Small cell and WiFi integration in EPC

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SmallcellandWi-FiintegrationinEPC
Introduction _____________________________________________________________________ 3
Introduction to Small Cells______________________________________________________ 3
Need for Small Cells and Wi-Fi___________________________________________________ 3
HetNets __________________________________________________________________________ 8
Introduction to EPC _____________________________________________________________ 11
Small Cells_______________________________________________________________________12
Small Cells __________________________________________________________________ 12
Small Cells standardization bodies________________________________________________14
HeNB Logical architecture ______________________________________________________16
LTE Deployment______________________________________________________________16
Option 1 _____________________________________________________________ 16
Option 2 _____________________________________________________________ 18
Option 3 _____________________________________________________________ 20
Traffic Offloading _____________________________________________________________22
SIPTO ________________________________________________________________23
LIPA _________________________________________________________________24
Wi-Fi ____________________________________________________________________________25
Wi-Fi_______________________________________________________________________26
Wi-Fi standardization bodies____________________________________________________26
IEEE 802.11 standards evolution_________________________________________________27
Wi-Fi integration to EPC________________________________________________________28
Wi-Fi integrartion to EPC_________________________________________________________ 28
Mobile IP____________________________________________________________________30
Proxy Mobile IP_______________________________________________________________31
Table of Contents

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2
3GPP ANDSF ________________________________________________________________ 32
UE Location ___________________________________________________________33
Discovery Information___________________________________________________34
Inter-system routing policy _______________________________________________35
Hotspot 2.0 and Carrier Wi-Fi___________________________________________________ 37
Wi-Fi roaming _________________________________________________________38
Protocol stack and authentication _________________________________________39
Hotspot 2.0 operation___________________________________________________41
SaMOG_____________________________________________________________________42
Seamless Connectivity_________________________________________________________43
Simultaneous access to 3GPP and non-3GPP _______________________________________44
MAPCON _____________________________________________________________44
IFOM ________________________________________________________________44
3GPP and Wi-Fi interoperability _________________________________________________44
Case study __________________________________________________________________45
Conclusion ______________________________________________________________________46
Wi-Fi or Small Cells? __________________________________________________________ 46
Concluding remarks___________________________________________________________47
About eXplanoTech _____________________________________________________________48
Our services_________________________________________________________________48
Technical Training ____________________________________________________________49
References _____________________________________________________________________ 50
List of References____________________________________________________________ 50
List of Abbreviations__________________________________________________________51
Table of Contents

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In the world of molecular biologists and genetists, the
term “small cells” leads to bacteria whilst in a prisoner’s
language it refers to a lifestyle. But, what do we mean by
small cells in telecommunications?
There is not a straightforward definition of a small cell as
the flavours and versions significantly vary. A small cell is
generally defined as a low-power cellular base station
operating in licensed spectrum typically propagating
within a shorter distance than the macrocell base sta-
tion. They are complementary to the macrocells provid-
ing connectivity to the mobile networks and help
achieve capacity improvement, offering mobile data off-
loading and coverage enhancement. A variety of back-
haul is available for use with the small cells ranging from
satellite to microwave and even copper and fibre.
At present, many different types and solutions of small
cells are available from 2G(GSM) to 3G(UMTS/CDMA2000) and even 4G(LTE). Small cells
are often touted as a basic technology for future 5G networks.
It is estimated that in the past 50 years the cellular network capacity has been increased
by a million times. As shown in Figure 1, during this period, the spectrum has increased
25 times. Although increasing bandwidth is a safe solution to improving channel capac-
ity, spectrum is costly solution and it is not optimum for the operators to increase chan-
nel capacity. The ongoing research in the improvement of the cell spectrum efficiency
has proved to be very important in the evolution of mobile networks and the delivery of
high speed data. Techniques such as OFDMA and MIMO have contributed to the signifi-
cant evolution of the cell spectral efficiency which in turn plays a major role into the
channel capacity increase. Despite the significant improvements in the quantity of spec-
trum and the cell spectrum efficiency, the factor responsible for the huge growth in the
Introduction to small cells
Need for Small Cells and Wi-Fi
Introduction

4
network capacity is the number of cells that
has roughly increased by 1600 times. This
figure is expected to drastically increase in
the coming years. Low cost small cells are
allowing the end users improve their recep-
tion and data speeds thereby leading to a
better quality of experience (QoE).
The increasing number of interconnected
devices has led to the experts forecasting
up to 50 billion connected devices by 2020
whilst the volume of data transmission is
forecasted to increase ten times in the
same period. The operators are shifting
Figure 1: Capacity million fold.
Figure 2: Global cellular traffic growth prediction from Mobile Devices
Source: Cisco VNI Global Mobile Data Traffic Forecast 2012—2017
Introduction

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5
their focus on to the 4G networks due to its ability to handle higher data volumes, in
addition to higher speeds and lower latency. The legacy networks on the other hand are
starting to shrink. Though it may not be straightforward to switch off the legacy net-
works due to M2M and other similar commitments, operators are increasingly reframing
the 2G/3G spectrum into 4G networks. 3G networks are still evolving with new features
coming regularly in every 3GPP release. This puts many operators in the challenging po-
sition as to whether to keep improving the 3G networks or focus on the newer 4G net-
works. Would the 3G networks be able to manage the massive volumes of data as pre-
dicted? Would rolling out small cells on the 3G networks help fix the capacity crunch
issues?
As the amount of data transfer increases, offloading is becoming increasingly important.
The obvious choices for offloading are small cells and alternative technologies like Wi-Fi.
Note that residential Wi-Fi is generally not considered as offload. In the year 2012 alone,
33% of the mobile traffic was offloaded to alternative means. Cisco in its Virtual Net-
working Index (VNI) predicted that by 2017, nearly half of the mobile traffic would be
Figure 3: Traffic offloading
Source: Cisco VNI Global Mobile Data Traffic Forecast 2012—2017
Introduction

6
offloaded to different technologies such as Wi-Fi, WiMAX etc.
Virgin Media installed a free public Wi-Fi network throughout the London Under-ground
in the UK, announced that their Wi-Fi network served more 1 million connections daily.
Online since the summer 2012, ready on time for the 2012 London Olympic Games, 92
“tube” stations have free Wi-Fi connectivity, a figure that is expected to extend to 120
before the end of 2013. At the same time BT in the UK reports that they have 5 million
hotspots nationwide. In the Wi-Fi sharing community, FON alone reports a massive 12
million Wi-Fi access points worldwide; widely successful in the UK, France, Portugal, Po-
land, Italy and Japan along with most of the large cities globally.
Contrary to what some analysts have predicted in the previous years, Wi-Fi will not get
replaced by small cells, instead it will be significantly developed. We believe that in the
following years, Wi-Fi will become increasingly important, playing the role of the third
RAN and will be the most popular data offload technology.
There was a time when there were many disagreements between the cellular and Wi-Fi
community. Operators discounted Wi-Fi as a useful technology because of interference
in the unlicensed band and not being able to guarantee the Quality of Service (QoS). Us-
ers saw Wi-Fi as a free resource and would be unwilling to pay for it, unless for business
Figure 4: (a) Wi-Fi internet connection speed (b) HSPA+ internet connection speed
Introduction

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7
use. Recently there has been a change in attitude of both the parties. Wi-Fi is being seen
as an alternative access technology, complementing the cellular technology, if it is seam-
less and can provide similar services to that of cellular networks.
Wi-Fi can provide high speed internet access while cellular networks cannot provide
broadband internet to all users simultaneously, given that the number of users in a Wi-Fi
access point is significantly lower than the number of users camped on a macrocell.
However, mobile internet connection is seamless and allows the user to access the inter-
net when in motion.
Wi-Fi operates in the unlicensed band and the equipment cost is significantly low.
Hence, the provision cost is a lot lower than that of a cellular network. Of course, cellular
communications are a lot more secure while international roaming is allowed.
Mobidia reports that a typical iPhone user uses approximately 4 GB of data per month
where the 82% come from Wi-Fi and only 18% from cellular resources. A typical Android
user downloads 2.9 GB of data per month 66% of which is transferred over Wi-Fi. A dif-
ferent research published by Maravedis—Rethink shows that a typical smartphone user
needs approximately 4 GB of data
per month with only a quarter of
it been transferred over cellular
networks.
Hence, it is more than obvious
that in the future a typical net-
work should be a combination of
macrocells for providing seamless
connectivity and support for mo-
bility sensitive applications (such
as voice calls) while small cells
and Wi-Fi will be used for offload-
ing and coverage improvement. A
combination of multiple access
technologies will result in a het-
erogeneous network. Figure 5: Wi-Fi versus cellular data usage
Introduction

