GAO's Modem Software Integrates ADSL and 56K
March 25, 1998
As consumers demand higher bandwidth for Internet applications, the ADSL modem will become the driving force of the modem market. Consequently, following directly on the heels of the development
of a software package for 56k PCM modem (GAO V.90), GAO Research & Consulting Ltd. has developed an ADSL modem software package. This package (GAO ADSL/V.90) integrates software for ADSL and the
previously released GAO V.90.
Toronto, Canada: GAO Research & Consulting Ltd., a leading supplier of modem technology, has released a new software modem package which integrates both ADSL and V.90 PCM modem functions and
allows the use of ADSL modem independent of or simultaneous with V.90 modem.
GAO ADSL/V.90 makes full use of the multi-channel feature offered by the ADSL technology which provides a high-speed downstream channel, a medium-speed upstream channel, and a POTS channel. The
ADSL modem function of GAO ADSL/V.90 offers extremely high bandwidth for Internet applications through the downstream and upstream channels. The V.90 modem function of the software package makes use
of the POTS channel and serves as a fallback if the ADSL service fails or is not available. Telephone service may also be accessed through the POTS channel if the V.90 modem is not used. GAO
ADSL/V.90 is implemented in ANSI C and is able to run with reduced ADSL rates on microprocessors such as ARM, MIPS, Pentium, SH3, and Hyperstone. GAO ADSL is also suitable for operation on such DSPs
as C4x, C6x, and SHARC.
The major module of the GAO ADSL/V.90 software is GAO ADSL. This module has been developed and tested on a host Pentium processor according to the American National Standards Institute (ANSI)
T1.413 ADSL standard based on DMT technology. The ADSL modem function of the GAO ADSL/V.90 software can provide subscribers with data rates of up to 8 Mbps downstream and 640 kbps upstream, in
compliance with the latest issue of the ANSI T1.413 ADSL standard (Issue 2). The main changes from T1.413 Issue 1 to Issue 2 are as follows:
- Rates > 8 Mbit/s are now provided for
- Transport of a Network Timing Reference is specified
- Reduced overhead modes are defined
- Loop timing is made mandatory, and some activation and acknowledgment signals are changed to facilitate it
- State machines for both ATU-C and -R are defined
- An expanded initialization sequence to enable Rate Adaptation is added
The International Telecommunications Union is now working toward a G.dmt standard for ADSL which is modeled after ANSI T1.413 Issue 2 and the European Technical Standards Institute Technical
Report 328. GAO ADSL will conform to this new standard when it is ratified.
An important feature of the GAO ADSL/V.90 software is its integration of the V.90 modem. The V.90 modem is a new technology that offers a higher data rate than V.34bis modems. The V.90 technology
assumes that an Internet service provider (ISP) is digitally connected to the Internet and to a telephone companyæŠ¯ central office (CO). The CO extends the downstream connection
via a line card with a digital to analogue converter (DAC), providing a pulse amplitude modulation (PAM) analog signal to a client modem. GAO V.90 integrates the following functions: V.90,
V.34bis/34, V.32bis/32, V.22bis/22, V.21, Bell 103, and Bell 212A plus protocols and control functions.
GAO Research & Consulting Ltd., a private corporation located in Canada, has established itself as a leading supplier of communications algorithms and software since its founding in 1992. GAO
now employs about 50 professionals, more than 40 of whom are DSP and communications engineers. Due to the growth GAO has experienced, the company has moved to bigger and better facilities at 305
Milner Avenue, Suite 1003, Toronto, Ontario, Canada, M1B 3V4. GAO offers a complete suite of modem, fax, telephony, and speech compression software, including V.34bis and all fallbacks, in fixed and
floating-point C for microprocessors such as Pentium, ARM, MIPS, and SPARC and in assembly languages for DSPs such as TMS320C6x/54x and ADSP21xx.
Application of GAO ADSL/V.90 Server and Client Modems
The basic engine of an ADSL DMT modem consists of the following parts:
- Transmitter: tone shuffler, constellation encoder, IFFT DMT modulator, and interpolator (illustrated in Figure 1, Transmitter of the ADSL Modem)
- Receiver: decimator, FFT DMT demodulator, constellation decoder, and tone reorder (illustrated in Figure 2, Receiver of the ADSL Modem)
- Error Control: CRC, Scrambler, Reed-Solomon FEC de/encoder, interleaver/deinterleaver
- Some special receiver components are the time domain equalizer, frequency domain equalizer, echo canceller, automatic gain control, and timing recovery
Figure 1, Transmitter of the ADSL Modem
Figure 2, Receiver of the ADSL Modem