3.1 Fast vertical handover via Designated Crossover Points (DCP)
In the chapter 2 we know that the mobile will change its association of the network and CoA, when a vertical handover happens. As a result, if without proper arrangement, the QCS-QNS negotiation for the resource reservation over IP backbone to the CE of the mobile induces a high latency of vertical handover and serious interruption of real-time services.
The latency hiding techniques would be useful to relieve the problem mentioned above. There are two approaches of such techniques possible: (a)
delaying the vertical handover , which means enabling the vertical handover after
the new path is established, and (b) multicasting the streams to the base stations where the mobile currently and possibly visits [9] [10]. Under the IP end-to-end QoS architecture, the efficiencies of both approaches depend on the location to join the old and new paths.We can do the join operation in the endpoint (CN or HA) or crossover router. When joining the old and new path in the end point, the latency induced by QCS-QNS negotiation will seriously affect the real-time service. To cut down the latency of the vertical handover, we can simply join the old and new paths at the crossover router [11] [12]. The original proposals on such a solution are to join at the optimal crossover point [13] when dealing with macro-mobility or a fixed gateway when dealing with the micro-mobility problem.
However, within the IP end-to-end QoS architecture, more considerations are needed to be taken for the vertical handover.
There are three possible crossover points to perform the join operation under the reference IP end-to-end QoS architecture in figure 3.1. As shown, if the
mobile moves from the network 15.5.0.0 to 15.6.0.0. The optimum crossover point is (a), which is a core router (P router). Secondly, (b) and (c) are a PE router and CE router, respectively. For the cases (b) and (c), the new path should be
derouted, performed by PE attaching to and CE residing in the network 15.6.0.0,
respectively, to meet the designated crossover point (DCP). At the first glimpse, placing the crossover point at (a) induces best routing efficiency. However, the case (a) or (b) raises other problems. The reservation needs the QCS-QNS negotiation, which will induce longer delay. The router in the provider network should be modified to recognize the micro flow, and in some case there will be multiple reservations in the network, which will waste the system resource.(b)
old path
P P
P P
PE
PE
CE/FA CE/FA PE
PE
15.6.0.0 15.7.0.0
15.8.0.0
(c)
(a) CE
CE
HA CN
15.5.0.0
Figure 3.1. Three possible locations for placing the designated crossover point (DCP)
With the above reasons, we focus on placing the DCP in CE router, as in case (c). Furthermore, to overcome the resultant routing inefficiency, we let the DCP to handover to CE of mobile. It is important to stress that the “DCP handover” is not the radio-level handover. Rather, it is proposed to re-route the reservation path over the IP backbone to enhance the routing efficiency. When incorporating with Mobile IP, the address of CE router where the DCP is located is always the CoA registered and bound at the HA and CN, respectively. A DCP handover then includes the operation that the change of CoA due to the last vertical handover is
reflected at both HA and CN.
3.2 cost minimization by VHE user profile
Virtual Home Environment (VHE) is a concept for Personal Service Environment (PSE) portability across network boundaries and between terminals.
The concept of VHE is such that users are consistently presented with the same personalized features, User Interface customization and services in whatever network and whatever terminal, and wherever the user may be located.
A user’s VHE is enabled by user profiles. A user may have a number of user profiles which enable her to manage communications according to different situations or needs, for example being at work, in the car or at home. Each user profile consists of two kinds of information – user interface related information and services related information [14] [15].
The user interface profile may include information such as: menu setting and terminal setting. The user services profile may include a list of favorite user services, as well as the personal configuration information for each of the above services and the service status whether the service is active or not. We can obtain the user profile from the network operator’s database, e.g., HSS. In the personal configuration of the user service profile we assume that there will be the moving characteristics and vertical handover transition probability (figure 3.2), so that we can minimize network cost and find the optimal policy according to the information (see in chapter 5). Since all of the computation is done off-line, the real-time service will not be affected.
P6
P5
P4
P3 P2
P1
WLAN 1
UMTS
WLAN 2
Figure 3.2. Vertical transition probabilities
We assume the mobile user moving form UMTS to WLAN 1 has the probability P1, and moving from UMTS to WLAN 2 has the probability P2. If the user is in the WLAN 1, we have the probability P3 for moving to UMTS, and have the probability P4 for moving to WLAN 2. If the user is in the WLAN 2, we have the probability P5 for moving to UMTS, and have the probability P6 for moving to WLAN 1. We show these vertical handover transition probabilities in the figure 3.2.