IEEE 802.11 in the Large: Observations at the IETF Meeting Andrea G. Forte Sangho Shin Henning Schulzrinne Department of Computer Science Columbia University

Introduction 65th IETF meeting Data collection Goals Dallas, TX March 19th ~ 24th Hilton Anatole hotel 1200 attendee Data collection 21st ~ 23rd for three days 25GB data, 80 millions frames Goals Identify unusual behaviors due to the highly congested environment 9/22/2018

Overview Introduction Related work Wireless network setup Measurement setup User behavior Load balancing Handoff behavior Overhead of multiple APs on a channel Conclusions 9/22/2018

Related Work Jardosh et al. Rodrig et al. Balachandran et al. Target 62nd IETF (’05) SIGCOMM ’04 SIGCOMM ’01 Attendee 1100 550 200 Clients detected 500 377 195 WLAN 802.11b Channels 1, 6, 11 (dynamic) 1, 8, 11 1, 4, 7, 11 Number of APs 38 5 4 Focused on New metric for channel congestion, ‘Link reliability’ Overhead of 802.11, the data transmission rate Load balancing: “No correlation b/w num of clients and traffic load” * * The number does not mean the total number of wireless clients in the IETF meeting, but the number of clients detected from the measurements. 9/22/2018

Wireless network in IETF meeting Many hotel 802.11b APs on channel 6 91 additional APs in 802.11a/b by IETF Cisco Aironet 1200 AP Channel 1 and 11 in 802.11b One subnet with one ESSID ‘ietf65 ’ No wireless security The largest wireless network measured so far Hotel APs 802.11b channel 6 IETF APs 802.11a/b ESSID : ietf65 9/22/2018

Measurement setup Four sniffers Channel assignment IBM T42 Think Pad Proxim ORiNOCO 11 a/b/g Sniffer software: Airopeek NX Channel assignment Three sniffers on channel 1, 6 and 11, respectively Fourth sniffer on all 8 channels in 802.11a 9/22/2018

Measurement setup Measurement place Room Chantilly The biggest room - 142’ x 80’, 600 persons Two biggest IETF sessions, and the plenary session in the evening Six IETF APs + Six Hotel APs in the room Session 2 & break Session 1 (AM) Lunch Session 1 (PM) Plenary 9:00 11:30 13:00 15:00 17:00 19:30 9/22/2018

The positions of the APs in the room Room Chantilly AP5 AP4 Seating area during IETF sessions and plenary Another seating area during plenary AP1 AP2 AP3 AP6 sniffers AP on channel 1 AP on channel 11 AP on channel 11 (estimated position) 142 feet screen Gate 80 feet Lobby 9/22/2018 AP9

Overview Introduction Related work Wireless network setup Measurement setup User behavior Load balancing Handoff behavior Overhead of multiple APs on a channel Conclusions 9/22/2018

User behavior Overall traffic in 802.11b 9/22/2018

User behavior Protocols 9/22/2018

User behavior Number of clients (all 8 channels) 9/22/2018

Overview Introduction Related work Wireless network setup Measurement setup User behavior Load balancing Handoff behavior Overhead of multiple APs on a channel Conclusions 9/22/2018

Load balancing Distribution of clients No load balancing feature was used Client distribution is decided by the relative proximity from the APs Ch 6 (ceiling) > Ch 1 > Ch 11 AP5 AP4 Seating area during IETF sessions and plenary Another seating area during plenary AP1 AP2 AP3 AP6 sniffers 9/22/2018

Load balancing Distribution of clients No load balancing feature was used Client distribution is decided by the relative proximity from the APs Ch 6 (ceiling) > Ch 1 > Ch 11 AP1 > AP2 > AP3 Number of clients in channel 1 9/22/2018

Load balancing Throughput Average throughput in 802.11a/b Average throughput in channel 1 9/22/2018

Load balancing Throughput per client Average throughput per client in 802.11a/b Average throughput per client in channel 1 9/22/2018

