tailieunhanh - Switching Theory: Architecture and Performance in Broadband ATM Networks phần 7

Một cách tiếp cận thay thế để cải thiện hiệu suất lưu lượng truy cập của một mạng lưới đa cơ bản bao gồm trong việc sử dụng các máy bay unbuffered song song cùng với xếp hàng bên ngoài. Việc áp dụng nhiều máy bay song song unbuffered chuyển đổi có nghĩa là đầu ra xếp hàng là bắt buộc để kiểm soát việc thực hiện mất gói tin. | 248 ATM Switching with Non-Blocking Single-Queueing Networks DA 0 0 0 4 r 7 i r 7 i r 7 i r 7 i r 7 i r 7 i r 7 i r 7 i r 7 i r 7 i Ĩ1Ị ĨĨỊ K - zfÃ1Hz ỉ-ĩ ỵ - adder - 1 k J4A2-1 Figure . Hardware structure of subnetwork B Input Queueing 249 transmission time n na of packet ACK i actoff j and the eventual additional time needed by the port controller to check if actoff j maxoff j and to sum j and actoff j . It can be shown Pat88 that these tasks can be completed in 1 bit time after the complete reception of packets ACK . . by the port controllers. Note that the subnetwork A of AN has no latency the result of the address comparison is available at the EX-OR gate output when the receipt of the destination field in packet REQ . . . is complete . Furthermore the latency of subnetwork B of AN must not be summed up as the running sum lasts 5 bit times and this interval overlaps the transmission time of fields priority and source in packet ACK . . this condition holds as long as 5 n p . We further assume that the channel logical address j actoff j is mapped onto the corresponding channel physical address in a negligible time. Hence the total duration of Phases I and II for a multichannel switch is given by TỊ_ H n n 4 na p 1 log2N log2N 4 I log2Rmax p 2 whereas Tj_ II log2_ 4 1 in a unichannel switch. Thus providing the multichannel capability to a Three-Phase switch implies a small additional overhead that is a logarithmic function of the maximum channels group capacity. For a reasonable value Rmax 64 a switch size N 1024 no priority p 0 and the standard cell length of 53 bytes that implies Tjjj 53 8 we have n in the unichannel switch and n in the multichannel switch. In order to reduce the switching overhead the multichannel three-phase algorithm can be run more efficiently by pipelining the signal transmission through the different networks so as to minimize their idle time Pat91 . In this pipelined algorithm it takes at least two slots to .