- Connectionless mode transmission
In a packet-switched network, connectionless mode transmission is a transmission in which each packet is prepended with a header containing a destination
address sufficient to permit the independent delivery of the packet without the aid of additional instructions.A packet transmitted in a connectionless mode is frequently called a
datagram .In
connection-oriented communication the stations about to exchange data first need to declare towards each other that they want to do so. This is called "establishing a connection". A connection is sometimes defined as a logical relationship between the peers exchanging data.An advantage of connectionless mode over connection-oriented mode is that it has a low data overhead. It also allows for
multicast and broadcast operations, which may save even more network resources when the same data needs to be transmitted to several recipients. In contrast, a connection is alwaysunicast (point-to-point).Unfortunately, in connectionless mode transmission of a packet, the service provider usually cannot guarantee that there will be no loss,
error insertion, misdelivery, duplication, or out-of-sequence delivery of the packet. (However, the risk of these hazards may be reduced by providing a reliable transmission service at a higher protocollayer of the OSI Reference Model.)Another drawback of the connectionless mode is that no optimisations are possible when sending several frames between the same two peers. By establishing a connection at the beginning of such a data exchange the components (
router s, bridges) along the network path would be able to pre-compute (and hencecache ) routing-related information, avoiding re-computation for every packet. Network components could also reserve capacity for the transfer of the subsequent frames of e.g. a video download.The distinction between connectionless and connection-oriented transmission may take place at several layers of the OSI Reference Model:
* At thetransport layer : TCP is a connection-orientedtransport protocol . UDP is connectionless.
* At thenetwork layer .
* At thedata link layer : TheIEEE 802.2 protocol at theLogical Link Control sublayer of the data link layer may provide both connectionless and connection-oriented services. In fact, somenetwork protocol s (such asSNA 'sPath Control in its early stages) require a connection-oriented data link layer. Others (like IP) do not. (After the appearance ofAPPN , SNA could operate on a connectionless Data Link Service as well.)References
*
Federal Standard 1037C
Wikimedia Foundation. 2010.