[pre-HIP] High level LongFi overview

[JayKickliter]

Before writing the first draft of LongFi, I'd like for this issue to serve as a place to ask a few high-level questions to help steer the direction of the protocol. It's become apparent that what we've been calling LongFi is two separate protocols, LowFi and HighFi. That leads to some questions. Please do not consider the answers below as gospel but as possibilities or outright bad ideas.

Glossary

• LowFi: a low-level device ⟷ hotspot protocol

  • MAC layer
  • Likely contains encrypted, application/organization-specific payload
  • Specifies only cleartext fields required to allow hotspots to forward packets to their organizations' routers, and routers to send downlink packets to the correct device
  • Specifies device and hotspot behavior necessary for regulatory compliance

• HighFi: a high-level device ⟷ router protocol

  • HighFi is to LowFi as TCP is to IP (ish?)
  • Can be application or organization specific
  • Where [de]fragmentation would live

• ACK: a small and possibly data-free packet sent to acknowledge the receipt of a data-bearing packet

  1. A → B: a data-bearing packet
  2. A ← B: ACK

• Uplink-ACK: a device ← router ACK in response to an uplink packet

• Downlink-ACK: a device → router ACK in response to a downlink packet

Q1: Should LongFi specify any of the high-level protocol (HighFi)?

Initial offline discussions lean towards no if possible.

RATIONAL: Not specifying HighFi keeps LongFi simple and easy for third-parties to implement and understand. Additionally, it removes some risk of early decisions leading to unintended consequences.

Q2: What must LongFi specify to support HighFi?

It depends on the semantics of HighFi.

Q3: Does LongFi have the notion of connections (or sessions)?

It appears that LongFi requires sessions from device to its organization's router to operate in a trustless network.

Q4: If LongFi has sessions, how will that work with multiple hotspots?

Sessions are between a device and its organization's router, not with any hotspot in particular. It doesn't matter which Hotspot relays a device packet to a router.

Q5: What about downlink packets?

At a minimum, downlink packets are required for Uplink-ACKs.

Q6: What packets get ACK'd?

Uplink-ACKs are optional, and the conditions on which they are sent are HighFi/application-specific. For example, a device/user/org may only care about receiving Uplink-ACKs occasionally or in response to uplink packets containing critical payloads.

Downlink-ACKs seem to be mandatory. Downlink-ACKs are the only way for a router to detect malicious hotspots who charge for downlink packets but purposely drop them on the floor [1].

1. Short of adding downlink-witness semantics to the network (which is worthy of further investigation).

TODO

Explain some things that came up at lunch today:

• Dance Dance Revolution
• Interaction between Downlink-ACKs and state channel (might need @Vagabond for that one)
• Timeshare
• Fallback slots

[lthiery]

I like this segmentation between LoFi and HiFi; this was nuance I had trouble putting words on and I think these will stick :)

That being said, I want to understand "Should LongFi specify any of the HLP? Tentative No". This simply means we don't specify/restrict HiFi because we can't thanks to the trustless network of hotspots?

That being said, we can and should provide a reasonable implementation of the HiFi/HLP because it's unreasonable to use LoFi without some notion of authentication between device and router (as alluded to in Q3/Q4).

Does that line up with your direction?

[amirhaleem]

Can you define what is meant by the "High Level Protocol"?

[JayKickliter]

@lthiery

I want to understand "Should LongFi specify any of the HLP? Tentative No". This simply means we don't specify/restrict HiFi because we can't thanks to the trustless network of hotspots?

Correct, but I am not convinced that I am correct one way or the other.

That being said, we can and should provide a reasonable implementation of the HiFi/HLP because it's unreasonable to use LoFi without some notion of authentication between device and router (as alluded to in Q3/Q4).

Does that line up with your direction?

Yep.

[JayKickliter]

@amirhaleem

Can you define what is meant by the "High Level Protocol"?

I replaced all instances of HLP with HighFi and added a glossary whith a description of HighFi.

[JayKickliter]

Pretty please, keep comments and questions coming. Unlike a real RFC where the thing is done and only critical comments are wanted, this issue is a malleable white-board.

[Vagabond]

I actually think there's a SuperFi protocol here that deals with the actual data being exchanged between device and router, LowFi deals with routing the fragments, HighFi deals in fragments re-assembled into packets and SuperFi deals with the actual data that the router and the end device are dealing with. So the actual key exchange comprising a join packet belongs at the SuperFi layer, and can actually be whatever that user wants, LongFi doesn't care because it's really just concerned with shuttling data around. Whether a router wants to pay for that data, or send downlink, is a private decision made based on the contents of the HighFi packets.

[Vagabond]

Like, if I want to use ROT13 encryption to talk to my AVR based shit board, I don't think we need to stand in their way as long as they're willing to pay for the LowFi packets.