Jeromie,

You raise some good points... and here are some more differences between Matt's fully-meshed WIRED network example and the real-world conditions under which WIRELESS mesh networks are so often deployed today.

1) REROUTING - Only a node failure or a high peak traffic load would normally force a routing path change on a fiber/copper network. On a wireless mesh, routing path changes will also result from interference caused by other same-network nodes, interference from other networks, and interference from other wireless non-network sources. Routing path changes will also be caused by the movement of obstructions and other rf-reflective objects such as trees and vehicles.

2. CAPACITY - Fiber/copper networks typically start out with high-capacity (compared to wireless) full-duplex links. Wireless mesh networks start out with low-capacity half-duplex links.

3. CONNECTIVITY - Fiber/copper mesh network nodes have two or more paths to other nodes. "Real-world" wireless mesh networks may contain nodes that, in some cases (the traditional "mesh" definition not withstanding) only have a path to one other node. For example, obstructions may block paths to all but one (or even no) other nodes.

4. ENGINEERING - Fiber/copper mesh networks are typically properly engineered for traffic-carrying capacity, QoS, latency, etc. "Real-world" wireless mesh networks are typically deployed in near-total ignorance of the Layer 1 (wireless layer) conditions. That's the great attraction (IMHO) of muni-mesh networking today. These networks are thrown up in the belief that they don't need any Layer 1 design or engineering expertise and that this will allow for quick, widespread deployment. Last time I looked however, there was still "no free lunch". I predict that the muni mesh networks that are "thrown up" today (Philadelphia will be a prime example, unless it's re-engineered correctly) will fail and fail miserably to meet the high expectations that have been raised like free or low-cost broadband for all. In addition, muni mesh networks today typically lack adequate traffic engineering and performance testing under load.

The way that muni networks are being marketed today will likely lead to a black eye for the entire license-free wireless broadband industry within 18 to 24 months.

I'm not saying that wireless mesh networks should never be used. There are certain (obstructed, short-link, low capacity) environments where they will be the best, most economical solution. I'm just saying that the false claims and marketing hype surrounding MOST (and let me repeat, MOST) of today's mesh networking claims, particularly mesh network nodes that contain just a single 2.4 GHz radio are going to come back to bite both the vendors and the cities that deploy these networks without sufficient wireless knowledge in the false belief that wireless mesh networks are just "plug-and-play".

Sorry about my rant, but other than a few responsible multiple-radio/multiple-band mesh equipment vendors, the current mesh marketing/hype environment is in a word - disgraceful.

jack


Jeromie Reeves wrote:

There is a very big difference from fiber mesh and wireless mesh. Wireless is classicly a bunch of HDX links where fiber is PtP links. Your example doesnt make it clear that the difference is what cause's 802.11[a|b|g] mesh "suck" and fiber/copper mesh's "not suck". The solution is multi radio units that can select peers based
on more then just essid (channel, hop count to the edge, packet loss, ect)

Jeromie

Matt Liotta wrote:

Attached is a quick rundown of basic mesh theory that I put together in light of the recent thread. It hasn't been peer reviewed or edited, which I would normally do before sharing publicly. But since I only wrote because of a thread on this list I figured I would just share it. Feel free to pick it apart.

I do want to point out a couple of things though. First, this was written in a generic way only covering mesh as a theory. As written it can be applied to various transport technologies from fiber to wireless; though I do provide an example using wireless P2P links. Applying mesh theory to wireless P2MP or ad-hoc networks would require special coverage.

-Matt




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