Provisioning end-to-end QoS under IMS over a WiMAX architecture

� Provisioning End-to-End QoS Under IMS Over a WiMAX ArchitectureWenhua Jiao, Jianfeng Chen, and Fang Liu

Worldwide Interoperability for Microwave Access (WiMAX) is considered acost-effective way to provide wireless access to an Internet protocol (IP)Multimedia Subsystem (IMS)-based core network. Determining how toprovide end-to-end quality of service (QoS) for the applications indicated is asignificant issue. This article highlights the IMS over WiMAX framework andproposes a layered QoS model with feasible signaling flow. Several techniquesare analyzed, especially cross-layer QoS mapping and an end-to-end QoSprovisioning signaling mechanism. © 2007 Alcatel-Lucent.

Bell Labs Technical Journal 12(1), 115–121 (2007) © 2007 Alcatel-Lucent. Published by Wiley Periodicals, Inc.Published online in Wiley InterScience (www.interscience.wiley.com). • DOI: 10.1002/bltj.20220

IntroductionWe are witnessing the convergence of networks

and applications. The Internet Protocol (IP) Multimedia

Subsystem (IMS) defined by the 3rd Generation

Partnership Project (3GPP*) [1] provides an access

network–independent architecture that supports wire-

line and wireless convergence. Furthermore, with the

advantages of high bandwidth, full IP, and connection-

oriented quality of service (QoS) support, Worldwide

Interoperability for Microwave Access (WiMAX) [7, 8,

12] allows new, personal, broadband, and real-time

multimedia applications and is considered an ideal

candidate for the access network in an IMS-based

networking architecture.

In order to give end users suitable and satisfying

services, an end-to-end session-based QoS guarantee is

necessary for applications such as gaming, video, and

Voice over IP (VoIP). It is composed of two parts: access

network QoS and IMS transport network QoS. Despite

variation among access networks, where QoS control

might differ as a result of network styles and standards,

there are many similarities to QoS management in the

IMS core network. Many technologies, such as code

division multiple access 2000 (CDMA2000), Universal

Mobile Telecommunications System (UMTS), wireless

local area network (WLAN), and digital subscriber line

(DSL), are suggested to support end-to-end QoS as

they interconnect with the IMS network [2, 9, 11].

However, to the best of our knowledge, there are few

studies of IMS over WiMAX. Furthermore, since the QoS

guarantee across an air interface is much more chal-

lenging because of poor channel conditions, the WiMAX

QoS should receive focus.

The next section addresses the IMS over WiMAX

QoS framework, and we follow with a proposed end-

to-end QoS provision mechanism. The final section

provides a summary.

IMS Over WiMAX FrameworkThis article proposes a cross-layer hybrid QoS

architecture to achieve end-to-end QoS in an IMS

over WiMAX network, which includes the following

processes:

1. Application layer QoS authentication at a policy

decision function (PDF)

2. Application layer and medium access control

(MAC) layer QoS mapping at user equipment (UE)

that can be either a subscriber station or mobile

subscriber station

116 Bell Labs Technical Journal DOI: 10.1002/bltj

3. MAC layer and IP layer QoS mapping at the

access service network (ASN)

4. Integrated services (IntServ) and differentiated

services (DiffServ) mapping at the packet data

gateway (PDG)

Figure 1 shows the QoS architecture in IMS over

a WiMAX network.

Mapping Application Layer QoS to a MAC Layer QoS Profile at UE

The UE is responsible for initiating QoS parame-

ter negotiation, resource reservation, and cancella-

tion. During the negotiation procedure, Session

Description Protocol (SDP) is used to negotiate with

participants for a set of QoS parameters such as the

media type, transmission rate, latency, and jitter. The UE

should be capable of mapping the negotiated session

level media attributes in SDP to the WiMAX MAC

layer QoS attributes and initiating the connection

setup for the bearer traffic. The resource reservation

follows after the negotiation process, which could be

triggered by a WiMAX MAC layer. Note that Resource

Reservation Protocol (RSVP) can be used to provide

per-flow-based QoS in WiMAX access networks.

