Ask HN: What startups are working on hard, technically challenging problems?

Tech looks good, company looks shaky.

In-protocol multiplexing must be pretty high up the list of necessary features

Yes :-)

but how about transparent multi-network roaming

Yes :-)

I'm talking about hopping between different transports.

Yes :-)

(I was thinking of writing a much more detailed answer to above, but it's so detailed that it would be far better as a blog post... I'll post the link here for a more inclusive discussion soon)

Now going back to your first question:

"what do you answer when the obvious comparison to (and lack of industry adoption of) SCTP is put forward?"

Oh... where to start.. OK. First off the comparison is not all that obvious. SCTP was never built for the mobile use case (4 way handshake??). There are some improvements over TCP (reliable, out-of-order message based delivery with multihoming are all good things), but there's a fatal flaw that prevents any serious use of this protocol. It's not TCP or UDP!! And there are umpteen middle-boxes on the internet who won't let it through. That's all you need to know to explain the lack of industry adoption of SCTP.

So we built our protocol on top of UDP (which we basically treat as a proxy for raw IP). Luckily for the mobile users, UDP based custom protocols are now well baked into various standard applications (DNS, VOIP etc.). A vast majority of middleboxes support it and the trend is in the right direction -- every new middle box has to support UDP passthrough/NAT by default barring exceptional circumstances.

Now, how do we expect our new protocol to get adoption. The answer is, we don't. We're not just building a protocol. We're building a turnkey service for mobile app developers. Our business case doesn't involve convincing anyone of the technical superiority of the protocol. We simply sell a superior user experience with minimal developer effort. And you'll learn as we get more open in the coming few weeks (wink, wink), it's not at all a hard-sell :-)

Feel free to connect with me directly or just continue the discussion here if you have more questions. I'm always happy to engage skeptical observers ;-)

> umpteen middle-boxes on the internet who won't let it through. That's all you need to know to explain the lack of industry adoption of SCTP.

Heh, I've dealt with IPSec. You don't have to convince me on the futility of getting new protocols ("the magic number on IP header") approved for end to end delivery. :) For better or worse, UDP encapsulation is the sensible thing.

I used SCTP as a fairly well known example of a protocol that has many of the modern technical requirements built in. As far as protocol features go, it is a pretty good yardstick.

Now, as for "turnkey service"... I would guess you're positing yourself as the platform provider. You need to control the server endpoints to work with multi-homing; you'll have to provide and maintain the mobile app libraries, along with best practices documentation and aids for debugging; you probably want to provide a patch for wireshark (dissector); and then there's the security to think about. That's just off the top of my head.

I am genuinely interested how you have solved the problems and where you have looked for inspiration. Because this is aimed at mobile developers, unreliable latency will be a major factor. That's something you do not have control over - maybe the protocol library can help a bit, and multi-homing already mandates graceful handling of concurrent retransmits. But mobile networks are not just unreliable, they are all too often outright crappy.

Can one ever work around that?