2017-02-10 Reliable data Transmission principle introduction

2017-02-10 Reliable data Transmission principle introduction

3.4 Principle of reliable data transmission

Reliable Data Transfer Protocol (reliable data Transfer Protocol)

Unidirectional data transfer (unidirectional data transfer)

Bidirectional data transfer (bidirectional data transfer) (i.e. full duplex data transfer)

3.4.1 structure reliable Data transmission protocol

1. Reliable data transfer via fully reliable channel: Rdt 1.0

Finite state machine (finite-state MACHINE,FSM)

Note that the above protocol assumes that a fully reliable channel is used, so the receiver does not need to provide any feedback to the sender.

2. Reliable data transmission via a bit error channel: RDT 2.0

Positive confirmation (positive acknowledgment)

Negative confirmation (negative acknowledgment)

These control messages allow the receiver to let the sender know what is being received correctly, and that the content is received incorrectly and therefore needs to be duplicated. In the computer network environment, the reliable data transmission protocol based on this retransmission mechanism is called automatic retransmission request (Automatic Repeat Request,arq) protocol.

The ARQ protocol also requires three additional protocols to deal with bit errors: error detection, receiver feedback, retransmission. When the receiver receives a packet that is in error, the sender will retransmit the grouped text.

When the sender is in the state of waiting for an ACK or NAK, he cannot obtain more data from the upper layer; that is, the Rdt_send () event is unlikely to occur; Such an event can occur only if an ACK is received and the state is left. Therefore, the sender will not send a new piece of data unless the sender confirms that the receiver has correctly received the current grouping. Rdt2.0 is also known as a stop-and-Wait (stop-and-wait) protocol.

He has a fatal error when an ACK or NAK packet is compromised.

One approach is that when the sender receives an ambiguous ACK or nak grouping, it is only necessary to retransmit the current array grouping. This approach introduces redundant groupings (duplicate packet) in the sender-to-receiver channel, but it also solves the problem of whether a grouping is a new grouping or a redundant grouping of repeated postbacks.

The solution to this problem is to add the ordinal number of the group (sequence numbers)

3. Reliable data transfer via Kanenobu with bit error: Rdt 3.0

If a packet undergoes a particularly large delay, the sender may retransmit the packet, even if the packet is changed and its ACK is not lost. This introduces the possibility of redundant data packets (duplicate-packet) in the channel of the sender to the receiver.

To implement a time-based retransmission mechanism, an inverted-count timer (countdown timer) is required, and rdt3.0 is sometimes referred to as the bit-alternating protocol (Alternating-bit protocol).

3.4.2 Pipeline Reliable Data Transfer Protocol

The usage of the sender (or channel) (utilization) is very low, so the pipelining (pipelining) is introduced.

3.4.3 Fallback N Step (GO-BACK-N,GBN)

In the fallback N-Step (GBN) protocol, the base sequence number (base) is defined as the ordinal of the oldest unacknowledged group, and the next ordinal (nextseqnum) is defined as the smallest unused ordinal, then the ordinal range can be divided into 4 segments.

n is often referred to as window length (Windows size), and the GBN protocol is often referred to as the Sliding Window Protocol (Sliding-window protocol).

1: Reliable data Transfer Protocol (reliable data Transfer Protocol), 2: Unidirectional data transfer (unidirectional data transfer), 3: Bidirectional data transfer (bidirectional data Transfer), 4: Full Duplex data transfer, 5: Finite state machine (Finite-state MACHINE,FSM), 6: Positive acknowledgment (positive acknowledgment), 7: Negative acknowledgment (negative acknowledgment), 8: Automatic retransmission request (Automatic Repeat Request,arq) protocol, 9: Stop (stop-and-wait) protocol, 10: bit alternating protocol (alternating-bit Protocol), 11: Sliding Window Protocol (Sliding-window protocol)