,Introduction
The proliferation of mobile applications has increased the amount of data in the 4G mobile network.
With the adoption of smartphones and broadband services, such as video streaming, cellular
network resources are increasingly constrained.
Wi-Fi technology is ideally positioned to add capacity to the cellular network. It is necessary to
improve the interworking between the 4G mobile network and the Wi-Fi network in order to offer
a global and consistent broadband access to the end-user.
In addition to growing traffic, users expect unrestricted access to applications whether at home, in
a business or on the road. For this reason, Wi-Fi technology, providing additional coverage, is an
appropriate solution for roaming users.
The ability to exploit unlicensed frequency bands in addition to the spectrum allocated to cellular
networks is of obvious appeal to network operators, who see Wi-Fi as another means of accessing
the 4G mobile network.
Many mobile phones currently sold include both cellular and Wi-Fi radio access and are capable
of simultaneously using both radios. This makes it possible to direct certain services to Wi-Fi
access and others to the cellular radio access.
The various standardization bodies, IEEE (Institute of Electrical and Electronics Engineers), WFA
(Wi-Fi Alliance) and 3GPP (3rd Generation Partnership Project), paved the way for the integration
of Wi-Fi technology into the cellular network, allowing the mobile to access its services through
Wi-Fi access.
I.1. 4G mobile network
I.1.1. Network architecture
The 4G mobile network, which is called EPS (Evolved Packet System), consists of an evolved
packet core (EPC) and an evolved universal terrestrial radio access network (E-UTRAN) (Figure
I.1).
The E-UTRAN access network provides the connection of the user equipment (UE). The core
network EPC interconnects access networks, provides the interface to the packet data network
(PDN) and provides mobile attachment and bearer establishment.
,Figure I.1. 4G mobile network architecture
The evolved node B station (eNB) compresses and encrypts traffic data on the radio interface, as
well as encrypts and checks the integrity of signaling data exchanged with the mobile.
The mobility management entity (MME) allows mobile access to the EPS network and controls
the establishment of bearers for the transmission of traffic data.
The SGW (Serving Gateway) entity is the anchor point for intra-system handover (mobility within
the 4G network) and inter-system handover in packet-switched (PS) mode, requiring transfer of
mobile traffic to a secondor third-generation mobile network.
The PGW (PDN Gateway) entity is the gateway router that connects the EPS network to the PDN.
It provides the mobile with its configuration (IP address) and traffic information to the online
charging system (OCS) for the prepaid and offline charging system (OFCS) for the postpaid.
The home subscriber server (HSS) is a database that stores data specific to each subscriber. The
main stored data include subscriber identities, authentication parameters and service profile.
The policy charging and rules function (PCRF) provides the PGW entity with the rules to apply
for the traffic (rate, quality of service, charging mode) when establishing the bearer. This
information is stored in the subscription profile repository (SPR) when the subscription is created.
I.1.2. Security architecture
The mutual authentication between the mobile and the MME entity is based on the EPS-AKA
(Authentication and Key Agreement) mechanism:
, – the HSS entity provides the MME entity with the authentication vector (RAND, AUTN,
RES, KASME) from the secret key Ki created during the subscription of the mobile;
– the MME entity provides the mobile with the random number (RAND) and the seal
(AUTN) of the network;
– the mobile calculates the seals (AUTN, RES) and the key KASME from its key Ki stored in
the universal subscriber identity module (USIM) of its universal integrated circuit card
(UICC) and compares the seal (AUTN) received with that calculated;
– the mobile transmits its seal (RES) to the MME entity, which compares it to that received
from the HSS entity;
– the KASME key is used to protect the signaling exchanged between the mobile and the
MME entity as well as the control and traffic data on the radio interface.
I.1.3. Bearer establishment
The EPS network transports the mobile data stream (IP packets) transparently to the PGW entity
that is routing the packets. The IP packet is transported in bearers built between the entities of the
EPS network (Figure I.2).
Figure I.2. Bearer establishment
The data radio bearer (DRB) is built between the mobile and the eNB entity. The RRC (Radio
Resource Control) signaling, exchanged between the mobile and the eNB entity, is responsible for
the construction of this bearer.
The S1 bearer is built between the eNB and SGW entities. The S1-AP signaling, exchanged
between the eNB and MME entities, and the GTPv2 (GPRS Tunneling Protocol-Control) signaling,
exchanged between the MME and SGW entities, are responsible for the construction of this bearer.
The S5 bearer is built between the SGW and PGW entities. The GTPv2-C signaling, exchanged
between the SGW and PGW entities, is responsible for the construction of this bearer.
