Cable Modem vs. DSL

27 posts
Hey Guys, what's the pros/cons of DSL over cable modems? I have a cable modem now, but I may want to switch. What hardware diff. is there? Is the DSL "always on" like the cable modem?
Most DSL providers won't have any problem with you putting up servers on your connection. On cable according to the service agreement, you aren't supposed to be doing this.

Some DSL is constant, some is connect on demand. To the end user, it appears the same, with a slight delay when it has to reconnect. You don't have to do any special dialup or anything, just use as you would normally use. I don't know if you can successfully run a server on "dial-on-demand" systems though, don't think the "demand" goes both ways.

I would go with whatever is cheaper. I have cable and my friend has DSL. Mine is faster most of the time, but did go out when the cable was out. Media One has a policy that you can only run it on one PC, but i got dual lan cards in my case and run it out to my parents computer as well. I also have another friend who ran his cable into a rotor and has it on a couple PC's. Says it works great. I'd probably stick with cable.
The General
Chicagoland area, N shore area, @Home / AT&T service - no servers allowed, frequent DNS and popmail outages, but most of the time just works. $42/mo, if you already have cable, $10.00/mo more if you do not have cable TV service, 2 Mbps off peak, 200-300Kbps peak time, pseudo-static IP (they use DHCP but give you the same IP address everytime, based on your computer name - great for video and voice over IP). bps = bits per second, Bps = Bytes per second, 1 Byte = 8 bits

Ameritech DSL - 768/128 service, allows servers, but for $39.95 you get a dynamic IP (see - speedpath service). They changed their FAQ, as they used to require an ATM25 network card in your computer - now it seems like they are OK with standard Ethernet. I have not used it, so I cannot comment on real life throughput, and some options (extra E-Mail addresses) are advertised but not priced on their web site.

Both place limits on the traffic for your personal web site hosted on their servers, with the cable guys listing a ridiculous number (25MB/month), and Ameritech DSL about 3Gbits / month (divide by 8!).

Prices and services vary greatly across the US, so my experience from Chicagoland may be totally irrelevant to you - you may want to restart this thread listing your location.

If you DO go with DSL, make sure you get an external modem. I opted for the cheaper internal, and now I'm doomed to languish in the Win98 gulags. I won't make that mistake again.
The cable that brings it into your house is less important than the provider connection. I have DSL here in LA and it USED to work great - but lately I can't even stream a goddamn 300kbps file. BURST rates are still adequate - but that's useless for "the real world." Better still, because it's DSL it doesn't matter if I go with someone else, because PacBell is the bottleneck, and all the other ISPs connect via the same "cloud."

I'd suggest you go to the local provider's web pages and contact some of their customers via their "user directories." Find out from the existing customers who actually delivers the quality of service they promise.


I'm from Switzerland and use a cablemodem. If u wanna play Quake3 or sth like that - stick to DSL ;-) Shared uplink suxx for that sometimes.
I have a static IP and 4Mbit down 256Kbit up for a bit more than 120$. Downloadspeed can get up to 340kb/sec (not bit) so thats possibly more than most people with dsl get. But as I said its not ideal vor gaming Q3A...
Hopefully u get a good ISP for ur cable. Its not important how fast u r sometimes...


If you have a hub is it really neccesary to have two NIC's in your PC if you want to share your DSL connection with other PC's on your home LAN?

I currently have a home network and use use Win98SE's Internet Connection Sharing to share my desktop's 56K connection with my laptop. It works fine.

If I can help it I'd like to avoid adding another NIC to my desktop - I won't have any PCI slots left if I do that!

Nope, you gotta have a second ethernet card. With the setup you have now, the 56k modem is performing the same function as an ethernet card would with a DSL/cable setup.
Precisely seandelk,

You will have to have a 2nd NIC in order to bridge the 2 segments and right now you modem is acting as a virtual "wan adapter" anyway.


Haarmann, man, maybe cable is inadequate for you in playing Q3A but its been heaven here. I live in an apartment complex and only one other person in this huge complex has Road Runner besides me, up and down speeds been a huge departure from 56k dial-up, hell I ping at an average of 85-95 when playing Q3A.


