Wi-Fi Offloading.PDF

Excursive summery
One of the critical challenge facing mobile operators is the massive expansion of the data traffic
flowing over 3G/4G mobile broadband network. With smart phones and the increasing of
multimedia application's needs for streaming music videos and the trend of live stream videos and
online gaming , the resources of existing cellular networks are becoming increasingly constrained.
In addition to traffic growth, the subscriber expectations are also changing. They expect ubiquitous
access to applications and content whether they are at home, at an enterprise, on the go or even
when traveling. For these reasons Wi-Fi Offloading becomes the most attractive and promising
solution for operators.
Thus, many mobile operators that are thinking strategically about investing in 4G LTE are also
considering how Wi-Fi can complement and enhance their existing infrastructure deployments is an
essential.
In fact, 3GPP has been working on a number of initiatives to improve Wi-Fi/Cellular interworking,
more specially 3GPP has been introduced an authentication protocols (EAP-SIM, EAP-AKA ,
EAP-AKA') that guarantee the same security level used tin mobile technology while trying access
to Wi-Fi network.
Additionally, 3GPP has spent several years standardizing the ANDSF which provides a framework
for operators to customize network steering policies and distribute those policies down to devices.
On the other hand 3GPP still not able to fulfill the needs of Wi-Fi offloading because of the
complexity and lake in visionary standard that can handle such a heterogeneous network. This
situation creates a gap between the immediate needs for Wi-Fi offloading from the MNOs and the
3GPP standard.
This gap drives to create a new business models which seek to support Wi-Fi offloading by the way
that is compatible with the 3GPP specifications, not restricted to uncompleted standard interface
leakage and the operator don't lose control and visibility of the subscriber.
the overall requirements of the system should be:
1. Seamless handover between mobile broadcast network and Wi-Fi network.
2. Detection of available Wi-Fi network and selection decision should be manageable and
optimized.
3. Roaming occurs by the same security level (Authentication process used to access mobile
network and Wi-Fi should be the same).
4. Accounting and belling solutions.

Methodology summery:
 Authentication
Authentication is a process in which the credentials provided are compared to those on file in a
database of authorized users' information on a local operating system or within an authentication
server. If the credentials match, the process is completed and the user is granted authorization for
access.
GSM authentication is based on a challenge-response mechanism. The A3/A8 authentication and
key derivation algorithms that run on the SIM can be given a 128-bit random number (RAND) as a
challenge. The SIM runs operator-specific algorithms, which take the RAND and a secret key Ki
(stored on the SIM) as input, and produce a 32-bit response (SRES) and a 64-bit long key Kc as
output.
3GPP has been developed EAP-Sim protocol in January 2006 as specified in RFC4186 to allow
Wireless LAN users to authenticate access to a Wireless LAN network using a mobile phone SIM
card.
Our solution build the authentication server (AAA Server) which is connected to the
authenticator (AP or NAS ) over RADIUS and connected to the Authentication data base
(HLR) over M3UA/SIGTRAN. By another word our authentication server works as a
gateway which decapsulate data packets carried over radius and re-encapsulate it again over
M3UA/SIGTRAN to be interfaced to HLR in mobile core.
As shown in the figure how Network architecture looks like. the authentication request will be sent
from user equipment and then forwarded to AAA server which begin to challenge the candidates
and ensure from the credentials of client.
The authentication process established between user equipment against AAA server and the Access
point only forwards data between two peers and HLR/AUC works as a data base which contains
credentials of all authorized users.
The following figure show the signaling in more details and snap shots of our server.

Snap shots of our already built RADIUS server
credentials of authorized users

Access Accept sent from AAA server to AP
 Detection and Selection polices
The Access Network Discovery and Selection Function (ANDSF) is a primary enabler of intelligent
network selection between 3GPP and non-3GPP access networks. ANDSF is an optional network
element in the 3GPP Evolved Packet Core (EPC), the purpose of which is to provide UE’s with
useful information and operator-defined policies to guide network selection decisions. ANDSF was
first defined in 3GPP Release 8, and continues to evolve until now.
ANDSF is a standalone node in that the UE-to-ANDSF S14 interface is the only interface to
ANDSF that has been standardized – any interaction between the ANDSF server and other network
elements is outside the scope until S14 recently standardized in 3GPP TS 23.402 [6].
ANDSF Rel-8
 Access network discovery – provides a list of access networks available in the UE's location.
 ISMP (Inter-System Mobility Policies) – used when only a single radio interface is used
 select the most preferable access technology (cellular over WLAN)
 when ISMP is allowed or restricted; availability conditions(PLMN, Cell Id, SSID,
geolocation, etc).

