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Stories By Fabian Pascal32-Bit ComputingPerformance
Tweaks The
Communications Subsystem Best
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|Feedback To Author | Feedback To Webmaster Copyright © 1999 by Fabian Pascal. All Rights Reserved 32 Bit ComputingBy Fabian Pascal I have intentionally refrained from discussing the communication subsystem because the 56K modem dialup is simply too slow relative to the other PC subsystems and none of the promising broadband technologies -- DSL, cable and satellite -- has been available/affordable in the San Francisco area. I did not deem either the ISDN option, or analog modem bonding over two phone-lines (which is not supported by most ISPs) cost-effective. There has been, however, some movement recently. @Home seems to be getting closer to cable rollout, which is probably what prompted Pacific Bell (PB) to roll out two aggressively priced DSL plans (see details at http://dialup.pacbell.net/dsl/dsl_pricing.html). They provided the service for my review. This article describes the enhanced DSL option vs. a 56K modem dialup and provides some performance comparisons. A more in-depth analysis, also covering the basic DSL option and, hopefully, the cable option will be forthcoming. DSL The DSL subsystem consists of: * Alcatel DSL "modem" Installation is pretty straightforward: a technician installs a POTS splitter that separates the line into DSL and phone/modem components, the latter being your old phone line. The former connects with a regular RJ-11 cable to the the DSL modem, which connects, in turn, with a RJ-45 (or 10Base) cable, to the Kingston network card installed into a PCI slot. The card is configured straightforwardly via the Network service in the NT (or Windows 95/8) Control Panel, using the driver diskette that comes with it. Instructions for configuring your email and browser programs are provided at http://dialup.pacbell.net/dsl/. At the end of the installation and configuration process you should be up and running. Aside from performance, DSL has several advantages over dialup connections. First, it is always on, which means that the hassle of dialing and hanging up each time you want to access the Net is over; and with properly configured email software, you get continuously notified of new mail, rather than via modem dialups. Second, you can initiate and receive phone or fax calls while online -- no longer do callers get a busy tone because you have only one line; and unlike ISDN, you do not pay for two calls when you use both channels. The enhanced DSL plan -- 1.5-6MBps download/384KBps upload -- is offered to users within 17,500 cable feet from a PB central office (you must find out if you qualify). PBl guarantees 1,500KBps and whatever you get beyond this it's luck. Note very carefully, however, that this is a guarantee of bandwidth, which is different from transfer rate. Bandwidth is how large your pipe is. File transfer is the rate at which you receive data from the server you are connected to. PB provides the following formula to translate the guaranteed bandwidth into download throughput (data transfer rate):
connect speed
Throughput = --------------- * .70
8
Connect speeds are measured in bits and throughput is measured in bytes (1 byte=8 bits). Thus, throughput for enhanced DSL (eDSL) is 1,500/8*.7=131.25 KBps. This is, however, the optimal throughput given no interference (i.e. line noise, excessive electromagnetic field, etc) and is guaranteed only within PB's circuit, that is, between a server and client within the PB Internet (PBI) network. 131.25 KBps rate is about 21 times the 56K modem net optimal throughput of 53kbps/8=6.3KBps (as we shall see, dialup connections are far from it). At these rates, files of various sizes should carry download times as shown in Figure 1. Figure 1: Download times at optimal rates File eDSL 56K (MB) ------------------- 9.73 1:14 26:00 5.07 :38 13:25 2.02 :15 5:20 1.08 :08 2:51 .191 :01 :30 .076 inst :12 =================== I tested the eDSL throughput within PBI by downloading a 9.46MB file from http://dialup.pacbell.net/download at different times during the week. Optimal download time should be 1:12. The actual times were consistently between 1:07-1:09 throughout the week, a tad over the optimal guaranteed by PBI. Outside the PBI circuit