tailieunhanh - Voic 802.11e over phần 3

Toán học cơ bản việc phân chia mã trong CDMA được thêm rất nhiều phức tạp hơn trong OFDM. OFDM thiết bị sử dụng một kênh widefrequency bằng cách phá vỡ nó ra thành một số subchannels thành phần. Subchannel từng được sử dụng để truyền dữ liệu. | Voice over Internet Protocol 41 of application parts. Common application parts include the intelligent network application part INAP and the mobile application part MAP 7 p. 311 . Routing Protocols VoIP is routed over an IP network via routers. To deliver the best QoS voice packets must be given priority over data packets. That means communicating to routers which packets have what priority. Router operations involve several processes. First the router creates a routing table to gather information from other routers about the optimum path for each packet. This table may be static in that it is constructed by the router according to the current topology and conditions. Dynamic routing is considered a better technique because it adapts to changing network conditions. The router uses a metric of the shortest distance between two endpoints to help determine the optimum path. The router determines the least cost most efficient path from origin to destination. Two algorithms are used to determine the least cost route distance vector and link state. Protocols that make use of these algorithms are called interior gateway protocols IGPs . The Routing Information Protocol RIP is an IGP based on the distance vector algorithm and the Open Shortest Path First OSPF Protocol is an IGP based on the link state algorithm. Where one network needs to communicate with another it uses an exterior gateway protocol EGP . One example of an EGP is the Border Gateway Protocol BGP . RIP RIP is a distance vector protocol that uses hop count the number of routers it passes through on its route to its destination as its metric. RIP is widely used for routing traffic on the Internet and is an IGP which means that it performs routing within a single autonomous system. Exterior gateway protocols such as BGP perform routing between different autonomous systems. RIP itself evolved as an Internet routing protocol and other protocol suites use modified versions of RIP. OSPF OSPF is a routing protocol .