 of service are defined for AAL-3/4: 1. Message Mode Service. This provides for the transport of one or more fixed-size AAL service data units in one or more CS-PDUs. 2. Streaming Mode Service. Here the AAL service data unit is passed across the AAL interface in one or more AAL interface data units (IDUs). The transfer of these AAL-IDUs across the AAL interface may occur separated in time, and this service provides the transport of variable-length AAL-SDUs. The streaming mode service includes an abort service, by which the discarding of an AAL-SDU partially trans- ferred across the AAL interface can be requested. In other words, in the streaming mode, a single packet is passed to the AAL layer and transmitted in multiple CPCS- PDUs, when and as pieces of the packet are received. Streaming mode may be used in intermediate switches or ATM-to-SMDS routers SO they can begin retransmit- ting a packet being received before the entire packet has arrived. This reduces the latency experienced by the entire packet. AAL-5. This type of AAL was designed specifically to carry data traffic typically found in today's LANs. AAL-5 evolved after AAL-3/4, which was found to be too complex and inefficient for LAN traffic. Thus, AAL-5 got the name "SEAL" for simple and efficient AAL layer. Only a small amount of overhead is added to the CPCS_PDU. There is no AAL level cell multiplexing. In AAL-5 all cells belonging to an AAL-5 CPCS_PDU are sent sequentially. To simplify still further, the CPCS_PDUs are padded 10 to become integral multiples of 48 octets, ensuring that there never will be a need to send partially filled cells after segmentation. 20.7 SERVICES: CONNECTION-ORIENTED AND CONNECTIONLESS The issues such as routing decisions and architectures have a major impact on connection- oriented services, where B-ISDN/ATM end nodes have to maintain or get access to lookup tables, which translate destination addresses into circuit paths. These circuit path lookup 10 Padded means adding "dummy" octets, octets that do not carry any signi