Connectionless mode transmission
Encyclopedia
In packet switching
networks, CL-mode or connectionless communication is a data transmission
method in which each data packet carries information in a header
record that contains a destination address
sufficient to permit the independent delivery of the packet to its destination via the network.
A packet transmitted in a connectionless mode is frequently called a datagram
.
In connection-oriented communication the communicating peers must first establish a logical or physical data channel or connection in a dialog preceding the exchange of user data.
The connectionless communication mode has the advantage over a connection-oriented mode in that it has low 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 always unicast
(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 protocol layer
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 (routers, bridge
s) along the network path would be able to pre-compute (and hence cache
) 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:
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
networks, CL-mode or connectionless communication is a data transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
method in which each data packet carries information in a header
Header (information technology)
In information technology, header refers to supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission, the data following the header are sometimes called the payload or body....
record that contains a destination address
Network address
Network address may refer to:*Base address*Classful address*IP address*IPX address*Logical address*Network layer address,*X.25/X.21 address*MAC address-See also:*Autonomous system *Host address*Link layer*Subnet mask...
sufficient to permit the independent delivery of the packet to its destination via the network.
A packet transmitted in a connectionless mode is frequently called a datagram
Datagram
A datagram is a basic transfer unit associated with a packet-switched network in which the delivery, arrival time, and order are not guaranteed....
.
In connection-oriented communication the communicating peers must first establish a logical or physical data channel or connection in a dialog preceding the exchange of user data.
The connectionless communication mode has the advantage over a connection-oriented mode in that it has low overhead. It also allows for multicast
Multicast
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
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 always unicast
Unicast
right|200pxIn computer networking, unicast transmission is the sending of messages to a single network destination identified by a unique address.-Addressing methodologies:...
(point-to-point).
Unfortunately, in connectionless mode transmission of a packet, the service provider usually cannot guarantee that there will be no loss, error
Error
The word error entails different meanings and usages relative to how it is conceptually applied. The concrete meaning of the Latin word "error" is "wandering" or "straying". Unlike an illusion, an error or a mistake can sometimes be dispelled through knowledge...
insertion, misdelivery, duplication, or out-of-sequence
Sequence
In mathematics, a sequence is an ordered list of objects . Like a set, it contains members , and the number of terms is called the length of the sequence. Unlike a set, order matters, and exactly the same elements can appear multiple times at different positions in the sequence...
delivery of the packet. (However, the risk of these hazards may be reduced by providing a reliable transmission service at a higher protocol layer
Layer
Layer may refer to:* A layer of archaeological deposits in an excavation* A layer hen, a hen raised to produce eggs* Stratum, a layer of rock or soil with internally consistent characteristics...
of the OSI Reference Model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
.)
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 (routers, bridge
Bridging (networking)
Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing, bridging makes no assumptions about where in a network a particular address is located. Instead, it depends on flooding and examination of source addresses in received packet headers to locate unknown...
s) along the network path would be able to pre-compute (and hence cache
Cache
In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
) 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 the Transport LayerTransport layerIn computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
: TCPTransmission Control ProtocolThe Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
is a connection-oriented transport protocol. UDPUser Datagram ProtocolThe User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
is connectionless. - At the Network LayerNetwork LayerThe network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
. - At the Data Link LayerData link layerThe data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
: The IEEE 802.2IEEE 802.2IEEE 802.2 is the IEEE 802 standard defining Logical Link Control , which is the upper portion of the data link layer of the OSI Model. The LLC sublayer presents a uniform interface to the user of the data link service, usually the network layer...
protocol at the Logical Link ControlLogical Link ControlThe logical link control data communication protocol layer is the upper sub-layer of the data link layer in the seven-layer OSI reference model...
sublayer of the data link layer may provide both connectionless and connection-oriented services. In fact, some network protocols (such as SNA's Path Control in its early stages) require a connection-oriented data link layer. Others (like IPInternet ProtocolThe Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
) do not. (After the appearance of APPN, SNA could operate on a connectionless data link service as well.)