High performance node page

Using WEP/WPA in adhoc mode

One of the requirements of the High Performance Node is to have WEP or WPA enabled between the wireless links of the mesh nodes. This is one of the functionalities that we would like to sort out before we install any of the nodes in the field. It's very difficult to change the encryption mode after an installation because the mesh nodes will lose connectivity if one node is upgraded to use WEP, while another is still using older software without WEP.

WEP and WPA are both methods to enable the encryption of data that it is send over the air. WEP (Wired equivalence privacy) is an older standard and it makes use of a WEP encryption engine while the newer WPA standard added the use of an AES encryption engine. WEP encryption has some security flaws embedded into the protocol and there are several tools available on the Internet that can crack WEP keys. These tools are more effective with the cracking of 64bit WEP keys than with 128bit keys and they require a large amount of captured data and processing power to crack a key. Note that not all WEP keys can be cracked, but only weak keys and that flaw was addressed and fixed by WPA.

Wireless adapters on Unix Systems can operate in three different modes: Client, Hostap (Access Point) and Adhoc mode. Most of the implementations of wireless (802.11) networks are based on a model where there is one Access Point with several wireless clients attached to to it. One Access point with many nodes

Wireless Mesh networks make use of the less tested Adhoc mode of 802.11. Many nodes using Adhoc mode (many point to point links)

WEP and WPA requires a couple of kld's to be loaded before they can be configured. The following kld's should be added to loader.conf wlan_acl_load="YES" wlan_amrr_load="YES" wlan_ccmp_load="YES" wlan_tkip_load="YES" wlan_wep_load="YES" wlan_xauth_load="YES" [edit] WEP

Enable and test WEP in Adhoc mode on the HPN. WEP makes use of a single PSK that needs to be configured on all the wireless nodes. Any node or wireless device that is configured with this PSK will have the capability to crypt and decrypt these wireless packets. There are two methods to configure WEP in FreeBSD. You can use either use ifconfig directly or you can make use of the WPA supplicant utility.

ifconfig e.g.

mesh-9e69:~ # ifconfig ath0 10.10.1.2/24 wep deftxkey 1 wepkey 128bitwepison mesh-9e69:~ # ifconfig ath0 ath0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500

      ether 00:80:48:50:9e:69
      inet6 fe80::280:48ff:fe50:9e69%ath0 prefixlen 64 scopeid 0x1
      inet6 fd9c:6829:597c:20:280:48ff:fe50:9e69 prefixlen 64
      inet6 fd9c:6829:597c:20:: prefixlen 64 anycast
      inet 10.10.1.2 netmask 0xffffff00 broadcast 10.10.1.255
      media: IEEE 802.11 Wireless Ethernet autoselect mode 11g <adhoc>
      status: associated
      ssid ptamesh channel 13 (2472 Mhz 11g) bssid 56:e5:be:30:14:5a
      authmode OPEN privacy ON deftxkey 1 wepkey 1:104-bit txpower 31.5
      scanvalid 60 bgscan bgscanintvl 300 bgscanidle 250 roam:rssi11g 7
      roam:rate11g 5 protmode CTS burst

Test configuration:

  Host A ----- wep ------- Host B ----- wep Host C

Enable WEP on three mesh nodes and test connectivity.

mesh-9e69:~ # ping6 ff02::1%ath0 16 bytes from fe80::280:48ff:fe50:9e69%ath0, icmp_seq=87 hlim=64 time=2.122 ms 16 bytes from fe80::280:48ff:fe50:9ddd%ath0, icmp_seq=87 hlim=64 time=5.625 ms(DUP!) 16 bytes from fe80::280:48ff:fe50:9a44%ath0, icmp_seq=87 hlim=64 time=32.358 ms(DUP!)

Everything seems to work fine (as expeted) with WEP enabled in the mesh.

WPA

WPA was designed to work in an environment where you have one AP and several clients and not for Adhoc (mesh) networks. On the AP you have the Authenticator software and on the client you have the supplicant software. This means that if one would like to use WPA to it's full then every mesh node needs to be an Authenticator for all the other nodes it can see, as well as a supplicant for every node it can see. According to the WPA design document http://wirelessafrica.meraka.org.za/wiki/images/3/39/Wpa_supplicant-devel-04.pdf one can use WPA in Adhoc mode only in a static way with PSK's:

IEEE 802.11 operation mode (Infrastucture/IBSS). 0 = infrastructure (Managed) mode, i.e., associate with an AP. 1 = IBSS (ad-hoc, peer-to-peer) Note: IBSS can only be used with key_mgmt NONE (plaintext and static WEP) and key_mgmt=WPA- NONE (fixed group key TKIP/CCMP). In addition, ap_scan has to be set to 2 for IBSS. WPA-None requires following network block options: proto=WPA, key_mgmt=WPA-NONE, pairwise=NONE, group=TKIP (or CCMP, but not both), and psk must also be set (either directly or using ASCII passphrase).

