@dz -- you and others asked... here you go: A quick overview post on (just a few) of the reasons all mesh isn't created equal (a.k.a., why Wi-Fi Direct is not a replacement for ad-hoc mesh):
1. Let me just start by saying the folks at Open Garden are damn cool, and the FireChat application is super-neat in what it can do. I view the project as a fellow traveller and support both their work and the innovations that they're making to bring distributed communications to the masses. This post is meant to discuss some of the issues that have been left out of mainstream reporting, not to be a rationale for railing against FireChat.
2. The awesome folks at Citizen Lab did a great write-up of FireChat -- https://citizenlab.org/2014/07/asia-chats-update-line-kakaotalk-firechat-china
(just scroll down to the FireChat section).
Most importantly, in Open Garden's own words...
“People need to understand that this [FireChat] is not a tool to communicate anything that
would put them in a harmful situation if it were to be discovered by somebody
who’s hostile,” he [Christophe Daligault, Vice President of Sales and Marketing
at Open Garden] said. “It was not meant for secure or private communications.”
3. Wi-Fi Direct have an affiliation-security problem -- as SAE designer and
cryptologist Dan Harkins summarized, "It’s 34 frames of compromised and
questionable security versus 8 of strong security. And both options can use the
identical credential for authentication, it’s just that mesh does it right and
WFD does it wrong."
In non-geek speak, it means that users of any system relying on Wi-Fi Direct may leak personal information
whenever they join together (say, to create a FireChat group). This is a problem endemic to the underlying tech -- which means that anonymity is way more difficult to maintain.
4. Link-state changes: Wi-Fi Direct uses infrastructure mode (i.e., a
hub-and-spoke model where clients can link to a "group owner" node); while groups can be linked together, this ownership has profound implications for
propagating link-state changes (e.g., mobility, changing RF environments, etc.). Furthermore, if the
owner (who acts as an access point for everyone connected to her) leaves a group, the group is entirely disbanded. On the more scary side, owners could also
silence all affiliated devices (via the "notice of absence" mechanism in Wi-Fi Direct) -- which means they can
forceably break links between themselves and their clients as well as any clients that
those devices are connected via them -- again, this is endemic to the underlying tech (and is one of the reasons why ad-hoc mesh is such a different beast than systems that interlink a bunch of hub-and-spoke architectures together).
5. Relatedly -- scalability: the routing overhead necessary to create large-scale networks
makes Wi-Fi Direct untenable. Judging from the specs, routing overhead is
linear (and possibly supra-linear) -- making large-scale networks difficult (and
possibly impossible) -- see Table 3 here:
http://developer.android.com/guide/topics/connectivity/wifip2p.html If I had to bet, we've seen very few multi-hop Wi-Fi Direct-based networks (say with 4 or 5 or more hops), and
probably nothing greater than a few hundred users on any one off-grid network (looking at all the stats in the media, they talk about simultaneous users, not size of any
FireChat network -- and yes, if you're wondering, the only way they could know
simultaneous users is if FireChat clients were phoning home with this data).
6. I'm more than a little scared about the overhyping of FireChat --
not because it's not a cool technology, but because it's being way oversold for a use case where people may be surveilled. For example, I'm not sure how it can be completely "off the grid" but still require registration of users with a central database -- that would seem to require being on the grid (as do the usage stats that are being collected).
FireChat is synergistic with, but completely different from Commotion Wireless (www.commotionwireless.net) and both have their own strengths and weaknesses (none are silver bullets for all situations). But, in this case, the over-hyping could be putting a lot of people at
substantial risk (and could create substantial blow-back for many other important mesh and circumvention tech projects that are doing great work all around the globe).