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Author Topic: Telly over IP  (Read 834 times)

Weaver

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Telly over IP
« on: May 03, 2018, 03:30:39 AM »

Does anyone use TV over IP, from the likes of BT? Is it live streaming? Does it use multicast?

I was wondering, I assume that with multicast you have had it if you get any corruption or other packet loss because there can not be any retransmissions, not unless you have some kind of auxiliary rarely used side channel where you could occasionally request a missing packet.

How often do such users see glitches or problems?

I wonder if anyone does the latter, because for live tv the delay is of no consequence, it's not like a phone call or video call where timeliness matters crucially and you just have to live with dropped packets because there is no time to wait for the retx. In live tv if you just decided to have a 1 s delay or more and buffer everything, then you could easily get a NAK out and a high-priority req back on a side channel as the round trip time would be fine.

It must be a huge load on the lines of Netflix where everything is unicast and so presumably can be a reliable transport and buffered as much as they want. On my ADSL2 pipe the traffic is only about ~50-70% or the pipe downstream, it's very good.
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Deathstar

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Re: Telly over IP
« Reply #1 on: May 03, 2018, 07:45:39 AM »

As far as I am aware BT and Plusnet both use multicast.
On our line, I very rarely see any glitches even on HD.
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adrianw

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Re: Telly over IP
« Reply #2 on: May 03, 2018, 06:24:59 PM »

I had BT TV for a while.
IPTV multicast  seemed to work fine with a BT router/modem, with no noticeable glitches. Not that I used it much.
Switched to pfSense and a router/modem in bridge mode and could not get IPTV to work.
Gave up on it when I escaped from BT.
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Weaver

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Re: Telly over IP
« Reply #3 on: May 03, 2018, 06:58:50 PM »

It's interesting what adrian says about it not working with non-BT kit. Could that be because it is being dealt with using ATM PVCs? Assuming we are talking about adrian having ADSL with ATM, not FTTC at that time.

Presumably it would use ethernet and VLANs now there is no more ATM.
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Deathstar

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Re: Telly over IP
« Reply #4 on: May 03, 2018, 07:51:23 PM »

I am not using BT kit, I have a Zyxel modem and Asus dsl-ac68u running in bridge mode with no issues
FTTC
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Weaver

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Re: Telly over IP
« Reply #5 on: May 03, 2018, 07:54:08 PM »

Deathstar, is that with BT telly ? As you are using FTTC, perhaps that isn't a test of my theory then.

Someone mentioned ATM multiplexing of telly just yesterday in another thread, isn't that true?

Particularly with ADSL users on slower links, I've always just assumed that the BT telly thing must crucify your download speeds? Is that right? Or maybe I'm thinking of the old days where there used to be a box that speculatively received tv content ahead of time and stored it for later, if my understanding is correct. I heard a story about one BT user who was given one of those old TV boxes aeons ago, and after it was installed, normal internet was ridiculously slow, so the user phoned up support and reported a fault, and BT staff couldn't even ‘diagnose’ it, according to the tale anyway.
« Last Edit: May 03, 2018, 08:01:59 PM by Weaver »
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kitz

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Re: Telly over IP
« Reply #6 on: May 04, 2018, 11:07:22 AM »

Quote
It must be a huge load on the lines of Netflix where everything is unicast and so presumably can be a reliable transport and buffered as much as they want.

They use CDN usually located near to the ISP PoP such as the various Telehouses.  Unlike backhaul services,  Interlink bandwidth and peering is cheap.  Therefore it's the ISP's who bear most of the cost when it comes to bandwidth for unicast.

Quote
On my ADSL2 pipe the traffic is only about ~50-70% or the pipe downstream, it's very good.

I was one of the very first trialists for BT's multicast services.   At the time I had a fixed 2Mbps line.   Mostly it was fine although streaming live action for some sports events could sometimes get a bit blocky, but stream quality is much better now than it was in the early days which only used a few hundred Mbps*.  For watching normal tv it was fine, the first ever multicast live stream was Wimbledon which was mostly ok, but watching the first football (world cup/athletics?) matches weren't too great at all. 

Quote
It's interesting what adrian says about it not working with non-BT kit.

