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Nagle
Nagle's algorithm, named after John Nagle, is a means of improving the efficiency of TCP/IP networks by reducing the number of packets that need to be sent over the network.
Nagle's document, Congestion Control in IP/TCP Internetworks (RFC 896) describes what he called the 'small packet problem', where an application repeatedly emits data in small chunks, frequently only 1 byte in size. Since TCP packets have a 40 byte header (20 bytes for TCP, 20 bytes for IPv4), this results in a 41 byte packet for 1 byte of useful information, a huge overhead. This situation often occurs in Telnet sessions, where most keypresses generate a single byte of data which is transmitted immediately. Worse, over slow links, many such packets can be in transit at the same time, potentially leading to congestion collapse.
Nagle's algorithm works by coalescing a number of small outgoing messages, and sending them all at once. Specifically, as long as there is a sent packet for which the sender has received no acknowledgment, the sender should keep buffering its output until it has a full packet's worth of output, so that output can be sent all at once.
Pseudocode
if there is new data to send
if the window size >= MSS and available data is >= MSS
send complete MSS segment now
else
if there is unconfirmed data still in the pipe
enqueue data in the buffer until an acknowledge is received
else
send data immediately
end if
end if
end if
Why do we refer to Nagle as a noticeable delay?
Nagle was invented to compensate for networks which were faster than the processing output routines. So instead of sending the word HELLO as potentially 5 packets: H,E,L,L,O. An algorithm was invented to assure these 5 characters would be collected into a single packet if presented fast enough. In today's world, Nagle is not really useful unless you have really poor networking environments.
Our product defaults to Nagle enabled as we have to assume you do not know what you are doing, and we assume you have not read our online documentation.
Related Keyword:
nagle,
data,
packet,
byte,
tcp,
packets,
output,
algorithm,
send,
sent,
mss,
small,
sender
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