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Operation Report of WiFi meshnetworks at WIDE 2012 SpringCamp Networkwide-tr-wi-wifi-mesh-camp-1203-00.pdf

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Title:Author(s):Date:Operation Report of WiFi mesh networks at WIDE 2012 SpringCamp Network
Keiichi Shima, Shoichi Sakane, Yuzo Taenaka
2012-3-26

Operation Report of WiFi mesh networks at
WIDE 2012 Spring Camp Network
Keiichi Shima∗

Shoichi Sakane†

Yuzo Taenaka‡

March 26, 2012

Abstract
Layer 2 and layer 3 WiFi-based mesh networks were provided as acomodity network infrastructure for participants of the WIDE 2012 SpringCamp meeting from 5th to 8th March 2012. This documents reports thesummary of the network configuration information and brief performancemeasurement results.

1Background

It is well understood that wireless radio communication technologies areuseful technologies for places where landline infrastructure is not well deployed. A conference network or an event network where we need a temporal Internet connectivity, or cases of disasters where we lose most of theexisting ground communication infrastructures, are examples. However,in reality, we usually construct wired network backbone for conference
and event networks. The only wireless section is the last 1 hop, between
a user terminal and a WiFi access point. In disaster cases, a satellite linkis the most major communication device to provide Internet connectivity
to the damaged area. From the satellite terminal, we extend the network
using a Ethernet cable and last 1 hop WiFi access point in most cases.
We know wireless links reduce the network construction burden a lot,
however we haven’t been using them seriously. There are some reasons ofnot using wireless links; for example, 1) the performance of wireless networks is much lower than wired networks, 2) management of the invisible
links are more difficult than wired links.
We thought that we had to have more experience on the operationof wireless based network construction and to find what were the realsources of the reasons why we though wireless-oriented network was hardto operate.

∗ IIJ Innovation Institute Inc.
† Cisco Systems G.K.

‡ The University of Tokyo1

2Specifications

We operated two different kinds of WiFi mesh networks in the WIDE2012 Spring Camp meeting. The one is a layer 2 mesh network, and theother is a layer 3 mesh network. The devices used to construct these meshnetworks are shown in table 1 and 2.

Table 1: Devices used to construct a layer 2 WiFi mesh network
PartRole
Cisco AIR-2125-K9
Wireless LAN Controller
Cisco AIR-1262N-Q-K9
Wireless LAN Access Point
Cisco AIR-PWRIJN4
Wireless LAN Access Point PoE
adapter
Cisco WS-C3560CG-8PC-S PoE Ethernet Switch

Table 2: Devices used to construct a layer 3 WiFi mesh network
PartRole
NTTPC Communications MR1200 Wireless LAN Access
Point (with customizedOpenWRT
operatingsystem)

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Meeting Rooms
Table 3: Meeting rooms
NameCapacity
Workshop (WS) for 200 people (1015m2 )Plenaryfor 150 (175m2 )BoF1for 60 (less than 100m2 )BoF2
for 60 (less than 100m2 )Boardfor 20 (less than 100m2 )The number of participants of the meeting was 166. There were 5rooms for the meeting. Table 3 and figure 1 show the rough size of therooms and their locations.
The WS room was used to host several workshops during the meeting.
The plenary room was used to have plenary sessions and some bof sessions.
The WS room and the plenary room were the most crowded space since
they might have the entire meeting participants, during the workshop
sessions or plenary sessions. The BoF1 and BoF2 rooms were used tohost bof sessions for working groups. They had roughly 50 members at

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Figure 1: The floor map of the venue (the size of the 2nd floor is 80m × 50m)
maximum during the meeting. The board room was a dedicated room for
the WIDE board members, and had around 20 members at maximum.
Each room was separated thick walls. The doors were closed whilethere were meetings in the rooms, except the WS room where most of thedoors were kept open.

