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 modem handshaking requirement packet data communication was not supported digjtal 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.


CDPD – Cellular Digital Packet Data

Hence it supports both data and voice communication. M-ES is full duplex.

The net data rate is 9. Both uplink and downlink are separated using FDMA.

CDPD – Cellular Digital Packet Data – Telecom ABC

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

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 MS. It is also known as Air interface. Let us cellulag 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 both frame relay switch and packet router. It does buffering of packets routed for M-ES.

Cellular digital packet data

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