## 5 Experiments and Analyses
### Performance on Different Packet Sizes  
In the second experiment, we wished to check the impact on performance of different packet sizes, including 500, 1000, 1500, 2000, 2500, and 3000 bits rather than 1.5 Kbits per packet listed in Table 11. The packet rate was also changed from a packet per 15 s to a packet per 10 s, _i.e._, 6 pkts/min. In other words, the request rates range from 300 bps (= 6 pkts/min \(\times\) 500 bits/pkt \(\times\) 6) to 1800 bps (= 6 pkts/min \(\times\) 3000 bits/pkt \(\times\) 6). Four schemes, including SPA-WP, Random, FCFS and SPA-Multipath, are tested, given the type ratio = 1:1:1, where FCFS is the algorithm with which Scheduler allocates resource nodes to requests, based on the sequence in which the resource nodes enter the system, and SPA-Multipath is a SPA-WP algorithm with a multipath routing approach [14]. On each test, the sizes of a user request and a data packet were the same. Each experiment lasted 100 s rather than 200 s listed in Table 11, implying a total of 60 (= 10 requests*6 nodes) requests were submitted. Also, in the following experiments, we did not transform the format of a video program. Thus, the time required to transmit a 10 MB video data is about 12 s (= 10 MB/11 Mbps + wireless channel contention time) where 11 Mbps is the wireless bandwidth. Since six nodes contend for the only wireless channel, a node on average needed about 72 s (= 12 \(\times\) 6) to wait to be transmitted again, and the average waiting time was 42 (= \((\sum\limits_{i=1}^{6}\)12\(\times\)_i_)/6) s. A node was allocated 10 requests by Resource Broker in average, and the turnaround time of first request was 42 s on average, the second request needed to wait for 42 s and the 10 th request waited 420 s. So the ideal average turnaround time was 231 (= \((\sum\limits_{i=1}^{10}\)42\(\times\)_i_)/10) s.  
Figure 11: Performance of the second experiment given different packet sizes. (**a**) Drop rates measured at the Resource Broker; (**b**) Throughputs measured at the Resource Broker; (**c**) Turnaround times measured at the Resource Broker. The experimental results are shown in Figure 11. Figure 11a illustrates that the drop rates were higher when packet size = 500 bits since with a shorter packet, we need more packets to transmit a fixed-length video program, leading to a higher probability of packet collision. The Random's and the FCFS's drop rates were higher than those of the other two because when receiving a request, due to using simple algorithms with lower overheads, the two algorithms pass the requests to the destination more quickly than the others do. Hence, packets have a higher probability to collide or be dropped. The reason for the high probability of packet dropping is that their queues were full much earlier than the queues in the nodes when the SPA-WP or SPA-Multipath was employed. As shown in Figure 11b, the throughputs increase when packet sizes are higher, since a longer packet can carry many more bits than a shorter packet can when a node's packet rate is fixed, and relatively fewer packets are generated to transmit a video program, leading to less channel contention. The turnaround times of these four algorithms are illustrated in Figure 11c in which, due to having more transmitted packets (_i.e._, Data size/packet size), higher drop rates and more channel contention, the shorter packet sizes' turnaround times were longer. The turnaround times of the SPA-WP and the SPA-Multipath were shorter than those with the Random and the FCFS. The reasons are mentioned above. The SPA-Multipath transfers packets with multiple paths, so its turnaround times were shorter than those with the SPA-WP. Now we can conclude that a high density of user requests will result in long turnaround time. In fact, the transmission delay of a 10 MB video program was only 7.3 s, but the turnaround time was up to 360 to 378 s when packet size = 500 bits, implying most of the packets were congested to contend for the only wireless channel before they were delivered by the AP.