Điện tử viễn thông c1 5 truyền thoại trên cơ sở hạ tầng viễn thông khotailieu

TRƯỜNG ĐẠI HỌC ĐIỆN LỰC
KHOA ĐIỆN TỬ - VIỄN THÔNG

TỔNG ĐÀI &
KỸ THUẬT CHUYỂN MẠCH

Chương 1: Lý thuyết tổng quan và cơ sơ
V. Truyền thoại trên cơ sơ hạ tầng viễn thông

Giảng viên: Phan Thị Thanh Ngọc
1

EPU - 2012


Nội dung
• Cơ sơ hạ tầng viễn thông truyền các loại dữ liệu sau:
– Voice
– DTMF signals
» over ISDN
» over ISDN + GSTN
» over GSM + ISDN/GSTN
– Data
» over ISDN
» over ISDN + GSTN
» over GSM + ISDN/GSTN
2

J.Tiberghien - VUB

TIN HIÊU DTMF 
Quay sô kiêu tone (Tone dialing)

1

2

3

4

5

6

*

0

#

3

1477 Hz

9

1336 Hz

8

1209 Hz

7

697 Hz
770 Hz
852 Hz
941 Hz

1

2

3

4

5

6

7

8

9

*

0

#

In - band signaling :
audio tones

J.Tiberghien - VUB


DTMF over the GSTN

PSTN

Voice
interface

Signaling
Prerecorded voice messages
Numerical answers

4

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DTMF over the ISDN
ISDN

Voice

interface

Signaling via D channel
Prerecorded voice messages (B)
Numerical answers (B)
Ad-hoc digital DTMF generator required in ISDN phones
5

J.Tiberghien - VUB


GSM : Main 
Characteristics
• Digital telephony
– Special vocoder (A/D converter) in telephone set.
» Data rate = 13 Kb/s.
» Not compatible with standard telephony codec
» High error rate (10-3)
– Separate digital signaling channel
» Calling party identification
» Other goodies similar to Belgacom’s “Comfort”
services

6

J.Tiberghien - VUB


DTMF over the GSM
PSTN

ISDN

GSM

Voice
interface

DTMF

Signaling
Prerecorded voice messages (B)
Numerical answers

DTMF

Numerical answers send to DTMF generator as short messages
7

J.Tiberghien - VUB


Data over the 
ISDN
ra

64 Kb/s
1920 Kb/s

ISDN

ra

Rate Adapter : appears to the user as a synchronous modem,
the clock being generated in the network.

n * 64 Kb/s possible but some timing problems
need to be solved in the RA's
(# delays over # channels !)
8

J.Tiberghien - VUB


IP over 
ISDN

• Usage :
– Temporary interconnections
– Back-up for leased lines
– Additional capacity for overloaded leased lines
• Main problem :
IP: Connectionless >< ISDN : Connection oriented
• Solutions :
– One call per datagram (fast connection)
– Keep connection for entire billing units

9

J.Tiberghien - VUB

Data over ISDN and the 
GSTN
ISDN

m

PSTN

m

PSTN

m

V110
ISDN

ISDN
10

m

PSTN m

m
J.Tiberghien - VUB


Data

Modem
Control

 V110 for 
ISDN
Async/
sync

M
U
X

ISDN
64 kb/s

Sampling

Data carried in 80 bit frames at 16 Kb/s
48 bit for data (=9600 b/s)
32 bit for
synchronization
modem signals
clock adjustment
real data rate
11

J.Tiberghien - VUB

Hybrid ISDN/PSTN 
modems

• Today's residential Internet access problem:
– Residential users
» most use analog lines (data rate <= 33600 b/s)
» don't want ISDN (64kb/s) because of cost
» almost entire GSTN digital at 64kb/s
– Internet Service Providers
» can afford ISDN
• A solution:
– Digital (64 kb/s) link from ISP to subscriber's local
exchange
– Special modems compatible with voice ADC.
12

J.Tiberghien - VUB


56 kb/s Modems
Analog / Digital
ABX
ABX
ABX

ABX
ABX

ABX

PABX

PABX
ABX

13

J.Tiberghien - VUB


56 kb/s modems

Analog subscriber line, Digital provider line 

Digital
switch

Modem

8000 baud, 128 states

64 kb/s
Digital
Analog

twisted pair, average length 2.5 Km Line
circuit
14

J.Tiberghien - VUB

GSM : Main 
Characteristics
• Data transmission : max 9600 b/s
– Between GSM and PSTN subscribers :
» DTMF via signaling channel
» Data via V110g modem access with error
correcting code over the GSM data channel
– Between GSM and ISDN subscribers :
» rate adapters also accessed with error correcting
code over the GSM data channel

15

J.Tiberghien - VUB


Circuit Switched Data over 
GSM
m v

PSTN

m

m

PSTN

m

ra

ISDN

ra

GSM

v

V110
GSM

GSM
GSM
16

m

J.Tiberghien - VUB


Data

Modem
Control

 V110 for 

GSM
Async/
sync

Sampling

M
U
X

ECC

GSM
13 kb/s

Raw data rate = 13 kb/s
Net data rate = 9.6 kb/s
Difference used for
Modem control signals
Forward error correction

17

J.Tiberghien - VUB


FAX over 
GSM
m

PSTN

m

m
m

18

GSM

m

PSTN

m

J.Tiberghien - VUB


•

GSM Data 
Via commonTransmission
channel
– SMS : limited to 160 bytes

• Via circuit switched voice/data channel (13 Kb/s)

GSM

m

PSTN

m

– GSM channel behaves like a modem cable
– Throughput = 9 600 b/s
– Long connection establishment delay
– Duration based billing
• High Speed Circuit Switched Data
– 2,3 or 4 normal voice/data channels combined
19

J.Tiberghien - VUB


GSM Radio Slots
frequency

Tx
200 KHz

45 MHz

Rx

3 radio slots

15/26 ms

time

Unused slots can be used for data packets

20

J.Tiberghien - VUB


GPRS System Architecture
(General packet Radio Services)
NSS

BSS

MSC

GSTN
ISDN

R
A
D
I
O

VLR

TRAU
HLR

BSC

BTS

21

INTERNET

NSS

Frame Relay

IP

MS

SS7

GSN

Other GSN

GPRS Switching Node
J.Tiberghien - VUB


GPRS Data 

Transmission

GSM+GPRS

Internet

• The GPRS network = Internet Service Provider
• GSM network and mobiles need to be adapted
• Data rate depends on traffic in cell
– Theoretical maximum : 171.2 Kb/s
– Practical throughput : 56 Kb/s
• Flat or volume based billing
• Little or no mobile terminated data transport
(difficult to bill traffic originating in Internet)
22

J.Tiberghien - VUB


Wireless Access Protocol
WAP
Gateway

SMS
CSD
(GPRS)

WML
content
WML defined by XML

23

HTTP
Internet
WWW
server
J.Tiberghien - VUB


Universal Mobile Telecommunications System
UMTS

Internet

• The UMTS network = Internet Service Provider
• Voice, images and data use the IP protocols
• Data rate depends on traffic in cell
– Theoretical maximum : 2 Mb/s
– Practical throughput : 128 Kb/s Kb/s
• No maximum number of users per cell
• QoS degrades when number of users increases
24

J.Tiberghien - VUB