Which field in a Transmission Control Protocol (TCP) header provides the next
expected segment?

The field in a Transmission Control Protocol (TCP) header that provides the next expected segment is; acknowledgement number

The different fields in Transmission Control Protocol (TCP) Segment Header include;

Source PortDestination PortSequence NumberAcknowledgement NumberHeader LengthFlagsWindow SizeTCP ChecksumUrgent Pointer

Among these 9 fields, the only one that provides the next expected segment is called Acknowledgement number. This is because acknowledgement number is simply defined as the sequence number of the next byte that the receiver expects to receive and as such it provides the next expected segment.

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In a Transmission Control Protocol (TCP) header next  Expected segment is provided by Acknowledgment Number

Explanation:

TCP is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in the Internet Protocol. The fields in TCP Segment Header are Source Port, Destination Port, Sequence Number, Acknowledgement Number, Header Length, Flags, Window Size, TCP Checksum and Urgent Pointer.The Acknowledgment Number is a  32 Bit number field which indicates the next sequence number that the sending device is expecting from the other device.The SYN packets consume one sequence number, so actual data will begin at ISN+1. The sequence number is the byte number of the first byte of data in the TCP packet sent. If the acknowledgment flag is set in the flags field, the acknowledgment number field holds the sequence number of the next byte that the receiver expects.

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