1 Telephony System Public switched telephone network The public switched telephone network (PSTN) is...
-
Upload
juliana-barker -
Category
Documents
-
view
216 -
download
1
Transcript of 1 Telephony System Public switched telephone network The public switched telephone network (PSTN) is...
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
packet-switched 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
Signal From To Function Off-hook User LE Signal intention to call Dial tone LE User Signal readiness for call Pulses & tones
User LE Signal destination
Ringback tone
LE User Signal destination phone is ringing
Ringing voltage
LE User Cause phone to ring
Busy tone LE User Signal busy destination On-hook User LE Signal action to end call Call waiting tone
LE User Signal another call on the way
Howler tone LE User Phone off hook alert
Signalling in Telephone Network
LE: Local Exchange (i.e., Central Office)
5
Dialling in Telephone Network
Rotary dialling(Pulse dialling)
Dual-tone Multi-frequency (DTMF)(Touch-tone dialing )
Dual tones for each key
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 ?
Scalability ?
1
2
n n connectio
n
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
• 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).
: LATA – Local access transport
areas:
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 EquipmentCentrex service:
• Very Dependable & Reliable -because services are maintained by Central-office (full-time maintenance & troubleshooting staff).
• Inflexible – additional lines can only be fitted by central-office.
• Inefficient – Calls within company are routed all the way through Central Office and back.
• Hence expensive – regular fees for each month
16
Customer Premises EquipmentPrivate Branch Exchange (PBX):
• Suitable for large business – provide thousands of lines.
• 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.
• Does not need local loop for each employee. Only a few local loops are needed for external call.
• Internal calls are free using ext. assigned to each one.
17
For Information Only (FIO)
18
Regulatory BodiesOFCOM
(Office of Communications)
ITC(Independent Television
Commission)
Radio Authority
Radio Communications Agency
OFTEL(Office of Telecommunications)
19
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:
Regulatory Bodies
emergency services;
public call boxes;
directory information; and
services in rural areas
20Tutorial
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?
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)?