Talk:Data link layer

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Untitled

• IMHO I Don't see what should need cleanup here. propose cleanup tag removal Ppchailley 08:30, 29 June 2006 (UTC) ppchailley

• Agreed. 158.59.224.224 14:58, 6 July 2006 (UTC)

vandalism on para 3

So in social contact, one needs to know at least one other person, but not necessarily know Fred Bob, Canada.

who is bod from canada...anyway shame on u boob. --59.93.2.240 05:31, 5 August 2006 (UTC)

OSI Data Link Layer mixed with TCP/IP one.

It doesnt exist an exact part where the differences are stated. As far as i know OSI is not the same as TCP/IP. --189.135.66.229 02:54, 23 October 2006 (UTC)

Radio Link Control sublayer

is used in some wireless systems. It should be mentioned here somehow. Mange01 (talk) 22:12, 18 March 2009 (UTC)

Perhaps you should write a section in a UMTS article first and give the term better context. Kbrose (talk) 00:07, 19 March 2009 (UTC)

Good idea. I have not found any good source however. Mange01 (talk) 16:27, 19 March 2009 (UTC)

Perhaps, when you do, you will discover that this is not a Data Link Layer issue, belongs to physical layer, well, or somewhere in between. Kbrose (talk) 18:11, 19 March 2009 (UTC)

Hmm. Perhaps you have Radio resource management in mind, which often concerns the physical layer. Mobility management (handover and roaming) taken care by the MAC sublayer if it is packet switched - and I don't know where it is situated if it is circuit switched. But RLC is something else. It was introduced in GPRS, and to my understanding it is about transferring packet data (i.e. data link layer) over a system that partly is based on circuit switched channel access. In the sources I have seen, it is placed above the MAC layer and below the LLC layer (the latter is not always mentioned). See

[http://books.google.com/books?id=4l8WqgF46YkC&pg=PA49&dq=radio+link+control+RLC+sublayer&hl=sv#PPA45,M1 George Aggelou, Mobile Ad Hoc Networks: From Wireless LANs to 4G Networks, McGraw-Hill Professional, 2005

ISBN 0071413057, 9780071413053, figure 1.22, page 45],

Keiji Tachikawa, W-CDMA Mobile Communications System: Mobile Communications System, John Wiley and Sons 2002, ISBN 0470847611, 9780470847619, Figure 3.3, page 98.. LLC frames are segmented into RLC data blocks, which are embedded in MAC frames. To my understanding, the LLC layer is responsible for the communication between the GGSN node (the "GPRS router" or "packet switch") and the mobile station. This communicaiton is mediated by the base station (BSS) and the base station controlling switching point (BTS). The RLC layer is responsible only for the communication over the radio link between the base station and the mobile station.Mange01 (talk) 22:55, 19 March 2009 (UTC)

Ghastly Second Paragraph

Parts of this article are atrociously written, such as this non-stellar opening to the second paragraph: "The data link is all about getting information from one place to a selection of other close, local places." The quality does not improve soon enough.

This is a poorly-worded jumble built on specious conceptions. I will try to clarify and correct some of this. --Talinus (talk) 00:30, 8 April 2009 (UTC)

Use of the Term LAN

"The Data Link Layer is concerned with local delivery of frames between devices on the same LAN." This statement might suggest to a casual reader that the Data Link Layer" is specific to Local Area Networks. That would be incorrect. All networks (LAN, MAN, & WAN) make use of frames to deliver the network layer PDU between devices. —Preceding unsigned comment added by 121.223.146.223 (talk) 14:22, 2 June 2009 (UTC)

Error detection and error correction

"The uppermost sublayer is Logical Link Control (LLC). This sublayer multiplexes protocols running atop the Data Link Layer, and optionally provides flow control, acknowledgment, and error recovery." The use of the term "error recovery" in this statement might cause confusion between the concepts of error detection and error correction. Layer 2 provides error detection or error notification, not error correction. —Preceding unsigned comment added by 121.223.146.223 (talk) 14:30, 2 June 2009 (UTC)

