TCPllä

TCPllä is a transport-layer protocol that extends the classic Transmission Control Protocol (TCP) with enhancements intended to improve performance in networks with variable latency and intermittent connectivity. It seeks backward compatibility with TCP by negotiating the use of TCPllä when both endpoints support it.

Key features include a dual-mode reliability mechanism: a standard reliable mode akin to TCP for general use, and a low-latency streaming mode that tolerates controlled packet loss to reduce head-of-line blocking. It supports selective retransmission, batched acknowledgments, and per-path flow control for multihomed hosts. It also introduces optional multipath transmission to utilize multiple network interfaces.

Operation of TCPlla involves a modified handshake in which an option is exchanged to enable TCPllä. Data is segmented with extended header fields for sequence numbers and stream state; congestion control combines traditional TCP-like algorithms with path-aware scheduling and ECN to mitigate congestion. Implementations aim to retain compatibility with existing middleboxes and firewalls, facilitating incremental deployment where possible.

Status and reception of TCPllä remain experimental and primarily in academic or research contexts. There is no standardization by major standards bodies, and only prototype kernel patches and user-space libraries have been reported in testing environments. Practical adoption faces interoperability and complexity challenges; performance gains depend on workload and network characteristics, and real-world benefits are typically workload-specific.

See also: Transmission Control Protocol, Multipath TCP, QUIC.