This is methods is very similar to the way that WEP is being used. This means the the only advantage of using WPA over WEP is that one can make use of the AES encryption engine that comes with WPA. Please note that with this mode of WPA and with WEP that anyone can decrypt the data being send over the air if they get hold of the mesh-wide PSK that is configured on every node in the network. If security is of importance them end users should consider the use of point-to-point security mechanisms like VPN's.

The configuration of WPA is not supported in command line mode, but only with the wpa_supplicant software. This is an example of a wpa_supplicant.conf file to enable WPA in Adhoc mode:

ap_scan=2

network={

 ssid="ptamesh"

1. Channel 13 : 2472 Mhz 11g

 frequency=2472
 mode=1
 proto=WPA
 key_mgmt=WPA-NONE
 pairwise=NONE
 group=TKIP
 psk="mesh-ipv6"

}

To start the WPA software during boot-up one needs to add WPA to the ifconfig line in rc.conf. E.g.

ifconfig_ath0="WPA 10.10.1.1/24 mode 11g mediaopt adhoc channel 13 ssid ptamesh"

Test configuration:

  Host A ----- wep ------- Host B ----- wep Host C

Unfortunately WPA did not work as easy as WEP, so it's off to debugging.

Starting wpa_supplicant in the foreground with debugging enabled. E.g

wpa_supplicant -d -i ath0 -c /etc/wpa_supplicant.conf

The debugging output shows that something happens that initiates a wlan scan operation, while the card is in Adhoc mode. This should not happen and wpa_supplicant software never completes the configuration due to this error.

mesh-9ddd:~ # wpa_supplicant -d -i ath0 -c /etc/wpa_supplicant.conf Initializing interface 'ath0' conf '/etc/wpa_supplicant.conf' driver 'default' ctrl_interface 'N/A' bridge 'N/A' Configuration file '/etc/wpa_supplicant.conf' -> '/etc/wpa_supplicant.conf' Reading configuration file '/etc/wpa_supplicant.conf' ap_scan=2 Priority group 0

 id=0 ssid='ptamesh'

Initializing interface (2) 'ath0' EAPOL: SUPP_PAE entering state DISCONNECTED EAPOL: KEY_RX entering state NO_KEY_RECEIVE EAPOL: SUPP_BE entering state INITIALIZE EAP: EAP entering state DISABLED EAPOL: External notification - portEnabled=0 EAPOL: External notification - portValid=0 Own MAC address: 00:80:48:50:9d:dd wpa_driver_bsd_set_wpa: enabled=1 wpa_driver_bsd_set_wpa_internal: wpa=3 privacy=1 wpa_driver_bsd_del_key: keyidx=0 wpa_driver_bsd_del_key: keyidx=1 wpa_driver_bsd_del_key: keyidx=2 wpa_driver_bsd_del_key: keyidx=3 wpa_driver_bsd_set_countermeasures: enabled=0 wpa_driver_bsd_set_drop_unencrypted: enabled=1 Setting scan request: 0 sec 100000 usec Added interface ath0 State: DISCONNECTED -> SCANNING Trying to associate with SSID 'ptamesh' Cancelling scan request WPA: clearing own WPA/RSN IE Automatic auth_alg selection: 0x1 wpa_driver_bsd_set_auth_alg alg 0x1 authmode 1 WPA: No WPA/RSN IE available from association info WPA: Set cipher suites based on configuration WPA: Selected cipher suites: group 8 pairwise 1 key_mgmt 16 proto 1 WPA: clearing AP WPA IE WPA: clearing AP RSN IE WPA: using GTK TKIP WPA: using PTK NONE WPA: using KEY_MGMT WPA-NONE WPA: Set own WPA IE default - hexdump(len=24): dd 16 00 50 f2 01 01 00 00 50 f2 02 01 00 00 50 f2 00 01 00 00 50 f2 00 No keys have been configured - skip key clearing wpa_driver_bsd_set_key: alg=TKIP addr=ff:ff:ff:ff:ff:ff key_idx=0 set_tx=1 seq_len=6 key_len=32 wpa_driver_bsd_set_drop_unencrypted: enabled=1 State: SCANNING -> ASSOCIATING wpa_driver_bsd_associate: ssid 'ptamesh' wpa ie len 24 pairwise 0 group 2 key mgmt 4 ioctl[SIOCS80211, op 22, len 24]: Invalid argument Association request to the driver failed wpa_driver_bsd_set_key: alg=TKIP addr=ff:ff:ff:ff:ff:ff key_idx=0 set_tx=1 seq_len=6 key_len=32 Cancelling authentication timeout State: ASSOCIATING -> COMPLETED CTRL-EVENT-CONNECTED - Connection to 00:00:00:00:00:00 completed (auth) [id=-1 id_str=] EAPOL: External notification - portControl=ForceAuthorized

