About CDPD Technology
As the GSM is basically circuit switched. By using a GSM phone, a mobile computer with a special modem you can call the same way it would be a place in a corded telephone. However, this strategy is problematic. GSM suffers from some drawbacks thesis are as follows: The first is transfers between base stations are common, sometimes with fixed users and each transfer of results in the loss of ca. 3000msec data. Secondly, GSM is related to the above error rate. Tie ‘a’ and echoed, ‘m’ is irritating quickly. Finally, wireless calls are more expensive and the cost of erecting, because the charge is per minute of the correct time, not byte sent.
Packet switched digital datagram service is used to solve these problems. It is based on the top of the amps and fully compatible with AMPS. Basically any idle channel 30 kHz may be temporarily unavailable for the delivery of data frames to a gross rate of 19.2 kbps. Because CDPD is a good nit of overheads, the net data rate is closer to 9600bps. However, a system linking wireless datagram for delivery of IP packets using the cellular telephone system is an attractive proposition for many users so their use is growing rapidly.
CDPD uses the OSI model closely. The physical layer related to the details of the modulation and radio transmission. data link protocols, network transport and present, but unused. CDPD system includes three types of stations: mobile hosts, base stations and base stations of the interface. These stations communicate with hosts and routers fixed standard species found in any WAN. The mobile hosts are laptop users. Base stations are transmitters that talk to the mobile hosts. The base stations of the interface are special nodes that interface all base stations in the area of a standard router CDPD provider for onward transmission over the Internet or other WAN.
CDPD defines three types of interfaces. The E-interface is called as external to the CDPD provider, which connects an area to a CDPD network. This interface must be well specified to allow CDPD to connect to several different networks. I-interface is called as internal CDPD provider, which connects two areas CDPD together. The third is the A-interface is called as the air interface, which is used between the base station and mobile host.
By using compression, data encryption and error correction are sent over the air interface. Units of 274 tablets using the error code and the correction of coded data bits are wrapped in locks of 378 bits. For each block of seven words 6-bit flag is added to form a total of 420 bits block. Each block of 420 bits is divided into seven microblocks of 60 bits, which are delivered consecutively. Each word is Microblock trademark of 6 bits, which is used to indicate channel status. In full-duplex mode, these microblocks go over 19. 2 kbps down channel or second channel 19.2 kbps uplink. As a result both downlink and uplink channel time is allocated as a sequence of 60 bits microblocks. Each Microblock ends after 3.125msec.
Each cell consists CDPD downlink single pair of uplink data. The downlink channel is easy to handle since there is only one transmitter per cell: the base station. All frames issued are issued with each team selecting mobile destined for it or for the whole world.
The difficult part of CDPD technology is the uplink channel, for all mobile machines wishing to communicate must compete. When a mobile host has a frame to deliver it is proved the downstream channel of a flag bit to say if the current uplink slot is busy or idle. If busy, then wait for the next time slot, it skips a random number of slots and tries again. If it becomes to find the uplink channel is busy, then wait a while doubles with every failed attempt. Finally, when the channel is supposed to idle, start transmitting its Microblock. The point of this algorithm is called Digital Sense Multiple Access. It is used to prevent all mobile hosts jumping on the uplink channel as it goes idle. It seems a little protocol slotted p-persistent CSMA which makes use of discrete slots issue on both channels.
An additional advantage is that users CDPD data users are second class. When a new voice call is about to be assigned to a channel that is currently used for CDPD, the base station transmits a special signal on the downlink, closing the channel. If the base station already knows the number of new channels CDPD, that declares it. Otherwise the mobile host has to find between a potential joint design of CDPD channels to find it. You can suck any spare capacity in a cell without interfering with the voice.
mobile phone companies australia
Processing your request, Please wait....
