Exercise 4.3: UMTS Access Level

UMTS access network

The figure shows the UMTS access network with the two main blocks:

${\rm UTRAN}$ $($"UMTS Terrestrial Radio Access Network", upper graph$)$: This monitors the radio transmission between the radio network layer and the transport layer;

${\rm CN}$$($"Core Network", lower graph$)$: This is responsible for switching data within the UMTS network.

The exercise will explain some of the abbreviations used in the figure.

Hints:

(1) Correct is Answer 3: UMTS networks support:

Circuit switching (English: CS): in this case, the radio channel is not available to other users during the entire switching period.
Packet switching (PS): The data stream is divided into small data packets in the transmitter and then sent together with other packets. The channel can thus be shared by several users.

(2) Correct Answers 1 and 2:

As can be seen from the diagram, UTRAN includes various base stations, usually called Node B in UMTS, and various Radio Network Controllers in each case.
The MSC (Mobile Service Switching Center) is a part of the core network.

(3) Correct Answers 1 and 2:

The Home Location Register (HLR) contains all subscriber data, for example, rate model, telephone number, service-specific authorizations, and keys of a network operator's own customers.
In contrast, the Visitor Location Register contains information about locally registered users and copies of the records from the HLR of its network operator.
This data is dynamic: as soon as the subscriber changes his location, this information is changed.
The GPRS register (GR) is part of the HLR. It contains additional subscriber information, but it is only needed for packet-switched transmission.

(4) Correct Answers 1 and 3:

The Gateway Mobile Switching Center (GMSC) is the switching center in mobile systems for forwarding data to the (circuit-switched) fixed network.
For packet data networks such as the Internet, the Gateway GRRS Support Node (GGSN) is responsible for this.
The Serving GRRS Support Node (SGSN) has similar tasks for packet switching as the MSC and the HLR have for circuit-switched transmission.

	Circuit-switching only,
	packet-switching only,
	both circuit-switching and packet-switching.

	The base stations,
	the "Radio Network Controller" $\rm (RNC)$,
	the "Mobile Service Switching Center" $\rm (MSC)$.

	the "Home Location Register" $\rm (HLR)$,
	the "Visitor Location Register" $\rm (VLR)$,
	the GPRS register.

	$\rm GMSC$ and $\rm GGSN$ forward to other data networks.
	$\rm GMSC$ and $\rm GGSN$ are active only when there is circuit-switching.
	$\rm SGSN$ has a similar function to $\rm MSC$ and $\rm HLR$.