Switching Chapter 2 Slides Prepared By: - Kaif Jamal Gilani (Course Coordinator) Kaif Jamal Gilani (Course Teacher) Department of CNET Faculty of CS&IS Jazan University

Switching Types of Switching classification of switching Switching of Physical circuits Switching of TDM signals Cells/Packets Switching Quality of Service Optical Crossbar Switches Digital Crossbar switches Traffic Patterns Queues structures Queuing Systems

What is a switch ? It is fundamental part of a network. It is a network device that connects devices to form a network. Switch uses different switching methods to receive, process and forward data to the destination.

Types of switching : - There are three types of switching Switching of physical circuit Switching of time division multiplexing signals. Switching of cell and/or packets .

Switching of physical circuits: - when the switching is done at the physical level of the protocol either on electrical or optical signal, it is called as switching of physical circuit. These switches take the input clock, captures each input bit carry out with some protocols and transfers that bit.

2) Switching of time division multiplexed signal:- Some protocol divide the bandwidth provided by physical layer. This is division with respect of time and is called as switching of time division multiplexed signals. This is very complex as compared to the physical circuit as it depends on N nodes.

3) Switching of Cell and/or packets : - Some protocols divide the bandwidth into cells of fixed length or packets of variable lengths. As this cell or packet carries address with them so this address redirects it to the particular output.

Switching classification Circuit Switching Packet Switching

Circuit Switching In a circuit switched network, a switched dedicated circuit is created to connect the two or more parties, eliminating the need for source and destination address information.

Packet Switching In a packet switched network, packets of data travel one at a time from the message source to the message destination. The packet of data goes in one side of the PDN and comes out the other. The physical path which any packet takes may be different than other packets and in any case, is unknown to the end users. Packet switches pass packets among themselves as the packets are routed from source to destination.

Packet Switching

Packet Switched Networks Connection-oriented Protocols A setup stage is used to determine the end-to-end path before a connection is established. Data flow streams are identified by some type of connection indicator.

Connection-Oriented Concatenation of Virtual Circuits Internetworking using concatenated virtual circuits.

Packet Switched Networks Connectionless Protocols No set up is needed. Each packet contains information which allows the packet to be individually routed hop-by-hop through the network.

Connectionless Internetworking A connectionless internet

Quality of service It means the service received by the user from the communication system. It is directly dependent upon the nature of signals. As the signals are good, the quality is good. QOS depends on the following factors: - Transmission delay Error rates, and Signal strength (bandwidth)

Optical crossbar switches It is an optical switch where multiple optical inputs are given for multiple optical outputs. It is in the form of matrix. It is good if the complete network is optical. If other devices are connected to the network then O-E-O device is required. So to avoid this optical crossbar switches are developed.

OPTICAL CROSSBAR SWITCH

Digital crossbar switch: - Digital crossbar switches use CMOS(capacitor metal oxide semiconductor) technology. When a digital electronic implementation is used, there is commonly an issue regarding the relative rates of the signals passing through the crossbar and the maximum rate at which signals can reasonably be transmitted across the silicon dies implementing the switch.

Traffic pattern : - The traffic pattern is the flow of frames in the network based on traffic load condition. There are two types of traffic load conditions: - Benign loads Hotspot loads

Benign loads : - A benign load is an ideal load Benign loads : - A benign load is an ideal load. It consist of permutations of frames such that each ingress and each egress is kept equally busy. This is the simplest conceptual load model. Hotspot loads : - A hotspot load has some concentration of bandwidth at some subset or egress ports, such that the sum of bandwidth directed at these outputs exceeds their capacity for some period of time.

Realistic loads : - Neither of the load model is intended as a realistic representation of actual network traffic. Actual behavior is much more complex, with dynamically changing requirements and traffic loads coming in periodic bursts.

It is possible to adopt the realistic loads by tuning the depth of queues in switches or by tuning the bandwidth of various network links. In excessive increases to queue depths leads to Increasing depth adds costs Adds to maximal latency traffic can experience. Excessive late delivery is compromise of overall quality of service. Research on bur sty nature of traffic indicates that the gains to be had from increasing queue depths are small.

Queues Structure As we know router and switches holds temporarily frames in queue waiting for output link. Each queue is a first in first out data structure . This implies that a new frame is always added to the end of queue and the older frame is removed first.

Queue input Queue output New frame added packet-cell queue

Water poured irregularly Water above threshold will be tagged Leaky bucket Water drains at a constant rate

Queuing system: - Queuing systems are found inside the switches. It is found inside and outside ports, multiplexer, demultiplexer, control signals queues and communication system. All the features are explained in the points below: - Input ports insert a frame into queuing system, when a frame comes to the port. It has a very little memory so a frame must be passed onto the rest of the queue system immediately, if not then the frame is lost.

Communication path has no memory, so the frame move from one location to another location as sequence of bytes. Queues are the only components that offer storage of frames. Multiplexers merge multiple frame flows into one united flow. De-multiplexers accept one frame flow and separate it into multiple output flows.

Input ports accept one frame at a given time and then emit it onto the output link. Control signals are used to push frames from their input port into queue and pulls frame from output port.

Videos What is Network switching ? https://www.youtube.com/watch?v=ApPruOqzd3M