WO1997049229A1

WO1997049229A1 - System and method for automatically selecting the mode of communication between a plurality of modems

Info

Publication number: WO1997049229A1
Application number: PCT/US1997/009020
Authority: WO
Inventors: Robert Earl Scott; E. Robert Lastinger, Jr.
Original assignee: Paradyne Corporation
Priority date: 1996-06-21
Filing date: 1997-05-29
Publication date: 1997-12-24
Also published as: TW349315B

Abstract

A system is provided for automatically selecting the mode of communication between a plurality of multi-mode modems. A calling modem (20) and an answering modem (24) are disposed for intercommunication across an established communication link (37) of a telephone netowrk. The calling modem (20) transmits a continuous calling signal across the established link (37), and the answering modem detects the calling signal and analyzes the calling signal to determine the configuration of the calling modem (20). In response, the answering modem (24) generates and transmits an answering signal across the established link (37). The calling modem (20) detects and analyzes the answering signal to determine the configuration of the answering modem (24). Finally, the system determines whether the established link (37) passes through a PSTN, and if so, transmits a 2100 hertz tone across the established link (37). Otherwise, the system proceeds directly to the modem training sequence.

Description

SYSTEM AND METHOD FOR AUTOMATICALLY SELECTING THE MODE OF COMUNICATION BETWEEN A PLURALITY OF MODEMS

Field of the Invention

The present invention generally relates to modem systems, and more particularly,

to a system and method for automatically and rapidly establishing the mode of communication between two modems.

Discussion of the Related Art

As is known, a variety of standards exist, which govern the protocol for

communication between modems. For example, V.21 , V.22, V.32, V.32bis, and V.34

are identifiers of differing communication modulation standards, just to name a few.

Simply stated, communication standards govern how modems communicate information

(voice and/or data) back and forth. With increased technology, more recent standards

generally incorporate more sophistication and versatility than older standards.

For instance, the V.34 standard, which is intended for use on connections on

general switched telephone networks and on point-to-point two-wire telephone type

circuits, includes the following primary characteristics: (1 ) full and half-duplex modes of

operation; (2) echo cancellation techniques for channel separation; (3) quadrature

amplitude modulation for each channel with synchronous line transmission at selectable

symbol rates; (4) synchronous primary channel data signaling rates ranging from 2,400

bits per second to 33,600 bits per second, in 2,400 bit-per-second increments; (5) trellis coding for all data signaling rates; and (6) exchange of rate sequences during start-up to

establish the data signaling rate. The features of the V.34 standard are documented in the

publicly-available V.34 specification and well known by those skilled in the art, and will

not be described in detail herein.

Another significant feature of the V.34 standard, as it relates to the present

invention, is the ability to automode to other V. -series modems that are supported by the

V.32bis Automode procedures. In this regard, the V.34 modulation standard defines

signal handshaking that two connecting modems exchange at startup in order to learn the

capabilities of the other modem to most efficiently exchange information.

While the V.34 modulation achieves efficient and generally high speed

communication between two communicating modems, it nevertheless possesses several

shortcomings that impede even more efficient operation. One such shortcoming relates to

its universal, but fixed configuration. While the V.34 modulation standard is "intelligent"

enough to identify and adapt its communication-to-communication protocols of other

modems, its operation is fixed in relation to its operating environment. That is, a modem

operating pursuant to the V.34 modulation operates in the same fashion regardless of whether it is communicating via cellular link, through a two-wire or four-wire PSTN

(Public Switched Telephone Network) network, through a leased line, a Tl , etc. It is

recognized, however, that certain "overhead" associated with the communication through

some of these mediums is not needed when communicating through other mediums. For

example, when communicating through a PSTN network, an initial two second connection period is required before information can be exchanged between the

communicating modems. As is known, this two second delay is a requirement imposed

by the FCC (Federal Communication Commission) for billing purposes - in early

telephone systems, customer billing did not occur during the first two seconds after the

connection was established. As a result, systems generally delay the transmission of

information for a period of two seconds after the initial connection is established.

Generally, when transmitting through a PSTN, this delay is accomplished by inherent

delay in the startup between two modems.

Other shortcomings in, not only the V.34 modulation standard, but other

contemporary modem systems relate to the initial transmission from the calling modem to

the answering modem. Presently, calling modems transmit the calling signal through a

tone cadence, where a calling tone is transmitted for a period of time (typically, 0.5 to 0.7

seconds in length), then the transmitter is turned off, while the calling modem "listens"

for a response from the answering modem. As is known, this cadence in the calling

signal originated from older systems which employed echo suppressers. The initial

startup sequence in systems employing echo suppressers is half-duplex. Therefore, the

calling modem has to stop transmitting the calling signal in order to "listen" for and

receive the answer signal. Although echo suppressers have been replaced by echo

cancellers (which permit full-duplex startup) in virtually all modern systems, modems

still transmit the calling signal in cadence form. As a result, if the answering modem makes use of the calling signal, the average time required for the calling and answering

modems to signal their initial connection is unduly lengthy.

