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Frequently Asked Questions---K56Flex Modem


A1: The International Telecommunications Union (ITU-T), sets the standards for modem protocols used worldwide. In early February, the ITU-T 56K standard was "Determined". This means that a published technical standard outlining the method for communicating at 56K will be available for all modem vendors to implement. This "Determination" was approved on February 5, 1998. The ITU-T is expected to ratify the V.90 standard in early Fall of 1998.

A2: Testing show that most users are able to get a connections from 42-52 Kbps. There are other factors that come into play as well, primarily being how many analog-to-digital conversion occur between your phone and the telephone comapny's central site. These may factors may preclude your 56K modem from performing optimally.

A3: The basic concept behind this communications technology is that the public switched telephone network (PSTN) is increasingly a digital rather than analog network. Existing analog modems, such as V.34, "see" the PSTN as an analog system, even though the signals are digitized for communications throughout most of the network. Rockwell's 56Kbps technology looks at the PSTN as a digital network which just happens to have an "impaired" section represented by the copper wire connection between the central office and the user's home, usually referred to as the analog local loop. To make the technology work over that analog loop, it must "equalize" the line using special technology that converts the signal samples seen by the user’s modem into the equivalent of what is being sent from the central office.

A4: No, the techniques used in V.34 (28.8Kbps) have been exploited to their limits. This is a new technique where the network is viewed as a digital transmission medium and the data is encoded for transmission over the user’s telephone line, also known as the analog local loop

A5: Yes, if one is a central-site modem with a digital connection to the network. On the other hand, two end-user modems incorporating this technology will not connect using this technique. Furthermore, 56Kbps speeds can only be achieved on good line conditions.

A6: 56Kbps technology-will primarily be used for faster web browsing and Internet access and for faster remote access to corporate LANs that digitally connect to the PSTN.

A7: Shannon's limit is theoretically determined by the impairments (noise) in the telephone link. This new technique relies on a reduced noise environment due to a digital connection to the network by the service provider and a new encoding technique

A8: Actually, the concept has been around for a number of years but it hasn't been practical because most modems installed at service providers used to use analog connections to interface to the network

A9: It is neither a compression algorithm nor a modulation scheme. Data is actually passed on the telephone line at 56Kbps. It is a technique for encoding data for transmission over the telephone line -- we prefer to refer to it as an encoding technique instead of a modulation scheme.

A10: In modulation, a carrier is modified so that it carries information. Ordinary modems modulate a carrier to carry digital data. In this new technique we encode the data. By "encoding," we mean that data is sent in digital form through the network, and encoded in such a manner that it can pass through the user's analog telephone link at a high rate.

A11: There are no relationships. In reference to all of these techniques the advantage of this new technique is that it works over the existing switched telephone network. It does not require the telephone company to replace or add any new equipment.

A12: ISDN, which provides two 64Kbps channels has not yet achieved a significant penetration in the home market. This 56Kbps technology will allow users to gain the speed advantages of almost one ISDN channel without having to order and pay for a new ISDN telephone line.

A13: This technology does not require new services. It will utilize the existing analog telephone service.

A14: Theoretically, the technology can approach 64Kbps; however there are a number of practical problems with achieving this speed including line noise. non-linear distortion, the quality of the network coded and others. The industry is working to push the technology to its highest possible data rate, and rates near 64Kbps may be possible in the future.

A15: Similar to end-users the ISP must have equipment that includes modems which support this technique. Additionally, the ISP must utilize a digital connection to the network. This will be an extremely straightforward process for ISPs who are installing new central-site equipment featuring the new 56Kbps modems. However ISPs who wish to upgrade existing central-site equipment to the new 56Kbps technology face two additional issues.Firsts ISPs will probably wish to use ISDN Primary Rate Interface (PRI) network connections rather than lower-performance T1 "robbed bit" interfaces. All other things being equal, users will be able to connect at a higher rate to an ISP utilizing ISDN PRI than to one utilizing a T1 "robbed bit" signaling. Many ISPs, therefore, will want to upgrade their network interface to ISDN PRI, as well as adding 56Kbps modem capability to their central-site equipment.Second, ISPs will need to make sure that their equipment provides adequate compression performance at 56Kbps operation. Without adequate compression performance, the "effective throughput" may not be much better than what users experienced at 28.8 Kbps or 33.6 Kbps. Some of the central-site modems which are being promoted as "upgradeable" to a 56Kbps encoding scheme may only have enough processing power to support adequate compression performance at 28.8Kbps and 33.6Kbps speeds. In these cases, users may not experience better throughput than when they were operating at 28.8Kbps or 33.6Kbps speeds. This is an especially insidious problem because it occurs at the central site, out of the control of the user. Even if the user has purchased a new 56 Kbps modem, the throughput may be limited by poor compression performance at the central site.

