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Telecommunications Technology and Services

Anne Flanagan

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Objectives

� To give an understanding of basic types of

infrastructure that are being used for all forms of

telecommunications including the Internet and

mobile

� To appreciate that limitations and capabilities of

network technologies affect choices

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Main types of network

� public switched telephone network PSTN

� legacy – but still widespread

� integrated services digital network ISDN

� Legacy and not widespread to individual users (basic

rate)

� Widespread for telephone connections to business

(primary rate)

� LANs / WLANs / Intranet / Internet

� Mobile: GSM / GPRS / 3G

� Broadband: ATM / ADSL / cable modem

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Transmission� Copper

� Telephony access network and in-building

� ADSL

� CATV including cable modem (coax)

� Ethernet

� Fiber� Long distance

� Trunk routes

� Access network to large businesses

� Data networks within businesses

� Radio� Mobile networks

� Point-to-point access and trunk connections

� Satellites – GEO / MEO / LEO

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Division of networks by sector

PBX

business customer

local exchange

trunk and international

exchanges

residential customer

access or local network

core network

access network

BSC

MSC

Also personal area networks

copper

often fibre

radio often

ra

dio

core network mainly fibre

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Wired communications based on

telephony

exchange

analogue digital

PSTN

fax

Dial-up modem

Analogue

Digital

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Broadband Networkexchange

ISP

ADSL modem

Existing copper

.. Cable modem too!

• over cable TV network• frequency bands allocated for up and downlinks

ADSL

IP

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ISDN

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digital digitalISDN

exchangeISDN phone

ISDN fax

terminal adaptor (TA)

S-bus

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Mobile networks

Still use the transmission and switching of

wired networks

Extra requirements are:

� Radio access

� Mobility

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Mobile communications

Over 2 billion mobile users globally

Analogue (1st Generation)Global System Mobile ( 2G)General Packet Radio Service (2½ G)Universal Mobile Telecommunications System (3 G)

4G ???

often a radio link to

network

Cable / radio

(Bluetooth) / infra red

PDA

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GSM Requirements� Services

� international roaming� PSTN/ISDN services

� hand held and vehicle mobiles

� Quality of Service� good as analogue mobile radio

� encryption with little extra cost

� Radio Frequency Utilisation� spectrum to co-exist with earlier systems

� high spectrum efficiency

� Network Aspects� ITU identification & numbers

� International Signalling System

� no modifications to PSTN

� protected signalling & control information

� Cost Aspects� system parameters chosen to limit cost to mobiles

� Systems� GSM (900 MHz)

� GSM1800 (was DCS1800)

� GSM 1900 (PCS in US)

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Geographical distribution - 2G

(i.e. Current technology)

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Cellular concept

GSM Base Station Subsystem

(BSS)

BTS = Base Transceiver Station

BSC = Base Station Controller

LA = Location Area

MT = Mobile Terminal

LA2

BSC

LA1

LA3

Abis

Interface

Radio

Interface

To MSC

BTS

Mobile

Terminal

BSC

Location

Area

A

Interface

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Locating a Mobile terminal

When a MobileTerminal (MT) moves from one location area to another:�MT initiates location updating procedure.

�Home Location Register is notified by the new Mobile SwitchingCenter/Visitor Location Register.

�HLR removes old MSC/VLR information

�HLR confirms and updates the new MSC/VLR.

�location area update is confirmed with the MT.

Roaming - incoming call

PSTN

BTS

BTS

MSC

VLR

BSC

MSC

VLR

GMSCHLR

MSC

VLRBSC

Home network

BTS

Visited network

Paid by caller

Paid b

y recip

ient

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Roaming - outgoing call

PSTN

BTS

BTS

MSC

VLR

BSC

MSC

VLR

GMSCHLR

MSC

VLRBSC

Home network

BTS

Visited network

Billing centre

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On the move

PC

GSM

GPRS

3G

Photos from Nokia press photos

WLAN 802/11b

WLAN AP

GSM BT

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Telephone Network

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So where 4G and beyond???

� Have we identified services that need greater

bandwidth

� ….. and are customers willing to pay for them

� Remember SMS! – We may not guess the

desired services in advance

� Technology always worth exploring, but are we

getting to the point when we have more

technology than applications

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Concept terminals

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Transmissions

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Representing information

� Natural signals are analogue (e.g. speech)� Most of the network is digital� Signals have to be converted to a suitable form for digital network:� Done in a “codec” (code/decoder)� Different codecs used for different signals

� Speech on wired networks� Speech on mobile networks� Video

� Some signals digital (e.g. from a computer)� Access PSTN network still analogue so a modem (modulator/demodulator) converts to analogue.

