both hardware and software• The price of the hardware is often only a small part of the

total costs.

– Costs during the who life span• What is the estimated life time of the network?• Cost of maintenance is usually underestimated

– Quality and costs must be in balance• Users’ needs and the budget are usually far a part• Find out the real requirements• Solve the necessary requirements without go bancrupt.


Contents 1) Connecting LANs

– Properties of different alternatives•Leased line, data transmission networks

– Some technology•structure and operation of an digital phone network•terminology: circuit switched and packet switched

etc.

2) Working at home– Properties of different alternatives

• ISDN, modem, GSM, kaapeliverkko, ADSL, wireless, power line networking, satellites

– Some technology• Modem basics etc.


Contents - 1Connecting LANs:

(Micro wave link)Leased line

• (Expensive). Fixed monthly rent• Security is generally good, even if the telephone company may tap the wire.

Data networksInternet

• Open. Combination of many different technologies. Connection through a ISP.• Inexpensive. No guaranteed speed. Not secure. Need encryption and firewalls

to make secure.

Data network• Closed system. Service bought from one tele operator. (Datanet, LanLink)

Note! Small enterprises can use same methods as are used at home.


Digital telephone network ...

Many names:

YPV = Yleinen puhelinverkkoPSTN = Public Switched Telephone

NetworkPOTS = Plain Old Telephone Service



Exchange

Exchange

Exchange

Exchange

Exchange

Exchange

Exchange

local telephone exchanges (concentrators)

Customer line (“last mile”, local loop)• Analog max 56 kbit/s• Digital (ISDN) max 2 * 64 kbit/s

155 Mbit/s (STM-1)34 Mbit/s (E3)Connections between exchanges are

always digital. Speed of connection: 2,5 Gbit/s (STM-16)


Digital telephone network ...• Even if speech is an analog signal connections between

telephone exchanges use digital signals.– Digital technology is cheaper and faster.– Error rate is smaller and data may be encrypted.

• Analog signal must be digitized:– Analog line: digitized in the closest exchange/concentrator– Digital line: ISDN terminal adapter (analog phone) or in

ISDN phone

exchangeexchange



Analog-digital conversion:– Analog signal is sampled at regular intervals.– A sample tells the amplitude of the signal at

the sample time.– Original signal can be regenerated from

samples with digital-analog conversion.

time0

127

-127

-127 sample 127,each sample is 8 bits



0110110001011011 . . . .

Sample rate is 8000 per second.Each sample is 8 bits. Transmission speed is 8000 * 8 bit/s = 64 000 bps

CODEC

CODEC =code/decode

samplesample….



Coding method• PCM pulse code modulation• Nyquist theory: sample rate must be at

least twice the signal frequency• Frequency of normal human speech is

between 300-3400 Hz• A sample rate 8000 1/s is selected. Upper

limit of the frequency range is therefore 4000 Hz. Higher frequencies are filtered out.


Digital telephone network ...In old telephone networks one cable was reserved

for every call.

– Its not possible to have a cable for each call in today’s telephone networks, because the number of calls have increased rapidly.

12

3

circuit switching


Digital telephone network ...In modern telephone netwoks

– Trunk cables between telephone exchanges carry several calls by time division multiplexing (channeling).

– Each call is given a time slice. Time slices are transmitted alternately in the cable. Number of time slices is constant (for example 32 in E1 cable).

– Network is still circuit switched. Each call gets a virtual circuit.

– The speed of one virtual circuit (or channel) is 64 kbps.


Digital telephone network ...Time division multiplexing • One cable can carry many calls. Samples of each

call are sent alternately.• For example in ISDN two calls are multiplexed in a

cable.

1/8000 s

1/8000 second

One sample is send in 1/16000 s

multiplexer

8-bit sample



Trunk cable types and speeds:E1 = 2 Mbps or 32 voice channels, (USA: T1 = 1,5

Mbps)E3 = 34 Mbps or c. 500 voice channels(USA: T3 =

45 Mbps)OC-3/STM-1 = 155 Mbps or c. 2 400 voice channelsOC-12/STM-4 = 622 Mbps or c. 9 600 voice

channelsOC-48/STM-16 = 2,5 Gbps or c. 38 400 voice

channels

OC-192/STM-64 = 10 Gbps or c. 153 600 voice channels.


Digital telephone network ...Sending data in telephone network• Each voice channel can carry 64 kbps data.• Several channels can be combined to

achieve higher speeds.– For example ISDN connection uses two channels

which can be combined together. This way the speed can be increased to 128 kbps.



Sending data in telephone network– Leased line:– Telephone companies lease channels from

trunk cables.– Connection is permanent.– Fixed monthly charge.– High speed– Cheap if traffic is high


ExchangeExchange

Exchange

Exchange

Telephone network

ExchangeE1

E1

Helsinki

TurkuNecessary number of channels leased from trunk cables

Connecting LANs with a leased line

Structure

Usually the whole cable to the closest exchange is leased for the connection



• Telephone company leases a point-to-point connection between LANs. – The cable to the closest telephone exchange

(or concentrator) is normally dedicated to this connection. Often a new cable must be installed.