Another significant shortcoming associated with the lengthy startup sequence, and

one which served as a motivation in developing the present invention, relates to

reliability. It has been found that, particularly over a cellular link, the long data exchange

sequence that occurs at startup results in higher incidents of failure and thus compromises

reliability.

In summary, while multi-mode modem communication systems are known, these

systems fail to recognize the communication environment or configuration, and therefore

fail to achieve a dynamic, time-efficient, and reliable startup.

Summary of the Invention

Accordingly, a primary object of the present invention is to provide an improved

multi-mode modem for use in a modem communication system.

A more specific object of the present invention is to provide a multi-mode modem

that provides a protocol for faster and more efficient startup operation based upon the

system configuration and the path of the established communication link. Another object

of the present invention is to provide a multi-mode modem that is capable of determining

whether the established communication link with a remote modem does not pass through

a PSTN and dynamically alter its startup sequence in such cases to achieve a more time-

efficient startup sequence. Still another object of the present invention is to provide a multi-mode modem

that has improved reliability over multi-mode modems in the prior art.

Yet another object of the present invention is to provide a multi-mode modem that

achieves a faster startup exchange than multi-mode modems in the prior art.

Additional objects, advantages, and other novel features of the invention will be

set forth in part in the description that follows and in part will become apparent to those

skilled in the art upon examination of the following description or may be learned via the

practice of the invention. Furthermore, the objects and advantages of the invention are

realized and obtained by means of the instrumentalities and combinations particularly

pointed out in the appended claims To achieve the foregoing and other objects, the

present invention is generally directed to a system for automatically selecting the mode of

communication between a plurality of modems. In accordance with one aspect of the

invention, a calling modem and an answering modem are disposed for

intercommunication across an established communication link of a telephone network.

The calling modem includes calling signal means for generating and transmitting a

continuous calling signal across the established link, and the answering modem includes

detecting means for detecting the calling signal. The answering modem further includes

analyzing means for analyzing the detected calling signal to determine the configuration

of the calling modem, and means for generating and transmitting an answering signal

across the established link. Similarly, the calling modem includes detecting means for

detecting the answering signal, and analyzing means for analyzing the detected answering signal to determine the configuration of the answering modem. Finally, the system

includes determining means for determining whether the established link passes through a

PSTN, and means responsive to the determining means for transmitting a 2100 hertz tone

across the established link only if the established link passes through a PSTN. In a

preferred embodiment, the configuration of both the calling and the answering modems is

determined by configuration settings that may be adjustably established during modem

installation into the system. For example, the configuration settings may be as simple as

hardwired set of DIP (Dual In-line Package) switches. Alternatively, a programmable

memory such as an EEPROM (Electrically Erasable Read Only Memory) may be

programmed during installation to contain the configuration settings. In this regard, the

configuration information, among other information, may contain connection

information. For example, whether the modem is connected to a cellular phone and thus

to a cellular network switch, or alternatively whether the modem is connected via a two-

wire connection, four-wire connection, Tl line, or otherwise connected through a PSTN.

The configuration settings may also contain information regarding the one or more

modulation protocols in which the modem is capable of transmitting.

Another aspect of the present invention relates to a method for automatically

establishing the mode of communication between modems. More specifically, several

aspects of the present invention are directed to efficiently and automatically establishing a

mode of communication between a calling modem and an answering modem in a

networked system having an established communication link between multi-mode

modems. One such aspect relates to the establishment of the initial communication

between the modems by transmitting a continuous calling tone. Transmitting continuous

calling tone reduces the average time required for the modems to exchange their initial

connect information. Another aspect relates to the ability of the modems, particularly the

calling modem, to determine whether the established communication link passes through

a PSTN. If the established link does not pass through a PSTN, then the initial two second delay required by the FCC may be avoided, providing for a faster startup.

Description of the Drawings

The accompanying drawings incorporated in and forming a part of the

specification, illustrate several aspects of the present invention, and together with the

description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a system diagram, illustrating a multi-modem system wherein a plurality

of modems are interconnected among a plurality of communication links;

FIG. 2 is a block diagram illustrating the primary handshaking and data exchange

sequences between a calling and an answer modem; FIG. 3 is a schematic diagram similar to FIG. 2, illustrating the signal exchange

during the automatic mode synchronization sequence of FIG. 2;

FIG. 4 is a software flowchart illustrating the architecture and operation of the

present invention when the calling modem is a cellular modem;

FIG. 5 is a software flowchart illustrating the architecture and operation of the

present invention when the answering modem is a cellular modem;

FIG. 6 is a software flowchart illustrating the architecture and operation of the

present invention when the calling modem is a central-site modem;

FIG. 7 is a software flowchart illustrating the architecture and operation of the

present invention when the answering modem is a central-site modem; and

FIG. 8 is a block diagram illustrating the principal internal components of a pair

of modems.

