Connection Oriented Service

COS or Connection Oriented Service is one of the two techniques that are used in the networking world at the layer 4 in the network, which is also known as the transport layer in the network, to transfer data in data communications that take place between the two or more active devices that are present in the network. In this service, as the name suggest a connection is required at the start of the session before the transferring of data can take place between the source and the destination and due to this one major reason connection oriented service guarantee a level of delivery which is not guaranteed in the connectionless service. The connection oriented service involves three different phases, to ensure the successful transferring of data. These phase are Connection establishment, data transfer and connection termination.

In the first phase, also named as the connection establishment phase the end nodes - between which the connection is to be made – maybe reserved for the connection. Apart from reservation the end nodes might also decided upon the size of the window through which the data is going to be transferred and this size of window depends upon the space or the capacity of the network. After the reservation has been made and the connection between the end nodes has been established the second phase begins, that is, data transfer takes place.

In the second phase the data is transmitted over the connection and during this process many lost data packets are resent by the source to the destination to ensure that the destined end point is receiving all the data that was to be sent. Once the data transfer phase is completed the third and the final phase of connection termination begins. The end points then terminate the connection ensuring that the data transfer has taken place. In this way the connection oriented service works.