Transcript ICN lecture Telephony Services

1
Telephony System
• Public switched telephone network
•The public switched telephone network (PSTN) is the concentration of the
world's public circuit-switched telephone networks, in much the same way
that the Internet is the concentration of the world's public IP-based packetswitched networks
• Originally PSTN is a fixed-line analog system
• Now, the PSTN is now almost entirely digital, and now also
includes mobile cellular network as well as fixed telephones. (e.g.
DSL, ISDN, cable system)
• Analogue telephony system will be covered 1st,as the introduction.
(Basic ISDN system will be covered, if time permitted)
2
A Simple Telephone
Off hook now !!
3
A More Realistic Telephone
On hook now !!
4
Signalling in Telephone Network
Signal
Off-hook
Dial tone
Pulses &
tones
Ringback
tone
Ringing
voltage
Busy tone
On-hook
Call waiting
tone
Howler tone
From
User
LE
User
To
LE
User
LE
Function
Signal intention to call
Signal readiness for call
Signal destination
LE
LE
User Signal destination phone is
ringing
User Cause phone to ring
LE
User
LE
User Signal busy destination
LE Signal action to end call
User Signal another call on the way
LE
User Phone off hook alert
LE: Local Exchange (i.e., Central Office)
5
Dialling in Telephone Network
Dual tones for each key
Rotary dialling
(Pulse dialling)
Dual-tone Multi-frequency (DTMF)
(Touch-tone dialing )
6
Why DTMF ?
• allows dialling numbers via microphone
• allows in-band signalling
• allows end-to-end signalling between two telephones
7
Telephone Network
Point-to-point telephone
connection
Mesh network
Resource utilisation ?
n  n  1
2
Scalability ?
connection
8
Telephone Network
Star network
•More efficient resource utilisation
•Scalable
•Allows hierarchical routing
9
Telephone Network Routing – Circuit Switching
10
Routing in Telephone Network
•Hierarchical routing paradigm : LATA – Local access transport areas:
• Intra-LATA services are offered by common carriers (Telephone
Companies) within a LATA. Handled by local exchange carrier (LEC).
• Inter-LATA services between LATAs are handled by interexchange carriers
(IXCs) or (long distance companies).
11
National/International Routing
POP – Points of Presence: A switching office that handles carriers exchange btw LEC & IXC
12
Voice Communication Service Offerings
•Wide Area Telecommunication Services (WATS)
 non-standard billing for businesses with high call volume
•Inward WATS
 business agrees to pay for all INCOMING long-distance calls from
certain areas (e.g., 0800, 0870)
•Foreign exchange
 phone numbers in distant cities where your customers can call your
company at local charges
•Leased lines
 permanent point-to-point connection
 annual rent
13
PART – C
Customer Premises Equipment
14
Customer Premises Equipment
• Centrex
– Central Office is acting as the customer’s exchange
or switch
• Private Branch Exchange (PBX)
– Acts as a mini-central office for a company,
dedicated to customer who owns it (not owned by
Central-Office).
15
Customer Premises Equipment
Centrex service:
• Very Dependable & Reliable because services are maintained by Central-office
(full-time maintenance & troubleshooting staff).
• Hence expensive – regular fees for each month
• Inflexible – additional lines can only be fitted by
central-office.
• Inefficient – Calls within company are routed all
the way through Central Office and back.
16
Customer Premises Equipment
Private Branch Exchange (PBX):
• Suitable for large business – provide thousands of lines.
• Internal calls are free using ext. assigned to each one.
• Does not need local loop for each
employee. Only a few local loops
are needed for external call.
• VERY flexible – can add/remove a line anytime
• Efficient – internal calls are routed within PBX
without going through Central-office, hence
provide quick access.
• Maintenance is CRUCIAL – need a team to
always maintain it.
17
For Information Only (FIO)
18
Regulatory Bodies
OFCOM
(Office of Communications)
Radio Authority
ITC
Radio Communications Agency
(Independent Television
Commission)
OFTEL
(Office of Telecommunications)
19
Regulatory Bodies
OFTEL's functions
• Promoting the interests of consumers.
• Maintaining and promoting effective competition.
• Making sure that telecommunications services are provided in the
UK to meet all reasonable demands, including:
emergency services;
public call boxes;
directory information; and
services in rural areas
Tutorial
Describe the signaling procedure for making a call through
telephone network.
List three signals that your phone sends to local exchange
List three signals that local exchange sends to your phone
Describe how rotary dialing and touch-tone dialing is made.
What is a mesh network?
What is a star network?
What is local loop and Central Office?
20
21
Why Telephone network uses star network?
Describe how your local call is routed.
Describe how your international call is routed.
Briefly describe two types of Customer Premises Equipment
Describe the advantages and disadvantages of using a Centrex
Service?
Describe the advantages and disadvantages of using a private
branch exchange (PBX)?