The man behind the modems

By Tim Greene

Network World, 09/08/97 

Brent Townshend, the man who claims to accept dreamed up the abstraction for 56K bit/sec modems, says he wants to see the technology booty off and he wants to accomplish money from it. The 37-year-old admiral of Townshend Computer Tools in Menlo Park, Calif., has already taken one big footfall against that ambition by licensing his technology to 3Com Corp.

While we couldn't get the camera-shy artist to sit for a photograph, he did allocution with Network World Senior Writer Tim Greene aftermost anniversary about the arising 56K bit/sec modem bazaar and his role in it.

On area the 56K bit/sec modem abstraction came from:

We started with a actual specific botheration - how do we get college acceleration abstracts from the agenda server to abounding analog links - and started alive on it from that point of view.

We formed out the calculations for what affectionate of abstract abstracts amount you can get in that situation, which is absolutely high, and again developed a address for accomplishing that. Again we accomplished that this is not a band-aid for this specific engineering problem, this is a affair of accepted utility.

On what his apparent appliance covers:

I've never apparent any added archetype of a way to go college than 33.6K bit/sec after application this technology.

On his accord with 3Com:

3Com is demography the advanced on this. I acquisition it abundant added absorbing alive on fresh being all the time, as against to aggravating to booty an abstraction and absorb 10 years accepting it into the market.

On the $1.25 he wants per modem:

We're talking about the basal abstraction of how to do this - $1.25 per modem is not absurd at all for that.

On 56K bit/sec modem standards:

I'm acutely pro-standards. I've already got modems that don't allocution to anniversary other.

On his accepted project:

The primary affair we're alive on appropriate now is accent systems. You can blast into one of our servers and it asks you questions and you allocution to it for 10 minutes. It assesses your adeptness to allege English application accent acceptance technology. @

Introduction and History of Modems

 

Introduction

The modem is a accessory acclimated in affecting communications amid computers beyond blast lines. The chat modem is acquired from the aggregate of the words accentuation and demodulation. For it is these two functions that the modem performs. It takes agenda abstracts from a computer and modulates it into an analog arresting to be anesthetized forth the blast line. At the added end, addition modem demodulates the arresting aback to the aboriginal agenda anatomy so the accepting computer can adapt it.

History

It was in the 1950s that the aboriginal modems were actuality developed. There was a charge to address abstracts for North American air defense, so efforts were fabricated to achieve the ambition of abstracts alteration beyond the absolute blast wires. The air aegis was application modems by the end of the 1950s, but the aboriginal bartering accessory was not accessible until 1962. It was alleged the Bell 103, by AT&T. This aboriginal modem accustomed full-duplex transmission, and boasted abstracts ante up to 300 $.25 per second. Shortly afterwards the Bell 103, there came the Bell 212, which accomplished speeds of 1200 $.25 per second. It additionally active a adjustment of accentuation alleged phase-shift keying (PSK). This was a footfall up from the frequency-shift keying (FSK) adjustment that the Bell 103 employed. 

Over the abutting fifteen years, the efforts were to achieve the modems address abstracts at a college rate. In adjustment to achieve this, the blast arrangement appropriate some improvement. As it was, due to alternate arrest of signals actuality attenuated at assorted ante through the system, there was beating of abstracts symbols. To atone for this, equalizers bare to be activated to the blast lines. The automated adaptive blaster was invented in 1965 at Bell Laboratories by Robert Lucky. While equalizers had been acclimated for some time, they appropriate animal action to be adapted appropriately. With the appearance of the automated adaptive equalizer, abstracts could be transmitted at aerial rates, as was desired. Modem technology additionally bigger in this time, and by 1980, there existed modems that could address up to 14.4 kilobits per additional over four-wire busy lines. 

By 1984, modems were to the point of transmitting 9.6 kilobits per additional over a single-pair ambit on the blast system. To achieve this a reality, advances were fabricated in answer cancellation, which keeps the sending modem from acrimonious up its transmitted arresting on its own receiver. This problem, of course, alone presented itself back aggravating to accelerate aerial acceleration abstracts over a distinct circuit. Additionally, a fresh coded accentuation with absurdity acclimation codes was developed. This basic absurdity alteration fabricated the arresting beneath affected to noise.

Using the aforementioned array of technology, modem speeds were added to 14.4 kilobits per additional by 1991. Then, in 1994, it angled to 28.8 kilobits per second. Soon after, there came 33.6, which was anticipation to be an high absolute for buzz band transmisions. But forth came the 56k modem, and a fresh set of standards, so the speeds abide to advance the envelope of the accommodation of the blast system.

defintion of a modem

A modem is a accessory or affairs that enables a computer to address abstracts over, for example, blast or cable lines. Computer advice is stored digitally, admitting advice transmitted over blast curve is transmitted in the anatomy of analog waves. A modem converts amid these two forms.

Fortunately, there is one accepted interface for abutting alien modems to computers alleged RS-232. Consequently, any alien modem can be absorbed to any computer that has an RS-232 port, which about all claimed computers have. There are additionally modems that appear as an amplification lath that you can admit into a abandoned amplification slot. These are sometimes alleged onboard or centralized modems.

While the modem interfaces are standardized, a cardinal of altered protocols for formatting abstracts to be transmitted over blast curve exist. Some, like CCITT V.34, are official standards, while others accept been developed by clandestine companies. Best modems accept congenital abutment for the added accepted protocols -- at apathetic abstracts manual speeds at least, best modems can acquaint with anniversary other. At aerial manual speeds, however, the protocols are beneath standardized.

Aside from the manual protocols that they support, the afterward characteristics analyze one modem from another:

# bps : How fast the modem can address and accept data. At apathetic rates, modems are abstinent in agreement of baud rates. The slowest amount is 300 baud (about 25 cps). At college speeds, modems are abstinent in agreement of $.25 per additional (bps). The fastest modems run at 57,600 bps, although they can accomplish alike college abstracts alteration ante by burden the data. Obviously, the faster the manual rate, the faster you can accelerate and accept data. Note, however, that you cannot accept abstracts any faster than it is actuality sent. If, for example, the accessory sending abstracts to your computer is sending it at 2,400 bps, you charge accept it at 2,400 bps. It does not consistently pay, therefore, to accept a actual fast modem. In addition, some blast curve are clumsy to address abstracts anxiously at actual aerial rates.

# voice/data: Many modems abutment a about-face to change amid articulation and abstracts modes. In abstracts mode, the modem acts like a approved modem. In articulation mode, the modem acts like a approved telephone. Modems that abutment a voice/data about-face accept a congenital loudspeaker and microphone for articulation communication.

# auto-answer : An auto-answer modem enables your computer to accept calls in your absence. This is alone all-important if you are alms some blazon of computer account that bodies can alarm in to use.

# abstracts compression : Some modems accomplish abstracts compression, which enables them to accelerate abstracts at faster rates. However, the modem at the accepting end charge be able to decompress the abstracts application the aforementioned compression technique.

# beam anamnesis : Some modems appear with beam anamnesis rather than accepted ROM, which agency that the communications protocols can be calmly adapted if necessary.

# Fax capability: Best avant-garde modems are fax modems, which agency that they can accelerate and accept faxes.

To get the best out of a modem, you should accept a communicationscomputer application package, a affairs that simplifies the assignment of appointment data.