Washington Apple Pi

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High Speed Internet Access
ISDN, ADSL or Cable

by Don Essick

Washington Apple Pi Journal, March/April 1999, pp. 43-46, reprint information

Frustrated by the glacial speed of internet access at home, I decided to check out the availability of a high-speed yet affordable internet connection to my home office. I could justify this, in part, as my wife is an independent consultant and often works at home and because I am terribly impatient. My initial research identified four alternatives which seemed to offer high-speed data services to the SOHO (Small Office/Home Office) market: ISDN, ADSL, Cable Modem and DDSS. OK, Cable modem sounds somewhat descriptive, but what is the rest of that alphabet soup?

ISDN is probably the most mature of the four technologies. ISDN stands for Integrated Services Digital Network. ISDN services support digital voice and data services over the regular copper wires which deliver your POTS telephone service. (POTS, one of my favorite acronyms, stands for Plain Old Telephone Service.) ISDN divides this digital line into 3 logical channels, 2 B channels which deliver voice and data services and a D channel which carries the LEC’s signaling information. (LEC is the Local Exchange Carrier; you know, Bell Atlantic, GTE, those corporate monolithic monopolies which provide our telephone service.)

The two B channels of ISDN each support data speeds of up to 64Kbps or about twice the speed of a 33.6Kbps modem. You can "bond" the B channels together and go surfing the net at 128Kbps. Remember that the B channels carry both voice and data. If a voice or fax call comes in to your number, one of the B channels will go offline and ring your telephone or fax machine (which must be plugged into the ISDN modem). This is one of the disadvantages of ISDN service. Unless you put ISDN on a second line from your main telephone service, you can’t use your in-house wiring to connect up multiple extensions. Your POTS phone must be plugged into the ISDN modem.

One of the great benefits of ISDN is that more than one person can share the line. Most ISDN modems include an integrated router, which lets several people share the ISDN connection over an ethernet network. This allows multiple-computer families like us get on-line without waiting for me to finish downloading large files. If you want to avail yourself of this option, you should make sure that the ISDN modem you choose has NAT (Network Address Translation) capability. You might also want to get DHCP (Dynamic Host Configuration Protocol) support. This allows your Mac to automatically configure itself when connecting using Open Transport.

Sounds good, but what will it cost? Well, that depends on what features you want in your ISDN modem and how much you will use it. Features you should look for in your ISDN Modem include things like NAT, Call Bumping, which "un-bonds" the B channels to let you take a voice call and then "re-bonds" the B channels when you hang up. The Dynamic Bandwidth Allocation feature automatically allocates one or both B channels depending on traffic volume across the connection. Unlike POTS service, you are charged for the time you are on-line during an outgoing ISDN data call. Thus, if you are using both B channels at the same time, you are charged double your basic B channel rate (see chart).

Another optional feature of some ISDN modems is Enhanced Calling Features which include Call Waiting, 3-Way Calling, Caller-ID, etc. You might also want to make sure your modem has more than one analog phone port for POTS service, just in case you want to hook up both a phone and Fax machine. Oh, I forgot to mention that you must be within a limited distance from your central office for ISDN service to work.

And now the bad news: as of this writing ISDN is a pretty expensive proposition. In addition to the charges you pay to your ISP (Internet Service Provider) such as WAP Explorer Service, some ISPs impose a surcharge for ISDN access. Bell Atlantic charges a one-time connection fee of $125 and may impose a $99 connection fee plus time and materials for any inside wiring at your home. The ISDN channel usage charges range from $23 + .02 per minute for each B channel minute basic rate to $249 per month for unlimited use. Remember that if both B channels are in use, you get charged double the per-minute rate. There are intermediate tier rates for 20, 60, 160, 300 and 500 minutes ranging from $31 to $120 per month. All except the unlimited rate charge $.02 per minute for time in excess of your package limit. ISDN Modems are available at a discount from Bell Atlantic and range in price from $129 for a basic unit to $759 for a top-of-the-line Ascend Pipeline 175 Modem and Router. There are special incentive packages available from Bell Atlantic which allow you to get connected to ISDN at a significant savings if you commit to Bell Atlantic as your ISP for one year.

