i hear from my prof that osi reference model is not used and seldom was,then why do i have to study that in my network paper
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i hear from my prof that osi reference model is not used and seldom was,then why do i have to study that in my network paper
OSI reference model not used ??? ..... OSI ISO model divides the complex process of networking into seven distinct but interrelated layers.So the benefit is that each layer
can concentrate on its task thereby helping the upper layers.Also vendors can concentrate
their products on a particular task/layer. ISO makes things easier !!
Maybe your prof was just joking and you took him to be serious. If it wasn't for the OSI model, the networks as we know them would not be. The OSI Reference Model is a standard for all communicating devices so that they can talk to eachother.
TCP/IP may be a little different, I think it only has 4 layers, where OSI has 7, but they still follow the same general rule. When you send info from one computer to another, it uses the OSI model to turn the data into segments, packets, frames, and then binary code in the form of analog/digital/radio/light signals. It goes from Layer 7 (Application) down to Layer 1 (Physical). When the data is received at the other end, it goes from layer 1 up to layer 7, turning the raw binary code back into the data. If it wasn't for the OSI model, this process would become too complex. What if the other computer tried to re-assemble the packet differently?
Put it this way, if it weren't for the OSI Model (or a different standard), a network would become a place where thousands of different languages are flying around in no particular order, and communication would never happen.
The OSI Model is definately alive and well. Learn it, study it, understand it. If you are like me and going for CCNA and CCNP, you have to know it. Perhaps your prof just meant that you don't really have to know it to plug computers together, just like you don't really have to know how physics works to drive a car. In my studies, the OSI Model is like god...
Regards,
Dave
Ask him to describe the difference between a layer 2 and layer 3 switch then tell you again about the OSI model..
Your prof is probably unschooled into the depth of protocols and protocol stacks. He is quite unaware that when he sends this or that across the net exactly what happens to make those nice little *standardized* packets that any system can read, but only the one it's addressed to gets (yes, I'm not counting sniffers here, this is basic stuff).
The reason for the model is to set a standard from which all protocols are based, so that computers everywhere can communicate - it's the very foundation of networking. Without it, we'd be blocked from communication by 'language barriers' between computers. (hence the International Standards Organization invented it).
Tell Prof to stick that in his pipe with whatever else he's been smoking.
/me looks up 2 posts and sees that this has already been stated in a much larger form and apols for repeating.
This isn't the first time I have heard this nonsense. You wouldn't be a University of Maryland student would you? Tell him that all the computing models in the world have moved on to layer 8 and layers 1-7 are no longer needed. ;)
Yeah, and speaking of switches, just imagine compairing a Hub to a Switch. Why are switches so much better? Why don't you see hubs as much as before? Don't they do the same thing?
HELL NO. Hubs are Layer 1 devices, basically just multi-port repeaters. Switches work on Layer 2, the 'Data Link' layer. Therefore Switches are better because since they work on Layer 2, they offer MAC filtering to help keep wasted traffic flow down. (Though as ss2chef said, there are Layer 3 switches too, which are more advanced. I haven't studied them yet, though I'm guessing they would even offer some kind of IP filtering as well as MAC filtering.)
If it wasn't for the OSI model, how could we have come to the conclusion that Switches are better than hubs?
Dude, seriously, get a different prof, lol :P
Dave
Dammit, dammit, dammit.....Quote:
i hear from my prof that osi reference model is not used and seldom was
This means that I have to read another 20 bloody networking books to find out what we are using today..... My brain's already full.....
This is why those that are graduating with their batchelors and masters in computer science are no use whatsoever to me..... Because their professors are dumber than the students.... Unfortunately, the students feel some strange desire to listen to the dimwits!!!!!
xmeta: While there is no real need to "use it" in day to day network administration it is imperative that you understand it exists and how and why it works. If you don't know about it and how it works then you will never understand how your network is working.... The unfortunate lot of many admins today..... That's all well and good until you have a problem... Then you are at a severe disadvantage.
OSI knowledge can be helpful in troubleshooting and although it's in the abstract, it's used in this
forum quite a bit. When questions are being thrown about.
When you have your T1 provider on the phone about a down line and they tell you they have
layer 2 connectivity from the ATM cloud to your DSU, you should probably know what they are talking about..:)
SS2.... Yeah.... that's what I said.... You were just more direct..... I want him to apply himself to it by making it sound a little "important".... becuase when he interviews with me I might ask him about it to see if his prof knew his ****.... ;)
Exactly as Tiger said, and just to add a point taken from Cisco " The OSI reference model is considered the best tool available for teaching people about sending and receiving data on a network"Quote:
Originally posted here by Tiger Shark
xmeta: While there is no real need to "use it" in day to day network administration it is imperative that you understand it exists and how and why it works. If you don't know about it and how it works then you will never understand how your network is working... Then you are at a severe disadvantage.
