Packet Switching

networking

Definition

]

Packet Switching

Let $N=(V,E)$ be a computer network with nodes $V$ and links $E$.

Packet switching is a data transmission method in which a message $M$ is partitioned into a sequence of packets $p_1,p_2,\dots ,p_k$, each routed independently through $N$ from a source $s\in V$ to a destination $t\in V$.

Each packet $p_i=(h_i,d_i)$ consists of a header $h_i$ carrying routing metadata (source, destination, sequence number) and a payload $d_i\subseteq M$ carrying a fragment of the message.

At each intermediate node $v$, the router inspects $h_i.\text{dst}$ and selects an outgoing link $e\in E$ according to a forwarding table $F_v$. Packets are stored-and-forwarded: a node receives the entire packet before forwarding it.

Mechanism

No dedicated path

No physical or logical circuit is established before transmission. Each packet is an independent datagram that may follow a different route through $N$.

Statistical Multiplexing

Links are shared by packets from many source–destination pairs. Resource allocation is on-demand rather than pre-allocated. This is called statistical multiplexing.

Store-and-Forward

A packet arriving at a node $v$ must be fully received and buffered before $v$ determines the next hop and begins transmission. This introduces a per-hop delay proportional to packet size.

Routing and forwarding

Each node maintains a forwarding table $F_v:V\to E\cup \{\perp \}$ mapping each destination to an outgoing link (or $\perp$ for local delivery). The table is populated by a routing protocol.