However, because of the bandwidth limitation of the

secondary management connection in an air inter-

face, it is not efficient to introduce RSVP between UE

and access service network (ASN). This point relates

to our previous work, which proposed a fast mecha-

nism to provide IntServ by mapping IP QoS to

WiMAX MAC QoS [4]. The MAC layer QoS mecha-

nisms within the WiMAX access network specify

transmission ordering and scheduling on the air inter-

face. Five scheduling services are defined [8]:

1. Unsolicited grant service (UGS)

2. Real-time polling service (rtPS)

3. Extended real-time polling service (ertPS)

4. Non-real-time polling service (nrtPS)

5. Best effort (BE)

To achieve the required differentiation, the

WiMAX network must classify the traffic into service

Panel 1. Abbreviations, Acronyms, and Terms

3GPP—3rd Generation Partnership ProjectAAA—Authorization, authentication, and

accountingASN—Access service networkBE—Best effortBS—Base stationCAC—Connection admission controlCDMA—Code division multiple accessCOPS—Common open policy serviceCSCF—Call session control functionCSN—Connectivity service networkDCD—Downlink channel descriptor DHCP—Dynamic Host Configuration ProtocolDiffServ—Differentiated servicesDSA—Dynamic service additionDSL—Digital subscriber lineertPS—Extended real-time polling serviceIEEE—Institute of Electrical and Electronics

EngineersIMS—IP Multimedia SubsystemIntServ—Integrated servicesIP—Internet ProtocolMAC—Medium access controlnrtPS—Non real-time polling service

P-CSCF—Proxy CSCFPDF—Policy decision functionPDG—Packet data gatewayPEF—Policy enforcement functionPF—Policy functionQoS—Quality of serviceRNG_REQ/RSP—Ranging request/responseRSVP—Resource Reservation ProtocolrtPS—Real-time polling serviceS-CSCF—Serving CSCFSDP—Session Description ProtocolSFID—Service flow identifierSFM—Service flow managementSIP—Session Initiation ProtocolUCD—Uplink channel descriptor UE—User equipmentUGS—Unsolicited grant serviceUMTS—Universal Mobile Telecommunications

SystemVoIP—Voice over IPWiMAX—Worldwide Interoperability for

Microwave AccessWLAN—Wireless local area network

DOI: 10.1002/bltj Bell Labs Technical Journal 117

flows that specify the scheduling service and QoS

parameters for a particular connection. QoS-based

scheduling [5] as well as connection admission control

(CAC) algorithms are deployed in a service flow man-

agement (SFM) entity of an ASN.

Policy Function at the Access Service NetworkAn ASN can consist of multiple base stations

(BSs) and one ASN gateway to simplify protocol pro-

cessing and reduce latency. The policy function (PF),

located in the ASN gateway, is in charge of evaluating

service requests against the QoS policy rules and avail-

able radio resources. PF should have users’ QoS profiles

and associated policies in the local database. The provi-

sioned information from authorization, authentication,

and accounting (AAA) must allow the PF to derive the

service flow type and parameters. The ASN gateway

processes the QoS mapping from the MAC layer to the

IP layer and initiates RSVP signaling for resource reser-

vations between the caller and callee ASN.

IMS PEF and PDF at the Connectivity Service NetworkThe policy enforcement function (PEF) is a logical

function implemented in the packet data gateway

(PDG) [1], which acts as a security gateway between

the transport and access networks. DiffServ architec-

ture is deployed in the transport network, while per-

flow-based QoS in WiMAX access networks can be

regarded as an IntServ architecture. The mapping

between IntServ and DiffServ is carried out at the

3GPP†—3rd Generation Partnership ProjectAAA—Authorization, authentication, and accountingASN—Access service networkCDMA—Code division multiple accessCSN—Connectivity service networkDSx—Dynamic service addition, change, or deletionHSS—Home subscriber serverIMS—IP Multimedia SubsystemIP—Internet ProtocolNSP—Network service providerQoS—Quality of serviceP-CSCF—Proxy call session control functionPDF—Policy decision function

PDG—Packet data gatewayPEF—Policy enforcement functionPF—Policy functionPSTN—Public switched telephone networkS-CSCF—Serving call session control functionSDP—Session Description ProtocolSFA—Service flow authorizationSFM—Service flow managementUE—User equipmentWiMAX—Worldwide Interoperability for

Microwave AccessWLAN—Wireless local area network

† Trademark of the European Telecommunications Standards Institute.

UE ASN

SFM SFA

CSN

CSN

IMSclient

applicationsSDP

handler

IP traffic manager

Translation/mapping

Wimax trafficmanager

WiMAX service flowcontroller

WiMAX service flow

WiMAXQoS

param.per

applic.type

SDP

R1

DSxBearerservice

Admissioncontrol

Service flowscheduling PF

HSS

PEF

PDG

P-CSCF S-CSCFAAAclient

Go

Gq Cx

R5

Mw

AAAserver

Subscriberdata

to 3GPP†

to CDMA

to WLAN

to PSTN

to Internet

to otherASN

Home NSP

Visited NSP

Local resourceinfo.

