Transcript Basic Concepts - Mahmoud Youssef

Telephony:
Internal and External
Chapter 6
Copyright 2003 Prentice-Hall
Panko’s Business Data Networks and Telecommunications, 4th edition
1
Figure 6.1: Telephony

Telephone Service is Expensive for Corporations

LANs Use Traditional Telephone Building Wiring

Telephone Technology is Basis for Much Wide Area
Networking

Telephone Regulation and Carriers Affect Wide Area
Networking

Desire for Converged Services: Integrated
Management of Voice and Data Networks
2
Figure 6.2: Internal PBX-Based
Telephone Network
Multi-floor
Office
Building
3
Figure 6.2: Internal PBX-Based
Telephone Network
3. Entrance
Facility
2. To
Phone
Co.
4. Termination
Equipment
5. PBX
Internal Telephone
Switch
7. Vertical
Riser
Space
6. Wire
Bundle
(Many Pairs)
1. Equipment Room in Ground Floor or Basement
4
Figure 6.2: Internal PBX-Based
Telephone Network
1. Vertical
Distribution
5. Horizontal Distribution
4. Cross-Connect Device
3. Telecommunications
Closet on Floor
2. Wire Bundle
5
Figure 6.2: Internal PBX-Based
Telephone Network
2. Final Distribution
Along or Through Wall
1. Horizontal Distribution
One 4-Pair UTP Cord
6
Figure 6.3: LAN Building Wiring
3. Entrance
Facility
4. Router
5. Core
Switch
(Chassis)
6. Vertical
Riser
Space
2. To
WAN
1. Equipment Room in Ground Floor or Basement
7
Figure 6.3: LAN Building Wiring
1. Vertical
Distribution
5. Horizontal Distribution
4. Workgroup Switch
3. Telecommunications
Closet on Floor
2. Optical Fiber
One Pair per Floor
8
Figure 6.3: LAN Building Wiring
Horizontal and Final Distribution
are the Same as in Telephony
1. Horizontal Distribution
One 4-Pair UTP Cord
9
Building Cabling Management

Structured Cabling Plans

Testing


Inexpensive just to test whether wires are
connected properly

More expensive to test for signal quality
Documentation and Neatness

Critical to avoid chaos in wiring
10
Figure 6.4: Public Switched Telephone
Network (PSTN)
Switching Office
Access Line
Local Loop
Analog Signaling
Single Twisted Pair
Customer Premises
(Residential)
Central Office
End Office
Digital
Customer Premises
(Business)
11
Figure 6.4: Public Switched Telephone
Network (PSTN)
Class 3
Switching
Hierarchy
Trunk Line
Digital
Class 4
Class 5
End
Office
Class 5
End
Office
12
Figure 6.4: Public Switched Telephone
Network (PSTN)
Circuit
End-to-End Connection
Between Two Subscribers
13
Figure 6.5: Trunk Line Technologies
Connect Pairs of Switches
Trunk Line
North American Digital Hierarchy
56 kbps (DS0 Signaling)
T1 (DS1 Signaling)
T3 (DS3 Signaling)
CEPT Multiplexing Hierarchy
64 kbps
E1
E3
Speed
56 kbps (sometimes 64 kbps)
1.544 Mbps
44.7 Mbps
64 kbps
2.048 Mbps
34.4
14
Figure 6.5: Trunk Line Technologies
Trunk Line
SONET/SDH*
OC3/STM1
OC12/STM4
OC48/STM16
OC192/STM64
OC768/STM256
Speed
156 Mbps
622 Mbps
2.5 Gbps
10 Gbps
40 Gbps
Notes: SONET and SDH speeds are multiples of 51.84 Mbps.
OCx is the SONET designation.
STMx is the SDH designation.
15
Figure 6.6: SONET/SDH Dual Rings
Telephone
Switch
Telephone
Switch
SONET/SDH Ring
Telephone
Switch
Rings can be
Wrapped if a
Trunk line
Is Broken
(Ch. 5)
Telephone
Switch
SONET/SDH Ring
16
Figure 6.7: Circuit Switching
1. Circuit
End-to-End Connection
Subscriber-Subscriber
2. Across
Multiple
Access Lines,
Switches, and
Trunk Lines
3. Circuit Switching:
Circuit Reserved for
Duration of Call
17
Figure 6.7: Circuit Switching