ADSL (Asymmetric Digital Subscriber Line) is a relatively new arrival. It was recently introduced to the local area by Bell Atlantic in selected areas of DC, Northern Virginia and Suburban Maryland. Unlike ISDN, ADSL is not routed over the switched telephone network. It is a service that multiplexes data traffic onto the copper wires servicing your home using frequency division multiplexing. Voice traffic is carried in the 0-4kHz band and the 100kHz - 2.2mHz is used for data transmission. The DSL "modem" is also a splitter which filters out the lower frequencies and passes the high frequency DSL traffic. Another difference between ISDN and ADSL is that A in the name. The service is asymmetric in that the downstream speed (from the internet to subscriber) is much higher than the upstream speed. Thus if you are a publisher who frequently sends large files to a service bureau, for instance, you might want to consider ISDN over ADSL. ADSL upstream speeds are approximately 90Kbps for low speed and 180Kbps for high speed service.

Another major difference between IDSN and ADSL is that ADSL is an "always on" service. You are actually part of the phone company’s wide area network with your own unique MAC address. That’s MAC (Media Access Control) and not Mac as in Macintosh. In fact, as of this writing, the iMac is the only Macintosh certified for ADSL. In theory, however, any Mac with and ethernet port and MacOS 8.1 or later should work. This means that all ADSL accounts are for "unlimited" service. There is no per-minute charge for ADSL service, though the ISP may have a different policy.

One of the superiority claims made by Bell Atlantic for ADSL is that access speed is not compromised by multiple users as it can be with cable modems. Personally, I find this claim confusing, since the central office server would suffer similar degradation as multiple users sign on. In addition, nobody has a dedicated copper wire from central office to the home. Some kind of fiber optic or copper trunk line usually carries the line to a pedestal somewhere in your neighborhood where it is split out to your individual line. Like ISDN, you must be close to your central office for ADSL to work (within 12,000 feet.) Contact Bell Atlantic or go to http://www.bell-atl/adsl/ for details.

What about cost? The ADSL service cost depends upon speed. Personal Infospeed 640Kbps service is $39.95 per month. Add $20 if you want to include Bell Atlantic.net as your ISP. Professional Infospeed 1.6Mbps service is $59.95 per month, ( add $50 for Bell Atlantic.net.) 7.1 Mbps Infospeed is $109.95 ( plus $80 for Bell Atlantic.net.) Not all ISPs will allow ADSL access so you may be stuck with Bell Atlantic.net or a limited list of other Internet providers. Other charges include a Service Connection Charge of $99 and $325 (!!!) for a "DSL Modem". If you want Bell Atlantic to come into your home and hook everything up and get you up and running on the service, it will cost you another $99. The $325 charge for the "DSL Modem" seems high, but remember although it’s called ADSL, unlike IDSN it really is still analog from the central office to your home. There is a little bit of creative defining here, but the system will become more digital as standards are solidified. Bell Atlantic currently has a "special offer" which includes an ethernet card (for Wintel machines), DSL Modem and turnkey installation for $99 if you sign up for a year of Personal Infospeed with Bell Atlantic.net.

Cable Modem is the third and most frustrating service I researched. Not because of any technical reason, but because I live in Fairfax County and am served by Media General Cable of Fairfax. They were in the process of rolling out their cable modem service, called Roadrunner, as this was being written in mid-December.

Media General (http://www.mgcable.com/roadrunner/) was selected as the cable supplier by the Fairfax County Board of Supervisors to provide Cable Television and related services to county residents in 1982. It now serves nearly a quarter million households in Fairfax County. They will be providing cable modem service over their existing dual coaxial cable lines which are capable of providing up to 60 channels on each cable. Media General has set aside one 6 MHZ Channel on each cable for its Internet service. This will provide a theoretical 27 Mbps internet access. The actual speed you experience will be determined by many factors. The slowest device on the network actually determines the effective speed. Generally, the limiting device in this case is your computer. The cable modem connects to your 10 base T ethernect card or connector. Upstream speeds are limited to 768Kbps. I also learned that there is often a lot of difference between theoretical speed and actual speed of cable access. Due to the way that all subscribers share a "channel" on the cable, (i.e. every cable subscriber on a loop is allocated part of the cable bandwidth on which the internet service is handled), the more people who have cable modems on a particular loop, the slower the service gets as more users log on. Media General claims in its FAQ that "even in our worst case scenario (In which we assume maximum simultaneous usage by every Road Runner user in any given neighborhood) Media General's Road Runner system is designed to provide bandwidth that will still exceed that of ISDN service."

