Talk:Link layer

Network access layer or Link layer

I suggest that the article should be renamed to "Network access layer". In rfc:s and books i have read, the bottom layer of the four layer tcp/ip model is named "Network access layer". For example in the Cisco literature. "Link layer" makes me associate to "Data link layer", and would probably cause the same confusion among others. At least the article should discuss the term "Network access layer", and give references that define these terms. Mange01 (talk) 14:54, 13 July 2008 (UTC)

There is no such term in the primary and authoritative literature. The articles cite the origin of their terms precisely. These documents are constantly under review by experts (!) and they have not seen the need to redefine the terms. The term "network access layer" doesn't even closely describe the scope of "link" layer. This term is in use in dozen of primary, normative documents that describe STANDARDS. No textbook makes a standard, they all just interpret history for the purpose of introducing novices to the field. Unfortunately they would do a much better job if they just studied the RFC's because they contain the most comprehensive expert insights in to these topics and are a lot more fun to read than most text books. If there is one "standard" textbook for TCP/IP networking, it surely is R. Steven's, and he doesn't redefine the standard either. He doesn't have to.

I know of no expert who confuses expert terms. There are certainly a lot of other terms in computing that are a lot more confusing than this. The fact is, that people have started to just assume that "data link layer" and "link layer" must be the same since they sound so similar without checking the facts. How CISCO documents make you feel about these terms is totally irrelevant, they are not definitive either. The fact that the original terms are deliberately not very precise, rigid definitions is a lesson to be learned, namely that this layering is not the goal, rather a guidance to abstract concepts.

Fact is that none of the lowest three levels, well all of them actually, of the TCP/IP model correspond with the OSI layer no matter how you lump them together or pick them apart. To make it fit, you need to invent a totally new model, and forget the old. An encyclopedia's job is not to invent new ideas but to reflect what the facts are from expert view without the in-depth technical complexities of the subject, which can be gained from the references.

You don't even quote what textbooks you have read. Textbooks come and go and have no authority as a reference. Teachers use all kinds of analogies to make a topic stick in a novice mind. Please cite the RFCs you have read as you state. I have been reading RFCs for 20 years, and even recent RFCs in the relevant area use the established terms. If terms had changed, there would be a revision RFC. The IETF is by no accident called the "Internet Engineering Task Force". They decide the standards of the Internet. If you want to change something, please join and convince them of your merits. The organization is open to anyone.

There are RFCs by other workgroups that deal with non-Internet protocols, such as IEEE 802 details, and Telecom issues perhaps, and they do use OSI layer type terms, but that's fine, they are not talking about the TCP/IP model. The TCP/IP model is the model of the INTERNET, not of media access technologies of which it is completely independent. TCP/IP "Link Layer" is simply a different concept than Physical layer and Data Link Layer combined. Changing the name to Network Access doesn't change the facts. The Link Layer simply is not the same concept. If you start reading and understanding the original references (all of them!) you will see the difference. Kbrose (talk) 15:44, 13 July 2008 (UTC)

I think that's a bit harsh on Mange01. And, at least as far as my understanding goes, it is also wrong. As the article itself says, this layer used to be called (at least when I was a young turk, and that was, unfortunately, a lot longer than 20 years ago) the network layer. I'm not sure why one would refer to this layer as the "link layer".

It is not true that there is no correspondence between the OSI layers and the TCP/IP layers. The layers are clearly defined, and the correspondence is there and it is very clear.

My experience with experts is rather different from your own. I know a lot of experts who make mistakes, and indeed also confuse "expert" terms from time to time. In fact, I don't think I know anyone who is infallible. But perhaps I have been around for too long.

In the usual TCP/IP/ethernet stack, the cables connecting your computers to the switch etc. are the OSI Physical Layer. This is what the physical layer is: a (not necessarily reliable) data connection directly connecting two points.

The part of the Ethernet stack which provides reliable communication over a direct data connection over these direct-node-to-node cables is the OSI Link Layer. This is what the link layer is: a reliable data connection directly connecting two points. One such well-known Ethernet OSI Link Layer Protocol is PPP, but there are others.

On top of these point-to-point connections, Ethernet provides a layer called the MAC layer. This is the OSI Network Layer. This is the layer which connects several nodes into a "network", an interface which connects possibly several nodes, over which data can be sent by packaging it into packets, labelling them with an "address" and letting the network layer find a way to deliver them to the right destination ("route" them). The OSI Network does not provide any guarantee of delivery, i.e. the delivery of datagrams is (potentially) unreliable.

The IP layer works on top of the MAC layer, and is also (another) OSI Network Layer, i.e. another layer which permits nodes to send unreliable addressed point-to-point datagrams.

Because the TCP/IP stack contains two OSI Network Layers, terms like "network layer", "network access layer", "LAN" to refer to the first of the two network layers and "inter-network layer", "WAN" etc. to refer to the second network layer were invented to distinguish between the two network layers.

Thus, the IP layer is an OSI Network Layer on top of another OSI Network Layer, the MAC/Ethernet layer.

TCP is a layer which operates on to of the IP layer which provides the reliable delivery of packets between addressed nodes on a network. This is the OSI Transport Layer: a layer providing reliable delivery of addressed packets between nodes on a network.

Although UDP is normally also called an OSI Transport Layer, it is, in fact, another OSI Network Layer on top of the IP OSI Network Layer.

There is nothing unusual about stacking OSI Layers in a way which doesn't build OSI Layer (n+1) on top of OSI Layer n. PPPoE is an OSI Link Layer stacked on top of an OSI Network Layer. ZModem run on a serial line provided by a modem which already provides v.42bis error correction is an OSI Link Layer stacked on top of another OSI Link Layer. ZModem run over ssh is OSI Link Layer run on top of an OSI Application Layer.

Thus, in my view, what Mange01 is saying is absolutely correct. The layer being described in this article is the TCP/IP network layer (one of the two OSI Network Layers in the TCP/IP stack). The naming of this article is misleading and wrong. It should be correctly named the "TCP/IP network layer".

Tarian.liber (talk) 19:00, 21 August 2013 (UTC)

Media level frames

Just started getting into this article and stumbled across this: "...that can deliver media level frames on the link". What is that supposed to mean? —Preceding unsigned comment added by 62.143.97.17 (talk) 15:03, 13 October 2009 (UTC)

Move discussion in progress

There is a move discussion in progress which affects this page. Please participate at Talk:Physical Layer - Requested move and not in this talk page section. Thank you. —RM bot 03:45, 19 October 2011 (UTC)