Transport Layer Flashcards

Flashcards covering key concepts from the Transport Layer lecture.

What is the sender's role in transport protocols?

Breaks application messages into segments, passes to network layer.

What is the receiver's role in transport protocols?

Reassembles segments into messages, passes to application layer.

What is the sender's role in transport protocols?

Breaks application messages into segments, passes to network layer.

What does TCP stand for?

Transmission Control Protocol

What does UDP stand for?

User Datagram Protocol

What services does TCP provide?

Reliable, in-order delivery, congestion control, flow control, and connection setup.

What kind of delivery service does UDP provide?

Unreliable, unordered delivery with no frills extension of best-effort IP.

On what are multiplexing and demultiplexing based?

Based on segment, datagram header field values.

How does UDP perform demultiplexing?

Using the destination port number (only).

How does TCP perform demultiplexing?

Using 4-tuple: source and destination IP addresses, and port numbers.

What may happen to UDP segments with best effort service?

Lost, delivered out-of-order to app

Why is UDP connectionless?

No handshaking between UDP sender, receiver and each UDP segment handled independently of others.

What are some uses for UDP?

Streaming multimedia apps (loss tolerant, rate sensitive), DNS, SNMP, and HTTP/3.

How is the UDP checksum calculated by the sender?

Treat contents of UDP segment (including UDP header fields and IP addresses) as sequence of 16-bit integers, checksum value put into UDP checksum field

How does the receiver validate the UDP checksum?

Compute checksum of received segment and check if computed checksum equals checksum field value.

What is UDP's approach?

Segments may be lost, delivered out of order; best effort service: send and hope for the best.

What are the advantages of UDP?

No setup/handshaking needed (no RTT incurred), can function when network service is compromised, and helps with reliability (checksum).

What approach is used to provide reliability over UDP?

Build additional functionality on top of UDP in application layer (e.g., HTTP/3).

What does 'stop and wait' mean in reliable data transfer?

Sender sends one packet, then waits for receiver response.

What are acknowledgements (ACKs)?

Receiver explicitly tells sender that pkt received OK

What are negative acknowledgements (NAKs)?

Receiver explicitly tells sender that pkt had errors

What should a sender do if an ACK/NAK is corrupted?

Sender retransmits current pkt if ACK/NAK corrupted.

What can the sender do to handle duplicates?

adds sequence number to each pkt and receiver discards (doesn’t deliver up) duplicate pkt.

How does make a NAK-free protocol?

Receiver sends ACK for last pkt received OK and receiver must explicitly include seq # of pkt being ACKed.

How do senders handle losses of packets?

Sender waits reasonable amount of time for ACK and retransmits if no ACK received in this time

Sender Utilization

Fraction of time sender busy sending

What action occurs during pipelining?

Sender allows multiple, “in-flight”, yet-to-be-acknowledged packets

Go-Back-N sender

Sender: “window” of up to N, consecutive transmitted but unACKed pkts • k-bit seq # in pkt header

receiver behavior in selective repeat

Individually acknowledges all correctly received packets • buffers packets, as needed, for eventual in-order delivery to upper layer