Re: [core] Fwd: FW: I-D Action: draft-zheng-core-coap-lantency-evaluation-00.txt

Hi，

Some questions:
1. How large the NS is set for CoAP- Cocoa?
2. The ICMP latency is measured when the FTP background traffic is exiting, 
or not?
3. For CoAP over TCP on GPRS, how many are the allocated bufffers inside the 
andoid terminal?

Regards,

Gengyu WEI
Network Technology Center
School of Computer
Beijing University of Posts and Telecommunications
-----原始邮件----- 
From: Zhen Cao
Sent: Tuesday, July 05, 2016 3:06 PM
To: Carles Gomez Montenegro
Cc: lwip@ietf.org ; core@ietf.org WG
Subject: Re: [core] Fwd: FW: I-D Action: 
draft-zheng-core-coap-lantency-evaluation-00.txt

Hi Carles,

Thanks for feedback.

On Mon, Jul 4, 2016 at 4:58 PM, Carles Gomez Montenegro
<carlesgo@entel.upc.edu> wrote:
> Hi Zhen,
>
> Thanks a lot for this draft!
>
> A few comments/questions:
>
> - Did you measure the native packet loss rate?

not really.  many paper has studied this, native packet loss rate for
cellular network is rather low in steady environment, because 3gpp
stack is very good at fast retransmission.

>
> - In Table 3 (Wi-Fi), latency of CoAP-CoCoA is the same regardless of the
> manually introduced packet loss rate. I would expect some C-RTT increase
> with packet loss rate increase... Which is the reason why C-RTT increase
> does not happen? Or is there maybe some increase below the millisecond
> granularity?

We only notice sub-ms increase in this set of data.  Because the data
is averaged for the 100 rounds, several retransmissions do not account
much probably.

>
> - I noticed that ICMP RTT for GPRS is 572 ms, while obtained C-RTT is
> often lower than that value. I guess that is due to the size of the ICMP
> packets used to measure the ICMP RTT? (It would be good to indicate the
> size of such packets)

ICMP packet size is smaller than CoAP+UDP.   ICMP Ping request is 40 bytes.

>
> - In GPRS, we also observed a slight retry ratio increase for CoAP-CoCoA
> in low congestion GPRS scenarios. However, the retry ratio was
> significantly lower for CoAP-CoCoA (compared to CoAP-RAW) in moderate to
> high congestion conditions. It would be interesting to measure what
> happens for different offered loads.

CoAP-RAW by default retries after 2 seconds.  If the RTT is higher
than 2s, CoAP-RAW will definitely be more aggressive than CoAP-CoCoA
which calculates RTO based on SmoothedRTT. So what's your RTT?

>
> - Which window size did you use for TCP?

Default on Android, which is TEN.

>
> Minor:
>
> - Is the CoAP client (over UDP) encapsulating the messages as CONs?

Yes,.
>
> - Apparently there is a jump from section 4.2 to 4.4.
>
> - Section 4.4:  s/as composed to/as opposed to
>
> - Reference [COAPCC]: s/Networks magazine/Communications magazine

we will correct the above three nits.

Many thanks,
Zhen

>
> Cheers,
>
> Carles
>
>
>> FYI.
>>
>>
>> -----Original Message-----
>> From: I-D-Announce [mailto:i-d-announce-bounces@ietf.org] On Behalf Of
>> internet-drafts@ietf.org
>> Sent: Monday, July 04, 2016 11:16 AM
>> To: i-d-announce@ietf.org
>> Subject: I-D Action: draft-zheng-core-coap-lantency-evaluation-00.txt
>>
>>
>> A New Internet-Draft is available from the on-line Internet-Drafts
>> directories.
>>
>>
>>         Title           : CoAP Latency Evaluation
>>         Authors         : Fei Zheng
>>                           Baicheng Fu
>>                           Zhen Cao
>>         Filename        : 
>> draft-zheng-core-coap-lantency-evaluation-00.txt
>>         Pages           : 9
>>         Date            : 2016-07-03
>>
>> Abstract:
>>    This document presents the evaluation results of CoAP in terms of
>>    various latency metrics over UDP/TCP under different network
>>    environments.  We conduct experiments via both GPRS and WiFi.  We
>>    also evaluate how the latency metrics are impacted by the background
>>    traffic.
>>
>>
>> The IETF datatracker status page for this draft is:
>> https://datatracker.ietf.org/doc/draft-zheng-core-coap-lantency-evaluation/
>>
>> There's also a htmlized version available at:
>> https://tools.ietf.org/html/draft-zheng-core-coap-lantency-evaluation-00
>>
>>
>> Please note that it may take a couple of minutes from the time of
>> submission until the htmlized version and diff are available at
>> tools.ietf.org.
>>
>> Internet-Drafts are also available by anonymous FTP at:
>> ftp://ftp.ietf.org/internet-drafts/
>>
>> _______________________________________________
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>>
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>
>

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