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56K Modem Technology
(Editorís note: This is the second edition of our White Paper on 56K modem technology. Information is developing so fast that we plan to update this document on a regular basis for the next few months. Since the first edition, information has surfaced about FCC regulations that appears to limit the technologyís speed, about advances in an interim standard being established by the Telecommunications Association (TIA), and about the effect that suburban Subscriber Link Concentrators (SLCs) will have on performance.
Multi-Techís position about the 56K modem technology has always been
that the technology promises to be one of the most important modem
developments in recent years. However, we believe that it has been
prematurely introduced and over hyped to the point that its real
potential to improve performance has been obscured and its reputation
potentially damaged. Our efforts, such as this white paper, are attempts
to keep in focus this very important technological development. As
deployment of 56K modem technology comes closer to reality, our
enthusiasm for its potential continues to
One of several new modem technologies on the horizon that promises to dramatically increase data communications speeds is the 56K modem technology. This newest iteration of what technologists have long claimed to be ìat the top end of the envelopeî promises to double the speed of current 28.8K bps modems that follow the ITU V.34 standard. What is this new technology? How does it work? How well will it work? When should you invest in it? And, will it really perform as promised? These are some of the questions todayís modem buyer must ask. This white paper will address some of these issues, plus provide a picture of the Multi-Tech solutions with 56K modem technology performance.
Certainly the driving forces behind the need for faster modems are headed by the rapid growth of remote access applications such as the Internet. In the past, few new data communications applications created as much excitement in the information business as the Internet. With such a rapid expansion over the past couple of years, it was inevitable that requested services would eventually become overburdened. This overburdening of the system is one of the reasons behind the search for a faster modem. However, keep in mind that the modem is only one piece of the system. Besides modems needing increased speed, the capacity of the infrastructure and server capacity may also cause problems. Phone lines and communications links between Central Offices (COs) were primarily designed to handle voice traffic of a relatively short duration, an average of about 3 minutes, not Internet calls with an average of over 30 minutes. In addition, the Internet Service Providers (ISPs) who sell Internet access time utilize sophisticated servers to handle the data traffic and keep track of activity. With the rapid expansion of Internet services, these ISP servers can become over burdened (especially during peak business hours). This can also cause slower access to the Internet. Even the PC used to connect to the Internet can be the culprit. An under powered PC can struggle to handle tasks such as complex graphics that require extensive data processing. All of these factors can make it seem that the modemís speed is the problem.
Besides the Internet, other forces driving the quest for faster modems include desktop video conferencing, telecommuting, and entertainment (games) software. In many of these cases, 56K modem technology will not enhance such applications because 56K modem technology does not work in an analog-modem-to-analog-modem connection. The 56K modem technology requires that there is a digital ISP-type system on one end. And finally, some applications, like groupware involving updates from a central server, will be accelerated more in one direction than the other. That is because the 56K modem technology transfers data faster from the server than to the server.
The jump to 56K modem technology is different than the modem speed increases of the past. In this latest case, there are a number of limitations inherent in the technology and the communications infrastructure. First of all, the technology will only work over high-quality lines, otherwise the modems will drop back to traditional V.34 speeds. The industry has already seen this phenomena with the V.34 modems that have problems connecting at the highest speeds over poor-quality lines. 56K modem technology also will not work over any link that has more than one analog-to-digital or digital-to-analog conversion, nor internationally where a conflicting digital conversion may be used. It will not work if there is an ADPCM compression in the link, or if any voice enhancer such as AT&Tís True Voice is employed. In addition, there are incompatible versions of 56K modem technology on the market, so the ISP equipment must be using the same 56K modem technology ìflavorî as the dial-in modem. And finally, the two leading technology versions are headed for a showdown at the standards committee which may delay a unified standard.
The message here is that 56K modem
technology is very exciting and holds the promise to improve performance
of many data communications applications, but selecting the applications
is key. Like any technology promise, one has to become familiar with the
pros and cons before one can make an intelligent decision on when to
invest, or even if 56K modem technology is the best technology for the
How it Works
The new 56K modem technology is one of the most talked about datacomm advances in recent history simply because it promises to double the speeds and throughput of todayís V.34 modems.
