6 ms·

An OSI model for the 21st century (2014)

90 points by eaguyhn 9y ago

tjalfi 9y ago
Please add (2014) to the title.
- hacknat 9y ago
  For sure! MacSec has gained in popularity lately, and a lot of the issues the author raises have been solved by other efforts.
justicezyx 9y ago
AFAIK, the general perception is that http is a transport & upper protocol. Not an application layer protocol. Anyway, OSI model is mostly a mental picture that bear little practical relevance. If someone want to follow OSI model and devise a new model, then itself is a wrong approach. TCP/IP was invented out of solving real internetworking problems, without regarding much to the OSI model or any pre-defined model per-se. As always, David Clark's "e2e principle" (https://en.wikipedia.org/wiki/End-to-end_principle https://en.wikipedia.org/wiki/End-to-end_principle) probably is the only guiding principle (or a after-fact summary) that is worth following.
- MrTonyD 9y ago
  I think it was back in the 80's when I was in a networking standards group (was it ANSI?? It's been a long time) and we were trying to define programming layers on top of sockets for UNIX. The effort completely failed - but the write-up about what we were trying to accomplish seemed to live on - getting revised and revised until it became the OSI model - with all its layers that we sort-of tried to implement. Of course, the new drivers and software layers didn't actually work, and the performance was abysmal, so the effort was abandoned. But the press and everyone else really liked the understandable text write-up about networking, which almost nobody understood at the time, so the write-up seemed to get a life of its own. Since then I've been scorned at job interviews and among peers for not having the model memorized, or not being able to explain the meaning of various layers. Just another example of our crazy methods of screening job candidates. Answering stupid questions from stupid people means more than actual experience.
  - Avernar 9y ago
    When I used to deal with people straight out of school they would always talk about the OSI model and it would drive me crazy. Everything we did would have to be categorized. What layer is this in, what layer is that in. I just want you to plug that Ethernet cable into that switch port and configure the static IP address in the software so we can get the hell out of here and have a beer. No amount of explaining that stuff in the real world doesn't neatly fit into those categories would get them to shut up about it. One guy nearly had a mental breakdown when he first came across a tunnel. "How can you have two network layers?!?" One day I was installing something in a computer lab at a college and on the wall was a giant poster of the OSI model with all the protocols imaginable listed on it. I had to fight the urge to set it on fire... Yes, models are great for teaching and for certain types of discussions (L2 vs L3 switches) but the real world is always more complicated and the lines in the model tend to blur. Take the basic computer model taught to new students with the CPU, memory, input, output, storage, networking all neatly connected in that familiar diagram. A real computer is never connected that way. Memory is all over the place, storage can be directly on the CPU or hundreds of feet away in another box, etc. Students quickly figure out that the computer model is just a teaching tool. Just holding a motherboard quickly makes them see that. But for networking they seem to hang on to the OSI model like if it were a piece of flotsam after a shipwreck.
    - gerdesj 9y ago
      "Two network layers?!?" Hah, yes and in the real world we do far weirder things than that. VXLANs running over [whatever], OpenVPN inside IPSEC and then ssh or RDP inside that. Obviously you don't do all of that routinely but I've seen some crazy shit to work around something or link up odd setups. I have seen a triple nested VPN: IPSEC within IPSEC and OpenVPN inside. I'm sure many here will have seen similar or worse.
    - deleted 9y ago
      [deleted]
    - dkffkld 9y ago
      > L2 vs L3 switches The fuck are those? Some Cisco bullshit as usual? I swear to God they must've already come up with every possible combination of switch and router by now.
- justonepost 9y ago
  Well, there are themes that are evolving that are worth cataloging in a new logical model that can help guide further innovation. I agree though, the model itself isn't the root.
- justonepost 9y ago
  Well, there are themes that are evolving that are worth cataloging in a new logical model that can help guide further innovation. I agree though, the model itself isn't the root.
