SDS

Sign in | Register    

Leading provider of z/OS mainframe software
and multi-platform encryption software

Support

SDS | On Alert 24/7, 365/year


The local date and time at SDS HQ is

server time

time zone

SDS offices are open now.
We will respond to your request promptly.

SDS is closed for ..
If your request is urgent,
please phone our after-hours number:
from North America,    763.571.9000
from elsewhere,  001.763.571.1134

 

 

 

More Support:

 

 

Home >

Support | TCP/IP Connections


TCP/IP, the protocol of the internet, communicates via relatively long-lived connections between server and client--between a web server and a web browser, for example. This page describes the how such a connection is established, managed, and shutdown.


Figure C: The Life-Cycle of TCP/IP Connections

In the process of opening and closing, a TCP connection progresses through a series of states, as illustrated below.

An HTTP connection is a type of TCP/IP connection. It follows the TCP/IP life-cycle.

A connection opens with a pair of SYNchronization messages. It closes with a pair of FINish messages. The messages are in pairs because they go one in each direction. This is the so-called "handshake" between two TCP/IP stacks.

Note that each state name is associated with a code number, "1 closed" for example. That code is the value used by an SNMP MIB (simple network management protocol, management information base).

 
Client*   Server*
*or vice-versa, though requests typically originate at clients.
 
2 Listening
Awaiting connection request.
3 Syn-Sent
Sent connection-request.1
Awaiting acknowledgement.1
Awaiting connection-request.2
arrow
Received acknowledgement.1
Received connection-request.2
Sent acknowledgement.2

arrow
arrow
4 Syn-Received
Received connection-request.1
Sent acknowledgement.1
Sent connection-request.2
Awaiting acknowledgement.2
 
5 Established
The connection is open.
Data moves both directions.
arrow 5 Established
Received acknowledgement.2
The connection is open.
Data moves both directions.
 
6 Fin-Wait.1
Sent close-request.a
Awaiting acknowledgement.a
Awaiting close-request.b
arrow
  8 Close-Wait
Received close-request.a
Sent acknowledgement.a
When finished sending data,
will send close-request.b
7 Fin-Wait.2
Received acknowledgement.a
Still awaiting close-request.b
arrow
or  
10 Closing
Received close-request.b
Sent acknowledgement.b
Still awaiting acknowledgement.a
arrow 9 Last-Ack
Sent close-request.b
Awaiting acknowledgement.b
 
11 Time-Wait
Received acknowledgement.a
Received close-request.b
Sent acknowledgement.b
Allowing time for delivery
of acknowledgement.b
arrow
 
1 Closed
A "fictional" state;
there is no connection.
  2 Listening
Awaiting connection request.
 
 

Explore SDS

Brand alliances

IBM HP

 

 

Brand partnerships

SSH ConicIT NETQ SMARTTSXL
SDS

Software Diversified Services | Copyright © 2014. All rights reserved.