Reference will now be made in detail to the description of the invention as

illustrated in the drawings. While the invention will be described in connection with

these drawings, there is no intent to limit it to the particular embodiment or embodiments

disclosed therein. On the contrary, the intent is to cover all alternatives, modifications,

and equivalents included within the spirit and scope of the invention, as defined by the

appended claims.

Detailed Description of the Preferred Embodiment

Turning now to the drawings, FIG. 1 shows a system diagram of a system having

multiple modems intercommunicating through a variety of mediums, including cellular

and PSTN. Indeed, as previously mentioned, a driving factor in the development of the

present invention was to design a system that provided improved reliability in data

communication over a cellular link. This goal has been achieve by providing a more

robust startup sequence for modem communication. Thus, FIG. 1 illustrates a multiple-

modem system centered around a cellular network switch 12.

As illustrated, a cellular modem system 14 may be disposed for communication

with the cellular network switch 12. More specifically, a portable computer 15 may be

connected via cellular modem 16 to a cellular phone 17, which in turn communicates

wirelessly with a cell tower 18 that communicates with the cellular switched network 12.

It is appreciated that the modem 16 recognizes that it is on the cellular side via a strap or

configuration setting, or alternatively, by a direct connect sensing of the cellular phone.

Therefore, and as will be discussed in more detail below, the modem 16 will know that it

is capable of communicating in accordance with the modulation standard of the present

invention.

The cellular network switch 12 is also connected to a modem pool, including

modems 20 and 24. The modems 20 and 24 are illustrated as connected in back-to-back

configuration and communicating to the cellular network switch 12 over links 22 and 26. 97/49229 PCΪYUS97/09020 -

As will be appreciated and discussed below, the links 22 and 26 will support different

communication protocols, or different modulation standards.

By way of definition, a "central-site" modem is one that is capable of supporting

the modulation standard of the present invention and is not connected to a cellular phone.

In this regard, all central-site modems are connected via a four-wire connection.

Examples which are illustrated in FIG. 1 include an MSC (Cellular) modem 20, an MSC

(PSTN) modem 24, an MSC (Single-ended) modem 28, and a PSTN (ETC2) modem 30 -

where an MSC modem is one that is connected at a Mobile Switching Center. A

significance of the distinction among these various types of modems relates to the startup sequence, which will differ slightly depending upon the type of central-site modem.

Preferably, a hardware identifier, such as a DIP switch or a firmware option configurable

at modem installation, defines the type of modem for purposes of the startup sequence.

In keeping with the description of FIG. 1, modem 20 is illustrated as an MSC

(Cellular) modem that is connected in a back-to-back mode with modem 24, an MSC

(PSTN) modem. Modem 20, therefore, is designed to support the ETC2 modulation

protocol of the present invention and simulate a cellular modem during the initial modem

startup routine. Modem 28 is an MSC (Single-ended) modem that, although it may

communicate with modems on the PSTN 34, will typically communicate only with

cellular modems. Indeed, when communicating with cellular modems the 2100 Hertz

tone, which is typically inserted to disable echo cancellers, is preferably omitted. Advantageously, elimination of this tone achieves a faster and more desirable modem

startup.

A PSTN (ETC2) modem 30 and a standard PSTN modem are connected via

PSTN 34 to the cellular network switch 12. The modem 30 is connected to the PSTN 34 via a four- wire connection 35 and modem 32 via a two-wire connection 36. Consistent

with the concepts and teachings of the present invention, the four- wire connection 35

facilitates the communication of modem 30 with a cellular modem 16, for example, in the

ETC2 modulation standard of the present invention. However, as will be appreciated by

those of ordinary skill in the art, merely ensuring a four- wire connection 35 alone will not

ensure proper system operation in accordance with the present invention. In this regard,

such a four- wire connection 35 may nevertheless pass through a two-wire connection, and

thus a hybrid converter circuit, at the central office. In this event, echo will be injected

into the signal and the abbreviated modulation standard of the present invention may be

compromised. There are, however, steps that may be taken to ensure proper operation of

the invention. These include, for example: (1) ordering a Direct Inward Dial connection

and instructing the phone company to avoid a two-wire connection for that setup; (2)

obtain a direct Tl to the Interexchange Carrier (for example, a "1-800" number); and

obtaining an ISDN PRI connection, as it will always support four-wire for both call

origination and call answer.

