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Hai bản sao của các Địa chỉ công nhận chỉ thị. Các nút đích thiết lập địa chỉ công nhận các chỉ số để chỉ ra rằng địa chỉ trong lĩnh vực Địa chỉ đích đã được công nhận. Hai bản sao của Frame Sao chép chỉ số. Nút đích thiết lập các chỉ số Khung hình các Sao chép để chỉ ra rằng khung thành công sao chép vào một bộ đệm trên các bộ chuyển đổi mạng. | Chapter 1 Local Area Network LAN Technologies 19 Frame Status The Frame Status field is a 1-byte field that contains the following Two copies of the Address Recognized indicator. The destination node sets the Address Recognized indicators to indicate that the address in the Destination Address field was recognized. Two copies of the Frame Copied indicator. The destination node sets the Frame Copied indicators to indicate that the frame was successfully copied into a buffer on the network adapter. Two copies of each indicator are needed because the FCS field does not protect the Frame Status field. The Address Recognized and Frame Copied indicators are not used as acknowledgments for reliable data delivery. The sending Token Ring network adapter uses these indicators to retransmit the frame if necessary. Note The FCS End Delimiter and Frame Status fields are not visible with Network Monitor. IEEE LLC Header The fields in the IEEE LLC header are defined and used in the same way as the IEEE LLC header for the IEEE frame format as discussed in the section titled IEEE earlier in this chapter. IEEE SNAP As described earlier in this chapter the value of 0x06 is defined as the DSAP and SSAP for IP. However it is not defined for use in RFC 1042 and not used in the industry. Therefore similar to the case of IEEE frames to send an IP datagram over an IEEE network the IP datagram must be encapsulated using SNAP as Figure 1-7 shows. For a 10-millisecond ms token-holding time the maximum sizes for IP datagrams are 4464 bytes for 4-Mbps Token Ring network adapters and 17 914 bytes for 16-Mbps Token Ring network adapters. If Token Ring source-routing bridges are present the maximum size of IP datagrams can be 508 1020 2044 4092 and 8188 bytes. For more information on Token Ring MTUs see RFC 1042. 20 Part I The Network Interface Layer DSAP SSAP Control 0xAA 0xAA 0x03 IEEE LLC Header Organization Code Ether Type llllllll .