Switching Fourth Meeting

Switching Modes Circuit Switching Continuous link Exclusive Packet Switching No continuous link Data is divided into packets Not exclusive Circuit Switching` Packet Switching`

Incurred Delay Circuit-switched fixed delay of transferring data Packet-switched Queuing delays Variable transmission delay because of the capacity of the link. Hi Mom

Multiplexing It improve the efficient use of the transmission capacity of physical media Two types of multiplexing Deterministic Statistical Deterministic Multiplexing transmission medium is divided between a fixed number of communication channels

Statistical Multiplexing The multiplexer and demultiplexer do not perform any switching The multiplexer stores the incoming packets in a buffer. Why? Data rates of the input channel and the multiplexed channel are different; and Packets may arrive simultaneously on several input channels. In the multiplexer, the packets are stored with a header with input channel number. In the demultiplexer, the packets are retrieved in reverse order The packet header identify the output channel. Buffers are required for each output channel The demultiplexer, over a short period of time, receive packets at a faster data rate than it can transmit.

Switching Structures Cross-points It connect input lines to output lines with a dedicated cross- point It is non-blocking Switching Arrays single-stage switch connects one input line to an output line using a single cross-point

Three stage-switching Blocking occurs N inputs = m groups * n inputs N outputs = m groups * n outputs The first stage m array switches. Each array switches n input lines k output lines The second stage k array switches Each array switch m input lines m output lines The third stage m array switches. Each array switches k input lines n output lines Switching Structures:3-Stage-Switching

How Many Cross Points The total number of cross-points = number of cross-points in the first stage plus number in the second stage plus number in the third. First stage Total = n × k × m Since N = n × m, then Total = N × k Second stage Total = k × m × m Since m = N/n, Then Total = k × (N/n) 2. Third stage (same as first stage) Total = N × k All three stages.

Three Stage Switching Example 6 input lines that is blocking. four first-stage arrays m = 4 Each array hasfour input lines n = 4 Five second-stage arrays k = 5 16 × 16 three-stage configuration has

Digital Space Switching Two types Digital space switching and Digital time switching. Digital space switching The first automatic telephone exchanges Paths were set up using electromagnetic devices

Space Switch Carries A Time Division Multiplexed (TDM)

Space Switch Multiplexer

Example Input 0 Multiplex X Multiplex Y Input 1 Input 2 Selects Control 0 Frame Selects 0 = 0 Selects 1 = 0 Time Slot 0 Output 0

Example Input 0 Multiplex X Multiplex Y Input 1 Input 2 Selects Control Frame 1 Time Slot 1 Output 0

Example Input 0 Multiplex X Multiplex Y Input 1 Input 2 Selects Control Frame 3 Time Slot 2 Output 0

Example Input 0 Multiplex X Multiplex Y Input 1 Input 2 Selects Control Frame 2 Time Slot 3 Output 0

Time Switching

Time Switching Implementation Use two memory devices Speech store All incoming data octets are stored in their sequence of arrival,  Octet 0 → location 0  Octet 1 → location 1  :  Cyclic counter Connection store, Contains the destination outgoing lines Has a cyclic counter

Example Counter 1 Counter 2 0 Input Time Slot Output Time Slot Time

Example Counter 1 Counter 2 1 Input Time Slot Output Time Slot Time

Example Counter 1 Counter 2 2 Input Time Slot Output Time Slot Time

Example Counter 1 Counter 2 3 Input Time Slot Output Time Slot Time

Example Counter 1 Counter 2 4 Input Time Slot Output Time Slot Time

Space Time Space Switching k = 1 n = 3

Packet Switching In the past, the delay associated with packet switching meant that it was not considered suitable for real-time applications such as voice communication. Packet-switching exchanges (PSEs) have used the concept of stored program control (SPC) since the first generation of exchanges, in the late 1960s

2 nd and 3 rd Generation PSE

Cell Switching Cell switching ≈ packet switching breaks a data stream into packets Cell switching ≠ packet switching Cells have a fixed size Cell switching ≈ circuit-switching connection-oriented service virtual circuit created. Cell switching ≠ circuit-switching circuit is virtual No reserving of network resources Virtual Path Switch 1 Virtual Path Switch 2 Picture source