A Survey of Analytical Modeling for Cellular/WLAN Interworking in .NET Integrated QR Code in .NET A Survey of Analytical Modeling for Cellular/WLAN Interworking

444 A Survey of Analytical Modeling for Cellular/WLAN Interworking using none toproduce none in web,windows application Microsoft Excel On the other ha none for none nd, there is a drawback of the loose coupling architecture. The signaling between the two separate networks may take a longer time as it needs to traverse a relatively long pathway. As a result, the corresponding handoff latency and the packet loss rate may be high.

Thus, the loose coupling architecture may not be able to provide seamless vertical handoff between WLANs and cellular networks. 19.2.

2 Tight Coupling Architecture The tight coupling architecture positions the WLAN in series with the cellular core network which is directly connected to the Internet [1], [2]. This logic aims to let all data originated from the WLAN to pass through the cellular core network before reaching the Internet. The tight coupling of the WLAN and cellular network is carried out at the reference point between the radio access network (RAN) and the SGSN/PCF [1] (for GPRS/CDMA2000 respectively) or the GGSN/PDSN [2] (for GPRS/CDMA2000 respectively), making WLAN appear as other cellular RAN in the cellular core network.

By incorporating certain interworking functions at the WLAN gateway, the cellular core network will not differentiate a routing area from WLAN radio technology or a routing area from GPRS or CDMA2000 radio technology. The tight coupling architecture is shown in Fig. 19.

2. The benefits that can be gained from the use of tight coupling architecture are as follows: First, a large number of elements in the cellular network can be reached and reused by the WLAN. For example, the WLAN and the cellular core network can share the same user database, a single charging system, and the same AAA server.

Moreover, many protocols from the cellular network can be used by the WLAN as well. Since the cellular network and WLAN are firmly coupled, seamless vertical handoff across two networks can be supported. Other important features such as enhanced security and guaranteed Qualityof-Service (QoS) are also available by the tight coupling scheme.

However, this approach also presents several disadvantages which may hamper its deployment. First, in order to support the vertical handoff between different RANs, the mobile terminals have to load the corresponding protocol stacks on top of their WLAN networking interfaces. Additionally, the WLAN gateway which interworks with the cellular core network needs to implement all the protocols (e.

g., mobility management, session management, authentication, etc.) required in the cellular network.

Currently, most WLAN terminals do not support the vertical handoff to cellular networks because they do not have the corresponding protocols on top of their WLAN networking cards. As a result, these WLAN terminals are not feasible for tight coupling scheme. Another drawback of this architecture is the cellular core network may become a network bottleneck, due to the high rate WLAN data traffic having to go through the cellular core network.

Moreover, as the cellular core network directly interfaces with the WLAN, both networks must be owned by the same operator, resulting in a situation in which there is no support from third-party WLAN operators. Thus, in order to deploy the tight coupling architecture, the complexity and the high cost associated with the reconfiguration of the WLAN terminals, gateways and some key elements in the core cellular network will make it difficult to compete with WLAN-only service providers or the networks that are configured with loose coupling architecture..

A Survey of Analytical Modeling for Cellular/WLAN Interworking 445 Tightly Coupled Network Cellular Core Network PDSN or GGSN Internet PCF or SGSN WLAN Gateway PDSN - Packet D ata Serving Node PCF - Packet Control Function GGSN - Gateway GPRS Support Node SGSN Serving GPRS support Node. RNC - Radio Net none for none work Controller BS Base Station AP Access Point WLAN Wireless local area network. UE User Equipment Figure 19.2: Tight Coupling Architecture. 19.2.3 Hybrid C oupling Architecture The hybrid coupling architecture, by its name, uses both the loose and tight coupling architectures to better integrate the WLAN and the cellular network [7].

The motivation behind this mechanism is that although the loose coupling architecture is preferable compared to the tight coupling scheme, it still cannot support seamless service continuity during the vertical handoff between different RANs, thus resulting in long handoff latency and a high packet loss rate. On the other hand, the tight coupling architecture is able to provide users with guaranteed QoS and seamless mobility, but the cellular core network may become the bottleneck of the system since its capacity may not be enough for accommodating the high data rate traffic from the WLAN. As a result, the new hybrid coupling scheme emerges to handle this problem by differentiating the data paths from the WLAN to the Internet according to the type of data traffic, thus achieving guaranteed QoS and seamless mobility of the services [7].

The hybrid coupling architecture is shown in Fig. 19.3.

The main difference between the loose and tight coupling architectures is the path that the data traffic traverses before reaching the Internet. The hybrid coupling scheme differentiates the data traffic in terms of whether it is real-time or non real-time. The realtime traffic (e.

g., voice over IP) typically demands lower bandwidth and seamless mobility support, so it is routed to the Internet using the tight coupling architecture. On the other hand, non real-time traffic (e.

g., a large file on a FTP server) usually requires higher data rate but is able to bear reasonable delay. Therefore the traffic is routed in the network constructed by loose coupling architecture.

It has been numerically shown in [7] that the hybrid coupling scheme is able to take advantage of both architectures. It achieves a lower packet loss probability than that of the tight coupling scheme and a lower handoff signaling cost than that of the loosely coupled scheme..

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