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CIRCUIT SWITCHED CELLULAR MODEM COMMUNICATIONS WHITE PAPER (7001)
This white paper compares and contrasts three technologies designed to maximize the performance of modem communications over the cellular network. These technologies are MNP-10™, developed by Microcom, ETC 1.0™ (Enhanced Throughput Cellular) developed by AT&T Paradyne, and TX-CEL™ (Throughput X-CELerator) developed by Celeritas Technologies, Ltd.
| Technology | Developer |
| MNP-10 TM | Microcom, Inc. |
| ETC 1.0TM | AT&T Paradyne, Inc. |
| TX-CEL TM | Celeritas Technologies, Ltd. |
Toshiba America Information Systems, Inc. (TAIS) has elected to support all three technologies in the Noteworthy NW144CR 14,400bps direct connect cellular-ready modem. It is assumed the reader is already familiar with the advantages and merits of anytime anywhere connectivity, made possible via the cellular network, therefore, a discussion of this topic is not included.
Microcom Network Protocol Class 10 (MNP-10) is an industry standard method for coping with adverse telephone line conditions such as those frequently encountered on, but not limited to, the cellular network. Typically these adverse conditions are characterized by noisy connections or connections whose quality varies over time. MNP-10 is an enhanced extension of the MNP standards and as such is essentially an error correction and session management protocol. MNP-10 is not a unique modulation scheme, it is designed to compensate for a phone line of degraded quality. It does not provide an optimization for the actual physical communications link. MNP-10 implements Adverse Channel Enhancements (ACE) to improve data communications performance (i.e., connectivity and throughput). In order to establish an MNP-10 session (and thus take full advantage of these techniques), both local and remote modems must support the MNP-10 standard.
There are essentially two phases to an MNP session, the link establishment phase where the connection is negotiated and the data phase where communication occurs. Each phase has several features.
The originating modem sends a Link Request message every two seconds for up to 15 attempts. Upon successful receipt of a Link Request, the answering modem responds by sending two Link Acknowledge messages. Link Acknowledge is sent twice by the answering modem under the premise that at least one will be received error free by the originating modem. This technique is used to improve the initial rate of connection.
MNP-10 tries to establish the connection at the most reliable (i.e., lowest) speed. This can be configured by the user to be as low as 1200 bps. The modems can subsequently attempt higher connection rates in a coordinated fashion (see next topic for more detail). This technique is used to improve the initial connection reliability.
The originating modem lowers its transmit level during negotiation and instructs the answering modem to do likewise. Once the connection is made, MNP-10 modems may shift their speed upwards to a higher rate. MNP-10 capable modems must perform the following sequence of events to shift their speed upward to a higher rate: drop the carriers, reconfigure for the higher rate, handshake, and adjust transmit levels as appropriate for the higher speed. Once negotiation to the highest possible rate is complete, the link establishment phase gives way to the data phase.
As link conditions dictate, MNP-10 allows for dynamic upshifting (fall forward) or downshifting (fall back) of the communications rate. Line quality and link performance are continuously monitored to determine the optimal speed. This technique is used to maximize throughput by providing the highest possible error free communications rate.
Depending on link conditions, MNP-10 allows for dynamic increases or decreases in each modems transmit power level. To determine the appropriate level, each modem evaluates the signal quality being received from the other and automatically calculates an optimal output level. Adjustments in output level to compensate for interference, attenuation, distortion, or improved signal quality can be made dynamically.
MNP-10 allows for a longer loss of carrier interval to prevent modem disconnect during hand-offs or drop-outs. MNP-10 also inhibits the transmission of data when carrier loss is detected.
MNP-10 allows a wider and more flexible range of data packet sizes ( from 8 to 256 bytes in increments of 1 byte). They are not as restricted as the fixed sizes specified by MNP 4 ( 32, 64, 128, and 256 byte block sizes). This permits MNP-10 modems to communicate initially using smaller packets than with MNP 4 and to gradually increase packet size until block error counts become excessive. At this point, the packet size can be backed-off to the next lower size. In an adversely affected communications channel, this technique allows a more efficient throughput by minimizing re-transmission time due to block errors while simultaneously determining the largest practical packet size.
