Due to popular for high data rates and relatively low cost wireless LANs's (WLANs) based on the IEE 802.11 family. Most of the networks WLANs used as access points(APs) it help as hotspot connectivity in the public places like railway stations airports,hotels,malles ,university campus and homes. By using access points (APs) as software defined radio (WLANs) it will supports multi interface, environment-aware, multimode, and multi band communication devices common place. this environment enables user can to access a exacting network depending on application needs and type of radio access networks (RANs) offered. Cellular networks, WLANs, wireless personal area networks(WPANs) are good example for this environment .if user wants downloading a large video file by cellular interface multi mode phone ,as higher data rate and lower cost connection during the home IEEE 802.11b AP becomes accessible ,the connection could be automatically switched from the cellular network to the home AP. It is not impractical to anticipate automatic connection and faultless network passage for a single call.
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// To providing effective and efficient data services is to integrate WLANs(IEEE 802.11a/b/g and Hiper LAN/2),wireless WANs (1G,2G,2.5G,3G , the proposed IEEE 802.20), WPANs (Bluetooth,802.15.1/3/4),and wireless MANs (IEEE 802.16) by observing a common chracteisrtic of one -hop (single hop or infrastructure) operation mode,//
In multi hop mode we are using mobile ad hoc network (MANET),in MANET consists of wireless devices act as a routers, router connectivity commonly changed in MANETs due to it allows communication without the use of AP/BS. Substitute connection provide inside hotspot cells.
In MANET devices often communicate through the WLAN/WPAN interfaces, the multi hop operation mode has several linked issues that are not considered in single hop operation mode.
An summary of projected architecture is given in figure (1), the basic interworking characteristics considered are network selection, authentication, authorization, and accounting (AAA), and the APs and the 3G network .Even though some fundamental components have been identified, some questions are still under conversation in 3GPP at the time of writing, for the most part concerning the interfaces connecting APs and 3G network components. The 3GPP2 group is also working on 3G/WLAN interworking, but it mostly addresses WLAN/cdma2000 interoperation (2).one important aspect regarding the consistency work in development at 3GPP and 3GPP2 is the fact that they only regard as the integration of WLAN APs with cellular networks, they do not consider WLANs operating in MANET mode as part of the architecture, and as a result do not address issues related to multi hop routing.
It is required to investigate a global heterogeneous architecture and services that mutually provide seamless integration of single hop networks and multi hop wireless systems (MANETs) while all these technologies are integrated with the internet, the possibilities are countless .this is not minor, however. In this heterogeneous environment, users would have profiles such as price, data rate, battery life, service grade, and mobility pattern. A RAN has to be particular for provided that wireless connections, and this should be finished based on the user profile and network state (eg: available bandwidth, congestion status).if a node is not directly within the coverage area of a RAN, we have to emphasize the chance of reaching a RAN during multi hop communication. Here, the node has to shape out what other nodes in its network can serve as gate ways and provide access to RANs.
WLANs,Wireless WANs, are transparent and self configurable in heterogeneous networks, as shown in the above figure (Access Point)AS s/(Base Station)BS s,(Mobile User Station)MS s,(core)IP and (Network)CN are the key components.BS s and AS s communication bridge for MS s. In heterogeneous architecture two type of modes,1 single hop mode(WLANs,Wireless WANs) 2 multi hop mode(MANET).
Two modes addresses separately in an integrated architecture due to different characteristics and particular issues. In hotspot areas multiple APs overlap to some extent, also a BS and AP may be collocated.MSs can be randomly move, at a given instant a particular MSs can either be within (or)outside the coverage of BS/AP.depends on coverage area mode must be change, if MS in within coverage it can be single hop,multi hop mode out of coverage area corresponding BS/AP.
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Factors influencing in heterogeneous network are1.multi interface MSs, 2 transmission router, 3 topology, 4.routing, 5 mobility, 6 hand off, 7 co channel interference, 8 load balance, 9 interoperability, 10 quality of service(QOS).
Mobile User Station (MSs):
Commonly mobile user station three types 1 single mode cellular, 2 single mode WLAN, 3 dual mode. 1. Single mode cellular: connection between MS and cellular network through BS. 2 single mode WLAN: APs are main communication channels. Building MANET, communication with other WLAN equipped terminals in ad -hoc mode.3 dual mode: it operate both modes, infrastructure mode(connect directly BS or AP).it supports user requirement with better connectivity.
Base station and Access point:
In cellular networks integration, single-hop, and multi-hop is not uncomplicated due to variÂous communication circumstances, different interface capabilities, and mobility patterns of MSs. Fixed network components, such as BSs and APs, can provide several services to MSs, including:
1 Access to internet
2 Resource control 3.Routing discovery 4 Security management 5 Interoperability of existing networks and future networks 6 Support of handoff between different wireless access networks
Both BSs and APs should have the ability of interoperability with each other, and also the opportunity of combination with new promising net-works for underneath handoffs between them. and BSs also have the conscientiousness to run and control radio resources for the MSs. In fact, frequency distribution becomes more compliÂcated while different wireless technologies may probably manage in the same frequency band, which makes coexistence mechanisms increasingÂly important. The high dispensation and power capacity of APs and BSs make them tactical components in selecting optimum routes between two MSs. Furthermore, the APs and BSs can implement load balance functionalities by switching connections from infrastructure mode to MANET mode.