It's really just a description of networks and how they existed. The problem is, in the OSI model, some protocols commonly in use span multiple layers. IP is technically both Layers 3 (Network) and 4 (Transport), while TCP is technically Layers 4 and 5 (Session). The trouble is, how do you describe UDP/IP on the OSI Model? UDP has no session layer, so it is Layer 4, and IP is Layers 3 and 4. You end up with quite a bit of duplication attempting to explain modern networking protocol use. That's just covering network layers, when you break it down, things like ASP and PHP are capable of encapsulating layer-5 implementations inside layer 7, while skipping layer 6 entirely. To retrieve a webpage, you go through Ethernet, IP, TCP, HTTP, possibly ASP/PHP Session protocols/handlers, and an interface rendering mechanism that renders HTML/DHTML/XHTML, CSS, JavaScript/VBScript, and so on.
It worked on pre-IP networks quite well, and it still serves a purpose today.
http://en.wikipedia.org/wiki/OSI_model
I think maybe this poor chap is confised. No system in the world uses OSI per se. Its not a protocol or anything of that nature. It is a way of describing how protocols operate. Mybe thats what his professor meant when he said nobody uses OSI.
Well..My professor said OSI IS the fundamental of networking. I think that's why ppl who finish masters can't connect two computers behind the router ...even if they connect it using the instruction manual ..they will lost on the further dis connection. LOL
Master degree sucks....wondering how i will b.
In my little and no practical knowledge. UDP and TCP both are in the transport layer difference is in the connection oriented and connection less. I never read anywhere that IP works on the transport layer. I don't think router works on the transport layer. Actually in the M$ networks router is a gateway and it works from 4-7 layers . dunno how it works...you may b right in this way butQuote:
Originally posted here by chsh
It's really just a description of networks and how they existed. The problem is, in the OSI model, some protocols commonly in use span multiple layers. IP is technically both Layers 3 (Network) and 4 (Transport), while TCP is technically Layers 4 and 5 (Session). The trouble is, how do you describe UDP/IP on the OSI Model? UDP has no session layer, so it is Layer 4, and IP is Layers 3 and 4.
http://en.wikipedia.org/wiki/OSI_model
How can IP b layer 4 protocol?
As per the wikipedia definition I linked:Quote:
Originally posted here by rajunpl
In my little and no practical knowledge. UDP and TCP both are in the transport layer difference is in the connection oriented and connection less. I never read anywhere that IP works on the transport layer. I don't think router works on the transport layer. Actually in the M$ networks router is a gateway and it works from 4-7 layers . dunno how it works...you may b right in this way but
How can IP b layer 4 protocol?
Because IP handles both QoS and routing, it fits on Layers 3 and 4. TCP fits here as well because of the fact that it tracks sessions, and handles retransmits. TCP also fits on layer 5 because it is stateful, and thus acts as the session layer. UDP is different, and is considered "connectionless" due to the lack of session capabilities.Quote:
* Network layer Layer 3. : The Network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the Transport layer. The Network layer performs network routing, flow control, segmentation/desegmentation, and error control functions. The router operates at this layer -- sending data throughout the extended network and making the Internet possible, although there are layer 3 (or IP) switches. This is a logical addressing scheme - values are chosen by the network engineer. The addressing scheme is hierarchical.
* Transport layer Layer 4. : The purpose of the Transport layer is to provide transparent transfer of data between end users, thus relieving the upper layers from any concern with providing reliable and cost-effective data transfer. The transport layer controls the reliability of a given link. Some protocols are stateful and connection oriented. This means that the session layer can keep track of the packets and retransmit those that fail.
* Session layer Layer 5. : The Session layer provides the mechanism for managing the dialogue between end-user application processes. It provides for either duplex or half-duplex operation and establishes checkpointing, adjournment, termination, and restart procedures. This layer is responsible for setting up and tearing down TCP/IP sessions.
I think what many organizations do is simply ignore the transport layer altogether, although if you examine both IP and TCP, you begin to see that they both perform functions that Layer 4 lists: IP manages transparent data transfer (seamless protocol encapsulation) and manages QoS stuff, while TCP handles retransmission of failed packets.
Whenever anything goes wrong, I think right .. layer 1 and move on from there :) It just comes naturally
a lot of the stuff you will learn you may think i wont need to know this .. but once you do you will probably use most of it automatically when your down the track and in an IT job .. like my statement above :)