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Toggling of H and 3G Symbols Near the Signal strength in Mobile Phone

If you are using GSM service you may note the toggling of 3G and H symbols in your mobile phone near the mobile signal strength. When the mobile phone is idle (It means no data transfer ), it turns to 3G but if we start Internet activities it will turn back to "H" from 3G. Maybe these symbols confuse a non-techie person. Before explaining this I think it is better to give a short description of data bandwidth technologies we are using right now. 2.5G is known by the term GPRS in data service and 2.75G is termed as EDGE. If you see the "E" symbol while using data service, it is EDGE network your mobile phone is connected. In the same way, "UMTS" technology is commonly termed as 3G and HSDPA is termed as H. However, there is a difference in mentioning 3G and "H". 3G carries both voice and data but "H" is purely data service.

Why showing H in 3G network
So if your handset is HSDPA enabled, it can transfer data up to 7.2Mbps speed in a 3G network. If your handset is not HSDPA enabled the maximum speed limit you can expect is 384 kbps. So when you start data transfer in your mobile phone, it will automatically change to maximum possible speed and the 3G symbol will change to H. When there is no data transfer your phone does not need to continue in H and it will come back to 3G.

However, do not confuse with the original 3.5G network where the data transfer speed limit is 42 Mbps (download limit). If you like to know more about these mobile data service technologies, follow the link below.
Compare EDGE, GPRS, 3G and HSDPA

Compare Speed Limits of Mobile Data Services -HSDPA, 3G,GPRS, EDGE

The major mobile data transfer technologies using are GPRS, EDGE, UMTS, and HSDPA. This article is about comparing the speed limits of these mobile data service technologies. GPRS is the abbreviation of "General Packet Radio Service" and its maximum data transfer speed limit is 115 kbps. When it comes to EDGE the theoretical maximum speed limit is 473.6kbps in eight-time slot device. In a four-slot device, the speed reduced to 236.8kbps and 118.4kbps in the two-slot device. EDGE is the abbreviation of Enhanced Data rates for GSM Evolution. UMTS(Universal Mobile Telecommunications System) has the theoretical maximum speed limit of 384 kbps for R99 handsets, and 7.2 Mbps for HSDPA handsets. H denotes HSDPA (High-Speed Downlink Packet Access) and its theoretical maximum download speed limit is 42 Mbps. 

Mobile Data Bandwidth technologies
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 2.5G     --------->  GPRS

 2.75G    --------->  EDGE

 3G       --------->  UMTS

3.5G      --------->  HSDPA 


Expansion of Data Technologies
-----------------------------

GPRS ---------->General Packet Radio Service

EDGE----------->Enhanced Data rates for GSM Evolution

UMTS----------->Universal Mobile Telecommunications System

HSDPA --------->High-Speed Downlink Packet Access

The theoretical speed limit chart for data services are: 

Compare Theoretical Speed Limits of Data Services
------------------------------------------------

GPRS  -----------> 115 kbps

EDGE  -----------> 473.6 kbps in 8-slot device

UMTS  -----------> 384 kbps / 7.2 Mbps (depends on handsets)

HSDPA -----------> 42 Mbps down

HSPA+ -----------> 84 Mbps down and 22 Mbps up

4G    -----------> 100 Mbps down and 50 Mbps up
These speed limits shown are theoretical values only and in real life, we cannot see this data transfer speed.