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Author Topic: PTM preemption  (Read 512 times)

Weaver

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PTM preemption
« on: May 26, 2018, 05:31:51 AM »

PTM preemption - what a stunning idea, an amazing achievement in my view. I would be really proud if I had though that up. I wonder if people thought about such a goal for a good while before coming up with a good solution?

As I understand it, which isn't saying much at all, ATM fails in this respect because even though the annoying small cells have the potential to help here and maybe were intended to form part of a solution, AAL5 doesn't permit this as you can't break a run in cells in AAL5 that is carrying an AAL5 SDU. I’m hoping that my understanding is correct on this?

My question: Is PTM preemption getting used now? for certain QoS cases? Or for VoIP (only)?

I read that you have to have two (abstract) ‘interface’ points at the <can't remember what> upper (upwards-facing) layer-boundary to use the feature. The second i/f accepts your high priority TX SDUs. I don't know what that means for the rest of the protocol stack. Perhaps it would be triggered by standard QoS markings of some kind, or optionally by some heuristic (not the right word) recognition of some pattern to suggest that something is the right type of service ‘deserving’ if this good thing. Some people treat all small packets as high priority to catch VoIP, TCP ACKs, maybe DNS queries (?) even if they haven't been QoS-marked.
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CarlT

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Re: PTM preemption
« Reply #1 on: May 27, 2018, 08:04:58 PM »

Don't even know what that is however as far as small packets go weighted fair queuing, among others, will prioritise small packets.

Indeed, our A&A links have this as an option, and they seem to run it on their host links, which makes a lot of sense. https://www.aaisp.net.uk/kb-broadband-shaping.html

Oh, never mind. PTM preemption is just a shaping system where a high priority queue is served immediately whenever data is in it.
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CarlT

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Re: PTM preemption
« Reply #2 on: May 27, 2018, 08:09:01 PM »

Sorry. Answering your question I'm not aware of it being used at all in the UK. Separate, higher priority VLAN on PPPoE/IPoE services, separate PVC on ATM-based stuff. This is at least how it's done in the UK in all the networks I've worked on or heard about.
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