Module 1: Foundations

Packet Switching — Store-and-Forward and Statistical Multiplexing

Learn about packet switching — store-and-forward and statistical multiplexing

Duration: 7 minutes
Level: Intermediate
Lesson: 12

The Revolutionary Idea

In Lesson 2, we saw that circuit switching reserves a dedicated 64 kbps channel for the entire duration of a call — even during silence. This guarantees quality but wastes capacity. In the 1960s, researchers at ARPA, NPL, and RAND independently arrived at a radical alternative: what if we chopped data into small pieces, sent them independently, and let the network figure out how to deliver them?

This is packet switching, and it's the foundation of the entire internet — including every VoIP call that traverses it.

Store-and-Forward vs. Cut-Through

Packet-switched networks use store-and-forward at each hop:

  1. A packet arrives at a router
  2. The router receives the entire packet and stores it in a buffer
  3. The router examines the header to determine the next hop
  4. The router forwards the packet to the next hop
  5. Repeat until the packet reaches its destination

This is fundamentally different from circuit switching, where the electrical signal flows continuously through pre-established connections. Each hop in a packet network introduces processing delay (examining headers), queuing delay (waiting behind other packets), and serialization delay (time to push all bits onto the outgoing link).

Cut-through switching is an optimization used in some Ethernet switches: the switch starts forwarding the packet as soon as it reads the destination address, before receiving the entire frame. This reduces latency but can't detect corrupted frames (no FCS check). It's relevant at Layer 2 but not at Layer 3 (routers always store-and-forward because they may need to modify headers, check TTL, etc.).

Statistical Multiplexing — The Efficiency Breakthrough

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