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Pulse code modulation used in

telephoneanalogue signal

sampled signal

quantising level

quantising samples to

nearest quantising level

bit patterns correspond to value of quantised

sample 64kbit/s (8bits@8kHz)

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telephone exchanges

Electromechanical exchange

picture courtesy of NortelElectronic exchange - one of the

College PBXs

Routing

� Route set up by signalling –

on demand control

� Early switches had little

intelligence in routing - direct routing from the number

dialled

� more intelligence is required

to translate the number dialed into a routing string:

� “director” areas in large cities

first steps in providing

translation

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0

1

0

1

0

1

06 4 8

route optimisation allows choice of

“best route” (least cost according to

some cost criterion)

alternative routing allows a

different route to be used under

conditions of congestion or failure

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Numbering, naming and

addressing

� Public network numbering

� in conformity with ITU E.163 or E.164

recommendation

� Regulatory issues

� Number portability; Carrier selection / pre-selection

� Number translation services (eg. 0800, 0345, 08XX)

� Calling-line identification (CLI)

� Scarce resource?

country

code

ITU and Numbering

00 area code local number

international

prefix

00 44 20 7882 5333full form from overseas

20 7882 5333 from within country0trunk prefix

7882 5333 from within area

national significant number

12 digits max

Geographical significance - unlike IP numbers

E. 163 and E .164

Main difference with E.164 is that numbers can be longer

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numbering plans

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5

2

3/4 7

89

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� 01 / 02 Geographic Area Codes

� 03 Reserved for Geographic Area Codes

� 04 Free

� 05 Reserved for Corporate Numbering

� 06 Free

� 07 Find Me Services: Personal Numbering, Paging, Mobile

� 08 Special Services up to national rate tariff

� 09 Premium rate services and reserved for multimedia

International codes

UK numbering plan

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Transmission

� Need to map the signals to the transmission

medium� “attenuation” requires “repeaters”

� “line coding” formats the signals

� a “modem” modulates the signal to suit the medium

� Multiplexing allows signals from lots of sources to

share the same transmission medium� frequency division (analogue) legacy apart from radio

� time division (digital)

� dense wavelength division (optical) – actually like

frequency division but for optical fibres

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TDM Multiplexing

Puts multiple signals on one transmission path:

N Tributaries

Individual bitrate: r

Link rate at least N*r

multiplexing demultiplexing

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Bit or byte interleaving

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

1 byte

3 tributaries multiplexed onto a link

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

Byte interleaving - most common now

1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8

Bit interleaving

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IP and the Internet

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The Internet

ISP PoP

Internet Backbone

routersDial-up

corporateLeased line

DSL

WLAN AP

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Basic points

� IP (Internet Protocol)� Packet-switched

� Connectionless

� Hop-by-hop routing through routers

� TCP� Over the top of IP (hence TCP/IP)

� Makes a connection-oriented connection over connectionless IP

� UDP� Equivalent to TCP but remains connectionless

� RTP� Like UDP but for real-time services

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Protocol Stack

Internet protocol stack

� application: supporting network applications

� ftp, smtp, http

� transport: host-host data transfer

� tcp, udp

� network: routing of datagrams from source to destination

� ip, routing protocols

� link: data transfer between neighboring network elements

� ppp, ethernet

� physical: bits “on the wire”

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Other common protocols over

TCP or UDP� SMTP - sending email

� POP / IMAP – different protocols for receiving email

� HTTP – web browsing

� HTTPS – secure web browsing

� SNMP – network management protocol

� NNTP – Internet news reading

� FTP – file transfer protocol

� Telnet – terminal session over TCP

� VoIP – Voice over IP

4 bytes

class A

class B

class C

multicast

reserved

0.......

10......

110.....

1110....

1111....

dotted quad notation

�dotted quad = xxx.xxx.xxx.xxx

�my PC at QM: 138.37.32.112

�Starting number, I, shows whether Class A, B or C

�Class A: I < 128

�Class B: 128 ≤≤≤≤ I < 192< 192< 192< 192

�Class C: 192 : 192 : 192 : 192 ≤≤≤≤ I

So the address at QM is a class B address

Internet addressing (IPv4)

Subnets allow the division of networks into smaller entities – e.g. EE

staff subnet is 138.37.32.xxx - too complex to consider here

The Internet is running out of addresses! IPv6 solves this problem

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cut-through switching

default operation

IP switching – mixes routers and

switches� First few

packets are

routed as

normal

� Control system

detects a “flow”

� Further packets

in the “flow”

are switched

directly

Router

Router

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Multiprotocol Label Switching

(MPLS).

� IETF standard to integrate routing with switching.� Forwarding Equivalence Class (FEC): Group of IP packets that are forwarded over the same path.

� Label: Short, fixed-length value that identifies a stream.

� Label Switched Path : used to forward the packets of a particular FEC.

� Label Distribution Protocol: distributes FEC/label bindings among participating devices to form LSP (signalling !!!)

� Label Edge Router (LER)

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Conclusions

� Rapidly developing technology� Fixed network capacity no longer scarce, but radio spectrum remains expensive and limited

� Distance no longer relevant

� Applications and services:� a service is what the customer pays for� an application is how a customer makes use of a service

� The successful business:� Sells customers the services they want

� At a price that customers are prepared to pay AND

� At a price that is profitable to the business

� Chooses the most cost-effective network to deliver the services

� Regulation- not unduly burden new technology