Talk:List of interface bit rates/Archive 2

message: Some of these numbers, especially in the ethernet and serial sections were wrong.
The modem numbers have an interesting derivation.  Before compression (introduced with 2400 baud modems), modems required at least one start and one stop bit per byte, so a 300 bps modem was 30cps due to 10 bit bytes on the wire.  With compression came packetization.  Bytes were transmitted as packets, with a single start and stop bit for the whole packet, giving much closer to 8 bits per byte on the wire.  Compression raises this even higher, so a 28kb modem possibly could go much faster.
In the ethernet section, I think some theoretical numbers were put in that had no basis in reality.  Similar to modem compression, ethernet packetizes bytes and adds start and stop bits.  However, the overhead is significantly higher, with a very large number of hardware start bits and header bytes on top of that.  In addition, there are manditory gaps between packets that are part of the protocol.
Fast ethernet may be able to transmit 12M/s in theory, but with protocol required start/stop bits and manditory gaps between packets, 9M/sec is more realistic, and 4M/sec more common.
I'm sure similar numbers are true for gigabit ethernet, but I have not studied it much.  Typically with gigabit ethernet, the packet size is increased by two orders of magnitude to drastically reduce overhead.
When you say bandwidth on this page are you referring to bidirectional or unidirectional bandwidth?  This is important when referring to specifications such as PCI Express since its physical interface has dedicated directional links (i.e. the page states 500MBps, however a PCI Express x1 link can only support a peak bandwidth of 250MBps in one direction).
: RS-232-C says it applied up to data rates of 20,000 bits per second. RS 422 says its applicable to 10 MB/s. While some "RS-232" compatible interfaces may be settable to 230 kB/s ( I thought the top  end on a PC serial card was only 115 kB/s? ), can someone tell me if that data rate is covered by the latest revision of RS 232-C?  My interest in serial communications is not deep enough to shell out $65 US for the latest edition of the standard, though it may be worth a trip to the library. --Wtshymanski 14:42, 18 Apr 2005 (UTC)
replies: text: Similarly to both of these murky issues, waybackwhen I was using a 56k modem, and then an early 512k broadband connection (optic cable), I regularly saw 6.5 - 7.0 and 60 - 64kibyte (~57,000 and ~524,000 bit/sec) sustained file transfer speeds from them, so the bit-for-bit efficiency was managing a good 1:1 ratio or better with compression/packetisation vs error correction... and I've seen PCs with up-to-date serial FIFOs offering COM port speeds of upto 921,600 bit/sec (112.5kibyte/s!). Of course, whether it could successfully use or even set this mode is an entirely different matter that may require some deep research 82.46.180.56 00:26, 4 September 2007 (UTC)
thread_title:  Some of these numbers are wrong 

message: There are several good reasons to change this table to use BITS as the unit of comparison.
* First, because bits are the canonical units of information, as used in Information Theory.
* Bytes do not exist in Information Theory, they're only useful constructions. Some theorics still use today the term "octects" to stress the fact that bytes do not exist, in scientific terms.
* Bits are also the greatest common denominator for device speeds, and as such, it should be the official measurement speed.
I'm willing to change the table, including more columns to help to clarify this and other obscure points. If someone don't like the idea, or wants to discuss it further, please leave your comments here.
CarlosRibeiro 12:37, 2 Aug 2004 (UTC)
replies: text: Similar to game ROM and memory chip manufacturers specifying their product capacity in kilo- or mega-bits (kibi & mebi?), even though the end users and game programmers all worked in bytes? A Sega Master System game on a 'Mega Bit' cartridge sounded much more impressive, until you discovered the math and figured it was a paltry 128kib... 82.46.180.56 00:26, 4 September 2007 (UTC)
thread_title:  The table should use BITS, not BYTEs, for comparison purposes 

message: Well, I finally did it, and added the kbit/s column. I'm not sure that the ethernet bandwidths are correct, but this edit was mainly for format rather than correctness (!).
I've also modified the text as these are not actually device bandwidths, but actually connection bandwidths, and I think the title of the article should actually say that.  Being a relative Wiki newbie, I don't know how to change that, and think it needs some discussion and agreement anyway.
If I've done an unpardonable Wiki sin, then please roll back to the previous text.
WLD 00:12, 10 Sep 2004 (UTC)
thread_title:  Added kbit/s column 

message: I've added ARCNET, Token Ring and FDDI to the LAN protocols.
I modified the bandwidths for Ethernet as I beleive the table should show that bit-rate for each technology, and discussions about actual effective throughput should be moved elsewhere - perhaps to my unfinished page on Measuring Data Throughput, where I've started on the detail of overheads etc. Beware of flame wars over the actaul effective throughputs of Token Ring and Ethernet
I've checked and modified some of the bandwidths, but in some cases I would need to go to the primary sources of the IEEE/OSI documents to make absolutely sure that the numbers are correct.  Unfortunately, the OSI standards documents are not gratis, and I don't have copies.  Unless I have the actual standard in front of me, I'm not going to document numbers as being definitely correct.
Thanks to ?Bobblewick for justifying the numbers.  I have one small request/suggestion 'though - could the actual names of the connection technologies be left justified?  I think it would lokk better that way, but I don't want ot get into an edit war, or be going against Wiki style.
WLD 18:02, 10 Sep 2004 (UTC)
thread_title:  Ethernet, checking and formating 

