Cellular Digital Packet Data. • IBM, McCaw Cellular. • Data network overlay on analog cellular telephone system. • Uses same 30 KHz channels @ MHz;. Introduction. Cellular digital packet data (CDPD) unites two dynamic technologies: internetworking and wireless communications. Designed as an overlay to. CDPD is a system for packet data transmission that uses idle voice channels of the AMPS or IS U.S. cellular phone system. Applications of CDPD include.

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Due to long established setup times and cellulag handshaking requirement packet data communication was not supported by AMPS. In order to support packet data, CDPD has been introduced in Though it has its own infrastructure it utilizes vacant AMPS assigned channels or gaps between the channels for packet communication.


CDPD architecture is explained below. It co-exist with AMPS network architecture. Hence it supports both data and voice communication.

CDPD – Cellular Digital Packet Data

M-ES is full duplex. The net data rate is 9.

Both uplink and downlink are separated using FDMA. In single mode phone can initiate data call or voice call. In this technique CDPD mobile checks for flag bit in downlink channel which informs whether uplink slot is idle or busy.

If idle, it utilizes for transmission. If busy, it waits for random period instead of transmitting in the next time slot.

Cellular Digital Packet Data

The figure depicts CDPD network architecture. There are three CDPD interfaces viz. E-interface, I-interface and A-interface. I-interface exists between two CDPD networks. A-interface exists between BS and Dxta. It is also known as Air interface. Let us understand network elements used in CDPD architecture. It functions similar to subscriber or mobile unit used in any cellular system.


It interfaces with radio equipment at It functions similar to Base Station. It broadcasts available channels for M-ES. It takes care of radio activities such as channel allocation, usage etc. It provides connectivity with internet and PSDN. It has functionalities of packdt frame relay switch and packet router.

It does buffering of packets routed for M-ES.

CDPD tutorial-CDPD features,CDPD network architecture

It also supports roaming management as it contains registration directory. Following are the advantages of CDPD: Following are the disadvantages of CDPD: Communication between them occurs via MDBS.

CDPD network architecture Fig