Circuit switching and packet switching
Circuit vs packet switching
- There are two ways to move data across a network.
- Circuit switching reserves a path; packet switching sends independent packets.
- The modern internet uses packet switching.
Circuit switching
- A dedicated path is set up between the two ends before any data is sent, reserved for the whole conversation, then released.
- Pros: reserved bandwidth and in-order delivery.
- Cons: inefficient during silences (the line is idle but reserved) and slow to set up.
- Classic example: the traditional telephone network.
Practice
In circuit switching:
Circuit switching reserves one path end-to-end (reserved bandwidth) — but it wastes the line during silences.
Packet switching
- The data is split into packets, each sent independently with the destination address and a sequence number.
- Routers make a per-packet decision, so packets may take different routes and arrive out of order; the destination reassembles them by sequence number.
- Pros: efficient (a link is shared by many conversations) and robust (reroute around failures). Cons: variable latency and possible loss (TCP handles reliability).
Practice
In packet switching, packets:
Each packet is routed independently; the destination reassembles them using sequence numbers.
Practice
A key advantage of packet switching is that it is:
Sharing links is efficient and rerouting makes it resilient. The trade-off is variable latency and possible loss (TCP fixes that).
Practice
How does the destination put packets back in the right order?
Each packet carries a sequence number, so the destination can reassemble the message and re-request any missing packet.
Comparison
| Aspect | Circuit switching | Packet switching |
|---|---|---|
| Path | dedicated, reserved | shared, per-packet |
| Setup | slow | none |
| Bandwidth use | inefficient | efficient |
| On failure | the circuit is cut | reroute around it |
| Suits | constant voice flows | bursty web/email |
Practice
The modern internet uses:
The internet uses packet switching for its efficiency and resilience.
You've got it
Key idea
- circuit switching reserves a dedicated path (reserved bandwidth, but wasteful + slow setup)
- packet switching sends independent packets that may take different routes
- packets carry sequence numbers so the destination can reassemble them in order
- the internet uses packet switching — efficient and robust