Comparison Between OSI And TCP / IP
Wednesday, June 3, 2009 2:46- In the TCP/IP model of the Internet, protocols are deliberately not as rigidly designed into strict layers as the OSI model.
- Compare reference models, not the protocol stacks.
- Differentiate Services, Interfaces, Protocols.
- Attachment to protocols.
- Number of layers.
- Connectionless vs. connection oriented
TCP is typically used by applications that require guaranteed delivery. It is a sliding window protocol that provides handling for both timeouts and retransmissions.
TCP establishes a full duplex virtual connection between two endpoints. Each endpoint is defined by an IP address and a TCP port number and is implemented as a finite state machine.
The TCP/IP architectural model has four layers that approximately match six of the seven layers in the OSI Reference Model. The TCP/IP model does not address the physical layer, which is where hardware devices reside.
The next three layers—network interface, internet and (host-to-host) transport—correspond to layers 2, 3 and 4 of the OSI model.
The TCP/IP application layer conceptually “blurs” the top three OSI layers. It’s also worth noting that some people consider certain aspects of the OSI session layer to be arguably part of the TCP/IP host-to-host transport layer.
A Critique of the OSI Model and Protocols:
Why OSI did not take over the world
- Bad timing
- Bad technology
- Bad implementations
- Bad politics
Bad Timing:
The apocalypse of the two elephants.
Timings
- Widespread adoption of the TCP/IP protocols preceded the formalization of the OSI model.
- Vendors already begun offering TCP/IP based products.
- OSI emerged about 5 years after industry had adopted TCP/IP.
- Vendors were reticent to add support for a second protocol stack until momentum had gathered behind OSI.
- The combination of these factors meant that OSI was never adopted in practice.
Technology
- Some parts of the OSI model are fundamentally flawed.
- Although there are 7 layers, 2 of these (session, presentation) are almost empty and 2 others (data link, network) are cramped.
- Additionally some functions such as addressing, error control are recurring at each layer.
Implementations:
- Early implementations of OSI were inefficient, contrast withTCP/IP implementations which are easy to use, scalable and robust.
Politics:
- OSI was widely perceived as the product of quasi-government standards processes rather than driven by good design processes.
A Critique of the TCP/IP MODEL:
- Lack of distinction between concepts.
- Doesn’t clearly distinguish between service, interface and protocol.
- Not adaptable – Not a general model and hence poorly adapted to other protocol Stacks.
- Ambiguous layers – Host-to-network is not really a layer, but an interface between network and data link layers.
- Omitted layers – Physical and data link layers are not present.
- Early implementations were fragile.
Jasper says:
August 9th, 2009 at 5:10 am
Before talking about Services, Interfaces and Protocols concepts, due to OSI Model, we could define these words :
Service : it tells only what the layer does, and not how entities above it access it or how the layer work.
Interfaces : it tells the processes above it how to access it, and specifies parameters and results.
Protocol : With this definition, the layer can characterize its own protocols, as many as he wants, and change them without affecting software in higher layers.
So we can introduce main differences between from these concepts :
OSI Model Reference
TCP/IP Model Reference
Service, interface
and protocol Service, interface and protocol are not clearly defined. For example, the only real services offered by the Internet layer are
- Send IP Packet
- Receive IP Packet Protocols in the OSI model are better hidden and can be replaced relatively easily as the technology changes, which is one of the main objective of layered protocols. Functionalities Because models were invented before protocols, functionalities put in each layer are not very optimized. In this case, the protocols have been invented before models, so the functionalities are perfectly described. Numbers of layers Seven layers, Network (Internet), Transport and Application layers being similar to TCP/IP Only four layers. Connectionless/
Connection-oriented communication Both connectionless and connection-oriented communication are supported in the network layer, but only connection-oriented communication in the transport layer. Only one mode in the network layer (connectionless) but both modes in the transport layer are supported, giving the users a choice.
Siddu says:
August 9th, 2009 at 5:13 am
As it can be seen from the previous pages there are a number of comparisons which can be drawn between the two models. This section will therefore be focusing on highlighting the similarities and differences between the OSI and TCP/IP models.
SIMILARITIES
The main similarities between the two models include the following:
They share similar architecture. – Both of the models share a similar architecture. This can be illustrated by the fact that both of them are constructed with layers.
They share a common application layer.- Both of the models share a common “application layer”. However in practice this layer includes different services depending upon each model.
Both models have comparable transport and network layers.- This can be illustrated by the fact that whatever functions are performed between the presentation and network layer of the OSI model similar functions are performed at the Transport layer of the TCP/IP model.
Knowledge of both models is required by networking professionals.- According to article obtained from the internet networking professionals “need to know both models”. (Source:
Both models assume that packets are switched.- Basically this means that individual packets may take differing paths in order to reach the same destination.
DIFFERENCES:
The main differences between the two models are as follows:
TCP/IP Protocols are considered to be standards around which the internet has developed. The OSI model however is a “generic, protocol- independent standard.”
TCP/IP combines the presentation and session layer issues into its application layer.
TCP/IP combines the OSI data link and physical layers into the network access layer.
TCP/IP appears to be a more simpler model and this is mainly due to the fact that it has fewer layers.
TCP/IP is considered to be a more credible model- This is mainly due to the fact because TCP/IP protocols are the standards around which the internet was developed therefore it mainly gains creditability due to this reason. Where as in contrast networks are not usually built around the OSI model as it is merely used as a guidance tool.
The OSI model consists of 7 architectural layers whereas the TCP/IP only has 4 layers.