Wednesday, 7 August 2013

Nostalgia is not what it used to be (modems)

So, I have been listening to some of this today :-

WAV: 38 seconds of modem negotiate and chatter

Why? you may ask. Well years ago, not having any copper phone lines in the house, I set up a sipura as an analogue phone line for the Sky boxes. After much tinkering it would work maybe 1 on 5 times to phone home. This was just about good enough as it would keep trying until it got through.

Modem sync with old SPA112 firmware
A couple of tips if you find yourself in the same predicament - for some reason Sky like it if all your multi-room boxes call from the same number. We used to have one ISDN line (an ISDN2e with DDIs) in the house, and the sky boxes all had separate numbers and sky complained (wrote to me). I pointed out that the terms said they had to connect to one line (they did, we only had one ISDN line) but did not say anything about having to present only one number. Anyway, eventually, I set them to the same number and they were happy. The other thing I found is that they won't take a call from anything but an 01 or 02 number. Sending from an 03 did not work at all. Both of these facts may be a couple of years out of date though.

Now, having changed IPs at home since, and forgetting the password, and so on, I decided that rather than try and work out how to reset the old sipura I would buy a new one. An SPA112, 2 port TA. They are branded cisco now, and I am not entirely sure about having a cisco of any sort anywhere near my network, but it is useful.

Obviously, technically, they are A&A equipment as A&A, as a teclo, are providing an analogue phone line to me using this equipment, and I am connecting that to my Sky boxes.

The main reason for looking at this at all is that I am getting some of the sky boxes upgraded, and the engineers try and get them to phone home as part of the install, as I recall. So a 1 in 5 pot luck was not going to be ideal.

The new SPA112 worked about as well, after I set it up without echo cancellation, a-law only, no fax detect, no jitter adjust (set to high), UK line impedance, zero gain, etc.

So I was a tad disappointed, but it would have to do.

Then, just for the hell of it, I upgraded the firmware. The version that came with it was Oct 2010. New code is July 2013!

To my surprise the sky boxes now seem to work first time every time. They negotiate differently too. Before it sounded like a conventional modem sync as you might get for 33k or lower. Now, and correct me if I am wrong, but the WAV included here sounds more like the 56k style negotiation. I can only assume some changes in the firmware have improved the operation somewhat. Obviously there is no reason why it should not work - what I am doing is the same as what is done in the telephone exchange but with a much shorter wire involved.

Modem sync using new SPA112 firmware
So now it should just work when the sky man arrives... We'll see.

Of course, what they should be doing these days, is ask for the boxes to be on one LAN, now they have, and use, network ports. They can then phone home via the Internet and check other boxes at a MAC/Ethernet level. It is crazy that modems are still in use. Even so, not a sound I have heard in a long time.

24 comments:

  1. I have a particularly useless skill. Being able to identify the negotiated speed by the sound patterns .. although I suspect this is a skill many older folk who used modems have.

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    1. Quite - but it has been a long time - do you agree that wav sounds like 56k style negotiations rather than 33k or lower?

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    2. I don't have audio on my work PC :( - apparently it's not ok you play hard rock in the office ;)

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    3. Sounds like a 33k6 to me... I can't hear the digital downstream training that you get on 56K ... See, about 20 seconds into: http://www.youtube.com/watch?v=5qWg6cgFnIU - a distinct lowish frequency buzzing which I believe is the downstream being calibrated (which for 56K uses discrete voltage levels instead of audio frequencies)

      WRT analogue VoIP adaptors, I've been using an SPA3102 to connect my POTS line to Asterisk - only because BT give me free calls on the POTS line and I have to pay for the line to get ADSL anyway. I've found the performance variable to say the least - sometimes its absolutely fine, but other times I get really bad echo, which as far as I can determine is far-end audio echo (i.e. the sound feeding back from the speaker into the mic of the POTS-side phone). I can only presume that when it is being echo-free, BT are echo-cancelling the far end for me. I must admit I've not tried connecting a modem through it though.

      Asterisk is able to do an analogue fax handshake and gateway the traffic over SIP using T.38, rather than shoving the raw PCM over the network - I wonder how much effort would be involved in doing the same with a 33k6 modem connection (of course that also involves the SS7 gateway to convert it back to an analogue modem signal).

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    4. There are distinctive parts to the sequence which sounds to me like the match what you linked to on youtube. Part of it I note is once you get to the full rate data part there is a period with one side, then the other, then both, for example. That is pretty distinctive to 56k I think. If someone was really clever they could decode that wav and fine my sky credentials :-)

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  2. It's totally nuts that they even need a phone connection these days. I'll be trying to provide one for my Sky box soon - not sure how to manage the onward connection yet - but they really ought, at least with HD, to do it differently.

