Telecommunications systems(Part 2)

School of BusinessEastern Illinois University

© Abdou Illia, Spring 2007

(Week 12, Thursday 3/29/2007)

T-1

Digital Subscriber Line (DSL)Cellular Telephone System

Integrated Services Digital Network (ISDN)

2Learning Objectives

Describe and compare types of connections offered by telephone companies

Explain Cellular Telephone System

T-1 Leased lines

4Trunk lines

Trunk lines = Type of transmission lines that connect nodes.

Trunk lines operate at speed from 56 kbps to 40+ Gbps

Trunk lines

T-1 1.544 MbpsT-3 45 MbpsSONET768 40+ Gbps

Synchronous Optical Network

5T-1 Lines

Computer TelephoneSwitch

TelephoneSwitch

TelephoneSwitch

Server

AccessLine

T-1 Trunk Line (1.544 Mbps)

T-1 Leased Line (1.544 Mbps)End-to-End Circuit with Trunk Line Speed

TrunkLine

6T-1 Leased lines

T-1 Leased lines:– Extend T-1 trunk line speeds to end-to-end circuits

between two locations (e.g. 2 customer offices)

– Require fiber optic or at least a special data-grade twisted Pair (Note: fiber optic is used for T-3 and SONET)

Data-Grade Twisted Pair

Q: What is the difference between T-1 Trunk line and T-1 Leased line?Q: In T-1 Leased lines, what kind of TP is used to connect a customer to the 1st telephone switch?

7T-1 Lines

The customer can request Fractional T-1 lines that offer low-speed choices, typically:

128 bps 256 kbps 384 kbps 512 kbps 768 kbps

T-1 Costs depend on distance:– ~$350-400/mo for local connection (non long-distance)– ~$1200/mo plus 2.50/mile for long-distance connection

Digital Subscriber Line - DSL

9Digital Subscriber Line (DSL)

Standard telephone line (Cat 1 UTP)– Capable of handling more than 3.1 Khz bandwidth

DSL exploits Standard telephone line’s “extra capacity” to transmit data without disturbing the line’s ability to transmit voice

Bandwidth usage for some Asymmetric DSL (ADSL) services:

– 0 - 4 Khz band for Voice conversation– Upstream data transmission in 25 – 160 Khz band– Downstream data transmission in 240 – 1500 Khz band

DSL uses filters (splitters) to separate voice and data signals– Typically a filter is needed for each analog device (telephone, fax, etc.)

10Digital Subscriber Line (DSL)

DataWAN

PSTN

DSLAM*

DSLModem

Splitter

Telephone

Telephone CompanyEnd Office Switch

Standard telephone line

PC

* DSL Access Multiplexer: (1) mixes data from many customers and (2) forwards mixed packets

UserEnd

11Digital Subscriber Line (DSL)

DataWAN

PSTN

DSLAM

DSLModem

Splitter

Telephone

UserEnd

Telephone CompanyEnd Office Switch

PC

Q: On the user end, what elements are needed to establish a DSL connection?

12Digital Subscriber Line (DSL)

DSL speed: 256 kbps – 24000 kbps

Digital Subscriber Lines (DSLs)– Asymmetric DSL (ADSL)

Standard ADSL– Downstream (to customer): 256 kbps to over 1.5 Mbps– Upstream (from customer): 64 kbps or higher

ADSL2– Downstream (to customer): 5 Mbps to aver 12 Mbps– Upstream (from customer): 1 Mbps to 3.5 Mbps

Q: How can a 3.5 Mbps upstream speed be achieved with Cat 1 UTP ?

13Digital Subscriber Line (DSL)

Digital Subscriber Lines (DSLs)– HDSL (High-rate DSL)

Needed in business. (ADSL primarily for home and small business access.)

Maximum range: 3 kilometers

Symmetric speed over voice-grade twisted pair

– HDSL: symmetric 768 kbps

– HDSL2: symmetric 1.544 Mbps or symmetric 2.3 Mbps

14

Summary Questions

1. What is the difference between a T-1 Trunk line and T-1 Leased line?

Answer: A T-1 trunk line only runs between two switches within the telephone network. T-1 Leased lines extend T-1 trunk line speeds to end-to-end circuits between 2 locations.

2. In T-1 Leased lines, what kind of twisted pair wire is used to connect a customer to the 1st telephone switch?

Answer: Data-grade TP which is a category 2 TP.

15

Summary Questions

3) On the user end, what elements are needed to establish a DSL connection?

A DSL modem and splitter(s) to separate regular analog channel from the DSL data channels.

