[NavigationTiming] requestEnd and reconciliation with server-side measurements

According to [1], the requestEnd attribute was removed because it
directly maps to responseStart, which is reflected in the non-normative
illustration in [2]. However, as any server-side developer of Web
technology will know, there is a processing time between the receipt of
the final byte of a HTTP request and the commencement of the delivery of
the response to that request. In some cases, the period between request
and response can be substantial, and this is often what end users
perceive as the major factor in Web site responsiveness.

 

I accept that the technology being described by the Group is client
site, and that there are factors (such as buffers in the network stack)
that make it difficult or maybe impossible for the browser client to
know when the request has been delivered to the server, but it may still
be of some statistical benefit to know when the last byte of the request
left the browser (presumably to be appended to the output buffer of the
network stack).

 

It might also be the case that in practice the time between HTTP request
commencement (requestStart) and complete delivery to the output buffer
(what I might call requestEnd) is negligible, and therefore the
measurement between requestStart and responseBegin is sufficient to
observe the latency of the Web site itself.

 

Alternatively, it might be the case that this time between requestBegin
and requestEnd is not negligible but is predictable/consistent and
therefore not of any great interest. That is, it can be discounted from
subsequent statistical analysis.

 

Whatever the case, I think the rationale for the omission of requestEnd
should be included in the document if there is sufficient justification
for the omission (preferably based on implementation experience), or the
Group should consider the re-introduction of the attribute if this
improves the accuracy of the measurement of latency (as seen from the
client's side). Currently the absence of any mention of requestEnd in
the document merely invites questions.

 

 

Regards,

____________________________

Dr Rotan Hanrahan

Chief Innovations Architect and CTO

MobileAware Ltd 

 

 

 

 

 

[1]
http://lists.w3.org/Archives/Public/public-web-perf/2010Oct/0017.html

[2]
http://www.w3.org/TR/2011/WD-navigation-timing-20110111/#processing-mode
l