Frames and Packets Differ | Generated by AI
Yes, you’re basically correct in your intuition, but in computer networks “frame” and “packet” are not exactly the same thing — they belong to different layers of the network model (OSI or TCP/IP), even though in everyday speech people sometimes use them interchangeably.
Here’s the proper distinction and how they relate to what you said (“separate large data into small ones with start/end and length”):
| Layer (OSI) | Unit Name | Typical Name | Contains | Has start/end markers? | Has length field? | Example technologies |
|---|---|---|---|---|---|---|
| Layer 4 (Transport) | Segment (TCP) / Datagram (UDP) | – | Application data + transport header | No official “start/end”, relies on lower layers | Sometimes (UDP has length) | TCP, UDP |
| Layer 3 (Network) | Packet | IP packet / IP datagram | Transport segment + IP header | No explicit start/end flag (relies on Layer 2) | Yes (Total Length in IPv4/IPv6) | IP (IPv4, IPv6) |
| Layer 2 (Data Link) | Frame | Ethernet frame, Wi-Fi frame, PPP frame, etc. | IP packet + Layer-2 header + trailer | Yes (explicit start delimiter and usually end delimiter or length) | Yes (length/type field) | Ethernet, 802.11 Wi-Fi, PPP, Frame Relay |
| Layer 1 (Physical) | Bits/stream | – | Raw bits of the frame | Uses special bit patterns or coding (e.g., 8B/10B, 64b/66b) | – | Cables, fiber, radio |
Why you are right about “start, end, and length”
When we send a large file or stream, the original data is indeed chopped into smaller units at multiple layers:
Application data (could be many MB
↓ (TCP)
→ Many TCP segments (usually ≤ ~1460 bytes payload)
↓ (IP)
→ Each becomes an IP packet (adds IP header)
↓ (Ethernet/Wi-Fi/etc.)
→ Each IP packet is wrapped into a Layer-2 frame (adds Ethernet header + FCS trailer)
Every Ethernet frame, for example, has:
- Preamble + Start Frame Delimiter (7 + 1 byte) → marks the beginning
- Destination & Source MAC addresses
- EtherType/Length field
- Payload (the IP packet, 46–1500 bytes typically)
- Frame Check Sequence (4-byte CRC) → marks the end and checks integrity
So the receiver can perfectly detect where one frame ends and the next begins, even though bits are streaming continuously on the wire.
Summary of the difference
- Packet = Layer 3 (IP) concept → “I have an IP address and I can be routed across networks”.
- Frame = Layer 2 concept → “I live only on one local network segment and I have explicit start/end so the NIC can synchronize and detect boundaries”.
In casual conversation, especially when talking only about Ethernet LANs, people often say “packet” when they actually mean “frame”, but technically they are different.
So your understanding is correct in spirit:
“We take big data → split into small chunks → each chunk gets a header with length and start/end markers so the receiver can reassemble the big one correctly.”
The only refinement is that “frame” is the chunk with physical start/end markers (Layer 2), while “packet” is the chunk that can travel across the Internet (Layer 3).