8
Traditionally, cellular networks have been rolled out as homogeneous networks. Homo-
geneous networks comprise of similar kinds of equipment, providing nearly uniform cov-
erage throughout the network. Networks containing only of macrocells would be an ex-
ample of this. A simple example of a cellular homogeneous network is shown in Figure 6
where each macrocell covers a large area that serves all the devices within its range. The
location and configuration of the macrocell are complicated and have to carefully choose
through deployment planning to maximize the coverage and minimize the interference
among other macro's. This deployment has served exceptionally in the past years when
the vast majority of the cellular network use of a user device were for voice calls. How-
ever, in the recent years, where access to the packet data network (PDN) is crucial more
than ever, the homogeneous cellular networks alone do not qualify to fulfil users' needs.
The problem that generally happens due to this is that there are large number of users
that need to be served by this macro layer limiting the data throughput that can be de-
livered to these users.
Figure 6: Traditional Homogeneous Network
HetNets
HetNets

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9
For the smooth operation of
homogeneous networks and
with the introduction of the
small cells, it was important
to introduce a hierarchical
structure to separate cells in
such a way that they do not
interfere with each other
and control the traffic they
can support given their re-
gion of coverage and the backbone. Hierarchical Cell Structures (HCS) are shown in Fig-
ure 7.
The reason to have different layers is generally based on a simple formula. The macro
layer provides coverage to a large area and is known as coverage layer while the other
cells like Micro, Metro, Pico, etc. are capacity layer.
Figure 8 shows a Heterogeneous cellular network (generally referred to as just HetNet)
Figure 7: Hierarchical Cell Structures
HetNets
Figure 8: Sample Heterogeneous Network (HetNet)

10
topology incorporating different forms of small cell deployments as an overlay on the
macrocell network. Small cells would generally use secure tunnels back to the core net-
work using existing broadband infrastructure.
Whereas in the HCS, different layers have different frequencies, thereby not causing ra-
dio frequency interference, in HetNets same frequencies can be used between different
layers. The same frequencies can cause radio frequency Interference and necessitates
the use of advanced Interference avoidance techniques. HetNets can also include differ-
ent radio access technologies (RAT’s) in the licensed band like GSM, HSPA, LTE and in
the unlicensed band like Wi-Fi. Interference Management is the biggest challenge in Het-
Nets but that is outside the scope of this document.
A homogeneous network operates over one big and same in size base station equip-
ment, using a set of communication protocols of the same set of standards. A HetNet is
composed of many smaller nodes, operating in the presence or absence of a macrocell,
making use of multiple Radio Access Networks of different sets of standards. A typical
homogeneous network can cover a range of up to 40 km while the coverage of a typical
heterogeneous network can have a range between a few hundred meters up to a few
km. Macrocells are carefully planned and configured in full details of the operators giving
them the full control. The cost of a macrocell deployment is massive and end users can-
not afford it. Given their significantly lower cost, HetNets can be installed by the opera-
tor, third party or the end users making interference management a challenge while
equipment ownership is moving off the operators. Finally, Wi-Fi is shorter in range, a lot
cheaper to install and maintain while interference challenge is a lot more feasible.
Heterogeneous networks will provide a cost effective solution for the improvement of
coverage at the cell edge but also in data traffic dense areas. Cell capacity shall increase
and hence users will enjoy the benefits of mobile broadband. HetNets reduce the cost of
installation and maintenance, they provide a fast and flexible deployment providing to
the end user the ability to self install whilst unlike the homogeneous networks, HetNets
devices are fully portable. Last but not least, HetNets are moving towards "greener" tele-
communications by keeping the power consumption low due to short distance or signal
propagation (2 Km compared to 40 Km).
HetNets

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11
The core network architecture did not change much from 2G to 3G. The architecture
created for the needs of GSM/GPRS was evolved and enriched to support advanced ser-
vices and a better quality of service. With the introduction of LTE networks in 3GPP Rel.
8, core network architecture significantly changed as it got drastically simplified. The
name given to the new core network is Evolved Packet Core (EPC) where circuit switch-
ing network support (voice calls) is completely abandoned.
The EPC is realized through four new elements that are separated by their function.
Serving Gateway (S-GW) is used to carry user traffic to and from the Packet Data Net-
work (PDN). It interfaces with the base station on the access network side and with the
PDN Gateway (P-GW) on the EPC side. P-GW is the device responsible to provide connec-
tion between the EPC and the outside world (PDN / Internet). P-GW also interfaces with
the Policy and Charging Rules Function (PCRF) for billing purposes. As it will be shown
Figure 9: 3GPP networks architecture
Introduction to EPC
Introduction to EPC

12
later in this document, P-GW is the anchor point for handover between 3GPP and non-
3GPP RANs. Finally, the Mobility Management Entity is the device used for the communi-
cation between the UE and the EPC. It practically interfaces with S-GW on the EPC side
and the eNodeB on the EUTRAN side.
Evolved UMTS Terrestrial Radio Access Network (EUTRAN) is also significantly changed in
comparison to the UTRAN. Evolved Node B (eNodeB - eNB) combines the functions of
UTRAN NodeB and Radio Network Controller (RNC) into a single entity.
HeNB entity shown in Figure 10, is the 3GPP defined term for Small Cell including Fem-
tocell which in the early days was referred to as a Femto Access Point (FAP) in the litera-
ture. In those days of
course, Small Cells were
only Femtocells. In this
document, the small cells
description is based on the
classification by the Small
Cell Forum which is the
most widely accepted dis-
tinction.
Based on the communica-
tion range , the number of
devices that it can accom-
modate, the maximum
transmit power required
and the administrative body
of a cell, it can be character-
ized as macro , micro , pico
or femto. A macro cell is
provided and completely
controlled by a mobile op-
erator. It is placed in a
Small Cells
Small Cells
Figure 10: Small cell integration to EPC

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13
tower and is a property of the operator. The transmission range is up to 40 km and the
maximum transmission power is 40 Watts. The cost of building, maintenance and rental
of space a macrocell base station is placed is normally significant. The connection to the
EPC is through ultra fast optical lines and is capable to accommodate more than 200
connected devices simultaneously (the number of simultaneous users depend on lots of
factors, mainly the bandwidth). The macro cells are ideal to build a mobile network of-
fering voice calls and internet access.
A Microcell can provide services to up to 200 people at a maximum radius of 2 km from
the small cell HeNB. The construction and maintenance costs are significantly lower to
that of macro cell while is in need of a small tower for placement. Microcells are often
found in public lamp posts and "the hunt for the ideal post" has lately become mobile
operators' hottest topic. The typical transmit power ranges between 1 and 2 watts and is
connected to the EPC through a dedicated connection to a HeNB-GW over the X2 inter-
face. Microcells are perfect to increase cell coverage and capacity to a busy neighbour-
hood, in a city canyon or a crowded public place. Microcells are also suitable for shop-
ping malls and stadiums although in this case, more than one cells are needed to be de-
ployed in order to host a couple of thousand users.
Picocells are small cells more suitable for indoor operation, capable to host up to 64 ac-
Small Cells
Figure 11: Types of small cells

14
tive users with a transmission range not exceeding 300 meters. They are also managed
by the service provider, they are connected to the EPC via a HeNB GW over the X2 inter-
face. The typical transmit power is about 250 mW and the deployment cost is signifi-
cantly smaller than that of a macrocell. Picocells ,also known as enterprise femtocells
are ideal for the increase of coverage and capacity in an enterprise environment,
crowded public places and hotels.
Femtocells are the smaller type of small cells, they can host up to 8 active users and the
transmit power does not exceed 20mW. They are very much suitable for indoor opera-
tion in small business and home. They are mostly used for coverage improvement and
they connect to the EPC over home / office internet connection (DSL, fibre optic, cable
etc). A femtocell is entirely managed by the end-user and the operator does not have
any access network planning control on it.
The Small Cell Forum (formerly the Femto Forum) is a not-for-
profit organisation seeking to enable and promote small cell
Small Cells
Figure 12: Operation range of small cells
Small Cells standardization bodies

