Design and implementation of a QoS oriented data-link control protocol forCBR traffic in wireless ATM networks

This paper presents a QoS oriented Data Link Control (DLC) framework for tr ansporting Constant Bit Rate (CBR) traffic over wireless ATM links. Data li nk control is usually omitted in fixed ATM networks because cell corruption due to channel error is extremely rare for reliable media like copper wire and optical fiber. However, for wireless, higher bit error rates are quite common due to shadowing, and other fading effects. The purpose of DLC in w ireless is to provide error-free transport to the higher layers by recoveri ng corrupted cells at the link layer. A selective reject (SREJ) automatic r epeat request (ARQ) based DLC protocol is used for CBR error recovery. For an ARQ based scheme, higher recovery rates can be achieved with larger cell transfer delay, caused by cell retransmissions. Since cell transfer delay and DLC recovery rate both translate to user-perceivable Quality-of-Service (QoS), it is important for the DLC to strike a balance between these two, depending on the application's requirements. To achieve this in our protoco l, the retransmission procedure for a CBR cell is constrained to complete w ithin a recovery time interval which is specified by the application at cal l-setup time. Also, a novel jitter removal scheme that reduces the cell del ay variation caused by cell loss and retransmissions, is incorporated as a part of the DLC protocol. The proposed protocol is implemented on NEC's WAT Mnet prototype system. The implementation and its experimental results are reported for illustrating the performance and feasibility of the presented CBR DLC protocol. The experimental results show that the DLC protocol can b e successfully applied for QoS-constrained error recovery of CBR traffic on a per-connection basis. These also indicate that the DLC can be programmed to attain a desirable tradeoff between cell transfer delay and cell recove ry rate.