By way of illustration, consider a call originated by the computer 15 and cellular

modem 16 to the standard PSTN modem 32. The established communication link will pass through the cellular phone 17 to the cell tower 18, through the cellular network

switch 12, across link 22 to the MSC (Cellular) modem 20, and to the connected modem

24 via RS-232 connection 37, across link 26, and back through the cellular network

switch 12 to the PSTN 34, and ultimately across the two-wire link 36 to modem 32. As

will become clear from the description that follows, the cellular modem 16 and the MSC

(Cellular) modem 20 will connect and startup in accordance with the communication

protocol of the present invention. However, since the established communication link

that passes from modem 24 to modem 32 passes through a PSTN 34 and a hybrid

converter, then the communication protocol of the present invention will not be adequately supported. Accordingly, and in accordance with the invention, the modems

24 and 32 will identify this situation and will connect and communicate using an

alternative communication protocol supported by both modems and capable of effective

transmission across the established link. In this regard, the overall communication link

does not realize the fast startup provided by the present invention, but the protocol of the

present invention ensures that the link between modems 16 and 20 achieves maximum

speed and reliability.

Indeed, a primary feature of the present invention is for connecting modems to

determine whether they are both compatible, in terms of communication protocol, and

whether they are connected through a line that passes through a PSTN. If the modems

are compatible and the established communication link is outside a PSTN (e.g., cellular

to MSC), or is to a PSTN modem with a 4-wire connection that has been configured for supporting this invention, then the modems may connect and begin their startup sequence

in accordance with the present invention. In this regard, the communication protocol of

the present invention is designed to be fast as well as robust and is accomplished by the

use of simple tones. The use of such simple tones facilitates the implementation of the

automatic mode select to be in a modem's control processor rather than the digital signal

processor (DSP) chip.

In addition to the preferred communication protocol of the present invention,

which will be discussed in more detail below, the preferred embodiment also includes

several "fallback" modulations. More particularly, the modem of the present invention

preferably includes ETCl, V.34, V.32bis, V.32, and V.22bis modulations. Thus, in the

previous example, modems 24 and 32 may communicate using one of these

communication protocols. These modulation protocols are documented, will be

understood by persons of ordinary skill in the art, and will not be discussed herein.

Suffice it to say, supporting the above-listed modulation standards greatly enhances the

flexibility and versatility of modems constructed in accordance with the present

invention.

To more particularly describe the initial startup sequence in accordance with the modulation standard of the present invention, reference is made to FIGS. 2 and 3. FIG. 2

illustrates the three principal components of modem exchange or communication. After

the cellular modem initiates the call, such that a communication link is established, the

modems enter a mode select operation 40. During this period, the modems exchange parameters that identify the modems and thus their communication protocol. This

operation 40, thus, synchronizes the modems for communication in accordance with the

same standard or protocol, such as ETC2-QC, V.34, V.22, V.22bis, etc.

Once the modems have synchronized their communication protocol, or

modulation standard, then they enter a training and startup sequence 42. In a manner

known in the art, during this sequence the modems may test the established

communication link for noise, bandwidth, etc. in order to determine an appropriate rate

for communication. The modems may also operate during this period to train their

internal echo cancellers by, for example, ranging the established link of communication.

In accordance with a related aspect of the present invention, under certain circumstances

the modem training and startup sequence may be significantly shortened to provide a more robust (both time-shortened and reliable) startup sequence. More particularly, the

"circumstances" which provide such a robust startup include communicating modems

constructed in accordance with the invention detecting an established link of

communication that does not pass through any two-wire connections.

After the modem training and startup sequence 42 has completed, the

communicating modems enter the information exchange/communication sequence 44.

During this sequence, the modems have exchanged operational and definitional

parameters and are communicating data back and forth. Error correction, dynamic autorating, and other similar features, whether known in the prior art or newly developed,

may be employed consistent with the concepts and teachings of the present invention. Referring now to FIG. 3, the initial automatic mode synchronization 40, executed in

accordance with the preferred embodiment, is illustrated. As shown, this sequence is

executed by exchanging signals between the calling modem and the answer modem. After

the calling modem transmits the dial tones to establish a communication link with the

answer modem, it transmits the calling signal "Clqck" 50. As will be described in more

detail in connection with the flowcharts of FIGS. 4-7, this signal may, in accordance with

the invention, comprise a 1900 hertz tone, or alternatively, may comprise a 1500 hertz tone

modulated with a 1900 hertz tone. If only a 1900 hertz tone is transmitted as Clqck, then

the answer modem knows that the calling modem is configured as a central-site, four-wire

modem (See FIG. 6). Alternatively, if the Clqck signal includes both 1500 and 1900 hertz

components, then the answer modem knows that the calling modem is configured as a

cellular modem.

