[AusNOG] Why not Symmetric ingress and egress?

[John Lindsay]

You know I don't actually follow your argument.

Internode's customers generally want the fastest possible downstream they can get and want to be able to download as fast as possible.  Some experimenting has shown that the limiting factors are backchannel bandwidth which needs to be in the ratio of 100/7 or better (as I recall) and CPE which needs to not be < $100 junk.  The Apple Airport Extreme / Timecapsule and Cisco boxes have proven to be excellent for FTTH whereas everything else, pretty much, has proven to crap out above 10 ~ 20 Mbps.

Our experience, and we have hundreds of FTTH customers on other networks, is that the vast majority of customers buy 25Mbps access because it's cheap.  If they do buy a faster connection and don't buy a good router they complain about not achieving line speed.

Our experience, particularly with a couple of hundred thousand ADSL subs is that asymmetric access results in fairly balanced in/out traffic at the head end presumably because quite a lot of the back channel is P2P and it will use whatever it can find.

Generally in Internode's network we send other networks more traffic than they send us because we are a large content source.  We don't need any more outbound traffic although we do have a little more headroom on the international links.

What's your experience Mark?

jsl
--
John Lindsay - GM Regulatory and Corporate Affairs - Internode and Agile
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On 17/06/2010, at 7:39 PM, Mark Smith wrote:

> On Thu, 17 Jun 2010 09:29:45 +0930
> John Lindsay <JLindsay at internode.com.au> wrote:
> 
>> It's mostly a way of differentiating business services from domestic services.
>> 
>> Access seekers will be paying by the megabit up and down.
>> 
>> When I say differentiating what I mean of course is "enabling charging more for".
>> 
>> Based on ISP experience asymmetric service keeps traffic in better balance.
>> 
>> There are also some limits in the FTTH network architecture that mean there is less total bandwidth in the back channel.
>> 
>> It is easy to prioritise the traffic from one head end to hundreds of end users.  It is much harder to control those end points when they each want to transmit over one shared path.  The network uses much the same protocol as WiFi for controlling this.
>> 
> 
> I think it would actually be more economic if symmetric was used.
> 
> Lets say you have 100 customers on 100 Down/8 Mbps Up. If, at your
> peak traffic time, 50% of them were fully utilising their 100Mbps down,
> to avoid congestion, your backhaul will need to be 5 Gbps towards
> the customers. As you end up buy symmetric backhaul, you'll also be
> buying 5Gbps upstream bandwidth. Even with all 100 customers utilising
> their 8Mbps up, you'll only ever utilise 800Mbps of the upstream 5Gbps.
> What a waste of 4.2 Gbps upstream backhaul!
> 
> If, OTOH, you can convince those customers to accept 50 Mbps/50 Mbps,
> you only have to buy 2.5 Gbps symmetric bandwidth for backhaul, and will
> possibly be able to fully utilise the upstream backhaul you've paid
> for. So you're buying less backhaul bandwidth in total, and gaining
> better efficiency out of what you've bought. This efficiency carries
> right through your network to your expensive transit links.
> 
> How hard would it be to convince people to accept 50/50? It seems 66%
> of the (debatably) technically savvy Whirlpooleans would be fine
> with it -
> 
> http://forums.whirlpool.net.au/forum-replies.cfm?t=1462456 
> 
> It'd also avoid the performance problems that TCP has with asymmetry -
> 
> RFC3449 - "TCP Performance Implications of Network Path Asymmetry"
> 
> http://tools.ietf.org/html/rfc3449
> 
> My guess is that ADSL was chosen as the broadband technology to use,
> rather than a symmetrical DSL technology (not in Australia, I'm
> talking by the broadband groups who standardise it i.e. the Annex M
> people), because it sounded right for the way people were using the
> Internet at the time (consumers rather than producers), rather than
> understanding that the Internet protocols have operated over symmetric
> links for most of their life and it is therefore an unstated design
> assumption. If that wasn't the case, I don't think the above RFC would
> exist and be a Best Current Practice RFC.
> 
> Regards,
> Mark.
> 
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