interim standard 95 (IS-95)

The IS-95(Interim Standard) standardized by the TIA/ EIA describes an air interface and a protocol stack used between the mobile terminals and the network. The protocol stack is based on three layers, where the lowest layer( L1) corresponds to the physical layer, the layer above ( L2) handles medium access control( MAC) and link access control( LAC), and the top layer ( L3) handles switching.

IS-95 defines bidirectional signalingin the forward direction from the network to the mobile device and that in the reverse direction. In the forward direction, the signals are transmitted from the base stations, which are synchronized in time with the GPS system. The forward transmission is in two- phase shift ke ying(BPSK) with a chip rate of 1.2288 Mc/s. The signals are spread with a Walsch code of 64 bits length and a pseudo-random number( PRN).

The standard IS-95 is available in two versions as IS-95A and IS-95B.

IS-95A: The revision of the IS-95 standard is from 1995 and forms the basis for many 2nd generation CDMA networks. IS-95 A describes the structure of a 1.25 MHz wide CDMA channel, its power control, the connection procedure and the registration technique for system operation. In addition to the voice service, there is a circuit-switched data link with a data rate of 14.4 kbit/s.

IS-95B: The revision of the IS-95 standard specified by ANSI is associated with the 2.5 generation networks. The specifications, which were also published in 1995, define a compatible standard for the frequency range from 1.8 GHz to 2.0 GHz according to Code Division Multiple Access (CDMA) for PCS systems. Data transmission is packet-switched at 64 kbit/s.