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TCP/IP Tutorial and Technical Overview phần 10

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và các ký tự đặc biệt khác trong phạm vi 128 đến 255. Lưu ý rằng nếu văn bản không chứa các ký tự với giá trị trên 127, các bộ ký tự được quy định như Cấu trúc liên kết kiểm soát mạng không dây Ad Hoc và mạng cảm biến | 22.14.1 Terminology Before describing the protocol we provide a definition of some L2TP terminology L2TP access concentrator LAC A device attached to one or more public switched telephone network PSTN or Integrated Services Digital Network ISDN lines capable of handling both the PPP operation and L2TP protocol. The LAC implements the media over which L2TP operates. L2TP passes the traffic to one or more L2TP servers LNS . L2TP network server LNS An LNS operates on any platform that can be a PPP endstation. The LNS handles the server side of the L2TP protocol. Because L2TP relies only on the single media over which L2TP tunnels arrive the LNS can have only a single LAN or WAN interface yet is still able to terminate calls arriving from any PPP interfaces supported by a LAC such as async synchronous ISDN V.120 and so on. Network access servers NAS A device providing temporary on demand network access to users. This access is point-to-point using PSTN or ISDN lines. Session Call L2TP creates a session when an end-to-end PPP connection is attempted between a dial-in user and the LNS or when an outbound call is initiated. The datagrams for the session are sent over the tunnel between the LAC and the LNS. The LNS and LAC maintain the state information for each user attached to a LAC. Tunnel A tunnel is defined by an LNS-LAC pair. The tunnel carries PPP datagrams between the LAC and the LNS. A single tunnel can multiplex many sessions. A control connection operating over the same tunnel controls the establishment release and maintenance of all sessions and of the tunnel itself. Attribute value air AVP A uniform method of encoding message types and bodies. This method maximizes the extensibility while permitting interpretability of L2TP. 876 TCP IP Tutorial and Technical Overview 22.14.2 Protocol overview Because the host and the gateway share the same PPP connection they can take advantage of PPP s ability to transport protocols other than just IP. For example L2Tp .