Part 9: Mobile Data / Mobility Management I. Mobile Data Services/ Management This broad area involves a lot of industrial applications. Mobile data services/ management is becoming another profitable market for wireless device manufacturers and service providers. In academia, research is mainly focus on context-aware, locationaware applications, service discovery, mobile data consistency, data replica, etc. [Several examples and demos]. II. Mobility Management [1] Mobility Management usually includes two parts: location management and handoff management. 1) Location Management Location Management Location management is a two-stage process that enables the network to discover the current attachment point of the mobile user for call delivery. The first stage is location registration (or location update). In this stage, the mobile terminal periodically notifies the network of its new access point, allowing the network to authenticate the user and revise the user's location profile. The second stage is call delivery. Here the network is queried for the user location profile and the current position of the mobile host is found. Current techniques for location management involve database architecture design and the transmission of signaling messages between various components of a signaling network. As the number of mobile subscribers increases, new or improved schemes are needed to effectively support a continuously increasing subscriber population. Other issues include: security, dynamic database updates, querying delays, terminal paging methods, and paging delays. The following figure associates these research issues with their respective location management operation.
(a) Location Management for PCS Current schemes for PCS location management are based on a two level data hierarchy such that two types of network location database, the home location register (HLR) and the visitor location register (VLR), are involved in tracking an MT. In general, there is an HLR for each network and a user is permanently associated with an HLR in his/her subscribed network. Information about each user, such as the types of services subscribed, billing information, and location information, are stored in a user profile located at the HLR. The number of VLRs and their placements vary among networks. Each VLR stores the information of the MTs (downloaded from the HLR) visiting its associated area. Network management functions, such as call processing and location registration, are achieved by the exchange of signaling messages through a signaling network. Signal System 7 (SS7) is the protocol used for signaling exchange and the signaling network is referred to as the SS7 network. The type of Cell Site Switch currently implemented for the PCS is known as a Mobile Switching Center (MSC).
(b) Location Management for Mobile IP, Wireless ATM, Satellite Networks We will not talk about these issues. Please refer to current Mobile IP Internet draft and paper [1]. (c) Location Management for Ad Hoc Networks/ Sensor Networks There are a lot of open questions in this field. Currently, there is no standard for location management in these types of wireless networks. The lack of centralized control point makes location management for ad hoc networks a very challenging task. For wireless sensor networks, the constraint of energy consumption is the main bottleneck for providing such service. 2) Handoff Management Handoff management enables the network to maintain a user's connection as the mobile host continues to move and change its access point to the network. The three-stage process for handoff first involves initiation, where either the user, a network agent, or changing network conditions identify the need for handoff. The second stage is new connection generation, where the network must find new resources for the handoff connection and perform any additional routing operations. Under Network-Controlled Handoff (NCHO), or Mobile-Assisted Handoff (MAHO), the network generates a new connection, finding new resources for the handoff and performing any additional routing operations. For Mobile-Controlled Handoff (MCHO), the MT finds the new resources
and the network approves. The final stage is data flow control, where the delivery of the data from the old connection path to the new connection path is maintained according to agreed-upon service guarantees. The handoff management operations are presented in the following figure. In handoff management, on-going calls are modified under two conditions: signal strength deterioration and user mobility. Deterioration of the radio channel results in intra-cell handoff, where the calls are transferred to new radio channels of appropriate strength within the same cell, or inter-cell handoff, where all of the MT's connections are transferred to an adjacent cell. User mobility always results in inter-cell handoff. In each case, the MT's connections may be passed to the new BS without interrupting communications with the old BS. This is called soft handoff. On the other hand, if the connections are interrupted at the old base station and then established at the new BS, the process is called hard handoff. Handoff management research concerns issues such as: efficient and expedient packet processing, minimizing the signaling load on the network, optimizing the route for each connection, efficient bandwidth re-assignment, evaluating existing methods for standardization, and re-assigning quality of service for wireless connections. Reference: [1] I. Akyildiz, J. McNair, J. Ho, H. Uzunalioglu, and W. Wang, "Mobility management in next-generation wireless systems," Proceedings of the IEEE, Vol. 87, No. 8, August 1999, pp. 1347-1384