The reason such high speeds are even possible is due to the increasingly digital nature of Plain Old Telephone Service (POTS) via the Public Switched Telephone Network (PSTN). Over the past two decades, the communications infrastructure between central offices (COs) has been almost completely converted to a digital network. As a result, the analog modem used to connect a PC to a distant computer or server uses analog communications for a very small part of the link. Most probably, at the first CO, the analog signal is converted to digital and remains so until the ìlast mileî where the call is connected to the modem on the other end. That means there is a analog-to-digital (A/D) conversion to get the signal onto the digital infrastructure, and a digital-to-analog (D/A) conversion at the other end.
The way 56K modem technology works is that the data is ìinterceptedî in its digital form by central site/ISP equipment and never has to go through the second conversion. Digital lines are cleaner (less noise) and faster. By dealing only with one analog to digital conversion, higher speed is inherently possible.
To achieve maximum throughputs, the link needs to have such digital ISP equipment on one end. Two 56K modem technology client modems cannot establish a 56K bps link because of the additional A/D conversion). In addition, the ISP equipment must be of the same 56K modem technology ìflavorî as the client modem for the whole thing to operate. As stated earlier there is more than one 56K modem technology available, and they do not yet interoperate.
As explained in the following section, transmissions
between a 56K modem technology client modem and ISP are not at maximum
possible speeds in both directions. Data from the ISP to the client
modem will be up to the maximum possible speed approaching 56K bps, but
data transfers from the client modem to the ISP equipment will be less.
For the interim standard proposed by the TIA, this speed will be 33.6K
bps per the enhanced V.34 standard. If the technology used is
Lucent-based, future releases could very well include speeds up to 40K
in the up-stream and even 45K bps in a full duplex
Shannonís Law and Analog Data Communications
Shannon's Law states that the theoretical maximum rate for error-free data communications over the PSTN (i.e., a defined bandwidth channel with noise present) is about 35K bps depending on the noise in the telephone link. This theoretical limit is for two analog modems communicating over the PSTN. The new 56K modem technology doesnít violate this limit because the data communications is not between two modems but between a modem and a digital ISP system which creates a reduced-noise link environment.
The diagram illustrating 56K modem technology communications shows two modems connected through the PSTN along with a digital ISP system. Communications between the ISP and modem are shown as up to 55K bps downstream and 33.6K bps upstream. Communications between the two modems are shown as 33.6K bps.
In client-to-client modem connections, the telephone network first converts the transmitted analog signal to a digital signal and then transmits that digital signal from one CO to the second CO. At the second CO, the digital signal is converted back to an analog signal and then sent via an analog phone line to the second modem. The noise introduced by the telephone networkís Analog-to-Digital converter is called quantization noise. In this type of connection, Shannonís Law determines the maximum speed to be around 35K bps. In a home-to-server type of connection 56K modem technology takes advantage of the fact that the network has no Analog-to-Digital conversions in the end userís downloading (downstream) path and effectively avoids the quantization noise impairments introduced by the telephone network. Therefore the theoretical line speed will be ultimately bounded by the telephone network capacity.
For upstream channel (data upload from client site to server site), this direction includes a phone network PCM encoder (Analog-to-Digital Converter); therefore, the quantization noise mentioned above does exist and limits the maximum data rate in the upstream direction. Therefore 56K modem technology will offer asymmetrical maximum speeds for end users downloading and uploading data exchanges with servers digitally connected to the PSTN.
As we know, the PSTN developed as a voice-only network. Modems were developed for communicating data over those voice-oriented networks by converting the digital signals of a computer into analog signals that could be transmitted as sounds. The newest V.34 modems are the most efficient examples of this technology. But, with the widely deployed digital technology existing in todayís PSTN, it only makes sense to look to a technology that is not limited to the assumption that both ends of a data communications link are analog. Thatís exactly what the 56K modem technology does.
The way the analog signal coming from a modem to a CO is converted into a digital signal is called Pulse Code Modulation (PCM mentioned earlier). The way it works is that the incoming analog waveform is ìsampledî 8,000 times per second; the resulting values are transformed into eight bit PCM codes.