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15
Small Cells
technology worldwide. Their main areas of activity is the standardisation, regulation and
interoperability along with the marketing and promotion. Its mission is to accelerate
small cell adoption to change the shape of mobile networks.
The 3rd Generation Partnership Project (3GPP) is the collabora-
tion of the Organizational Partners. The initial objective of 3GPP
was to design the third-generation (3G) mobile phone system
specification. The objectives were later broaden to development and standardization of
the evolution of the 3G technologies and it still going with the birth of LTE and evolution
towards 4G and beyond.
The Wireless Broadband Alliance (WBA) is an industry associa-
tion formed to promote interoperability between operators in
the Wi-Fi industry. WBA is promoting interoperability initiatives, including the Next Gen-
eration Hotspot (NGH) and Wi-Fi Roaming. Members of the WBA include mobile opera-
tors and broadband providers and telecommunication vendors.
The Broadband Forum (formerly the DSL forum) was
founded in 1994 by 200 telecommunication operators and
vendors. Its initial purpose was to establish the standards for
DSL family of technology. By keeping an eye into the future of broadband, they got in-
volved with the research and standardisation of Femto Cells and they issued Femto Ac-
cess Point Service Data Model in April 2009, later revised and released as version 2 in
November 2011.
The GSM Association (GSMA) was formed in 1995 by a trust of operator and
vendor companies. Spanning more than 220 countries and with the participa-
tion of 800 cellular operators worldwide, GSMA plays a significant role in the
broader mobile ecosystem including small cells.
NGMN (Next Generation Mobile Networks) is mobile telecommunications
association, members of which are cellular operators and manufacturers. It
was founded in 2006 aiming into the development of a common view of
solutions for the evolution of wireless broadband. NGMN is looking at be-
yond 3G services and architecture while it is acknowledged by both the 3GPP and IEEE.

16
Figure 13 shows a logical architecture for the HeNB that has a set of S1 interfaces to con-
nect the HeNB to the EPC. Home eNB Gateway (HeNB GW) is generally present to allow
the S1 interface between the HeNB and the EPC to support a large number of HeNBs in a
scalable manner. The HeNB GW serves as a concentrator for the C-Plane, specifically the
S1-MME interface. The Security Gateway, even though showed as a separate entity, is
often on the same physical element as HeNB-GW. The S1-U interface from the HeNB
may be terminated at the HeNB GW, or a direct logical U-Plane connection between
HeNB and S-GW may be used.
The HeNB GW shall connect to the EPC in a way that inbound and outbound mobility to
cells served by the HeNB GW shall not necessarily require inter MME handovers. One
HeNB serves only one cell.
HeNB architecture option 1 for the deployment is as shown in Figure 14. HeNB-GW
Figure 13: 4G HeNB Logical architecture
Source: 3GPP TS 36.300
HeNB Deployment
Small Cells
Option 1
HeNB Logical Architecture

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17
serves as a concentrator for the C-Plane and also terminates the user plane towards the
HeNB and towards the Serving Gateway.
Advantages:
There is only one SCTP association between HeNB-GW and MME. One SCTP association
exists between each HeNB and HeNB-GW. By increasing the number of HeNBs in the
network, SCTP association towards MME remains unaffected.
Serving Gateway scalability requirements for GTP/UDP/IP connections respectively are
reduced comparing to other options. Number of UDP/IP Paths and the number of GTP
Echo messages that S-GW needs to manage remains minimum. Increasing the number of
HeNBs does not increase the number of UDP/IP Paths and GTP Echo messages to be
managed by S-GW.
IP addresses of MME and S-GW can be hidden from HeNB. This would result in a more
secure architecture as none of the core Network IP addresses / address space is revealed
Figure 14: 4G HeNB Network Architecture Option 1
Source: Small Cell Forum Rel.1 Doc. 025.01.01: May 2011
Small Cells

18
to the home user.
HeNB GW can implement a Denial of Service (DoS) shield to protect the EPC(S-GW and
MME). It can detect and filter out the attack traffic while maintaining the QoS of useful
traffic.
This variant allows Traffic offload (SIPTO) as show in later chapters, to be done at the
HeNB-GW. Local S-GW and P-GW functionality for SIPTO may be implemented within the
HeNB-GW reducing the need for a new network element.
Handover optimization & reduction of Handover related signalling load to MME/S-GW
can be realized. User Plane Path switch message exchange between MME and S-GW will
be reduced for handover between HeNB Access points (in case core network does not
need to know about change of serving cell).
Disadvantages:
HeNB-GW needs to forward GTP-U T-PDU (Transport PDU) by switching the tunnel from
HeNB-GW – S-GW tunnel to HeNB-GW – HeNB tunnel and vice versa. Processing load as
regards U-plane is proportional to traffic.
HeNB connects to a single HeNB-GW at one time. It reduces redundancy and load shar-
ing possibilities in comparison with option 2.
Operators that have deployed the 3G HNB generally would be able to use the GW infra-
structure and would prefer this option for deployment. For the operators who want to
deploy the HeNB network starting directly with the LTE HeNB cells, this option can be
beneficial too. In these scenarios the number of HeNBs in the network is expected to be
large or very large, which will be reflected in a large number of SCTP associations and
UDP/IP paths resulting in huge scalability requirements on MME and S-GW. Additionally
the operators would want to minimize the impact to the EPC network as much as possi-
ble when the number of HeNBs increases beyond a certain number in the overall net-
work.
HeNB architecture option 2 for the deployment is as shown in Figure 15.
Small Cells
Option 2

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19
Small Cells
Advantages:
There are less failure points in the system and no additional single point of failure. If one
HeNB network element fails below the MME/S-GW, the other HeNBs are not affected
like in case of HeNB-GW failure.
Simple flat architecture of this variant has less network elements to be operated and is
consistent with macro architecture (e.g. S1 flex support on HeNB).
Lower latency and reduced system level processing is achieved, because the S1 C-plane
and U-plane are directly connected from the HeNBs to the MME and S-GW without pro-
tocol termination at the HeNB-GW.
There are less upgrade and compatibility issues in supporting new feature in later re-
leases since there is no HeNB-GW to be upgraded to ensure that new S1 IEs or messages
are processed correctly.
In case gateways are deployed for SIPTO in a distributed manner, option 2 does not re-
quire, unlike option 1, the deployment of HeNB GW co-localized with SIPTO gateways.

20
Disadvantages:
This variant does not provide SCTP/GTP-U connection concentration.
In residential scenario, the end user may often switch on and off the HeNB causing
therefore frequent SCTP association establishments and releases. Maintenance of a
large number of SCTP association as well as the frequent establishment and release of
the SCTP associations may generate a lot of CPU processing load in MME if the connec-
tion between the MME and HeNB is direct.
In case of increasing number of HeNBs in the network, the UDP/IP contexts might cause
an overload situation in S-GW.
In case of increasing number of HeNBs in the network, the period for GTP-echo mes-
sages might need to be increased to avoid an overload situation in S-GW.
Dedicated MME/S-GW might be required to solve the possible over load situation. In
case dedicated S-GW are deployed, additional GW relocation load may occur for macro-
HeNB and HeNB-macro handovers.
Support of S1 flex (optional) will introduce additional complexity in HeNB implementa-
tion.
The option 2 provides the main benefit in deployment scenarios where the number of
HeNBs is rather limited or scattered within the network with reduced cost effect, so that
the number of the HeNBs per MME is not causing any scalability issues.
HeNB architecture option 3 for the deployment is as shown in Figure 16. HeNB-GW is
deployed and serves as a concentrator for the C-Plane. The S1-U interface of HeNB is
terminated in S-GW, as per eNB.
Advantages:
There is only one SCTP association between HeNB-GW and MME. One SCTP association
exists between each HeNB and HeNB-GW. By increasing the number of HeNBs in the
network, SCTP association towards MME remains unaffected.
Small Cells
Option 3