1.MNP-10 requires an error free training sequence (Link Req/Link Ack) to complete successfully. If a hand-off, channel change, transmit power command, dropout, or other signal path interruption occurs during this training, the sequence must be restarted. Conceivably, this can happen repeatedly and will thus prolong the interval before communications can begin.
2.MNP-10 cannot make the required corrections rapidly enough to meet the dynamics of the cellular connection. Due to an inherent latency in MNP-10, several error blocks must be received before a compensatory tactic is executed. By this time, link quality may have again changed for better or worse.
3.MNP-10 has no capabilities to support fax.
4.MNP-10 does not fall forward quickly. It must dwell at the largest packet size for a sufficient interval before an up-shift in communications rate will occur.
5.Training sequences following signal interruptions or blackouts can be extremely long (i.e., 30 seconds). Therefore, long intervals can occur where no actual data communications are in progress.
6.MNP-10 attempts up to three retraining sequences before modem disconnect. When traversing from a cell to a cell boundary (which can straddle three cells), the occurrence of multiple hand-offs can inadvertently force MNP-10 modems to hang up prematurely due to failure of all three retraining sequences. This problem occurs most frequently when the user is in a moving vehicle and will rarely, if ever, occur when stationary.
7.For small file transfers, MNP-10 is less than optimum as the link negotiation time is longer than the time required to transfer the file.
MNP-10 currently enjoys a large installed base and has shown to be technology in great demand. For these reasons, Toshiba has chosen to support MNP-10 in its direct connect cellular-ready modem.
The next sections focus on two newer technologies developed as alternatives to MNP-10. Although lesser known, they are extraordinarily capable of improving data communications performance over cellular networks.
ETC 1.0 is a proprietary development of AT&T Paradyne, Inc. The specification for MNP-10 is well documented in the public domain; however, the specification for ETC 1.0 is only made available to firmware and hardware developers who license it for implementation into modems. Explicit detail regarding ETC 1.0 cannot be made readily available. However a number of publicly available test and evaluation reports have documented some of its features.
Essentially ETC 1.0 provides optimized cellular performance through enhancing options within the V.32bis and V.42 standards. Examples of these enhancements include:
1)modification to transmit packet size
2)selective packet reject
3)carefully chosen transmit power levels
4)short initial training
5)quick retraining
6)longer carrier loss time-out
7)link negotiation at lower speeds (4800 and 9600 bps) with fast fall forward under good signal conditions
8)improved auto rating algorithm (dynamic communications speed fallforward/fallback)
9)plus a few signal processing tweaks.
Test results from such independent companies as Cellular One and Vector Development indicate that ETC 1.0 offers superior performance to MNP-10 and wholly recommend the use of modems that feature ETC 1.0.
As a consequence, ETC 1.0 provides a greater connection success rate as well as improved data communication rates and higher throughput. ETC 1.0, like MNP-10, does not employ a unique modulation method and is designed to be used with conventional landline modems that are connected directly to a cellular telephone. Unlike MNP-10, ETC 1.0 can be used in a single ended application, although most of its benefit is realized by having it at both ends of the communications link. Since ETC 1.0 most closely resembles a protocol scheme, it cannot be used in conjunction with MNP-10.
Until now, the main limitation of ETC 1.0 has been its unavailability apart from modems manufactured by AT&T Paradyne. However, with the incorporation of ETC 1.0 into the Noteworthy direct connect cellular-ready modem, the user will profit directly from the benefits of this robust technology.
TX-CEL is the newest of the three technologies presented in this paper and by itself offers a tremendous performance increase and operational advantage. Toshiba is the first company to offer this innovative and exciting technology in a commercially available communications product. When used in conjunction with ETC 1.0 or MNP-10, the user will enjoy the most flexible and powerful cellular capable modem on the market.
