Propagation of transmission level switching overvoltages.pdf
Transmission and Switching PDF
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Transcript of Transmission and Switching PDF
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Telecom Overview
Tuan May 2011
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Transmission & Switching: Switching in Telephone Network
Transmis
sion
Switching
Switching
Switching
Transm
ission
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Switching
Switching types
Connectionless/ connection oriented
Packet/circuit
Node 1 Node 2
Node 3
Access
Trunk Network
TerminalsTerminals
Access
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Circuit Switching
Cross-point
controlled
by CS
Cross-point
controlledby CS
TDMA
Time switch
- Makes switching between time slots
- In the figure incoming slot 3 is moved to
outgoing slot 3 for one voice direction
- Each coming timeslot stored in Speech Store (SS)
- Control store (CS) determines the order the slot
are read from SS
- The info in CS is determined during setupphase of the call
Space switch
- makes switching between PCM lines
- works with electronic gates controlled by CS
Circuit switching
- dedicated path
- constant delay/bandwidth
- voice/data
- paid by time
- examples: PSTN, VPN
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The Time-Space-Time (TST) Switch
Works in local exchange and subscriber stage
Performs PCM concentration, usually 10:1 3:1
Connects subscribers also to information tones
and test equipment
Time switch contains one bus for incoming and outgoing calls (full-duplex)
Subscrib
erstage
Space switch
Time switch
Time switch
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Switching: Telephone Exchange (Conceptual Model)
Switching
Matrix
Line Circuit
Line Circuit
Line Circuit
Line Circuit
Line Circuit
Control Computer
trunk lines +Inter-office
signaling
Register
Register
Register
Register
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Packet Switching
Node structure
Packet structure
Seq: sequence number
Op code: message/control
identifier
CRC: Cyclic Redundancy
Code
Note:
- source address
required for retransmission
in ARQ (Automatic Repeat reQuest)
- byte count could be also an
end flag
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Connection-oriented and Connectionless Switching
Connection oriented
- Applies same route
- QoS well defined
- Phases
- Connection setup
- Data transmission
- Release
- Packets received in same order
- Example: ATM, Frame Relay, PCM
Connectionless
- Use of different routes foreach packet possible
- Each packet have address fields
- QoS not guaranteed
- Packets may come in different order
- Example: IP (Internet Protocol),
TCP takes care of cleaning the mess
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Transfer Modes & Connections summarized
Circuit switching
Packet switching
Connection oriented
Connectionless
- hand-shaking
- strict error requirements
- for fast data transfer
- broadcasting
- modest error ratesoften accepted
- fast data in good channels
Transfer modes Connection types
- developed for data
- nowadays also for voice- Statistical multiplexing
- variable delays
- developed for voice
- nowadays also for data
- well-specified delays
- echo problems
PSTN
ISDN
PCM
IP, Frame-relay
ATM
X.25
ATM
Frame-relay
IP, UDP*
*User Datagram Protocol
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Transmission & Switching: Transmission in Telephone Network
Analog / Digital
PABX
SW
SW
SW
SW
SW
PABX
SW
SW
Satellite
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Optical Transmission
Optical Fiber or Microwave Link
Digital
switch
Digital
switch
HighTDM
HighTDM
Low
TDM
Low
TDM
TDM
Packet
IWF
TDM
Packet
IWF
TDM Frames
Packets with Gap
Native Packets Native Packets
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Low Time Division Multiplexing (TDM)
Unique bit pattern to
delimit frames
1 0 0 1
0 1 0 1
1 0 0 10 1 0 1
Low
TDM
XX
1 Frame
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Thank You !