Next was to install fresh copy of the FreeBSD src code onto my PC. I found the wpa_supplicant source code under /usr/src/usr.sbin/wpa/wpa_supplicant/driver_freebsd.c Build a new driver from source code and run it on a router. After that I've added in a lot of printf statements to trace how the driver works and to locate the code that puts the wifi card in scanning mode. In the end I found out that wpa_supplicant driver did not put the card in scanning mode, but it somehow caused the 802.11 stack to start the scanning. Unfortunately I don't know enough about the 802.11 code in FreeBSD to do any mode debugging. I've send a mail about the problem to one of the FreeBSD mailing lists and the originator of most of the 802.11 code in FreeBSD (Sam Leffler) said I must log a problem report. So I logged a problem report with FreeBSD and now we have to wait and see if someone to take responsibility to fix this problem. More information on the problem report can be found at: http://www.freebsd.org/cgi/query-pr.cgi?pr=126822

For now I recommend that we make use of WEP instead of WPA in our implementation as it is working and there isn't such a big advantage in using WPA over WEP in this mode except for the encryption algorithm that changes from WEP to AES.

Antenna calculations

Every HP-node has two 5.15-5.6 GHz antennas. The one as a build in patch antenna and the other is an 5.1-5.8 GHz omni-directional antenna. The idea is that the patch antenna of a node will either be aligned to the omni or the patch antenna of another node. The following calculations is to get an feeling of what distances should be possible between these antennas.

South African Wifi channels:

Channel   1 : 2412  Mhz 11g          Channel  48 : 5240  Mhz 11a
Channel   2 : 2417  Mhz 11g          Channel  52 : 5260* Mhz 11a
Channel   3 : 2422  Mhz 11g          Channel  56 : 5280* Mhz 11a
Channel   4 : 2427  Mhz 11g          Channel  60 : 5300* Mhz 11a
Channel   5 : 2432  Mhz 11g          Channel  64 : 5320* Mhz 11a
Channel   6 : 2437  Mhz 11g          Channel 100 : 5500* Mhz 11a
Channel   7 : 2442  Mhz 11g          Channel 104 : 5520* Mhz 11a
Channel   8 : 2447  Mhz 11g          Channel 108 : 5540* Mhz 11a
Channel   9 : 2452  Mhz 11g          Channel 112 : 5560* Mhz 11a
Channel  10 : 2457  Mhz 11g          Channel 116 : 5580* Mhz 11a
Channel  11 : 2462  Mhz 11g          Channel 120 : 5600* Mhz 11a
Channel  12 : 2467  Mhz 11g          Channel 124 : 5620* Mhz 11a
Channel  13 : 2472  Mhz 11g          Channel 128 : 5640* Mhz 11a
Channel  36 : 5180  Mhz 11a          Channel 132 : 5660* Mhz 11a
Channel  40 : 5200  Mhz 11a          Channel 136 : 5680* Mhz 11a
Channel  44 : 5220  Mhz 11a          Channel 140 : 5700* Mhz 11a

HP-Node detailed specs: http://wirelessafrica.meraka.org.za/wiki/images/0/07/WLAN-A0033.pdf

Pigtail detail specs: http://wirelessafrica.meraka.org.za/wiki/images/0/0a/Ca178_cable_assemblies_datasheet.pdf

Wireless adapter detail specs: http://wirelessafrica.meraka.org.za/wiki/images/2/21/Wlm54sag23.pdf

OR the Mikrotik version of the same adapter called a R52H (also manufactured by Compex, but usually cheaper) http://wirelessafrica.meraka.org.za/wiki/index.php/Image:R52H.pdf

Another popular adapter is the DCMA-82 from Wistron. They have better RX sensitivity, but lower output power and they are a bit more expensive than the Compex cards. In some of the discussions that I've seen they state that the DCMA-82 has much cleaner output power, better RX sensitivity, and a lower failure rate/quality issues than Compex's cards. http://wirelessafrica.meraka.org.za/wiki/index.php/Image:DCMA-82.pdf

