Latency. FaceTime on WiFi/LTE.

“I think to myself, what a wonderful world!”

Everyday there is something new to learn!

Learn a lot form two CDN veterans this morning:
1.DNS-based global server load balancing will response to the nameserver of the resolver, the resolver’s nameserver will then query again the hostname in the the respond. If the hostname is pointing to a CDN host, then the CDN nameserver will response to the resolver’s nameserver. These two DNS resolutions are independent of each other and they can use different logics/mechanisms.

Some high-traffic websites use “intelligent” DNS-based GSLB to implement multi-CDN strategy to further improve site performance and ROI. Latency caused by an additional round of CNAME resolution is a good trade-off.

2.Jakob Nielsen, in 1993, published the “3 important limits” of response time:
-0.1 second is the limit for having the user to feel the system in reacting
-1.0 second is the limit for having the user to stay uninterrupted
-10 seconds is the limit for having the user to keep attention

3.Fiona Nah’s study in 2004 found tolerable wait time (TWT) of web user was 4 second. People are losing patience and unwilling to wait.

4.Google experienced 20% drop in traffic (and revenue) if there was a 500ms load time increase. Amazon found a 1% drop in sales resulted from a 100ms page load time delay.

5.80% of response time is front-end related for landline users and 97% for mobile users! We have more latencies in 3G than xDSL/FTTB.

6.In the last decade there were many technology development and upgrades in datacenter and last mile. To leverage these investments, telcos should provide CDN services.


I did some simple tests to compare my 3G (MBA to 4S to 3G) and FTTB (MBA to AE to FTTB) services:

96ms vs 5ms…

What cause the latency in 3G? Network equipment, air interface and user equipment. From a 2009 Nokia Siemens whitepaper, we have the following “expected” roundtrip latencies:
HSPA: 41ms
HSPA+: <25ms
LTE: <20ms

Video conferencing connects people at different locations. That’s why biz people use telepresence, WebEx, Skype… Responsiveness is the major quality factor in video conferencing. When LTE becomes the most common cellular (it is a more politically correct term, thanks Apple!) technology, then we will have true mobile communication!

FaceTime on LTE (&HSPA+). One More Thing for iPhone 5?

What a wonderful world, Louis Armstrong, youtube

5 Comments on “Latency. FaceTime on WiFi/LTE.”

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