SACK
SACK (Selective Acknowledgment, RFC 2018) lets the receiver acknowledge discontinuous blocks of data so the sender retransmits only the lost segments.
Purpose
It avoids retransmitting already-received segments on lossy links, improving recovery efficiency—especially for large-window connections.
Mechanism
The TCP SACK option carries up to four [left, right] boundary pairs marking the non-contiguous received blocks. From these, the sender retransmits only the gap segments instead of everything since the last ACK.
Use cases
- Recovery on high-loss links
- Large-window TCP
- Satellite and wireless networks
Related tools
HTTP Status Codes
Reference table of common HTTP status codes (1xx-5xx) with names, categories, and descriptions. Free, private, and 100% client-side. TOOL
URL Parser
Parse a URL into its components: protocol, host, path, query, hash, port, username, and password. Free, private, and 100% client-side. TOOL