R2

R6

R3

Data pathfunction

PDFRequest

Qosauthorization

Figure 1.Architecture of IMS over WiMAX.


PDG. The combination of resource-based and policy-

based admission control mechanisms in the PDG

makes it possible to support QoS control in both the

DiffServ and IntServ domains [10]. RSVP messages

transmit through the DiffServ networks transparently.

One of the PEF’s functions is to police uplink

and downlink IP flows on the bearer path according

to the maximum bandwidth and QoS class. It has a

service-based policy “gate” function that can be selec-

tively opened or closed. The gate function is controlled

by the PDF.

The PDF makes the decision whether or not to

authorize QoS requests by considering the SDP from

the proxy call session control function (P-CSCF), the

IMS subscription, and the policy database. Therefore,

after the PDF obtains the negotiated QoS parameters

by Session Initiation Protocol (SIP) and SDP, it maps

the application layer QoS to the IP layer QoS, which

is applied to evaluate the QoS authorization request

in the common open policy service (COPS) initiated

by the PEF.

Cross-Layer QoS Parameters Mapping TableBy analyzing the QoS requirements of the appli-

cations in different layers, we developed a QoS para-

meter mapping strategy. Table I shows a QoS mapping

that covers these four layers. In implementation,

predesigned look-up tables can be used by bearer

services.

End-to-End QoS Provisioning ProcedureThis section describes the proposed end-to-end

QoS provisioning procedure under IMS over a

WiMAX architecture. Figure 2 shows a best case

example for both call setup and release at the calling

(1) QoS mapping in (2) QoS mapping at UE (3) Map rule for IntServ services PDF from SDP from SDP traffic specification in path (4) DiffServ

Media type Max. MAC layer QoS Bandwidth Delay/jitter/loss(m-line in SDP) class services parameter requirements rate DSCP

Bidirectional A UGS 1, 2 Constant Min. packet EFaudio or video bandwidth delay, jitter and

loss rate

Single directional B rtPS 2, 3, 4, 5 Guaranteed Regular delay, AF4audio or video jitter require

Application (VoIP A ertPS 1, 2, 3, 5, 6 Guaranteed Regular delay, AF3with activity jitter requiredetection)

Data (Data E BE 2, 5 Not guaranteed Long delay, AF2transfer, web jitter requirebrowsing)

Control C nrtPS 2, 3, 5 Basic N/A AF1connection

Others F BE 5 Basic N/A BEconnection

Table I. QoS parameter mapping.

1. Maximum latency2. Maximum sustained traffic rate3. Minimum reserved traffic rate4. Maximum latency5. Traffic priority6. Jitter

AF—Assured forwardingBE—Best effortDiffServ—Differentiated servicesDSCP—Differentiated services code pointEF—Expedited forwarding

ertPS—Extended real-time polling serviceIP—Internet ProtocolMAC—Medium access controlnrtPS—Non-real-time polling servicePDF—Policy decision functionQoS—Quality of servicertPS—Real-time polling serviceSDP—Session Description ProtocolUE—User equipmentUGS—Unsolicited grant serviceVoIP—Voice over IP

AAA—Authorization, authentication, and accountingASN—Access service networkBS—Base stationCOPS—Common open policy serviceCSCF—Call session control functionDCD—channel descriptorDHCP—Dynamic Host Configuration Protocol

P–CSCF—Proxy CSCFPDF—Policy decision functionPEP—Policy enforcement pointPRACK—Provision response acknowledgmentQoS—Quality of serviceREG—RegistrationRNG—RangingS-CSCF—Serving CSCF

Access accepted, provide user profile

BS request EAP authentication from AAA

UE ASN AAA PEP PDF Signaling GWP-CSCF S-CSCF

Access accepted

SIP register

SIP INVITE (SDP1) INVITE (SDP1)

183 Ses.Prog.

(SDP2)

Call setup

Answered

Registration granted

SIP INVITE

Bearer resource reservation

QoS authorization resp provided userprofile, including resource available

SIP register

Registration granted

QoS authorization query

RingingRinging

Map/DCD/UCD

RNG

REG.req

DHCP

Dynamic serviceaddition

IP connection

200 OK (Answered)200 OK (Answered)

ACKACK

(Call is established)

BYE BYE

200 OK200 OK

Release bearer resource

Call release

Bearer traffic

Mapping parameters fromSDP to authorized IP QoS1

2

DSA.req

DSA.rsp

PATH COPS

Synchronization

Ranging:Capabilityauthentication andregistration

REG.rsp

2 Mapping parametersfrom SDP to DSA QoS

DSD.req

UE registration

183

COPSRESV

Dynamic servicedelete

DSD.rsp

PATHCOPS

COPSRESVRemove QoS mapping

183 Ses.Prog. (SDP2)

Bearer resource confirmation

PRACK (SDP2)

