CitrusNet Network
|| ||WaFreeNet How does the backbone of WaFreeNet work? The following graphic shows the most likely possible ways the backbone is formed. This is an example only, but this image will be referred to throughout the rmainder of the page. You may wish to open this page in another browser window to enable easy referral to the image.
The backbone is made up of multiple Access Points (AP's) connected in various ways. This image shows the four most common methods for linking two AP's. [Method 1] AP2 has a client link to AP1 (and is a client of AP1). [Method 2] Client B is a client of both AP2 and AP3 (has two seperate wireless cards and dishes). Client B is acting as a router for these AP's. [Method 3] AP3 and AP4 are connected by a dedicated wireless link between them (using adhoc settings).
With this interconnection and routing, client 1 is able to directly communicate with client 33. This is how the WaFreeNet network actually works. Of course it is not as simple as that though, we also have to consider the capabilities of the wireless network.
Capabilities of the Wireless Network SPEED
WaFreeNet uses an 802.11b wirless protocol. There is much available on the internet about this protocol and it's capabilities so I'll not go into great detail. In a nutshell however; Depending on strength of signal, the half duplex maximum speed of a wireless connection will be 11, 5.5, 2 or 1 mbps. In the real world, the 11mbps connection equates to an approximate maximum of 500kB/s.SPEED OF CLIENTS TO THEIR AP AND TO OTHER CLIENTS
Let's look at AP1 in the image at the top of this page.
- AP1 has four clients, being clients 1-2 and AP2. The maximum bandwidth that can pass through this AP at any one time is ~500kB/s. If all clients were idle, apart from client 1, then client 1 would have all of this bandwidth available to him. So client 1 can transfer a file to the AP1 server at 500kB/s. If client 2 then decides to download a file from the AP1 server, they must both share this bandwidth, so each user will have to share this maximum bandwidth. If we assume that the AP performs perfectly (which it doesn't, and we'll talk about that later), imagine how slow the network would be if the AP had 15 clients all trying to transfer files stimultaneously.
Recommendation 1 - "Orchestrate non-essential traffic at times when the network is not likely to be required for more important bandwidth."
Recommendation 2 - "AP admins should rate limit traffic to file servers according to peak / off-peak usage of their AP"
Lets now consider the situation where client 1 would like to transfer a file to client 2. The data must travel through AP1. Client 1 and Client 2 are therefore stimultaneously using the bandwidth of AP1. The stream of data from Client one is tagged for the AP to then send on to it's destination. The AP reads this 'tag' and then retags it for the receipt of Client 2 and sends it back into the air for Client 2 to receive. During this process there are many collisions (the nature of half duplex networking) and utilising the full ~500kB/s that the AP is capable of, will likely only result in Client 2 receiving the file at about 150kB/s. <-- This is with all of the bandwidth being available! During this time client 3 may also be rendered invisible to the network. The AP is handling so many packets and trying to organise how to send and receive the intensive "node-node" (or client-client) traffic that it just doesnt get time to listen to the packets of Client 3. Once again, imagine the effect of this node-node traffic with more users on the AP.
Recommendation 3 - "Point - to - point traffic hogs network bandwidth and severely affects the usefullness of the network to other clients. Avoid this type of traffic whenever possible and try to limit such traffic to protocols that use only the smallest amount of bandwidth (such as IRC, other text based communication methods, and perhaps games that use small amounts of bandwidth)."
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Recommendation 4 - "When transferring files, use a file server situated on the AP you are connected to and inform the recipient of the location of the file. If there is no file server available, then do the transfer very slowly."- There is little we can do to increase the maximum bandwidth of this wireless protocol. However, to minimise the collisions and hidden node issues, we can use commercial firmware and accompanying software to improve the way traffic and routing is handled. Minimising hidden node issues with commercial solutions (or even open source solutions if available) will be excellent, but will still not solve the problem of diminished bandwidth due to excessive point to point transfers. Also related to minimising unneccesary bandwidth, is preventing traffic that really has no place on a non-local network. This includes SMB and windows broadcasts. Imagine the unneccesary accumulative load of this traffic if every single client over multiple AP's contributes to it.
Recommendation 5 - "All clients should ensure that SMB and windows broadcasts are firewalled from getting through to the AP they are connected to."
SPEED BETWEEN AP'S
The different ways AP's connect to each other will affect the maximum speed at which transfers can be done to either clients of another AP or the server of another AP. Let us gaze upon the image again;
AP2 has a client link to AP1, so the AP2 admin and the AP2 clients (including Client
can use the AP1 file server without being point-to-point (p-p) traffic. Any traffic between AP1 clients and AP2 clients will be p-p traffic. The AP that is affected by p-p traffic is the one that is required to receive and then send on the same traffic to another location, utilising the same antenna. Keeping this in mind we can see some strange possibilities regarding what is and is not p-p traffic using the image at the top of this page. Client B has two antennae linking AP2 and AP3. We can see that AP2 clients transferring directly to Client B will be p-p traffic. However, if we look closely we notice that Client B can transfer not only to the AP1 fileserver without it being p-p traffic, but transfers to the fileservers on AP 3 and even AP4 will not be p-p either. To further illustrate this, all the clients of AP4 will be able to transfer a file to the file server on AP1 without the traffic being p-p. This is mostly thanks to the dedicated links of Client B, and that joining AP3 and AP4. Such links are rare however, as it is more financially viable to use a spare dish to connect to another AP and increase the backbone size, rather than utilising a dish to improve bandwidth between AP's. We should also mention that even though AP4 clients are able to transfer files to servers as far away as AP1 without it being p-p, it should still be avoided as this traffic is using bandwidth on every AP on the way through.
Recommendation 6 - "Understand how the AP you connect to links into the backbone of the network. This knowledge will enable you to figure out what traffic is point to point traffic. Point to point traffic and traffic that must pass through multiple AP's before it reaches it's destination should be avoided or limited to protocols that use minimal bandwidth."
Ettiquette of WaFreeNet I will recap the recommendations I have made throughout this page as it is important to understand what will be frowned upon by your fellow WaFreeNetizens. Many of the WaFreeNet users congregate on our IRC channel. Please find the time to wander over there as frequently as possible. If you are having problems, or are causing problems, we can all sort it out on IRC.
"Orchestrate non-essential traffic at times when the network is not likely to be required for more important bandwidth."
"AP admins should rate limit traffic to file servers according to peak / off-peak usage of their AP"
"Point - to - point traffic hogs network bandwidth and severely affects the usefullness of the network to other clients. Avoid this type of traffic whenever possible and try to limit such traffic to protocols that use only the smallest amount of bandwidth (such as IRC, other text based communication methods, and perhaps games that use small amounts of bandwidth)."
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"When transferring files, use a file server situated on the AP you are connected to and inform the recipient of the location of the file. If there is no file server available, then do the transfer very slowly.""All clients should ensure that SMB and windows broadcasts are firewalled from getting through to the AP they are connected to."
"Understand how the AP you connect to links into the backbone of the network. This knowledge will enable you to figure out what traffic is point to point traffic. Point to point traffic and traffic that must pass through multiple AP's before it reaches it's destination should be avoided or limited to protocols that use minimal bandwidth." Please enjoy the network!
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