Cable all the way, (at least til everyone else gets it, then its DSL!!!!)

[This message was edited by Tres-a.k.a.-=ion55=- on April 24, 2000 at 10:04.]

I have no DSL experience, but I love my cable modem. I've had it since late 97, and it seems as if the average speed is just getting faster. I was downloading a large file this weekend, and it was peaking at 700-800 KB/s.
I've been a Roadrunner cable modem user in San Diego for 2 years now. Since I began running a Linux IPmasq/firewall box between the cable modem and my HUB, I am able to observe an average of 3 attacks on my box each week. Port sentry works well to deny these hosts after they attack, but my node is scum.

Maybe if you leave in a less urban area, with a less technically sophisticated population, this could be less of an issue.

Is this attack from customers on the same node common to most cable modem users? How is DSL in this aspect?

Ok, so I'll share DSL by using two NIC's in my main PC, with one connected to the DSL modem and the other connected to my hub.

But will this setup be a real security risk? Realistically, would I be better advised to go ahead and shell out the $$ for a router? Or is the threat perhaps overstated?

A router may be better for security, but you may need to do some tweaking, as some applications will stop from from working properly with a NAT / firewall box in place (NetMeeting is one of the popular offenders).

Linksys BEFR41 is low cost solution - dedicated NAT box plus 4 port 10/100 switch for about $160. If you do not already have a hub or a switch, and are not familiar with setting up and securing a firewall/NAT box, it may be something to look at.

I like my DSL. I just stuck the modem on the hub's upink and it works fine, don't need 2 NIC's on the linux router. Since I'm using PPPoE :/ I have to log in (takes 3 seconds).
Ok's here's a Question how's uploading with cable vs DSL, also i keep hearing different stories on sites I've read about which is actually fastest, Which is it? I know cable can fluctuate and I heard DSL is always a constant speed? is this true? I on a T3 at work but still using crappy 56k at home at least for now... thanxs


DSL's point-to-point. Provided the router can handle it, if you're subnet neighbor decideds to download a movie while you're gaming, you'll never feel it.

On cable, if someone on the same wire as you decides to download something large, you'll feel it. You're sharing the media with other people.

Both on cable and DSL you are sharing bandwidth with other people. Once you get to your ISP, (actually when you hit the first router - cable node or ADSL point of presence,) your link to the rest of the world is shared, and oversubscribed. I've read that @Home (cable) has its bandwidth oversubscribed up to 1500:1 for some nodes, and would like to get it down to 100:1. I do not think that DSL providers are much better.
Even if you have 768Kbps or 4Mbps clear and unshared connection from your desktop to the first router/point of presence using a DSL connection, from that point on, you have shared bandwidth, and the very same oversubscriber issues as you have with cable.

The uplink bandwidth available to any cable node or ADSL concentrator is much less then the sum of all downlinks, simply because of economics - not all downlinks will be used all the time at full speed, and you do not want to pay for wasted bandwidth. In fact, for @Home or other big ISPs, you have successive levels of oversubscribing, as they try to minimize the costs associated to linking their points of presence.

This is the same theory as employed for big Telephone Central Offices, where the number of phone lines linking a CO to the next is much smaller then the total numbers of phone lines coming into that CO, or for small PBXes, where you commonly see 3:8 and 4:16 models (3 outside lines and 8 extensions).

If your buddy is local, on the same cable node or ADSL point of presence, you will have shorter ping times then if he is across the country (both of you are on the same router). If he lives across the street and his ADSL line goes to another POP/central office, while he is on the same cable node, (not so uncommon here in Chicagoland,) ping times between the two of you may be better on cable then ADSL.

As more people are added, some will move around from cable to ADSL and back, based on cost and performance, so I expect that both cost and performance will be in the same ballpark, in a given area, for both technologies, after some time. ADSL is likely to hold an edge for ping times and real-time games, but for surfing and downloading stuff, they should be pretty much the same

With cable, you compete DIRECTLY for access to the local wire - you SHARE THE MEDIA

With DSL, you DO NOT share the media. Your wire is yours alone.

