ATM AAL receiver design supporting threshold based buffering mechanism

• Main Authors: Ren, Deng Yi, 任登義
• Other Authors: Lai, Fei Biao
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/35021372177170968123

碩士 === 國立臺灣大學 === 資訊工程學研究所 === 84 === A broad-band terminal adaptor (BTA) is needed in the internetworking unit between LANs and ATM network to provide the necessary conversion of data packets. The ATM adaptation layer (AAL) design is the kernel component in BTA. In this thesis, we examine the AAL5 BTA implementation problems and discuss some of their solutions. Design issues of AAL5 consists of the transmitting end and the receiving end. In the transmitting end, AAL5 deals mainly with data segmentation and generates CRC field. At the receiving end, the AAL5 entry receives ATM cells, reassembly them into a upper layer PDU, detects error and handles cell loss. In this thesis we focus design issues at the receiving end. Since an AAL5 may support multiple virtual channels at the same time, at AAL5 entry receiving end needs to be equipped with sufficient reassembly buffers to temporarily store many partially-reassembled messages. Meanwhile, if the host interface is busy and network is heavy loaded, how the BTA handle heavy traffic becomes an essential issue. For example, if one can reduce the events of discarding cells due to buffer overflow the packet level throughput can be improved. Here we propose a useful buffer management mechanism, which is named Threshold-Based Buffering Mechanism, to reduce performance degradation level. This mechanism sets a threshold on reassembly buffer. In congestion, once reassembly buffer space excesses threshold, the receiving end BTA will choose the longest packet in reassembly buffer and then deliver part of it to the upper layer even it is still incomplete.