Communication Systems doc

Communication Systems
Lecturer: M.E. P.T.A. Quang
Contents
 Chapter 1: Introductory Concepts
 Chapter 2: QoS
 Chapter 3: Transmission and switching
 Chapter 4: Digital networks
 Chapter 5: Signaling
 Chapter 6: PSTN
 Chapter 7: VoIP
 Chapter 8: Mobile communication
 Chapter 9: Satellite communication
 Chapter 10: Fiber-optic communication
Introductory Topics in Telecommunication
 End-users, nodes, and connectivities
 Telephone numbering and routing
 Tandem switches
 Hierarchical structure
 Busy hour and grade of services
 Simplex, half-duplex, and full duplex
 One-way and two-way circuit
 Double seizure
 Supervision signals
 Network topologies
 Variations in traffic flow
End users, nodes, and connectivities
 End-users: inputs to the network / recipients of network
outputs
 Node: a point or junction in a transmission system where lines
and trunks meet. (switching function)
 Connectivity: links an end-user to a node, and from there

possibly through other nodes to some final end-user
destination
Telephone numbering and routing:
 Every subscriber has an unique number related to physical
location.
Call 447-8765
Route: look up trunk to 447
Subscriber loop
trunk
Tandem switches in Local Area Connectivity
 Traffic concentrator  reduce the connection  economic
expedient
Hierarchical structure
Busy hour and grade of service
 Busy hour: period of maximum usage demand
 Grade of service = blocking probability
 B=1% : during busy hour, 1 in 100 calls can be expected to meet
blockage
Simplex, half-duplex, and full duplex
 Simplex: one way operation; no reply channel
 Half-duplex: two-way service. Only one direction at a time
 Full duplex: two-way independent transmission (PSTN)
One-way or two-way circuit
 Two-way circuit: any trunk can be selected for operation in
either direction
a) two-way
b) One-way
c) Hybrid scheme
Double seizure
 In bothway groups, it can happen that the exchanges at

both ends of a trunk group seize the same trunk at the
same time (double seizure).
 Solutions: it can be arranged that one exchange continues
the setup, and the other exchange backs off (tries to. seize
another trunk for its call). The signaling on bothway
trunks includes provisions to alert the exchanges when a
double seizure occurs.
Supervision signals
Double seizure
 After A seizes a trunk, it expects to receive a backward
change to off-hook (wink signal). However, this change
may also mean that exchange B is sending a seizure signal.
 Wink: return on-hook within 100-1000ms. If the off-hook
duration >1s  double seizure
Network topologies
Mesh
Full-mesh
Star
Multiple-star
Variations in traffic flow:
 Busy hour is different from countries to countries
 Noncoincident busy hour
Quality of service
 How happy the telephone company is keeping the
customer
 Customer satisfaction
 GoS
 Can connectivity be achieved?
 Delay before receiving dial tone
 Post dialing delay

 … (refers to material)
Standardization in telecommunications
 ITU (international telecommunication union)
 ISO (international standardization organization)
 IEEE (Institute of Electrical Electronic Engineers)
 ETSI (European Telecommunications Standards Institute)
 EIA (Electronic Industries Alliance)
Telecommunication companies

Mobile Telecommunication Co. in VN

Mobile Telecommunication Co. in VN