Slow Write Performance Using IBM DOS Lan Requester

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In the Network Monitor trace below, the client uses a send window of 1. With this send window, the client does not send any more frames before the last frame has been acknowledged. When Windows NT receives this frame, it does not immediately acknowledge it to optimize the number of frames sent in return. If several frames arrive in a short period of time, they can be acknowledged in one reply. When the server has any data to send back to the client, the acknowledgement can be sent together (piggybacked) with the response.

To use these optimizations (also known as delayed acknowledgement), Windows NT NetBEUI waits for a maximum of 150 ms (T2), and then sends an acknowledgement.

This causes a round-trip delay of about 200 ms for each frame, seriously degrading throughput.

 303 17.903 SMB C write block raw, FID = 0x802, Write 0xfd8 of 0xabec at
 0xabec
 304 18.086 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x5E
 305 18.089 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 306 18.286 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x5F
 307 18.289 NETBIOS Data Only Last (0x16): LSN = 0x04, RSN = 0x3D, Length =
 2028
 308 18.292 NETBIOS Data Ack (0x14): LSN = 0x3D, RSN = 0x04
 309 18.292 SMB     R write block raw
 310 18.292 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x26
 311 18.293 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x27
 312 18.293 NETBIOS Data Ack (0x14): LSN = 0x04, RSN = 0x3D
 313 18.486 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x61
 314 18.490 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 315 18.687 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x62
 316 18.691 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 317 18.887 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x63
 318 18.890 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 319 19.087 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x64
 320 19.090 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 321 19.287 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x65
 322 19.291 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 323 19.489 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x66
 324 19.492 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 325 19.688 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x67
 326 19.691 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 327 19.888 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x68
 328 19.891 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028
 329 20.089 LLC     RR DSAP=0xF0 SSAP=0xF1 R N(R) = 0x69
 330 20.092 NETBIOS Data First Middle (0x15): LSN = 0x04, RSN = 0x3D,
 Length = 2028