Core: Data Plane Transport
In one line The transport layer decides reliability, ordering, congestion behaviour, and how visible traffic is to the network - and that shapes buffering, load-balancing, and security design. The three you must reason about * TCP - connection-oriented, reliable, ordered, congestion-controlled. The workhorse for web/APIs, storage, and bulk transfer;
Core: Data Plane Transport
In one line TCP throughput is governed by window / RTT / loss, so the network's latency and drop behaviour directly cap application speed. The mechanics that matter * Windowing + bandwidth-delay product (BDP): max in-flight = window; throughput ~= window / RTT. Long-fat networks (high BW x high RTT) need window
Core: Data Plane Transport
Requirement / business driver Move full-size packets end to end without silent black-holing - the classic, hard-to-diagnose failure when MTU and overlays collide. The mechanics * IPv4 can fragment in transit (DF bit aside); IPv6 does NOT fragment in transit - only the source may, guided by PMTUD. * PMTUD relies
Core: Data Plane Transport
Requirement / business driver Absorb transient bursts and signal congestion without either dropping latency-sensitive traffic or adding bufferbloat - a core data-centre and WAN-edge decision. The forces * Microbursts: sub-second spikes that overrun interface buffers even when average utilisation is low (see Factors affecting convergence) - they cause drops that
Core: Data Plane Transport
Requirement / business driver Spread traffic across parallel paths/links evenly and without reordering - the basis of CLOS/spine-leaf and LAG scaling. How it works * ECMP / LAG hash a flow (typically the 5-tuple) to one path, keeping a flow's packets in order. Per-packet balancing spreads better
Core: Data Plane Transport
Requirement / business driver Secure data in transit while preserving the visibility and control the network needs - a tension that grows as encryption becomes pervasive. The shift * TLS over TCP, DTLS over UDP, and QUIC's mandatory TLS 1.3 mean most traffic is now encrypted by default. * QUIC rides