The ABCs of TCP/IP, 2nd Edition

The Transport Layer

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Pointer field indicates the offset in bytes from the current sequence number

where the Urgent data is located.

ACK Bit

Setting the ACK bit indicates that the segment contains an acknowledgment

to a previously transmitted datagram or series of datagrams. Then the value

in the Acknowledgment Number field indicates the correct receipt of all bytes

through byte n by having the byte number n + 1 in the field.

PSH Bit

The third bit position in the Code Bit field is the Push (PSH) bit. This one-

bit field is set to request the receiver to immediately deliver data to the

application and flags any buffering. Normally, the delivery of urgent informa-

tion would result in setting both the URG and PSH bits in the Code Bits field.

RST Bit