Management Message in WiMAXnetwork

PRACK (SDP2)

200 OK

PRACK

200 OK200 OK

3

Diameter1

(SDP2)

3 Mapping parametersfrom DSA to IntServ (PATH)

To callee4

4 Mapping parametersto DiffServ (DSCP)

Net

wo

rk e

ntr

y an

din

itia

lizat

ion

Init

iate

app

.C

all p

roce

ssin

g

DiffServ—Differentiated servicesDSA—Dynamic service additionDSCP—Differentiated services code pointDSD—Dynamic service deleteEAP—Extensible Authentication ProtocolGW—GatewayIMS—IP Multimedia Subsystem IP—Internet Protocol

SDP—Session Description ProtocolSIP—Session Initiation ProtocolUCD—Uplink channel descriptorUE—User equipmentWiMAX—Worldwide Interoperability for Microwave Access

Figure 2.End-to-end QoS provisioning procedure at the calling network under IMS over WiMAX.



network. In the situation in which the WiMAX net-

work acts as a called network, the mechanism is sim-

ilar, but the ASN provides the mapping function

between IP QoS and MAC QoS and triggers the

dynamic service addition (DSA) request to the UE

called thereafter.

• Network entry and initialization. First, the UE syn-

chronizes to the base station downlink and obtains

downlink and uplink parameters with a DCD/UCD

message. Contention- or noncontention-based

RNG_REQ/RSP messages are exchanged to obtain

the correct timing offset and power adjustments.

Dynamic Host Configuration Protocol (DHCP) is

used to establish IP connectivity.

• UE registration. Next, applications in the UE regis-

ter to the IMS network via an SIP registration pro-

cedure [3].

• Negotiating QoS parameters via SIP/SDP. The UE ini-

tiates services with the QoS-related application-

level parameters in the SIP INVITE with SDP1

specifying the bandwidth requirement and sup-

ported codecs A and B. The P-CSCF verifies that

the UE is registered and checks the local policy

before forwarding the INVITE to the serving-CSCF

(S-CSCF). The S-CSCF verifies that the requested

service has a valid subscription by checking the

QoS parameters in the SDP [6]. Then the session

is routed to the called network elements.

Assuming the called network agrees with the UE’s

QoS proposal using codec B (SDP2 is generated), the

P-CSCF queries the PDF to get a token and forwards

it in a SIP message to the UE across the ASN. The PDF

authorizes the IP flows of the chosen media compo-

nents by mapping from SDP parameters to author-

ized IP QoS. After receiving SDP2, the UE sends an

acknowledgment. The called replies with “200 OK.”

Both caller and called agree with SDP2 as the set of

authorized QoS parameters. Thus a session is estab-

lished and the procedure that follows is initiated:

• Mapping SDP to WiMAX QoS at the UE. The UE

maps SIP SDP to WiMAX radio QoS classes or

profiles. Then the DSA request message with QoS

parameters is issued from the UE to the ASN for

bearer resources based on negotiated QoS in SDP.

• ASN resource control. In the ASN, the DSA request

is evaluated by CAC and PF. After mapping the

MAC QoS to IntServ QoS, this request is for-

warded to the callee party by RSVP messages.

• PDF authorization. The PDF makes a decision

whether or not to authorize the QoS request from

the PEF. Then it forwards authorized QoS and

flow information to the PEF via COPS. After that,

the PEF creates a gate for media flow and

responds to the ASN with the authorized QoS.

• Bearer traffic transmission. After receiving a DSA

response with acceptable QoS, the UE will trans-

mit bearer traffic once the “Ring 200 OK” mes-

sage is received. The UE classifies the data into a

service flow then applies the appropriate sched-

uling services. When the radio bandwidth request

is granted to the UE, it transmits the data to the

ASN. The ASN maps the service flow identifier

(SFID) to a generic tunnel to maintain the QoS

differentiation from the ASN and PDG. In the

PDG, per-IntServ flows are aggregated to a

DiffServ flow and traverse the DiffServ network.

The preceding procedure is a control-driven

resource reservation mechanism, in which both the

air interface WiMAX resource and the IMS core net-

work resource are reserved before traffic is transmit-

ted. This mechanism is especially suitable for UGS,

rtPS, and ertPS services. A data-driven QoS resource

reservation mechanism is preferred for nrtPS and BE

services, in which resource reservation begins only

after the bearer traffic is generated.

