Importance Of CDPD Technology
The GSM we use is basically a circuit switched network. So, making calls with this GSM on a mobile computer became problematic. In order to overcome this inconvenience, CDPD is introduced and defined by cellular telecommunications and internet associations (CTIA). CDPD is nothing but Cellular Digital Packet Data technology which is mainly used for the data transfer in mobile services. The mechanism is entirely based on AMPS and in fact compatible with AMPS mobile devices with a range of about 800 MHz to 900MHz. A speed of 19.2 Kbps is possible with this CDPD. This CDPD is mainly used in cases of providing wireless internet access for the packet switched networks.
This 19.2 kbps speed of data delivery can be even achieved by an idle channel of 30 KHz. The net data rate of CDPD is around 9.6 Kbps. It basically supports TCP/IP protocol and all kinds of connectionless protocols. A wireless featured datagram along with connectionless protocols incorporated in a system which is being used by a mobile phone is the main fact behind the maximum number of users of this CDPD mechanism.
The entire OSI concepts are being used by the CDPD system. Modulation details and transmission of radio waves are related to physical layer. Similarly other layers of OSI too found but never used for any purposes. Three stations that are involved in CDPD are mobile hosts, base stations and base interface stations. Mobile hosts basically act as the portable computers of users. Transmitters come in the name of base stations. All the base stations of CDPD are linked together with the help of base interface stations which can beget further more transmissions via WAN.
Mainly three types of interfaces are involved in CDPD as E-interface (external), I-interface (internal) and A-interface (air). E is used to make the CDPD to be connected with a network. It can also be used to connect CDPD with a myriad of networks. I-interface is mainly used to interconnect two CDPD with each other. A is responsible for linking mobile hosts with the base stations.
Data transfer over the air interface undergoes certain authenticating processes as data compression, error correction and encryption for security purpose. Data compressions for 274 units and data encryption for 374 bits are applied using error detection and correction methods. For each and every block of bits, flag words of 6 bits are amended so as to make it around 420 blocks of bits. These blocks are further divided into micro blocks each of 60 bits. In cases of full duplex modes, 19.2 Kbps of downlink speed and over 19.2 Kbps of uplink speed are achieved. Hence both uplink and downlink channel allocation are taken place within a micro block which ends after 3.125 msec.
Downlink channel is comparatively easier to access than that of the uplink channels since the uplink channel is tricky in CDPD. Usually all kinds of internet service providers are supported by CDPD. Simply this CDPD is just the extension of traditional data networks which is built over an M-ES (Mobile End System). The message is finally delivered to the F-ES (Fixed End System). For the faster data transfer purposes in cellular devices, it is better to receive with this CDPD.