If someone decides to start videoconferencing on the cable wire where you live, you will see your download rates plumet, relative to what they were.

If someone does that on my DSL subnet, I will not feel it, unless you think an ATM link can be easily oversubscribed.

You get a smooth, dedicated amount of bandwidth with DSL. As load on the internal infrastructure rises, everyone's equally affected. Routers, switches, etc. will BUFFER data. They're not going to arbitrarly drop packets until the load becomes too great, and when that happens there's major infrastructure problems and everyone will feel it who uses that router.

With cable, your bandwidth is all over the map. With no one on your local wire, you're in great shape. If 20 people move onto your wire, your bandwidth will be cut to 1/20th of what you had, if everyone decides to talk at once. Meanwhile, your friend across town on a still unoccupied wire will not feel the effects of your 20 new neighbors.

What Luc fails to realize is the impact that sharing media can have on a connection. Sharing media with others means your ping times and download speeds are going to vary widely. With DSL, I get a CONSISTENT ping and download speed. It's always the same. It doesn't matter if the others in my subnet decide to download at the same time or not. Upstream of us is where the chokes are, and that will affect EVERYONE EQUALLY, as opposed to sharing media, where it's a best-effort system and contention based.

As far as I know, Cablemodems don't use a token passing system to control access to the wire. It all comes down to who grabs it first. Theoretically, as with Ethernet, your cablemodem could wind up NEVER accessing the media (it is theoretically possible). That's not true in the DSL case.

Either one is better than 56k. Cable's got more raw bandwidth, but uses a contention-based system to determine who gets access to the local media. DSL's got less bandwidth, but you're not contending with anyone else for media access, so it is more stable.

What do you want? A sub-50 ping that spikes to 250, or a consistent 100 to 120ms ping?

That's the difference between cable and DSL.

IceStorm, if all the guys on your subnet decide to download big files at the same time, your uplink will degrade the performance for all. If you live next to a central point of presence where the uplink is ATM at 155Mbps, you are in good shape. If your ISP has one T1 line running from the telco POP where he has the equipment for hooking up his 20 ADSL customers in your area, to his site and from there he has a fractional T3 uplink, you may run out of luck, as the bottleneck is going to be the T1 between the central office and the ISP. In an ideal world, you should not see such a setup, but for now, it is more common then a lot of folks realize.

I do agree with you, that given a choice, ADSL may be a better alternative compared to cable (I too value consistency more over burst rates), but I am pointing out to the oversubscription issue, which will get worst fast before it gets better, and was not mentioned before in this thread.

Re. cable, you have a 25Mbps down channel which is shared, so it will take more then 2 computers connected at 10Mbps to saturate it.

I was hoping to see from you some comments regarding network architecture variations between various ISPs, and how do they connect to the backbone routers, as this will become more and more important into the future, in the context of oversubscribing bandwidth. I see more and more small ISPs with only one uplink, or when they are multihomed, they have asymetric connections - a T3 and a T1, for example. Also, peering is going down, due to big guys charging the smaller ISPs to enter into peering agreements, and this reduces the reliability of the big net as a whole, as you cut down the number of possible path between any two points. Care to comment

I would also like to mention that on cable modems, the router in the head-end determines what comes down the pipe; you can have no collisions in the 25Mbps downward pipe, the data is coming down as fast as possible, and if the router is doing his job properly, no data stream for any given client will monopolize the pipe. On the upload path, the cable modem does some buffering, and you have more then one small shared pipe going up. It is more like a bunch of small pipes, and the modem will pick up one which is free (frequency division) - again, much more efficient then classic shared medium Ethernet. This is the only way they can oversubscribe cable more then 1000:1 and get away with it..
Luc, you're not getting it.

Cable media access is CONTENTION based. You'll never get 100% utilization of the wire. The best you'll get is 40 to 60%. After that, it collapses under the retransmission and collisions, so that 25Mbit/sec you're quoting becomes roughly 12.5Mbit, and then that's divied up between users.

