UMA Today Magazine: UMA Jumpstarts Femtocells Page 12

COVER STORY

grates the traffic into the existing mobile core network
through standard Iu-CS and Iu-PS interfaces on the
core network side.

As RAN Gateway-based solutions leverage an operator's

existing core network through standard interfaces, they
allow for full-service transparency as well as a low initial
cost of deployment and low overall disruption to the
operations of an operator's existing network.

In addition, as the RAN Gateway approach employs a

"Flat IP" architecture in which a number of the functions
of a standard RNC are moved to the femtocell itself, the
scaling issues associated with the Iu-b over IP approach
are avoided.

Due to the service transparency, cost and scaling advan-

tages, the majority of femtocell solutions are now based
on the RAN Gateway approach for device-to-core network
connectivity.

The nexT ChAllenge: deFining The
"iU over ip" inTerFACe

With the industry

now focused on the RAN Gateway approach to femtocell
device-to-core network connectivity, the key remaining
challenge is to fully define and standardize the "Iu over
IP" interface between the femtocells and a RAN Gateway.

As of mid-2007, there are two primary approaches being

discussed to address this challenge: (i) to define and stan-
dardize an entirely new interface; or (ii) to extend the existing
3GPP UMA standard, which is, for all intents and purposes, a
successful 3GPP RAN Gateway interface already used to ser-
vice dual-mode Wi-Fi handsets over the internet.

As is often the case, it helps to first define the key

operator requirements for the "Iu over IP" interface when
comparing alternative proposals, which include:

1. Provides a clear and fast path to standardization

As discussed above, operators do not want to be
`locked in' to a vendor-specific interface between
femtocells and the RAN gateway. Traditional
RAN vendors have effectively created a closed
market in the macro RAN access network with
vendor specific flavors of the `Iu-b' protocol. But
for the femtocell market to flourish, an open,
standardized interface would enable operators
to select from multiple femtocell access point
manufacturers, driving up overall volumes and
driving down overall costs.

2. Meets the unique challenges of mobile service

delivery over the internet As in the case of
dual-mode Wi-Fi handsets, femtocells present a
number of unique demands as they involve the
delivery of mobile services over the inherently
unreliable and unsecured public internet. As
a result, defining the "Iu over IP" interface is
significantly more complex than solely defining
a method to transport Iu traffic out from the
core over an IP network. For example, key
areas that need to be defined and standardized
include IP security, discovery and registration,
authentication, authorization, roaming and
handover, link reliability, regulatory compliance,

Figure 3: The "Iu over IP" Interface

UMA TodAY

FALL 2007