ally documented and became fully store-and-forward. Bearer Services The digital nature of GSM enables data, both synchronous and asynchro- nous, to be transported as a bearer service to or from an ISDN terminal. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Introduction to GSM Chapter 1 Data can use either the transparent service, with a fixed delay but no guar- antee of data integrity, or a nontransparent service, which guarantees data integrity through an Automatic Repeat Request (ARQ) mechanism, which unfortunately introduces a variable delay. The data rates supported by GSM are 300 bps, 600 bps, 1,200 bps, 2,400 bps, and 9,600 bps. One can imagine in this new millennium that these data speeds are intolerable for the mainstay of data transmission. In fact, if someone were to offer us Inter- net access at speeds of up to 9,600 bps, we would probably become very dis- interested in the service. Yet, from a mobile perspective, these speeds were considered quite fast. Enhancements from Phase II also included better throughput for data transmission of data using a synchronous dedicated packet data access operating at 2.4 to 9.6 Kbps. Phase I only accepted an asynchronous access to a dedicated packet assembler/disassembler (PAD). The access of data through a dedicated PAD at the entrance of an X.25 network enables access to a higher degree of reliable data transport, helping to overcome the link layer problems on the radio. Data is now available over the GSM Phase II at both send and receive speeds of up to 9.6 Kbps. In the earlier releases, slower data was more prevalent. The use of the GSM network enables the integration of various network platforms such as Plain Old Telephone Services (POTS) ISDN access and emulation Packet data network access (X.25 and IP are the most common) Circuit-switched data transfer across and X.25, X.31, and X.32 s