Core IP network:
It is backbone for network. It provide services like seamless mobility, multi-hop cooperation, and security, Internet connectivity and packet data services.CN supports both mobile IP and cellular IP. To avoid attacks by supporting authentication for all types of MSs.
"There are three unique features significantly affecting the design of integrated solutions, namely, the availability of multiple interfaces for an MS, the integration of cellular networks and WLANs, and multi-hop communication."
key issues consist of transmission power choice for a specified communication interface, co-channel interÂference, topology discovery, route creation, mobility and handoff management, and load balÂancing, but all these design factors will depends on the MS's capabilities, connectivity preferences offered at the current location, the user's mobility profile, the QoS estimated, and the service cost. for example, the choice of which interface to utilize should be routinely made by the system, the choice of the end-to-end route for a exacting connecÂtion may be based on the user's service level agreement (SLA). further the aim of fulfilling the user necessities, the choice of a given technology or the conclusion to perform a vertical handoff can also be used to improve the overall system performance or to apply the funcÂtionality of load balance.
The Protocol Stack:
During a heterogeneous environment as shown in Fig. 1, dissimilar mobile devices can
Perform unusual protocols for a specified layer. The protocol stack of a dual-mode MS is particular in Fig. 3. This protocol stack consists of multiple physical, data link, and medium access control (MAC) layers, and network, transport, and appliÂcation layers. so, it is important to choose the most suitable combination of lower layers (link, MAC, and physical) that can offer the finest service to the upper layers. moreover, some manage planes such as mobility manageÂment and connection management can be additional. These control planes be capable of ultimately utilize informaÂtion from several layers to execute their funcÂtionalities. In Fig. 3, the network layer have a essential role in this progression, while it is the interface linking existing communications interfaces (or access technologies) to control in a point-to-point approach, and the end-to-end (transport and application) layers. In other words, the charge of the network layer is to provide a consistent substrate above which transport (e.g., TCP and UDP) and application protocols be able to capably run, self-governing of the access techÂnologies used in each of the point-to-point links in an end-to-end connection. While there are issues in all layers, the network layer has received more consideration than any other layer, and slight combination related work has been complete at the lower layers. Definitely, integrated architectures are estimated not to require modifications at the lower layers so that different wireless technoloÂgies can operate autonomously. However, this integration task is particularly complex, and it requires the maintain of integration architecture in conditions of mobility and connection management.
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The Physical Layer:
Physical layer is able to access multiple networks simultaneously, because MSs equipped with multiple network interface. MSs are not fully able to access multiple wireless network in SDR based, even it performs only discover access networks available for connected network. If MS is acted as switch between cellular network and access point(AP), its in coverage area(with in AP range).
During a heterogeneous environment, different wireless technologies could be operating in the same frequency band, and it is important that they coexist without humiliating the presentation of each other. Therefore, interference improvement techniques are vital. For MSs far away from their APs, for example, multi-hop communiÂcation links might effect in less interference than direct transmission to the AP, while multi-hop links amid MSs nearer to the AP may considÂerably reduce its capability due to interference. Power control techniques have been functional to bound interference in code-division multiple access (CDMA)-based cellular networks and MANETs.
The Data Link Layer:
This layer can be separated into logical link control (link) and MAC layers. The MSs will be capable to utilize a centralized MAC, such as time-division multiple access (TDMA) or CDMA, while connecting to a cellular network, such as transporter sense multiple access with collision avoidÂance (CSMA/CA), in an IEEE 802.11 WLAN. These access methods can grant different serÂvice levels in terms of capacity and delay. The data rate in the cellular interface can reach up to 2.4 Mb/s though an 802.11b interface can provide up to 11 Mb/s. The possible through-put and delay in CSMA/CA. extremely depends on the traffic load. Tribulations such as secret and showing terminals are recognized to frontier the capaciÂty of IEEE 802.11. Additionally, when two MSs are communicating during various intermediÂary hops in MANET mode, performance can be yet inferior due to MAC layer arbitrary access difficulties in every intermediary hop. It is recognized that the CSMA/CA scheme used in the IEEE 802.11 usual has staid performance limitaÂtions as used in a multi-hop environment. Mechanisms such as power control and power-aware MAC protocols can be used to develop performance.
During a heterogeneous network, an end-to-end connection be able to engage a series of some difÂferent links & MAC-layer connections, and the final end-to-end performance will be restricted by the "weakest" link in this chain of connections; cross-layer propose may participate an significant role in provided that useful information to upper layers. Security is also an significant issue to be considÂered at the link/MAC level. Even though end-to-Âend security is measured in the application layer, some wireless access technologies endow with a sure level of security at the lower layers.