What is the difference between packet and datagram

Eddie Eddie There's a problem with this answer - the same as with JFL's see my comment there — z33k. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Explaining the semiconductor shortage, and how it might end. Does ES6 make JavaScript frameworks obsolete? Upcoming Events. Featured on Meta. Now live: A fully responsive profile.

Related 2. Hot Network Questions. Question feed. Unfortunately, these terms can also cause confusion, because they are not always applied in a universal or even consistent manner.

Some people are strict about applying particular message designations only to the appropriate technologies where they are normally used, whille others use the different terms completely interchangeably. This means that you should be familar with the different message types and how they are normally used, but you should still be prepared for the unexpected.

The most common terms used for messages are the following: Packet This term is consided by many to correctly refer to a message sent by protocols operating at the network layer of the OSI Reference Model.

However, this termin is commonly also used to refer generically to any type of message, as i menitoned earlier. Datagram This term is basically synonymous with packet and is also used to refer to network layer technologie. It is also often used to refer to a message that is sent at a higher level of the OSI Reference Model more often than packet is.

In particular, it is most commonly seen used in reference to data link layer messages. It is occasionally also used to refer to physical layer messages, when message formatting is performed by a layer 1 technology. A frame gets its name from the fact that it is created by taking higher-level packets or datagrams and "framing" them with additional header information needed at the lower level. Cell Frames and packets, in general, can be of variable length, depending on their contents; in contrast, a cell is most often a message that is fixed in size.

For example, the fixed-length, byte messages sent in ATM are called cells. Like frames, cells are usually used by technologies operating at the lower layers of the OSI Model.

I should also point out that there are certain protocols that use unusual names, which aren't used elsewhere in the world of networking, to refer to their messages. One prominent example is TCP, which calls its messages segments. In this book, i have made a specific effort not to imply anything about the nature of a message solely based on the name it uses, but i do follow the most common name used for a particular technology.

All forum topics Previous Topic Next Topic. Accepted Solutions. Peter Paluch. Hall of Fame Cisco Employee. In response to Peter Paluch. Again, thank you very much. Your answers are truely and literally priceless!

Joseph W. Hall of Fame Expert. I just want to add some old but reliable information found at IETF. According to RC, datagram is IP data blocks and packet is resultant of datagram fragmentation. In response to mmeridaa1. Further IP supports fragmentation and reassembly of long datagrams through "small packet" networks. The way I would read the above, datagrams is being used as a term specific to IP.

Further, packet switched networks can carry IP datagrams along with other packets. In response to Joseph W. Hi Joseph. I agree with you almost totally. My english is very bad and I thik that to use the word "resultant" was not a good idea. Second, a packet-switched network might not be limited to only IP. Fragmented or non-fragments packets are forwarded alike. Again, if fragmented, the fragmented datagrams packets are forwarded generally the same as any other non-fragmented datagram packet.

However, the fragmented packets receiver will reconstruct the original datagram. Post Reply. Latest Contents. The IT Blog Awards is now accepting submissions! Created by caiharve on PM. Submit your blog, vlog or podcast today. They make geeky cool. A packet is a general term for a formatted unit of data carried by a network.

It is not necessarily connected to a specific OSI model layer. For example, in the Ethernet protocol on the physical layer layer 1 , the unit of data is called an "Ethernet packet", which has an Ethernet frame layer 2 as its payload. But the unit of data of the Network layer layer 3 is also called a "packet".

A frame is also a unit of data transmission. In computer networking the term is only used in the context of the Data link layer layer 2.