School of Business
Eastern Illinois University
Telecommunications systems
(Part 2)
(Week 12, Thursday 3/29/2007)
T-1
Digital Subscriber Line (DSL)
Cellular Telephone System
Integrated Services Digital Network (ISDN)
© Abdou Illia, Spring 2007
Learning Objectives

Describe and compare types of connections
offered by telephone companies

Explain Cellular Telephone System
2
T-1 Leased lines
4
Trunk lines

Trunk lines = Type of transmission lines that connect nodes.

Trunk lines operate at speed from 56 kbps to 40+ Gbps
T-1
1.544 Mbps
T-3
45 Mbps
SONET768
40+ Gbps
Synchronous Optical Network
Trunk lines
5
T-1 Lines
T-1 Trunk Line (1.544 Mbps)
Access
Line
Computer
Telephone
Switch
Trunk
Line
Telephone
Switch
Telephone
Switch
T-1 Leased Line (1.544 Mbps)
End-to-End Circuit with Trunk Line Speed
Server
T-1 Leased lines

6
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?
T-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
7
Digital Subscriber Line - DSL
Digital Subscriber Line (DSL)

9
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.)
Digital Subscriber Line (DSL)
User
End
10
Telephone Company
End Office Switch
Data
WAN
PC
DSL
Modem
Standard
telephone line
Splitter
DSLAM*
PSTN
Telephone
* DSL Access Multiplexer: (1) mixes data from many customers and (2) forwards mixed packets
Digital Subscriber Line (DSL)
User
End
11
Telephone Company
End Office Switch
Data
WAN
PC
DSL
Modem
Splitter
DSLAM
PSTN
Telephone
Q: On the user end, what elements are needed to establish a DSL connection?
Digital Subscriber Line (DSL)

DSL speed: 256 kbps – 24000 kbps

Digital Subscriber Lines (DSLs)
–
12
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 ?
Digital Subscriber Line (DSL)

13
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.
Twisted Pair wires
16
Cellular Telephone System
18
Cells, Cellsites, MTSO
PSTN
Mobile Telephone
Switching Office
Cellsite
G
D
B into cells.
Metropolitan service area is divided
Cellsite in each cell A
communicates E
with cellphones. C
MTSO controls all cellsites,
links cellular system to PSTN.
K
H
N
L
I
F
O
M
J
P
Cellular Telephone: The big picture
PSTN
19
Mobile Telephone
Switching Office
Cellsite
G
D
H
B
A
K
E
C
Cellsite main components:
- Transceiver
- Devices for supervising cellphones’ operation
(initiating calls, terminating calls, etc.)
N
L
O
I
F
M
J
P
20
Why cells?
PSTN
Mobile Telephone
Switching Office
Cellsite
G
Channel
47
D
H
B
A
K
E
C
N
L
I
Why cells?
F
So channels can be reused in different cells.
Channel reuse allows more customers J
to be supported.
P
O
M
21
Mobility

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.
N
L
P
O
Handoff
22
Generations of Cellular Technology
Generation
Year
Signaling
Data Transfer Rate
Technology
1G
2nd
3G
1980
1990
2002
Analog
Digital
Digital
Data transfer
is difficult;
~5 kbps
10 kbps
30 kbps to
500 kbps
Frequency
Division
Multiplexing
FDM
Code
Code
Division
Division
Multiplexing Multiplexing
CDM
CDM
Summary 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.
23
Integrated Services Digital Network- ISDN
25
Integrated Services Digital Network
Original idea: one voice channel, one data channel
Personal
Computer
1.
64 kbps B Channel
Digital Signal
On Serial Cable
(1010)
2.
64 kbps B Channel
Analog Voice Signal
On Telephone Wires
Desktop Telephone
ISDN
Wall
Jack
(RJ-45)
Integrated Services Digital Network
Personal
Computer
Internal DSU
Converts Serial Port
64 kbps B Channel Signal to Digital
Digital Signal
B Channel
On Serial Cable
Signal at 64
(1010)
kbps
(1010)
“ISDN Modem”
ISDN
Wall
Jack
(RJ-45)
All-digital
Service
(1101001..)
The Data Channel
Desktop Telephone
26
Uses 232 Serial Cable
Integrated Services Digital Network
Personal
Computer
The Voice Channel
Uses Home Telephone Cord
“ISDN Modem”
64 kbps B Channel
Analog Voice Signal
On Telephone Wires
Desktop Telephone
27
All-digital
Internal Codec
Service
Converts
(1101001..)
Analog Voice
Signal to Digital
B Channel
Signal at 64 kbps
(000010000))
ISDN
Wall
Jack
(RJ-45)
Integrated Services Digital Network
Personal
Computer
Internal DSU
Converts Serial Port
64 kbps B Channel Signal to Digital
Digital Signal
B Channel
On Serial Cable
Signal at 64
(1010)
kbps
(1010)
“ISDN Modem”
ISDN
Wall
Jack
(RJ-45)
All-digital
Service
(1101001..)
Bonding
Desktop Telephone
28
Use Both B Channels for Data
Send and Receive at 128 kbps
Integrated Services Digital Network

29
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
ISDN 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
30
ISDN Costs

Need “ISDN modem” (expensive)

Costs for standard ISDN service
–
31
$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 alwaysactive 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 dialup 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