DSL is NOT contention based. My 640kbit/sec is MY 640kbit/sec. I have yet to find an instance where my download speed was limited by my ISP. I get my 640kbit (minus %20 for protocol overhead) all the time.

No one person can hog all of the bandwidth on a DSL subnet. As load increases on infrastructure, it will slow everyone down EQUALLY. As I've said, I have yet to see this occur. Even durning peak usage times, I get 55 to 60kbytes/sec.

On cable, it is possible for ONE SINGLE USER to grab ALL the bandwidth on the local wire, even IF there is enough availble upstream to handle two or three people at full load. This is the problem with contention-based media access:


If your ISP used a T1 to tie together cable or DSL POPs, they're not a very good ISP, and you'll know that right away. Mine uses ATM links to feed from the DSLAM into a switched network that uses more ATM to feed up to the routed network, and out into the GSP's network. ATM, for a telco, is cheap, as it integrates directly into their existing SONET backbone.

With cable, you're pretty much stuck with ONE ISP. They own the infrastructure and the modems and the access points. I'm not aware of much, if any, competition within regions. Where I live, there's only one cable provider, and the town won't open up to multiple providers, so even if cablemodems were available, I'd be stuck with @home's offering (128kbit/sec upload cap).

With DSL, there are not too many layer 2 providers, but there are a large number of ISPs. I'm on Bell Atlantic DSL, which peers with Qwest/Iconnnet (same company). Other regions use GTE as their ISP (still BA Infospeed DSL). I'm screwed if the Qwest link goes down. My second line, should it ever be installed, will be from Speakeasy, and go to InterNAP, which peers with 12 different ISPs, so the speed with which I feed into other GSPs and ISPs should go up, as there will only be 3 to perhaps 5 hops between myself and another ISP/GSP besides InternNAP. I'm still screwed if InterNAP's link to Speakeasy goes down, but that's why I'm not dropping the BA DSL line.

Cable tries to treat the Internet as a LAN. It's not. DSL treats it as a WAN, which is what it still is.

IceStorm, please read a couple of cable modem specs....

In a cable modem system, your download channel is ONE, the uploads may be more then one, and they ARE ALL SEPARATE. The separation is in frequency, and they are FULLY INDEPENDENT. On the download 25Mbps channel, there is only ONE transmitter, in the head-end. You CANNOT have collisions on the download path with only one transmitter. The bandwidth is 25Mbps in the current generation installations, all 100% of it. I hope that you are up to speed with frequency separated communication channels - they've been in use for well over 50 years (radio is a good example).

Cable modems have a 10Mbps 10BT interface; the electronics in the modem capture the packets comming your way at 25Mbps and if they are addressed to your modem, they are regurgitated at 10Mbps to your computer. I repeat, the 25Mbps is a clear DOWNLOAD ONLY channel, which cannot be interferred with. If the router spits out too many packets addressed to your modem, without interleaving some packets for other folks, you will have an overrun condition in your modem, and actually loose packets.

The return path from cable modems is where you may have trouble with contention, not on the main path. I repeat, on the main path, you have a router spitting out packets as fast as possible, at full 25Mbps. The potential problem on the upload path is why cable modem systems are not happy with heavy uploads - you can create trouble for everybody if you run a web server or stream music, even at a low rate. The fact that you may have more then one upload channel, which the modem choses dynamically based upon availability, helps but cannot eliminate the issue. If your request packets do not reach the head-end router, or get discarded latter on due to traffic, you will not get what you expect on the main channel, and after a while your computer will timeout the request, and try again. If everybody is just surfing the web, with no heavy upload activity, the degradation in performance with the number of users, is handled by the head-end router, and is smooth.

The router in the head-end is in charge to insure that everybody gets packets. It is not possible for a single user to grab the whole channel, as long as the router gets requests from more then one computer. With more then one upload channel available, you would have to lock away ALL UPLOAD CHANNELS, and you cannot do it with a single computer (only one upload channel per modem at a time rule). Even locking away ONE upload channel is close to impossible, due to the safeguards built into the cable modem itself.

