Re: Idea for packet numbers

[Magnus Westerlund <[e-mail]>]

Hi Martin,

Den 2017-07-20 kl. 12:38, skrev Martin Thomson:
> Are you talking about the use of the NEW_CONNECTION_ID message,
> because what you propose would be possible, but it would cause an
> improvement to linkability.

This is in reference to any changes to the public header information. 
The current draft version do have the packet number as part of the 
public header. I understand we will continue the discussion on what is 
public, and I think there has been suggestions all over the place. Thus, 
I want add this as a possibility assuming that the consensus is that we 
will have any parts of the packet number in the non-encrypted part of 
the packet.

I personally do think there are reasons for keeping at least the least 
significant parts of the packet number being non-encrypted. I don't see 
the linkability need to be significantly impacted. A single QUIC flow 
will still have the 5-tuple of IPvX+UDP that enables to identify where 
it comes from and where it goes. I still haven't seen any good 
motivation why you would actually have multiple QUIC connections on the 
same 5-tuple. Thus, the single path of the connection will leak very 
little additional information other than how the flow is being treated 
by the network.

For a 3rd party observing this from the outside, for flows with little 
losses you still see most packets, in this case I don't see that 
determining that losses are present upstream affects how you can 
correlate this with other. In the case of continuing a flow on another 
path, I would not really have problem with introducing a larger gap to 
reduce the linkability between the different flows that are used by the 
connection. Because, from my perspective, it would be preferable that 
each flow over different path actually are treated as individual 
sub-flow. Thus, they could have completely independent packet numbers. 
Such a direction appear to reduce linkability, without preventing 
exposing the basic flows transport progress.

Cheers

Magnus

> On 20 July 2017 at 11:59, Magnus Westerlund
> <[e-mail]> wrote:
>> Hi,
>>
>> There has been some discussion around packet numbers. For passive detection
>> of packet loss in measurements and network management, it would be really
>> good if the packet numbers where continuous and not only monotonically
>> increasing. As this enables one to determine losses upstream of the
>> measurement point. At the same time I understand there are benefits with
>> being able to introduce gaps into the packet number to test the receiver's
>> behaviour.
>>
>> To enable both of these capabilities I would propose that the N least
>> significant bits of the packet number are strictly increased by one. Then
>> one can introduce gaps in the bits above the N ones. Yes, that will burn
>> through the packet number space faster as the gaps may become larger than
>> was the case without this. However, I don't see that this will have
>> significant effect unless the sender introduce gaps very frequently so that
>> the length of the packet number field needs to be much larger due to the
>> outstanding sequence number space is much larger.
>>
>> The value of N can clearly be discussed but it should be selected so that
>> reordering and common burst durations are shorter than the time to wrap the
>> strictly increase amount of bits. If the higher bits are available to
>> measurement node, some possibility to infer gaps will also be possible. It
>> might be that N needs to be scaled with throughput with a minimal value. N=8
>> would mean 256 packets between wraps. I think that is a reasonable minimal
>> value. However, that will wrap in 28 ms at 100 mbps of payload (assuming
>> 1400 bytes of payload per packet).
>>
>> So what people think about this idea?
>>
>>
>> Cheers
>>
>> Magnus Westerlund
>>
>> ----------------------------------------------------------------------
>> Media Technologies, Ericsson Research
>> ----------------------------------------------------------------------
>> Ericsson AB                 | Phone  [phone]
>> Torshamnsgatan 23           | Mobile [phone]
>> SE-164 80 Stockholm, Sweden | mailto: [e-mail]
>> ----------------------------------------------------------------------
>>
>>

-- 

Magnus Westerlund

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Media Technologies, Ericsson Research
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Ericsson AB                 | Phone  [phone]
Torshamnsgatan 23           | Mobile [phone]
SE-164 80 Stockholm, Sweden | mailto: [e-mail]
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