4) ADSL provides for higher downstream speeds than upstream speeds. (a) Is this good for web service? (b) Is it good for videoconferencing?

a) Asymmetric speeds are good for web service because http requests tend to be small but downloaded material are large.

(b) It is not good for videoconferencing, which needs high speed in both directions.

16Twisted Pair wires

Cellular Telephone System

18Cells, Cellsites, MTSO

B

E

H

D

I

G

L

K

F

C

M

A

J

N

P

O

PSTN

Mobile TelephoneSwitching Office

Cellsite

Metropolitan service area is divided into cells.

Cellsite in each cell communicateswith cellphones.

MTSO controls all cellsites,links cellular system to PSTN.

19Cellular Telephone: The big picture

B

E

H

D

I

G

L

K

C

M

A

J

N

PO

PSTN

Mobile TelephoneSwitching Office

Cellsite

Cellsite main components:- Transceiver- Devices for supervising cellphones’ operation (initiating calls, terminating calls, etc.)

F

20Why cells?

B

E

H

D

I

G

L

K

F

C

M

A

J

N

P

O

PSTN

Mobile TelephoneSwitching Office

Cellsite

Why cells?So channels can be reused in different cells.

Channel reuse allows more customersto be supported.

Channel47

21Mobility

Handoff– Switching service from one cellsite to another when

users move from cells to cell in a system (city)

Roaming– Switching service from one MTSO to another when

users move from one system (city) to another.

L

N

PO

Handoff

22Generations of Cellular Technology

Generation 1G 2nd 3G

Year 1980 1990 2002

Signaling Analog Digital Digital

Data Transfer RateData transfer

is difficult;~5 kbps

10 kbps30 kbps to500 kbps

Technology

FrequencyDivision

Multiplexing

FDM

CodeDivision

MultiplexingCDM

CodeDivision

MultiplexingCDM

23Summary Questions

1) In cellular technology, what is:a) A cell?b) A cellsite?

2) What is the benefit of using cells instead of a large geographical area?

3) What are the main functions of a Mobile Telephone Switching Office (MTSO)?

4) Distinguish between handoff and roaming.

Integrated Services Digital Network- ISDN

25Integrated Services Digital Network

PersonalComputer

Desktop Telephone

2.64 kbps B ChannelAnalog Voice SignalOn Telephone Wires

1.64 kbps B Channel

Digital SignalOn Serial Cable

(1010)

ISDNWallJack

(RJ-45)

Original idea: one voice channel, one data channel

26Integrated Services Digital Network

PersonalComputer

Desktop Telephone

“ISDN Modem”

64 kbps B ChannelDigital Signal

On Serial Cable(1010)

Internal DSUConverts Serial Port

Signal to DigitalB Channel

Signal at 64kbps

(1010)

All-digitalService

(1101001..)

ISDNWallJack

(RJ-45)

The Data ChannelUses 232 Serial Cable

27Integrated Services Digital Network

PersonalComputer

Desktop Telephone

64 kbps B ChannelAnalog Voice SignalOn Telephone Wires

“ISDN Modem”

Internal CodecConverts

Analog VoiceSignal to Digital

B ChannelSignal at 64 kbps

(000010000))

All-digitalService

(1101001..)

ISDNWallJack

(RJ-45)

The Voice ChannelUses Home Telephone Cord

28Integrated Services Digital Network

PersonalComputer

Desktop Telephone

“ISDN Modem”

64 kbps B ChannelDigital Signal

On Serial Cable(1010)

Internal DSUConverts Serial Port

Signal to DigitalB Channel

Signal at 64kbps

(1010)

All-digitalService

(1101001..)

ISDNWallJack

(RJ-45)

BondingUse Both B Channels for DataSend and Receive at 128 kbps

29Integrated Services Digital Network

Dial Up: Not always connected– Do not have to pay for full-time use– Good if usage is small per day, say to upload sales data

from retail once per night

30ISDN Costs

Must install an ISDN line– Will cost more than telephone line

Actually, could use your existing phone line– But then would need one B channel for telephony

31ISDN Costs

Need “ISDN modem” (expensive)

Costs for standard ISDN service– $40/mo plus $1.00/minute for usage

ISDN tend to be used as a backup service. Example: Most banks communicate with headquarters using T-1, SONET, etc. If these services fails, they activate the ISDN connection.

32

Summary Questions

5. (a)  What is the highest speed you can have to and from an ISP using ISDN? (b) Is ISDN an always-active service? (c) How is it likely to be used in corporations? Why?

(a) With bonding, ISDN can provide 128 kbps Internet access.

(b) ISDN is NOT an always-on service. It is a dial-up service like ordinary telephone service.

(c) It is likely to be a backup service because ISDN payments are modest except when the service is being actively used