How data flows through seven layers — and what each layer does in three real-world scenarios
Application Layer
User-facing protocols and data formats. The interface between software and the network.
HTTPS + DASH/HLS
YouTube app requests video segments via HTTPS. Adaptive streaming (DASH/HLS) selects quality based on bandwidth.
HTTP/2, QUIC
gRPC / Protobuf
Ground control software sends typed RPC calls (e.g. SetThrottle, GetTelemetry) serialised as Protocol Buffers.
gRPC, Protobuf
HTTP/HTTPS
Browser sends an HTTP GET request for the page URL. Server responds with HTML, CSS, JS resources.
HTTP/1.1, HTTP/2
Presentation Layer
Data translation, encryption, and compression. Ensures both ends speak the same data format.
TLS + H.264/VP9 Codec
TLS encrypts the stream. Video codec decodes compressed frames into raw pixels for the display.
TLS 1.3, VP9/AV1
TLS + Protobuf Encoding
Optional TLS secures the channel. Protobuf binary encoding translates typed structs into compact bytes.
TLS, binary encoding
TLS Encryption
TLS handshake establishes shared keys. All HTTP traffic is encrypted and decrypted transparently.
TLS 1.3, X.509
Session Layer
Establishes, manages, and terminates conversations between applications. Handles reconnection and checkpointing.
QUIC Connection / HTTP/2 Stream
A persistent QUIC session multiplexes video, audio, and metadata streams. Survives brief network interruptions.
QUIC, multiplexing
HTTP/2 Session over gRPC
gRPC uses HTTP/2 which maintains a long-lived session with bidirectional streaming for real-time telemetry.
HTTP/2 streams
TCP Session / Cookie
TCP connection is the session. HTTP Keep-Alive reuses it for multiple requests. Cookies track authenticated state.
Keep-Alive, cookies
Transport Layer
End-to-end delivery, segmentation, error recovery, and flow control between ports on two hosts.
UDP via QUIC
QUIC runs over UDP — allowing the stack to retransmit lost packets without head-of-line blocking that plagues TCP streams.
UDP port 443
TCP (port 50051)
gRPC defaults to TCP for reliable, ordered delivery of commands. Lost commands are retransmitted automatically.
TCP port 50051
TCP (port 443)
TCP three-way handshake, sequence numbers, ACKs, and congestion control ensure reliable page delivery.
TCP port 443
Network Layer
Logical addressing (IP) and routing across multiple networks. Packets find their path hop-by-hop.
IP Routing via LTE/5G
Phone has a public or NAT'd IP. Packets route from carrier core to YouTube CDN edge node nearest the user.
IPv4/IPv6, BGP
IP over Radio Link
IP radio creates a point-to-point or mesh IP network. Both laptop and drone have IP addresses; packets are routed between them.
IPv4, static routes
IP + DNS Resolution
DNS resolves the domain to a server IP. Router uses IP routing table to forward packets toward the destination.
IPv4/IPv6, DNS
Data Link Layer
Reliable transfer between adjacent nodes on the same physical medium. MAC addressing, framing, and error detection.
LTE/5G Radio Frames
LTE/5G protocols (MAC sublayer) schedule radio time slots and provide HARQ error correction between the phone and base station.
LTE MAC, HARQ
Radio MAC Protocol
The IP radio (e.g. 900 MHz or 2.4 GHz) uses its own link-layer framing with error correction and ARQ over the RF channel.
TDMA/CSMA, ARQ
Ethernet / Wi-Fi Frames
Ethernet or 802.11 Wi-Fi frame wraps the IP packet. MAC addresses identify src/dst on the local segment. CRC detects bit errors.
802.3 / 802.11
Physical Layer
Raw bit transmission over a medium. Defines voltages, frequencies, modulation, connectors, and cable specs.
RF Radio Waves (LTE/5G)
Bits are modulated onto radio frequency carriers (e.g. OFDM on LTE). The phone antenna transmits and receives electromagnetic waves.
OFDM, MIMO
RF Link (900 MHz / 2.4 GHz)
IP radio modulates data onto a sub-GHz or 2.4 GHz carrier. Directional or omni antennas establish the air link.
FSK/FHSS, RF power
Ethernet Copper / Wi-Fi RF
Wired: voltage pulses on copper (100BASE-TX) or light pulses on fibre. Wireless: OFDM modulated signals on 2.4/5/6 GHz bands.
Cat6 / 802.11ax
Data travels down all 7 layers on the sender — each layer adds a header (encapsulation) — and back up all 7 layers on the receiver, stripping headers as it goes.