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TCP/IP Tutorial and Technical Overview phần 8

được định nghĩa cho các loại văn bản, quy định cụ thể văn bản chưa định dạng. Tham số tùy chọn có thể được bao gồm với cặp type / subtype này để xác định bộ ký tự của văn bản. Các giá trị sau đây được phép tham số này: - us-ascii: văn bản bao gồm các ký tự ASCII trong phạm vi 0-127 (thập phân). | implementing an end-to-end connection WP-TCP behaves like any other TCP application establishing a connection directly with the origin server. This is illustrated in Figure 18-9. Wireless client Origin server Figure 18-9 The end-to-end approach The decision to implement the end-to-end approach over the split-TCP approach is usually determined by service server and hardware provisioning or the specific needs of the application layer. WP-TCP optimizations As noted previously certain scenarios exist on a wireless network that make a purely TCP connection less desirable. Such scenarios include Frequent packet loss Smaller window sizes Long periods of silence or connection loss due to exponential back-off retransmission mechanisms Redundant transmission Periods of disconnection due to lack of coverage 676 TCP IP Tutorial and Technical Overview The profiling of TCP for WP-TCP sought to optimize the protocol to compensate for these scenarios. Specifically eight optimizations were included in WP-TCP. These are Large window size Built in to TCP is the use of the Bandwidth Delay Product BDP calculated from the available bandwidth and the round-trip time to calculate the minimum window size. It also calculates the maximum window size using the smallest value of the send or receive buffers. WP-TCP can opt to use the maximum window size relying on the congestion control mechanisms built into TCP to regulate the data as needed. The WP-TCP specification indicates that implementation of this optimization is recommended but not required. The window scale option Entities that opt to use the large window size are required to also implement the window scale option defined by RFC 1323. If an entity does not support the large window size optimization implementation of the window scale optimization is optional. Round-trip time measurement Also defined in RFC 1323 round-trip time measurement RTTM is recommended for use by any entity that implements window sizes larger than 64 K. This also