Abstract:
A method of forming a V.90 connection on an all digital connection. The method includes transmitting a request to connect from a digitally connected client modem ( 28 ) to a digitally connected server modem ( 24 ) and transmitting, by the client modem ( 28 ) to the server modem, a message requesting to form a V.90 connection, identifying the digitally connected client modem ( 28 ) as an analog connected modem.

Description:
RELATED APPLICATIONS 
   The present application is a U.S. national application of PCT/IL00/00198, filed on Mar. 29, 2000. 
   FIELD OF THE INVENTION 
   The present invention relates to communication systems and in particular to modems. 
   BACKGROUND OF THE INVENTION 
   Modems are used for transmitting data over communication links. Generally, two modems on opposite ends of a communication link send each other data by converting the data into electrical signals suitable for transmission on the link. In order to allow modems of different vendors to transmit data to each other, standards have been defined stating exactly how the signals should be modulated. These standards include, for example, the V.34 standard which allows transmission on both analog and digital links, the V.90 standard which is defined for connections between clients connected to analog lines, such as home users, and servers connected to digital lines (e.g., T1/E1 lines), such as Internet service providers, and the V.91 standard which is meant for pure digital connections. 
   The V.34 standard is described in “A modem operating at data signalling rates of up to 33 600 bit/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits”, ITU-T Recommendation V.34, 2/98, the disclosure of which is incorporated herein by reference. 
   The V.90 standard is described in “A digital modem and analogue modem pair for use on the public switched telephone network (PSTN) at data signalling rates of up to 56 000 bit/s downstream and up to 33 600 bit/s upstream”, ITU-T Recommendation V.90, 9/98, the disclosure of which is incorporated herein by reference. 
   The V.91 standard is described in “A digital modem operating at data signalling rates of up to 64 000 bit/s for use on a 4-wire circuit switched connection and on leased point-to-point 4-wire digital circuits”, ITU-T Recommendation V.91, 5/99, the disclosure of which is incorporated herein by reference. 
   The V.34 standard allows transmission rates of up to 33.6 Kbps in both directions. The V.90 standard allows transmission at a rate of up to 56 Kbps in one direction (referred to as the downstream direction) and 33.6 Kbps in the other direction. The V.91 standard allows transmission at 64 Kbps in both directions. The V.91 standard, however, is relatively new and it is expected to take many years, if at all, until most of the modems in the market implement the V.91 standard. 
   Usually modems implement a plurality of different standards. Generally, when two modems form a connection they search for a highest transmission rate standard which they both implement and use this standard for transmission over the connection. The search for a common transmission standard is usually performed in accordance with the V.8 standard. 
     FIG. 1  is a schematic illustration of a V.90 connection as is known in the art. A client modem  12 , connected to a public switching telephone network (PSTN)  19  through analog lines  14 , forms a connection with a server modem  24  which is connected to PSTN  19  through a digital link  32 . Usually, modem  24  belongs to a modem pool, for example of an Internet service provider (ISP)  29 . Generally, a line card  16  translates the signals from analog lines  14  to a digital link  36  of PSTN  19 , and vice versa. It is noted, that in most cases, except for analog lines  14  which connect line card  16  and client modem  12 , PSTN  19  is formed of substantially only digital links, represented in  FIG. 1  by a digital network  23 . 
   Client modem  12  comprises a signal processing unit  13  and a sampler and reconstructer  15  which turns digital signals into analog signals for transmission and analog signals from lines  14  into digital signals. When a computer  10  requests to a connection to ISP  29 , client modem  12  forms a negotiation V.8 connection with server modem  24 . During the negotiation connection, client modem  12  identifies as an analog modem and server modem  24  identifies as a digital modem such that the modems agree to use a V.90 connection for transmission of data. Thereafter, modems  12  and  24 , sequentially as defined by the V.90 protocol, transmit test signals used to check the characteristics of links  14  and  32 . 
   After the tests are concluded, modems  12  and  24  move into transceiving states according to the V.90 standard. Signals transmitted from computer  10 , are prepared for transmission by processing unit  13  of modem  12  at a rate of up to 33.6 Kbps and are then converted to analog signals by a D/A of sampler and reconstructer  15 . Signals transmitted by server modem  24  are transmitted from the modem at a rate of up to 56 Kbps as described above. The transmitted signals from server modem  24  are converted to analog signals by line card  16  and are passed on link  14  to modem  12 . An A/D of sampler and reconstructer  15  of modem  12  samples the analog signals at a high enough rate which allows proper operation of the modem, i.e., proper synchronization of a clock of sampler and reconstructer  15  in receiving modem  12  to the timing of transmitting modem  24 . Generally, to allow for rate correction, the A/D of sampler and reconstructer  15  samples the signals at a rate higher than 8000 samples per second. The sampled digital signals are then passed to processing unit  13  for processing. 