Dedicated Capacity
Data
Burst

Full capacity always available to pair of
subscribers during their call

Wasted if not used, and callers pay for whether
use it or not

Good for voice, in which there is almost always
someone talking

Expensive for data, which is bursty, having short
transmissions mixed with long silences
Time
18
Figure 6.8: The PSTN: Mostly Digital
with Analog Local Loops
Original Telephone Network: All Analog
Local
Loop
(Analog)
Residential
Telephone
(Analog)
Local
Loop
(Analog)
Switch
(Analog)
Switch
(Analog)
Trunk Line
(Analog)
Switch
(Analog)
Business
Telephone
(Analog)
19
Figure 6.8: The PSTN: Mostly Digital
with Analog Local Loops
Today’s Telephone Network: Predominantly Digital
Local
Loop
(Analog)
Residential
Telephone
(Analog)
Local
Loop
(Digital)
Switch
(Digital)
Switch
(Digital)
Trunk Line
(Digital)
Switch
(Digital)
PBX
(Digital)
20
Figure 6.9: Codec at the End Office
Switch

Subscriber Access Line is Analog

Switch is Digital

Codec Converts Between Them
End Office
Analog
Subscriber
Signal
ADC
Digital
Internal
Signal
Digital
Switch
Codec
Local Loop
Access Line
DAC
21
Figure 6.10: Sampling for Analog-toDigital Conversion (ADC)

Codec First Bandpass Filters the Voice Signal



Cuts of all energy below about 300 Hz
Cuts off all energy above about 3,400 Hz
Bandwidth of about 3.1 kHz
Signal
Energy Distribution for
Human Speech
O Hz
300 Hz
~3,400 Hz
Bandwidth (~3.1 kHz)
20 kHz
22
Figure 6.10: Sampling for Analog-toDigital Conversion (ADC)

Codec

Constantly samples the intensity of the analog
voice signal from the customer
Sample
0110010
1/8,000 sec
23
Figure 6.10: Sampling for Analog-toDigital Conversion (ADC)

Codec

Divides each second into 8,000 sampling periods

Only measures intensity of voice signal in each
Intensity
Value
0110010
Sample
1/8,000 sec Sampling Period
24
Figure 6.10: Sampling for Analog-toDigital Conversion (ADC)

Codec

Measures voice intensity as an 8-bit intensity
(loudness) value (0-255)

Overall, sends 8 bits 8,000 times per second (64
kbps)
Intensity
Value
0110010
Sample
1/8,000 sec Sampling Period
25
Figure 6.10: Sampling for Analog-toDigital Conversion (ADC)

Codec

This is why telephone channels are 64 kbps
 Designed
for digitized voice
 Carrier
often “steals” 8 kbps for
supervisory signaling, so 56 kbps
8,000 samples/second * 8 bits/sample = 64 kbps
64 kbps – 8 kbps = 56 kbps
26
Figure 6.11: Digital-to-Analog Conversion
(DAC)
1/8000
Second
(8 bits)
00000100 00000011 00000111
Arriving Digital Signal
From Telephone Switch
(8000 Samples/Second)
DAC
Generated Analog Signal
For Subscriber Line
Sounds smooth if there
are enough samples
per second
27
Question

If you have an audio CD player, it contains
a(n) _____.

