Ahdemo Mode

Tedunix

发现一种新的模式组建无线Mesh网络，多跳之后，带宽并没有下降。之前做的无线mesh网络，最大的问题就是网络经过n跳之后，带宽基本呈1/n的趋势下降。这种模式经过实验，带宽在多跳之后并没有下降，在以后的项目实践过程中应该可以很好地利用起来。
原文：
AHDEMO Mode

Usage

Create the VAP device with:
wlanconfig ath0 create wlandev wifi0 wlanmode ahdemo
See tickets
#728
&
#729
for patches to correct the
reported rate control Stats with ahdemo.
What is Ahdemo (Pseudo-IBSS) mode
and why use it?
Ahdemo mode is handy for long shot point to point connections as you avoid
the RTT and inefficiency of the control packets in BSS/IBSS mode.
The pseudo ad-hoc mode (Pseudo-IBSS mode, ‘lucent ad-hoc demo’ mode, PIM) is
a pre-standards, pre-IBSS ad-hoc mode without beaconing ( no management frames
at all: no beacons, no association, no probes, just data), which means that all
the nodes in the mesh need to have channel assigned manually and won’t hop
channels. This will give you slightly better throughput than regular ad-hoc mode
because it doesn’t bother with the beaconing/probe response packets. But since
beaconing is ignored you don’t know the capabilities of the other nodes (like
WME).
With ahdemo mode you can get rid of beacon synchronization and IBSS merging
(coalescing) problems in an easy way, especially in situations where you don’t
actually need the “beaconing features” of IBSS, like for non-interoperable mesh
solutions, for example.
Adhoc demo is not ibss. There is no ’standard’ for “adhoc demo” “pseudo-ibss”
mode,
MadWifi

implements it as “ibss minus beacons”
At least with old Lucent cards, pseudo adhoc mode did not use auth/assoc at
all, it just started using IBSS (BSSID=00:00:00:00:00:00) immediately.
Features

1. The BSSID will be all zeros.
2. There is no distributed beaconing mechanism
3. As long as the cards on the same channel and within the radio range, all
the cards can hear each other. There is no separate cells at the link layer.
4. A card in PIM will not send out any management frames (Probe
request/response, beacon, authentication, deauthentication, ATIM, association
request/response, reassociation request/response, disassociation)
5. What is the impact on the nearby 802.11 IBSS communication? Ubder testing
802.11 IBSS won in getting bandwidth. Running flood ping on both connections,
802.11 IBSS retry on corrupted packets gained, after a short time, all of
bandwidth and pseudo IBSS connection had lost it. So you will need clear channel
or very strong signal or send very small packets.
6. There are no Control frames (except the ACK frames).
7. The two cards in PIM set up the communication like classic cable Ethernet?
Messages are broadcast to the current channel and the IP layer decide whether it
should “receive” the data.
8. Packets are sent at rate you set. One needs to set the same rate on every
card.
Testimonials

Mar 09 01:35:38 mattbrown It’s working really well btw.
Jun 15 18:33:16 foobarian i get 27Mbps with UDP when I use cwmin=5
Jun 15 18:34:20 ignuss got over 35mbit UDP and 33mbit TCP without turbo in
5ghz band , well, signal has been perfect
Jun 15 18:34:32 foobarian but when i use cwmin=1 i get 41Mbps
Jun 15 18:43:53 foobarian i think you would run
iwpriv
ath0 cwmin 0 1
Ago 01 2007 20:10:48 soulhunter This is great!, improved my throughput from
around 100kB/s to around 250 ~ 300kB/s. (10 miles link).
摘自：
http://madwifi.org/wiki/UserDocs/AhdemoInterface
               
               
               

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