Cable vs. DSL, Explained

Alan Shutko writes "Simson Garfinkel has a great article on Salon which explains the relative merits and disadvantages of cable modems and DSL. This should quiet the cable/DSL wars seen occasionally. " Very good overview of the difference between cable and DSL, cutting through the hype of the various companies.

Comments

DSL technical details

[Narbo]

Just for informational purposes im quickly going to run thru the major methods of getting a DSL connection. I imagine the same applies for cable.

When you power up your DSL modem the first thing that happens after the power on test is it attempts to sync with a line card in the captive office. Depending on what kind of system you are on this could be at anywhere from 100kbps to 9Mbps and down. Typically up tends to be significantly less then down (usually in the 320kbps to 1.5Mbit range) but it does not have to be.

There are several encapsulation methods used to get packets over the DSL wire all of them revolving around ATM.

The end to end connection typically looks something like this:

PC --Ethernet-> Modem --DSL-> LineCard --ATM-> ATM Switch/Router --Whatever-> Internet

From there it your data can bounce around the net
being re-encapsulated until it eventually becomes ethernet again. :)

Typical encapsulation methods over DSL are:

RFC 1483 Ethernet over ATM (most common)
RFC 1577 Classical IP over ATM
RFC 2364 PPP over ATM

1483 encapsulation involves setting up a bridge group on your router. A bridge group is essentially a software hub that sucks in packets from multiple connections and forwards them along to wherever they need to go.
If you have a setup like this, when you look in your arp cache you should only ever see the (fictional) MAC address of your bridge group.
(and your modems MAC assuming its not a dumb bridge either)

1577 isnt used much in the real world as it requires more effort to setup and maintain.

2364 is becoming more prevalant, especially a nasty variant called PPP over Ethernet which is like a combo of PPP over ATM and 1483 bridging.

Just so you can see all the work thats going on
here are the quick protocol stacks for the data encapsulation methods before the data ever hits the phone wire. (pretty complicated :P)

1483: TCP/IP->802.3->RFC 1483->AAL5/ATM->ADSL
1577: TCP/IP->AAL5/ATM->ADSL
2364: TCP/IP->PPP->RFC 2364->AAL5/ATM->ADSL
PPP over Ethernet: TCP/IP->PPPOE->802.3->RFC 1483->AAL5/ATM->ADSL

Anyhow, hope this was useful.

Oh yes, one last note about speeds. While most DSL available today sits in the 1Mbit range or so
within a year or so high speed DSL will start to roll out offering equal or better bandwidth compared to cable (i.e up to full 10Mbit down and 1.5Mbit+ up)

Enjoy the competition, its good for you the end user.

-N

DSL vs cable

[Captain_Lou_Albano]

I work for an DSL provider in Wisconsin. I see these arguments all the time. I rarely try to argue anymore.

The reason for this is because when you see a cable vs DSL argument on the irc, in newsgroups, or even in person, the people arguing are almost always arguing about the cable modem service in THEIR AREA vs DSL service in THEIR AREA. It's never an argument about the technology, always about the providers. They always talk about bandwidth on adsl or sdsl being less, but this is probably a function of the provider throttling it down. Everyone talks about security on cable, but this is all relative as adsl or sdsl can be just as lax if not implemented properly. It's almost an apples and oranges argument.

This Salon article is no different. He is comparing PacBell dsl (which sucks) to MediaOne's cable service. This is not representative of the technologies involved and frankly makes me a little upset.

Hopefully someone (maybe me) can find a good link to post that compares technologies, not services.

Or maybe someone who really is involved with cable technology can write a article here on cable technology, and I or someone else would be happy to reply with a similar paper on DSL technologies.

-=Ex-manager of Wrestlers=-

Plug for cable?

[pod]

The article was anything but impartial and well balanced, I found.

The description why cable modems are cool (page 2) applies equally well to DSL. In fact, take the first few paragraphs, replace cable with DSL and you have a perfectly good and valid piece of writing.

To say that a DSL line is shared with the phone service is a lame excuse. The phone line bandwidth is so tiny compared to the total frequency range of the line DSL uses, that it's not even an issue, certainly nothing even close to the amount of sharing going on on cable lines.

In the same paragraph saying that cable is the king of bandwidth and that the writer gets 7 mb/s is the statement that the modem is limited to 600 kb/s. So which is it?

And then the dismissal of the issue of line sharing (page 3). If you get 600kb/s on a cable modem, and that's enough to satisy you, then DSL will do fine as well. I routinely get 600kb/s on DSL and I'm near the bottom of the serviceability scale for DSL.

Then you have the upload speeds. How can standard cable service even compete with the ul caps?

And prices for DSL are coming down fast these days, at least over here (Calgary, Canada). You can get a 768kb/s line for some $50/month (Canadian!, that's like 5 cents US), which almost matches cable service prices.

I will admit, that from reading warious posts around /. and other forums, DSL service (as in people service) sucks; this gives a lot of advantage to cable service. But the article is not a well balanced article on cable vs DSL; rather it's cable vs 'something I've never really tried just heard about and I hate it and I think cable is oh so cool' article.

So lets keep things in perspective; this article does cut through some of the hype about cable, but merely mentions DSL in passing as some other internet technology.

Ugh, it's too early for this...