ABSTRACT
With the increase of link rate, the arbitrator of centralized switch fabric becomes too complicated to implement. A parallel switch fabric based on crossbar, named as PSFBC (Parallel Switch Fabric Based on Crossbar), has been proposed in this paper. PSFBC is composed of k switches whose rate is 1/k of link', these switches exchange cells in parallel; this increases the arbitrator's period and make it easy to implement. Load is evenly distributed to each switch with FCFS (First Come First Serve) rule, it can keep the order of cells in one stream. A multi-class queue scheduling policy is used in PSFBC to ensure the quality of realtime streams. Experiments show that the load on each switch in PSFBC is well balanced, its average delay of cells is little and its performance is very close to centralized switch; and with the increase of number of parallel switches, the loss of PSFBC's performance keeps very small, it becomes easier to implement.
ABSTRACT
The arteries of the spinal cord on surface have been observed in 62 Chinese adults and 39 children.Anteriorly, the spinal cord was divided into 3 areas, according to the arterial supply.The superior cervical area(segments of C_(1～3) or C_(1～4))was mainly supplied by the anterior spinal arteries; the cervical enlargement area (segments of C_4 or C_5 to T_5 or T_6) was mainly supplied by the arteria intumescentia cervicalis and the lumbar enlargement area (below the segments of T_6 or T_7) was mainly supplied by the arteria intumescentia lumbalis. In the intermediate places between these areas (segments of C_(3～4) and T_(5～6)), the anterior median artery was often narrow or interrupted. Usually the anterior spinal artery united with its fellow of the opposite side to form a single trunk (46.53%). The anterior radicular arteries averaged 5.2 (2～10) in number. The arteria intumescentia cervicalis frequently existed at C_7 and C_8 (C_5～T_3). The arteria intumescentia lumbalis mostly located at T_9 (T_6～L_2), and 72.28% of them being on the left side.Posteriorly, the arteries developed well on the two enlargements. The posterior spinal arteries arised frequently from the vertebral artery (76.41%). The posterior radicular arteries averaged 9.3 (5～21) in number.The authors have raised an objection to the view that the segments of T_4 and L_1 of spinal cord are poor supplied with blood.