As will be appreciated by those of ordinary skill in the art, other calling signals may

be transmitted by the calling modem. For example, calling signals consistent with that of a

facsimile transmission, or calling signals consistent with other modem modulation

standards, such as V.34, V32, V32bis, etc. may be transmitted. Since automatic connection

and synchronization to facsimile and these other modulation standards is well known it will

not be discussed herein. Indeed, the significance of the present invention is achieved when

both the calling modem and the answer modem are capable of communicating in

accordance with the modulation protocol herein described. Once the Clqck signal is received by the answer modem, then the answer modem

transmits its response back to the calling modem. The purpose of this answer signal is not

only to signal receipt of the calling signal, but also to uniquely identify the answer modem.

Again, as is known in the art, this answer signal may comprise ANS or ANSam signals, as

are known by the V.34 and V.22 communication protocols. If so, then the calling modem

will then startup and train 42 and communicate 44 in accordance with the appropriate

modulation standard. Significant to the present invention, however, is when the answer

signal is ANSqck, which is defined by either a 1680 hertz tone or an 800 hertz tone.

As illustrated in FIG. 4 (assuming the calling modem is a cellular modem), if

ANSqck is an 800 hertz tone, then the calling modem knows that the answer modem is

configured as a four-wire connection and can communicate with the calling modem in

accordance with the communication protocol of the present invention. In addition, the 800

hertz ANSqck signals the calling modem that the answer modem is connected to a PSTN 34

(see FIG. 1). Therefore, the calling modem transmits a 2100 hertz tone for approximately

one second. This, as is known, serves to pad, or occupy, the initial two second connect

period, as required by the FCC for billing purposes. Furthermore, it serves to disable the

echo cancellers within the PSTN 34.

If ANSqck is a 1680 hertz tone, which is the center tone of V.34 "S", then the

calling modem knows that the answer modem is configured as a four-wire connection and

can again communicate with the calling modem in accordance with the communication

protocol of the present invention. More significantly, it tells the cellular calling modem that the answer modem is not connected to a PSTN 34. Therefore, both the calling modem and

the answer modem can determine that the established communication link is entirely

outside the PSTN 34. Accordingly, the FCC billing delay need not be inserted.

Furthermore, certain assumptions may be made in regard to bandwidth, or transmission

quality. For example, the established communication link will not pass through echo

cancellers, and as a result, the calling modem need not transmit the 2100 hertz tone.

Instead, upon receiving the ANSqck answer signal, the calling modem may immediately

enter the modem training and startup sequence 42.

As will be further appreciated by those of ordinary skill in the art, by making certain

assumptions regarding the line quality of the established link, the modem training and

startup sequence may be shortened. For example, in the preferred embodiment, the system

initiates communication by assuming a 9600 baud rate. It has been found that most cellular

connections may transmit at this rate, and certain front-end savings may be realized by

defaulting to this initial startup rate. Of course, this rate may be increased, or autorated

upwardly, in accordance with methods known in the prior art, after the initial startup and

training sequence 42 has been completed.

Referring now to Fig. 4, a top-level flowchart is shown, illustrating the automatic modes synchronization of a cellular calling modem constructed in accordance with present

invention. Once the calling modem has completed transmitting the dialing sequence, it

transmit the Clqck, which for a cellular calling modem includes modulated 1500 and 1900

hz tones (step 60). Once the calling signal has been transmitted, the calling modem will wait to receive the answer signal from the answer modem. In order to exchange data using

the modified modulation standard of the present invention, the calling modem looks to

receive one of two answer signals. The first valid answer signal as in 1680 hz tone, which

is the center tone of the V.34 "S" signal (step 61). This tone signals to the calling modem

that the answer modem is not only compatible to transmit in the modified modulation

standard to the present invention, but further indicates that the answer modem is connected

via four wire connections, and does not interconnected to a PSTN. Accordingly, since the

calling modem is a cellular modem, then the established communication link does not pass

through a PSTN and the initial two second FCC-required delay need not be inserted into the

start-up sequence. Moreover, since the entire communication link is four wire, then the

modems need not transmit the 2100 hz signal to disable echo cancellor.

A second valid answer signal is an 800 hz tone, which also indicates that the answer

modem is connected via four wire and therefore can communication in accordance with the

modified modulation standard of the present invention. In addition, the 800 hz tone

indicates that the answer modem is connected to a PSTN, (see step 62). Assuming, as

previously discussed, that the requisite steps have been taken to ensure that the established

communication link does not pass through a two wire connection, then certain savings or

efficiencies can be gained during the modem start-up and training sequences (e.g., eliminate

echo training since no hybrid circuits are present in the communication link). Nevertheless, the FCC-required delay is inserted and, therefore, a 2100 hz tone is transmitted at step 63

by the calling modem for a duration of approximately one second. The amount of the 2100 hz tone will "pad" the total modem automode and startup time to two seconds. This assures

that no customer data is transferred in the first two seconds (which meets FCC

requirements.). Thereafter, calling modem proceeds with the modem training and start-up

sequence (step 64).

