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 What’s the difference between GPRS and UMTS?

 What’s the relation between GPRS and IP?

 Can you do voice calls with GPRS?

 What is the relation between GPRS and SIP?

 What is the relation between UMTS and SIP?

 What is the relation between CDMA (1X) and SIP?

 Does SIP care at all about the access network that uses it?

 Can SIP run on top of 802.11?

 What is IMS? What is the relation between IMS and SIP?

What’s the difference between GPRS and UMTS? 

This is quite confusing for many people. According the 3GPP standard (TS 23.060) GPRS defines the packet data services provided by a common core network to two main types of  access networks - GSM based and WCDMA based (UMTS).

GPRS uses IP based signaling/control protocols between its components. Beyond that it transparently carries IP packets between the mobiles and the Internet. This is done by method known as encapsulation and tunneling.

GPRS provides an IP data pipe. Therefore by definition you can do anything on top of it including voice. QoS is a major issue though for voice over GPRS, and IMS (IP Multimedia Subsystem) tries to resolve it.

SIP rides transparently over GPRS just like any other IP based protocol. IMS and QoS muddy this picture a bit. You can read all about it in 3G IMS Illustrated.

What is the relation between UMTS and SIP? 

Same as GPRS.

Very similar to GPRS/UMTS and SIP. the designers of CDMA 1X (3GPP2) has adopted the 3G way (IMS) for doing VoIP/multimedia.

No, apart from QoS impact, which may dictate what codecs will get used and what quality you may expects from a multimedia session.

Sure. In SIP's eyes 802.11 is just another type of access network, which can carry it.

This is explained thoroughly by 3G IMS Illustrated.