Ad hoc applications?

[JimGeier]

Just wondering what experiences some of you might have had with ad hoc mode WLANs. Does anyone use ad hoc mode beyond a couple users? What types of applications do you use ad hoc for? Any experiences with mesh network topologies?

[computeradam]

i setup 2 laptops with ad hoc and nothing happened

[JimGeier]

What type of settings did you use? You'll probably need to set each radio NIC to the same channel.

[computeradam]

I don't remember. But I am sure there is a logical reason for this feature. I will try again as soon as i get another card shortly.

[Dan]

Jim,

I read your recent article about mesh, and I've been aware of the company for a while. I've been wondering, though - how do you provide security for the individual streams as they pass through all these "routers"? And how do you provide security for the data on the "router" box?

Thx for your thoughts. --Dan

[JimGeier]

I'm not sure exactly how MeshNetworks handles this, but I think it would be difficult to provide security. You can't realistically implement WEP, because ad hoc users will likely not know each other and won't know what to set the WEP key to (and there's no access point to implement dynamic WEP).

[hans]

I saw mesh network's booth at the 802.11 expo in june. They certainly did not spare any money on bells and whistles for their presentations.

But, I am not sure about their business model.

My PhD thesis was on routing and scheduling in Packet Radio Networks. The conclusion I came to was that PRNETs made most sense when:

1) The users were "on the same team" (fire fighters, military) and therefore could 100% trust each other. Apart from security, what incentive do I have to waste my battery on transmitting/forwarding someone else's traffic.

2) There is no pre-existing communication infrastructure (e.g., base-station, access point), or the existing infrastructure has been damaged, and the only option is to set up the communcination capablity in an ad hoc fashion.

The other thing that doesn't make sense for a PRNET / mesh network is for it to be a purely "flat" network with no hierarchy. Routing would be a nightmare. If a hierarchical structure was necessary for wired networks, then it has to be necessary for wireless networks. So for a mesh network to be viable, it needs super-nodes aka access points.

Well then in a commercial setting, why would I not want to transmit directly to the access point, as opposed to multi-hop over others' devices? Obviously being out-of-range of an access point would be a good reason - but in that case I would rather shift to cellular (assuming 802.11/cellular roaming becomes a reality).

The way I see it, mesh networks is a reincarnation of Ricochet.

[JimGeier]

Good comments. Interesting, our research background is very similar -- I also did my thesis (about ten years ago, though) on routing in packet radio networks. I'd defined a distributed routing algorithm that accounts for various impariments of wireless networks.

You're correct, routing over distributed nodes is difficult in a wireless environment. There's a lot of dependence on the proximity of other nodes, which can be a big problem with the relatively short ranges of 802.11b devices.

[wirelessgeek]

Ad hoc mode is designed to connect a few computers together with out using an access point. This is typically done to save money, however you do give up some security and functionality that you would have from connecting to an access point. You also have to have your computers pretty close to each other for ad hoc to be effective.

[hans]

Jim,

This is very interesting indeed. My dissertation was on minimum-energy routing in PRNETs. It revolved around developing a mathematical framework for solving minimum-energy routing, such that the problem became mathematically identical to minimum-delay routing for wired networks. The advantage of that was the ability to re-use algorithms developed for routing in wired networks. But I also had to deal with scheduling issues, because as you probably know, scheduling and routing are very intertwined in PRNETs. BTW, you probably get swamped with gazillions of private messages, but did you get mine from a few days ago?

Regarding meshnetworks, I remember hearing, just a few days ago, that the FCC gave them a license to offer their service nationwide.

[JimGeier]

I looked through my emails and didn't see yours. Please resend it if you could please.