Installation requires a cable outlet near your computer and a visit by two Media General technicians. One to install the cable outlet and one to install the cable modem and NIC (Network Interface Card) if necessary. The technician will also install a customized version of Microsoft Internet Explorer 4.01. The MGC FAQ warns against using other than the supplied browser for vague reasons.

The modem supplied by MGC is the Motorola CyberSURFR wave cable modem. (See techincal specifications at http://www.mot.com/MIMS/Multimedia/prod/specs/waveSpec.html ). So how much will this cost? Currently, installation is $99 (including NIC) and the monthly charge to full service cable subscribers is $49 per month, which includes rental of the cable modem, unlimited internet access, up to 4 e-mail addresses and 5MB of space for you own web site.

Here's a side-by-side comparison of the different options. To try to make it as meaningful as possible, I've assumed that you want a second line for internet access.

DDSS Direct Digital Satellite Service - Forget it, only available for Wintel machines and requires separate phone line for uplink. Also has the most arrogant salespeople I've ever encountered.

 High Speed Internet Access Cost Comparison Chart


56K Modem

(Bell Atlantic)


(Bell Atlantic)

Cable Modem

(Media General)

Installation and Hardware

Includes purchase of a 56K modem for $119 and Installation of a second phone line from Bell Atlantic for $87.75


Includes lowest price ISDN Modem for Mac ($225) and installation of ISDN Service ($99) and Activation of ISDN Service ($99)

$99 - $523

Includes discounted installation special from Bell Atlantic (requires 1 year contract with Bell Atlantic.net) Without one year commitment, package is $523.


Includes installation of Cable outlet, cable modem, software and NIC if required.

Recurring Costs**

Includes $19.95 unlimited internet from many ISPs and $17.60 for second phone line from Bell Atlantic


Charge for monthly unlimited ISDN internet from Bell Atlantic.net ($34.95) and Unlimited ISDN telephone service charges ($249)

$59.95 - $109.95

Includes unlimited ADSL internet access from BellAtlantic.net and ADSL service from Bell Atlantic. $59.95 for 640Kbps, $109.95 for 1.6Mbps


Includes Unlimited Internet access, rental of cable modem.

Annual Costs**
$719.40 (640K)

$1319.40 (1.6M)


53Kbps downstream and 33.6Kbps upstream

128Kbps upstream and downstream

640Kbps or 1.6Mbps downstream, 90Kbps upstream

10Mbps downstream, 768Kbps upstream *

* assumes maximum speed of NIC card. ** All costs exclude taxes and fees 

Of course the above are based on the costs at the time this article was written. The Bell Atlantic special pricing on ADSL was due to expire on 12/31/98 but due to the slow pace of the rollout, I expect that will be extended.

If you are looking to invest in higher speed internet access, good luck. This is cutting edge technology and many of the people you will talk to from Bell Atlantic and the cable companies will be poorly trained and know little more than you do. The best thing to do if you realize that the person you are talking with is just as clueless as you are, is to leave your name and number and have them connect you with a specialist. This takes longer, but the chances of getting correct answers are much improved.

Learn more

http://www.cnet.com/Content/Features/Techno/Cablemodems/ss07.html - has a map and status of cable modem access availability to most of the US. Information is a bit dated. Also has links to information on modems, services, "gotchas", speeds and more.

http://www.cablenet.org/Cablenet/operators.html - has a list of cable operators with links to site information.

http://www.adsl.com/adsl_forum.html - has lots of info on ADSL. technical info and vendor information

About the author. Don Essick is Vice President for Macintosh of the Washington Apple Pi. He is also a self-described "mainframe database geek" and Macintosh enthusiast. He works for Logicon Syscon corporation in Falls Church, Virginia. He has a web site at http://members.wap.org/don.essick/index.html if you really want to know more.


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Revised April 11, 1999 Lawrence I. Charters
Washington Apple Pi
URL: http://www.wap.org/journal/