What is difference between Location Area (LAU) and Routing Area (RAU) update?

Location Area Update :

The location update procedure allows a mobile device to inform the cellular network, whenever it moves from one location area to the next. 

Mobiles are responsible for detecting location area codes. 

When a mobile finds that the location area code is different from its last update, it performs another update by sending to the network, 

a location update request, together with its previous location, and its Temporary Mobile Subscriber Identity (TMSI).


Routing Area Update :

The routing area is the PS domain equivalent of the location area. 

A "routing area" is normally a subdivision of a "location area". 

Routing areas are used by mobiles which are GPRS-attached. GPRS is optimized for "bursty" data communication services, 

such as wireless internet/intranet, and multimedia services. 

It is also known as GSM-IP ("Internet Protocol") because it will connect users directly to Internet Service Providers (ISP).


The bursty nature of packet traffic means that more paging messages are expected per mobile, 

and so it is worth knowing the location of the mobile more accurately than it would be with traditional circuit-switched traffic.

A change from routing area to routing area (called a "Routing Area Update") is done in an almost identical way to a change from location area to location area. 

The main differences are that the "Serving GPRS Support Node" (SGSN) is the element involved.

From : http://www.telecomsource.net/showthread.php?2780-What-is-difference-between-Location-Area-(LAU)-and-Routing-Area-(RAU)-update