a. Analog-to-digital converter

b. Digital-to-analog converter

c. Both

d. Neither
28
Figure 6.12: Cellular Telephony
Mobile Telephone
Switching Office
PSTN
Cellsite
G
D
1. Divide Area
Into Cells
2. Cellphone
Communicates
Via Cellsites,
MTSO
H
B
A
K
E
C
N
L
O
Handoff
I
F
P
M
J
29
Figure 6.12: Cellular Telephony
PSTN
Cellsite
G
3. Use
Channel
47
D
2. Use
Channel 47
In Cell A
H
B
A
K
E
C
N
L
I
F
P
O
M
J
1. Reuse Channels in Non-Adjacent Cells
30
Figure 6.12: Cellular Telephony
PSTN
Cellsite
G
D
1. Use A, D, and F
2. Reuse
Channel 47
Next
In What Cells?
H
B
A
K
E
C
N
L
I
F
P
O
M
J
31
Importance of Channel Reuse


Channels are Scarce

Only ~800 in First Generation Cellular Systems

Only ~2,500 More for Second Generation Systems
You Can Only Have an Average of 20
Customers per Channel

Assumes each will use the system 5% of the time
(generous)

Only 16,000 to 50,000 customers without channel
reuse
32
Importance of Channel Reuse

Can Reuse Channel in Nonadjacent Cells

In adjacent cells, signals will interfere

To tell how roughly how many times you can reuse
a channel on average


Divide the number of cells by 7

Rough estimate but very useful

20 cells / 7 = 3 (Round off: It’s not exact)

100 cells / 7 = 14
You can multiply the possible number of
subscribers by this factor
33
Importance of Channel Reuse

Example

800 channels

20 cells

3 (20/7) channel reuse factors

2,400 effective channels (800 x 3)

20 subscribers/channel maximum for good service

48,000 maximum subscribers (2,400 x 20)
34
Importance of Channel Reuse

Example

2,400 channels

100 cells
35
Compression

Multiplies Number of Possible Subscribers by
About a Factor of 3

2,400 channels

100 cells
36
Figure 6.12: Cellular Telephony
Mobile Telephone
Switching Office
PSTN
G
D
1.
Automatic
Handoff Between
Cellsites as
Phone Travels
Between
Cells
H
B
A
K
E
C
N
L
O
Handoff
I
F
P
M
J
37
Handoffs versus Roaming


Handoff

Moving between cells within a single cellular
system

Cellular telephony

802.11 wireless LANs
Roaming

Moving between systems

Cellular telephony: use cellphone in another city
38
Figure 6.13: Generations of Cellular
Service
Generation
First
2nd
2.5G
3G
Technology
Analog
Digital
Digital
Digital
Data Transfer
Rate
Data Transfer
Is Difficult
10 kbps*
Channels
~800
~800 +
2,500
~800 +
2,500
?
Large/
Medium
Large/
Medium
and Small/
High
Based
on 2G
?
Cells/ Channel
Reuse
20 kbps to 384 kbps
384 kbps to 2 Mbps
*Sufficient for Short Message Service (SMS) and wireless Web access
using the Wireless Access Protocol (WAP) or i-mode
39
Figure 6.13: Generations of Cellular
Service
Generation
World
Standardization
(and therefore
roaming)
U.S.
Standardization
First
Poor
2nd
Good
(GSM)
2.5G
3G
? (W-CDMA,
CDMA-2000,
Based
and other
on 2G
systems
may compete)
Poor (GSM,
Good
Based
CDM, TDMA,
(AMPS)
on 2G
& CDPD)
?
40
Figure 6.14: Regulation and
Deregulation

Regulation

Carriers: carry signals between customer premises

Rights of Way: government permission to lay wire

Monopoly: Service was originally provided by a
single telephone carrier

Regulation: This monopoly carrier was regulated to
prevent abuse of the monopoly

Tariffs specify a service’s specific service
parameters and pricing to prevent discrimination
and guarantee service parameters
41
Figure 6.14: Regulation and
Deregulation

Deregulation

Initially, regulated protected monopoly service

Deregulation: remove protections & restrictions

To increase competition, lowering prices

Varies by country

Varies by service within countries
 Data, long-distance, and customer premises
deregulation is high.
 Local voice service deregulation is low.
42
Figure 6.15: Regulation and Carriers