4Network Configuration

4.1Layer 2 WiFi Mesh

In the layer 2 WiFi mesh configuration, we used a wireless LAN controller
appliance sold by Cisco Systems (table 1). The WiFi band allocation
policy is as follows.
Backhaul 802.11a 5GHz (36 for a single band or 36 and 40 channels fora channel bonding)User 802.11gn 2.4GHz automatic allocation (1, 6, and 11 channels)
Figure 2 shows the initial location of access points. There were 11access points (AP-1 to AP-10, and AP-14) located at the venue. AP-1
was the only access point connected via a Ethernet cable since it wasacting as a root access point of the entire mesh network. All the accesspoints were under control of the wireless LAN controller (indicated as
WLC in the map).
We started with the configuration shown in figure 2, however, when
we finished the first plenary session in the plenary room in the afternoon
on 5th March, we noticed that that most of the users in the plenary room
were connected AP-10 and the AP was overloaded. We moved AP-4 from3

AP-8

AP-6AP-5

AP-9

AP-2

AP-4

AP-7
AP-14

AP-10

AP-1

GW

AP-3

Figure 2: Initial access point location map for layer 2 WiFi mesh network

the workshop room to the plenary room in the evening on 5th and kept
the configuration until we finish the meeting. Figure 3 shows the location
map we used during the most of the meeting period.
The protocol used to build and maintain the layer 2 mesh topology wasAWPP (Adaptive Wireless Path Protocol, which is a proprietary protocolof Cisco).

4.2Layer 3 WiFi Mesh

In the layer 3 WiFi mesh configuration, we used a OpenWRT-based wireless router provided by NTTPC Communications (table 2). The WiFiband allocation policy is as follows.
Backhaul 802.11a 5GHz (36 channel)
User 802.11gn 2.4GHz static allocation• AP-1: Channel 1• AP-2: Channel 6• AP-3: Channel 11• AP-4: Channel 1• AP-5: Channel 11• AP-6: Channel 6• AP-7: Channel 1• AP-8: Channel 1• AP-9: Channel 6• AP-10: Channel 114

AP-8

AP-6
AP-5

AP-9

AP-2
AP-7
AP-14

AP-10

AP-4

AP-1

WLCAP-3

Figure 3: Final access point location map for layer 2 WiFi mesh network

Figure 4 shows the location of each access point. AP-1 acted as anInternet gateway in addition to as an access point and mesh router.
The protocol used to build and maintain the layer 3 mesh network wasOLSRv2.

5Topology Transition

Figure 5 and 6 are the snapshot images of the layer 2 and layer 3 meshnetworks as of 20:00 5th March 2012 and 12:00 6th March 2012 respectively.
The red arrows in figure 5 indicate parent access points.
The red arrows in figure 6 indicate next hop access points, and thegray arrows indicate neighboring access points.
The layer 2 mesh topology is simpler than that of the layer 3 mesh network topology. This is because the layer 2 mesh topology is constructed
as a tunnel link from each access point to the WLC as an Internet gateway. CAPWAP (Control And Provisioning of Wireless Access Points)[RFC5461] was used to maintain the tunnel links. Thus, all the traffic
received from user terminals are once tunneled to the Internet gateway,
decapsulated at the Internet gateway, and forwarded for the final destination.
On the other hand, all the access points of the layer 3 mesh network areequal footing each other. Each access point advertises subnet information
which is assigned to that particular access point to accommodate users.
The subnet information is exchanged among access points and the cost tothe destination subnets are calculated based on the OLSRv2 algorithm.
Finally each access point will have next hop information to which it should5

AP-8(Ch 1)
AP-6(Ch 6)

AP-5(Ch 11)

AP-4(Ch 1)

AP-9(Ch 6)
AP-7(Ch 1)
AP-10(Ch 11)

AP-2(Ch 6)

AP-3(Ch 11)

AP-1 (GW)(Ch 1)

