ISO is a theoretical model on how things work, suitable for teaching and for reference. In reality, there are only 4 layers and not the finely chiseled concern-separating layers at the bottom.
The IP suite is not nearly as neatly layered as OSI was and the OSI model doesn't neatly fit the IP suite since it wasn't actually designed for IP at all. In the IP suite layers 5 and 6 basically don't exist in the OSI sense, TCP handles things that are part of both layers 4 and 5 in the model despite being a single protocol, etc. The OSI model is often considered obselete as it just doesn't actually fit the IP world all that well but it's been around so long and does have uses in certain situations that it tends to stick around.
ISO/OSI is a neatly separated model mostly used on theory.
In practice, actual network stacks are often modeled after a simpler model that is called TCP/IP. Which despite the name is not actually TCP specific.
Here's the general description and correspondence to ISO/OSI:
Host to network / network access layer: it's mostly the nic and nic driver. It's sometimes numbered as 0 because some don't consider it part of the TCP/IP stack, but simply the nic driver. Corresponds to:
Physical
Datalink
Network layer: Corresponds to:
3. Network
Transport layer: Corresponds to:
4. Transport
Application layer: everything that's part of the application and not the network stack. Corresponds to:
5. Session
6. Presentation
7. Application
Or, you can just not care about how the actual software stack is separated, and continue to use the most complete model, knowing that everyone will understand what you when you say "layer 2/3/4" anyway.
Plus, some could say that the TCP/IP model is equally unfit because the Linux network subsystem doesn't care about layers.
Edit: I hope the formatting of that table isn't broken on your client, because it is on mine
IP is the internet layer which is layer 2 and TCP is the transport layer which is layer 3.
Why split physical and data link when they are so closely related? You can't use vpi/vci on an ethernet port, you can't use MAC addresses on a frame relay port. Bundle that shit together.
Presentation, application, and session are all dealt with by the application anyway so why bother splitting them out from a network point of view?
Why split physical and data link when they are so closely related?
100 mb Ethernet can be run over cat 5e, Cat 6, etc. You can even have Ethernet frames running over coax. (Not just the original standard which was coax but there are modern bridges for using cable TV coax in your house to reach rooms where you can't pull cat5.)
Why split physical and data link when they are so closely related?
You can run Ethernet on any medium that has the capacity to transmit digital signals. It can be copper, optical, over-air laser, radio, on top of an analog carrier wave (ASK, FSK, PSK). The Ethernet traffic can be completely independent from the physical medium by using encapsulation (L2TP or any other protocol that encapsulates Layer-2). It can be pigeons carrying printouts of the Ethernet frames, scanned and reassembled at the destination. The same can be said about most Layer-2 protocols.
As long as the proper interfaces are present, the physical layer is completely transparent to the data link layer.
(edit) I should point out that Ethernet, specifically, transmits extra data before and after the frame (the preamble and inter-packet gap) that are used to configure the Rx circuit for reception, but the Layer-2 frame will be identical regardless of the medium.
OSI is much more important when you are doing wireless protocol design. TCP/IP is when you want to abstract out a lot of the lower layer functionality which is concerned with collision domains. It is definitely still taught in engineering school for a reason.
Application: full of itself; just look at it; leaking out of its constraints.
Presentation: not happy; has to talk to the app.
Session: chillin; don't start nothin, won't be nothin.
Transport: ready for whatever comes its way.
Network: acting up as usual.
Data Link: Hidden but watching, well-behaved, compliant.
Physical: draping out of the rack
It's missing layer 8 with a cat slowly and intentionally pushing the stack over while looking the IT cat directly in the eyes as it finally topples over. Then complains that nothing's working but also not providing any helpful information.
41 Comments
slazer2au@lemmy.world · 31 pts · 270d
Easier way is to remember that the ISO model is defunked and you should use the TCP/IP model.
BaroqueInMind@piefed.social · 25 pts · 270d
IP is layer 3 and TCP is layer 4.