Cable may be less efficient then ADSL, but please don't present inaccurate information about alleged collisions in the 25Mbps channel, or say that one computer can lock away a whole node - it is not true.

Hope this helps.

[This message was edited by Luc on April 27, 2000 at 16:49.]

A short summary:

ADSL - POP router handles downstream download/upload connections and traffic issues.

Cable - node router handles downstream download traffic issues, but you have contention on the upload channel(s). There is no extra contention on the download channel, compared to ADSL - the router fits as many packets as possible in the available slots. The slots are in the same physical channel for cable (time division), and on separate lines for ADSL, but this is not relevant here. On the upload data path, there may be more then one data stream going to the router. As long as upload data activity is light, performance is quite similar to ADSL. Under heavy upload activity, with many users trying to stream data, you may get gridlocks - nobody can send requests for data, so nothing comes through the main download channel (which may theoretically even get idle, under extreme conditions).

For both, downstream and upstream download bandwidth are not the same, with more slots available downstream then upstream. In other words, total possible bandwidth for all ADSL or cable csutomers connected to the same router most likely exceeds uplink bandwidth, and the router will decide what packets to drop. For downstream data, they work the same way

[This message was edited by Luc on April 27, 2000 at 17:32.]

The FAQs on cablemodem that I've read have said that the modems are SHARING the wire. They're using TDMA, not CDMA. Each one is apparently getting timeslices on the wire. Assuming that one cannot take another's timeslice, then yes, the available channel carved for cablemodems can be used (don't forget that the wire's also delivering cable TV service).

However, you're still fighting with your neighbors for a slice of the SAME wire. You don't get a 25Mbit channel all to yourself, you get a SLICE of it. And even if you had a 25Mbit channel to yourself, you couldn't use it all.

Again, the more people you stick on the local wire, the worse the performance is.

And you are AGAIN confusing wire with subnet. Because they're all on one wire does NOT necessarily mean they're the ONLY ones on a router interface. That's the point of the separation of layers. I would suspect they're aggegated, then fed to a router using something other than a cable medium.

This is what is deployed today. This is what you can get today. Future rollouts may use a totally different system, perhaps what you're talking about, but the fact remains the more people you put on a cable segment, the lower your available bandwidth is, and it's not because of a router bottleneck, it's due to the way the wire is accessed.

And then you get into the systems which don't use security to prevent other modems from seeing all the wire traffic. Pop a sniffer on that, and you can see passwords, e-mail, etc. And those older systems still exist. Again, all "benefits" of a SHARED MEDIA.

DSL doesn't have this problem. You can choose your provider with more flexibility. You can choose different speed grades and even guaranteed delivery speeds. You have a lot more flexibility with DSL than you do with cable. And you get your wire all to yourself.

Yep, you have many modems and TVs, all connected to the same cable - that's sharing! On one cable you have many RF channels - Tv, radio, internet access band, etc. - first layer of separation, based on frequency. In the internet access RF band, you have to use a modulation of some sort to transfer data and create your upload/download data channels. What modulation you use is less important, you still have a downwards data channel with one transmitter and many receivers attached to it, and one (or more then one) return channels, each with one receiver and many transmitters. The fact that multiple data channels share the same spectrum DOES NOT mean that they are not fully independent and it DOES NOT mean that they interfere with each other.

Looking at the main 25Mbps downwards data pipe, you have data packets, each one for a different computer. This is time division for sending data. There is no contention on this channel, as only the head-end may talk on this channel - all cable modems are listening for data, and pick up their share. On older systems, the ethernet card was used to pick up the right address so you could sniff. On newer systems, the data rate on the downwards datastream is much higher (25Mbps), and a 10BT interface cannot keep up for sniffing or finding its packets.

On the returns channel(s), you have a fight for ownership of the channel, so that you can ask for data. This is the botleneck on current cable systems. More then one return data channel is nice, but not THE FIX

[This message was edited by Luc on April 27, 2000 at 18:33.]

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