Subject: Re: [ledbat] open issues, ACK rate

From: Mirja Kuehlewind <[email-masked]>
Date: Thu, 8 Jul 2010 18:02:46 +0200

Hi,

> 4. ACK rate
> In the framing and wire format section, Stas promised to add a statement
> that LEDBAT needs to send (and receive) ACKs frequently in order to work
> properly. This is an open issue that needs to be solved. As this has not
> happened yet, text to include from the WG is more than welcome. Details on
> what frequently should mean in practice is open for discussion.
Actually section 5 says 

"Consider a protocol that uses packets of equal size and acknowledges each of 
them separately." 

Okay, it does say anything about loss of acks. Maybe there should something in 
the algorithm that says: if I don't see acks for 'some' time I will reduce my 
cwnd...? Does anyone did some experiments with lost acks?

One more point for the pseudo code: the part of halving the congestion window 
in case of (data packet) loss is missing here.

Mirja

---

From: Stanislav Shalunov <[email-masked]>
Date: Mon, 12 Jul 2010 13:57:29 -0700

As I'm going over the open issues last time before submitting the draft, I
wanted to note that if you don't get any ACKs, you'll timeout and conclude
losses are occurring, thus quickly and radically reducing the window by a
factor of two per RTT.

This is one of the stated reasons for multiplicative decrease:

"Further, *to deal with severe congestion when most packets are lost* and to
provide a safety net against incorrect queuing delay estimates, we'll halve
the window when a loss event is detected." (emphasis added)

On Thu, Jul 8, 2010 at 9:02 AM, Mirja Kuehlewind <
[email-masked]> wrote:

> _______________________________________________
> ledbat mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/ledbat
>

-- 
Stanislav Shalunov
BitTorrent Inc
[email-masked]

personal: http://shlang.com