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  3. Latest firmware update on my Sky box states I no longer need a phone line to order movies, just connected via Ethernet.

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  4. I thought part of the reason for the phone line connection was to try and prove the device was in the UK in terms of rights restrictions etc - while clearly you can get round that by using an ATA, I guess a large number of people who might otherwise just take the box abroad wouldn't have the knowledge to do so.

    It might also explain the 01/02 restriction they have in place - as far as I know nobody provides a real analogue POTS line that's on anything else...

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    1. Depends what you mean by a real analogue POTS line. AFAIK there are/were 0800 POTS lines back in the day. But even so, A&A is a telco and can provide a "real analogue POTS line" going all the way to a sipura (as A&A do in my house) on any number you like pretty much (well, any area code / prefix). It may be that we can SIP interconnect to BT or TT or someone to do on lines taht are analogue all the way to the exchange real soon now. That will impact Sky's logic (I hope).

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    2. AFAIK the point of phone connection is to prove that multiroom boxes are physically located in the same house (connected to the same line/number).

      Without multiroom, a box bought from Sky (including upgrade) must be connected to phone line for a year (only), no need for ebay or re-seller bought upgrade (a call to Sky to change your box serial is enough). The reason was originally to avoid the resell of "nearly new" subsidised box (as it would change phone number), and at the same time ensure that everything is in place to easily buy pay-per-view (which is also provided over IP by last update).

      To limit the number of box abroad, the need for a UK address and payment (Direct Debit, card) is I believe the main mean of control.

      With multiroom, all the boxes need to be permanently connected (no 1 year limit).

      A box sent abroad, is still full scale revenue for Sky, multiroom boxes in different place is a loss revenue for Sky...

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    3. Their interest is in being confidence both boxes are in the same home. On a "normal" (01/02) line they feel relatively happy, but other numbers make it obvious you're doing something "odd" - like having the boxes on SIP adapters instead of plugged into your home phone line. Without that check, for example, my brother and I could share a single Sky subscription, paying £10/month for multiroom instead of a whole second subscription, and doing cunning SIP redirection so Sky sees both sets of boxes calling home from the same number.

      Sky boxes are pretty picky about the connection - I'm not sure if that's intentional (to make it harder to pull that trick off) or just wobbly design, but I remember getting the Sky nastygram when one of them was connected via a DECT extension rather than hardwired.

      My next little project is trying to get decent bandwidth over a spare short run of coax between floors; the best pair of bridges I can find so far seems to be around the 200 Mbps mark, which is disappointing. Then to try SIPifying my own Sky boxes ...

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    4. The phone connection is used to prove multi-room boxes are in the same room (years ago I "dodged" this by waiting til I got the letter moaning, taking the other box to the place of the first, forcing it to dial up a couple times, taking it back.

      I didn't feel it particularly wrong since I just wanted to watch my Sky sub in the 2 different places I lived at the time and wasn't prepared to pay for another full sub given I wouldn't be able to watch both at once (and this is before Sky+ etc).

      The "first year" thing as I understood was because the interactive TV part was provided by someone else and gave a subsidy as long as it could dial-home and thus provide the interactive part.

      More recently I've agreed that Sky can upload data on my viewing habits in return for paying next to sod all. I'm sure they'll be thrilled at the number of times I watch repeats and the amount I record, never get chance to watch and find deleted before I am home long enough, but hey...

      It's the CLI they use to determine where the box is, and yes, it only accepts 01/02 otherwise 2 boxes in another country would also be "OK"

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  5. I have to say it really does make me reminisce when I hear these sounds

    https://www.youtube.com/watch?v=0iuI1ej36o0

    ending with ... *youve got mail* .... arrrrgh!

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  6. I have to ask what number does your sky box call as mine wants to call 1272 which an A&A sip trunk won't allow :-(

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    1. An 0800. The 1272 may be some carrier pre-select. Check the settings on the box.

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    2. It does seem to be used by some sky boxes.. Possibly older ones. Obviously won't work on non-BT providers (unless A&A rewrite the number to the proper one :p)

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  7. Nope I did. If you dial it from a BT line a modem answers

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  8. I've got a couple of pap2t doing this, with my clid set to my landline.

    I completely failed to get it to work with a dect extender.. With VoIP you can tweak things like gain until it works.

    Still not got the multiroom card yet though (two weeks and counting..)

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  9. I think the "boing boing" sound towards the end of the negotiation was added when 56k came it.

    Cheers,
    Howard

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  10. Can you share the config for the spa112?

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    1. It is on the A&A wiki somewhere.

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  11. This is so sad, that I recognize this as greater than 33.6 K. Sound like 48K to 56K. V90 if memory recalls.

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