Whilst re-reading an article by Bob Frankson on QoS, I was thinking about the difference between what users value from the telephony application (speak to someone not physically present) and what the telcos value (connect devices through a network with 99.999% availability).
The uptime of the application (as opposed to the network) is the chance you can communicate with your intended target given that the target is physically willing and able to receive a phone call. But if they have the TV turned up loud and don't hear the phone ringing then the network might as well not be there. If they're out of the house and you phone their landline instead of their cellphone, you get 0% availability. In many ways, a small amount of presence or location information can make a big difference to the "true" application availability. The cost-effectiveness of the last few 9's of network uptime is questionable. The system is only as good as its weakest link.
The end-to-end perspective is that you have to view the system from the perspective of the user, and not any intermediary. The value of the system is defined by the users at the end points.
Posted by Martin Geddes at 5:49 PMTrackBack URL for this entry:
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