A question about DACS boxes

Lemming

Hi guys

I've been noticing that when I dial up to my ISP (dna/utvinternet) that my connection rates are rather bad of recent weeks.

I used to connect at a fairly consistent 45+ kbps for the last few years, but now my connections are sub 40kbps. Also, the dial up tone seems to get to the point where it should be finishing, then starts again, etc. My connections are lasting anywhere between 3 seconds and 15 mins. typically in the last 3/4 weeks.


My question is this .... is everything described above symptomatic of EirW*nk installing a DACS box on my line?? I need to know before I ring them up and give them SERIOUS abuse over it

dahamsta

My question is this .... is everything described above symptomatic of EirW*nk installing a DACS box on my line?? I need to know before I ring them up and give them SERIOUS abuse over it

I'll leave the actual answer to comeone else - I don't know - but here's a tip: don't start talking about DACs boxes when you talk to Eircom. It's a misnomer that's gotten a wee bt out of control on the IO forum, and it's /not/ how lines are split.

adam

Lemming

Cheers adam!

bkehoe

A DACS box usually limits connection speed to 33.6k and below. I'd suggest that you check all your cables, e.t.c. It could simply be a loose connection, or there is a small contact on the actual wire on the poles (recently saw an isdn line suffering miserably with around 80% packet loss as there was a slight contact on the line; if it were analogue there would have been cracks/pops).

Brendan

Fergus

OK everyone... heads up..

The thing that splits your metallic pair (i.e. the telephone wires coming into your house) into multiple phone lines is a LOOP CARRIER SYSTEM - NOT A 'DACS' BOX.

DACS is 'digital access cross-connect system'. This is a different thing. It is a way of automatic switching (cross-connecting) between multiple digital streams (like T-1 lines). afaik, it also covers switching of lower rate data streams ('bearers') carried within the T1 stream. Anyway, it's not what you've got on your line.

History:

Back in the early 70s, phone companies started running out of pairs (actual metal phone wires) over which to run local loops (phone lines). So, they started devising ways of getting more than one line onto a single pair..

Early solutions were known as 'multi-party lines' or 'party lines' (ahem). These were 'analogue loop carrier' systems. In simple terms, what they did was mix higher frequency waves on top of the standard audio signal on the phone line, and the audio for the additional lines (up to 8) was modulated on these 'carrier' waves. A box was fitted at the exchange end ('FXO') and another in your house ('FXS'). These boxes took the different pairs at the exchange end for the different telephone numbers, and did the multiplexing of them all onto one pair. And at your house, another box was fitted to demodulate the encoded 'carrier' line(s) and convert them back to individual pairs for you to connect your telephones to, etc.

So, in your typical one-extra-line situation, you had the original line's signal coming in on the pair unchanged, but a Loop Carrier box was added to filter off the higher frequency 'carrier' from the physical line, and provide a socket for the secondary 'carrier' line.

Hence, eircom would refer to a 'physical' line and one or more 'carrier' lines.

These loop carrier systems got more sophisticated and became digital affairs (afaik, the signal encoding on the carrier is done digitally). These are known as DLCs - Digital Loop Carriers.

I dunno what the state of affairs with eircom stuff is exactly, but I think there are probably various types of analogue and digital loop carrier units in service, depending on when they were put in.

In any case, they are all designed to only deliver PSTN (standard phone line) bandwidth on each line, which is 3100Hz. The universal service obligation for PSTN is to be able to support 2400 bits-per-second data or Group III fax. The latter means the most you can expect is 9600 bits-per-second full-duplex, or 14400 bits-per-second half-duplex.

As regards the original query about line quality.. there are lots of possibilities. However, I don't think V.90 modems are capable of achieving speeds above 33k6 (as was mentioned) unless they have a direct path to the exchange's ADC (analog-to-digital conversion). That means no carrier system on the line that would introduce additional stages of ADC/DAC.. I'm not sure about this - I'm open to correction.

btw, I think whoever you ring in repairs can tell from their database what lines are on carriers, and what lines are physical.

Lemming

Thanx guys!!

I'm gonna check out my cable running from the box in my room to the main phone box (its basically just an extension of the line).

I remember an Engineer mentioning something about the wires being rather fragile looking.
I'll ring Eircom whilst I'm at it.

I'll let ye's know how it went (if you're interested at all - or if anyone else is having problems like me?)

Fergus

Some master sockets (the first one on the line where it comes into your house) have a detachable lower cover. When you remove this, it disconnects all the other sockets in the house from the loop (assuming they've been connected in correctly). If you want to test your own setup, remove this cover, and then plug your PC in directly to the master socket using a short known-good lead. If it's all ok then, it's a local wiring problem.

Fergus

ok.. correction to previous msg.. DACS in the European context appears to be Digital Access Carrier System, which supercedes a previous analogue system apparently known to some as WB900 Analogue Pair Gain System).

Please see this page for more info.

Lemming

Hmmm ... I downloaded the DUN 1.3 file (and a couple of other related ones) from M$, which *kinda* fixed the problem of constantly dropping packets, although this still happened on a random basis.

Then a few days later the connection speeds just righted themsevles (along with the issue of freezing connections).

SO either every ISP was cocking up (or EirCon were up to their usual shenanigans of shagging up the telephone lines).