Karteikarten
Reliable Data Delivery
Karten in diesem Stapel (16)
- 1Define data rateA measure of the speed of data transmission, measured in bits per second
- 2Define error rateAn estimate on the reliability of a communication channel, the proportion if corrupted bits to uncorrupted bits
- 3Messages sent from transport entities are sent in... What does it store in its header file?TPDUs - Transport Protocol Data Units
- Source and destination process IDs
- Identifier to indicate this TPDU actually contains info.
- Message length indicator - 4An error in each of the TPDU fields has a consequence, what are they?Destination Process ID - TPDU is not delivered to the receiver
Source Process ID - Reply not returned to sender
Transport Layer Payload - Requires error detection
Length of Field - Only part of the TPDU received - 5What are the two variants of acknowledgement schemes?1. Positive Only Acknowledgement Scheme (ACKs)
2. Full Acknowledgement Scheme(ACKs, NAK's) - 6What is the positive only acknowledgement scheme also known as?Stop and wait protocol
- 7What happens in a positive only acknowledgment scheme?- Sender starts a timer when sending TPDU
- Receiver sends ACK when they have correctly received TPDU
- If senders timer times out:
1. Enquires receiver about problem or
2. Retransmits the TPDU - 8What is a problem with the positive only acknowledgment scheme and how is it resolved?Send packet may have been lost or receivers ACK may have been lost
Resends data packet to resolve (wasteful) - 9How does sequence numbering workSender sends 0
Receiver flips bit and returns
Sender checks bit it correct, sends again otherwise - 10What is the main drawback of positive only acknowledgement schemes (stop and wait) and what is the name of the solution to this problem?Cannot transmit anymore packets until ACK has been received or times out
Sliding Window Protocols - 11What are sliding window protocols and what are they also know as?Allowing sender to send N messages before their ACKs have been received
AKA: Pipeline protocols - 12What are the 2 main types of Sliding Window Protocols?1. Go Back to N
2. Selective Repeat - 13What happens on the sender side of Go back to N?- Buffer N messages
- Sequence numbers
- Range of consecutive number values - 14What happens on the receiver side of Go back to N?- Track sequence No. of next message expected, discarding all other messages
- Send ACK - 15What happens when the sender receives a ACK from receiver and what happens when a NAK is received or time out occurs?- Advance send window values
- Sender retransmits message and all subsequent messages - 16What happens in a selective repeat?Only retransmit packets that were lost
Sender buffers each packet and sends NAK indicating a packet loss