Page 577 - Cloud computing: From paradigm to operation

XaaS 3

Appendix IV

Value for response time limit
(This appendix does not form an integral part of this Recommendation.)

The response time is specified in clause 7 as a general requirement for DaaS. The value of the response time-
limit is needed in order to meet the CSC’s acceptable QoE.
This appendix only provides general information relevant to response time. However, the response time
described in here is not specific to cloud computing and DaaS.

Figure IV.1 shows a response time model [b-Shneiderman].

User Arrival Server begins Server completes Event User's device User's device
initiates of user's to process processing result begins completes
request request user's request user’s request delivered response response

4) Transport delay 3) Server processing time 4) Transport delay 5) Render time
1) Response time
2) Interaction time
Y.3503(14)_FIV.1

Figure IV.1 – Model of response time

As shown in Figure IV.1, the response time includes transport delays, server processing time and rendering
time on a client as defined hereafter:
• Response time: An interval from the moment when user initiates an activity until that user's device
begins to present its result on the display;
• Interaction time: The same as response time;
• Transport delay: An interval from the moment when user's request is sent until it is received by a
server or the time from the moment a server sends;
• Server processing time: Operation time used by a server to process the user's request;
• Rendering time: Duration for generating an image with the received event results screen on the
user's device.
Values for acceptable response times may differ depending on the use case, but experimental studies show
that a user starts to be bored or interrupts if there is no response within one second [b-Tolia]. It seems
common that users are intolerable if the reaction time takes more than one second.
As shown in Table IV.1 [b-Tolia], in the range from 150 ms to one second users become increasingly aware of
the response time, and unhappy after one second.

Table IV.1 – Impact of interactive response time [b-Tolia]
Response time Subjective impression

< 150 ms Crisp
150 ms to one second Noticeable to annoying
One to two seconds Annoying
Two to five seconds Unacceptable
Longer than five seconds Unusable

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