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Data Link Layer Issues

Data Link Layer Issues. Dealing with Different Types of Networks. Types of Networks. Network hardware can be categorized into: Circuit-switched (e.g. telephone) Prior to communication, the hardware establishes a dedicated end-to-end connection

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Data Link Layer Issues

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  1. Data Link Layer Issues Dealing with Different Types of Networks www.assignmentpoint.com

  2. Types of Networks • Network hardware can be categorized into: • Circuit-switched (e.g. telephone) • Prior to communication, the hardware establishes a dedicated end-to-end connection • Since there is a dedicated connection, a continuous stream of bytes can be sent • Frequency or time-division multiplexing can be used to share links in such a network • Packet-switched (e.g. Ethernet, ATM) • Data is divided into packets of limited size, and each is forwarded through the network to the destination • This can be done by routers or switches www.assignmentpoint.com

  3. Types of Networks • Disadvantages • Circuit-switched • A dedicated connection that has no transmission means wasted bandwidth • A connection is time consuming if short, infrequent, or sporadic communication is to occur • Packet-switched • Forwarding each packet means that each router must decide the next hop for every packet (even for the same destination) • Routers are typically network slowdowns due to the amount of processing, as well as input/output buffering www.assignmentpoint.com

  4. Types of Networks • Circuit-switching is used in a telephone conversation • A connection to the receiver is established by the sender (the caller) • The telephone company reserves a certain bandwidth (64 Kbps for voice communication) for this call • If the bandwidth is not used by the callers, it is wasted • Packet-switching is similar to the postal service • Each message (envelope) is addressed to the recipient individually, and the postal service delivers each message to the recipient • The postal service may deliver these envelopes through different cities and methods of transport (airplane, truck, …) • It can be said that these messages can be delivered using different routes www.assignmentpoint.com

  5. Talk Call: B Talk Disconnect Circuit-Switching A Telephone Company Switching System B www.assignmentpoint.com

  6. Circuit-Switching A Telephone Company Switching System B www.assignmentpoint.com

  7. Packet-Switching Quebec, QC Buffalo, NY Montreal, QC A Windsor, ON B Toronto, ON Niagara Falls, ON London, ON Ottawa, ON Kitchener, ON Postal Network www.assignmentpoint.com

  8. Types of Packet-Switching • Virtual circuit-switching • A ‘virtual circuit’ is created between source and destination • This VC is used for all subsequent sending of packets • Datagram • Each packet is routed individually www.assignmentpoint.com

  9. Virtual Circuit Packet-Switching Advantages • After the first message, routing is faster • A route must only be determined once, for the first message • Once the route has been determined, the path used by the router is reused for all messages • As a result, routing tables are much smaller (and can be searched more quickly) • Because a connection is created, the connection identifier can be used (alone) to address packets • Typically, such as with ATM cells, this can reduce the size of a cell/packet’s header • Messages do not arrive out of order • As a result, receivers do not need to reorder the cells www.assignmentpoint.com

  10. Virtual Circuit Packet-Switching Disadvantages • Connections take some time to create • Routers/switches must intercommunicate in order to create the connection • Infrequent messaging is not suitable for connection-based messaging • The connection may be lost after a timeout, and will have to be recreated again and again • The time delay for creating the connection may outweigh the speed benefits of using connection-based transport • Routing tables will be dynamic, and routing algorithms are more complex www.assignmentpoint.com

  11. Datagram Packet-Switching Advantages • Connections need not be created • Infrequent messaging is perfect for connectionless messaging • Connectionless messaging can be resumed after any amount of delay, any number of times, without any delays due to the resumption of communication • Routing each message separately allows for load balancing • Some messages may be sent through one route, but when that route becomes saturated, messages may then be sent through a different route in order to achieve the most optimal communication possible www.assignmentpoint.com

  12. Datagram Packet-Switching Disadvantages • Each message takes a certain amount of time to transmit (including transmission, routing, reception, etc.) • Nodes communicating large amounts of information in a short time will: • Use a lot of bandwidth for things such as header information • Waste a lot of time routing messages to the same destination • Messages may arrive out of order • Messages must be reordered by the recipient www.assignmentpoint.com

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