– Trunk cables between exchanges have normally a very high capacity. Only required number of channels is leased.

• For example 2 Mbps => 32 voice channels (32 * 64 kbps = 2048 kbps)


Costs– Initial costs depend on the speed.– Monthly charge depends on the speed and

distance between networks. The amount of traffic does not effect.



Security • Leased line is relatively secure if the

telephone company can be trusted.– Security can be improved by using encryption

Who can use leased lines?• Medium to large companies. Cost effective

if network traffic is high.• Leased lines are also used to connect to

the Internet.




Lan need a router and a cable modem to connect to a leased line.

E1-cable


Contents - 1

Connecting LANs:Leased line

• Expensive. Fixed monthly rent• Security is generally good, even if the telephone company may tap the

wire.

Data transmission networksInternet

• Open. Combination of many different technologies. Connection through a ISP.

• Inexpensive. No guaranted speed. Not secure. Need encryption and firewalls to make secure.

Data network• Closed system. Service bought from one tele operator. (Datanet,

LanLink)

Note! Small enterprises can use same methods as are used at home.


Data transmission network• Data transmission networks are designed

to data transmission not for speech– Connection times are longer in data

transmission.– Capacity of the telephone network is waisted,

because data is not sent continuously.– Small delays are acceptable in data

transmission.

• Data transmission networks are based on packet switching.– Better use of capacity

• Charge is based on amount of trasfered data and speed.


Data transmission networks1) X.25 (traditional packet network)

– Originally meant for terminal connections– Max 64 kbps– Not recommended any more.

2) Frame Relay– Meant for connecting LANs– Max 2 Mbps– Rather expensive– Internet more popular

3) ATM– Designed to be a universal network (video, voice, data)– Speed: 155 Mbps, 622 Mbps, 2.5 Gbps, …– Used as LAN and Internet backbone– Complicated and expensive


Open and closed data network

• Specialized data transmission networks, like Frame Relay, are based on one technology. They are closed networks owned by one operator.

• Internet is an open network which uses many different technologies.


TerminologyCircuit switched ... • Telephone network is base on circuit switching and

time division multiplexing• For each call a fixed amount of capacity is reserved

from the network. • A call reserves the capacity until the call is ended.

Piirikytkentä = circuit switching


Circuit switchingA virtual circuit is made between terminals. Each call gets a time slice.In the picture every fourth time slice is reserved for the green connection.

21

6

5

4

7

3

data

Terminology

switch


TerminologyPacket switched• Data is split to packets. Each packet contains

several bytes. • Packets of different connections are carried in the

same cable.– If only one connection is sending, it can use the

whole capacity. – Each packet contains information of the

connection.

Pakettikytkentä = packet switching


21

6

5

4

7

3

data address

Terminology

Packet switched- A connection reserves capacity only when sending data.

B

A

BB

B

B

BB

B

B

B

B

C

C

B

C

CC

C

C


firewall

ISP

Internet

ISP

VPN (encrypted connection between LANs)

Connecting LANs through the Internet

HelsinkiTurku

Connection with a leased line or ADSL

No fixed route or speed.



Internet – Internet is a packet switching data

transmission network.– Internet uses many different

technologies.– Internet is made of networks connected

with routers.– No guaranteed speed!

• The connection to the Internet may be fast (for example 2 Mbps). Still speed between LANs may be only a few kbps.



Enterprises connect to the network of an ISP (Internet Service Provider):– Many different ways to connect. Most popular

are:• Medium and large enterprises: leased line (2, 34, 155

Mbps)• Small enterprises: ADSL

– Different sites can use different technology and speed.



Security– Internet is on open network. It is not secure:

– It’s relatively easy to listen and even to change any transmission.

– Network can be attacked through Internet.

– Improving security:– Firewall prevents unauthorized connections– VPN (Virtual Private Network) creates a secure

connection between to LANs.– Virus protection, user authentication, encrypted

mail…


Connecting LANs through the InternetCosts

– Internet is cheaper than an dedicated connection between netwoks.

• Internet connection is needed anyway.

– Costs include:• Connection to the Internet. Leased line or ADSL. Fixed

monthly charge.• Traffic based charge for using Internet.• Additional services: email, web hosting, domain name

registration.


Working at home:

• ISDN • Analog modem• GSM• ADSL• Cable modem• Wireless connection• Power line • Satellite

Direct connection to enterprise network or through ISP

Connection through ISP

ISDN

Contents - 2


ISDN ...• What does ISDN mean ;-)

ISDN = It Still Does NothingISDN = I See Dollars NowISDN = Integrated Services Digital Network


ISDN• ISDN developed in the beginning of 1990’s

– Because telephone network is nowadays digital, it seems natural to have also digital subscriber lines.