If neither of the foregoing answer signals are received, then the system operates to

determine whether another valid answer signal has been transmitted from the answer

modem. Step 65 broadly designates this function. It should be appreciated that well known

answer signals, such as ANS or ANSam, may be transmitted by the answer modem and, if

received, the calling modem may synchronize to the appropriate modulation standard (step

66). Although not separately designated in FIG. 4, it should be further appreciated that if no

valid answer signal is received by the calling modem within a given period of time, then the

calling modem will time out and abort the attempted communication. Also, and as

illustrated at step 67, the calling modem will abort the attempted communication if a busy

signal is received.

Fig. 5 shows a top-level flowchart illustrating the architecture of the software for,

and the operation of, a cellular answer modem constructed in accordance with the present

invention. Once the communication link has been established and a call has been initiated,

the answer modem looks to detect the Clqck calling signal (step 70). In the presently

preferred embodiment, cellular to cellular modem communications are not supported.

Therefore, a cellular answer modem will assume that a calling modem transmitted a Clqck

signal will transmit only a 1900 hz tone, rather than the modulated 1500 and 1900 hz tones. Having said this, it should be appreciated that with certain designed implications that

cellular -to -cellular communications could be supported and thus are within the scope of

the present invention.

In keeping with the description of Fig. 5, once the answer modem has received the

Clqck calling signal, it transmits the ANSqck answer signal (step 71). It then waits for the

calling modem to enter the modem start-up and training sequence. This sequence is

identified by receiving the "S" signal as assigned by the V.34 modulation standard (step

72). Once this signal is received, then the answer modem will transmit back to the calling modem the appropriate "S" signal.

Alternatively, if the answer modem, within a period of two seconds, has not

received Clqck calling signal, then it will proceed with the start-up sequence in accordance

with an alternative modulation standard. This, therefore, assumes that the modified

communication protocol of the present invention is not supported by the calling modem,

and the answer modem will typically respond to the calling signal of an alternative

communication signal by transmitting a 2100 hz tone (step 74).

Referring now to Fig. 6, a software flowchart illustrating the top-level software

architecture and operation of a central site calling modem is shown. As depicted, the

calling modem originates the call and establishes a communication link at step 80. Once

the communication link is established, the calling modem transmits the Clqck calling

signal, which in the case of a central site calling modem comprises a 1900 hz signal tone

(step 81). If the 1680 hz ANSqck answer signal is detected (step 82), then the calling modem recognizes the answer modem as one capable of transmitting pursuant to the

modified communication protocol of the present invention. Thereafter, the calling modem

determines the network configuration of the established communication link (step 83). That

is, the central site calling modem will determine whether the established communication

link passes through a PSTN or not. If it is determined that the established link passes

through a PSTN, then, as in the case of the cellular calling modem, the calling modem

transmits a 2100 hz signal for approximately one second (step 84). Thereafter, the calling

modem enters the modem start-up and training sequence (step 85).

Alternatively, if the calling modem detects the ANS answer signal (2100 hz) (step

86), it communicates with the answer modem using the ETC 1 communication protocol and

the V.32bis training (step 87). If the ANSam answer signal is detected (step 88), the

modem will startup in standard V.34 mode, which is well known in the art and therefore not

described herein. The modem will also monitor for ANSqck (step 82), which in this

example is a 1680Hz tone. If this is not detected, then the modem will startup under an

alternate low speed standard (step 89), which is well known in the art and therefore not

described herein. If ANSqck is detected, the modem will operate differently depending on

whether it is connected to the PSTN network or not (step 83.) The modem will know

whether it is connected to the PSTN via a configuration option which was set at install time.

If connected to the PSTN, the modem will transmit a 2100 Hz tone for one second (step

84) then proceed to the ETC2 training sequence (step 85.) If the modem is not connected to the PSTN (step 83), it can proceed directly to the ETC2 training sequence (step 85),

avoiding the additional one second of startup shown in step 84.

Reference is now made to Fig. 7, which is a software flowchart illustrating the top-

level software architecture and operation of a central site answer modem. As illustrated in

the flowchart, and in accordance with the presently preferred embodiment, when the answer

modem is a central-site modem, it assume that any transmissions made in accordance with

the modulation standard with the present invention will be via a communication link with a

cellular calling modem. Therefore, step 90 indicates detection the Clqck calling signal in

the form of a modulated 1500 and 1900 hz tones, as transmitted by cellular calling modem.

