Mapping Qos Classes in Loose Coupling Heterogeneous Networks

One of the main objectives of Heterogeneous Wireless Access Networks (HWAN) is to integrate the different wireless access technologies, such as Universal Mobile Telecommunication System (UMTS), Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN), with a common IP-based network in order to offer mobile users continuous and unified service in a transparent way. However, one of the major issues is to support end-to-end Quality of Service (QoS) across all these technologies at all stages of the service from setup to handoff. We present, in this study, a novel method of mapping QoS of UMTS and WiMAX over a loose coupling environment across Internet Protocol/Differentiated Service (IP/DiffServ) network.


INTRODUCTION
Existing wireless networks (e.g., 2G/3G, LTE, WiFi, WiMAX, cdma, cdma2000, etc.), have been independently designed and deployed without cooperating with each other.In order to provide, at anytime and anywhere, the end-users with the best service at the lowest cost, incorporating between these networks, through Heterogeneous Wireless Access Network (HWAN) also known as Next Generation Wireless Network (NGWN) and referred to as the 4 th Generation network (4G), becomes a must; however it will introduce new challenges; such as Security Billing, Handoff, Mobility management, End-to-End QoS (Sarraf and Ousta, 2008), due to the different radio access characteristics with varying bit rate, available and allocated bandwidth, fault tolerant levels and handoff methods and protocols.
This paper addresses the issues of supporting QoS in loose coupling approach of 4G wireless networks from End-to-End point of view and presents novel mapping mechanisms between UMTS CoSs, IP/DiffServ and WiMAX QoS categories in loose coupling approach; however it does not address the other issues and challenges-neither mapping the QoS between the other wireless access networks nor in tight coupling.
4G networks: Since the 4G wireless networks are composed of multiple heterogeneous radio access networks as illustrated in Fig. 1, mobile users should seamlessly be connected and handed-off between those multimode radio access capabilities (Stratogiannis et al., 2010).However, even if the terminals can adapt to the different radio interfaces, maintaining the service continuity and the offered QoS through diverse environments is a complex issue that current methods do not support.
In order to achieve this interconnection between the various wireless access networks, two main approaches have been considered: Integrated and Interworking networks approaches.
In integrated networks-Tight Coupling-method, the air interfaces from different radio access technology are coupled at Radio Access Network (RAN) or Core Network level (CN) (Wu et al., 2001).Whereas, interworking networks-Loose Coupling-method is constructed by introducing edge gateways and linking between the latters to connect different wireless systems and exchanging information as well as signaling through those gateways (Song et al., 2005;Masip-Bruin et al., 2007;ETSI-TR.101-957, 2001).
In loosely coupled architecture, the different wireless access networks are independent of each other providing a flexible framework.However the main disadvantage is the mobility management where the signaling messages may traverse long path causing relatively high latency for handoff and QoS.

QUALITY OF SERVICES OVER DIFFERENT SYSTEMS
UMTS: Four classes of services namely, Conversational, Streaming, Interactive and Background, have been defined in UMTS with different QOS parameters and attributes used for prioritization, scheduling and queuing.Some of the most important attributes are Maximum Bit Rate (MBR), Guaranteed Bit Rate (GBR), Traffic Handling Priority (THP) and Allocation/Retention Priority (ARP) that may be used, within the same class, for further differentiation, as detailed in Table 1.
WiMAX: Similarly five QoS categories, named service flows, have been defined in WiMAX; a service flow refers to unidirectional flow of packets that is associated with a particular QoS.These five services flows as defined in (IEEE Std 802.16e, 2009) are listed in Table 2.
It is worth noting that in WiMAX network, the Medium Access Control layer (MAC) is responsible for handling QoS according to a parameter set defined for each service flow.Per-Hop-Behavior (PHB) in turn defines the scheduling treatment of the packet and the drop probability for the packet.Three types of PHBs are identified, Default PHB, 2-Expedited Forwarding (EF) PHB and 3-Assured Forwarding PHB (AF1x, AF2x, AF3x, AF4x), supporting different types of traffics and applications (Nicolas et al., 1998;Davie et al., 2002;Exist et al., 1999).

MAPPING STRATEGIES
Achieving an End-to-End QoS between 3G/UMTS and WiMAX in a loose architecture heterogeneous wireless network would consist of first, mapping the QoS of one wireless network into IP/DiffServ and second, mapping the QoS between IP/DiffServ and the other wireless network.
WiMAX-IP/DiffServ-mapping: UGS class of WiMAX supports services with minimum delay and jitter requirements with higher priority than other types of traffics; it is possible to map this class to the EF class of a DiffServ network.On the other hand, the rtPS class of WiMAX supports real time applications with less tolerant and can have traffic priorities, so the mapping process between this class and AF3 class of DiffServ network is recommended (ITU-T-R, 2011).
In the case of nrtPS class, which supports non real time applications with higher delay tolerance, the better class that is matched to nrtPS in DiffServ domain is AF2 or AF1.As extended rtPS class is a combination of UGS and rtPS class, the ertPS traffic is mapped to higher AF class like AF4 and the best-effort class is mapped to the default DiffServ class or lower AF class with high drop precedence, as described in Table 3.In order to provide an End-to-End QoS, a novel mapping mechanism between the CoS of UMTS to WiMAX QoS categories, across IP/DiffServ backbone, has been proposed.The proposed mechanism recommends a mapping of the CoSs of UMTS associated with their attributes to WiMAX QoS categories with their corresponding attributes.

Fig. 1 :
Fig. 1: Heterogeneous wireless access network IP/DiffServ system: The Internet Protocol is a connectionless best effort protocol; therefore it does not support QoS.Consequently, a Differentiated Service technique is used to support QoS over backbone network.DiffServ Code Point (DSCP) and Per-Hope Behaviors (PHB) are the main components which are used to classify different classes of service in DiffServ domain.The DiffServ (DS) Domain consists of a contiguous set of nodes that guarantee Service Level Agreement (SLA) requirements.On ingress to DiffServ domain, the traffics are classified using implicit classification methods into a limited number of traffic classes.The classification process depends on the content of the packet header by a Differentiated Service Code Point (DSCP).

Table 5 :
Mapping QoS classes between UMTS and WiMAX systems over IP/DiffServ backbone network