Trif - cable/dsl -
Just thought I'd pass along this nice little bit of info on a comparison on them...
Originally posted to comp.dcom.modems.cable
They see the (50|100)x faster than a standard modem tagged on Cablemodems and ADSL alike, but they don't understand some of the fundamental differences as well as similarities. I'll briefly run them out for everyone now. For the sake of this post I will refer to bits as a 'b' and bytes as 'B', therefore kilobits = kb & kilobytes = kB.
1. Preformance
------------------------------------------
ADSL- Has fixed upstream/downstream capabilities. Most providers limit at 1.5mbit/s downstream and anywhere from 256kbit to 640kbit upstream. ADSL is technically capable of about 8mbit downstream and 1mbit
upstream, but I have yet to see a prodiver that gives this (and that is pushing the distance/noise envelope). This means that at *NO* time will you be able to burst above about 180kB/s downstream (assuming 1.5mbit downstream, all ADSL comments are based on BellSouth's service, which is on par with the industry) and locally about 25kB/s upstream (256kb upstream on the local ADSL).
Cable- While bandwidth "caps" are common on the upstream connection (or will soon be), I have never seen the downstream limited. The bandwidth cap can very from provider to provider and area to area, as many of the new "suber" cable co's are just really a bunch of local cable companies under the same name. Locally the limit is about 60kB/s for the Mediaone modems, equating to about 480kb/s upstream.
Technical limitations of most cable modems place the system and the Ethernet at the same preformance (10mbit both ways and assuming 0 collisions and 100% utilization, is about 1.2MB/s or 1200kB/s), which is probably why they called the Bay Networks cablemodems LANCity, since you really did make a LAN of the city.
All currently available external 2-way products (all I have read about are external) are limited by the factor their Ethernet jacks are only 10bT and you can only get 10mbit each way, no matter how fast the network is capable of going (I haven't seen any 2-ways capable of anything higher than 10mbit on the cable side, as line noise is a big problem with sending data over the line).
For practical purposes you can expect 200kB/s downloads almost all of the time, and on some Saturday mornings I have been known to get upwards of 400kB/s from INTERNET sites, the rates are normally much higher for inter-network transfers (IE- from the cable's webservers), and these expirences seem to occur all over, no matter what brand of modem you are using.
------------------------------------------------
2. Sharing bandwidth
------------------------------------------------
ADSL- The line from you to the Phone company's CO (central office) is not shared, so it is just like your phone line (party lines are no longer popular). No one can tap in on your bandwidth or potentially listen to your traffic, no matter how many people are surfing. Be weary of RADSL, which is ADSL but it's RATE ADAPTIVE DSL, which means your actual bandwidth varies on line condition (sounds like a really
souped-up analog modem, dosen't it?). RADSL is probably worse than cable ever is, and I would steer clear of it. RADSL is used sometimes because since it can adapt to poorer line conditions you can normally get greater distance out of it.
Cable- You share the bandwidth with your entire node (most cable co's will tell you the approx size/households serviced by the node if you really want to know). This means that 10mbit of service is available for your entire node. Essentially this can be seen as a really big LAN in a star config (for you networkers out there it's like using a hub, NOT a switch), spanning multiple houses and sometimes several thousand feet. This means that if you live in a heavily-populated area and everyone has a 2-way modem, and they *ALL* want to surf at 8PM every night you could see slower preformance, but even on the most
heavily-used nodes you'll probably see 75kB/s and up, even when everyone is using it (since most just get 50-100kB of data each time they hit a webpage).
COMMON (between ADSL and Cable)- Whether you guys realize it or not everyone shares bandwidth up the pipe. Normally this means that your entire city will concentrate onto an Internet pipe somewhere, and this info is kept top-secret by the service providers. If you are trying to get onto the net, you can probably count on 100-200kB/s transfers from most all sites (except those on the same backbone as you or have special peering agreements with your cable/phone co), since you have to fight for traffic the same way as the rest of the net users, including the modem users.
-----------------------------------------------
3. Security
-----------------------------------------------
ADSL- Since it's a phone line, the only problem you could have would be a wiretap, but there really isn't much you can do about this.
Cable- Since it's a LAN other people can probe around (the LAN setup is why you can hit "find local game" on Q3 and see your neighboor's Q3test server) and possibly even see your traffic. While the number of people technically capable of this feat are relitively few (until 2600 posts the howto), the threat exsists. Nothing can pay off more than a properly secured network (on Linux shutdown public services where necessary, use *GOOD* passwords [alpha + case changes or numerics or both], and make sure you have some firewalling rules in place; for windows turn off file and print sharing), no matter if you use ADSL or Cable.
----------------------------------------
4. Availibility/Maturity
---------------------------------------
ADSL- the new boy on the block, just beginning rollouts and you can always expect growing pains (since most telco's don't have big pipes to the net yet you might get slower-than-expected service until they get their ducks in a row). Also is limited by which CO you are connected to and how far from it you really are (you might be able to spit on a CO from your roof, but that dosen't mean that you are connected to that one). Remember- many telco's do dialup and they don't need near the bandwidth for dialup, so they might take a while to realize the need and get more connectivity installed.
Cable- Been around for 3-4 years, depending on area. Technology is fairly stable, and most cable co's have sufficient bandwidth to provide maximum preformance. Availibility is fairly widespread in most major markets, and is rapidly coming to the outlying areas. This isn't as dependent on distance, since the cable service you get would be really poor if the signal was that weak. Rates don't depend directly on distance either.
--------------------------------------
Wrapup
--------------------------------------
ADSL- good if you need a faster upstream (and your local service provider gives you a bigger upstream than your local cable), or a static IP (most sp's give static IP's and many offer subnets of real IP's for additional fees). Also good if you hate cable service and have a satellite anyway. Most of the time ADSL will cost you US$ 200-300 to get installed and between US$50-US$70 a month. Many companies make you buy the modem as well.
Cable- Good if your friends are pleased with the service, and it has been available in your area for a while. If you want to keep your IP just buy a Linux box, hook it up with 2 NICs and get a UPS for it and never turn it off. It's not a sure-fire plan, but if your machine and cablemodem never turn off you can normally be assured your IP won't change. Also lost cheaper, normally US$50-US$100 for install, you don't have to buy the modem (that may be changing with the deployment of standards-based cablemodems), and service is US$30-US$50 monthly. Many hate the customer service response time (1-2wks to get a tech out to check your broken modem is standard), but if your node is stable you shouldn't have to deal with it, and it can save you money if you put up with it.
----------------------------------------
That's they skinny on ADSL/Cable (in a nutshell).
-Robert Gash
www.gashalot.com
llater,
Tony B |