ANDSF Rel-9
 Roaming -enables access network discovery & selection for the roaming scenario.
 Specify functionality to enable the ANDSF retrieve for example;
 security information
 the UE's current position
 ISMP from another entity
ANDSF Rel-10
 ISRP(Inter-System Routing Policy) – used when UE can route IP traffic simutaneously over
multiple radio access interfaces; filter rules based on;
 APN the UE uses for given connection.
 destination IP address the UE sends traffic to.
 the destination port number the user equipment connected to.
Data Identification in ANSD (DIDA) Rel-11
 ISRP extensions to provide to operators a better control of the network resources used for
each application or IP flow.
 Identification of traffic based on:
 Application
 content type /content size
 Destination domain
Operator polices for IP interface selection(OPIIS) Rel-12
 Enhance operator polices for IP interface selection among both 3GPP and non-3GPP
accesses
 Selection across multiple IP interfaces applies to both physical interfaces (cellular Vs.
WLAN) and logical interfaces(Selection among multiple PDN connections).
Although, ANDSF provides a useful framework for distributing flexible operator-defined
network selection information and policies. there is additional information that is likely
available in an operator’s network and which could be used to improve network selection
decisions, but that is not captured in the current iteration of ANDSF. Examples of these items
as follows:
Network Conditions:
One of the most important aspects of an intelligent networks selection decision is a consideration of
the current network conditions of all of the relevant access networks.
this could have a dramatic impact on a given users quality of experience, and could influence
a decision to select that access network relative to the other available options.
User/Subscription Information:
there is no standardized interface between ANDSF and the user’s subscription/profile information
(e.g., between ANDSF and UDR or HSS).
Other types of network-based info:
There are several other pieces of information about a given access network that may be available to
the network operator but which are currently not captured in ANDSF policy. For example, there are
many different types of Wi-Fi access points with a wide range of supported capabilities.
Network-based policy for local UE-info/intelligence:
In addition to all of the information that is available in the network, there is a considerable amount
of information/intelligence that is local to the UE and which could be used to improve network

selection decisions. For instance, a UE’s current battery utilization level is known locally to the
device and that information could be used to influence whether one or multiple radios are used at a
given time.
In order not to block onto leakage of interfaces and weakness in achieving higher QOE we
introduce the functionality of ANDSF and added features to ensure high QOE and meet
MNOs needs on a web server and Android application installed in user equipment.
Detection and Selection techniques consists of two sides
 Application on the UE side
Application in UE side is responsible for capture offered data rate already delivered per UE in the
coverage area, as the problem of mobile broadcast network is the inability to track the service per
user. So application take these responsibilities;
1. Current location detection of the user.
2. Throughput monitoring of the serving network (WLAN or Cellular).
3. Keep user in touch with the enhancement of the MNOs network and the availability of
WLAN.
 Web server side
the web server contains policies of MNOs and the criteria by which Wi-Fi is preferred over the
mobile broadcast network or not. Also it's configurable and flexible to ensure balance in the
network and high QOE. So this side take the responsibility of
1. provide list of access network available in the current location of UE
2. organize data of throughput monitoring captured by application into two tables one for
WLAN and the other for cellular network.
 Mobile broadcast network monitoring is used to gain knowledge about instantaneous
condition of the network.
 WLAN throughput is used to avoid backhaul problem and ensure of the level of QoS.
3. All data captured about the condition of the networks is weighted by special algorithm
resulted a number reflect the priority of each AP provided in the location.
Snap shots of already built server showing throughput monitoring Databases

