Idea for packet numbers

[Magnus Westerlund <[e-mail]>]

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]
----------------------------------------------------------------------