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56K Modems - FAQs Are 56K modems just a further development of V.34 modems? When will there be a single standard for 56K modems? Which modem technology to choose - K56flex or x2? Why is there a limit on the upload speed of a 56K modem? Will the upstream speed be limited to V.34 rates? Is it worth having a modem that only offers a higher speed in one direction? Can a 56K modem be used for anything other than a "home-to-ISP" connection to the Internet? Can two 56K modems connect at speeds in excess of V.34 when used in a home-to-home connection? Can I use a 56K modem to connect to an ordinary analogue modem such as V.34? If I purchase a 56K modem, will I always connect at the speeds possible with 56K technology? Will all types of 56K modems connect with each other? Is it true that 56K modems are limited to 53Kbps? If I can't even achieve 28.8Kbps / 33.6Kbps now, should I even consider a 56K modem?" Does 56K technology mean there is now no need for ISDN?
Are 56K modems just a further development of V.34 modems? No. 56K technology is based on a totally different concept from V.34 modems. It will only work where the end-user modem connects, via analogue phone line, to a server-site modem which is directly linked to the digital telephone network via a T1 or PRI line. This new type of connection can be referred to as a home-to-ISP (Internet Service Provider) connection
Two manufacturers, Lucent Technologies and Rockwell, produce modem chip sets that implement the same 56K technology. The high-speed modem protocol employed by these devices is called K56flex™.
x2™ Technology is the name of a transmission scheme developed by US Robotics (now part of 3Com) that is capable of line speeds of up to 56Kbps.
When will there be a single standard for 56K modems? An ITU standard for 56K isn't likely until sometime during the second half of 1998 at the earliest. Will K56flex or x2 become the standard? In all probability it will be neither, but instead it will most likely be a combination of elements of both the current x2 and K56flex technologies.
Which modem technology to choose - K56flex or x2? One answer is to choose the one your Internet Service Provider is using or is going to use (or choose an ISP who provides support for both). Whatever you do, you should check that the modem you are going to buy will be upgradable - preferably by a free software program - to the final ITU-T 56K standard when it is established. That way your investment is protected for the future.
Experts said that 33.6Kbps was about as fast as a modem could go - how does 56K technology exceed this? Shannon's Law theoretically defines the maximum line speed based on the impairments (including all kind of noise) in the telephone link between two points and the bandwidth of the channel. In home-to-home connections, the telephone network will first convert the analogue signal transmitted from user A's modem to a digital signal. This will then be transmitted digitally from the telephone exchange in user A's area to the exchange in user B's area. This digital signal will be converted back to an analogue signal before being sent via analogue phone line to user B's modem. The telephone network's analogue-to-digital converter introduces noise, technically called quantization noise, and the maximum speed determined by Shannon's Law is around 35 Kbps using this type of connection. In a home-to-ISP type of connection, 56K technology takes advantage of the fact that the network has no analogue-to-digital converter in the end-user's downloading path. This eliminates the quantization noise that would have been introduced if the connection from the server to the telephone network were analogue.
Why is there a limit on the upload speed of a 56K modem? When downloading over a 56K connection, data is passed directly to the digital telephone network and requires no conversion until it reaches the end-user’s telephone exchange. Here the data is changed from a digital signal to an analogue signal. Conversion of a signal from digital-to-analogue does not cause any impairment to the data, so downloading at speeds up to 56Kbps is possible. However, when uploading, data is changed from an analogue signal to a digital signal by a process known as quantization. There is a problem here because analogue waveforms are continuous and binary numbers are discrete, so when the digits that are sent across the telephone network are converted back at the other end, the resultant signal only approximates to the original analogue waveform. The difference between the original analogue waveform and the reconstructed quantized waveform is called quantization noise. This noise limits modem speed.
Will the upstream speed be limited to V.34 rates? At the moment, yes. The initial implementations of 56K technology use V.34 rates for upstream (uploading) data. Future developments may utilise additional techniques to enable rates higher than V.34 rates in the upstream direction.
Is it worth having a modem that only offers a higher speed in one direction? The great majority of Internet traffic is asymmetrical in that the largest amount of data travels from the Internet to the end user (downstream) in the form of text and graphics. Most communication from the end user to the Internet (upstream) consists only of mouse clicks and keystrokes. 56K technology is therefore ideally suited to Internet connections.
Can a 56K modem be used for anything other than a "home-to-ISP" connection to the Internet? Yes, although Internet connection is the obvious use. 56K technology could also be useful for other applications, subject to the proviso that at least one end of the connection is digitally terminated. For example, it could find application in business solutions where users connect to a private business server and where most data traffic is downstream from the server to the end user.
Can two 56K modems connect at speeds in excess of V.34 when used in a home-to-home connection? No, they can’t. 56K technology is designed for home-to-ISP connections and demands that the ISP site has a digital connection to the telephone network and that the end user connects to an analogue phone line. However, you can still use 56K modems for home-to-home communications because in this case the modems will automatically connect to each other in V.34.
Can I use a 56K modem to connect to an ordinary analogue modem such as V.34? Yes you can. A 56K modem automatically detects the capabilities of a remote modem and will use a feature called "automode" to match itself to the capability of the remote modem. And remember, if the rules for a half-digital connection are broken, a 56K modem will fall back to a V.34 connection.
If I buy a 56K modem, will I always connect at 56Kbps? You can only achieve 56K rates when you connect to a compatible 56K modem at an ISP that has a digital connection to the telephone network. Therefore, 56K modems must be in use at all the sites you plan to connect to, and furthermore they must be of compatible types (K56flex™ or x2™). In addition, remember that the speed of 56Kbps demands a perfect telephone connection; in practice you can expect to connect at a slower speed than this.
Will different makes of 56K modems connect with each other? The first and most important thing you need to know about 56K modems is that there are two 56K protocols, and that these protocols are incompatible. These proprietary 56K protocols are known as x2™ from U.S. Robotics (now merged with 3Com), and K56flex™ from Rockwell and Lucent Technologies. Modem manufacturers who produce 56K modems will use one or the other of these two protocols. If you buy a modem that uses K56flex protocol, you won't be able to call a modem using the x2 protocol and get the full speed. 56K modems will, however, fall back to a V.34 connection if the other modem is not compatible, so you can still connect even though it won’t be at 56Kbps.
Is it true that 56K modems are limited to 53Kbps? Partly true. Because of FCC limitations, x2 is effectively limited to 53Kbps in the U.S., at least initially, but K56flex is not affected. This isn't a major issue, as most people probably wouldn't connect at the full 56Kbps anyway, due to the telephone line constraints that prevent many people from connecting at 28.8 or 33.6Kbps. In any event, the difference between 53Kbps and 56Kbps is hardly of great significance.
If I can't even achieve 28.8Kbps / 33.6Kbps now, should I even consider a 56K modem?" The answer is that you can get potentially higher connection speeds with 56K. The half-digital nature of 56K means that your connect rates will be higher than with pure analogue technology.
Does 56K technology mean there is now no need for ISDN? No, it doesn’t mean that at all. In fact, ISDN can provide much higher data transmission speeds. Also, bear in mind that the fastest speed the 56K modems can reach is heavily dependent on the telephone line conditions and other network related issues. On the other hand, the wholly digital nature of ISDN means that its higher speeds are virtually guaranteed. The 56K modems are designed specifically for end users that want higher speed connections to the Internet without having to change their existing analogue telephone connection.
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