Please elaborate your nonsensical comment.
bleistift2@sopuli.xyz · 25 pts · 270d
ISO is a theoretical model on how things work, suitable for teaching and for reference. In reality, there are only 4 layers and not the finely chiseled concern-separating layers at the bottom.
credo@lemmy.world · 7 pts · 269d
ISO is an organization. OSI is a model.
Edit: there are also definitely more than four “layers” (standard handoff points).
Physical involves the media and transmission format (e.g. EMF, waveform, etc)
data link involves multiplexing and addressing on the local segment
Network involves beyond-segment addressing
Transport involves standard endpoint communication methods (tcp/udp)
Are you implying this is where everything ends?
What about application level multiplexing (sockets)?
a_non_monotonic_function@lemmy.world · 1 pts · 269d
I'm not implying anything.
Scoopta@programming.dev · 16 pts · 270d
The IP suite is not nearly as neatly layered as OSI was and the OSI model doesn't neatly fit the IP suite since it wasn't actually designed for IP at all. In the IP suite layers 5 and 6 basically don't exist in the OSI sense, TCP handles things that are part of both layers 4 and 5 in the model despite being a single protocol, etc. The OSI model is often considered obselete as it just doesn't actually fit the IP world all that well but it's been around so long and does have uses in certain situations that it tends to stick around.
edinbruh@feddit.it · 10 pts · 270d
ISO/OSI is a neatly separated model mostly used on theory.
In practice, actual network stacks are often modeled after a simpler model that is called TCP/IP. Which despite the name is not actually TCP specific.
Here's the general description and correspondence to ISO/OSI:
Or, you can just not care about how the actual software stack is separated, and continue to use the most complete model, knowing that everyone will understand what you when you say "layer 2/3/4" anyway.
Plus, some could say that the TCP/IP model is equally unfit because the Linux network subsystem doesn't care about layers.
Edit: I hope the formatting of that table isn't broken on your client, because it is on mine
slazer2au@lemmy.world · 3 pts · 270d
IP is the internet layer which is layer 2 and TCP is the transport layer which is layer 3.
Why split physical and data link when they are so closely related? You can't use vpi/vci on an ethernet port, you can't use MAC addresses on a frame relay port. Bundle that shit together.
Presentation, application, and session are all dealt with by the application anyway so why bother splitting them out from a network point of view?
Blue_Morpho@lemmy.world · 8 pts · 270d
100 mb Ethernet can be run over cat 5e, Cat 6, etc. You can even have Ethernet frames running over coax. (Not just the original standard which was coax but there are modern bridges for using cable TV coax in your house to reach rooms where you can't pull cat5.)
rtxn@lemmy.world · 7 pts · 270d
You can run Ethernet on any medium that has the capacity to transmit digital signals. It can be copper, optical, over-air laser, radio, on top of an analog carrier wave (ASK, FSK, PSK). The Ethernet traffic can be completely independent from the physical medium by using encapsulation (L2TP or any other protocol that encapsulates Layer-2). It can be pigeons carrying printouts of the Ethernet frames, scanned and reassembled at the destination. The same can be said about most Layer-2 protocols.
As long as the proper interfaces are present, the physical layer is completely transparent to the data link layer.
(edit) I should point out that Ethernet, specifically, transmits extra data before and after the frame (the preamble and inter-packet gap) that are used to configure the Rx circuit for reception, but the Layer-2 frame will be identical regardless of the medium.
ulterno@programming.dev · 0 pts · 269d
RFC 2549
coolman@lemmy.world · 3 pts · 270d
Nobody responding to you understands that this is a joke, which kinda boggles the mind
BaroqueInMind@piefed.social · 1 pts · 270d
What worries me more is that no one here, including myself, actually understands the concepts of the OSI model that is foundational knowledge.
UnculturedSwine@lemmy.dbzer0.com · 1 pts · 269d
TCP/IP is also the name of a model different from OSI. It has 4 layers instead of 7: https://www.hostwinds.com/blog/osi-vs-tcpip-differences-and-similarities
aubeynarf@lemmynsfw.com · 3 pts · 270d
invictvs@lemmy.world · 2 pts · 264d
Yes, except if you are in my University, where professors are fossils and knowing OSI is required to pass the CN exam.
socsa@piefed.social · 1 pts · 269d
OSI is much more important when you are doing wireless protocol design. TCP/IP is when you want to abstract out a lot of the lower layer functionality which is concerned with collision domains. It is definitely still taught in engineering school for a reason.
neidu3@sh.itjust.works · 1 pts · 270d
TCP/IP model is Limited and incomplete.
