Kbase 20142: TCP/IP Terms Explained: SYN, ACK, and SYN/ACK
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
10/15/2008 |
|
Status: Unverified
GOAL:
Defining SYN, ACK, and SYN/ACK in TCP/IP.
FIX:
The terms are:
- SYN (SYNchronizing packet)
This is the first packet of a communication sent by, for
example, a client using the TCP protocol. It is used to
initiate and synchronize the two ends of a network
connection and prepare for establishing a TCP/IP connection.
- ACK (Acknowledgement)
A response packet sent by a receiver (for the example below,
a server) to indicate (acknowledge) the successful reception
of a SYN signal/message. In the example, an ACK is a
response to a SYN.
- SYN/ACK
If the receiver (server) is listening and ready, it sends
back a SYN/ACK packet (an acknowledgment of the original
SYN) to the client.
When the client receives the SYN/ACK, it sends back yet
another packet to acknowledge it (the ACK of the SYN-ACK).
When the server receives this packet, it removes the SYN
from the pending queue and initiates the TCP connection.
Graphically, this appears as follows:
__________ __________
| Server | | Client |
| |-----> SYN -------->| |
| | | |
| |<----- ACK <--------| |
| | | |
| |-----> SYN/ACK ---->| |
| | | |
| |<----- ACK <--------| |
| | | |
| |<----> TCP/IP <---->| |
|________| |________|