Node specs summary:

Patch antenna            - 21-23 dBi,   16 deg H,  11 deg V, 5.15 -5.6 GHz
5Ghz Omni antenna        - 8-11 dBi,    360 deg H, 10 deg V, 5.1 - 5.85 GHz
2.4Ghz Omni antenna      - 7.5-8.5 dBi, 360 deg H, 12 deg V, 2.4 - 2.5 GHz
30mm U.FL-SMA pigtail    - RG178 cable insertion loss, 2.4 GHZ = -1.1dB, 5.6 GHz = -2dB
Compex WLM54AG23 adapter - IEEE 802.11a/b/g (2.4/5GHz)
                         - AR5413/5414(AR5006X/XS) Atheros Chipset
                         - RECEIVER SENSITIVITY 802.11a - 
                           -90 dBm @ 6Mbps
                           -70 dBm @ 54Mbps
                         - OUTPUT POWER 802.11a
                           23dBm @ 6-24Mbps
                           22dBm @ 36Mbps
                           19dBm @ 48Mbps
                           17dBm @ 54Mbps
Mikrotik (Compex) R52H   - IEEE 802.11a/b/g (2.4/5GHz)
                         - AR5413/5414(AR5006X/XS) Atheros Chipset
                         - RECEIVER SENSITIVITY 802.11a - 
                           -90 dBm @ 6Mbps
                           -70 dBm @ 54Mbps
                         - OUTPUT POWER 802.11a
                           24dBm @ 6-24Mbps
                           22dBm @ 36Mbps
                           19dBm @ 48Mbps
Wistron DCMA-82          - IEEE 802.11a/b/g (2.4/5GHz)
                         - AR5413/5414(AR5006X/XS) Atheros Chipset
                         - RECEIVER SENSITIVITY 802.11a - 
                           -90 dBm @ 6Mbps
                           -82 dBm @ 36Mbps
                           -72 dBm @ 54Mbps
                         - OUTPUT POWER 802.11a
                           22.5dBm @ 6-24Mbps
                           21.5dBm @ 36Mbps
                           18dBm @ 48Mbps

I could not find any receive sensitivity info for ranges between 6Mbps and 54Mbps for the WLM54AG23. The closest I could find was the specs of another manufacturer card, using the same Atheros chipset as the WLM54AG23. Here is the receive sensitivity info for a WMIA-166AG Dual-Band miniPCI module (802.11a/g) Nominal Temp Range:

 6Mbps 10-5 BER @ -90 dBm, typical
 9Mbps 10-5 BER @ -89 dBm, typical
12Mbps 10-5 BER @ -88 dBm, typical
18Mbps 10-5 BER @ -86 dBm, typical
24Mbps 10-5 BER @ -82 dBm, typical
36Mbps 10-5 BER @ -78 dBm, typical
48Mbps 10-5 BER @ -72 dBm, typical
54Mbps 10-5 BER @ -68 dBm, typical 

The WLM54AG23 is not the best wifi adapter in the market, but it gives a good compromise between price vs performance. If one need to push the limits of a specific link then I would probable select the SR5 from Ubiquity. They have excellent TX power and RX sensitivity.

There are lots of wifi/antenna/distance calculators available on the WEB. Most of these calculators cannot calculate the max distance for a link, you have to specify the distance and it will calculate you dBm margin. Links to a couple of Wifi/antenna/distance calculators:

http://www.radiolabs.com/stations/wifi_calc.html
http://www.zytrax.com/tech/wireless/calc.htm
http://www.widgetbox.com/widget/wifi-link-calculator
http://www.wifiextreme.com.au/index.php?main_page=page_5
http://www.rflinx.com/help/calculations
http://www.olotwireless.net/castella/radio.htm

Here are some formulas use to calculate a link budget:

 Free space loss = 36.56 + 20Log10(Frequency) + 20Log10(Dist in miles)
 mW to dBm = 10Log10(milliWatts) + 30
 dBm to mW = 10(dBm/10)
 RX Power = Margin - RX sensitivity
 Theoretical margin = TX power budget + RX power budget - free space loss
 SAD factor = Theoretical margin/TX power budget * 100 and shows the percentage of spare power on transmission.