     FIG. 2  is a schematic block diagram of an exemplary receiving path  40  of processing unit  13  of modem  12 , as is known in the art. Path  40  receives samples from sampler and reconstructer  15  on a line  42 . The samples are added to correction values provided by an echo canceller  44  and are then filtered by a channel filter  46 . The filtered samples are passed to a timing recovery unit  48  and a rate converter  50 , which correct for timing drifts of the received samples. The samples are passed through an automatic gain control (AGC) unit  52  and are then provided to an equalizer  54  which corrects phase and amplitude distortions of the received samples. The samples from equalizer  54  are passed to a symbol decision module  56  which determines for each sample which symbol it represents. Symbol decision module  56  also detects attenuation pad impairments and performs robbed bit signaling (RBS) in order to better perform the determination of the samples which represent the symbols. The symbols are then passed through a symbol to bit converter  58  which translates the symbols into bits, and through a descrambler  60  which descrambles the bits. 
   The definition of the V.90 connection is such that it can only be established between an analog connected client (as most client modems are home modems connected through analog wires to the public switching telephone network (PSTN)) and a digitally connected server modem (as most server modems belong to ISPs which are connected digitally to the PSTN). In recent years, many computers connect to ISPs through all-digital connections, for example, using cellular phone connections which are entirely digital. Until the V.91 protocol is widely implemented, these computers must use, at most, the V.34 protocol which provides a maximal transmission rate of 33.6 Kbps in both the upstream and downstream. 
   SUMMARY OF THE INVENTION 
   An aspect of some preferred embodiments of the present invention relates to a method of establishing a V.90 connection between two modems connected over digital lines. The signals sent from a first one of the modems are changed such that the second modem thinks the first modem is connected through analog wires and agrees to form a V.90 connection. No changes are made to the second modem or to the signals transmitted from the second modem. 
   In a preferred embodiment of the present invention, the first modem does not perform steps required for handling analog signals usually performed in receiving downstream V.90 signals. Rather, the signals from the digital connection preferably enter the first modem through a bypass which leads directly to a symbol decision module. 
   There is therefore provided in accordance with a preferred embodiment of the present invention, a method of forming a V.90 connection on an all digital connection, including transmitting a request to connect from a digitally connected client modem to a digitally connected server modem, and transmitting, by the client modem to the server modem, a message requesting to form a V.90 connection, identifying the digitally connected client modem as an analog connected modem. 
   Preferably, the method includes forming a negotiation connection between the client modem and the server modem responsive to the request to connect and transmitting the message requesting to form a V.90 connection includes transmitting during the negotiation connection. 
   Preferably, the client modem does not perform, during the negotiation connection, tests required to determine analog connection parameters. Alternatively, the client modem disregards results of tests required to determine analog connection parameters. 
   Preferably, the method includes receiving, by the client modem, symbols transmitted in accordance with the V.90 connection, and passing the received symbols to a symbol decision module of the client modem which determines which signals are represented by the symbols, immediately upon receiving the signals by the modem. 
   There is further provided in accordance with a preferred embodiment of the present invention, a method of receiving downstream signals transmitted from a server modem to a client modem in accordance with the V.90 standard, including receiving the transmitted signals by the client modem, deciding which symbols are represented by the received signals, immediately upon receiving the signals by the client modem, and converting the decided symbols into bits. 
   Preferably, receiving the transmitted signals includes receiving digital samples. Preferably, receiving the transmitted signals includes receiving samples at a rate of 8000 samples per second. Preferably, deciding immediately upon receiving the signals includes deciding without performing echo cancellation, automatic gain control, rate conversion and/or channel filtering. 
   There is further provided in accordance with a preferred embodiment of the present invention, a V.90 supporting modem, including an input from a digital trunk line which receives signals transmitted in accordance with the V.90 standard, and a digital interpretation unit which receives samples directly from the input from the digital trunk line. 
   Preferably, the digital interpretation unit is connected directly to the digital trunk line. Preferably, the digital interpretation unit includes a symbol decision module which receives samples directly from the input from the digital trunk line. Preferably, the symbol decision module is connected directly to the digital trunk line. Preferably, the input from the digital trunk line receives symbols at a rate of 8000 symbols per second. 

   
     BRIEF DESCRIPTION OF FIGURES 
     The invention will be more clearly understood by reference to the following description of preferred embodiments thereof in conjunction with the figures, in which: 
       FIG. 1  is a schematic illustration of a V.90 connection as is known in the art; 
       FIG. 2  is a schematic block diagram of an exemplary receiving path of a V.90 modem, as is known in the art; 
       FIG. 3  is a schematic illustration of a V.90 connection, in accordance with a preferred embodiment of the present invention; 
       FIG. 4  is a flowchart of the actions performed by a V.90 modem in forming an all digital connection, in accordance with a preferred embodiment of the present invention; and 
       FIG. 5  is a schematic block diagram of a receiving path of a V.90 modem, in accordance with a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3  is a schematic illustration of a connection  20  which may operate using the V.90 standard, in accordance with a preferred embodiment of the present invention. A mobile unit  22 , such as a wireless access protocol (WAP) unit, forms a communication connection with a server modem  24  (usually belonging to a modem pool) of an Internet service provider (ISP)  29 . It is noted that although  FIG. 3  shows formation of a digital connection between ISP  29  and a mobile unit  22 , the present invention is not limited to any specific digital connection. For example, a computer may connect to client modem  28  through an ISDN connection instead of through cellular link  30 . The signals transmitted and received by mobile unit  22  are preferably passed over a cellular link  30  to and from a base station  26  of a cellular company. Preferably, the signals to and from mobile unit  22  are passed through a client modem  28  (also generally belonging to a modem pool) associated with base station  26  or with another base station of the cellular company. Modem  28  is connected to modem  24  through a digital network  23  which is preferably formed only of digital links, such as E1 or T1 links. Digital network  23  may belong to a private or public communication network, such as PSTN  19  ( FIG. 1 ), and/or may comprise a plurality of concatenated data links or may be formed of a single link. Modems  28  and  24  preferably connect to digital network  23  through digital lines  36  and  32 , respectively. 
