Number of aps Max ap degree Max connected No. of connected (i. e,# neighbors) omponent size components Portland 8683 54 San Diego 34 76 93 1345 San Francisco Table 2: Statistics for APs measured in 6 US cities(Place Lab data set 1.03 1.13 1.15 1.12 1.31 3.4 Table 3: Channels employed by APs in the Wifimaps Figure 1: Distribution of AP degrees(Place Lab data set classified APs, or about 93, are 802.11g. Given the rela- tively recent standardization of 802.11g(June 2003), these 8683 nodes measured had 3 or more neighbors. Since only measurements suggest that new wireless technology gets de- three of the 802. 11b channels are non-overlapping(channel ployed relatively quickly. 1, 6 and 11), these nodes will interfere with at least one other node in their vicinity 3.2. 4 Vendors and AP Management Support The fourth column in Table 2 shows the size of the max. Vendor mum connected component in the interference graph of a Percentage of APs ty. The final column shows the number of connected com- nents in the interference graph. From these statistics, we Linksys( Cisco) find several large groups of APs deployed in close proxim Aironet(Cisco) 122 ty. Together, these statistics show that dense deployments 96 of 802. 11 hardware have already begun to appear in urban D-Link settings. As mentioned earlier, we expect the density to ole Computer continue to increase rapidly. Netgear AN Communications 3 3.2.2 802.11 Usage: Channels Delta Networks Table 3 presents the distribution of channels used by APs the WiFiMaps data set. This provides an indication of I Acer whether users of APs manage their networks at all. Notice Others hat many APs transmit on channel 6, the default on many channels in 802. 11b(i.e, channels 1 and 11). While this does Table 4: Popular AP vendors(Wifimaps data set) ntify particular conflicts, this distribution suggests that many of the APs that overlap in coverage are probably To determine popular AP brands, we look up the MAC ad- dresses available in the wifimaps data set against the ieee Company -id assignments [4] to classify each AP according to 3.2.3802.bws.802.lg the vendor. For the aps that could be classified in this man- The Pittsburgh wardrive data set contains information ner(2% of the APs in the Wifimaps data set did not have about rates supported for about 71% of the measured APs, a matching vendor name), the distribution of the vendors is or 472 out of the 667. We use this information to classify shown in Table 4. Notice that Cisco products(Linksys and these APs as 802. 11b or 802.11g. We find that 20% of the Aironet)make up nearly half of the market. This observaCity Number of APs Max AP degree Max. connected No. of connected (i.e., # neighbors) component size components Chicago 2370 42 54 369 Washington D.C. 2177 20 226 162 Boston 2551 85 168 320 Portland 8683 54 1405 971 San Diego 7934 76 93 1345 San Francisco 3037 39 409 186 Table 2: Statistics for APs measured in 6 US cities (Place Lab data set) 0 1000 2000 3000 4000 5000 6000 7000 2 4 6 8 10 12 14 16 18 20 Nodes with d >= x Degree Boston Chicago Portland San Diego San Francisco Wash D.C. Figure 1: Distribution of AP degrees (Place Lab data set) 8683 nodes measured had 3 or more neighbors. Since only three of the 802.11b channels are non-overlapping (channel 1, 6 and 11), these nodes will interfere with at least one other node in their vicinity. The fourth column in Table 2 shows the size of the max￾imum connected component in the interference graph of a city. The final column shows the number of connected com￾ponents in the interference graph. From these statistics, we find several large groups of APs deployed in close proxim￾ity. Together, these statistics show that dense deployments of 802.11 hardware have already begun to appear in urban settings. As mentioned earlier, we expect the density to continue to increase rapidly. 3.2.2 802.11 Usage: Channels Table 3 presents the distribution of channels used by APs in the WiFiMaps data set. This provides an indication of whether users of APs manage their networks at all. Notice that many APs transmit on channel 6, the default on many APs, and only 14% use the remaining two non-overlapping channels in 802.11b (i.e., channels 1 and 11). While this does not identify particular conflicts, this distribution suggests that many of the APs that overlap in coverage are probably not configured to minimize interference. 3.2.3 802.11b vs. 802.11g The Pittsburgh wardrive data set contains information about rates supported for about 71% of the measured APs, or 472 out of the 667. We use this information to classify these APs as 802.11b or 802.11g. We find that 20% of the Channel Percentage of APs 1 3.04 2 12.29 3 3.61 4 1.03 5 1.13 6 41.15 7 1.75 8 1.12 9 1.31 10 3.42 11 11.04 Table 3: Channels employed by APs in the Wifimaps data set. classified APs, or about 93, are 802.11g. Given the rela￾tively recent standardization of 802.11g (June 2003), these measurements suggest that new wireless technology gets de￾ployed relatively quickly. 3.2.4 Vendors and AP Management Support Vendor Percentage of APs Total classified 98 Linksys (Cisco) 33.5 Aironet (Cisco) 12.2 Agere Systems 9.6 D-Link 4.9 Apple Computer 4.6 Netgear 4.4 ANI Communications 4.3 Delta Networks 3.0 Lucent 2.5 Acer 2.3 Others 16.7 Table 4: Popular AP vendors (Wifimaps data set) To determine popular AP brands, we look up the MAC ad￾dresses available in the Wifimaps data set against the IEEE Company id assignments [4] to classify each AP according to the vendor. For the APs that could be classified in this man￾ner (2% of the APs in the Wifimaps data set did not have a matching vendor name), the distribution of the vendors is shown in Table 4. Notice that Cisco products (Linksys and Aironet) make up nearly half of the market. This observa-