 Accounting and Billing
Accounting refers to tracking of the consumption of NAS resources by users. Accounting does
not only include cost recovery in the form of billing. It can also be used for capacity planning,
to generate trend graphs, and to know more about the resource usage at a given point in
time. In this chapter, we will see how accounting is done in RADIUS server.
Accounting in RADIUS server is independent from authorization and authentication. It uses
a separate port and consists of Accounting-Request packets sent by the client to the
server. The server responds with Accounting-Response packets to acknowledge the
requests.
Accounting data is used to measure usage on a network. An NAS can report on the time a
user is connected to the network as well as the data usage of the user.
Accounting records do not reflect details like websites a user has visited during a session.
They only indicate time and data usage.
In order to improve a billing system for Wi-Fi offloading, we should first deeply understand billing
system in mobile broadcast network which based on PCRF, PCEF, OCS, OFCS and SPR. The
following figure shows the billing system as introduced by 3GPP.
(1) User equipment(Mobile Station) wishes to establish a data application(data access/internet), so it
request to BTS/Node B.
(2) Node B forward its request to BSC/RNC.
(3) After all queries and procedure related to authentication, IMEI check & subscriber static
information(HLR), BSC/RNC forward subscriber request to SGSN. Some of the queries are
performed by SGSN.
(4) SGSN requests to GGSN for PDP context/data access.
(5) GGSN signals/query to PCRF(Policy & Charging Rule Function) about UE/MS data session
establishment over Gx interface.
(6) PCRF queries the Subscriber Profile Repository(SPR) for dynamic information of subscriber

over Sp interface.
(7) SPR sends all information about the subscriber policy/quota/rules to PCRF over Sp interface.
(8) PCRF installs policies for subscriber on GGSN(by PCEF)(per access point name[APN] and per
bearer quota grants).
(9) If required, over Gx interface, Deep Packet Inspection(DPI) intimates PCRF on traffic
detection.(Ud interface in the case of TDF[Traffic Detection Function])
(10) PCRF installs policies for application control on DPI and DPI begins tracking usage.
(11) Now data session is established and the subscriber starts consuming the data.
(12) Over Gy interface GGSN/PCEF talks to OCS(Online Charging System) for charging/credit.
(13) GGSN receives the information from OCS about balance/quota.
(14) GGSN signals policy server(PCRF) that device has exceeded data/quota grant or credit is low.
(15) Over Sy interface OCS also sends the credit limit report to PCRF.
(16) Policy server may grant additional grant, after consulting with subscriber by sending SMS
notification over SMPP.
So, to provide a billing system to Wi-Fi offloading we need to build a box which has the ability
to play the role of GGSN/PDN in the side of WLAN network with an interface to PCRF over
Gx standard interface.
This box will be a special RADIUS server which receive NAS reports on the time a user is
connected to the network as well as the data usage of the user (Accounting port 1813 in on
side) and forward these packets to PCEF via Gx interface to gain knowledge about rules and
policies and complete the cycle of billing system.
WLAN controller the special RADIUS server PCRF
So if we summing the overall system we will take all benefits of a complementary WLAN
network to the mobile broadcast network and ensure a high level of both QOS and QOE
which together reduces the chrun and of course achieve high ARPU and freeing the cellular
band for new business models and follow the steps of a new trends.

The overall Network architecture will be as follows,
 Business Case
The Intelligent Wi-Fi Offloading Business Case was developed not only to offer the capability to
extend the network by the power of WLAN network as discussed but also to keep in touch with the
tradeoff of building a Wi-Fi Offloading network over small cells strategies or buying new licensed
band for less air interface limitations.
We have the tools which can help the MNOs to analyse the conditions where Wi-Fi offloading is
more helpful , and recommend in which the investment will be more benefitable and optimize the
configuration of the Wi-Fi offload network to maximize Return On Investment (ROI).
it is extremely important to pay great attention to the right balance of Wi-Fi coverage area and the
density of Access Points (APs) in order to offload the optimum amount of traffic while maintaining
or improving the user experience. Implementing too few APs could result in not capturing enough
data traffic. On the other hand, implementing too many APs per square kilometer would drive the
business case into a negative ROI.
Also our business case care about the end user, maybe it's not our direct client but they directly
reflects our achievements. So we pay our attention to keep customers have all the knowledge about
the operator's Wi-Fi deployments as an advertising trick for the operator itself by the application
installed on UEs, and we improve a complete advertising system as a location based services. As if
we have the information about the BSSID that users already accessed in an enterprise we will have
an accurate vision about where are our clients and if so we can forward advertising shows over the
WLAN network without any headache in the cellular network side.

Wi-Fi Offloading.PDF

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