The proliferation of mobile applications has increased the amount of data in the 4G mobile network.
With the adoption of smartphones and broadband services, such as video streaming, cellular
network resources are increasingly constrained.
Wi-Fi technology is ideally positioned to add capacity to the cellular network. It is necessary to
improve the interworking between the 4G mobile network and the Wi-Fi network in order to offer
a global and consistent broadband access to the end-user.
In addition to growing traffic, users expect unrestricted access to applications whether at home, in
a business or on the road. For this reason, Wi-Fi technology, providing additional coverage, is an
appropriate solution for roaming users.
The ability to exploit unlicensed frequency bands in addition to the spectrum allocated to cellular
networks is of obvious appeal to network operators, who see Wi-Fi as another means of accessing
the 4G mobile network.
Many mobile phones currently sold include both cellular and Wi-Fi radio access and are capable
of simultaneously using both radios. This makes it possible to direct certain services to Wi-Fi
access and others to the cellular radio access.
The various standardization bodies, IEEE (Institute of Electrical and Electronics Engineers), WFA
(Wi-Fi Alliance) and 3GPP (3rd Generation Partnership Project), paved the way for the integration
of Wi-Fi technology into the cellular network, allowing the mobile to access its services through
Wi-Fi access.
I.1. 4G mobile network
I.1.1. Network architecture
The 4G mobile network, which is called EPS (Evolved Packet System), consists of an evolved
packet core (EPC) and an evolved universal terrestrial radio access network (E-UTRAN) (Figure
I.1).
The E-UTRAN access network provides the connection of the user equipment (UE). The core
network EPC interconnects access networks, provides the interface to the packet data network
(PDN) and provides mobile attachment and bearer establishment.
,Figure I.1. 4G mobile network architecture
The evolved node B station (eNB) compresses and encrypts traffic data on the radio interface, as
well as encrypts and checks the integrity of signaling data exchanged with the mobile.
The mobility management entity (MME) allows mobile access to the EPS network and controls
the establishment of bearers for the transmission of traffic data.
The SGW (Serving Gateway) entity is the anchor point for intra-system handover (mobility within
the 4G network) and inter-system handover in packet-switched (PS) mode, requiring transfer of
mobile traffic to a secondor third-generation mobile network.
The PGW (PDN Gateway) entity is the gateway router that connects the EPS network to the PDN.
It provides the mobile with its configuration (IP address) and traffic information to the online
charging system (OCS) for the prepaid and offline charging system (OFCS) for the postpaid.
The home subscriber server (HSS) is a database that stores data specific to each subscriber. The
main stored data include subscriber identities, authentication parameters and service profile.
The policy charging and rules function (PCRF) provides the PGW entity with the rules to apply
for the traffic (rate, quality of service, charging mode) when establishing the bearer. This
information is stored in the subscription profile repository (SPR) when the subscription is created.
I.1.2. Security architecture
The mutual authentication between the mobile and the MME entity is based on the EPS-AKA
(Authentication and Key Agreement) mechanism:
, – the HSS entity provides the MME entity with the authentication vector (RAND, AUTN,
RES, KASME) from the secret key Ki created during the subscription of the mobile;
– the MME entity provides the mobile with the random number (RAND) and the seal
(AUTN) of the network;
– the mobile calculates the seals (AUTN, RES) and the key KASME from its key Ki stored in
the universal subscriber identity module (USIM) of its universal integrated circuit card
(UICC) and compares the seal (AUTN) received with that calculated;
– the mobile transmits its seal (RES) to the MME entity, which compares it to that received
from the HSS entity;
– the KASME key is used to protect the signaling exchanged between the mobile and the
MME entity as well as the control and traffic data on the radio interface.
I.1.3. Bearer establishment
The EPS network transports the mobile data stream (IP packets) transparently to the PGW entity
that is routing the packets. The IP packet is transported in bearers built between the entities of the
EPS network (Figure I.2).
Figure I.2. Bearer establishment
The data radio bearer (DRB) is built between the mobile and the eNB entity. The RRC (Radio
Resource Control) signaling, exchanged between the mobile and the eNB entity, is responsible for
the construction of this bearer.
The S1 bearer is built between the eNB and SGW entities. The S1-AP signaling, exchanged
between the eNB and MME entities, and the GTPv2 (GPRS Tunneling Protocol-Control) signaling,
exchanged between the MME and SGW entities, are responsible for the construction of this bearer.
The S5 bearer is built between the SGW and PGW entities. The GTPv2-C signaling, exchanged
between the SGW and PGW entities, is responsible for the construction of this bearer.
