two-way communication Two-way communication is a form of transmission in which both parties involved transmit information. Two-way communication has also been referred to as interpersonal communication. Common forms of two-way communication are: * Amateur radio, CB o ...

, whenever a frame is received, the receiver waits and does not send the control frame (acknowledgment or ACK) back to the sender immediately. The receiver waits until its network layer passes in the next data packet. The delayed acknowledgment is then attached to this outgoing data frame. This technique of temporarily delaying the acknowledgment so that it can be hooked with next outgoing data frame is known as piggybacking.

Working principle

Piggybacking data is a bit different from

sliding window protocol A sliding window protocol is a feature of packet-based data transmission protocols. Sliding window protocols are used where reliable in-order delivery of packets is required, such as in the data link layer (OSI layer 2) as well as in the Tra ...

s used in the

OSI model The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...

. In the data frame itself, we incorporate one additional field for acknowledgment (i.e., ACK). Whenever party A wants to send data to party B, it will carry additional ACK information in the PUSH as well. For example, if A has received 5 bytes from B, with a sequence number starting from 12340 (through 12344), A will place "ACK 12345" as well in the current PUSH packet to inform B it has received the bytes up to sequence number 12344 and expects to see 12345 next time. (ACK number is the next sequence number of the data to be pushed by the other party.) Three rules govern the piggybacking data transfer. * If station A wants to send both data and an acknowledgment, it keeps both fields there. * If station A wants to send the acknowledgment, after a short period of time to see whether a data frame needs to be sent, then decide whether send an ACK frame alone or attach a data frame with it. * If station A wants to send just the data, then the previous acknowledgment field is sent along with the data. Station B simply ignores this duplicate ACK frame upon receiving.

Advantages and disadvantages

Advantages: * Improves the efficiency * Usage cost reduction * Improves latency of data transfer * Better use of available channel bandwidth.Tanenbaum, Andrew & Wetherall, David. Computer Networks, 5th Edition, Pearson Education Limited, , 2014, p 226. Disadvantages: The receiver can jam the service if it has nothing to send. This can be solved by enabling a counter (receiver

timeout Time-out, Time Out, or timeout may refer to: Time * Time-out (sport), in various sports, a break in play, called by a team * Television timeout, a break in sporting action so that a commercial break may be taken * Timeout (computing), an enginee ...

) when a data frame is received. If the count ends and there is no data frame to send, the receiver will send an ACK control frame. The sender also adds a counter (emitter timeout). If the counter ends without receiving confirmation, the sender assumes

packet loss Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is either caused by errors in data transmission, typically across wireless networks, or network congestion.Ku ...

, and sends the frame again.

References

{{DEFAULTSORT:Piggybacking (Data Transmission) Data transmission