data transfer rates are impacted by a number of different factors such as the number of hubs the transfer is sent through, whether any of these hubs are experiencing problems and server hardware, software and congestion. So all bets are off: actual throughput for both DSL and dialup changes constantly and can be far from optimal. While the number of hubs may increase with the geographical distance from your location to the server, there are violations to this rule. Neither can it be assumed that the number of hubs correlates well with performance. Figure 2 shows the actual download times from six sites outside the PBI network. The first two sites yielded a relatively stable throughput at a tad over the optimal rate, while the last four are very far from their optimum and exhibit considerable variation. Figure 2: Actual download times - enhanced DSL File Fr/5pm Sat/1pm Sun/12pm Th/3pm (MB) Server Location Hops[b] ------------------------------------------------------------------------------------- 9.73 www.netscape.com Mountain View/CA 19? [a] 1:04 1:05 1:05 5.07 www.eudora.com San Diego/CA 13! :35 :36 :35 :40 2.02 www.hotfreeware.com Cedar Rapids/IA 12! 1:45 1:08 1:28 1:07 1.08 www.webroot.com Mt Holly/NC 12! :16 :19 :23 :39 .191 home1.pacific.net.sg Singapore 14 :09 :08 :08 :07 .076 www.euronet.nl Amsterdam 8! :05 1:34 :48 1:23 ===================================================================================== [a] not tested [b] ! denotes network problems reported by VisualRoute; ? signifies unknown total hops Yet Visual Route (see recommended software) reports about 19 hops from San Francisco to Mountain View for the first site (Figure 3a) and only 8 hops for the last in Amsterdam, Holland (Figure 3b)!!! Furthermore, the program reported problems for most routes at various points in time, as the figure indicates. Figure 3a
Figure 3b
The situation is similar for browsing. In general, DSL is considerably faster than dialup. If routings and sites are unproblematic, pages pop up instantaneously, but otherwise you may not notice much difference from a 56K connection. Browsing is also slowed down by Java scripts, applets, or applications. The version of Java used by the browser (Sun's, used by Netscape and Opera) is slower than Microsoft's). 56K Dialup Subsystem If broadband access is not available in your area, or you can't afford it, there is always the good old dialup subsystem, which consists simply of a 56K modem. In fact, even if you opt for broadband access -- be it DSL or cable -- since it leaves your phone line intact, you can still use the modem for faxing and as a backup, just in case. In fact, I did experience a failure of the DSL service (see below) and dialup access saved the day. For those with just one phone line, there is even a way to avoid losing important calls while online. Working in conjunction with the Call Waiting option from the phone company ($3.50/month from PB), the HotCall device from Command Communications sits between your line and phone/modem and rings if a call comes in while you are online. It holds your online session for about 10 seconds, enabling you to defer the call. Should you continue talking beyond that time, however, the session will be dropped, of course. While modems do vary in performance, the differences are not significant. Even though the 3Com/USR 56K Voice Pro modem offers a slight performance edge (and USB to boot, for NT 5), I am making MultiTech's MessageSaver part of the recommended system. I like its small size, full set of LEDs and ability to serve as an answering machine, both via software and independently, when the computer is off. It comes with nifty fax software. The Message Saver is a Kflex modem, but is V.90 ready. If your ISP supports X2 and is not V.90 ready, the connect speed may fall to 44K, slightly less than the 45.3K rate achieved by the 3Com X2 modem.. The actual download time from the PBI site on a Wednesday
at 12:40pm was 34:40, about 8 minutes more than optimal. Figure
4 shows the download times from the same sites using the Message