     FIG. 4  is a flowchart of the actions performed by modem  28  in forming an all-digital connection between mobile unit  22  and ISP  29 , in accordance with a preferred embodiment of the present invention. Upon receiving ( 70 ) a request to form a connection with ISP  29  from mobile unit  22 , modem  28  preferably establishes ( 72 ) a V.8 negotiation connection with server modem  24  of ISP  29 . During the negotiations of the V.8 connection, client modem  28  requests ( 74 ) to form a connection using the V.90 standard identifying itself as an analog (i.e., client) modem. Upon agreement of server modem  24 , tests are performed ( 76 ) in order to evaluate the quality of link  32  and/or to determine parameters of the connection, as is known in the art. In a preferred embodiment of the present invention, client modem  28  skips ( 78 ) those tests required to determine analog connection parameters and/or to evaluate analog lines. Alternatively, client modem  28  performs the tests, so that server modem  24  does not realize that client modem  28  is not analog connected, but discards the results. Thereafter, a V.90 connection ( 80 ) is established. 
   In the V.90 connection, signals transmitted from modem  28  to modem  24 , i.e., in the upstream direction, are preferably transmitted, as is known in the art, at a rate of up to 33.6 Kbps in accordance with the V.90 and V.34 standards which are identical regarding the upstream transmission. Any changes in the transmission required due to the fact that modem  28  is connected directly through digital link  32 , are performed in accordance with the digital transmission of the V.34 standard. For example, modem  28  preferably does not convert the transmitted signals to analog signals as client modem  28  is connected through a digital connection. 
   Preferably, no changes are made in the way server modem  24  receives the upstream signals, as the upstream signals are transmitted by client modem  28  substantially without changes. Further preferably, no changes are made in the way server modem  24  transmits signals. Thus, no changes are required in server modem  24  of ISP  29  which preferably does not know that client modem  28  is actually connected directly to digital link  32  (or to a digital network). 
   Referring back to  FIG. 2 , it is noted that receiving path  40  may be viewed as formed of two major parts. A first part, an analog to digital conditioning unit, comprises units  44 ,  46 ,  48 ,  50 ,  52  and  54 . The analog to digital conditioning unit brings the analog signals received on line  42  substantially back to the state at which they were before the conversion performed by line card  16  ( FIG. 1 ). A second part, a digital interpretation unit, comprises units  56 ,  58  and  60 . The digital interpretation unit translates the digital signals provided by the analog to digital conditioning unit into a form tangible by computer  10 . 
     FIG. 5  is a schematic block diagram of a receiving path  90  of modem  28 , in accordance with a preferred embodiment of the present invention. Preferably, modem  28  receives digital signals on an input line  88  and passes the digital signals directly to a digital interpretation unit  86 . Preferably, the digital signals received on input line  88  are passed directly to symbol decision module  56  of digital interpretation unit  86 . Preferably, symbol decision module  56  performs detection of attenuation pad impairments and robbed bit signaling (RBS) in addition to determining the samples which represent the symbols. As the downstream digital signals from ISP modem  24  were not converted by a line card  16  ( FIG. 1 ) to analog signals, modem  28  preferably does not perform the tasks of the analog to digital conditioning unit of path  40 , i.e., modem  28  does not perform echo cancellation ( 44 ,  FIG. 2 ), and does not pass the signals through channel filter  46 , timing recovery module  48 , rate converter  50 , AGC unit  52  and equalizer  54  ( FIG. 2 ). 
   It is noted that in some preferred embodiments of the invention some or all of the elements of modems  28  and  100  shown in  FIG. 5  are implemented in software on one or more processors. 
   It will be appreciated that the above described methods may be varied in many ways, including, changing the order of steps, and the exact implementation used. It should also be appreciated that the above described description of methods and apparatus are to be interpreted as including apparatus for carrying out the methods and methods of using the apparatus. 
   The present invention has been described using non-limiting detailed descriptions of preferred embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. It should be understood that features described with respect to one embodiment may be used with other embodiments and that not all embodiments of the invention have all of the features shown in a particular figure or described with respect to one of the embodiments. Variations of embodiments described will occur to persons of the art. Furthermore, the terms “comprise,” “include,” “have” and their conjugates, shall mean, when used in the claims, “including but not necessarily limited to.” The scope of the invention is limited only by the following claims: