A Network Controlled QoS Model over the 3GPP Evolved Packet Core

anisesecretaryMobile - Wireless

Dec 12, 2013 (3 years and 11 months ago)

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A Network Controlled QoS Model over the 3GPP Evolved Packet
Core



*Marius Iulian Corici, *+Fabricio Carvalho de Gouveia, *+Thomas Magedanz


*

Fraunhofer Institute FOKUS, Kaiserin
-
Augusta
-
Alee 31, D
-
10589, Berlin, Germany


*+ Technical University of Berlin
, Franklinstr.
28
-
29, D
-
10587, Berlin, Germany


{marius
-
iulian.corici@fokus.fraunhofer.de
,
fabricio.gouveia@fokus.fraunhofer.de
,
thomas.magedanz@fokus.fraunhofer.de
}


1.

Introdu
ction

Present network devices are able to access
services over various technologies e.g. WLAN,
UMTS, WiMAX, LTE etc.

and to exchange data
simultaneously

ove
r them, as depicted in
Figure
1
.
In order to optimize the
service continuity in this environment with multiple heterogeneous access
networks
, various handover mechanisms are currently studied

(
e.g. IEEE 802.21 Media
Independent Handover

[1]
)
.

They concentrate especially on the seamle
ss qu
ality of the sessions,
considering that the network where the user is relocated after the handover has the necessary
resources to sustain the service continuity.





Figure
1
: Typical Mobile Network Connectivity


However the
user end
-
points decid
e to which network to connect, this leading to a general
tendency of over
-
saturating the access networks where the cost is minimal. In this case the
network provider can not offer the required quality of service for the connected users
, even though
it could have provided services over other access networks.

Being agnostic to the momentary load of the networ
ks, a multi
-
card user end
-
point will choose
its network selection based on the user preferences
, on

the knowledge gained from previo
us
connections and on the static policies introduced by the network operator in the devices.
Therefore
the network binding
and session parameters
decided without taking into consideration the
momentary parameters of the network. In a worse case scenario
, t
he user end
-
point connects to
one network only to find that its requirements are not supported. Thus, for receiving the required
service, it has to connect to another network, where this problem could repeat.

At this moment, the provisioning of resources
is done by the user end
-
point. When
a service is
started, the user end
-
point has to send som
e messages in order to negotiate the parameters of the
session
and to reserve resources according to them

in order to ensure the quality of the data
transmission. I
f the service can be provided at different levels of resource requirements, the
reservation has to be repeated until one of the levels is satisfied, which can be extremely time
consuming over
some of the access technologies.

To remedy this shortcomings of
the user end
-
point oriented QoS architecture, a new model is
proposed.
It considers that the resource reservation is triggered not by the client directly, but by a
network entity to which the service was signaled. The decision on the level of resources to
be
reserved is done by passing through a set of filters, in a policy oriented manner and with respect to
the momentary resources available on the access networks.

The main focus is on the scenarios of a single operator able to offer services over multiple

access technologies.

First
a state
-
of
-
the
-
art on QoS mechanisms in 3GPP is done. T
he existing
architectural designs are presented from a Quality of Service perspective, than the improvements
are
asserted. The conclusions are drawn from the comparison of t
he existing infr
astructures and
the one here proposed.


2.
QoS
and
Architecture

State
-
of
-
the
-
Art

The IP Multimedia System (IMS)
[10]

represents today the global service delivery platform. The
IMS is a complete s
ignaling framework, able to integrate different types of services in a unified
manner as seen from the user’s perspective, using as signaling protocol the Session Initiation
Protocol (SIP)
[5]
. The IMS structur
e also enables the connectivity of devices using different
access networks in a unified manner
[12]
, reducing the management cost of the operators that
deploy multiple types of access technologies.
By its abilit
y to integrate multiple services as
application servers, the IMS enables various services to be defined and deployed

in a fast and
flexible manner.

The Open IMS Core developed at FOKUS
[11]

serves as the signali
ng platform for the
architecture here presented. It contains the structures necessary for user registration and user
reachability. The user end
-
point (or User Equipment


UE) access to the network is done in a
network controlled manner. Also access to vari
ous services, both local to the home domain of the
operator and remote to other parties is done on a network technology agnostic level, offering an
interface easy to integrate in various user end
-
point devices.

The 3GPP IMS has adopted a Policy based appr
oach for QoS provisioning
[4]
. Policy based
networking allows a dynamic and automated control of network resources by the operator, where
resource allocation decisions are done based on session information and
local policies, which
define the expected behavior of the network. High level policies are specified without interfering
with IP
-
CAN specific management. A critical component in this architecture is a logical entity that
has a northbound interface to the
signaling plane and a southbound interface to the bearer plane to
provide linkage and
synchronization

between the two planes.
This system was chosen to manage
resources on both the session and bearer levels in a tight but flexible manner decoupling the cor
e
network components and procedures from the subtleties of the access technologies.
Such an
intermediate node has been defined under several standards and given different functional names
including Policy Decision Point
[6]
, Resource and Admission Control Function (RACF)
[7]
, or in the
3GPP release 7 and IMS architecture such an element is called a Policy and Charging Rules
Function (PCRF)
[3]
.

The Evolved Packet Core (EPC) is a new network architecture defined by 3GPP for the System
Architecture Evolution (SAE) (
[1]
,
[14]
)
, able to int
erconnect the signaling with the QoS on the
access networks, thus connecting the offered signaled services to the data transmission path in a
standardized manner.

IMS is integrated at the network layer with the Evolved Packet Core (EPC)

[13]
,
[14]
, which enables the actual resource reservations and the policy control on the different
access technologies. As depicted in
Figure
2

it comprises of the following e
ntities:



Mobility Management Entity (MME)


It is responsible for managing and storing UE context
and for generating temporary identities to be allocated to the UEs. It also is responsible for
checking the authorization whether the UE may connect to the PL
MN (Public Land Mobile
Network).



Serving Gateway
-

a router situated in the local domain of the user end
-
point which has to
function transparently for the agnostic internet, and is able to offer local provisioning, like
access control, translation from cir
cuit switched to packet switched networks and resource
provisioning.



Packet Data Network Gateway
-

the PDN Gateway has a similar functionality with the
Serving Gateway, but it relates only to packet switched networks and it is located in the
home domain of

the user end
-
point.



Policy and Charging Rules Function (PCRF) is the entity that interconnects the EPC with
the IMS control network. It receives the policies that have to be enforced on the data path,
keeps the state of the session and announces the IMS c
ontrol of the exception cases. One
of the goals of EPC is to be able to offer not only home domain, but also visited domain
break
-
through for data. For this reason the PCRF functionality was separated into home
domain functionality and visited domain one (
hPCRF and vPCRF).



For untrusted network access an evolved packet data gateway was considered (ePDG). It
authenticates the users and controls the traffic.

The EP
C

appeared from the necessity to converge different types of networks, thus having as main
goal
the transparency of access technology features to the core network of the service provider. At
this moment, the EP
C

is in the early stages of specification and has not defined the mechanisms
necessary for an end
-
to
-
end communication.

However the central co
mponent of the architecture is
the PCRF, which ensures a backwards compatibility and gives a perspective on the evolution of
the 3GPP standards.

The Evolved Packet Core is introduced in order to transparently unify the parameters of different
technologies
, like the UMTS, the 3GPP WLAN, non
-
3GPP access technologies (e.g. WiMAX) and
a future Evolved Radio Access Network called Long Term Evolution (LTE) or Evolved
-

UMTS
Terrestrial Radio Access Network (E
-
UTRAN). Each of these technologies comes with its own

specific access functions. The core itself manages and stores the user end
-
point context and the
user end
-
point services and network information in a Mobility Management Entity (MME).



Figure
2
. Evolved Packet System


An evolved

Policy and Charging Resource Function (PCRF)
[3]

is connected to the core in order
to provide the necessary information for controlling the data information received from the user
end
-
points.

The overall QoS c
oncept of EP
C
, and of the new technology it is introducing, the E
-
UTRAN,

is
based on the control of the EP
C

Bearer QoS parameters QoS Class Identifier (QCI) and Allocation
and Retention Priority (ARP)
[13]
. QCI
is a scalar (also called Label) that represents the QoS
characteristics that the EP
C

is expected to provide for the Service Data Flow (SDF). This Label is
used by routers to access node
-
specific parameters that control bearer level packet forwarding
treatm
e
nt (e.g.
admission thresholds, queue management thresholds), which are specified by the
operator. This Label Characteristic is standardized and comprises the following elements:



Bearer Type (GBR or Non
-
GBR)



L2 Packet Delay Budget



L2 Packet Loss Rate.

The

Bearer Type parameter is for checking if the EP
C

bearer is permanently allocated. The L2
Packet Delay Budget denotes the time that a link layer Service Data Unit (SDU) (e.g., an IP packet)
may reside within the link layer between an access node and a UE.
The L2 Packet Delay Bucket is
meant to support the configuration of scheduling and link layer functions. Last, The L2 Packet Loss
Rate determines the rate of SDUs of non congestion related packet losses. This is for allowing
appropriate link layer protocol

configurations
[13]
.

The ARP is the parameter used to decide whether a bearer establishment / modification request
can be accepted or rejected (in case of resource limitations like available radio capacity for
GBR
bearers). It is also used to decide which bearers to drop during exceptional resource limitations
(e.g. at handover).

Each GBR bearer is associated with a Maximum Bit Rate (MBR) QoS parameter. The GBR
corresponds to the minimum bit rate to be provided

to a GBR bearer and the MBR limits this bit
rate in order to avoid packets discarding a rate shaping function. The MBR may be greater than or
equal to GBR for a particular GBR bearer.
Table
1

depicts the QCI/Label

characteristics

[13]
.

Table
1

-

Standardized QCI/Label Characteristics

(Source
[13]
)

QCI
Characteristic

L2 Packet Delay
Budget

L2 Packet Loss Rate

Example Se
rvices

1 (GBR)

< 50 ms

High (e.g.10
-
1)

Realtime Gaming

2 (GBR)

50 ms (80 ms)

Medium (e.g.10
-
2)

VoIMS

3 (GBR)

250 ms

Low (e.g.10
-
3)

Streaming

4 (non
-
GBR)

Low (~50 ms)

e.g. 10
-
6

IMS signalling

5 (non
-
GBR)

Low (~50ms)

e.g. 10
-
3

Interactive Gaming

6 (no
n
-
GBR)

Medium(~250ms)

e.g. 10
-
4

TCP interactive

7 (non
-
GBR)

Medium(~250ms)

e.g. 10
-
6

Preferred TCP bulk
data

8 (non
-
GBR)

High (~500ms)

n.a.

Best effort TCP bulk
data


The
IEEE 802.11 standard

defines two types of services: the distributed coordination f
unction
(DCF) which supports delay
-
insensitive data and the point coordination function which supports
delay sensitive transmissions (PCF).

The first mechanism is based on the CSMA
/
CA where the stations compete for the
transmission environment. For collisi
ons, it considers a random idle time between some specific
boundaries. The second function is a centralized polling
-
based approach which avoids collisions by
polling the mobile nodes individually for transmission. This function o
ff
ers a better primitive fo
r
service di
ff
erentiation between stations. However, the mechanism leads to a longer time usage of
the channel for the mobile nodes with a lower rate transmission. Also stations, being the only ones
that know the type of tra
ffi
c transmitted, do not take pa
rt in the decision of the polling, making it a
static one in regard to the quality of service required.

In order to solve these problems two new functions were introduced in a Quality of Service
standard
[16]
. First one, the En
hanced Distributed Channel Access (EDCA), is similar to DCF, but
it considers a dynamic value for the idle time, depending on the type of tra
ffi
c the terminal has. For
this, four types of priority are defined. The packets are classified by the mobile node
into one of
these categories and queued for transmission, based on the priority level. The second one, the
Hybrid Coordination Controlled Access (HCCA) extends the rules of the EDCA by introducing a
polling mechanism for the stations, depending on their re
source reservation and the time prior
reserved. By using the HCCA, the stations are able to pre
-
reserve a specific access time on a
regular period.

The HCCA is similar to the QoS solution for UMTS
[8]
. It also considers a set o
f priority classes
and a channel reservation for each specific terminal. The reservation is done considering two main
parameters: the maximum bandwidth and the guaranteed bandwidth for each session flow. This
enables to discriminate between di
ff
erent flows

and their priorities, not considering the whole
mobile node tra
ffi
c as to have a specific priority.

In WiMAX (
[15]
,
[16]
) each flow has a pre
-
defined set of parameters and a set of parameters
that
is communicated when the resources are reserved. This enables a more detailed resource
reservation which can be dynamically changed if the user preferences change and the network
conditions allow it.

The QoS support mechanisms presented
here
for some speci
fic access technologies do not
presume a method of provisioning. Each one of them introduces some control mechanisms and
communication protocols. The scope of this paper is not to evaluate and compare these
mechanisms, but to introduce a new perspective on

how the resources may be reserved using
the
already existing mechanisms. The new concept and the complimentary architecture are described
in the next section
s
.


3. Network controlled QoS


Concept Descriptio
n

Each of the forward

presented technologies

off
ers a method for provisioning the required
resource res
ervations, user end
-
point based. This mechanism enables no signaled services to
have the requirements fulfilled based on the client
expectations and considering an agnostic
network.

In this section the

client controlled resource reservation and the new proposed network
mechanism are described and assessed in a single operator scenario.

As depicted in
Figure
3
, a user end
-
point (UE) is communicating with a servi
ce provisioning
infrastructure, in order to obtain the service required by the user. The UE communicates using one
access technology and is able to transmit data to the internet through an Access Network Gateway.
In order to control the resources available

in the network and also for charging proposes, the
operator of the access technology uses some access network control, here depicted for simplicity
as one entity.




Figure
3
: Service and QoS Provisioning Architecture


The client

oriented resource reservation presumes that the service provisioning infrastructure is
not able to communicate with the resource reservation path. Thus after the service is pro
visioned,
by this understanding that the communicating parties negotiate a comm
on session profile, the UE
has to use a separate mechanism to enforce the resource reservation on the data path.
This may
lead to multiple
exception cases when the network is not able to offer the required resources
as the
two signaling fl
ows are separated
.

The network controlled QoS presumes that during the session negotiation for a specific service,
the service provisioning infrastructure communicates with the access network control of the
network where the user is located, which at its turn enforces the

policies both on the access
network and on the access network gateway.
On a first empiric evaluation the network controlled
QoS is introducing a larger delay in the session provisioning. But considering that the client
oriented resource reservation is don
e after the session profile negotiation
and using a different
signaling, this may lead not only to a larger delay, but also to multiple possible error cases
, e.g
. a
session profile is negotiated, but only one of the parties involved in the session is able
to reserve
resources in its access network.

In the architecture presented in the previous section, the communication between the service
infrastructure (i.e. IMS) and the data path
is done using the Evolved Packet Core (EPC)
standardized by 3GPP. By integr
ating the two infrastructures, a new possibility of network control
QoS appears. It presumes a trade
-
off by reducing the terminal knowledge and introducing it as part
of the network control.

The present IMS scenarios use the client controlled resource rese
rvation for the access
networks and the network based one for the core network QoS. With the increase number of
terminals that can
use

multiple access networks simultaneously (e.g. U
MTS and WiFi or WiMAX
and WiFi), the resource reservation on the access ne
tworks depends more on the knowledge of
the terminal.


Even though the Evolved Packet Core offers a convergent model for accessing the required
services, it does not consider user end
-
points with the capacity of parallel attachment to multiple
access syste
ms. Thus the reservation of resources and its connection to mobility still remain as
open issues.

A multiple access could be resource consuming if no prior information is exchanged with the
Packet Core. The decision of connecting to a specific access poin
t is taken by the user end
-
point,
based on some criteria like cost, signal strength and prior knowledge
[8]
. For a possible second
connection, even though the first one has been established, the user end
-
point c
ontinues to
consider only those local policies. Thus, it remains agnostic of the load information that is kept by
the core, decreasing the possibility of finding a network able to offer the required surplus of
resources.

Some of the access technologies, li
ke WLAN
[9]
, use frequencies from the public spectrum.
Thus the user is left to choose from multiple networks, from which some pertain to the operator and
can offer the required services and some pertain to othe
r independent parties. In order to eliminate
this shortcoming, knowledge of the candidate networks is required.

An alternative is to store all the information about all the networks of the operator in the user
end
-
point. This will lead to memory consumptio
n and to a possible duplication from malicious third
-
parties. The same problem would appear in the case a static criterion of determining the possible
good networks is inserted in the terminal. Therefore the only acceptable alternative is to receive
inform
ation about usable networks, using another communication channel, if established. This
information should be restricted to the geographical position of the user end
-
point

and the user
profile
.