A16: It is important to first understand how modems work. Data is first sent into a modem, where it is compressed and sent over the telephone line to another modem, where it is then decompressed. The amount of data that can be sent into the modem and effectively transmitted to the other end is called the effective throughput. The level of compression that the modem's processing power can support affects the effective throughput. The better the compression, the higher the effective throughput. And the higher the effective throughput, the faster the Web pages will come up on the user's screen.

A17: Products incorporating this new technology will also contain all previous modem modulations, including V.34, V.32bis, and facsimile modulations. During the initial stages of a connection the two modems will determine what modulation and at what speed the transmission will occur.

A18: It is more difficult to equalize the upstream channel, and therefore more difficult to achieve the same high data rates as are achieved in the downstream charmed However, for Internet access, the data rate in the upstream direction is less important than downstream, since the upstream channel transmits mostly "key strokes and mouse clicks." At present, a data rate of around 30 Kbps can be attained in the upstream directional but research continues toward increasing that rate.

A19: Although it appears that most companies are using the same basic technique to achieve 56Kbps operation the specific design choices are unlikely to be the same. However, if two modems are unable to connect at 56Kbps, they will drop down to a mutually interoperable industry-standard data rate like 28.8Kbps or 33.6Kbps. Rockwell is working with the appropriate standards bodies, toward the development of a ratified specification that will serve as a worldwide interoperability vehicle.

A20: The ITU sets international standards and thus would be the preferred standards body for this technology. On November 13, 1996, Rockwell Semiconductor Systems hosted the TR-30 Pulse Code Modulation (PCM) ad hoc group, the first standards meeting aimed at creating draft standards for PCM modem technology. These draft standards are being developed to ensure interoperability between 56Kbps products from a broad spectrum of modem vendors and other communications equipment suppliers. Rockwell was joined at the meeting by a number of leading U.S. PC and communications companies including Intel, Lucent, gayest Motorola, IBM, Compaq and Cisco. This ad hoc committee has been created under the direction of the Electronics Industry Association (EIA) and Telecommunications Industry Association (TIA) to develop an EIA/TIA interim standard for U.S. 56Kbps PCM modems by mid-1997. The TIA TR-30 group also will serve as the advisory committee to the U.S. government on modem-related issues involving the International Telecommunications Union (ITU). It is expected that the group's interim work in the U. S. will form the basis for a U.S. submission to the ITU for a worldwide standard for 56Kbps modem technology. Rockwell is a charter member of this TIA group and is the assistant editor for the draft standard, working with Motorola.

A21: Interoperability is critical to any modem technology. In the case of 56Kbps modems the technology introduces new issues which may require slightly different handling by the industry standards bodies as compared to previous 28.8Kbps and 33.6Kbps efforts. Rockwell is working with a number of other leading PC, modem, and telecommunications equipment vendors to address these new issues which may impact the future success of 56Kbps modems. Also, Rockwell has joined with Lucent to announce that the two companies will make their 56Kbps modem chipsets interoperate at 56 Kbps. Agreements like this help to ensure that customers who purchase a modem that implements Rockwell's K56Plus will have the highest probability of achieving a connection at speeds up to 56Kbps.

A22: The diffusion rate for a new modem technology like this will be slow, and it is critical that the industry develop worldwide standards. Early installations of 56Kbps will likely be "show POPs" rather than general deployment. Network operators will likely move slowly to avoid problems for their users. The issue of "which 56Kbps?" will disappear when there are standards. Rockwell is an active participant in the standards-development process, and is also working very closely with the central-site equipment suppliers who provide the critical ISP technology to make 56Kbps work.

A23: No, this new technology will work over a single existing analog phone line.

A24: The user must have a modem which implements this new technology.
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