TX-CEL is a proprietary (patent pending) development of Celeritas Technologies, Ltd. It is designed to maximize connectivity and throughput rates for data and fax communications when using conventional landline modems connected directly to a cellular telephone. Unlike other technologies (e.g., Microcom MNP-10 or AT&T Paradyne ETC 1.0) which basically strive to achieve the same purpose, TX-CEL is not a protocol scheme, compression algorithm, or a unique modulation method (e.g., ZyXEL ZyCellular or US Robotics HST). Although TX-CEL functions optimally when it is implemented at both ends of a communications link, its use is not predicated upon this, in contrast to the aforementioned technologies. Modest performance improvements can be gained even when using TX-CEL at only one end. It is much easier to implement than MNP-10 or ETC 1.0 and can be used in conjunction with these competing technologies (Celeritas claims that TX-CEL will actually enhance performance of both MNP-10 and ETC 1.0). An important feature is the TX-CEL fax capability which is not present with MNP-10.
TX-CEL achieves its benefits by residing in the physical layer of the communications link. Since the patent is pending on this technology, a detailed description cannot be offered at this time. However, Celeritas has successfully identified major and inherent impairments to transmitting data/fax when using a cellular phone, and has also developed a satisfactory compensatory scheme against them. TX-CEL is best described as a signal processing technique that is applied to the audio signal paths of the modems interface to the cellular phone. By doing so, TX-CEL essentially makes the communications path more amenable for data communications by removing impairments to transmission. While MNP-10 and ETC 1.0 achieve their enhancements primarily through sophisticated error correction techniques and intelligent manipulation of transmission block size, they do not directly address the design shortcomings of the communications technology being used when attempting to carry non-voice traffic. TX-CEL prevents the error from occurring by eliminating the impairments.
Cellular carriers recognize the fact that these three technologies achieve their optimal performance and maximum enhancement when implemented at both the mobile and host ends of the connection. The cellular carriers have begun installing back to back modem pools as part of the gateways in their cellular networks. These modem pools are developed by Primary Access Corporation of San Diego, CA, and will offer support for TX-CEL, ETC 1.0, and MNP-10. By dialing through a carrier modem pool, a mobile user will obtain the benefits of the cellular enhancement technologies even if the end destination host modem does not support these technologies.
The Noteworthy NW144CR cellular-ready modem is appropriately positioned to capitalize on the services offered by the modem pools, making it an ideal choice for the mobile communications user.
Since TX-CEL offers the single most profound improvement in cellular modem communications, Toshiba recommends that the TX-CEL be continuously enabled when in cellular mode. Due to additional significant improvements to data performance, Toshiba also recommends that ETC 1.0 be continuously enabled when in cellular mode.
The performance of MNP-10 would seem to been superseded by the newer technologies. However, due to its large installed base, Toshiba is positioned to support this standard and recommends its use as an alternative cellular technology.
The improved data communications performance benefit of these three technologies is unquestionable. The flexibility and robust capability available in the Noteworthy NW144CR direct connect cellular-ready modem will be unmatched by any competitors product. Use of this modem will result in improved overall reliability in making cellular connections, consistent completion of data file transfers and faxes, higher modulation speeds, and greater throughput with consequent decrease in cellular transmission time (i.e., reduced cost to the user).
Thanks to Celeritas Technologies, Ltd., AT&T Paradyne, Inc., Intel, Cellular One, and other computer industry sources for additional information supplied in the preparation of this document.
Technical commentary on this document should be directed to:
Allen J. Huotari
Sr. Design/Development Engineer
Toshiba America Information Systems, Inc.
Computer Systems Engineering
Multimedia Architecture Development
Internet: allenh@tais.com
MNP is a trademark of Microcom, Inc.
ETC 1.0 and Enhanced Throughput Cellular are registered trademarks of AT&T Paradyne, Inc.
TX-CEL and Throughput X-Celerator are trademarks of Celeritas Technologies Ltd.