Load balancing How? Study of Balanchandran et al. [1] Number of clients? – Simple, but not accurate Throughput ? - Accurate, but too complex Study of Balanchandran et al. [1] “No correlation between the number of clients and traffic load” “Throughput per client needs to be considered” In the large scale wireless network like IETF meeting? [1] A. Balanchandran et al. “Characterizing user behavior and network performance in a public wireless LAN”, SIGMETRICS ‘02 9/22/2018

Capacity in the channel Load balancing Number of clients vs. throughput in Ch. 6 Capacity in the channel 9/22/2018

Capacity in the channel Load balancing Number of clients vs. Throughput Capacity in the channel Clear correlation between the number of clients and throughput The number of clients can be used for load balancing with low complexity of implementation, in large scale wireless networks 9/22/2018

Effect of screen Small number of clients on AP3 Effect of a screen? Number of clients in channel 1 9/22/2018

Effect of screen An experiment 30 ~ 100 feet 9/22/2018

Overview Introduction Related work Wireless network setup Measurement setup User behavior Load balancing Handoff behavior Overhead of multiple APs on a channel Conclusions 9/22/2018

The number of handoff per hour Handoff behavior Handoff is triggered generally, by low signal strength in congested channel, by frame loss Effect of layer 2 handoff Increase of traffic Disruption of network (0.5 ~ 1.5 sec) The number of handoff per hour in each IETF session 9/22/2018

Handoff behavior Handoffs between channels Handoff to the same channels : 72% Handoff to the same AP : 55% 9/22/2018

Handoff behavior Distribution of session time: time between handoffs Too often handoff Disruption of network 0.5 ~1.5 sec per handoff Increase of traffic due to handoff related frames – probe request and response 10.4% of total 9/22/2018

(based on the number of handoffs during the whole day) Handoff behavior Handoffs per vendor Distribution of vendors Distribution of handoffs per vendor (based on the number of handoffs during the whole day) 9/22/2018

Handoff behavior Handoffs per vendor (session time) 9/22/2018 Cisco Apple 9/22/2018

Overview Introduction Related work Wireless network setup Measurement setup User behavior Load balancing Handoff behavior Overhead of multiple APs on a channel Conclusions 9/22/2018

Overhead of having multiple APs Overhead from replicated multicast and broadcast frames All broadcast and multicast frames are replicated by all APs  Increase traffic Router A channel 9/22/2018

Overhead of having multiple APs Overhead from replicated multicast and broadcast frames All broadcast and multicast frames are replicated by all APs DHCP request (broadcast) frames are replicated and sent back to each channel Router A channel 9/22/2018

Overhead of having multiple APs Overhead from replicated multicast and broadcast frames All broadcast and multicast frames are replicated by all APs. DHCP request (broadcast) frames are replicated and sent back to each channel. Multicast and broadcast frames : 10% 9/22/2018

Overhead of having multiple APs Co-channel interference 14 APs around the room Chantilly in channel 6 Co-channel interference and too many clients are responsible for the very low throughput of channel 6. 9/22/2018

Conclusions Uneven distribution of clients and throughput among channels and APs Correlation between the throughput and the number of clients The number of clients can be used for load balancing with low complexity in highly congested wireless networks Too many inefficient handoffs Disrupt network and increase traffic Need better handoff algorithms Having multiple APs on a channel Increases the traffic due to replication of multicast and broadcast frames Decrease throughput due to co-channel interference 9/22/2018

Most Recent Results 9/22/2018

Ongoing Work Apple vs. Intel (Thank you Norbert!) Apple When to scan? Who to associate to? Intel (newest chipset) Roaming aggressiveness Too many handoffs? 9/22/2018

Thank you! Questions ? 9/22/2018

Backup slides 9/22/2018

Handoff behavior Total number of handoffs Total number of handoffs Number of handoffs per hour 9/22/2018