Subject: Re: [tsvwg] A question about packet loss when multiplexing

From: "Black, David" <[email-masked]>
Date: Fri, 14 Aug 2015 02:19:46 +0000

Jose,

<WG chair hat OFF>

> 2- If you lose a multiplexed packet, you lose a number of packets. But the packet loss probability may be the same overall. For example:

Not exactly ... it's a function of the error or loss distribution.
I'll explain based on error distribution ...

If the 1% loss is caused by link/signal corruption, the worst case is
uniform error distribution ... for which the math happens to be simple.

> You send 1000 pps with a 1% packet loss. So you lose 10 pps.

To make the math easy, assume that these are 1250 byte packets, so we
have 1000 packets/sec * 1250 bytes/packet * 8 bits/byte = 10 million
bits/sec.

To lose 10 packets, assuming isolated 1-bit errors, we need 10 errors,
or a BER (Bit Error Rate) of 10**(-6) (i.e., 1 in a million bits are in
error).

> If you multiplex in groups of 10 packets, then you only send 100 pps.

Ok.

> So you will only lose 1 pps,

Nope, that only happens if the error distribution is so skewed that all
10 errors occur in the same 1 multiplexed packet.  If the error distribution
is uniform, the 10 errors occur in separate multiplexed packets, so we still
lose 10 packets, each of which ...

>  ... will have 10 small packets inside.

... for a total loss of 100 small packets, which is the worst case.

This discussion is primarily for explanatory purposes, as error
distributions found in the real world are almost never uniform.
I'll leave it to someone with more background and statistical expertise
to suggest the error (or packet loss) distribution(s) that should be used
here and compute what the resulting expected packet loss(es) after
multiplexing would be ...

... but I'm reasonably confident that it is incorrect to assume that the
errors (or drops) are concentrated in a single multiplexed packet.

</WG chair hat OFF>

Thanks,
--David

From: tsvwg [mailto:[email-masked]] On Behalf Of Jose Saldana
Sent: Tuesday, July 28, 2015 11:38 AM
To: [email-masked]
Cc: [email-masked]
Subject: [tsvwg] A question about packet loss when multiplexing

Hi, Gorry,

Last Wednesday in Prague you asked me about the of effect packet loss of compressed tunnel packets, and if this is stressed in wireless scenarios.

There are some things to be considered here:

1- If you use header compression, a lost packet may be translated into a burst of wrong packets, because you may lose the ROHC context. You can use ROHC bidirectional to minimize the effect of this.

2- If you lose a multiplexed packet, you lose a number of packets. But the packet loss probability may be the same overall. For example:
You send 1000 pps with a 1% packet loss. So you lose 10 pps.
If you multiplex in groups of 10 packets, then you only send 100 pps. So you will only lose 1 pps, but that packet will have 10 small packets inside.

3- But (2) may not be entirely true if you are in a wireless scenario, where packet loss probability may grow with packet size.

In the Bar-BoF on Thursday we also talked about the potential utility of multiplexing in satellite scenarios. What do you think?

BR,

Jose

---

From: "Jose Saldana" <[email-masked]>
Date: Fri, 14 Aug 2015 17:12:59 +0200

Thanks, David.

Another thing we have in mind is to run some real tests with our Simplemux
implementation. We have only run laboratory tests so far (wired and
wireless), but we could also consider tests with packets travelling through
the Internet, or through different wireless technologies.

And there is still another question to be studied: what happens if you use
ROHC in addition to Simplemux? I mean, if you lose one packet, then the ROHC
context may be desynchronized, so the decompressor may be unable to rebuild
a burst of packets. How does this interact with multiplexing? 

Best regards,

Jose

De: Black, David [mailto:[email-masked]] 
Enviado el: viernes, 14 de agosto de 2015 4:20
Para: Jose Saldana <[email-masked]>; [email-masked]
CC: [email-masked]
Asunto: RE: [tsvwg] A question about packet loss when multiplexing

Jose,

<WG chair hat OFF>

> 2- If you lose a multiplexed packet, you lose a number of packets. But the
packet loss probability may be the same overall. For example:

bits/sec.

error).

Ok.

</WG chair hat OFF>

Thanks,
--David

From: tsvwg [mailto:[email-masked]] On Behalf Of Jose Saldana
Sent: Tuesday, July 28, 2015 11:38 AM
To: [email-masked] <mailto:[email-masked]> 
Cc: [email-masked] <mailto:[email-masked]> 
Subject: [tsvwg] A question about packet loss when multiplexing

Hi, Gorry,

Last Wednesday in Prague you asked me about the of effect packet loss of
compressed tunnel packets, and if this is stressed in wireless scenarios.

1- If you use header compression, a lost packet may be translated into a
burst of wrong packets, because you may lose the ROHC context. You can use
ROHC bidirectional to minimize the effect of this.

2- If you lose a multiplexed packet, you lose a number of packets. But the
packet loss probability may be the same overall. For example:

If you multiplex in groups of 10 packets, then you only send 100 pps. So you
will only lose 1 pps, but that packet will have 10 small packets inside.

3- But (2) may not be entirely true if you are in a wireless scenario, where
packet loss probability may grow with packet size.

In the Bar-BoF on Thursday we also talked about the potential utility of
multiplexing in satellite scenarios. What do you think?

BR,

Jose