If the Clqck calling signal is detected, then the answer modem determines the network

configuration at step 91. More specifically, the answer modem determines whether the

established communication link passes through a PSTN or not. In the event that the

established link does in fact pass through a PSTN, then the answer modem will transmit an

800 hz ANSqck answer signal (step 92). As illustrated in Fig. 4, this instructs the calling

modem to transmit the 2100 hz tone. Alternatively, the answer modem will transmit the

1680 hz tone, which instructs the calling modem to proceed directly with the modem start¬

up and training sequence (step 93). Thereafter, the answer modem will await transmission

of the "S" signal in accordance with the V.34 start-up sequence (step 94). Thereafter, the

answer modem will respond by transmitting the "S" of the V.34 start-up (step 95). Since

the V.34 start-up sequence is well-known in the art, it would not be described herein. The remainder of the flowchart depicted in Fig. 7 illustrates the central-site answer

modem operation and connects sequence in accordance with alternative standards that are well-known in the prior art and need not be discussed herein.

Regarding the implementation of the present invention, FIG. 8 generally

illustrates the components of MSC(cellular) modem 20 and MSC(PSTN) modem 24.

The MSC(cellular) modem 20 comprises a digital signal processor (DSP) 112, a central

processor 114, and a DTE interface 116. Likewise, the MSC(PSTN) modem 24

comprises a DSP 118, a control processor 120, and a DTE interface 122. The DTE

interface 116 of the MSC(cellular) modem 20 interfaces with the DTE interface 122 of

the MSC(PSTN) modem 24 via the connection 38, which can be implemented by any

suitable interconnecting device such as, but not limited to, an Electronic Industry

Association (EIA) standard RS-232 cross-over or a backplane bus between the modems.

As shown in FIG. 8, each modem 20, 24 is configured essentially the same, and thus, they operate in essentially the same manner. However, each modem is provided with

operating code which is stored in a memory device 124 provided with the central

processor 1 14, 120, though addition memory can also be provided, if necessary, and

connected to the central processor 114, 120 if desired. In the context of the present disclosure, a memory device is a computer readable medium that is embodied in an

electronic, magnetic, optical or other physical device or means that can contain or store a

computer program, such as the operating code for the modem 20, 24, for use by or in

connection with a computer related system or method. The operating code includes control logic that controls, among other things, the type of modulation and error

correction techniques utilized which is dependent upon whether the modem is used for

cellular or land-line connections. Accordingly, the central processor 1 14, 120 operates

on, or executes, the operating code that is in memory device 124 and configured for

implementing the present invention so as to control the operation of modem 36, 38.

The foregoing description has been presented for purposes of illustration and

description. It is not intended to be exhaustive or to limit the invention to the precise

forms disclosed. Obvious modifications or variations are possible in light of the above

teachings. The embodiment or embodiments discussed were chosen and described to

provide the best illustration of the principles of the invention and its practical application

to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use

contemplated. All such modifications and variations are within the scope of the invention

as determined by the appended claims when interpreted in accordance with the breadth to

which they are fairly and legally entitled.

Claims

CLAIMSWhat is claimed is:

1. A system for automatically selecting the mode of communication between

a plurality of modems comprising:

a calling modem and an answering modem disposed for

intercommunication across an established communication link of a telephone network;

calling signal means for generating and transmitting a continuous calling

signal across the established link;

answering modem detecting means for detecting the calling signal;

answering modem analyzing means for analyzing the detected calling

signal to determine the configuration of the calling modem; answering signal means for generating and transmitting an answering

signal across the established link;

calling modem detecting means for detecting the answering signal;

calling modem analyzing means for analyzing the detected answering signal to determine the configuration of the answering modem;

determining means for determining whether the established link passes

through a public switched telephone (PSTN); and transmitting means responsive to the determining means for transmitting a

2100 hertz tone across the established link only if the established link passes through a

PSTN.

2. The system as defined in claim 1 , wherein the configuration determined by

the answering modem analyzing means includes information relating to the capabilities of

the calling modem.

3. The system as defined in claim 1 , wherein the configuration determined by

the answering modem analyzing means includes information relating to the environment of the calling modem.

4. The system as defined in claim 3, wherein the environment information

includes an identification of the type of telephone network that the modem is connected

to.

5. The system as defined in claim 1 , wherein the continuous calling signal

includes frequency components of 1500 hertz and 1900 hertz.

6. The system as defined in claim 1, further including configuration means

associated with the calling modem for adjustably defining the configuration of the calling

modem.

7. The system as defined in claim 6, wherein the configuration means

includes DIP switches.

8. The system as defined in claim 6, wherein the configuration means

includes a programmable circuit that is adapted for configuration when the calling modem is installed in the system.

9. The system as defined in claim 1 , further including configuration means

associated with the answering modem for adjustably defining the configuration of the

calling modem.

10. The system as defined in claim 9, wherein the configuration means

includes DIP switches.

11. The system as defined in claim 10, wherein the configuration means

includes a programmable circuit that is adapted for configuration when the answering modem is installed in the system.