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21
HeNBs do not have to support S1-Flex on C-plane that will both reduce the overall num-
ber of S1 C-plane connections and simplify HeNB implementation. In U-Plane, there are
less failure points in the system and no additional single point of failure.
Lower latency and reduced system level processing is achieved in U-Plane, because the
S1 U-plane is directly connected from the HeNBs to S-GW without protocol termination
at the HeNB-GW
This variant allows to implement in HeNB-GW a mechanism to avoid overflooding of
MME in case of massive failure of HeNB, due for example to a power outage.
In case gateways are deployed for SIPTO in a distributed manner, option 3 does not re-
quire, unlike option 1, the deployment of HeNB GW co-localized with SIPTO gateways.
Disadvantages:
This variant does not provide GTP-U connection concentration.
Small Cells

22
In case of increasing number of HeNBs in the network, the UDP/IP contexts might cause
an overload situation in S-GW.
In case of increasing number of HeNBs in the network, the period for GTP-echo mes-
sages might need to be increased to avoid an overload situation in S-GW.
Additional or dedicated S-GW might be required to solve the possible over load situa-
tion. In case dedicated S-GW are deployed, additional GW relocation load may occur for
macro-HeNB and HeNB-macro handovers.
In C-Plane, HeNB connects to a single HeNB-GW at one time. It reduces redundancy and
load sharing possibilities in comparison with option 2.
When total number of HeNB increases, an obvious impact with option 3 is the increased
requirement on scalability of S-GW. The highest resource requirement on S-GW to man-
age large number of HeNBs comes from processing of GTP-echo mechanism, but the
impact of additional UDP and GTP contexts must also be considered. Option 3 based de-
ployments can re-use from the pre-existing WCDMA HeNB infrastructure the Security
GWs and transport infrastructure.
Cellular networks are highly centralized with communication nodes that manage all data
traffic to and from the core network. From last many years, the trend has moved from
voice only to voice and data. With the advent of 4G, even voice is now treated as data in
this new ‘all-IP networks’. With the explosion of Apps, and always-on requirements,
these central nodes are getting over-loaded.
Small cells, especially femtos and enterprise femtos need to also be used for local area
networks. However, legacy networks were designed neglecting the future development
towards small cells, forcing all traffic to be tunneled to the core network. As a result of
this issue, the mobile core is becoming the bottleneck of its own network.
Since this issue has been highlighted, 3GPP is working hard, developing techniques to
reduce the load on the core network. Certain types of traffic can now be sent to
(offloaded) the Internet before reaching the core network as we will see in the following
sections.
Traffic Offloading
Small Cells

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23
Selective IP Traffic Offload (SIPTO) supports offload of IP traffic that a policy decides it is
not necessary to be routed through the core network while the destination address is
not in the local network. Hence traffic is being forwarded from the HeNB to a Local Gate-
way via S-GW, to the PDN / Internet. Traffic offloading policy must be carefully selected
so that applications requiring uninterrupted communication (VoIP, Video Streaming etc)
will be routed through the core network which provides seamless mobility to the UEs.
For the its operation a Local Gateway (L-GW) is utilized. L-GW has access to the PDN via
alternative connection other than the core network. Data packets are sent from the
HeNB to S-GW which decides to reroute them through the L-GW away from the core
network. Nearly 35—40% of the mobile traffic is produced by the transfer of video files
(e.g. Youtube) while another 10% is caused by web browsing. If an operator decides to
offload video and web browsing traffic outside the core network via the L-GW, they can
reduce core network traffic by almost 50%. This is a significant benefit for mobile opera-
tors.
SIPTO allows the use of older technology UEs as it does not depend on the UE capabili-
ties whilst no changes are needed in the radio access network. SIPTO does not affect the
lawful intercept capability and security is of the mobile standard. SIPTO does not affect
mobility in any way.
Figure 17: Selective IP Traffic Offload
Small Cells
SIPTO

24
Another source of unnecessary traffic in the core network could be the one between
different terminals of the same local network. Local IP Access (LIPA) is responsible to
handle all local IP traffic through the local gateway. Just like with SIPTO, a network policy
is implemented to select which type of traffic is routed locally.
In Figure 18 a HeNB operating in LIPA mode has been represented with its S5 interface.
Only if the HeNB supports the LIPA function, it shall support an S5 interface towards the
S-GW and an SGi interface towards the residential/IP network. For a LIPA PDN connec-
tion, the HeNB sets up and maintains an S5 connection to the EPC. The S5 interface does
not go via the HeNB GW, even when present. Requirements on the secure backhaul link
for the S5 interface are specified in 3GPP TS 33.320. The mobility of the LIPA PDN con-
nection is not supported and the LIPA connection is always released at outgoing hand-
over (handout) 3GPP TS23.401. The L-GW function in the HeNB triggers this release over
the S5 interface.
LIPA required minor changes to the UE signalling and it is sorted out in 3GPP Rel. 10.
LIPA suffers from low mobility capability where the UE that moves between cells need to
reroute traffic through the macrocell and hence through the core network. Since local
traffic is rerouted through the L-GW and no core network entities are involved, lawful
interception is not possible with LIPA. For the operation of LIPA a HeNB is mandatory.
Figure 18: Local IP Traffic
Small Cells
LIPA

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LIPA can be used combined with SIPTO. Given that there is a well defined policy, the L-
GW can route traffic to the local area without passing it through the PDN while it can
also handle data transfer to distant communication node routed through the PDN /
Internet. SIPTO and LIPA are functions of the core network and hence no special features
are necessary to be installed on the UE. SIPTO and LIPA can also be used in roaming
situations given that the visited network supports the appropriate function. LIPA and
SIPTO need certain changes to be made to the MME and eNodeB.
Wi-Fi, also known as WLAN, is a wireless data communication network, standardized by
IEEE and specified by the IEEE 802.11 family of technology which defined the physical
layer (PHY) and medium access control (MAC). Wi-Fi took its first steps in early ‘90s
when got integrated to laptops. Since then Wi-Fi has gradually evolved and found its way
to become inseparable from portable computers, mobile devices, tablets and lately pe-
ripherals (e.g.. Printers). Wi-Fi was developed as an extension to the Ethernet specifica-
tion, however due to its wireless nature it got successful very soon. Nowadays, Wi-Fi
access points can be found in enterprise and domestic use, in stores, offices, shopping
malls, hotel foyers, streets or stadiums.
Wi-Fi
Figure 19: EUTRAN architecture with HeNB
Wi-Fi

26
As mentioned earlier, in the past Wi-Fi was used as an alternative to using the cellular
data. Their research, development and standardization happened independently of each
other. Whereas Wi-Fi was believed to be inferior in quality and security, offering no ad-
ditional benefits like seamless connectivity and roaming, it was free or comparatively
very cheap. In the recent years this thinking has changed and the cellular community has
realised that Wi-Fi can complement cellular data very well. Based on this revised under-
standing, the cellular and Wi-Fi standardisation bodies have been working closely to-
gether for the cellular devices to be able to take advantage of Wi-Fi offering.
Over the last few years, 3GPP has been developing new functionality that allows a Wi-Fi
access point to connect to the EPC. As a result, the operators are able to offer a carrier
grade Wi-Fi which would allow for the cellular subscribers to offload to Wi-Fi whenever
possible. Wi-Fi roaming has also become possible recently, thanks to the developments
in Wi-Fi standards. The next challenge is to be able to seamlessly roam between cellular
and Wi-Fi.
IEEE (Institute of Electrical and Electronics Engineers) is the
world's largest professional body dedicated to advancing tech-
nological innovation. Its standards on Information technology
802.11 specify wireless local area networks (WLANS) as well as enhancements to the
existing medium access control (MAC) and physical layer (PHY) functions.
Wi-Fi Alliance (WFA) is an association aiming into the promotion of Wi-Fi
technology and certifies Wi-Fi products complying with the appropriate
standards. Not every IEEE 802.11 is been certified by WFA as not every
device is compliant. WFA owns the Wi-Fi trademarks and only certified
devices can use the Wi-Fi logo. Its main goal is driving adoption of high-
speed wireless local area networking with a vision of “seamless connectivity”.
IETF’s (Internet Engineering Task Force) mission is to make the Internet
work better by producing high quality, relevant technical documents that
influence the way people design, use, and manage the Internet.
Small Cell Forum and WBA (Wireless Broadband Alliance)
cooperation to simplify Next Generation Hotspot (NGH) ac-
cess. NGH is making Wi-Fi more accessible by removal of
Wi-Fi Standardization bodies
Wi-Fi