To transmit the resulting PCM
codes, it takes 64K bps digital bandwidth (8 bits, 8,000 times/second).
This 64K signal is transmitted over any number of 64K bps ìpipesî in the
telephone system as a single channel (or DS0) of a T1 communications
line. In fact a ìchannelized T1î link can carry 24 of these signals.
There are more efficient digitizing methods which may use less than 64K
such as 32K ADPCM. These methods cannot be used for 56K modem technology
Applications for 56K Modem Technology
Just understanding the technology will go a long way in helping to plan how to use it. By knowing that there must be a digital end involved for a 56K modem technology link to work, certain applications are eliminated (e.g., those consisting of client-to-client modem communications.) But even keeping in mind these basics, one still needs to approach this technology with realistic expectations.
The ìtrueî picture of 56K modem technology development is that it is too early to tell what kind of throughput can be expected when the technology is deployed. Weíve already learned that the signal level of digital transmission equipment, as regulated by the FCC, appears to limit the speed of 56K modem technology to under 56K bps. This is because, unlike any other modems, the performance of 56K modem technology is directly dependent on the transmission level of the modem transmitter signal. The actual speed limit will be dependent on a number of factors which can be different for each specific link. This factors include the quality of the line, and the number of analog to digital or digital to analog conversions.
Assuming that the technology turns out to provide an acceptable
increase in throughput over conventional modem to modem links, the best
use for this new approach will obviously be the Internet. The higher
speed downstream data rates mesh nicely with an application where a few
keystrokes make a request that results in a large amount of data being
sent in response to the request. Thatís often what the Internet does. On
the other hand, an application like Internet phone or Lotus Notes, where
updates in both directions require extensive data transfers, the faster
transmission in one direction will help to a lesser
56K Modem Technology Limitations
By calling this new technology 56K bps, the industry has once more set the userís expectation too high, reminiscent of V.34ís claims of 28.8K bps. Just as V.34 modems fail to connect at 28.8K over many phone lines, the new 56K technology modems may not provide 56K speeds even with one end fully digital. In fact, as mentioned earlier, until such time that the FCC changes its regulations regarding the signal strength of digital transmission equipment, the top speed of this modem technology will probably not be 56K bps. The truth is that no one knows what kind of performance can be expected. Currently there is no test equipment available to simulate 56K operation, so the only valid tests will be in real-life deployment. As 56K modem technology modems roll out this year, and the various testing labs around the country start to work them over, the real performance of these products will become known.
The Regional Bell Operating Companies (RBOCs) have been silent about this technology. As we know, the infrastructure is already being burdened by the extras local traffic due to Internet calls, so a large increase of modem traffic due to 56K modem technology will certainly not help the situation. In fact it could be speculated that when the FCC investigates the possibility of increasing signal strength of digital lines to help facilitate 56K bps speeds, the RBOCs and other carriers will not be too eager to allow it. Other technologies like ADSL will promise to offer higher speeds and off-load data traffic from CO switches. Add to that the fact that ADSL, like ISDN, will give RBOCs the chance to raise prices, and one see why RBOCs may not be 56K modem technology supporters.
As stated earlier, claiming that 56K modem technology alone is going to speed up Internet access is very misleading, because slow speeds on the Internet are often caused by heavy traffic, overloaded servers, and under-powered PCs. When a user is connected to the Internet, and the send/receive lights of the modem flash once every 10 or 20 seconds, it does not matter how fast the modem is, the problem is that the net is congested. Itís kind of like driving a Porsche during rush hour. The heavy traffic over the Internet has gotten lots of attention, and indeed, the infrastructure is being upgraded. The question is, will yet faster modems clog up the net even more? Related to that question is whether the server hardware now in existence can handle more data. A recent article in Data Communications magazine (October 1996) titled ìClose-Up on Remote Access Serversî, tested several ISP hardware solutions with the results showing that as traffic increases, the throughput of the servers decreases per connection. This is a reflection of a server design that is not optimized for many users doing heavy data transfer, but optimized for something lower.