12. The system as defined in claim 1, wherein the calling signal is dependent

upon the established link.

13. The system as defined in claim 12, wherein the calling modem includes an

adjustable configuration that identifies the established link.

14. In a networked system having an established communication link between

multi-mode modems, including a calling modem and an answering modem, a method for

automatically establishing the mode of communication between the modems comprising

the steps of:

transmitting a continuous calling signal from the calling modem across the

established link, wherein the calling signal includes information relating to the

configuration of the calling modem; detecting the calling signal at the answering modem;

analyzing the calling signal to determine the configuration of the calling

modem; transmitting an answering signal from the answering modem across the

established link, wherein the answering signal includes information relating to the

configuration of the answering modem;

detecting the answering signal at the calling modem;

analyzing the answering signal to determine the configuration of the

answering modem;

determining whether the established link passes a two-wire connection;

and transmitting from the calling modem a 2100 hertz tone across the

established link, only if it is determined that the established link passes through a PSTN.

15. The method as defined in claim 14 further including the step of timing the

transmission of the 2100 hertz tone.

16. The method as defined in claim 15 further including the step of controlling

the transmission of the 2100 hertz tone to maintain the transmission of the 2100 hertz

tone until a time that the entire startup sequence takes two seconds.

17. The method as defined in claim 14 wherein the step of transmitting the

calling signal includes transmitting a signal comprising 1500 hertz and 1900 hertz

frequency components.

18. A multi -mode modem for intercommunication with another multi-mode

modem across an established link of a networked system, wherein the multi-mode

modems initiate their intercommunication during startup sequence that includes a

segment for automatically establishing the communication protocol, the multi-mode

modem comprising:

a first signal generator configured to transmit a continuous calling signal across the established link, the calling signal uniquely identifying the configuration of the

modem; a first signal receiver configured to receive and identify valid calling

signals transmitted from a remote modem;

a first signal analyzer configured to analyze the received signal to

determine the configuration of the remote calling modem;

a second signal generator configured to transmit an answer signal across

the established link, the answer signal uniquely identifying the configuration of the

modem; a second signal receiver configured to receive and identify valid answer

signals transmitted from a remote modem; a second signal analyzer configured to analyze the received signal to

determine the configuration of the remote answering modem; and means for analyzing the established link and selectively transmitting a

2100 hertz signal to the remote modem only if the established link passes through a

PSTN.

19. In a multi-mode modem for intercommunication with another multi-mode

modem across an established link of a networked system, wherein the multi-mode

segment for automatically establishing the communication protocol, a method for

initiating the startup sequence comprising the steps of:

generating a calling signal that uniquely identifies the configuration of the

calling modem;

transmitting the unique calling signal in a continuous fashion across the

established link; simultaneously monitoring the established link to identify an answer

signal transmitted from a remote modem; and

terminating the transmission of the calling signal upon receipt of an

answer signal.

20. In a system comprising a multi-mode calling modem disposed for

intercommunication with a multi-mode answering modem across an established link of a

networked system, wherein the multi-mode modems initiate their intercommunication

during startup sequence that includes a segment for automatically establishing the

communication protocol, a method for initiating the startup sequence comprising the

steps of: generating a calling signal that uniquely identifies the configuration of the

calling modem;

transmitting the unique calling signal from the calling modem across the

established link;

monitoring the established link by the answering modem to identify the

unique calling signal;

generating an answer signal that uniquely identifies the configuration of

the answering modem;

transmitting the unique answer signal from the answer modem across the

established link; and terminating the transmission of the calling signal upon receipt of an

answer signal.

21. In a system comprising a multi-mode calling modem disposed for

steps of:

transmitting a unique calling signal from the calling modem that uniquely identifies the configuration of the calling modem;

detecting at the answering modem the unique calling signal;

transmitting a unique answer signal from the answering modem that

uniquely identifies the configuration of the answering modem; detecting at the calling modem the unique answer signal;

determining whether the established link passes through a PSTN; and

transmitting a 2100 hertz signal from the calling modem over the

established link, when the link is determined to pass through a PSTN.

22. A computer readable storage medium containing program code for

controlling the operation of system for automatically selecting the mode of

communication between a plurality of modems comprising:

a calling modem and an answering modem disposed for

intercommunication across an established communication link of a telephone network; calling signal means for generating and transmitting a continuous calling

signal across the established link;

answering modem detecting means for detecting the calling signal;

answering modem analyzing means for analyzing the detected calling

signal to determine the configuration of the calling modem;

answering signal means for generating and transmitting an answering

signal across the established link;

calling modem detecting means for detecting the answering signal; calling modem analyzing means for analyzing the detected answering

signal to determine the configuration of the answering modem;

determining means for determining whether the established link passes through a public switched telephone (PSTN); and

transmitting means responsive to the determining means for transmitting a

PSTN.