8 Questions
What does the term 'cumulative' mean in the context of TCP acknowledgment numbers?
It indicates that a party has received all the bytes up to the acknowledgment number.
What does the 'Checksum' field in a TCP segment signify?
Error checking for the header and data
How is the header length (HLEN) field represented in a TCP segment?
4 bits
In TCP, what does the 'Urgent pointer' field signify?
Indicates urgent data that needs immediate attention
How many bytes make up the header of a TCP segment when there are no options?
20 bytes
What is the purpose of the 'Sequence number' field in a TCP segment?
Identifies the next expected byte by the receiving party
Which field in a TCP segment defines the port number of the sending application program?
'Source port address' field
What aspect of TCP segments does the 'Options and padding' section influence?
Header length variations
Study Notes
Selective-Repeat Protocol
- Send window and receive window sizes are the same.
- Packets in send window can arrive out of order and are stored until delivered.
- Receiver never delivers packets out of order to application layer.
Receive Window in Selective-Repeat
- Shaded slots in receive window define packets that have arrived out of order and are waiting for earlier transmitted packet to arrive.
- Receive window stores packets that can be received and stored for later delivery.
Timer and Resending in Selective-Repeat
- Theoretically, Selective-Repeat uses one timer for each outstanding packet.
- When a timer expires, only the corresponding packet is resent.
- If a corrupted ACK or an error-free ACK with ackNo not related to outstanding packets arrives, the ACK is discarded.
Receiver Operation in Selective-Repeat
- Receiver is always in the ready state.
- Three events may occur: request comes from process, time-out, and ACK arrives.
Finite State Machine for Sender and Receiver
- FSMs for SR protocol are shown in Figure 23.34.
UDP Features
- UDP is a connectionless protocol.
- Each UDP packet is independent from other packets sent by the same application program.
UDP Pseudoheader
- 32-bit source IP address and 32-bit destination IP address are included in the pseudoheader.
- 8-bit protocol and source port address are included.
- UDP total length, destination port address, and checksum are included.
- Data with padding to make the data a multiple of 16 bits is included.
Optional Inclusion of Checksum
- The sender of a UDP packet can choose not to calculate the checksum.
- If the sender decides to calculate the checksum and the result is all 0s, the checksum is changed to all 1s before being sent.
TCP and UDP Applications
- Both high speed and low cost are desirable features in delivery of a parcel, but they are in conflict with each other.
- UDP is suitable for applications that need to send short requests and receive short responses.
TCP Features
- TCP is a connection-oriented protocol.
- Connection-oriented service creates more delay compared to connectionless service.
TCP Segment Format
- The format of a segment consists of a header of 20 to 60 bytes, followed by data from the application program.
- Header fields include source port address, destination port address, sequence number, acknowledgment number, and window size.
Test your knowledge on UDP checksum calculation and pseudoheaders with this quiz. Learn about how to calculate and verify the checksum to ensure data integrity in UDP communications.
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