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27
username and password. WBA provides interoperability between operators in the
WLAN industry. The members of WBA include a mix of cellular and WLAN operators and
telecommunication vendors.
Broadband Forum is an industry consortium dedicated in devel-
oping broadband technologies. Broadband Forum predecessor
was DSL Forum founded in 1994. Broadband Form is responsible
for DSL standardisation TR 069 framework for zero touch provisioning of Small cell (FAP).
NGMN (Next Generation Mobile Networks) is mobile telecommunications
association members of which are cellular operators and manufacturers. It
was founded in 2006 aiming into the development of a common view of solu-
tions for the evolution of wireless broadband. NGMN is looking at beyond 3G
services and architecture while it is acknowledged by both the 3GPP and IEEE.
Wi-Fi got introduced as 802.11 standard in 1997, in an attempt to replace the wired
Ethernet connections of the LANs. Since then, there have been multiple changes to im-
prove this initial standard. Improvements have been seen in terms of data transfer
speed, data management and technological features. The main success factors attrib-
uted to Wi-Fi is the low cost of equipment and the fact that it uses ISM (Industrial Scien-
tific and Medical) radio band, a portion of spectrum reserved internationally to be used
for research purposes. This means that any equipment using any flavour of 802.11 does
not need to pay any fees to any government or authority in any part of the world for the
lease of the spectrum. This fact alone made collaboration between IEEE and 3GPP im-
possible since cellular networks
operate on dedicated (and gener-
ally expensive) spectrum where
they do not expect any interfer-
ence from any other technology.
However, in the recent years, a
notable effort has been made by
both standardization bodies into
the direction of integration of Wi-
Fi in 3GPP EPC.
Wi-Fi
IEEE 802.11 standards evolution
Figure 20: Evolution of IEEE 802.11

28
The release of Ap-
ple iPhone back in
2007 changed the
cellular industry
forever. Operators,
struggling to make
a case for data con-
nectivity had to no
longer convince
anyone. Data has
overtaken the voice
not only in the usage but also in the revenue. Operators hunting for the ‘Killer App’ have
come to realise that fast and reliable Internet connectivity is what they have been look-
ing for. The modern smartphones and other new connected devices providing always-on
connectivity using any form of connectivity, including cellular and Wi-Fi, have become
must have gadgets without which the modern people are not ready to live. New termi-
nology like nomophobia, FOMO, digital detox, etc. is entering our vocabulary to highlight
the dependency on connectivity of the devices.
It was these
trends, that were
obvious years
back, that led to
3GPP proposing an
All-IP EPC. IEEE
was independently
working on im-
proving the 802.11
family of technolo-
gies with enhance-
ments, improve-
Wi-Fi integration to EPC
Wi-Fi integration in EPC
Figure 21: Cellular to Wi-Fi Integration
Figure 22: Presence of Wi-Fi Access Points

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29
ments and new
t e c h n i q u e s .
Industry bodies
like Wi-Fi Alli-
ance and Wire-
less Broadband
Alliance have
helped create a
common road-
map for the
3GPP and IEEE
family of technologies that is of mutually benefit to everyone.
Initial versions of 802.11 standards used only the 2.4GHz frequency band, since then
another band in 5GHz has been gaining popularity. Higher frequency bands imply lower
penetration in buildings but this band provides a much higher bandwidth, meaning that
it’s possible to provide much higher speeds.
Since Wi-Fi hotspots operate in the ISM band and the spectrum is unlicensed, there in no
requirement for coordination between access networks. Hence, once a UE access PDN
services over a Wi-Fi AP, the cellular network loses visibility especially if the access net-
work does not belong to the same operator. As Wi-Fi and 3GPP move towards integra-
tion two models of interworking have been defined, loosely coupled networks and
Tightly coupled networks.
Loosely coupled networks do not guarantee the user a certain QoE or IP session continu-
ity. This means that the connection might break at any time during a session or band-
width cannot be warranted. The most common situation is when the operator does not
posses a private Wi-Fi network, it partners with a Wireless Internet Service Provider
(WISP) to provide its customers with Wi-Fi broadband. However, mobility policies are
defined by the WISP and not the cellular operator. Nevertheless loosely coupled net-
works can provide offloading (Figure 23) capabilities to the cellular operator.
Tightly coupled networks are within the control of a 3GPP cellular network, providing IP
Figure 23: Seamless Connectivity

30
session continuity and a certain QoE. Even if the Wi-Fi access is provided by a WISP part-
ner, the cellular operator defines policies for the cellular customers assuring QoE. The
WLAN network should be a "trusted" one (where UE can move between cellular and Wi-
Fi access network without the need for authentication) as defined in a later chapter.
The integration of Wi-Fi into EPC comes with some significant standardization chal-
lenges. WLANs are in fact lower power wireless systems operating within a short range
(with respect to the macrocell). Once a connected UE is moving in the coverage of a Wi-
Fi AP it shall connect on it to carry on with the IP session. However, if that happens to
soon, near the Wi-Fi coverage edge, without a prior throughput test, the user might end
up experiencing lower connection speed.
In a similar manner a heavily loaded Wi-Fi AP might offer better reception than an LTE
macrocell. If the UE moves to the Wi-Fi without a throughput test it will again end up
with a degraded service. Another possibility is this where the Wi-Fi AP has slower back-
haul speed than the one provided by the cellular network. Finally, in the areas where the
WLAN and 3GPP access networks have a signal power of approximately the same magni-
tude, the UE will bounce between the macrocell and Wi-Fi experiencing a poor service
due to the "ping pong" effect.
IP session continuity (often referred to as seamless connectivity—Figure 23) is not a new
concept. A lot of work has been
made in the past towards seam-
less connectivity and roaming in
Wi-Fi. The first Wi-Fi handover
and roaming technique was Mo-
bile IP (MIP) as shown in Figure
24.
The UE moves outside the cover-
age of HPLMN. In the new loca-
tion a different PLMN offers Wi-
Mobile IP
Figure 24: Mobile IP architecture

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31
Fi services to the UE. For that purpose a temporary IP address is assigned to the UE
which is often referred to as the Care-of Address (CoA). Through the VPLMN IP networks
and using the CoA, the UE communicates with the Home Agent (HA), an entity located at
the HPLMN and it provides information about its current location. HA performs associa-
tion of the Home Address (HoA) with a CoA (a procedure known as “binding”) and once
binding is complete a binding acknowledgment is sent back to the UE.
Before moving to the VPLMN the UE held an active connection with a Correspondent
Node (CN) which is located in the PDN. CN sends traffic to the UE HoA but traffic reaches
the HA instead of the UE. HA establishes a dedicated traffic tunnel between the HA and
UE using the CoA at the other end of the tunnel (destination address). The UE receives
all data packets from the CN and it can respond either using CoA (and perform binding to
the CN by updating network information) and update routing or keep the same routing
and communicate through the established channel via the HA.
MIP routes data packets to and from a UE by providing session continuity by means of
the HA. The UE can route traffic via the anchor HA by utilizing HoA or through its tempo-
rary IP address (CoA). MIP was initially designed for use with IPv4 networks but it was
later extended to support IPv6 addresses too (MIPv6) and further extended to support
dual stack (IPv4 and IPv6).
Proxy Mobile IP (PMIP) has significant differences from its ancestor MIP. The HA is being
replaced by a Local Mobility
Anchor node that is in control
of all incoming and outgoing
traffic on the dependent net-
works. All traffic between the
dependent networks and the
PDN is routed through the
LMA. In addition to the LMA, a
Mobile Access Gateway entity
is being introduced responsi-
Proxy Mobile IP (PMIP)
Figure 25: Proxy Mobile IP architecture

