Telecommunications systems(Part 1)

School of BusinessEastern Illinois University

© Abdou Illia, Spring 2007

(Week 12, Tuesday 3/27/2007)

2Learning Objectives

Describe and compare types of connection to subnets and networks offered by telephone companies

3Types of connection

Dial-up: standard telephone line

56K Leased line

T-Carrier (T-1, T3)

Integrated Services Digital Network (ISDN)

Digital Subscriber Line (DSL)

(Frame Relay)(Asynchronous Transfer Mode - ATM)

4Dial up: standard telephone line Many home computer users use standard telephone lines

and conventional modems to connect to networks.

A dial-up connection is not always active

Speed limited by:– Bandwidth of standard telephone line (3.1 KHz)

Shannon Equation:Maximum speed = Bandwidth * Log2 (1 + Signal Power/Noise)

~ 35 kbps

5Modems Standards

Name Receiving speed Sending speed

V.92 56 kbps 48 kbps

V.90 56 kbps 33.6 kbps

V.34 33.6 kbps 33.6 kbps

Modem standards

V.32 bis 14.4 kbps 14.4 kbps

6

Dial up connection with modem at both ends

PSTN (Digital)

Client A

Server A Telephone

Telephone33.6kbps

Modem

Digital Signal ModulatedSignal

Modem

Need Modem at Each End

* PSTN: Public Switched Telephone Network

7

Standard telephone line w/ Digital Access Line

PSTN (Digital)

Client B

ServerBTelephone

Digital Access Line

56 kbpsModem

For 56 kbps Download SpeedServer Must Have a Digital Connection, Not a Modem

8Standard telephone lineAlthough only 35 kbps can be sent

through a typical 3.1 Khz telephone bandwidth, telephone system is digital internally with 56 kbps channels for

individual telephone calls

9Standard telephone line

ADC limits transmission speed

ADC needed because internal telephone system is digital

10Standard telephone line

Internet Service Provider (ISP) is not going through ADC

So, ISP can make full use of telephone system’s 56 kbps

11Standard telephone line

When 56 kbps signal reaches the last telephone switch:– DAC translates the digital signal into an analog signal– DAC sends the analog signal to your telephone (therefore to modem)

* DAC do not impose 3.1 kHz limitations. So modem can receive at 56 kbps

12Standard telephone line (w. modem)

Typical max speed

33.6 Upstream56 kbps Downstream

Characteristics

Data or Voice

Both

Cost per month

~$12.00

Mode of connection

Dial-up

13

56K Leased line

PSTN (Digital)

56K leased Line

For 56 kbps Upload/Download SpeedAlways on

LAN A

LAN B

56K leased Line

Most businesses need permanent high-speed connection:– to the Internet– to other businesses– to remote databases

A 56K Leased line is a an option

Q: what type of conversion device will be needed at the LANs ends?

1456K Leased line 56K leased lines:

– Are dedicated lines leased from telephone companies– Connect the Client to another party (Office, ISP, supplier, etc)– Are always active (No need for Dial)– Transfer data at 56,000 bps

Cost depends on distance:– ~$100/mo for local connection (non long-distance)– ~$500/mo plus 1.00/mile for long-distance connection

For more about 56 Leased lines, see:– http://en.wikipedia.org/wiki/Leased_line– http://www.mva.net/support/56kfaq.html

15Summary Questions

1. When a standard telephone line is used to connect to a network: (a) What device limits the speed? (b) Where is this device located?

(a) The analog-to-digital converter (ADC).

(b) It is located at the telephone company’s switch at the end of your local loop access line.

2. (a) In using a V.90 modem for dial-up connection to the Internet, what is needed at the ISP end? (b) What does the telephone company need?

(a) A digital access line to the telephone carrier (and some internal equipment).

Note: The ISP does not have a V.90 modem. If it did, it could only transmit at 33.6 kbps.

(b) The telephone company does not have to do anything differently.

Note: the telephone company does not have to install ADCs. These are already there. You use ADCs and DACs every time you make a voice telephone call.

16

Summary Questions

3. (a) How are 56K Leased lines and standard telephone lines different in terms of their operation? (b) How are they different in terms of speed and cost?

(a) With standard telephone lines you need to dial a telephone number to connect. The connection is not permanent (active only during a call). With 56K Leased line, there is no need to dial a telephone number, and the connection is always active.

(b) 56K Leased lines are faster and more expensive.

17Elements of the Public Switched Telephone Network (PSTN)

1. Customer Premises Equipment 1. Customer Premises Equipment

18Elements of the Public Switched Telephone Network (PSTN), Continued

2.Access Line(Local Loop)

2.Access Line(Local Loop)

The Access System consists ofthe access line to the customer

(called the local loop)and termination equipment at the end office

(nearest telephone office switch)

19Elements of the Public Switched Telephone Network (PSTN), Continued

3. Transport Core

3. TrunkLine

3.Switch

The Transport Core is a subnet. It includesTelephone switches and Trunk lines that

interconnect the teelphone switches.