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mdf



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Topic # 114385 18-Feb-2013 11:37
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A query about the underlying technology of cable vs DSL internet (and whether I closed a door in a guy's face unnecessarily).

We're on TelstraClear's cable/inhome network in Wellington (naked broadband, using VOIP for phone services, generally very happy).

I got door-knocked at the end of last week by someone representing/trying to flog off Telecom services, particularly Telecom broadband. He got my usual response (this has happened before) of "thanks but no thanks, happy with Telstra, I think their technology is better than yours".

To my surprise, the guy started arguing pretty vehemently that the technology was actually the *same*, and that Telstra used ADSL2+, which was exactly what Telecom was offering - even going so far as to say that the modem I already had (a venerable Motorolla surfboard) was an ADSL modem. By the time I started to get a story about "my mate that used to work at Telstra", the door was closing.

I am sure there is probably scope for argument about the respective merits of cable vs DSL, and that my view that cable is better (at least in Wellington for now) may well be wrong. But I wasn't prepared for an assertion that it was both the same - I had understood that DSL and cable broadband technologies were fundamentally different. However, I don't have a clue about the actually technology and why they're different (though I can quote some acronyms I found on Google), so I then started to wonder whether he was just a bit inarticulate and that maybe the *underlying* technology or some such was the same. Professor Google seems to support my initial view that cable (or at least, HFC cable) and DSL are fundamentally different. However, most of the articles were reasonably old and focused on the States.

Is anyone able to help me shed my nagging sense of guilt?

Cheers,

[EDIT: spelling/formatting]

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  Reply # 764072 18-Feb-2013 11:41
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They are different technologies, however TC do also deliver services over DSL in some areas as well - perhaps the sales guy thought you were in a DSL area?

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  Reply # 764074 18-Feb-2013 11:43
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They are different technology, you are absolutely right.

ADSL is a point-to-point connection over a twisted pair:

http://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line

Cable is delivered over coaxial cable (and one cable is shared by several subscribers) - it works more like ethernet.

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  Reply # 764075 18-Feb-2013 11:45
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Nah, I told him at least twice that we were on cable. I even pointed at it (we are "lucky" enough to have the big fat black cable on the lampposts, not trenched). He also referred to Telstra's "gigabit" plans (which I'm not sure actually exist), but I'm picking aren't a DSL thing.

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  Reply # 764079 18-Feb-2013 11:46
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Awesome, thanks. Nagging sense of guilt definitely shed. 

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  Reply # 764080 18-Feb-2013 11:46
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The salesman needs a bullet.

Cable is completely different to ADSL. He just assumed you were on ADSL rather than Cable but after you told him he should have figured that out. Would love to see the salesman when you showed him the Cable modem. "yea you can just plug your line cord in to.... oh.... umm..... BYE!"

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  Reply # 764081 18-Feb-2013 11:48
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A bullet might be a bit much. I favour the SPCA approach - capture, neuter (or at least, retrain), release.

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  Reply # 764088 18-Feb-2013 11:52
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Cable and DSL are different.  Cable is actually quite similar to GPON UFB: there's a shared downstream and upstream channel, and a head end that arbitrates who gets to talk on the shared upstream.  There are lots of these channels and corresponding headends.  Your cable modem picks out the data destined for it on the shared downstream, and ignores the data for other subscribers.  Then the headend talks to a router and your data gets to/from the internet via that.

DSL is point to point, your modem gets what is essentially another modem at the other end of the line (at the roadside cabinet or exchange) to talk to.  Which sounds great, right, it's not shared!  Unfortunately it's also not that fast.  And the modem at the exchange end (that's the DSLAM) then connects to a router, so the pipe from the exchange onwards is shared.

There's no fundamental reason why one has to be faster than the other, up to a certain point -- you can get faster DSL modems (VDSL2), and you can get faster cable modems and headends (DOCSIS3), and you can vary the number of subscribers sharing a headend.  But at least with what's available in NZ at present, cable is faster because you can't squeeze 100MBps over VDSL2.

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  Reply # 764101 18-Feb-2013 12:06
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Cable uses DOCSIS technology, with TCL having deployed DOCSIS3 on their network which requires a newer Surfboard modem.

There are pros and cons to both technologies, but the main difference being DOCSIS architecture is a shared connection whereas xDSL is a point to point connection.


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  Reply # 764106 18-Feb-2013 12:17
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My only comment is, that with cabinetisation if you these days are comparing 15Mb/s HFC services to DSL then there is not much of a difference, well at least in the performance of the connection from the network to your house, depending on what ISP you with on DSL can make a difference.

Cyril

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  Reply # 764158 18-Feb-2013 13:54
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sbiddle: Cable uses DOCSIS technology, with TCL having deployed DOCSIS3 on their network which requires a newer Surfboard modem.

There are pros and cons to both technologies, but the main difference being DOCSIS architecture is a shared connection whereas xDSL is a point to point connection.


  • The current DOCSIS 3.0 modems being used by TC^H^HVodafone Fixed are Cisco.
  • xDSL is dedicated up to the DSLAM and shared thereafter. DOCSIS is shared up to the CMTS (rough equivalent of DSLAM) and shared thereafter, except that the shared bandwidth of DOCSIS is measured in Gbps, not Mbps.

Also, since no-one runs Annex B in NZ, the upstream of ADSLx is <=1Mbps (Annex B would raise it to <=2Mbps). TC^H^HVodafone Fixed run a minimum of 2Mbps upstream and could run higher—DOCSIS 3.0 can do 100/100 although that tends to be a bit greedy of upstream resource.

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  Reply # 764170 18-Feb-2013 14:11
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I think you mean Annex M Michael. Tongue Out

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Reply # 765590 19-Feb-2013 09:17
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sbiddle: I think you mean Annex M Michael. Tongue Out

[blush] I probably do Steve.


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