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McGraw Hill - 2002 - W-CDMA and cdma2000 for 3G Mobile Networks_10

Tham khảo tài liệu 'mcgraw hill - 2002 - w-cdma and cdma2000 for 3g mobile networks_10', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 326 Chapter 9 environment andover MS Figure 9-18 RSVP in a mobile PATH PSPDN RESV services to cells 1-4 and R3 to cells 5-7.10 Initially when the mobile station MS is in cell 1 it reserves resources along the path shown by the thick lines from base station 1 to R2 to R1. If the MS now moves into cell 2 it is attached to base station 2 and makes a reservation along the new route from base station 2 to R2. In RSVP because a receiving host cannot initiate a reservation request using the RESV message until it has received a PATH message and because a data source sends the PATH message periodically the MS must wait before it can make the new reservation. Meanwhile R2 continues to send packets along the old route to cell 1 10Notice that router R1 is functionally equivalent to a Gateway GPRS Support Node GGSN of a GPRS or all-IP wireless network. Similarly routers R2 and R3 correspond to Serving GPRS Support Nodes SGSN . Quality of Service QoS in 3G Systems 327 and so these packets are lost by the MS. This problem may be somewhat mitigated by modifying RSVP so that as soon as the MS is handed over to the new cell R2 issues a PATH message. However since the resource reservation process is rather slow the associated delays may still be too long to avoid any packet loss. The problem becomes particularly severe if the MS moves into a cell where the traffic is already quite high. In this case the MS must renegotiate with the network for the allocation of required resources leading to even longer delays and further loss of packets. And depending upon the requested QoS the network may not be able to guarantee the desired quality and consequently may even deny the reservation request. This problem can be solved if the network has some prior knowledge of how a mobile station is going to move around in a serving area. Reference 12 suggests an extension of RSVP called Mobile RSVP MRSVP based upon this idea. In this protocol the network maintains in its database a list of all nodes .