Which is not a layer of the OSI Model
- Presentation
- Data Link
- Packet
- Transport
EXPLANATION
A network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data, which is also known as the payload
A packet is a small amount of data sent over a network, such as a LAN or the Internet. Similar to a real-life package, each packet includes a source and destination as well as the content (or data) being transferred. When the packets reach their destination, they are reassembled into a single file or other contiguous block of data.While the exact structure of a packet varies between protocols, a typical packet includes two sections — a header and payload. Information about the packet is stored in the header. For example, an IPv6 header includes the following fields:
- Source address (128 bits) - IPv6 address of the packet origin
- Destination address (128 bits) - IPv6 address of the packet destination
- Version (4 bits) - "6" for IPv6
- Traffic class (8 bits) - priority setting for the packet
- Flow label (20 bits) - optional ID that labels the packet as part of a specific flow; used to distinguish between multiple transmissions from a single origin
- Payload length (16 bits) - size of the data, defined in octets
- Next header (8 bits) - ID of the header following the current packet; may be TCP, UDP, or another protocol
- Hop limit (8 bits) - maximum number of network hops (between routers, switches, etc) before the packet is dropped; also known as "TTL" in IPv4
Packets are intended to transfer data reliably and efficiently. Instead of transferring a large file as a single block of data, sending smaller packets helps ensure each section is transmitted successfully. If a packet is not received or is "dropped," only the dropped packet needs to be resent. Additionally, if a data transfer encounters network congestion due to multiple simultaneous transfers, the remaining packets can be rerouted through a less congested path.
