The 32kbit/s data transmission service became commercially available in April, 1998. Since then, a variety of e-mail, location information service, and other applications have been introduced and are growing in recognition and demand. Traffic is reported to be growing rapidly for all three PHS operators.
And now, three PHS operators are introducing the world's first wireless 64kbit/s data transmission service. ASTEL Tokyo Corporation (ASTEL) launched its service on November 30, 1998. NTT Mobile Communications Networks Inc. (Access www.nttdocomo.co.jp for the detailed update on the 64kbit/s trial of NTT DoCoMo.) launched its field trial on December 1, 1998 towards the commercial service on April 1, 1999. DDI Pocket Telephone (DDI-P) plans to launch its service in the summer of 1999. Many service providers and businesses are preparing to take advantage of this unique transmission speed service.
There are two protocols being used for 64kbit/s service. ASTEL will transmit data by using two PHS terminals and adapters based on the 32kbit/s *PIAFS protocol. ASTEL's network combines the two 32kbit/s and then transmits them as one PIAFS 64kbit/s. On the other hand, NTT DoCoMo and DDI-P will provide the service using the PIAFS 64kbit/s protocol.



PIAFS 32kbit/s and PIAFS 64kbit/s
With the PIAFS 32kbit/s protocol, one PIAFS data frame is divided into four parts. These four divided parts are sent to a Cell Station (CS) separately, then the CS restores these frames to the original single data frame. The CS adds a dummy bit to the frame, and sends this back to the PHS network or to the ISDN network at 32kbit/s.
PIAFS 64kbit/s will use the same data frame as PIAFS 32kbit/s.
With PIAFS 64kbit/s transmission, one PIAFS data frame is divided into four frames. Two of the divided four frames are sent to CS as one set. The remaining two frames are sent to the CS separately. The CS restores those frames to the original one data frame.
With PIAFS 32kbit/s, the CS sends the data frame to the PHS or ISDN network by adding one dummy bit. With PIAFS 64kbit/s, however, the CS will insert one PIAFS 32kbit/s data into the dummy bit and then will send it at 64kbit/s.
Therefore, PIAFS 64kbit/s occupies two communication slots at once to transmit these data frames, that is, PIAFS 64kbit/s data transmission occupies two channels between a PHS terminal and a CS.
Note: *PIAFS(PHS Internet Access Forum Standard)