08-08-2012, 01:32 PM
Computer Network Basics
02computer_network_basics.ppt (Size: 912 KB / Downloads: 64)
Communication Devices
Synchronous communication uses a clock signal separate from the data signal- communication can only happen during the ‘tick’ of the timing cycle
Asynchronous communication does not use a clock signal- rather, it employs a start and stop bit to begin and end the irregular transmission of data
A closer look at network structure:
network edge: applications and hosts
network core:
routers
network of networks
Reliability
A network service is (data) reliable if the sender application can rely on the error-free and ordered delivery of the data to the destination
In the Internet the reliability can obtained mainly by acknowledgements and retransmission
In such a way the losses in the underlying layers can be retrieved
Network Layering
Layering: building complex services from simpler ones
Each layer provides services needed by higher layers by utilizing services provided by lower layers
The physical/link layer is pretty limited
Packets are of limited size (called the “Maximum Transfer Unit or MTU: often 200-1500 bytes in size)
Routing is limited to within a physical link (wire) or perhaps through a switch
Our goal in the following is to show how to construct a secure, ordered, message service routed to anywhere: