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
--
Jack Unger ([EMAIL PROTECTED]) - President, Ask-Wi.Com, Inc.
Serving the License-Free Wireless Industry Since 1993
Author of the WISP Handbook - "Deploying License-Free Wireless WANs"
True Vendor-Neutral WISP Consulting-Training-Troubleshooting
Phone (VoIP Over Broadband Wireless) 818-227-4220 www.ask-wi.com
--
WISPA Wireless List: [email protected]
Subscribe/Unsubscribe:
http://lists.wispa.org/mailman/listinfo/wireless
Archives: http://lists.wispa.org/pipermail/wireless/