Fibrechannel, infiniband, and many RDMA protocols, just to make a few, don't fit in the TCP/IP model, while the OSI model fits them just fine.
slazer2au@lemmy.world · 2 pts · 270d
How don't they fit?
neidu3@sh.itjust.works · 1 pts · 270d
Neither TCP, UDP, nor IP, is involved.
slazer2au@lemmy.world · 2 pts · 270d
But they don't run CLNS so the ISO model doesn't fit either.
neidu3@sh.itjust.works · 1 pts · 270d
OSI model != OSI protocols
CLNS is not a pre-requisite for Layer 3.
recursivethinking@lemmy.world · 25 pts · 270d
Accurate
Application: full of itself; just look at it; leaking out of its constraints.
Presentation: not happy; has to talk to the app.
Session: chillin; don't start nothin, won't be nothin.
Transport: ready for whatever comes its way.
Network: acting up as usual.
Data Link: Hidden but watching, well-behaved, compliant.
Physical: draping out of the rack
DickFiasco@sh.itjust.works · 18 pts · 270d
Internet is cats, all the way down.
Flyswat@lemmy.dbzer0.com · 14 pts · 270d
Please Do Not Throw Sausage Pizza Away !
Bougie_Birdie@piefed.blahaj.zone · 14 pts · 270d
My professor tried to teach us that one too, but a classmate came up with an unforgettable mnemonic. Very cursed ::: spoiler Mildly NSFW
Please Daddy, Not The Sex Pipe Again :::
The professor hadn't heard that one before
Deebster@infosec.pub · 3 pts · 269d
Given that the internet is a series of tubes, it's a better mnemonic since the pipe connection will help you remember it.
Randelung@lemmy.world · 9 pts · 270d
Ah yes, the EtherCAT.
aeternum@lemmy.blahaj.zone · 9 pts · 270d
SGG@lemmy.world · 4 pts · 270d
But Few Purchase Software (Bits, Frames, Packets, Segments)
wasabi@lemmy.eco.br · 4 pts · 270d
Please Do Not Throw Sausage Pizza Away
AngryCommieKender@lemmy.world · 3 pts · 270d
Well I was Gonna eat It so, No Worries.
b3nj@lemmy.world · 2 pts · 269d
People Don't Need Their Stupid Packets Anyway
GreenKnight23@lemmy.world · 7 pts · 270d
I have only ever know two devs that knew what the fuck OSI was. two out of at least one-hundred and fifty.
it's nice to see a technical joke on here that's more than just "hehe your language is bad".
_thebrain_@sh.itjust.works · 2 pts · 270d
I think "technical" is a bit of a stretch... But who doesn't like a good cat meme?
Big_Boss_77@lemmynsfw.com · 7 pts · 269d
Layer 8...
socsa@piefed.social · 6 pts · 270d
Please do not touch Sally's pretty anus.
Brickhead92@lemmy.world · 6 pts · 270d
It's missing layer 8 with a cat slowly and intentionally pushing the stack over while looking the IT cat directly in the eyes as it finally topples over. Then complains that nothing's working but also not providing any helpful information.
lucg@lemmy.world · 5 pts · 269d
Missing the latest addition to the OSI model: AI!
Layer 8 (sender): turning a few keywords into a well-formed text
Layer 8 (receiver): summarising text back into its short form
elvith@feddit.org · 5 pts · 270d
I thought the easy way were "A Pussy So Tight No Dick Penetrates"?
dreadbeef@lemmy.dbzer0.com · 3 pts · 270d
Believe it or not this made it harder
Little8Lost@lemmy.world · 3 pts · 270d
https://http.cat/status/509
Gonzako@lemmy.world · 2 pts · 270d
thank god I dropped out before going into the real nerd stuff