Is that old info and what do you mean by non-BT kit?.   The router has to be able to do IGMP  but doesn't need to be BT's - mine wasn't. 
For ADSL 20CN BT multicast from the BTw RADIUS, therefore only available to ISP's who used BTw backhaul services eg PN, Zen etc and was done over ATM.  The ISP's had to reconfigure their gateways too - iirc you could only connect via some of PN's centrals which terminated on what was then their newer Juniper ERX's

For FTTC they broadcast from the L2switch which are in the headend exchanges and as you say has a prioritised VLAN.

Quote
Particularly with ADSL users on slower links, I've always just assumed that the BT telly thing must crucify your download speeds?

Any streaming service that uses up bandwidth will affect download speeds.   If you only have a 4Mbps connection and IPTV is using 2Mbps then that will only leave 2Mbps for other services.  The weakest link is always going to be your connection speed between DSLAM and modem.

I did some tests here to show the effects of Internet TV on available bandwidth.    HD stream used appx 3.5Mbps.


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* lol I just found this page still in my bookmarks.   This was the original list of channels available when testing in 2005 when multicast was originally just 350kbps or 128kbps for radio.   The 1Mbps streams weren't added until later.   BT didn't even own PN back then.
https://support.bbc.co.uk/multicast/streams.html
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adrianw

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Re: Telly over IP
« Reply #7 on: May 04, 2018, 03:32:21 PM »

Is that old info and what do you mean by non-BT kit?.   The router has to be able to do IGMP but doesn't need to be BT's - mine wasn't. 
December 2017/January 2018, with a Netgate SG-2220 running pfSense and a bridged VMG1312-B10D.
My problems may well have been down to my configuration incompetence.
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kitz

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Re: Telly over IP
« Reply #8 on: May 04, 2018, 04:38:20 PM »

For some reason IGMP can be tricky to configure.   I seem to recall some issues with some TP-link modems, but people got there in the end.

I had problems configuring my VMG8324 to use Chromecast which has multicast services and spent a good while trying to get it to work on FTTC.
It was a few years ago now as I use Firesticks (unicast) for streaming these days, but there will be a post somewhere on here about my settings for with Chromecast.  One of the things I found out was that Chromecast didn't like the inbuilt IGMP proxy set in the router.. and you must set the VLAN tagging for 802.1p = 1 to give IGMP multicast priority.

Can't recall were I actually found the info but it took some digging at the time..  From memory IGMP proxy and IGMP snooping are meant to have the same end result but don't quite work in the same way as they work at different network layers, so you may need to play around with IGMP settings and the VLAN priority settings.   

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ETA just after I hit send I had a flashback to the early days of multicast, back then I used several different modems, but I had to tweak my SAR110 to enable multicast - link.
« Last Edit: May 04, 2018, 04:46:45 PM by kitz »
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j0hn

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Re: Telly over IP
« Reply #9 on: May 04, 2018, 06:27:56 PM »

There's a great post on the BT forums about getting 3rd party routers working with BT TV.

https://community.bt.com/t5/YouView-from-BT/Using-a-3rd-party-router-for-Multicast/td-p/1048582

I've had both Talktalk TV and BT TV and both played absolutely perfect.
With BT TV I regularly have 2 HD channels recording concurrently, while watching a 3rd programme via catch up. I never have even the slightest glitch in picture quality.

I know any router needs igmpv3 to work. Then there's multicast snooping/forwarding/etc. Different vendors use different terminology.
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Weaver

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Re: Telly over IP
« Reply #10 on: May 04, 2018, 10:46:07 PM »

Do these systems get away with packet loss by error concealment techniques in the application layer so the user doesn't notice (as CD players do)? Or are users set to very conservative DSL reliability levels to ensure a low error rate?
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CarlT

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Re: Telly over IP
« Reply #11 on: May 26, 2018, 01:04:47 PM »

It's interesting what adrian says about it not working with non-BT kit. Could that be because it is being dealt with using ATM PVCs? Assuming we are talking about adrian having ADSL with ATM, not FTTC at that time.

No. Needs to support https://en.wikipedia.org/wiki/Internet_Group_Management_Protocol and play ball with BT's multicasting.

Regarding packet loss it can be left to the transmission network or there are a variety of options to take care of it both at transport layer and MPEG itself. DSL settings as far as I know not changed regardless of being a BT subscriber or not.


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