I'm a huge fan of WiFi. I just wish it was more ubiquitous. There are a plethora of technologies coming to market to help make this happen, such as "mesh networks" that will help improve WiFi network coverage.
The beauty of the "mesh" is that you can quickly create new wireless networks or extend existing WLANs without needing a wired connection to each access point (AP). Mesh-enabled APs are good at load balancing because they can choose the most efficient path for data.
Basically, think of your cell phone when you ae driving. You are "hitting" the most optimal cell tower (strongest signal typically) and as you drive along, the cell tower "hands off" the connection to the next most optimal tower.
The next extension of WiFi "mesh networks" is to add VoIP to it. This could in theory render cell phone carriers obsolete! Think about it. A SIP-enabled PDA or WiFi-enabled cell phone can logon to the Internet via the WiFi mesh network and make phone calls for FREE!
Of course, the mesh networks no doubt will charge something for the data/Internet access, but if you are like me and you want Internet access anywhere you go, and are willing to pay for it, then having voice access (via VoIP) is just icing on the cake!
Well I was intrigued to learn that there is a company that is providing VoIP using the SIP protocol across a WiFi mesh network.
Here's an excerpt of its features:
- Make and receive calls to any SIP compatible phone service
- Use wired or wireless devices over the mesh for full function telephony services
- Roam all over the mesh, using the same phone number
- Call to other Internet users for no charge
The LocustWorld MeshAP now supports standards based Voice over IP, with SIP routing capability at every node
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There is more hype than reality around mesh networking. In the end, that can cause the bubble around mesh to bust - rapidly. Its time for a reality check on what mesh can and cannot do.
First, Mesh networks are not a new concept. In some ways, the internet is a mesh network. And it works, despite its size - because it does not suffer from the limitations of conventional wireless mesh networks:
1-Radio is a shared medium and forces everyone to stay silent while one person holds the stage. Wired networks, on the other hand, can and do hold multiple simultaneous conversations.
2-In a single radio ad hoc mesh network, the best you can do is (1/2)^^n at each hop. So in a multi hop mesh network, the Max available bandwidth available to you degrades at the rate of 1/2, 1/4, 1/8. By the time you are 4 hops away the max you can get is 1/16 of the total available bandwidth.
3-That does not sound too bad when you are putting together a wireless sensor network with limited bandwidth and latency considerations. It is DISASTROUS if you wish to provide the level of latency/throughput people are accustomed to with their wired networks. Consider the case of just 10 client stations at each node of a 4 hop mesh network. The clients at the last rung will receive -at best- 1/(16,0000) of the total bandwidth at the root! Not even enough for VOIP.
4-Why has this not been noticed as yet? Because first there are not a lot of mesh networks around and fewer still that operate beyond 1-2 hops. Also they have not been tested under high usage situations. Browsing and email don’t count.
Try video - where both latency and bandwidth matter - or VOIP where the bandwidth is a measly 64Kbps but where latency matters. Even in a simple 4 hop ad hoc mesh network with 10 clients, VOIP phones wont work well beyond the first or second hop – the latency and jitter caused by CSMA/CA contention windows (how wireless systems avoid collisions) will be unbearable.
Mesh networks are a great concept. But the challenge lies in managing the dynamics of mesh networks so users receive an acceptable level of performance in terms of both latency and throughput.
Its time to focus on solving some real problems to make mesh networks scale and provide stable performance - regardless of how many hops you are away from the Ethernet link.
If mesh networks are doomed to operate within only 1-2 hops away then they will not be able to sustain the large coverage needed to make this economically viable.
In my next submission I shall delve into some challenges for high perfomance - enterprise class - wireless mesh networking for both voice and data. Regardless of how many hops you are away from the Ethernet link :-)
Francis daCosta
Founder and CTO
www.meshdynamics.com
VoIP on mesh is no big deal these days. Submitted for independent testing, Strix Systems scored the highest against other vendors in throughput and low latency but even more interesting are the results for multi-hop performance. Where multi-radio vendors like BelAir and Mesh Dynamics claim high performance and supporting many hops, there is no real comparison. Strix today, in real live networks are supporting upwards of 7 or 8 hops in situations where wired backhaul is not available.. In the testing it was reported that 35MB/s was sustained and constant for not only 4, but 5 hops, which exceeded the test case. In reality, VoIP is a common application for the near future while data applications are common. Also interestingly is that video surveillance has become a high priority and the application for public safety, Department of Homeland Security, Railway and municipalities is beginning to take off.. See http://video.google.com/videoplay?docid=6068041406442550856