Saver and PBI's dialup access. ====================================================================================== File Fr/5pm Sat/1pm Sun/12pm Wed/1pm (MB) Server Location Hops[b] -------------------------------------------------------------------------------------- 9.73 www.netscape.com Mountain View/CA 19? [a] [a] 37:57 38:05 5.07 www.eudora.com San Diego/CA 13 18:01 17:49 18:35 20:42 2.02 www.hotfreeware.com Cedar Rapids/IA 12! 7:21 7:23 7:15 8:23 1.08 www.webroot.com Mt Holly/NC 14! 3:42 3:40 3:49 7:00 .191 home1.pacific.net.sg Singapore 14 :36 :36 1:16 :39 .076 www.euronet.nl Amsterdam 8! 4:28 4.28 5:15 8:11 ====================================================================================== Clearly, dialup's throughput is much further from optimal than DSL's. Conclusions and Recommendations Even though DSL does not perform at the optimal rate, it is still much faster than dialup. Using the slowest DSL and fastest dialup downloads for each site, DSL was faster by the factors in Figure 5. Note that relative to the optimal factor of 21, the biggest gains are for large files -- x35 and x27. However, that's probably because the sites belong to corporations with better resources. Smaller, less endowed sites yield poor throughput. Figure 5: Actual performance gain factors - enhanced DSL
over dialup ============================================================================= File Max eDSL Min 56K Gain (MB) Server Location Time Time Factor ----------------------------------------------------------------------------- 9.73 www.netscape.com Mountain View/CA 1:05 37:57 35 5.07 www.eudora.com San Diego/CA :40 17:49 27 2.02 www.hotfreeware.com Cedar Rapids/IA 1:45 7:15 4 1.08 www.webroot.com Mt Holly/NC :39 3:40 5.5 .191 home1.pacific.net.sg Singapore :09 :36 4 .076 www.euronet.nl Amsterdam 1:34 4:28 3 ============================================================================= Once you get used to DSL and its convenience, it is really hard to go back to modems. Furthermore, DSL's advantage over cable is that performance does not vary with the number of users in your area who are online. The caveat is maintenance and support. Telcos and cable companies have aggressive rollouts for which they do not seem well prepared and organized. In the PB case, there are too many people/groups involved, who do not seem sufficiently coordinated, informed, consistent and knowledgeable. At one point I lost my access and the problem persisted for more than 24 hours. The DSL modem's manual is very skimpy on troubleshooting. Users report problems to 611, who is supposed to identify the DSL line and route the problem to the office that can isolate it to Prime Services [the equipment], the ISP [PBI], or a PacBell line issue. While this is the correct approach, it does not seem to work well in practice. * the System Status page did not report any problems in
San Francisco On the other hand, support is not much better for dialup access, its only advantage is that rates are cheaper. There is an installation fee of $198 for both DSL plans, and
access is unlimited. The monthly rate of $129 ($199 for up to
256 users) makes enhanced DSL more of a business option. At $49/month
basic DSL is a more affordable option for individuals and requires
only 14,000 cable feet distance from a Central Office, but I
will reserve judgement until I test it. These rates require a
one year commitment, with a $125 penalty for early cancellation;
and include PBI as ISP (the weakest link in the PB system), and
150 hours/month dialup access which can be used as backup. The
month-to-month rates (using an ISP of your choice) are $149/299
for enhanced and $59 for basic. (I would like to thank PB's Mark Gallegos for providing the installation for review and Ken Pulverenti for his help) RECOMMENDED SLOT 1 SYSTEMSYSTEM BOARD BX6 [1] PROCESSOR SUBSYSTEM Pentium II/300Mhz Processor [2] .tw VEK-12 CPU Cooler [3] PC100 SDRAM CAS2 GRAPHICS SUBSYSTEM FlexScan FX-E8 21" Monitor Millenium G200 Graphics Adapter [4] SCSI DISK SUBSYSTEM AHA-2940U2W 64bit PCI Ultra2Wide Dual Channel Controller [5] Cheetah 9LP Ultra2Wide 9GB 10,000rpm Drive [6] UltraPleX 32X Ultra CD-ROM Drive GlobalWIN King Kong Drive Cooler [7] FLOPPY SUBSYSTEM SuperDisk LS-120 IDE Floppy Drive COMMUNICATION SUBSYSTEM [8] DSL INPUT SUBSYSTEM Cordless Desktop Keyboard and Mouse Combo SYSTEM CASE EN-8900 ATX Tower Case (lockable) SYSTEM INTEGRATION DSi Inc. ALTERNATIVES AND OPTIONS [1] [2] Preferably SL2W8 with Deschutes 450MHz core [3] If not overclocking [4] for 3D users [5a] Dual Channel [5b] Single Channel [6a] 10,000rpm SE [6b] 7,200 rpm LVD [7] [8a] 56K Dialup HotCall 2000 [8b] USB (NT 5.0) |