32
ble to provide a link between LMA and WI-Fi APs. All APs in a WLAN network are con-
nected to a network specific MAG, which is the gateway to the LMA and the internet,
hence, each network needs a MAG to gain access to LMA. MAGs usually reside in the
access routers that most of the times are the AP themselves. The LMA and the attached
MAGs together form a mobility domain, which allows the UE to move between networks
in a transparent mode.
Mobility between networks is detected through standard terminal operations, however
the signalling associated with this movement is being taken care of MAGs. Bi-directional
tunnels are setup between the LMA and MAGs in a such a way so that the UEs do not
need to change their IP address within the mobility domain. Due to the LMA dominant
position, it is responsible to know the location of every UE under its mobility domain.
Any packets addressed to a specific UE are transferred to the responsible MAG over the
dedicated tunnel reducing this way the mobile device’s signalling functions while it re-
lieves it from the need to manage IP packet routing.
Access Network Discovery and Selection Function (ANDSF) has been developed by 3GPP
in order to optimize the discovery of non-3GPP networks such as Wi-Fi (WLAN), WiMAX,
CDMA2000 etc. The main objective of this document is to discuss the integration of Wi-
Fi and 3GPP access networks and therefore other non-3GPP access networks are beyond
the scope of this document. ANDSF is a
function introduced in 3GPP Rel. 8 and
upgraded for visited and home net-
works in 3GPP Rel. 9. The UE interfaces
with the ANDSF server through IP net-
work and UE needs to dynamically re-
trieve the ANDSF server’s IP address.
Note that throughout this document
the authentication shall be treated as
an integrated entity in the ANDSF ser-
vice. It is possible that a Wi-Fi service
provider may have a roaming agree-
3GPP ANDSF
Figure 26: ANDSF roaming

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ment with the cellular operator, in which case ANDSF is used to provide necessary roam-
ing information to the UE. A roaming UE has IP access to both Home and Visited ANDSF
commonly referred to as the H-ANDSF and V-ANDSF respectively.
ANDSF entity is responsible to provide the UE with:
1. Discovery information
2. UE Location
3. Inter System Mobility Policies (ISMP)
4. Inter System Routing Policies (ISRP)
The UE may send location information to the ANDSF server (Figure 28) which will be
based on either of the following options:
The UE gets location information from the System Information Blocks (SIB) of the macro
cell. The PLMN identity, Tracking Area Code (TAC) and cell identity can provide sufficient
location information to the ANDSF server.
Location information are also given by the Wi-Fi network by HESSID, SSID, BSSID mes-
sages sent over the beacon.
Some Access Networks share Latitude and Longitude information with the UE over Ra-
dius. Latitude and Longitude information can also be taken by GPS receivers, since most
UEs have them nowadays.
Figure 27: Evolution of ANDSF in 3GPP standards since 3GPP Rel. 8
Source: 4G Americas, Integration of Cellular and Wi-Fi networks, Sept 2013
UE Location

34
Once the UE switches on a 3GPP network, it follows the PLMN selection procedure as
specified in 3GPP TS 23.122, 3GPP TS 24.234 and 3GPP TS 36.304 before any other Ac-
cess Network discovery procedure is initiated. Once PLMN is chosen, the UE shall first
select an Access Network and then determine the presence of such network in the local
area. The selection of an Access Network is made based upon a priority list. According to
3GPP TS 24.302, if a higher priority Access Network is detected and is connected to the
selected PLMN (or a PLMN with a higher priority), then the UE shall attempt to attach via
that network. The Access Network type of interest in this document is WLAN which is
assumed to be the one with the highest priority.
For the detection of the supported WSIDs of the WLAN, the UE will initiate either the
passive or active scanning functions defined by IEEE Std 802.11 [2007]. In passive scan
operation, the UE monitors the wireless medium for beacon frames that provide the UE
with timing and advertising information. In this type of scanning, the UE listens to every
Figure 28: UE Location
Discovery Information

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channel of the wireless medium, one at a time. In active scan operation the UE takes the
initiative to associate with an AP by sending a Probe Request message on each probed
channel, one by one, and waits for a Probe Response message from the reachable APs. If
no Response messages are received within a timer expires, then the UE assumes the
channel inactive and moves on to the next one. The WLAN name is provided in the SSID
information element.
Upon successful discovery procedure the UE shall attempt to camp on cellular and WLAN
cells. Therefore, location information shall be provided.
Inter-system routing policy (ISRP) shown in Figure 30 has been developed by 3GPP and it
is part of the ANDSF. It is used to provide the UE with necessary information about rout-
ing certain types of traffic. In fact, operators must offer the best service to every user
with a high level of QoE, depending of course on their subscription. Therefore, the man-
Figure 29: Discovery Information
Inter-system routing policy

36
agement of data traffic to and from their network must be carried out in the best possi-
ble way. ISRP will indicate the UE which type of traffic should be routed through the cel-
lular access network and which should be routed through WLAN. ISRP rules has a home
PLMN leaf and a roaming leaf given that PLMN allows roaming. At any given time at least
one IRSP rule applies which is referred to as the “active rule” while in roaming situations,
a Visited PLMN rule applies on top of the Home PLMN rule. In this case, the active rule
shall be the one from the Visited access network.
The ISRP information is divided into 3 categories depending on whether the operator
allows and supports seamless mobility between access networks or not.
The first category (ForFlowBased) specifies the routing individual flows of data packets
carrying traffic to and from the same distant IP address. It is likely some data packets to
be forwarded through the Wi-Fi route while some others are routed through the cellular
core network. The choice of the access network for each flow of data packet is a choice
of the access network selection policy for each operator. ForFlowBased is designed for
IP Flow Mobility (IFOM) offloading, as shown further down this document.
Figure 30: Inter-system routing policy (ISRP)

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The second category (ForServiceBased) specifies the routing of data packets carrying any
type of traffic from and to different IP addresses simultaneously. Hence, in this case, the
UE might simultaneously use cellular and Wi-Fi resources, where each access network is
used to carry different types of traffic. ForServiceBased is been designed for Multiple
Access PDN Connectivity (MAPCON) offloading shown further down this document.
The third category (Non-seamless Offload) specifies the traffic behaviour for non-
seamless offloading. In this case the UE is able to choose between access networks on a
per IP flow basis however, the WLAN is not routed through the P-GW. Hence traffic is
routed on the PDN via alternative route non involving 3GPP entities. Session continuity
and QoE cannot be guaranteed since WLAN is not controlled by the operator or is also
not a roaming partner.
In 2010, Hotspot 2.0 Task groups in Wi-
Fi Alliance was formed and created a
set of standards to improve the end
user experience, interoperability and
roaming issues. Technology segmenta-
tion increases as much as Wi-Fi access
is getting popular. Hotspot 2.0 can be
wither MAC or user name and pass-
word based. It is also known as HS2 and
Wi-Fi Certified Passpoint. Hotspot 2.0 is
based on IEEE 802.11u “Interworking
with External Networks” and it defines
functions and procedures aiding net-
work discovery and selection. Mobile
devices will automatically join a Wi-Fi
network whenever it is available as
Hotspot 2.0 allows Wi-Fi roaming, it
provides the end user with a better
bandwidth and ultimately offloads
Hotspot 2.0 and Carrier Wi-Fi
Figure 31: Interoperability between 3GPP and IEEE
Figure 32: The main features supported in Passpoint
Rel. 1 and 2.

38
macrocell. However, the success of Hotspot 2.0 is the interoperability with 3GPP net-
works by the development of appropriate techniques. There are millions of Wi-Fi Access
Points (AP) around us making seamless communication possible. We live in a world full
of Wi-Fi access points. You can find them everywhere, at home, work, restaurants, shops
and any sort of public places.
Hotspot 2.0 handles roaming between Wi-Fi Access Points. UE can move outside the cov-
erage of the home network, entering into the coverage of a Hotspot 2.0 roaming part-
ner. Hotspot 2.0 will handle handover from home network to roaming network. Hotspot
2.0 will allow mobility between macro-cell and a Hotspot 2.0 roaming partners for cover-
age improvement (cell edge etc) purposes. Hotspot 2.0 allows international roaming.
Legacy networks do not support internet connection speed comparable to broadband.
3G – 4G macrocells can support high speed internet only to a limited number of users at
the same time. Mobile broadband connection speed is dependent on noise and interfer-
ence that is larger in the big cities. Users near the cell edge or in a very crowded cell will
suffer from limited connectivity and slow speed.
Wi-Fi roaming
Figure 33: (a) Hotspot 2.0 allows Wi-Fi roaming (b) Wi-Fi for coverage improvement at cell edge
Figure 34: Hotspot 2.0 protocol stack

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The authentication values transferred are expressed as an Extensible Authentication Pro-
tocol (EAP) flavour, with EAP-SIM, EAP-AKA, EAP-TLS, EAP-TTLS and EAP-FAST being the
most common ones.
The Authentication Key Agreement (AKA) is defined by the 3GPP and it is the security
Protocol stack and authentication
Figure 35: Carrier Wi-Fi

