TAILIEUCHUNG - emerging wireless multimedia services and technologies phần 7

bằng cách sử dụng các thông tin liên kết được trả về bởi các file PDF. Các thẻ ủy quyền có được thông qua bởi mỗi PEF tại GGSN để PDF của nó để xác định số lượng tài nguyên đã được ủy quyền, nếu các bằng hoặc thay thế những yêu cầu, | 256 Wireless Multimedia in 3G networks The next step is for both UEs to independently activate appropriate PDP contexts at their GGSNs using the binding information returned by the PDFs. The included authorization tokens are passed by each PEF at the GGSN to its PDF to determine the amount of resources that have been authorized if these equal or supersede those requested each PEF installs the corresponding filters reports it to the PDF and informs the UE that the PDP contexts have been activated. At this point the reservation of resources is complete but the gates are closed since the session has not been established. Eventually the session is established as indicated by a final SIP message sent by the called UE to the caller UE via the CSCFs. As this message passes through the PCF at each P-CSCF the PCF instructs the PEF at the GGSN to open the gates and the PEF confirms that the gates have indeed been opened. When the final SIP message reaches the caller UE the gates are already open at both GGSNs therefore session data may start flowing in both directions. Summary This chapter provided an introduction to the support for IP based multimedia services on 3G wireless cellular networks focusing on the IP Multimedia Subsystem IMS and the Multimedia Broadcast Multicast Service MBMS . An overview of cellular networks in general and UMTS networks in particular was first presented to lay the groundwork for the following discussion. Then the features and services of the IMS and the MBMS were introduced followed by detailed descriptions of both. Finally the QoS issues for IP based multimedia services were discussed emphasizing the policy based QoS control scheme of UMTS and its application to the IMS. Glossary of Acronyms 1G 2G 3G First Second Third Generation 3GPP 3rd Generation Partnership Project 3GPP2 3rd Generation Partnership Project 2 AAL2 5 ATM Adaptation Layer 2 5 AMPS Advanced Mobile Phone Service AMR Adaptive Multi-Rate AS Application Server ATM .

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