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

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

Types of Networks Disadvantages Circuit-switched Packet-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

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

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

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

Packet-Switching A B Postal Network 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

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

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

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

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

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