By having multiple interfaces, on a service provisioning, a mal
icious user might send multiple
resource reservation requests on all the interfaces available. Using the actual QoS model, in which
the user has to reserve resources on the data path, various types of attacks could affect the
network.

Also in the public f
requency networks the users can not be completely identified. Other devices
could “take over” session provisioning of a user end
-
point and duplicate it, creating a denial of
service attack. In order to limit this possibility a network provisioned QoS model

was considered.

Presently the services could be offered on multiple levels of quality. This is due to the
coalescence of multiple services in a new service e.g. voice and whiteboard and to the appearance
of different transmission mechanisms that could ada
pt in real
-
time to different bandwidth changes
e.g. the video codecs H.261, H.263. Therefore the QoS provisioning mechanism should adapt to
this evolution in the service.

In the actual architectures, the reservation of a tiered service is done by multiple
requests sent
by the user end
-
point until the constraints of one class of reservation is satisfied. For example for
an IPTV service multiple transmission rates could be considered. If the best one considered by the
user end
-
point cannot be satisfied, a req
uest for the subsequent one is required. This process can
repeat until the resources for one class can be reserved.

This could lead to overly
-
extended session setup delays, which affect the user perception of
the service as a whole. The
network controlled

QoS model h
ere proposed is able to solve the
resource allocation using only one step request.


4. Network controlled QoS


Architecture

Figure
4

depicts the enhancements to the 3GPP
EPC
. A new function was introdu
ced: the QoS
Information Function (QIF) which keeps track of the resources that are available on the access
networks and pre
-
reserves them on requests coming from the PCRF.

The information is

either

gathered from the MME which communicates directly to the
technology
specific enforcement points

or by other administrative mechanisms
. Triggered by the service
signaling, the PCRF filters the requested profile of the user according to the information received
from the QIF. After the policy class is decided for t
he required service, it is enforced
both to the
access network using the specific mechanism and to the Serving and PDN Gateways, which act as
access network gateways, having the possibility of
exchanging packets with the core network.

This
way the resource
s are reserved on the full path from the UE to the Access Gateway and in the core
network.

The new interfaces introduced, have both the function of enforcement of different policies and of
transmitting information about the momentary load of the resource o
n which the policies are
enforced. Through interface I1, information about network resources availability is sent from the
QIF to the PCRF. Using this information, the user profile and the cost information the PCRF is able
to decide which
the most appropri
ate access technology for the user is.
The QIF receives
information using interface I2 from the
access networks
. When a specific QoS is enforce
d on the
access network
, it also sends a message to the QIF

on an administrative path
.


The enforcement of the Q
oS resources is done by the PCRF both on the
access networks

us
ing interface I3 and on the Access Network Gateways

using interface I4. It is necessary for the
resources to be enforce
d on the access network gateways

as to be considered for the connection
be
tween the operator network and the other networks. The QoS request has also to be enforced
on the
access networks

in order to be sent to all the technology specific entities in the path
between the user end
-
point and the
access gateway
.


I5 is a the typica
l IMS interface (Rx+) on which information about the IP filters necessary to
identify the session and the QoS requirements of the user end
-
point are sent. Using this interface
messages about policy control and charging are transferred from the user end
-
poi
nt to the Packet
Core, in a protected way, by passing through the IMS signaling infrastructure.

If one of the connections of the user end
-
point is done using a large coverage network, like the
3GPP UMTS, a Tracking Area is defined for the user. Having this

information, the
PCRF

is able to
determine the networks using other access technologies in the vicinity of the user end
-
point. By
correlating this information with the information about the momentary load of the networks in the
QIF and with the user speci
fic policy and charging policies
, the PCRF

can

announces the user end
-
point

to which networks could connect in order to enhance the quality of the service.



Figure
4
. Enhanced System Architecture Evolution


By using the mechanism
s of IMS, the user is geographically localized in a network secure
manner, also offering the possibility to enhance the resources used accordingly to the specific
service requests.

Two typical scenarios illustrating the usage of the architecture are furth
er analyzed: the
registration scenario and the QoS service provisioning scenario.

3.1. Registration Scenario

This scenario, as depicted in
Figure
5
, describes how a default signaling channel is allocated,
when a ne
w terminal registers with the network, in a technology transparent manner.