The modem industry lost some of its credibility with the introduction of 28.8K bps modems a few years ago. Before V.34 was released, there were pre-standard modems being sold as if they were standard. 28.8K was also the first speed plateau where users could not often get the stated speed. Previously every new speed plateau (2400, 9600, 14.4K and 19.2K) had modems which connected at the stated speed. That was not the case at 28.8K bps for number of reasons, all of which boil down to the technology approaching its physical limit. Tech support departments of all modem companies and ISPs are still explaining why userís 28.8K bps modems donít achieve the highest speeds labeled on the box. This scenario is found to repeat itself with the premature introduction of 56K technology modems which, as previously mentioned, will not be able to achieve 56K bps speeds at all. The same set of problems for tech support will exist with 56K bps, but with the extra complication of never having been designed to do client-to-client modem or 56K bps upstream transfers.
Also, 56K bps modem technology will not work where there are any conversions of the digital signal within the link. Such conversions are done when communicating between the US and Europe (A-law to µ- or mu-law or vice versa.). Conversions are also done when the more efficient ADPCM compression is used instead of PCM, as in some international links.
And lastly, 56K technology will not work if there
is more than one conversion in the link. As it turns out, much of the
U.S. is now wired with remote CO equipment that concentrates analog
phone lines into digital T1 lines before sending the signals to the CO.
This process is done by the use of Subscriber Line Concentrators (SLCs).
Some SLC technology uses multiple analog/digital conversions for the
process. Suburbs equipped with such SLCs will reportedly not benefit
from 56K modem technology. This is, again, an area where the actual
effect of an inhibiting factor on the technology is not known. It is
being reported that this could affect a large number of potential
The Standardization of 56K Modem Technology
As in all modem communications, interoperability through standards compatibility is the key to wide acceptance. The standards for 56K modem technology operation will eventually be set by the International Telecommunications Union (ITU). The U.S. organization which submits recommendations to the ITU is the Telecommunications Industry Association (TIA). The standardization process through the ITU is long, complicated, and has been known to take years to complete.
In the mean time, there are two different 56K technologies currently being developed by their respective groups. One group is headed by Lucent and Rockwell, whose current modem technologies are installed in over 70% of the central site/ISP systems. The second group is headed by U.S. Robotics. U.S. Robotics strength is in retail and they are heavily marketing their version of 56K to that user segment.
Considering the importance of 56K modem technology, Lucent and Rockwell are supporting an interim standard via the TIA. This interim standard, called K56flex, is expected to be passed by the TIA this year. One of the key provisions of the K56flex standard is that the upstream data flow will be ITU standard V.34. While this does not reflect the eventual higher speed capability of the Lucent technology, it will make for faster approvals internationally and the quicker deployment of the technology in the U.S.
The obvious problem is that
the Lucent/Rockwell and USR technologies do not interoperate, and until
a standard is defined by the ITU, no one knows if the modems being sold
today as upgradeable will be upgradeable to that standard. The first
meeting of the ITU which includes an agenda item for 56K modem
technology, will be in March of 1997.
Multi-Techís 56K Modem Products
Multi-Techís 56K modem technology products include central site ISP server systems, plus both internal and external client modems. The technology used follows the K56flex interim standard proposal by Lucent and Rockwell. By using Lucentís K56flex chips in these products, Multi-Tech expects to provide even better performance in the future. As stated earlier, the K56flex interim standard uses V.34 speeds of up to 33.6K bps for upstream (modem to server) communications, but the Lucent technology is capable of more than that. It is expected that future upgrades of Multi-Tech products will allow upstream speeds to 40K bps and even full-duplex communications to 45K bps.
The Multi-Tech central site server system is the CommPlete Communications Server, and the announced client modems include an external MultiModemZDX (model MT5634ZDX), an internal ISA-bus MultiModemZPX (model MT5634ZPX), and a Windows 95 ISA-bus internal MultiModemZPW (model MT5634ZPW.)