40
procedure of the 3GPP networks. EAP-SIM and EAP-AKA create the same authentication
challenges as the ones used by the 2G and 3GPP (3G, 4G) networks respectively and they
are mostly used by the mobile operators who provide complementary Hotspot 2.0 Wi-Fi
network to their subscribers. Hence, users can freely handover between cellular and
carrier Wi-Fi and cellular networks (of the same operator) using a common authentica-
tion mechanism.
The Transport Layer Security (TLS) and Tunnelled Transport Layer Security protocols use
Radius for authentication onto Hotspot 2.0 Wi-Fi network. They are mostly used for the
authentication of pure Wi-Fi operator subscribers, where SIM-based authentication is
not possible (or not supported by every device). EAP-TLS uses a UE stored certificate for
authentication while the EAP-TTLS authenticates a server which is reachable by utilizing
user credentials. EAP-FAST (Flexible Authentication via Secure Tunnelling) is a proprie-
tary of Cisco systems and it proposes the use of a Protect Access Credential (username
and password) for authentication of the user onto the Wi-Fi network.
Figure 36: Hotspot 2.0 operation

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As shown in an earlier section, WFA is independent from IEEE and the certification pro-
grams they run does not concern all of the IEEE technologies. Hotspot 2.0 is based on
the IEEE 802.11u/I specifications and is standardized in two phases. The Passpoint Re-
lease 1 certification is already in progress and it contains the Hotspot Security and Auto-
matic Login, Network Selection procedure giving a priority selection of Wi-Fi Networks
and Network Selection by Access Network Query Protocol (ANQP). The Passpoint Re-
lease 2 certification will run independently from Release 1 and is expected to start soon.
It will contain the online sign-up function and the operator specific policy. ANQP is a
query and response protocol that allows a Wi-Fi enabled UE to discover the available Wi-
Fi APs within coverage.
The Hotspot 2.0 Wi-Fi Access Point broadcast a Beacon message practically advertising it
supports Hotspot 2.0 or IEEE 802.11u. If the UE is embedded with IEEE 802.11u, it will
pick up this message and will try to camp on the AP by initiating the ANQP signalling. The
UE will send an ANQP Query message utilizing the Generic Access Service (GAS) protocol,
part of the 802.11u. The AP will forward the Query to the ANQP Server which will re-
spond with “ANQP Response” message back to the UE, via the Wi-Fi AP, containing a
capability list, expressed in a set of values that practically define the type of authentica-
tion supported, types of services supported, the domain name and the supported roam-
ing partner list. The Home PLMN (HPLMN) operator decides if a non-3GPP Access Net-
work is trusted (Figure
37) or untrusted (Figure
38).
As discussed earlier, mo-
bile operators worldwide
are investing in the devel-
opment of carrier Wi-Fi
networks for traffic off-
loading and high speed
connectivity. Hence,
Home PLMN owned Wi-Fi
Hotspot 2.0 operation
Figure 37: Trusted

42
network is considered to
be a trusted non-3GPP
Access Network while the
non-owned WLAN is
(most of the times)
treated as an Untrusted
non-3GPP Access Net-
work.
Officially, 3GPP defines a
trusted non-3GPP Access
Network the one that
provides a secure com-
munication between the UE and EPC. All communication between the Access Network
and the EPC is transmitted over pre-established, operator-managed, secure links. Other-
wise, when the connection between the UE and EPC is not secure, the non-3GPP IP Ac-
cess Network is declared as untrusted and in order to secure communication between
the UE and the EPC an IPSec tunnel needs to be established between the UE and ePDG
for all IP connections as shown in Figure 35. The trusted operation interface is the S2a
which provides direct connection between the mobility controller gateway and the PDN.
The disadvantage of this technique is the lack of security. On the other hand, for the op-
eration of an untrusted network, an enhanced Packet Data Gateway (ePDG) entity has
been introduced to interface the EPC with the Wi-Fi APs. ePDG sets up a secure tunnel
with P-GW over S2b interface and eventually Wi-Fi network becomes more secure with
it.
S2a-based Mobility over GTP access to 3GPP (SaMOG) is been standardized by 3GPP and
it is designed to allow UE to seamlessly roam between cellular and Wi-Fi access net-
works. SaMOG introduces a Trusted Wireless Access Network (TWAG) entity that inter-
faces EPC with the WLAN as shown in Figure 39. SaMOG is responsible to create a secure
tunnel between the Mobility Controller Gateway and the P-GW. Eventually, the Wi-Fi
will not connect directly to the PDN but P-GW shall provide connectivity. Hence, carrier
Figure 38: Untrusted
SaMOG

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Wi-Fi becomes more se-
cure and since P-GW be-
comes the anchor for
mobility between 3GPP
and non-3GPP networks.
ANDSF and SaMOG de-
veloped by 3GPP and
Hotspot 2.0 developed by
Wi-Fi Alliance make
seamless connectivity
between Wi-Fi and cellu-
lar networks possible.
Wi-Fi to cellular mobility is based on the PMIP principle. In fact the P-GW of the EPC will
play the role of the LMA providing connectivity of the access network to the PDN. A con-
nected UE is located within the coverage of Wi-Fi AP. The macrocell allows offloading
and traffic flows (denoted with yellow dotted line) via the Mobility Controller Gateway
to the AP. The UE moves outside of the AP coverage and hence it need to handover to
the macrocell. eNodeB will
detect the current location
of the UE and from ANDSF
information will know that
it is outside the coverage of
the AP, hence it will initiate
a handover. The P-GW will
play the role of the anchor
and the traffic will be re-
routed through the S-GW
to eNodeB. The seamless
connectivity model is the one shown in Figure 40 which is a variation of PMIP for mobil-
ity between Wi-Fi and Cellular access network.
Figure 39: Trusted with SaMOG
Seamless connectivity
Figure 40 WLAN to EPC handover with PMIP

44
MAPCON is developed in or-
der to allow the UE gain si-
multaneous connection to
more than one IP addresses
via both 3GPP and non-3GPP
access networks subject to UE
capability. MAPCON is mainly
used to offload traffic from
the core network. Mobility
sensitive applications (e.g. VoIP, Video streaming) shall not be offloaded as IP connection
may fail during handover. MAPCON is a function run at the EPC side and it does work
fine with MIP non compatible devices.
IFOM is a function that allows
traffic to be routed trough
either 3GPP or non-3GPP ac-
cess network, with individual
flows to the same PDN con-
nection. IFOM is based on
network policies where differ-
ent types of traffic is been
forwarded to and from the UE
through different Access Net-
works via individual flows. IFOM requires UE to be compatible with MIP family stack.
With the new order of things in mobile communications and with the coexistence of the
two dominant radio access technologies in the telecommunications arena, the biggest
MAPCON
Figure 41: MAPCON
Simultaneous access to 3GPP and non-3GPP
IFOM
Figure 42: IFOM
3GPP and Wi-Fi interoperability

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45
benefit will come from the collaboration between the two. So UEs should support both
3GPP and Wi-Fi with future aim of convergence of the two technologies. When the evo-
lution towards consolidation is completed a device should be capable of seamless mobil-
ity between the two access networks while a combination of 3GPP and Wi-Fi will enable
smart traffic offloading and improved routing capabilities.
In a typical international airport there is an average of 1000 smartphone users where
each uses 50 MB during business hours. The entire area of an international airport can
be covered by a single macro cell. But the capacity needs during peak hours reaches 110
Mbps. To achieve this connection speed there are two options, the deployment of 6 pi-
cocells that can provide a cumulative data rate of approximately 120 Mbps at an esti-
mated cost of $170.000. If instead of the 6 picocells 100 Wi-Fi AP are deployed the over-
all network speed can reach 5,400 Mbps at a cost that will not exceed $100.000. There-
fore Wi-Fi option could result to a 40% saving when compared to the picocells option
whilst the connection speed is 45 times greater.
Figure 43: 3GPP and Wi-Fi interoperability
Source: “Integrating Wi-Fi in the HetNet”, Caroline Gabriel, Maravedis-Rethink
Case study
Figure 44: Case study
Source: Hetting consulting