When a new user end
-
point registers to a technology specific access network, in
formation is
sent to the technology specific access control point

(1), which can determine the identi
ty of the user
for specific network types e.g. UMTS or cannot for other networks e.g. WLAN. In both situations
the information has to be passed to the PCRF (2), in order to reserve a user specific or a general
minimal default resource as to make the signal
ing possible. First the resources have to be reserved
on the anchor point of the access networks (3, 4), then
confirmed as to be reserved

and enforced
through the network to the user (5, 6).

The user specific policy might ensure more resources for the defa
ult resources than the
anonymous default reservation. Therefore after the user registers with the IMS infrastructure (7), a
reallocation of the default resources is considered, if the momentary network capacities permit it.
The PCRF receives the user infor
mation from the IMS structure (8) and taking into account the
information from the QIF it enforces it on the anchor point and on the access network to the user (9,
10).

UE
QIF
PCRF
IMS
Network Registration(1)
Network Registration(2)
Default Reservation(3)
Default Reservation(4)
Network Registration(5)
Network Registration(6)
IMS Registration(7)
User Default
Reservation(8)
User Default
Reservation(9)
User Default
Reservation(10)
User Default
Reservation(11)
User Default
Reservation(12)
Access
Network
Gateway
Access
Network
Controller
UE
QIF
PCRF
IMS
Network Registration(1)
Network Registration(2)
Default Reservation(3)
Default Reservation(4)
Network Registration(5)
Network Registration(6)
IMS Registration(7)
User Default
Reservation(8)
User Default
Reservation(9)
User Default
Reservation(10)
User Default
Reservation(11)
User Default
Reservation(12)
Access
Network
Gateway
Access
Network
Controller

Figure
5
. Registration Scenario with the Enhanced
EPC



By s
eparating the anonymous registration from the user registration a better allocation of the
resources is obtained. Also due to the fact that all the traffic passes through the
access gateways

a filter could be added. This can help in restricting the access

of anonymous users to other
domains than the one controlled by the operator. Therefore the service provider could secure the
network from being used by unregistered parties.

If in the future the default resource allocation is decided to be used as a bear
er of data for third
party services, the allocation of the resources
can

be done dynamically, using a profile inserted in
the registration messages and evaluated by the PCRF. For example if the operator decides that
for a specific connected user, a specif
ic bandwidth should be available for non
-
signaled services,
after the user registers with the IMS infrastructure, this service

can

be offered, by using this re
-
allocation mechanism. Also this resource
can

be dynamically adjusted by subsequent registration
requests.

3.2. QoS Provisioning Scenario

A typical resource reservation scenario using the same network oriented QoS provisioning in the
access network is depicted in
Figure
6
. When a resource allocation request a
rrives from one of the
user end
-
points

(e.g. a SIP INVITE request)

(1), the IMS signaling infrastructure makes a request
to the PCRF (2). The PCRF, after combining the user information, with the set of policies and with
the momentary load of the network re
ceived from the QIF, decides for a specific resource class
and enforces it into the
access gateway
(3). Also this enforcement request is sent to the
access
network controller

(4), signaling that the resources that are reserved are less than the user requir
ed
,

if necessary.

The
access network controller

allocates the resources to the terminal on the access network;
also if the user has the possibility to use other interfaces and they are in an inactive state, based
on the Tracking Area of the end
-
point it cr
eates a list of the interfaces which can be found by the
terminal (5). The usable networks are than passed through a filter of the QIF (6), in order to keep
only the ones that are highly probable of sustaining the resources required and send to the IMS
inf
rastructure (7). The confirmation for the low level QoS that was reserved and the information
about other networks that could enhance the service quality are sent back to the user end
-
point (8).
At this moment the service could be started with a low resour
ces allocation.


