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52 lines
3.5 KiB
C
52 lines
3.5 KiB
C
/*
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Serval Overlay Mesh Network.
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Basically we use UDP broadcast to send link-local, and then implement a BATMAN-like protocol over the top of that.
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Each overlay packet can contain one or more encapsulated packets each addressed using Serval DNA SIDs, with source,
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destination and next-hop addresses.
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The use of an overlay also lets us be a bit clever about using irregular transports, such as an ISM915 modem attached via ethernet
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(which we are planning to build in coming months), by paring off the IP and UDP headers that would otherwise dominate. Even on
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regular WiFi and ethernet we can aggregate packets in a way similar to IAX, but not just for voice frames.
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The use of long (relative to IPv4 or even IPv6) 256 bit Curve25519 addresses means that it is a really good idea to
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have neighbouring nodes exchange lists of peer aliases so that addresses can be summarised, possibly using less space than IPv4
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would have.
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One approach to handle address shortening is to have the periodic TTL=255 BATMAN-style hello packets include an epoch number.
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This epoch number can be used by immediate neighbours of the originator to reference the neighbours listed in that packet by
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their ordinal position in the packet instead of by their full address. This gets us address shortening to 1 byte in most cases
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in return for no new packets, but the periodic hello packets will now be larger. We might deal with this issue by having these
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hello packets reference the previous epoch for common neighbours. Unresolved neighbour addresses could be resolved by a simple
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DNA request, which should only need to occur ocassionally, and other link-local neighbours could sniff and cache the responses
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to avoid duplicated traffic. Indeed, during quiet times nodes could preemptively advertise address resolutions if they wished,
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or similarly advertise the full address of a few (possibly randomly selected) neighbours in each epoch.
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Byzantine Robustness is a goal, so we have to think about all sorts of malicious failure modes.
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One approach to help byzantine robustness is to have multiple signature shells for each hop for mesh topology packets.
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Thus forging a report of closeness requires forging a signature. As such frames are forwarded, the outermost signature
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shell is removed. This is really only needed for more paranoid uses.
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We want to have different traffic classes for voice/video calls versus regular traffic, e.g., MeshMS frames. Thus we need to have
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separate traffic queues for these items. Aside from allowing us to prioritise isochronous data, it also allows us to expire old
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isochronous frames that are in-queue once there is no longer any point delivering them (e.g after holding them more than 200ms).
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We can also be clever about round-robin fair-sharing or even prioritising among isochronous streams. Since we also know about the
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DNA isochronous protocols and the forward error correction and other redundancy measures we also get smart about dropping, say, 1 in 3
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frames from every call if we know that this can be safely done. That is, when traffic is low, we maximise redundancy, and when we
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start to hit the limit of traffic, we start to throw away some of the redundancy. This of course relies on us knowing when the
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network channel is getting too full.
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This file currently seems to exist solely to contain this introduction, which is fine with me. Functions land in here until their
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proper place becomes apparent.
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*/
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#include "mphlr.h"
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int overlay_socket=-1;
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int overlayMode=0;
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overlay_txqueue overlay_tx[4];
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