5 ms·

To be really specific, they are not "packets" but at the TCP protocol level, they are "segments" TFA appears to use both terms sort of interchangeably, which i

To be really specific, they are not "packets" but at the TCP protocol level, they are "segments" TFA appears to use both terms sort of interchangeably, which is uncool when describing a formalized protocol standard! Segments are encapsulated in IP datagrams, or packets, which are, in turn, encapsulated in other PDU types, such as Ethernet frames.

Ekaros 2y ago
And one could ask are segments without well data segment a segments? As mostly 2 first PDUs in exchange do not contain data...
- AStonesThrow 2y ago
  Yes they are. I don't know what "well data segment" is, but perhaps you mean a payload. TCP streams consist of segments, and the fragmentation or collection of those logical segments into packets is a function of the lower-layer protocols which are not TCP. https://www.rfc-editor.org/rfc/rfc9293.html https://www.rfc-editor.org/rfc/rfc9293.html
  - tsimionescu 2y ago
    I think one important mention here is that fragmentation happens at two levels: most commonly, an upper layer protocol message (such as an HTTP request) is fragmented into several TCP segments, each with one TCP header. Those TCP segments themselves can sometimes be fragmented into multiple IP packets if the TCP MSS (maximum segment size) is larger than the Ethernet MTU (maximum transmission unit). IP fragmentation is typically avoided, and in IPv6 it is only allowed at the originator of a packet - if a router is trying to route an IPv6 packet larger than the MTU of the outgoing link's MTU, it must drop the packet and send a signal about the MTU back. An IPv4 router may fragment the packet, but this rarely works well in practice.
    - AStonesThrow 2y ago
      I suppose, if you want to squeeze it into the definition given in RFC 9293, but that same RFC only uses "fragmentation" to denote "internet fragments" or IP-level fragmentation. You're referring to "segmentation" which is also defined in that RFC. https://www.rfc-editor.org/rfc/rfc9293.html#name-segmentation https://www.rfc-editor.org/rfc/rfc9293.html#name-segmentatio...
iwontberude 2y ago
Appreciate pedantry when it’s absolutely warranted. Well said!

Ekaros 2y ago

And one could ask are segments without well data segment a segments? As mostly 2 first PDUs in exchange do not contain data...

AStonesThrow 2y ago
Yes they are. I don't know what "well data segment" is, but perhaps you mean a payload. TCP streams consist of segments, and the fragmentation or collection of those logical segments into packets is a function of the lower-layer protocols which are not TCP. https://www.rfc-editor.org/rfc/rfc9293.html https://www.rfc-editor.org/rfc/rfc9293.html
- tsimionescu 2y ago
  I think one important mention here is that fragmentation happens at two levels: most commonly, an upper layer protocol message (such as an HTTP request) is fragmented into several TCP segments, each with one TCP header. Those TCP segments themselves can sometimes be fragmented into multiple IP packets if the TCP MSS (maximum segment size) is larger than the Ethernet MTU (maximum transmission unit). IP fragmentation is typically avoided, and in IPv6 it is only allowed at the originator of a packet - if a router is trying to route an IPv6 packet larger than the MTU of the outgoing link's MTU, it must drop the packet and send a signal about the MTU back. An IPv4 router may fragment the packet, but this rarely works well in practice.
  - AStonesThrow 2y ago
    I suppose, if you want to squeeze it into the definition given in RFC 9293, but that same RFC only uses "fragmentation" to denote "internet fragments" or IP-level fragmentation. You're referring to "segmentation" which is also defined in that RFC. https://www.rfc-editor.org/rfc/rfc9293.html#name-segmentation https://www.rfc-editor.org/rfc/rfc9293.html#name-segmentatio...

iwontberude 2y ago

Appreciate pedantry when it’s absolutely warranted. Well said!