UE
PCRF
IMS
QoS Request (1)
QoS Request (2)
User Specific
Reservation (3)
User Specific Reservation Request (4)
Allocating resources
& Localization (5)
User Specific Reservation Response
with other usable networks (6)
User Specific QoS Response
with other usable networks (7)
QoS Response with other usable networks (8)
Connecting to
another network (9)
QoS Request for re
-
reservation (10)
QoS Request (11)
User Specific
Reservation (12)
User Specific Reservation (13)
User Specific QoS
Response (14)
QoS Response for re
-
reservation (15)
Access
Network
Controller
Access
Network
Gateway
UE
PCRF
IMS
QoS Request (1)
QoS Request (2)
User Specific
Reservation (3)
User Specific Reservation Request (4)
Allocating resources
& Localization (5)
User Specific Reservation Response
with other usable networks (6)
User Specific QoS Response
with other usable networks (7)
QoS Response with other usable networks (8)
Connecting to
another network (9)
QoS Request for re
-
reservation (10)
QoS Request (11)
User Specific
Reservation (12)
User Specific Reservation (13)
User Specific QoS
Response (14)
QoS Response for re
-
reservation (15)
Access
Network
Controller
Access
Network
Gateway

Figure
6
. QoS Provisioning Scenario


In the meantime, using the information received in the QoS request, about possible free
networks in the vicinity, the end
-
point connects to

another

network, authenticates and
receives a
default reservation as it was previously described (9). This user end
-
point decision should not
consider only the information received, but also the signal strength of the network it wants to
connect to and the mobility of the user end
-
point. Wh
en the connection to the secondary network is
completed the UE sends a new QoS Request for the same service session (10). The request is
then processed by the PCRF and QIF and enforced on the complete data path from the user end
-
point to the
access gateway
.


3.3. Policy Provisioning

A policy description, as received from the signaling core, can be a set of codecs and their usage
as in the case of present scenarios. From this set of codecs the bandwidth and the service class
are deduced and sent from the IMS

Core to the Evolved Packet Core.

Information containing possible networks to which the user could connect is received from the
location management which may be present for some access technologies (e.g. UMTS)
. This
enables the PCRF to select a set of pol
icies that could be enforced if the resources permit it. The
PCRF receives the degree of occupation of the networks from the QIF. By combining this
information with the policies from the PCRF a reply is sent to the user. It contains a set of networks
and w
hich resources could be used if the user connects to that network.

This enables the user end
-
point to receive information about the neighbor networks and their
possibility to sustain its services. Also information about networks of other operators can be

sent by
using this mechanism
,

if roaming service is required and desired.

The information of network locations can be introduced statically in the
location mechanism
. It
does not have to match exactly the networks that are seen by the user at one specific

moment, but
it has to cover that set in order to give a larger set of possibilities to the user end
-
point. Thus, the
networks that are considered by the PCRF
can

cover a larger area than the exact location of the
user. This enables the user to select the
network to connect based on its mobility and on other
local criteria.

This information is particularly useful for users that are already connected to a network and the
network cannot sustain anymore the service requirements e.g. the signal of the network i
s rapidly
decreasing due to an increase of the distance between the access point and the user end
-
point.
This way the handover decision does not contain only the signal strength and the mobility
parameters of the user, but also the degree of QoS availabili
ty in the network to which the user
end
-
point is going to connect.

User end
-
point requests and network resource availability is sent using the service signaling.
This enables the user end
-
point to send QoS requirements, which, by this mechanism, can be
re
solved in a network secure manner. It also allows information to be sent from the network to the
user end
-
point containing the reserved resources and the possible other resources available. The
network is completely controlled by the operator, thus reducin
g the risk of possible attacks and the
error recovery

delay
.

By using this complex mechanism, services have at the beginning at least a minimal resource
reservation. Afterwards, if the network momentary capacities permit it, supplementary resources
could

be allocated according to the request of the parties involved. This leads to a provisional
client satisfaction and to a multiple class behavior of the QoS provisioning.

Multiple
-
card end
-
points can effectively use their network capacities in order to get

access to
more resources in a centralized coordinated manner controlled by the network operator. Thus the
operator can control tighter the data traffic through the core. This increases the degree of usability
of the network and decreases the delay due to
exception mechanisms in the QoS provisioning.
Also the multi
-
card terminals do not have to bind the second interface to some random network,
expecting some user
-
space service to use the provided resources. By using the double reservation
protocol here pre
sented, the second card can be connected only after some resources are required,
thus reducing the power consumption of the user end
-
point.



4. Conclusions


In this paper we presented an enhancement to the 3GPP
EPC

able, to optimize the QoS
provisioning i
n a single operator scenario. It is improving the service user perception, especially for
multi
-
card end
-
points and for tiered services. Transparent inter
-
operator scenarios have to be
studied, in order to ensure roaming possibilities.

