High Speed Downlink PacketAccess HSDPA

Peak data rate increased significantly higher than 2Mbps in HSDPA. HSDPA is a new protocol for mobile telephone data transmission. It is known as a 3.5G (G stands for generation) technology which is upgradation
of 3G 3gpp ralease.

GSM

What is GSM ?

GSM stands for Global System for Mobile Communication. 
Definition of GSM : GSM is combination of both TDMA and FDMA technologies. It was originally called Groupe Spécial Mobile.  

GSM is a standard set developed by the European Telecommunications Standards Institute (ETSI) to describe technologies for second generation (2G) digital cellular networks.

The use of the SIM card allows GSM network users to quickly move their phone number from one GSM phone to another by simply moving the SIM card.

 GSM is world's most widely used cell phone technology.GSM and CDMA differ in terms of coverage, data speed, roaming, and SIM cards.

GSM bands

The frequency bands used in GSM are
  
900 MHz
1800 MHz
1900 MHz