10.3 2.5/3G TDMA: GPRS and EDGE

Having discussed the 3G CDMA systems in the previous section, we now move on to the 3G systems using TDMA technology. We focus on systems arising out of, and compatible with, GSM. As noted earlier in the introduction to this chapter, and, as is apparent from the choice of title for this section, these TDMA-based 3G systems are often considered 2.5G systems as well: they are designed to provide GSM with a packet-switching capability for data transmission as quickly as possible, with as few changes to the GSM architecture as possible. There are two basic sets of standards defined to provide these changes, GPRS (general packet radio service) and EDGE (enhanced data rates for global evolution). ^[1] GPRS consists, as we shall see below, of two basic parts:a core network portion and an air interface standard. EDGE, as indicated by the meaning of the acronym, is designed to provide substantially increased bit rates over the air interface. It was also noted earlier that it is expected that IS-136 systems will move to incorporate these new technologies and architectural features as well (IEEE, ^{[IEEE. 1999.]}). The combination of GPRS and EDGE is sometimes called EGPRS, for enhanced GPRS. We first describe GPRS and then EDGE. The core network portion of GPRS uses a layered architecture with the Internet-based TCP/IP protocols playing a key role. We thus take time out to briefly review the concept of layered architectures in packet-switched systems, using TCP/IP layering...