– ISDN was not popular at first. It was too expensive and didn’t offer any real advantages to ordinary users.

– ISDN became popular only when Internet came to homes.

• ISDN is not recommended any more. New solutions like ADSL are better and prices are almost the same.

• First ISDN was to expensive. Now it’s to slow.


… ISDN

• BRI - Basic Rate Interface– 2 B-channels and 1 D-channel – Ordinary telephone line– used as a home connection

• PRI - Primary Rate Interface– 30 B-channels and 2 D-

channels– Need an E1 cable– Used to connect telephone

exchanges and modem pools.

PRIPRIB-CHANNELB-CHANNEL

D-CHANNELD-CHANNEL

BRIBRIB-CHANNELB-CHANNEL

D-CHANNELD-CHANNEL

B-CHANNELB-CHANNEL

There are two types of standars connections

B-channel = voice channelD-channel = control channel


ISDN, BRI

B channel

B channel

2B+D

All channels in one cable

ISDNTerminal adapter

D channel: controls the connection.

Terminal adapter converts analog signal to digital.

Analog connection can be converted to ISDN.


ISDN, BRIISDN uses time division multiplexing to

send all channel in the same cable 2 B channels– Two simultaneous connections possible. For

example a phone call and Interner connection.– Both channels can be used together for higher

speed (128 kbps)

1 D channel– D channel is meant to carry signalling and control

information– D channel is always open. In some countries D

channel can be used to carry data.


Working at home:


Direct connection to enterprise network yrityksen or through ISP


Contents - 2


Analog modem

Digitalsignal(1101)

modeemi

Analogsignal

Digitalsignal(1101)

modem

Analogsignal

Modulation

Demodulation

Digitalsignal(1101)


Analog modem

Internet-connection:

More information about modems:http://computer.howstuffworks.com/modem.htm


Working at home:




Contents - 2


GSM-network ...– A computer can be connected to a

GSM phone with a GSM modem. Modem depends on the model of the phone. New phones can use infrared or Bluetooth connection.

– Connection between the phone and a base station is encrypted.

– Data speed is about 6 kbps.

Base station

Radio waves• wireless• encrypted Internet

Cell phone network


GSM-network ... Mobile network is made of cells. (cellular

network)• Each cell has a base station• One base station controller controls many base

stations• Cells may overlap.

Base stationcontroller


GSM-network ...

BTS= BaseTransceiver Station

Cell

BSC= Base Station

Controller

MSC = Mobile Switching Centre NSS = Networkand Switching

Subsystem

OthernetworksBSS = Base Station System MS =

MobileStation

SIM-card = Subscriber Identity Module

HLR, ...

databases


GSM-network ...


GSM-network ...

Databases in mobile telephone network– Home Location Register (HLR)

• Basic information of subscribers, current locations of the telephones and subscribed services

– Visitor Location Register (VLR)• Information of visiting subscribers. Information is copied

from subscribers home location

– Authentication Center (AuC)• Authentication information and encryption keys

– Equipment Identity Register (EIR) • List of authorized telephones• International Mobile Equipment Identity (IMEI)


Working at home:




Contents - 2


ADSL (Asymmetric Digital Subscriber Line) ...• Uses normal telephone cable

– Can be used simultaneously with a normal telephone call. ISDN and ADSL may not work together.

• Asymmetric: incoming speed is higher than outgoing speed.– For example 256/128 kbps, 512/256 kbps, 1

Mbps/256 kbps

• Used only to connect to the Internet– Need an ADSL modem.

– Permanent connection. Firewall needed.– Maximum cable length to the telephone exchange

is about 5 km.

• Costs: installation + fixed monthly charge


ADSL (Asymmetric Digital Subscriber Line)

• ADSL is not one standard. Different providers may have different systems.

• Different ways to connect:

ADSL modem connected to a single computer. Computer can share the connection to other computers. Personal firewall needed.

ADSL modem with a switch (hub). Personal firewall needed in every computer

ADSL ADSL ADSL

ADSL modem with switch and firewall


Cable modem• Works only where a cable TV is available.• Permanent connection to Internet. Does not need a

telephone line. – Firewall necessary

• Asymmetric– Incoming speed: 500 kbps - 10 Mbps – Outgoing speed about 64 kbps


Wireless

• Customer connection is wireless. Permanent Internet connection– ISP installs a base station near the customer

and connects the base station with a cable to ISP’s own network.

– The customer needs a WLAN adapter and in some cases an external aerial.

– The customer should use a firewall!

• Used WLAN technology (IEEE 802.11)– A limited number of connections in each base

station


Power line

• Uses normal electric power line.• Only available in some areas.• For more information:

http://computer.howstuffworks.com/power-network.htm

06.01.04 tie29d - © ritva laiho 1

Technology

digital telephone network

information network

digital technology

network requirement

telephone company

digital signals

analogdigital conversion

digitalanalog conversion