- Avernar 9y ago
  The end to end principle pretty much made the flow control and re-transmission functions of the LLC sublayer of the data link layer obsolete. So now we pay a 6 to 8 byte penalty (8 bytes if the MAC can tell us the packet length) on every frame transmitted. Wired/optical Ethernet does not normally use LPD (LLC Protocol Discrimination, i.e. 802.2 LLC/SNAP) but unfortunately WiFi does. So in 2014 while the author is advocating for the data link layer to ensure packets are received by other devices on the channel like the current OSI model does, the IEEE is encouraging new standards to use EPD (Ethernet Protocol Discrimination) instead of LPD. The IEEE just wants the LLC sublayer to only do multiplexing of protocols now. The author completely missed how the upper layer protocols, i.e. TCP/IP, has made some parts of the lower layer protocols unnecessary. Having a basic model is good thing for classifying different parts of the network and makes discussions clearer. But in the real world things rarely fall into categories that neatly.
convolvatron 9y ago
its hiding in the discourse, but I think author would be better off completely abandoning the notion of a canonical stack and provide a categorization of functions - routing, identity, reliability, etc
oldandtired 9y ago
I have read the various comments against the OSI model and the one interesting observation is that none of you seem to have ever worked with a compliant implementation of the OSI model. Honeywell had a commercial product called DSA (Distributed Systems Architecture). We did write distributed applications that used the OSI protocol stack communications and it worked well. Within the applications, we didn't have to worry much about what was happening at the lower levels as those levels simply provided specific services we used. It was used for many years with very good results. One of the features of the software at the time was that you get two dumb terminals to communicate with each other across the network by simply using the relevant connection protocols. This allowed simple communication streams to occur without having any applications involved, it was handled by the protocols themselves. It also meant that it was very easy to replace those dub terminals with an application without having to change any of the configurations in the network. TCP/IP rose to the fore due to various reasons that were not related to their technological superiority. To see this you have to look more closely to the history of those times.
- wogna 9y ago
  For my job I had the opportunity to work with quite some OSI standards on top of TCP/IP (X.216, X.227 and X.500, X.400 as application layers). My experience is quite in line with the common critique: most of these standards add more overhead than they're worth. It was also quite hard to bend these protocols into our use case (when bandwidth comes at a premium, it doesn't take long before the customer starts complaining). I don't really see how a "dumb terminal" is a noteworthy feature of OSI? That's essentially what telnet does, and it too can just piggyback on top of TCP (probably the only protocol that makes use of all TCP flags available).
  - oldandtired 9y ago
    What commercial software were you using? TCP/IP was not part of the protocol stack we were using. The dumb terminal was sitting at the top of the protocol stack and wasn't using an application like telnet to access remote devices or applications. The point of my example was simply that a dumb terminal or any device or an application were treated the same in relation to the protocol stack. It did not matter. The top speed of our links was the enormous 64 kb/s and we often had to use far slower services. We found that the overheads of the communication protocols was very small compared to the application processing overheads. It was a different time, I suppose and I find that I have to wait longer these days even when using ADSL than I did in those days.
carapace 9y ago
John Day maintains that OSI was never fully implemented. Cf. "Recursive InterNetwork Architecture" https://en.wikipedia.org/wiki/Recursive_InterNetwork_Architecture_(RINA) https://en.wikipedia.org/wiki/Recursive_InterNetwork_Archite...
mmmBacon 9y ago
Well it turns out that security is getting set up in other layers but these are for more specialized applications than general run of the mill internet usage. For example there is encryption available at the physical layer even at very high data rates. Additionally there is MacSec which is a layer 2 technology. It's curious that the author mentions neither.