A simple model was p
roposed for describing the user policies and the mechanism of processing
these policies both on the IMS and on the Evolved Packet Core. A future study
may

present how
the policies are provided by the user end
-
point to the Evolved Packet Core, the entities
in the IMS
Core that should modify and transmit the messages and how the selection is done by the PCRF,
QIF and
access technology controller

inside the core.

We have then proposed some additions to the 3GPP specification, in order to optimize the
service p
rovisioning. From both the operator and the user end
-
point, the services are better
provided using a network QoS provisioning, which ensures a better QoS management from the
operator and a better mechanism for exception handling as in the former 3GPP
archi
tecture
.

A QoS Information Function (QIF) in the Evolved Packet Core able to register the load of the
access networks was considered. This function is able to receive information about the various
networks of the operator and to provide filters for selecti
ng the ones that have enough resources
for
the
services

required by the user
.
For some access technology the EPC
has knowledge of the
user location by using a Tracking Area. An extension to this Tracking Area mechanism was
introduced. It contains not only
the networks of the tracked type e.g. UMTS, but also the networks
that can be reachable by the user, by means of other technologies e.g. WLAN.

A correlation between the QIF information and the information on the available networks
provided by the extende
d Tracking Area provides a better network selection for multi
-
card user
end
-
points. In order to obtain this correlation and the enforcement of the resources, two interfaces
were considered. The first one, between the PCRF and the
access network controller
,

is able to
enforce policies on the mobility access and to inform about these enforcements. The second one,
between the PCRF and the
access gateways, both System Gateway and PDN Gateway
, is able to
enforce the policies in a transparent manner as seen from
other parties involved in the service.

The concepts here presented apply to the access networks of an operator. It remains also as an
open issue the optimizations that have to be considered for the
roaming
user end
-
point
s

in order to
benefit from these cor
e enhancements.

5. References

[1]

IEEE 802.21Working Group. Ieee p802.21/D7..1: Draft ieee standard for local

and
metropolitan area networks: Media independent handover services (work in

progress,
2007.

[2]

3GPP TR 23.228, “3GPP System Architecture Evolution


Rep
ort on Technical Options
and Conclusions”, November 2006.

[3]

3GPP TS 23.203, “Policy and Charging Control Architecture”, December 2006.

[4]

TS 23.107 Quality of Service (QoS) Concept and Architecture, www.3gpp.org; 2006.

[5]

J Rosenberg, et al., “SIP: Session Initiat
ed Protocol”, RFC 3261, June 2002.

[6]

RFC 2753 (A Framework for Policy
-
Based Admission Control, January 2000).

[7]

ES 282 003 “Resource and Admission Control Sub
-
system (RACS); Functional
Architecture”.

[8]

3GPP TS 23.107, “Quality of Service (QoS) Concept and Archit
ecture”, June 2005.

[9]

3GPP TR 23.836, “Quality of Service (QoS) and Policy Aspects of 3GPP


Wireless Local
Area Network (WLAN) Interworking”, December 2005.

[10]

3GPP TS 23.228 “IP Multimedia Subsystem (IMS)”, December 2006.

[11]

D. Vingarzan, P. Weik, T. Magedanz, “
Introducing the FOKUS Open Source IMS Core
System for Multi Access Multimedia Service Environments”, IIR’s Telecoms Signalling
World Forum 2006, London, October 2006.

[12]

K. Knuettel, D. Witaszek, T. Magedanz, “The IMS playground @ FOKUS


an open
testbed for
generation network multimedia services”, Tridentcom 2005, February 2005.

[13]

3GPP TS 23.401 “GPRS Enhancements for E
-
UTRAN access”, October 2007.

[14]

3GPP TS 23.402 “3GPP Architecture Enhancements for non
-
3GPP accesses”, May 2007.

[15]

IEEE 802.16 group. IEEE Standard
for Local and metropolitan area networks

Part 16: Air
Interface for Fixed and Mobile BroadbandWireless Access Systems

Amendment for
Physical and Medium Access Control Layers for Combined

Fixed and Mobile Operation in
Licensed Bands., 2004.

[16]

IEEE 802.16 grou
p. IEEE Standard for Local and metropolitan area networks

Part 16: Air
Interface for Fixed and Mobile BroadbandWireless Access Systems

Amendment for
Physical and Medium Access Control Layers for Combined

Fixed and Mobile Operation in
Licensed Bands., 2005.