[WEBINAR] The New Normal: Dealing with the Reality of an Unsecure World

Initial Sequence Numbers (ISN)

Definition - What does Initial Sequence Numbers (ISN) mean?

Initial sequence numbers (ISN) refers to the unique 32-bit sequence number assigned to each new connection on a Transmission Control Protocol (TCP)-based data communication. It helps with the allocation of a sequence number that does not conflict with other data bytes transmitted over a TCP connection. An ISN is unique to each connection and separated by each device.

Techopedia explains Initial Sequence Numbers (ISN)

An ISN is designed to randomly select a sequence number for the first byte of data transmitted in a new TCP connection. The ISN can be any number from 0 to 4,294,967,295. Each byte can select any ISN unless it is in use not by a current connection.

The TCP protocol assigns an ISN to each new byte, beginning with 0 and incrementally adding a number every four seconds until the limit is exhausted. In continuous communication, it takes up to four hours to consume all available ISN options. Thus, when the TCP returns to the beginning, it generally starts with ISN options that are released from the completed/closed connections.

Techopedia Deals

Connect with us

Techopedia on Linkedin
Techopedia on Linkedin
"Techopedia" on Twitter

Sign up for Techopedia's Free Newsletter!

Email Newsletter

Join thousands of others with our weekly newsletter

Free Whitepaper: The Path to Hybrid Cloud
Free Whitepaper: The Path to Hybrid Cloud:
The Path to Hybrid Cloud: Intelligent Bursting To Amazon Web Services & Microsoft Azure
Free E-Book: Public Cloud Guide
Free E-Book: Public Cloud Guide:
This white paper is for leaders of Operations, Engineering, or Infrastructure teams who are creating or executing an IT roadmap.
Free Tool: Virtual Health Monitor
Free Tool: Virtual Health Monitor:
Virtual Health Monitor is a free virtualization monitoring and reporting tool for VMware, Hyper-V, RHEV, and XenServer environments.
Free 30 Day Trial – Turbonomic
Free 30 Day Trial – Turbonomic:
Turbonomic delivers an autonomic platform where virtual and cloud environments self-manage in real-time to assure application performance.