bit được gửi lại phát hiện rằng nó đã đến các chuyển mạch ATM trong đó các chuỗi bắt đầu, nó sẽ bắt đầu áp dụng các thuật toán định tuyến Chuỗi. Giả sử điện thoại di động roams vào 6 cell và được gửi trở lại thông qua các tuyến đường chuỗi. Khi các bit được gửi lại thấy CASL, | COMBINED QoS-BASED PATH OPTIMIZATION SCHEME 229 The idea of the delay-based path optimization algorithm is that the path extension continues until the delay variation is violated during handoff. When a MT first requests handoff during the call the previous path is reserved. The rerouting path is the extension of the previous path. That means the rerouting path is extended from the previous switch to the current switch. This is the simplest and the fastest way to do path rerouting and it ensures a seamless handoff. After the path extension is completed the new path s delay is the sum of the previous path delay and the delay between the new source node and the previous source node. Here we assume the destination node is stationary during handoff. We also assume the previous path does not exceed the maximum delay limitation. After path extension rerouting the delay of the path may exceed the required maximum delay value. This may cause the call to drop. If the delay variation is violated the path optimization is activated. The new shortest path that is the lowest delay path should be found to substitute the previous path to ensure a continuous connection. In the hop-based algorithm the path extension is done when there is a handoff request until the number of path extensions exceeds the maximum allowed path extension hops. When the number of path extensions exceeds the maximum allowed path extension hops path optimization is activated when there is a handoff request. This algorithm only considers the number of path extensions. It does not consider the delay variation to activate the path optimization scheme. The rerouting path searching procedure for delay-based hop-based and combined rerouting algorithms is the shortest path search. The delay-based algorithm extends the path each time when handoff occurs until the link delay is larger than the allowed maximum delay. In our simulation we use MAXDELAY to indicate the allowed maximum delay. When the MAXDELAY is large .