90 points by eaguyhn 9y ago

tjalfi 9y ago

Please add (2014) to the title.

hacknat 9y ago
For sure! MacSec has gained in popularity lately, and a lot of the issues the author raises have been solved by other efforts.

justicezyx 9y ago

AFAIK, the general perception is that http is a transport & upper protocol. Not an application layer protocol. Anyway, OSI model is mostly a mental picture that bear little practical relevance. If someone want to follow OSI model and devise a new model, then itself is a wrong approach. TCP/IP was invented out of solving real internetworking problems, without regarding much to the OSI model or any pre-defined model per-se. As always, David Clark's "e2e principle" (https://en.wikipedia.org/wiki/End-to-end_principle https://en.wikipedia.org/wiki/End-to-end_principle) probably is the only guiding principle (or a after-fact summary) that is worth following.

MrTonyD 9y ago
I think it was back in the 80's when I was in a networking standards group (was it ANSI?? It's been a long time) and we were trying to define programming layers on top of sockets for UNIX. The effort completely failed - but the write-up about what we were trying to accomplish seemed to live on - getting revised and revised until it became the OSI model - with all its layers that we sort-of tried to implement. Of course, the new drivers and software layers didn't actually work, and the performance was abysmal, so the effort was abandoned. But the press and everyone else really liked the understandable text write-up about networking, which almost nobody understood at the time, so the write-up seemed to get a life of its own. Since then I've been scorned at job interviews and among peers for not having the model memorized, or not being able to explain the meaning of various layers. Just another example of our crazy methods of screening job candidates. Answering stupid questions from stupid people means more than actual experience.
- Avernar 9y ago
  When I used to deal with people straight out of school they would always talk about the OSI model and it would drive me crazy. Everything we did would have to be categorized. What layer is this in, what layer is that in. I just want you to plug that Ethernet cable into that switch port and configure the static IP address in the software so we can get the hell out of here and have a beer. No amount of explaining that stuff in the real world doesn't neatly fit into those categories would get them to shut up about it. One guy nearly had a mental breakdown when he first came across a tunnel. "How can you have two network layers?!?" One day I was installing something in a computer lab at a college and on the wall was a giant poster of the OSI model with all the protocols imaginable listed on it. I had to fight the urge to set it on fire... Yes, models are great for teaching and for certain types of discussions (L2 vs L3 switches) but the real world is always more complicated and the lines in the model tend to blur. Take the basic computer model taught to new students with the CPU, memory, input, output, storage, networking all neatly connected in that familiar diagram. A real computer is never connected that way. Memory is all over the place, storage can be directly on the CPU or hundreds of feet away in another box, etc. Students quickly figure out that the computer model is just a teaching tool. Just holding a motherboard quickly makes them see that. But for networking they seem to hang on to the OSI model like if it were a piece of flotsam after a shipwreck.
  - gerdesj 9y ago
    "Two network layers?!?" Hah, yes and in the real world we do far weirder things than that. VXLANs running over [whatever], OpenVPN inside IPSEC and then ssh or RDP inside that. Obviously you don't do all of that routinely but I've seen some crazy shit to work around something or link up odd setups. I have seen a triple nested VPN: IPSEC within IPSEC and OpenVPN inside. I'm sure many here will have seen similar or worse.
  - deleted 9y ago
    [deleted]
  - dkffkld 9y ago
    > L2 vs L3 switches The fuck are those? Some Cisco bullshit as usual? I swear to God they must've already come up with every possible combination of switch and router by now.
justonepost 9y ago
Well, there are themes that are evolving that are worth cataloging in a new logical model that can help guide further innovation. I agree though, the model itself isn't the root.
justonepost 9y ago
Well, there are themes that are evolving that are worth cataloging in a new logical model that can help guide further innovation. I agree though, the model itself isn't the root.
Avernar 9y ago
The end to end principle pretty much made the flow control and re-transmission functions of the LLC sublayer of the data link layer obsolete. So now we pay a 6 to 8 byte penalty (8 bytes if the MAC can tell us the packet length) on every frame transmitted. Wired/optical Ethernet does not normally use LPD (LLC Protocol Discrimination, i.e. 802.2 LLC/SNAP) but unfortunately WiFi does. So in 2014 while the author is advocating for the data link layer to ensure packets are received by other devices on the channel like the current OSI model does, the IEEE is encouraging new standards to use EPD (Ethernet Protocol Discrimination) instead of LPD. The IEEE just wants the LLC sublayer to only do multiplexing of protocols now. The author completely missed how the upper layer protocols, i.e. TCP/IP, has made some parts of the lower layer protocols unnecessary. Having a basic model is good thing for classifying different parts of the network and makes discussions clearer. But in the real world things rarely fall into categories that neatly.

convolvatron 9y ago

its hiding in the discourse, but I think author would be better off completely abandoning the notion of a canonical stack and provide a categorization of functions - routing, identity, reliability, etc

oldandtired 9y ago

I have read the various comments against the OSI model and the one interesting observation is that none of you seem to have ever worked with a compliant implementation of the OSI model. Honeywell had a commercial product called DSA (Distributed Systems Architecture). We did write distributed applications that used the OSI protocol stack communications and it worked well. Within the applications, we didn't have to worry much about what was happening at the lower levels as those levels simply provided specific services we used. It was used for many years with very good results. One of the features of the software at the time was that you get two dumb terminals to communicate with each other across the network by simply using the relevant connection protocols. This allowed simple communication streams to occur without having any applications involved, it was handled by the protocols themselves. It also meant that it was very easy to replace those dub terminals with an application without having to change any of the configurations in the network. TCP/IP rose to the fore due to various reasons that were not related to their technological superiority. To see this you have to look more closely to the history of those times.

wogna 9y ago
For my job I had the opportunity to work with quite some OSI standards on top of TCP/IP (X.216, X.227 and X.500, X.400 as application layers). My experience is quite in line with the common critique: most of these standards add more overhead than they're worth. It was also quite hard to bend these protocols into our use case (when bandwidth comes at a premium, it doesn't take long before the customer starts complaining). I don't really see how a "dumb terminal" is a noteworthy feature of OSI? That's essentially what telnet does, and it too can just piggyback on top of TCP (probably the only protocol that makes use of all TCP flags available).
- oldandtired 9y ago
  What commercial software were you using? TCP/IP was not part of the protocol stack we were using. The dumb terminal was sitting at the top of the protocol stack and wasn't using an application like telnet to access remote devices or applications. The point of my example was simply that a dumb terminal or any device or an application were treated the same in relation to the protocol stack. It did not matter. The top speed of our links was the enormous 64 kb/s and we often had to use far slower services. We found that the overheads of the communication protocols was very small compared to the application processing overheads. It was a different time, I suppose and I find that I have to wait longer these days even when using ADSL than I did in those days.

carapace 9y ago

John Day maintains that OSI was never fully implemented. Cf. "Recursive InterNetwork Architecture" https://en.wikipedia.org/wiki/Recursive_InterNetwork_Architecture_(RINA) https://en.wikipedia.org/wiki/Recursive_InterNetwork_Archite...

mmmBacon 9y ago

Well it turns out that security is getting set up in other layers but these are for more specialized applications than general run of the mill internet usage. For example there is encryption available at the physical layer even at very high data rates. Additionally there is MacSec which is a layer 2 technology. It's curious that the author mentions neither.