Carriers

Public Telephone and Telegraph (PTT) authority is
the traditional domestic monopoly carrier in most
countries.
 Domestic
transmission: within a country
 UK: British Telecoms
 Japan: NTT
43
Figure 6.15: Regulation and Carriers

Carriers

LATA
In the United States
 U.S.
is divided into regions called local
access and transport areas (LATAs)
 About 200 LATAs nationwide
 Small states have just one LATA
 Large states have 10 to 20 LATAs
44
Figure 6.15: Regulation and Carriers LATA
LEC

Carriers

ILEC
CLEC
In the United States
 Local exchange carriers (LECs) provide
service within a LATA
 Incumbent LEC (ILEC) is the traditional
monopoly carrier in the LATA
 Competitive LEC (CLEC) is a new
competitor
45
Figure 6.15: Regulation and Carriers

Carriers

In the United States
LATA
IXC
LATA
 Inter-exchange
carriers (IXCs) provide
service between LATAs

LEC versus IXC distinction is used by data carriers
as well as voice carriers.
46
Figure 6.15: Regulation and Carriers

Carriers

In the United States
 Point of Presence (POP) is a place in a
LATA where all carriers interconnect to
provide integrated service to all
customers
LATA
POP
ILEC
CLEC
IXC
IXC
47
Figure 6.15: Regulation and Carriers

International Service (Between Pairs of
Countries)

Provided by international common carriers
(ICCs)

Allowed carriers, prices, and conditions of
service are settled through bilateral
negotiation between each pair of countries
Country 1
ICC
Country 2
48
Figure 6.15: Regulation and Carriers:
Recap

U.S.

Intra-LATA
 LECs
 ILEC
 CLECs

Inter-LATA
 IXCs

Most of the World

PTTs for domestic service
49
Figure 6.16: Converged Services

Integrate Voice and Data Networks

Often referred to as voice over IP (VoIP) and IP
telephony
50
Figure 6.16: Converged Services

Provide Voice and Data on a Single Network

Save money compared to traditional
telephony

Reducing staff and economies of scale in
purchasing with one network

Encoding voice to less than 64 kbps so fewer bits
need to be sent

Packet switching to reduce transmission costs for
bit sent
51
Figure 6.16: Converged Services

Other advantages

Computer-telephony integration (CTI)
 Provide
integrated voice and data
applications
 E.g., when a customer calls, their
information can be brought up on-screen
52
Figure 6.17: PBX-PBX IP Telephony
Ordinary
Telephone
Ordinary
Telephone
IP
Packet
Frame Relay, ATM, or
the Internet
PBX with
IP Telephony Module
PBX with
IP Telephony Module
53
Figure 6.16: Converged Services

Implementation

PBX-to-PBX connectivity is easy and saves money
on long-distance calls

LAN implementations are more difficult, less welldeveloped, and may not save money
54
Figure 6.16: Converged Services
Telephone Price
Gap
VoIP Price

Will Cost Savings be Realized?

Convergence justified by gap between high longdistance and international telephone charges and
possible savings through IP telephony

Falling traditional telephone prices are reducing
the gap

Packet transmission inefficiency is reducing the
theoretical savings and therefore the gap

Does the remaining gap justify convergence?
55
Figure 6.16: Converged Services

Service Quality

Availability (less than the PSTN’s 99.999%)

Sound quality
 latency
produces pauses
 Millisecond-to-millisecond inconstancy of
speed produces jitter

Sound quality is addressed by using a single ISP to
connect all sites
 Service
Level Agreements (SLAs)
56
Figure 6.18: Using a Single ISP for
VoIP
Congestion in Site A-B Communication
Because of Passage Through Internet Backbone.
Site A
Site C
ISP 1
Backbone
ISP 2
Site B
No Congestion in Site A-C Communication
Because All Traffic Passes through a Single ISP.
It Avoids the Congested Internet Backbone.
57
Voice/Data Cultural Concerns

Data Networking Concerns


Will all this voice traffic mean that my data cannot
get through well?
Telephony Concerns

Will people get the same level of voice quality?

Will they get secondary services (3-party calling,
call waiting, etc.)
58