46
Small cells operate over the licensed spectrum which is defined by standards. The spec-
trum is expensive but has the added advantage of only one operator or service provider
being able to use. The same is not true for unlicensed bands. Any technology or device is
allowed to use the ISM band. This is the reason it is used in Wi-Fi, Bluetooth, micro-
waves, baby monitors, etc. Any technology designed for the use in the ISM bands should
be able to manage this interference and be prepared to suffer quality degradation due
to interference. The real advantage of the unlicensed bands is generally the amount of
spectrum available. For example the ISM band in 2.4GHz band has 85MHz available for
the use. Most operators would struggle to have even a 40MHz contiguous band for use.
Add to this, the new 5GHz band has 2 bands of 160MHz available for use, nearly univer-
sally. This is very appealing for the operators who can clearly see the potential to use
this big chunk of spectrum along with their licensed bands. With the advancements in
802.11 technology, Wi-Fi has similar or in some cases even better latency than 4G tech-
nology. Critics are quick to point out that security over Wi-Fi is not as good as cellular but
this advantage is marginal. Wi-Fi security is improving and there are different levels of
security available for devices with USIM and without a USIM. In fact non USIM based
devices could also be securely connected over Wi-Fi whereas they would not be able to
use cellular connectivity. Finally, it is worth mentioning that the cellular spectrum is very
fragmented and devices can only cater for some of the bands in each model; for example
iPhone 5 has some seven different models to cater for different LTE bands. In compari-
son, the ISM band is universal and same Wi-Fi can be used anywhere in the world.
Small cells and Wi-Fi can both add values and at the same time introduces new problems
for the cellular network. When a user is offloaded to either of them, the overall capacity
Wi-Fi and/or Small Cells?
Figure 45: 3GPP and Wi-Fi coexistence
Conclusion

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47
of the network increases. At the same time, the user can experience better speeds and
hopefully the quality thereby improving their QoE. The question should better be re-
phrased as both Small Cells and Wi-Fi are required wherever possible.
As we have discussed over the course of this workshop, Wi-Fi is matured enough to be
considered as a new RAN that can be deployed alongside of cellular technologies like 3G
and 4G. The initial intention was to use Wi-Fi for data traffic off-loading and capacity
injection, however recent developments clearly show that the future is about the inte-
gration of Wi-Fi into the core. Mobile operators are investing in the deployment of new
carrier Wi-Fi networks that is allowing seamless connectivity between their cellular and
Wi-Fi networks. Along with offloading and improving coverage and capacity, this is also
allowing new business models thereby increasing revenue and connecting more devices
which would not have been possible with cellular technology on its own.
The development of Hotspot 2.0 marks a new era in WLAN networks. Wi-Fi is gradually
becoming as secure as cellular and the cellular devices can now move transparently be-
tween cellular and Wi-Fi without the need to enter any login and password information.
The networks are evolving from a traditional Homogeneous networks into Heterogene-
ous networks. Small cells, even though around from a long time are just gaining popular-
ity with the operators who are getting more confident in using them. Different kinds of
small cells are being used to solve different problems. The predicted 50 billion con-
nected devices by 2020 would need much more than just small cells. HetNets are proba-
bly the best option for the future of mobile networks and the research on small cells and
Wi-Fi integration in the core networks are steps towards this direction.
With the discussions and research about the future 5G networks having already started,
most players are unanimous about certain aspects of this future network. The future
hyper dense networks will operate in a mesh topology where any connected device will
be capable to communicate with peers and the operator's network. Without a doubt,
seamless connectivity, development of HetNets and integration of new RANs into the
core network is a step towards the future.
Concluding remarks
Conclusion

48
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Technical Training

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References
[1] Hotspot 2.0—Making Wi-Fi as easy to use and secure as cellular, Ruckus, White Paper
[2] Small Cells Inside the Enterprise—The “Who, What & Where”, by Caroline Gabriel,
Maravedis-Rethink, June 2013, White Paper
[3] 3GPP TS 24.312 v 11.6.0 Rel. 11—Technical Specification
[4] 3GPP TS 23.261 v 11.0.0 Rel. 11—Technical Specification
[5] 3GPP TR 23.829 v 10.0.1 Rel. 10—Technical Report
[6] 3GPP TR 23.852 v 2.0.0 Rel. 12—Technical Report
[7] Small cells— what’s the big idea?, Femtocells are expanding beyond the home, Small
Cell Forum, White Paper
[8] Interworking Wi-Fi and Mobile Networks, The choice of mobility solutions, Ruckus, White
Paper
[9] Hotspot 2.0: Brining Cellular-like Roaming to Wi-Fi Hotspots, John Lombardi, Ruckus
[10] WLAN Traffic Offload in LTE, Rohde & Schwarz, White Paper, February 2012
[11] Rising to meet the 1000x Mobile Data Challenge, Qualcomm, White Paper, 2012
[12] System Requirements and Architecture, Jan Ellsberger, NGNM, White Paper
[13] Mobile Traffic Offload, NEC’s cloud centric approach to future mobile networks, NEC,
White Paper, 2013
[14] Integrating Wi-Fi in the HetNet, Caroline Gabriel, Maravedis-Rethink, February 2013
[15] LTE Advanced, An evolution built for the long-haul, Qualcomm, White Paper, 2013
[16] Wi—Fi & Packet Core Integration, Kwangwon Kim, Ericsson-LG, 2012
[17] Cellular—Wi-Fi Integration, A comprehensive analysis of the technology and standardiza-
tion roadmap, InterDigital, White Paper, June 2012
[18] Small Cells Call for Scalable Architecture, Jean-Christophe Nanan, Barry Stern, Frees-
cale, Whtie Paper, 2012
[19] Wi-Fi Consulting Services, Independent Wi-Fi Offload Network, Maravedis-Rethink, We-
binar, October 2013
[20] Cisco Visual Networking Index (VNI), Global Mobile data Traffic Forecast Update, Dr
Robert Pepper, Cisco, February 2013
[21] Wi-Fi Packet Core Integration, Sergei Gotchev, Djorgje Vulovic, Cisco, March 2012
[22] Wi-Fi roaming—building on ANDSF and Hotspot 2.0, Alcatel-Lucent & BT, White Paper,
2012
[23] An adaptive multimedia-oriented handoff scheme for IEEE 802.11 WLANs, Ahmed Riadh
Rebai & Said Hanafi, Internationa Journal of Wireless & Mobile Networks (IJWMN) Vol.
3, No. 1, February 2011
[24] Mobile Broadband Explosion, The 3GPP Wireless Evolution, Rysavy Research for 4G
Americas, White Paper, August 2013
[25] Integration of Cellular and Wi-Fi Networks, 4G Americas, White Paper, September 2013
[26] Understanding the Role of Managed Public Wi-Fi, in Today’s Smartphone User Experi-
ence, Informa, Mobidia, White Paper, 2013
List of References

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51
References
2G / 3G / 4G 2nd / 3rd / 4th Generation
AAA Authentication, Authorization and Accounting
AKA Authentication and Key Agreement
ANDSF Access Network Discovery and Selection Function
EAP Extensible Authentication Protocol
eNB evolved Node B
EPC Evolved Packet Core
ePDG evolved Packet Data Gateway
EUTRAN Evolved UMTS Terrestrial Radio Access Network
GSM Global System for Mobile Communications
HeNB Heterogeneous eNB
HetNet Heterogeneous Network
HSPA High Speed Packet Access
IFOM IP Flow Mobility
IPv4 Internet Protocol v4
IPv6 Internet Protocol v6
ISM Industrial Scientific & Medical
LIPA Local IP Access
LTE Long Term Evolution
LTE-A Long Term Evolution—Advanced
M2M Mobile to Mobile
MAPCON Multiple Access PDN Gateway
MIMO Multiple-Input Mobile-Output
MIP Mobile IP
MME Mobility Management Entity
OFDMA Orthogonal Frequency Division Multiple Access
PCRF Policy and Charging Rules Function
PLMN Public Land Mobile Network
PMIP Proxy MIP
QoE Quality of Experience
QoS Quality of Service
RADIUS Remote Authentication Dial In User Service
RAT Radio Access Technology
SaMOG S2a-based Mobility over GTP
SIPTO Selective IP Traffic Offload
UMTS Universal Mobile Telecommunications System
UTRAN UMTS Terrestrial Radio Access Network
Wi-Fi Wireless Fidelity
WLAN Wireless Local Area Network
WISP Wireless Service Internet Provider
List of Abbreviations

52
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