"Software" and "Hardware" Layers

"The Data Link Layer is often implemented in software as a "network card driver"." This statement is incorrect and confusing. The driver can only implement the functionality of the hardware. It can never implement layer two functionality independently of the hardware. The upper three layers (5, 6 and 7) of the OSI model are referred to as "Software Layers" because they are fully implemented in software. The bottom four layers of the OSI model are referred to as "Hardware Layers" because they are heavily dependent on hardware devices. —Preceding unsigned comment added by 121.223.146.223 (talk) 14:46, 2 June 2009 (UTC)

Plagiarised from ...?

What's all the "Figure 4-39" stuff in the huge chunk of unattributed text in the "Data Link Layer Switching" section? Where's that been lifted from? —Preceding unsigned comment added by Gordonjcp (talk • contribs) 10:59, 5 January 2010 (UTC)

Misleading pedagogy

Section Media Access Control sublayer, second paragraph:

If two people speak at the same time, they will back off and begin a long and elaborate game of saying "no, you first".

No, that's not Media Access Control. The explanation is outright stupid. The real explanation should be:

If two people speak at the same time, they will pick up a 1000 sided die from their respective pocket, and throw it, observing the number that comes up. Then both of them will take up their stop watch and wait for that number of /seconds (or other time unit)/ and after that try to speak up again.

Rursus dixit. (^mbork³!) 09:02, 27 July 2011 (UTC)

Your 1000-sided die and stopwatch sounds elaborate to me. Also, rolling the die and running the stopwatch has the intended effect of letting someone else go first most of the time... — Dgtsyb (talk) 09:20, 28 July 2011 (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)

'The uppermost sublayer, LLC, multiplexes protocols running atop the data link layer, and optionally provides flow control, acknowledgment, and error notification.'

'error notification' and later 'error control'.. correct term would be 'error detection'. And actually this is false because CRC is added by MAC sub-layer. The Frame Check Sequence (FCS) field in the Trailer is used to determine if errors occurred in the transmission and reception of the frame, and thats where CRC is placed. Error detection is part of Data Encapsulation, next to frame delimiting and addressing. And data encapsulation is one of primary responsibilities of MAC. - that should be fixed

"Stretched" Layer 2

I came accross this term today. Refers to methods to "virtually" extend a datalink layer accross WAN links I assume. Can't seem to find any related information on Wikipedia currently? Might be a good addition if it is not yet available.

Refimprove - can it go?

A refimprove template was added to this page in 2013. Since then the article has gained five references. Some of the references contain plenty of information to support the information in the article although there are areas where the citation of these is not given. Nevertheless we don't have to cite for every sentence. All quotations and any controversial statements should be cited. So I wonder whether we have sufficient citations to remove the refimprove. I am going to boldly remove the refimprove now for the following reasons:

1. Article has gained 5 new citations supporting the material 2. The template is not working. After six and a half years we gained just five new refs. 3. Removing the template may encourage editors to add "citation needed" to specific material they believe needs support, which could stimulate focused collation of sources.

-- Sirfurboy (talk) 10:06, 3 December 2019 (UTC)

Checksum and CRC

kvng (talk · contribs) has backed out my whole copy edit here.[1]. The edit summary raises two issues that we now need to discuss under WP:BRD. From the edit summary:

• checksum is not good engineering practice.

What you are describing here is a checksum.That is, a datum derived from a block of digital data (the frame) for the purpose of detecting errors. I do not understand your argument here. Checksum is simply the correct term for your non standard phrasing: "redundant information".

• CRC is not computationally expensive

Not very, but it is indeed more expensive than the algorithm you suggested (a series of additions) or the checksum used in, say, IP header checksums (again, a series of additions using ones complement arithmetic). CRC provides improved positional checksum capability using modulo two polynomial division. The algorithm is efficient but you can't beat simple addition. However, even if we leave out mention of the greater expense of the algorithm, the rest of the edit can stand perfectly well without it.

