Discuss the characteristics of AAL5.

characteristics of AAL5, which is used for TCP/IP: • Message Mode and Streaming Mode Assured Delivery • Non-Assured Delivery (used by TCP/IP) • Blocking and Segmentation of Data • Multipoint Operation The AAL type is known by the VC endpoints through the cell setup mechanism and is not carried in the ATM cell header. For PVCs, the AAL type is administratively configured at the endpoints when the connection (circuit) is set up. For SVCs, the AAL type is communicated along the VC path through Q.93B as part of call setup establishment and the endpoints use the signaled information for configuration. ATM switches generally do not care about the AAL type of VCs.

The AAL5 format specifies a packet format with a maximum size of 64 KB - 1 byte of user data. The primitives, which the higher layer protocol has to use in order to interface with the AAL layer (at the AAL service access point, or SAP), are rigorously defined. When a high-layer protocol sends data, that data is processed first by the adaptation layer, then by the ATM layer, and then the physical layer takes over to send the data to the ATM network. The cells are transported by the network and then received on the other side first by the physical layer, then processed by the ATM layer, and then by the receiving AAL. When all this is complete, the information (data) is passed to the receiving higher layer protocol. The total function performed by the ATM network has been the non-assured transport (it might have lost some) of information from one side to the other. Looked at from a traditional data processing viewpoint, all the ATM network has done is to replace a physical link connection with another kind of physical connection. All the higher layer network functions must still be performed (for example, IEEE 802.2).