Switching concepts Data communication and networks
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This slide explains you about the different types of sxitching networks like circuit switched network , datagram network , virtual circuit network , message switched network
![Drawbacks of multistage switch and
clos criterion
• The multistage switch has one drawback-blocking during
periods of heavy traffic .
• The whole idea of multistage switching is to share the
crosspoints in the middle-stage crossbars.
• Sharing can cause a lack of availability if the resources are
limited and all users want a connection at the same time .
• Clos criterion: condition of non-blocking
– n = (N/2)1/2
– k > 2n – 1
– Crosspoints ≥ 4N [(2N)1/2 – 1]](https://image.slidesharecdn.com/chapter8-180218045950/85/Switching-concepts-Data-communication-and-networks-15-320.jpg)
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Switching concepts Data communication and networks
- 1. Switching Chapter 8 Data communication and networks
- 2. Switching • Switches are devices capable of creating temporary connections between two or more devices linked to the switch
- 3. Circuit-switched Network • A circuit-switched network is made of a set of switches connected by physical links, in which each link is divided in “n” channels. • When end system A needs to communicate with end system M . “A” needs to request a connection to “M” that must be accepted by all switches as well as by M itself. This is called the setup phase. Combination of channels defines the dedicated path. After the dedicated path is established, data transfer can take place. • The stations must make a reservation for the resources to be used during the communication
- 4. 4x8 means 4 input and 8 output . 4 output ports are folded into the i/p ports to allow communication between computers in the same office. 4 other o/p ports allow communication between the two offices. This example 17 25 38 46
- 5. three phase(setup , data transfer , teardown phase) Setup phase : • system A needs to connect to system M. • Sends a setup request that includes the address of system M, to switch I. • Switch I finds a channel between itself and switch IV that can be dedicated for this purpose. • Switch I then sends the request to switch IV,. • Switch IV finds a dedicated channel between itself and switch III. • Switch III informs system M of system A's intention at this time. • End-to-End addressing is required for creating a connection between the two end systems. Data Transfer Phase : After the establishment of path the two parties can transfer data Teardown Phase: When one of the parties (system) needs to disconnect, a signal is sent to each switch to release the resources.
- 6. DATAGRAM-NETWORKS (Connectionless network) • In a packet-switched network, there is no resource reservation; resources are allocated on demand . • When a switch receives a packet, no matter what is the source or destination, the packet must wait if there are other packets being processed . • In a datagram network, each packet is treated independently of all others. Sometimes referred to as connectionless networks . • This approach can cause the datagram’s of a transmission to arrive at their destination out of order with different delays between the packets. • There are no setup or teardown phases
- 7. Routing table , delay , efficiency of (datagram-network) • The routing tables are dynamic and are updated periodically. • A switch in a datagram networks uses a routing table that is based on the destination address • The destination address in the header of a packet in a datagram network remains the same during the entire journey of the packet • The efficiency of a datagram network is better than that of a circuit-switched network, resources are allocated only when there are packets to be transferred . Routing table Delay( transmission time + propagation delay + waiting time)
- 8. VIRTUAL-CIRCUIT NETWORKS (VCN) • It is a hybrid technique. • Setup, data transfer, and teardown phases as in a “CSN” • Resource allocated during setup phase, as in a CSN, or on demand as in (DN) • As in DN, data are packetized and each packet carries an address in the header. The address has local jurisdiction, not end-to-end jurisdiction. • As in CSN, all packets follow the same path established during the connection • VCN is normally implemented in the data link layer, while CSN is in physical layer and DN in the network layer
- 9. Addressing • Two types of addressing in a virtual-circuit network: global and local (virtual-circuit identifier: VCI) • Global address is used only to create a VCI • The identifier that is actually used for data transfer is called the “VCI” . • When a frame arrives at a switch, it has a VCI; when it leaves, it has a different VCI . • VCI does not need to be a large number since each switch can use its own unique set of VCl’s.
- 11. Setup Phases: Setup Request and Acknowledgement Setup request Setup acknowledgement
- 12. Teardown phase and total delay in VCN • source A, after sending all frames to B, sends a special frame called a teardown request. Destination B responds with a teardown confirmation frame. All switches delete the corresponding entry from their tables . • In virtual-circuit switching, all packets belonging to the same source and destination travel the same path; but the packets may arrive at the destination with different delays if resource allocation is on demand.
- 13. Space-division: crossbar switch • The number of switches is huge. connect n inputs by m output require n * m crosspoint. • Inefficient fewer than 25% of the crosspoints are in use at given time , rest are idle .
- 14. Space-division: Multistage Switch • Three steps – Divide the N input lines into groups, each of n lines. For each group, use one crossbar of size n x k, where k is the number of crossbars in the middle stage – Use k crossbars, each of size (N/n) x (N/n) in the middle stage – Use N/n crossbars, each of size k x n at the third stage • Total no of crosspoints = N/n(n x k) + k(N/n x N/n) + N/n(k x n) = 2kN + k(N/n)2 • Which is much smaller than the number of crosspoints in a single-stage switch (N2).
- 15. Drawbacks of multistage switch and clos criterion • The multistage switch has one drawback-blocking during periods of heavy traffic . • The whole idea of multistage switching is to share the crosspoints in the middle-stage crossbars. • Sharing can cause a lack of availability if the resources are limited and all users want a connection at the same time . • Clos criterion: condition of non-blocking – n = (N/2)1/2 – k > 2n – 1 – Crosspoints ≥ 4N [(2N)1/2 – 1]
- 16. TDM, with and without TSI (Time slot interchange)
- 17. Time- and Space-Division Switch Combination • Space division: instantaneous, crosspoints • Time division: no crosspoint, processing delay • Space-and time-division switching combinations take advantage of the best of both
- 18. Structure of Packet Switch
- 19. Structure of Packet Switch • Packets are decapsulated /encapsulated and errors are detected and corrected at input/output ports • Routing processor: network layer functions – Table lookup: searching the routing table by destination address • Switching Fabric: Most difficult task is to move from input queue to output queue. The speed at which this is done affects the size of the input/output queue and overall delay in packet delivery. – Crossbar switch – Banyan switch – Batcher-Banyan switch
- 20. Banyan Switch • Multistage switch with micro-switches at each stage that route the packets based on the output port represented as a binary string • “n” i/p and “n” o/p with log2n stages with n/2 micro-switches at each stage • Input 1 to output 6 Binary representation (110) • Input 5 to output 2 binary representation (010)