Figure 4: Access point location map for layer 3 WiFi mesh network

send packets received user terminals.
The layer 2 mesh network was operated from 15:00 on 5th to midnight
8th March, except 12:00 to 18:00 on 6th March. The layer 3 mesh network
was operated from 12:00 to 18:00 on 6th March. The animated topology
transition images for each mesh network are available from the links below.
• Layer 2: http://member.wide.ad.jp/˜shima/publications/20120306wifi-mesh-takeda-route.m4v• Layer 3: http://member.wide.ad.jp/˜shima/publications/20120306wifi-mesh-uesugi-route.m4v

6Performance

We performed a simple TCP bandwidth measurement using the iperf tool.
Figure 7 and 8 are the measurement results of the layer 2 mesh network.
We put 2 client nodes, one is attached to the switch directly connected
to AP-1 and the other to attach several access points as shown in thefigures. For example, in the rightmost column of figure 7, we put one
client near AP-10 and performed the iperf command. The ’UP’ means
the direction from the leaf area to the Internet gateway, the ’DOWN’means the opposite direction.
From the figures, we can see that the 40Mhz backhaul gives us almost
twice as much performance than the 20Mhz backhaul configuration. We
also can see the performance decreases as the number of hops is increased
basically.
Figure 9 shows the result of the layer 3 mesh network bandwidth measurement. For the layer 3 measurement, we didn’t use any client nodes

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Figure 5: Layer 2 WiFi Mesh topology as of 20:00 5th March 2012

to perform the iperf command. Instead, we used the access point itself toexecute the iperf command. So, the measurement environment is different from the layer 2 cases. In this case, the performance quickly decreases
when the number of hops increases.

7Summary

We are now trying to achieve operation experiments to build wirelessbased Internet and finding out what are the show stoppers to make it. Asa part of the activity, we build two different types of WiFi mesh networks
during the WIDE 2012 Spring Camp meeting. One is a layer 2 meshnetwork built with Cisco products, the other is a OLSRv2-based layer 3
mesh network.
We found that both mesh networks can be built but stability is different. The product level layer 2 network worked well, although the throughput was not ideal (around 1Mbps with 5 hops). We can consider this performance as a reference performance of the current product level devices.
The layer 3 mesh networks can build the mesh network however, when
the access points start hosting many users, the stability decreases rapidly.
In addition to that, the performance degradation when we increase thenumber of hops is much quicker than the cases of the layer 2 mesh network. We haven’t found the real cause of this issue however, our guess at
this moment is the design of the wireless chipset and circuit to drive thechip, and traffic management of the backhaul links.
Our next steps are as follows.
• achieve reference performance measurement using a clean environment using wired antennas and attenuaters

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Figure 6: Layer 2 WiFi Mesh topology as of 12:00 6th March 2012

• propose a performance model of WiFi mesh network• build reference WiFi routers to verify the model• perform experiments in real environment such as following WIDE
meetings

Acknowledgment
We thank Yoshihiro Onodera and Koichi Shibakawa from Cisco Systems
G.K. for their great support providing us many Cisco wireless network
products and useful advice when configuring the devices. We also thank
NTTPC Communications to give us a chance to operate a layer 3 WiFi
mesh network using their devices.

8L2 Mesh Throughput(backhaul 20Mhz)
Up

Down

8Mbps
6Mbps
4Mbps
2Mbps
0Mbps

AP-1

AP-5-1AP-7-14-1

AP-9-8-5-1

AP-10-9-8-5-1

L2 Mesh Throughput(backhaul 40Mhz)

Figure 7: Layer 2 WiFi Mesh throughput with 20Mhz backhaul frequency allocation(from Client-AP...AP-Client)

Up

Down

18Mbps
14Mbps
9Mbps
5Mbps
0Mbps

AP-1AP-1-7

AP-1-4-10

L3 Mesh Throughput

Figure 8: Layer 2 WiFi Mesh throughput with 40Mhz backhaul frequency allocation(from Client-AP...AP-Client)

DownUp50Mbps38Mbps
25Mbps
13Mbps
0Mbps

AP-2

AP-3

AP-4

AP-5

AP-6

AP-7

AP-8

AP-9

AP-10

Figure 9: Layer 3 WiFi Mesh throughput (from AP to AP)

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