The WiFi Emporium Blog

When you use the term “Wireless Repeater” most people in the wireless networking business immediately think of WDS (Wireless Distribution System) because this is the method used by most of the inexpensive wireless routers and wireless access points in use the last 3 to 4 years.  While WDS is one method to extend the range of the wireless signal there are other, better methods to use as well.  I have compiled several “questions” that have been asked of me, a short FAQ if you will.

What is a “wireless repeater” and how is it used in relation to wireless hotspots?

What is WDS (Wireless Distribution System) and what are the Pro’s and Con’s to using such a system?

Wireless Distribution System (WDS for short) is a method where a wireless access point “monitors” a specific radio channel and SSID (Service Set IDentifier – the “name” of the wireless access point) then, when a wireless local area network (WLAN) radio packet is received and the access point has not seen it before the access point will re-transmit the radio packet to it’s next-in-line neighbor.  The access point “knows” it’s neighbor by the fact the information was setup in it’s configuration when the wireless router was installed.  The configuration information is static in nature which mean the wireless router can not change the configuration information by itself.  Since the wireless access point is located in a different location from the main wireless access point or wireless router this has the effect of “extending” the radio coverage area of the WiFi Hotspot location.  An added bonus is a wireless client using the WiFi Hotspot will be able to move around within the area covered by the WDS repeater(s) and the main wireless access point/router since the SAME identification information is used for the wireless client within the coverage area – this is NOT the case when you have multiple hard-wired wireless access points/routers used to extend the WiFi Hotspot coverage area.

Now – there are “down-sides” to this repeater configuration!

Since you can only have ONE transmitter sending out a signal on a specific channel at one time and since most wireless access points/routers only have ONE radio within them you cut the total bandwidth of the area covered in half for each WDS repeater you have setup!  An example is if you had three WDS repeaters setup within an area you wanted to cover for a WiFi Hotspot location.  If a wireless client connected to the “base” wireless access point/router then the client would see full speed operation minus any repeater traffic that occurs normally during identification packets that inform the base unit where the client is in relation to the WDS network – this is called OVERHEAD and you can not get around it.  Now – if the client connects to the first WDS repeater in the string then the client’s packet goes to the WDS repeater, then is ‘repeated’ to the base unit (two hops) and then out to the Internet – the reverse path is true for the responding packets back to the wireless client as the base unit knows “how” to reach the client through the WDS system by virtue of the WDS repeater overhead traffic.  Since the client’s response packet now has to go “through” the WDS repeater it takes two hops to reach the client.  In other words it takes over twice as long than if the client was “connected” directly to the base unit radio.  As you can see adding additional WDS repeaters will divide the total throughput in half (plus additional repeater information overhead) for each repeater added to the system.  Practically speaking you do not want to have more than three WDS repeaters in a WiFi Hotspot otherwise the total throughput of the system will be so low as to make it very slow for your wireless clients!

There is a second disadvantage to using WDS in that the packets transverse the WDS system “through” the repeaters to their destination.  Just like a string of Christmas tree lights, if one of the WDS repeaters in the “string” fails the WDS repeaters “downstream” will not be able to communicate with the base unit as WDS is setup as a “Static” wireless network – it can not “change” it’s configuration to take into account hardware failures within the wireless network.

What are MESH networks and aren’t they the same as WDS repeater systems?

There is a second method used to build an “extended” wireless network and is based on a network methodology called MAN (Mobile Area Network).  This type of wireless network “learns” where each of it’s neighboring repeaters are and what the “cost” is in communicating with it’s neighbors.  In this case “cost” refers to the signal quality between each of the repeaters and the software that makes up the Mesh Network application chooses the “best” path to send wireless packets.  The capability to “learn” on the fly the best routes to send packets make a Mesh Network “self-healing” in that if one of the repeaters fails and the other repeaters can “see” each other the system will still operate as the working repeaters will reconfigure themselves to bypass the failed repeater.

Now – there is also a “down-side” to Mesh Networks but this can be overcome!

The Mesh network suffers from the same receive / re-transmit issue as is found in WDS systems.  There can be only ONE transmitter active at a time in the network.  The wireless packet speed through the network is predicated by this fact.  The way to get around this issue is to use more than one radio at each Mesh Router location!  If you put two radios in the Mesh router then it can receive on one channel and transmit on the second radio channel at the same time!  Of course the wireless client’ radio traffic will cause the total throughput to drop being it has only one radio but the overall throughput of the system no longer follows the “divide-by-2″ issues as is found in the WDS system.  If you add a third radio to the Mesh router for the client to use then you can actually get almost total throughput in a Mesh Network configuration!

You probably are wondering, at this point, as to “why” most WiFi Hotspot locations don’t use a multi-radio Mesh router wireless network instead of WDS.  Well – the answer is very simple.  Mesh networks with multiple radios are not as easy to setup as a WDS system and they cost more per repeater location than WDS systems do.

BTW: An “added” advantage of a Mesh Network system is all of the wireless repeaters can be mobile and the system will still work as each Mesh router continuously determines the best path (route) to send the packets within the system.  This is the type of system you read about where emergency services, police forces and the military need mobile communications that can handle mobile networks.

Are there other wireless repeater systems or methods?

I have seen articles where people have taken Mesh Network equipment and made a “hybrid” system out of wireless and wired routers to extend a Mesh Network over a large area.  The advantage of using “wired” equipment with wireless access points attached is in reducing costs where the specific Mesh Network Node does not need to be mobile, such as the Gateway location for access to an external network such as the Internet.  As for any other methodologies most variants are based on either a Mesh Network or WDS … Ad Hoc comes to mind but it is not suitable to WiFi Hotspot applications by virtue of the method and inherent limitation of Ad Hoc mode (limit of 8 total wireless network nodes I believe).

I hope you found this article to be informative and useful!