The CommPlete Communications Server combines dial-in/dial-out operation with digital channelized T1 and ISDN PRI WAN access in one system. In addition, the new CommPlete Communications Server features management via web browsers, SNMP, telnet and FTP clients. The CommPlete system allows remote users to dial into an IP or IPX network using analog or ISDN modems utilizing all-digital communications links. The question of server power is addressed by the systemís high-end processors and segmented multiple bus design. It utilizes one Pentium processor per segment/T1 line, to ensure that each port has sufficient processing power for high-speed file transfers. The CommPlete system was designed for 56K modem technology products. It includes flash upgradeable modems to ensure that the latest standards and features are just a modem connection away.
There are four segments in each rack with each segment containing one server and four device slots. Each segment can be configured for either direct T1 or PRI interface. Each segment also can be set up to run the same remote access solution as on all other segments or different remote access solutions per segment to provide access for different remote clients. The independent nature of each segment allows for greater flexibility when providing access to the Internet or corporate intranets. The CommPlete Communications Serverís multiple bus backplane includes four buses involved in the transfer of data. Each segment has a 16 meg data bus for data moving to the RAS segment server, a T1 bus for calls coming in (used to provide the signal interface between the T1 daughter board and modem boards and to assign time slots for each modem), a control bus which spans the segments, and the 10 meg Ethernet bus which takes the data from all four RAS segment servers and puts it onto one Ethernet port.
The new 56K modem technology MultiModemZPX is an internal ISA-bus modem for PC applications. It will work with any PC operating system and hardware platform. In addition to supporting the K56flex interim standard, it also supports standard V.34 and lower speeds along with V.17/Group 3 fax operations.
The new 56K modem technology MultiModemZPW is a Windows 95 ìPlug and Playî compatible internal ISA-bus modem that supports the ITU V.80 standard is used with video conferencing applications. In addition to supporting the K56flex protocol, this modem will also support traditional V.34 datacomm and V.17 faxing, plus voice mail, telephone answering machine, and fax/document-on-demand operations via the bundled Windows 95 based communications software.
The new 56K modem technology MultiModemZDX is ideal for both large
business and SOHO applications that require moderately priced modems.
Also supporting V.34 ITU datacomm and V.17 fax operation, the
MultiModemZDX comes bundled with data communications and fax software.
Computer access is via an RS232 DB-25S connector. Advanced modem
features such as remote configuration, caller ID reporting (select
models) and data/fax auto detect, makes this modem perform to the
highest application demands.
As the old saying goes, those who ignore history are doomed to repeat it. V.34 (28.8K bps) modems were introduced in a mad scramble that sidestepped important procedures for testing and standardizing. Such testing and standardization is vital for the promised performance to be enjoyed by the vast majority of users. Now we have modem makers throwing 56K modem technology modems at the public before a standard is set, while two distinct technologies are at odds, and while a basic understanding of what the higher speed can and cannot do is largely absent. Itís deja vu all over again.
Hopefully this White Paper has given cause to step back and evaluate any planned move to 56K modem technology. It promises to bring yet another incredible performance increase to the modem market, but it must be understood before it can be properly applied. Specifically, keep in mind these points:
* 56K modem technology makes sense in some applications, and not in others. For instance, modem-to-modem links (desktop video conferencing, telecommuting, and games) cannot run at the higher speeds, because a digital ISP-type system is required at one end.
* Internet access is an ideal application for 56K modem technology, but higher speeds apply only from the server to the client. Upstream links from client modem to server may not be faster than V.34. Also keep in mind that many of the delays encountered on the Internet are traffic-related and cannot be improved by increased modem speed.
* Two 56K modem technologies are under development. One, headed by Lucent and Rockwell, is incorporated in technology currently installed in over 70% of central site/ISP systems, and it is the heart of the proposed TIA interim standard. The other, headed by U.S. Robotics, is being incorporated (some say prematurely) into products directed and heavily marketed to the retail segment of the market. Both are vying for satisfaction from standards organizations.
The best advice in selecting your 56K modem technology is to be an informed buyer, and call your ISP to find out which technology it will be supporting before you select a modem. Until standards are established and incorporated into products on the shelf, it is the best way to ensure you will get the performance you deserve. We hope this white paper will be of some help in the selection process. Call us at (800) 328-9717, visit us on the Internet at http://www.multitech.com, or email us at email@example.com.
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