Handover has not been addressed in the preced-

ing details. Seamless mobility without interruption of

sessions and associated service flows is a major tech-

nical accomplishment in WiMAX. The mobility char-

acter of WiMAX terminals and handling end-to-end

QoS in the case of handover are to be studied further.

ConclusionThis article addresses QoS provisioning issues in

IMS over a WiMAX network. We propose a cross-

layer QoS solution and present key techniques

including QoS parameter mapping and end-to-end

QoS-supported session call flowcharting.

*Trademarks3GPP is a trademark of the European telecommunica-

tions Standards Institute.

CDMA2000 is a registered trademark of the Telecom-munications Industry Association (TIA-USA).


References[1] 3rd Generation Partnership Project, “IP

Multimedia Subsystem (IMS), Stage 2 (Release 6),” 3GPP TS 23.228, v6.10.0, June2005, <http://www.3gpp.org/ftp/Specs/html-info/23228.htm>.

[2] 3rd Generation Partnership Project, “End-to-End Quality of Service (QoS) Signaling Flows(Release 6),” 3GPP TS 29.208, v6.5.0, Sept.2005, <http://www.3gpp.org/ftp/Specs/html-info/29208.htm>.

[3] G. Camarillo and W. Marshall (eds.), and J. Rosenberg, “Integration of ResourceManagement and Session Initiation Protocol(SIP),” IETF RFC 3312, Oct. 2002, <http://www.ietf.org/rfc/rfc3312.txt?number=3312>.

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[6] M. Handley and V. Jacobson, “SDP: SessionDescription Protocol,” IETF RFC 2327, Apr.1998, <http://www.ietf.org/rfc/rfc2327.txt?number=2327>.

[7] Institute of Electrical and Electronics Engineers,“Part 16: Air Interface for Fixed BroadbandWireless Access Systems,” IEEE 802.16, June2004, <http://www.ieee.org/web/standards/home/index.html>.

[8] Institute of Electrical and Electronics Engineers,“Part 16: Air Interface for Fixed and MobileBroadband Wireless Access Systems,Amendment 2,” IEEE 802.16e, Dec. 2005,<http://www.ieee.org/web/standards/home/index.html>.

[9] M. A. Siddiqui, K. Guo, S. Rangarajan, andS. Paul, “End-to-End QoS Support for SIPSessions in CDMA2000 Networks,” Bell LabsTech. J., 9:3 (2004), 135–153.

[10] D. Sun, J.-P. Joseph, F. R. Magee, Jr.,A. Mukhopadhyay, and B. Tang, “A SIP-Enabled All-IP Architecture for ConvergedNext-Generation Networks,” Bell Labs Tech. J.,9:3 (2004), 15–37.

[11] S. van der Gaast, A. Hajjaoui, and E. Meeuwissen, “Quality of Service for SIPSessions in 3GPP-Based Networks,” Bell LabsTech. J., 9:3 (2004), 127–134.

[12] WiMAX Forum, “WiMAX End-to-End NetworkSystems Architecture (Stage 2),” Network WG,Mar. 1, 2006, <http://www.wimaxforum.org/technology/documents>.

(Manuscript approved November 2006)

WENHUA JIAO is a member of technical staff in BellLabs Research China in Beijing. He holds aPh.D. degree in communications andinformation systems from the Departmentof Electronics, Peking University, in Beijing.His Ph.D. dissertation was devoted to

medium access control (MAC) protocol of packetCDMA networks. Dr. Jiao’s research interests includeprotocol design in wireless and optical networks. Hehas published more than 20 papers in this area.

JIANFENG CHEN is a member of technical staff in BellLabs Research China in Beijing. He receivedhis M.S. degree in computer science andtechnology from Tsinghua University inBeijing. His research interests includescheduling mechanisms for broadband

wireless networks, SIP-based applications, and keytechnologies for IP Multimedia Subsystem (IMS) clientdevelopment. He has recently published seven papersabout WiMAX networks for IEEE conferences.

FANG LIU is a technical manager in Bell Labs ResearchChina in Beijing. Her research interestsinclude all-optical network managementprotocols and software systems, wirelessapplications, IP Multimedia Subsystem(IMS), WiMAX, advanced Internet

technologies, and network protocol validation andtesting. She received a Ph.D degree in communicationand information systems from Shanghai JiaotongUniversity in Shanghai, China. Dr. Liu served as atechnical program committee member of IEEE Infocom2002 and 2003. �

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Provisioning end-to-end QoS under IMS over a WiMAX architecture