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Author Topic: Musings. Split From: Draytek Vigor 166 G.fast Modem / Router Review  (Read 1223 times)

Alex Atkin UK

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You pointed out that this device when being a modem can talk to a Draytek router and send it stats. That’s an excellent bit of design; I wonder how they do it in protocol terms? Presumably some proprietary protocol over ethernet rather than IP. I wish there was a standard for this, including more information than just DSL link stats as well. Can other Draytek modem and router combinations do this?

Typical a company would FINALLY figure this out, right at the point where it should start to be redundant due to FTTP.  :lol:
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Weaver

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Re: Musings. Split From: Draytek Vigor 166 G.fast Modem / Router Review
« Reply #1 on: September 29, 2020, 09:52:45 PM »

@Alex exactly! Someone could have designed such a protocol twenty years ago and we could all have been enjoying it. It needs to be something that can be passed on by a router and republished to hosts on the LSN too. But even with FTTP there should be a need for an information publishing protocol, like some of the functions of DHCP in certain respects. However it ought to feature not just publishing of fixed information, but also have events for notifications of state changes - such as link down/failed. Even with FTTP we want to know if the physical link fails because someone has put a digger through it or because the ONT has died / lost power or whatever. I would also like to know what the link speed up/down is; publishing that would be excellent.

With my four modems, I grope the ASCII full stats listing that I can obtain by polling the modem (which uses our very own Johnson’s firmware) and I get the up/down sync rates from that. Then I convert them into effective IP rates and put those into a customised XML config file which gets pushed into the router so that it can send stuff using the right balance of rates according to what each link can handle. Line 3 is 25% slower upstream than the others, for some completely unknown reason, so this rate split is important. I don’t know when the rates change though; I just have to use my psychic powers, so any rate change is always too late. I have no proper protocols and no event mechanism. Also I have to use forbidden knowledge to convert sync rates into IP rates based on my knowledge of the PPP-ATM-DSL protocol stack and its byte-bloat factors, knowledge which isn’t published automatically; I just have to know it. Yes, much of the particular detail will be forgotten in the FTTP era, but some basics such as link rates will still be there.

I have been thinking about how to tune TCP slow start to be less painful, wondering if you could somehow work out what the first-hop link rate is and what the path bottleneck rate is. For many hosts the first hop (discounting LAN hops to the WAN link) is the bottleneck. For servers the bottleneck could be at the far end of the path. A good way of handling the first case would be to be able to obtain link rate info from some info publishing protocol. Another method which I have thought of would be that of caching bottleneck rate info from previous TCP connections; however detecting when the path changes would be a nightmare, difficult anyway without such a protocol, especially if there is a path change in the middle of the path that creates a different bottleneck. In my setup, when the router goes into failover from DSL to 3G, then no notification of the new reduced speed can be given to hosts since we lack an appropriate protocol. (Luckily TCP just adapts, but you might not be using TCP.)
« Last Edit: September 30, 2020, 04:21:05 AM by Weaver »
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Alex Atkin UK

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Re: Musings. Split From: Draytek Vigor 166 G.fast Modem / Router Review
« Reply #2 on: September 30, 2020, 04:02:11 AM »

Question is if the speed profile is capped further up the chain or at the ONT?  Does the ONT even know what your speed profile is?

Logically I'd think they would want to cap upstream at the ONT and download further up (so excessive traffic is dropped well before it hits a bottleneck).
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Weaver

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Re: Musings. Split From: Draytek Vigor 166 G.fast Modem / Router Review
« Reply #3 on: September 30, 2020, 04:32:47 AM »

I don’t know which nodes in the path are the nearest ones that know what the link rate is in optical links; the ISP knows so information could be obtained all the way fro them. This is where PPP with suitable extensions could do the job, but you might not be using PPP. If not then it needs to be some protocol over ethernet end-to-end or something.



I keep thinking about TCP slow start. Think how ridiculous it is. Say you’re a web browser; you keep starting slow and then ramping up to exactly the same figure again and again in a short period of time, as the loath doesn’t change. The only problem there though is that additional traffic from other connections or UDP or other hosts could slow your link down so the max rate you remember from the last slow start might not be valid any more as the amount of competing traffic could have changed. You can add up all of your own TCP connections and divide up that total to give multiple slow-start max rate figures allocated to each connection, but you still won’t know about other hosts. There has to be something more intelligent that can be done but I also think that the probability of getting it wrong can be significant in all such awkward cases.
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Alex Atkin UK

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Broadband: Zen Full Fibre 900 + Three 5G Routers: pfSense (Intel N100) + Huawei CPE Pro 2 H122-373 WiFi: Zyxel NWA210AX
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Weaver

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Re: Musings. Split From: Draytek Vigor 166 G.fast Modem / Router Review
« Reply #5 on: September 30, 2020, 11:20:11 AM »

Thank you so much for that link. The thing that makes no sense to me is that if the queue is non-empty then throughout is already maxed out; you can only increase the delay and cannot make things exit the queue any faster. So ledbat seems the only sane option of the two.
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meritez

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Re: Musings. Split From: Draytek Vigor 166 G.fast Modem / Router Review
« Reply #6 on: September 30, 2020, 12:15:26 PM »

Draytek 130 can also talk to Draytek Routers in modem mode, and send statistics.

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Weaver

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Re: Musings. Split From: Draytek Vigor 166 G.fast Modem / Router Review
« Reply #7 on: September 30, 2020, 02:36:40 PM »

Thanks, Meritez
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Robbie

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Re: Musings. Split From: Draytek Vigor 166 G.fast Modem / Router Review
« Reply #8 on: September 30, 2020, 04:08:11 PM »

I didn't notice the split thread and I answered a couple of things on the original.

Must keep up.

👍
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