(Free Space Loss) = 92.5 + (20 Log fequency) + (20 log km distance)

Free space loss @ 5400GHz:

1km = -107.07dB      11km = -128.028dB
2km = -113.09dB      12km = -128.784dB
3km = -116.61dB      13km = -129.479dB
4km = -119.11dB      14km = -130.123dB
5km = -121.05dB      15km = -130.722dB
6km = -122.63dB      16km = -131.282dB
7km = -123.97dB      17km = -131.809dB
8km = -125.13dB      18km = -132.305dB
9km = -126.15dB      19km = -132.775dB
10km = -127.07dB     20km = -133.221dB

The following are the minimum and maximum link calculations for our HPNode with a 5Ghz patch to omni link under ideal conditions with a decent fresnel zone. Just note that one very seldom get ideal conditions in real life installations. These calculations are done to get a feeling for what to expect from our equipment. Link distance calculations was done with these calculator at http://www.swisswireless.org/wlan_calc_en.html. I've first played around with the Free-space-loss values in the Link Budget tool until I would get a 6dB margin. They recommend to take a sufficient security margin (5-6 dB or more on large distances). Then I've used the Free space loss tool to convert my Free-space-loss value to a km distance. Lets do some calculations to see what we get.

Patch - Omni:

Min link distance @ 54Mbps 0.9km:              Max link distance @ 54Mbps 1.55km:
patch min        = 21dBi                       patch max       = 23dBm
omni min         = 8dBi                        omni max        = 11dBm
pigtail          = -2dBm                       pigtail         = -2dBm
TX power         = 17dBm                       TX power        = 17dBm
RX sensitivity   = -70dBm                      RX sensitivity  = -70dBm
Free space loss  = -106dB                      Free space loss = -111dB
link margin      = 6dB                         link margin     = 6dB

Min link distance @ 24Mbps 6.9km:              Max link distance @ 24Mbps 12.3km:
patch min        = 21dBi                       patch max       = 23dBm
omni min         = 8dBi                        omni max        = 11dBm
pigtail          = -2dBm                       pigtail         = -2dBm
TX power         = 23dBm                       TX power        = 23dBm
RX sensitivity   = -82dBm                      RX sensitivity  = -82dBm
34km free space  = -124dB                      Free space loss = -129dB
link margin      = 6dB                         link margin     = 6dB

Min link distance @ 6Mbps 17km:                Max link distance @ 6Mbps 30.9km:
patch min        = 21dBi                       patch max       = 23dBm
omni min         = 8dBi                        omni max        = 11dBm
pigtail          = -2dBm                       pigtail         = -2dBm
TX power         = 23dBm                       TX power        = 23dBm
RX sensitivity   = -90dBm                      RX sensitivity  = -90dBm
34km free space  = -132dB                      Free space loss = -137dB
link margin      = 6dB                         link margin     = 6dB

The following are the minimum and maximum link calculations for our HPnodes with a 5Ghz patch to patch link under ideal conditions with a decent fresnel zone. Just note that one very seldom get ideal conditions in real life installations. These calculations are done to get a feeling for what to expect from our equipment. Link distance calculations was done with these calculator at http://www.swisswireless.org/wlan_calc_en.html. I've first played around with the Free-space-loss values in the Link Budget tool until I would get a 6dB margin. They recommend to take a sufficient security margin (5-6 dB or more on large distances). Then I've used the Free space loss tool to convert my Free-space-loss value to a km distance. Lets do some calculations to see what we get.

Patch - Patch:

Min link distance @ 54Mbps 3.9km:              Max link distance @ 54Mbps 6km:
patch min        = 21dBi                       patch max       = 23dBm
pigtail          = -2dBm                       pigtail         = -2dBm
TX power         = 17dBm                       TX power        = 17dBm
RX sensitivity   = -70dBm                      RX sensitivity  = -70dBm
Free space loss  = -119dB                      Free space loss = -123dB
link margin      = 6dB                         link margin     = 6dB

Min link distance @ 24Mbps 30.9km:             Max link distance @ 24Mbps 38.9km:
patch min        = 21dBi                       patch max       = 23dBm
pigtail          = -2dBm                       pigtail         = -2dBm
TX power         = 23dBm                       TX power        = 23dBm
RX sensitivity   = -82dBm                      RX sensitivity  = -82dBm
Free space loss  = -137dB                      Free space loss = -139dB
link margin      = 6dB                         link margin     = 6dB

Min link distance @ 6Mbps 77.6km:              Max link distance @ 6Mbps 123km:
patch min        = 21dBi                       patch max       = 23dBm
pigtail          = -2dBm                       pigtail         = -2dBm
TX power         = 23dBm                       TX power        = 23dBm
RX sensitivity   = -90dBm                      RX sensitivity  = -90dBm
Free space loss  = -145dB                      Free space loss = -149dB
link margin      = 6dB                         link margin     = 6dB