Pros and Cons of Emulating RNC

The main advantage of this interconnection together with the dual mode
WLAN/UMTS protocol stack on MS, as shown in Figure 2.16, is that the
mobility management, roaming, billing, and location-related issues are taken
care of by UMTS network. Subscriber identity module (SIM) and UMTS SIM
(USIM)–based authentication of a subscriber for WLAN offers a 2G/2.5G
and 3G operator the following benefits:
• The WLAN subscriber credentials are of identical format to
2G/2.5G or 3G and therefore easier to integrate subscriber into the
current HLR. Therefore, all existing roaming capabilities and settlements
are inherited from GSM.
• The security level offered by WLAN will be identical to that of
GSM/GPRS/UMTS. GSM SIM-based security is based on a
challenge-response mechanism. It offers better tamper resistance
because SIM runs an operator-specific confidential algorithm, which
takes a 128-bit random number (RAND) and a secret key, Ki, stored
on the SIM as an input to produce a 32-bit response (SRES) and a
64-bit data encryption keys, Kc(n), as an output. Kc(n) are never
sent over the air, nor are they used in calculation for message
authentication code for RAND and SRES. Kc(n), together with
international mobile subscriber identity (IMSI) and Ki, are used by
the network and the client to calculate independently the key K that
will be used for the encryption of data over the air interface. So the only data exposed over the air interface are the random numbers,
K(n).
Strong security provided in the UMTS network and QoS for real-time
services may now be provided over WLAN, thereby resolving the drawbacks
of current IEEE 802.11a/b/g WLAN threats. Minimum changes are
required in the UMTS network, and this will create a master-slave relationship
between UMTS and WLAN as discussed in Section 2.6. This is not
optimal. Using UMTS PDCP frames over WLAN may create bottlenecks.
In this scenario, the UMTS backbone may be a bottleneck for the WLAN
traffic. WLAN data rates with 11 Mbps with IEEE 802.11b and 54 Mbps
with IEEE 802.11a would be degraded to the speed of the UMTS terminal
(2 Mbps). This type of interconnection requires modifications to standard
WLAN terminals, which in turn would make them more expensive. Two
attractive WLAN components (i.e., speed and price) would be lost in this
type of connection.