Location-aware multimedia proxy handoff over the IPv6 mobile network environment

Abstract

In a server-proxy-client 3-tier networking architecture that is executed in the mobile network, proxies should be dynamically assigned to serve mobile hosts according to geographical dependency and the network situation. The goal of proxy handoff is to allow a mobile host still can receive packets from the corresponding server while its serving proxy is switched from the current one to another one. Once proxy handoff occurs, a proper proxy should be selected based on the load balance concern and the network situation concern. In this paper, a 3-tier Multimedia Mobile Transmission Platform, called MMTP, is proposed to solve the proxy handoff problem in the IPv6-based mobile network. A proxy handoff scheme based on the application-layer anycasting technique is proposed in MMTP. A proper proxy is selected from a number of candidate proxies by using the application-layer anycast. An experimental environment based on MMTP is also built to analyze the performance metrics of MMTP, including load balance among proxies and handoff latency.

Introduction

The key issue of mobile communication is mobility management. The handoff process of terminal mobility can determine latency and packet loss rate. For an IP-based mobile network, two types of handoff that are widely discussed are (1) access point (AP) handoff and (2) IP handoff. AP handoff, that occurs in the MAC layer, means that a mobile host (MH) moves from the radio coverage of one AP to another one. IP handoff, that occurs in the network layer, denotes that an MH moves from one subnet to another one. After performing either AP handoff or IP handoff, an MH is still able to access the Internet. Many handoff approaches (Koodli and Mar, 2002, Markus and Vera, 2002, Perkins, 2000, Sangheon and Yanghee, 2002, Tekinay and Jabbari, 1991) have been proposed to solve these problems.

According to past researches, the server-proxy-client 3-tier network architecture is widely adopted to decrease transmission latency and packet loss rate in the Internet. For example, WWW and video transmission are suitable to use the 3-tier architecture. Hence, applying the 3-tier architecture to the mobile network is inevitable for the same concerns in the wired network. When an MH, which receives requested data via the proxy P, keeps moving, the transmission path between the MH and proxy P becomes longer and longer. It is unreasonable that the MH still receives the requested data from proxy P. For example, let one take train from Paris to Madrid. It is unpractical that his serving proxy is still the one located in Paris when the train is in the southern France or in the northern Spain. One reasonable solution is that an MH should dynamically change its proxy according to geographical dependency and the network situation. Under the above concerns, the original two types of handoff, AP handoff and IP handoff, cannot resolve this problem. Therefore, the third type of handoff called “proxy handoff” are proposed in the application layer. Proxy handoff means that an MH dynamically switches the current proxy to another one according to its location. After performing proxy handoff, the MH can still receive its requested data via the new proxy.

To support the complete handoff control in the 3-tier architecture, we proposed a 3-tier Multimedia Mobile Transmission Platform (MMTP) that is implemented in the IPv6-based mobile network. MMTP provides AP, IP, and proxy handoff operations and keeps the multimedia streaming sessions in progress even if an MH performs AP handoff, IP handoff, and/or proxy handoff. For AP handoff, IEEE 802.11b is adopted for implementation and experiments. Although AP handoff can be supported by the new operation system, such as Microsoft Windows XP, the performance of the automatic AP handoff control function provided in the operation system is not good enough to satisfy MMTP’s requirement. For example, AP handoff in Microsoft Windows is triggered when packet loss rate has reached 50% or even 80%. Thus, a mobile-controlled AP handoff scheme is proposed in place of the function of the operation system. By monitoring the signal quality of the current wireless link, an MH can decide to execute AP handoff and avoid too much packet loss when signal quality is becoming worse. For IP handoff, MMTP incorporates the IPv6 stateless address allocation scheme (Koodli et al., 1998, Thomson and Narten, 1998) with a simple notification method. The notification method is built on IP protocol stack in Microsoft Windows system. After receiving the notification, the MH can send IP address update messages to the corresponding servers. In this way, MMTP can keep track the current location of MHs. For proxy handoff, MMTP adopts a control scheme based on the application-layer anycasting technique. When an MH needs to perform proxy handoff, some proxy servers are selected as the candidate proxies to form an anycast group according to the selection policy. The selection policy essentially takes load balance and transmission delay into consideration. Then, a proxy server will be selected from the anycast group. To have smooth handoff, the media server transmits packets to candidate proxies using multicast before the proxy handoff is executed. In this way, candidate proxies can cache a certain amount of packets before it serves the corresponding MH.

The remaining part of this paper is organized as follows. Section 2 briefly introduces related works. Section 3 presents the system architecture of MMTP. Section 4 describes handoff control schemes, including AP handoff, IP handoff, and proxy handoff. Section 5 presents system execution procedures in MMTP. Section 6 depicts the performance analysis. Finally, Section 7 gives conclusion remarks.