I don't want to get into citing sources for using a standard term like checksum, so hopefully we can reach consensus here. -- Sirfurboy (talk) 14:39, 17 January 2020 (UTC)

ETA:

Position-dependent

The simple checksums described above fail to detect some common errors which affect many bits at once, such as changing the order of data words, or inserting or deleting words with all bits set to zero. The checksum algorithms most used in practice, such as Fletcher's checksum, Adler-32, and cyclic redundancy checks (CRCs), address these weaknesses by considering not only the value of each word but also its position in the sequence. This feature generally increases the cost of computing the checksum.

From: Checksum Wikipedia page. -- Sirfurboy (talk) 14:43, 17 January 2020 (UTC)

@Sirfurboy: Your edit primarily replaced error detection code with checksum. A checksum is but one type of error detection code and a poor one at that. This replacement I consider a regression. I didn't find the other copyedits you made to be a significant improvement. I did retain your new paragraph about CRC but I removed your assertions that it was more complex or expensive. CRC is done with a bit-shift and XOR. Binary addition, because of carry operations, is similar complexity for digital hardware. ~Kvng (talk) 16:12, 17 January 2020 (UTC)

kvng (talk · contribs) It is apparent to me that you mean something different by checksum than I do, but on reflection, I think I see where you are coming from in that CRC (which is, of course, by far the most common algorithm implemented for the FCS in IEEE 802.x) is not technically a check SUM. As such my usage is perhaps too loose for this article (although I note that it is a very widely understood usage. GIYF, but as an example: [2]). I agree we should leave it as error detection code (although clearly the algorithm described in this piece is a checksum). As for speed - well I overstated it, but CRCs are slower. I won't push that point.

I missed that you had retained mention of CRC. Thanks for that. As CRC is so commonly used in the FCS, I think that is appropriate, and I will withdraw the other edits. -- Sirfurboy (talk) 20:18, 17 January 2020 (UTC)

Requested move 16 October 2021

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: not moved. (closed by non-admin page mover) Vpab15 (talk) 22:14, 24 October 2021 (UTC)

---

Data link layer → Data-link layer – It seems like this would be more grammatically correct because data link is arguable a compound modifier of layer. It will be significant work to make the change to the article content and incoming links so I'd like to see some support before WP:BOLDLY making the change. ~Kvng (talk) 17:57, 16 October 2021 (UTC)

Grammatically that would be absolutely correct but OSI didn't name it like that and literature sources don't use it either. Should we go by the "official" name or by the correct one? I think we need to have WP:RS for such a change since WP describes what is and not what should be. --Zac67 (talk) 21:41, 16 October 2021 (UTC)

I believe the spirit of WP:COMMONNAME applies and the title should use the spelling from the majority of sources. Compare HTTP referer where the title is definitely a typo, as acknowledged in the article. Johnuniq (talk) 22:44, 16 October 2021 (UTC)

There is an important distinction between common name and official name. Zac67 is asserting that data link layer is both. I don't think Johnuniq's argument that we should be using the official name here is particularly strong.

The purpose of the hyphen is to make the language less ambiguous for readers. Adding the hyphen potentially puts Wikipedia out of step with how the phrase is punctuated in sources, creating a different kind of ambiguity. My assessment is that data-link layer is readily recognizable as data link layer and that there's a net reduction in ambiguity by adding it. ~Kvng (talk) 15:29, 19 October 2021 (UTC)

• Oppose for the reason stated by User:Johnuniq. "Data link layer" is definitely by far the more common usage. WP policy is to follow, not lead. --Coolcaesar (talk) 13:39, 22 October 2021 (UTC)
• Oppose. Sources typically do not hyphenate (see e.g. Kurose and Ross, Computer Networking: A Top Down Approach 6th ed.); we should follow what they do. Also see ngrams. Adumbrativus (talk) 20:19, 23 October 2021 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.