10.1.4 This page will introduce two types of delivery systems, which are connectionless and connection-oriented.
These two services provide the actual end-to-end delivery of data in an internetwork.
Most network services use a connectionless delivery system. Different packets may take different paths to get through the network. The packets are reassembled after they arrive at the destination. In a connectionless system, the destination is not contacted before a packet is sent. A good comparison for a connectionless system is a postal system. The recipient is not contacted to see if they will accept the letter before it is sent. Also, the sender does not know if the letter arrived at the destination.
In connection-oriented systems, a connection is established between the sender and the recipient before any data is transferred. An example of a connection-oriented network is the telephone system. The caller places the call, a connection is established, and then communication occurs.
Connectionless network processes are often referred to as packet-switched processes. As the packets pass from source to destination, packets can switch to different paths, and possibly arrive out of order. Devices make the path determination for each packet based on a variety of criteria. Some of the criteria, such as available bandwidth, may differ from packet to packet.
Connection-oriented network processes are often referred to as circuit-switched processes. A connection with the recipient is first established, and then data transfer begins. All packets travel sequentially across the same physical or virtual circuit.
The Internet is a gigantic, connectionless network in which the majority of packet deliveries are handled by IP. TCP adds Layer 4, connection-oriented reliability services to IP.
The next page will discuss the IP header.
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