8/11/2019 Small Cell Architectures
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------ SMALL CELLS TYPE OF SYSTEM ARCHITECTURE -------
Iub over IP:
This approach reuses the same cellsite protocols as for 3G
macrocells running over IP.
This is defined in the mobile standards by 3GPP Release 5 and
connects the femtocell directly to the RNC using the Iub interface.
It allows existing RNC vendorsto reuse their products with minimum
redevelopment to support femtocells.
There are some issues with this approach:
a) Timing and Synchronisation. The standard Iub interface is
used for synchronisation and requires very high quality
communication between the femtocell and theRNC. It is intolerant to
delay, jitter and packet loss as typically experiencedover the
public internet.
b) Scalability of RNCs. These were designed to handle several
hundred high capacity NodeBs connected via ATM, and may require
substantial re-architecting to support thousands or tens of
thousands of femtocells via IP.
c) Managability. Macrocellular UTRANs are not designed to handle
thousands of cellsite moves and changes per day.
d) Security: There is no standard in place to secure the IP
connection between the femtocell and RNC, although an IPsec tunnel
could be used for this purpose.
e) Vendor Interoperability: Often the Iub interface
implementation is not standard, and many vendors have added
additional proprietary functions. This makes support of
multi-vendor femtocell deployments more difficult.
f) Network operator bypass: Iub implementations cannot easily be
architected tooffload direct internet traffic at the femtocell
itself, and instead would needto tunnel all data traffic to the
mobile operators core network.
Autonomous SIP based Solution:
This incorporates more functionality into the femtocell,
including the SGSN andGGSN core network functionality. Voice calls
continue to be routed to the MSC over Iub. If the end user is able
to use Voice over IP (VoIP) application rather than the normal
phone voice service, then this can be handled entirely as VoIP
using an IMS core. In this case, handover is handled using the VCC
standard (VoiceCall Continuity), but typically this does not
support data session handover. Offload of large data usage is
possible and substantially reduces the load on thecore network.
There are some issues with this approach
- Security: For prepaid users, the control and monitoring of
charging requires the femtocell to provide accurate information. If
this aspect of the femtocell wa
s hacked/intercepted, then potentially free calls/services may
be obtained.
- Difficulty of use: The end-user experience of making and
receiving calls on amobile phone today using VoIP is quite complex.
Such users are already likely tohave low cost VoIP phones in their
homes already, where the benefit arises whenmaking international or
other high priced calls. The bundling of minutes withinthe mobile
phone tariff would reduce the benefit of low cost VoIP.
Motorola appears to be the main vendor promoting this solution,
which is targeted more at enterprise deployments within offices as
well as home users.
