hello my name is Mikael Kalinin I'm from
harmony team first of all I'd like to
credit alex philosoph who has been
investigating in these complexities in
aggregation ok let's move on so here is
the we have a station votes you are
already familiar with them from
yesterday's talks about beacon chain
technical introduction so we have cross
links to charts
we have finality checkpoints and we have
a fork choice vote as well so the
attestation is a very important thing
for the big and chain this is how we can
chain makes the consensus happen let's
see how it's progressing through a slot
so at the beginning of the slot a
proposer produces a block and send it to
the wire so all the daters can receive
it through the wire in the middle of the
slot committees start to produce their
other stations basically this could
happen not in the middle of the slot one
may produce at the station upon the
receive in this block and important this
to its chain after that a testers should
deliver their added stations to the
proposer of the next block to be
included on chain and they are eager to
do this because their rewards depend on
that and if proposer of next slot for
some reason fails to include some of
those SATA stations each those at the
station should be delivered to proposer
of this lot of after the next one and so
forth up to 64 slots ahead okay so what
proposer does with those stations it
aggregates them
and includes them into a blog body
aggregation reduces verification
complexity and it means that instead of
verifying hundreds of signatures you
should in the best case you should
verify only one signature pin very
common T it also reduces size demand on
the blog body
this chart shows e y axis is megabytes
of data and x axis is million of eath at
stake
so this green line is the aggregated
case and orange line is not aggregated
case and you can see how aggregation
saves our lives so ok let's talk about
attestation delivery how to deliver
those at the stations to a proposer we
might probably do direct delivery just
send those other stations directly to
let's say five or ten proposers of the
next blocks whatever number we find
reasonable but this this way is we're
efficient and fast but in that case we
are willing proposal rate the entity it
means that adversary may match proposer
public key and its network ID and
organize a coordinated attack to this
particular proposal kick them off of the
network so we're not doing it that way
instead of this we're using p2p overlay
that includes all other daters of the
beacon chain and gossiping the
attestation x' through this overlay so
everybody is happy everybody all
proposers
receiving those data stations nobody
knows who are proposers who proposers
are and these this p2p overlay is big
enough and everybody knows that there
are some valid errors
in it but it's hard to to organize an
attack on this because there are a lot
just a lot of notes and nobody knows who
is the proposer of the next lot or who
are the participants of the committee
internet workers network because
identity is not reveal that gossiping to
everybody gossiping in the p2p overlay
is prone to Byzantine failures and to
cope with Byzantine failures we have to
keep the degree of the p2p mesh on a
certain level and it brings a redundancy
the degree is the parameter that is just
a number of peers that your peer is
connected to so let's say your peer is
connected to ten peers and you are
receiving the air to stay the same
attestation message from five of them
and send in this attestation propagating
this attestation message to the other
five so we have like redundancy by a
factor of five and this redundancy is
about inbound and outbound traffic and
also nodes must do verification to
prevent epidemic attacks where the
network can be flooded by just bad at
stations invalid and this brings a high
demand on resources at scale so these
numbers are a factor of redundancy in
the p2p of the p2p mesh and this like
triple redundancy is a blue line and if
probably on the face zero we are okay we
are here where is it ten million each
what are the 18 but when we start to
approach to 50 million eath we are
having like
mmm 50 megabits per second as a
requirement and this is calculated for
60 seconds per slot what do we do with
this instead of sending single
attestation to this Peter Pan mesh where
we want to partially aggregate them in
relatively small overlays and only after
that send it to the to the beacon
attestation where everybody sign to this
is where aggregate and overlays comes
into play so what options do we have for
those overlays we can build them for
each people because we know what
committees are in each chip o-64 slot
beforehand it's like six minutes so we
could probably just build them for each
Ipoh or there is another option and to
use short subnets these are like natural
overlays for for the earth 2.0 so the
requirements are to the overlay are like
first of all it should be relatively
small and efficient enough to do this
partial aggregation in the fractions of
slot because we need to send those
aggregates to that be to be matched so
it takes
we are very restricted in time so it
should be incentivized a the
participants of this overlay should be
incentivized to do the aggregation and
the only one who are incentivize did the
committee's that produce those data
stations it should be Byzantine tolerant
being relatively small it should be
tolerant to kind of see bill and Eclipse
attacks and if we want to build the
overlay for each shaper we have a six
point five minutes to do the
so this time restriction okay so para
Baja overlays are very efficient because
you can build this overlay with whatever
topology and properties that you want
and it could be after that leveraged by
your aggregation strategy but the
drawback of that is that you need a
reliable source of peers within a small
amount of time and the topic discovery
will probably not help here because if
you don't have a reliable source of
peers your overlay will be prone to
civil and eclipse attacks so this is
very difficult part of building this
epoch very paja overlay we can use short
subnets they already exist they are
relatively weak and they are like more
long plain network units and the hence
they are resistant to kind of attacks
like Eclipse and civil and but the
problem is that one committee is spread
across all the shard subnets so let's
say you have 10 peers attend validators
of one committee in one in charge subnet
number one then in charge subnet number
five and so forth
and they just can't talk to each other
that is the problem for the aggregation
strategies so two strategies so one is
coordinated it's like handle you
probably heard about that it's very like
optimal so you can get clean aggregates
without overlapping with lower network
demand but this kind of strategies
requires those overlays to be built very
poor and we have this difficulty with
reliable source of peers and they are
not be to be friendly
it should be there should exist direct
connection between validators and that's
why we have let's we are getting back to
this anonymity problem here again we can
use chart subnets and to fire a gossip
based strategy so it's just you know
everything is ready for it but and you
can send messages you can send at the
station within one subnet make those
aggregates and yeah well the dealers of
the committee that produced those at the
stations can aggregate them but it's
requires higher Network demand because
we're working in a p2p mesh and it's not
that advice what is the threshold for
the aggregation and when it's ready to
be sent to the beacon attestation topic
and that's probably the problem here and
this problem is amplified by spreading
committee occurs different chart subnets
because you don't know how much of the
participants in your charts net so you
don't know how big aggregate you can
combine within the resources that you
have at far so let's summarize that we
have to use p2p overlay to deliver at a
station to proposer and it scale it puts
some big requirements to bandwidth we we
are considering a partial aggregation in
a smaller overlays is a solution but it
have a number of complexities there is
also another possible solution to use
onion wrote wrote in and similar
techniques but they will bring their own
complexity as well so need to invest it
just investigating that and for a zero
and probably for his one is not affected
because it's not
it's not it's not expected to have like
big amount of eath validating so thank
you so much I'm tom
[Applause]
you