13/113GPRS-2 (Phase 1 network). This means that at the moment 13.4 kbit/s is the maximumspeed for one time slot.3+1: 40.2 kbit/s + 13.4 kbit/s.2+2: 26.8 kbit/s + 26.8 kbit/sIt is also important to remember that peak bit rate is only one part to the actual end userexperienced performance.GPRS Modulation CoderateData rate /time slot (kbit/s)Two slots(kbit/s)Three slots(kbit/s)GPRS-1 GMSK 0.50 9.05 18.1 27.15GPRS-2 GMSK 0.64 13.4 26.8 40.2GPRS-3 GMSK 0.74 15.6 31.2 46.8GPRS-4 GMSK 1.00 21.4 42.8 64.22.3.3 Terminal classesThree classes of GPRS MSs have been defined:• Class-A MS can operate GPRS and other GSM services simultaneously• Class-B MS can monitor control channels for GPRS and other GSM servicessimultaneously, but can only operate one set of services at one time• Class-C GPRS MS can exclusively operate GPRS services.The Nokia D211 is a class B terminal.The Nokia D211 can be attached to GSM and GPRS services simultaneously. Data calls canbe received during GPRS activity. No data calls, however, are possible when GPRS datatransmission is active, and no GPRS data transmission is possible when a data call is active-> GPRS is put to suspend mode when there is an active data call.2.3.4 GPRS securityGPRS security functionality is equivalent to the existing GSM security. The SGSN performsauthentication and cipher setting procedures based on the same algorithms, keys, andcriteria as in existing GSM. GPRS uses a ciphering algorithm optimised for packet datatransmission. However, as GPRS data packets are transmitted using the Internet, VPN(Virtual Private Network) is recommended for end-to-end security in corporate networks.2.3.5 GPRS summaryData rates depend on the availability of channels in use per cell and on the channel quality.In weak channel conditions more protection (stronger channel coding) for user data bits isneeded and this naturally means that less user data bits can be sent in a given time period.In good channel conditions the situation is obviously the opposite. The theoretical maximumdata rate in GPRS is 64.2 kbit/s. The uplink and downlink data rates are asymmetric as inHSCSD.
