[AusNOG] AAB Statement

[Jason Ashton]

Hi Adrian,

I fully acknowledge that you can't compare PTP to PTMP systems in terms of latency.

However as well as making use of point to point microwave systems we also operate 1st generation WiMAX networks (shared medium, TDMA) and we see real world "loaded" end user latency of around 15msec in the radio hop. The key to managing "QoS" and latency is to ensure that capacity exceeds demand for the aggregate "time sensitive" traffic. We do this by building more cells/sectors as demand increases. The mobile carriers can/will do the same.

The fact is however that the LTE standard represents a substantial improvement over HSPA+ (Telstra Next G) in terms of radio efficiency and per user allocation of resources and it is also a simple flat architecture. As a result of all this it is far more scalable (which will help operators manage capacity requirements).

I personally  expect we will see real world latency of <10msec on the last (radio) hop for LTE versus what people see today on Telstra Next G (50msec+) which is HSPA+.

http://3g4g.blogspot.com/2008/01/comparison-hspa-vs-lte.html

cheers
Jason

>> >From page 3 - " End-user latency <10mS"
>> 
>> In my experience with next generation radio technologies the latency for large packets is typically double the >latency for small packets, which again is hardly application impacting. And future generations of wireless systems will >have even lower latency. 
>> 
>> We see latency as low as 25 microseconds (0.25 msec) on our high capacity point to point microwave links.
>
>I've not gone digging into it and thus it's completely possible that something in the 3G-nextgen spec(s) cover this, but >just to be "correct":
>
>Your equating of a PtP microwave link behaviour as somehow indicative of the behaviour of a shared (time, code, >frequency)-division media is a bit off-base.
>
>I'm not talking about minimum latency, I'm referring to the maximum latency on the last-hop. Obviously(!) the >provider may have latency creep in due to "the internet", so I'm focusing on last-hop.
>
>Current 3G "internet" tech has a -wide- range in latency. Perhaps the spec allows for IP-style "QoS" and a maximum >per-user connection latency but this isn't how it's deployed in the real world. From my very, very coarse >understanding, 3G low-latency is achievable only with significant drops in client carrying capacity and link throughput. >Again, I haven't done any in-depth digging; I could be wrong. If so I'd appreciate a bit of schooling in this matter.
>
>Your PtP link has that low latency because it's just that - point to point; single user or a small number of users. 802.11 >also has similar issues - pre-11n definitely has upper limits on subscriber count because of the small (sub-few >hundred) packets per second you can throw across the wire.
>Add too many concurrent clients trying to do stuff and you end up exceeding how many pps you can actually transmit. >11n changes the game a bit (as there's packet aggregation magic in there which I haven't yet had to implement; so I >don't yet understand it fully) which changes the behaviour profile from pre-n 802.11 behaviour.
>
> (And strictly speaking - the same issues can and have crept up with non- wireless tech; it's just the per-subscriber >bandwidth nowdays doesn't
> (totally) thrash the "medium" bandwidth limits - for example, the backplane of your DSLAM/DSL aggregation >device/dialup unit/etc. Some devices implement that as a shared medium. :)
>
>In short - "Comments not fully thought out; more data needed thx."
>
>
>
>Adrian