message: Should we split up the Computer Interfaces section into two:
* One for interfaces/buses that are usually external (serial, SCSI, USB, IEEE 1394);
* One for interfaces/buses that are usually internal (AT, PCI etc)?
--WLD 22:14, 23 Nov 2004 (UTC)
replies: text: Why? Well, it seemed a useful distinction to make for those not particularly familiar with the technlogies. And there's certainly a room for a third category of interfaces/buses that are used for both.  Just trying to make the article more useful. WLD 17:07, 21 Jan 2005 (UTC)
thread_title:  Internal & External buses 

message: I'm thinking about adding a "symbol rate" column.
Some interfaces have bit rates *less* than the symbol rate:
* a 300 baud modem has a maximum data rate of 300 symbols/s * (8 data bits / 10 symbols) = 240 data bits per second, because it takes 10 binary symbols to transmit 8 data bits ( 8B/10B encoding ? )
* GPS runs at 1.023 Msymbols/s (the symbols are called "chips" in spread spectrum jargon) -- a much higher rate than the 300 baud modem. It has a navigational data rate of 50 data bits per second, far slower than a 300 baud modem.
* 100BASE-TX Ethernet is 125 Msymbols/s. But because it uses 4B/5B code, the maximum data rate is 125 M symbols/s * (4 data bits /5 symbols) = 100 data bits per second. ( MLT-3 Encoding has no effect on the bit rate ).
Other interfaces have bit rates *more* than the symbol rate (this requires amplitude modulation and/or parallel signal paths):
* Gigabit Ethernet (1000BaseT) is also 125 Msymbols/s. But because it uses PAM-5 modulation, the maximum data rate per pair 125 M symbols/s * (2 data bits / symbol) = 250 M data bits/s per pair. (Then it uses 4 pairs of wire in parallel to get 1000 Gigabits of data per second).
(see http://www1.us.dell.com/content/topics/global.aspx/power/en/ps4q01_patward?c=us&l=en&s=gen )
I hesistate, however, to label the symbol rate column with the technically correct name "baud rate", because historically it has caused a lot of confusion.
But an encyclopedia is exactly the right place to fix this confusion.
I know that historically modems have used the term "start bit" and "stop bit" ... but shouldn't they be "symbols" if we use modern terminology ?
-- DavidCary 02:21, 13 Jan 2005 (UTC)
replies: text: Be bold, and add it, preferably with links to articles explaining what the symbold rates are, and the differing encodings. WLD 17:09, 21 Jan 2005 (UTC)
thread_title:  "symbol rate" column 

message: I added DSL as 64 mbps since VDSL talks about a "theoretical limit" of 52 Mbit/s downstream and 12 Mbit/s upstream. Since the downstream and upstream share of the line can be configured at will, the line capacity is 64 mbps within 500 meters, perhaps? - Jerryseinfeld 02:19, 4 Dec 2004 (UTC)
replies: text: If the limit is 52 Mbit/s, then surely it can't carry more than 52 Mbit/s?  If you mean 52 Mbit/s at a particular range from the CO, then that range should be stated, as it is not unusual for the possible bandwidth to be higher at ranges closr to the CO.  Note that one should not sum the upstream and downstream capacities.  If the technology is asymmetric, the upstream and downstream rates should be listed seperately. WLD 09:27, 4 Dec 2004 (UTC)
replies: text: I believe "the downstream and upstream share of the line can be configured at will". - Jerryseinfeld 21:49, 23 Dec 2004 (UTC)
thread_title:  DSL 

message: This footnote seems to imply ADSL suffers from contention:
Some ADSL & SDSL connections have a higher bandwidth than T1 but their bandwidth is not guaranteed, and will drop when the system gets overloaded where as the T1 type connections are usually guaranteed & have no contention ratios.
Surely ADSL is a point-to-point connection, and does not ever suffer from contention (unlike some cable modems). Of course whatever it is connected to on the other end might, but that is nothing to do with ADSL. It might however have problems with line quality meaning that the theoretical maximum bandwidth can't be reached on some lines.
—Preceding unsigned comment added by 192.171.3.126 (talk • contribs) 
:T1 is equivalent with a physical wire, dedicated to you, going to point to point. Never is the T1 bandwidth shared with other users (and if you don't use it, it is left unused). This is not the case with ADSL, where x number of users share y amount of total bandwidth.
:Oh, and post new discussion at the bottom.
:--Anss123 14:19, 19 June 2007 (UTC)
replies: text: Your particular DSL is not shared (well, I share mine) but you are sharing a DSLAM and its back end connection with other DSLs. Jim.henderson 18:05, 19 June 2007 (UTC)
thread_title:  ADSL Contention? 

message: Hi folks. I stumbled across this article, and had a spare afternoon, so I've
reformated the table to fit in with orders of magnitude. I wrote a
perl script to to the conversion, so it (or I) may have messed up some values
(which is why its here on the talk page). I read the bits/bytes discussion
above, and so the table is based in bits per second, with the bytes per
second conversion from the old table.
This is part of a plan to move the article to [[Orders of Magnitude
(bandwith)]], and add it to the orders of
magnitude template.  Osric 01:24, 14 Mar 2005 (UTC)
replies: text: could that not be handled by redirect? copying the same information across articles means one ends up stale. SchmuckyTheCat 21:11, 14 Mar 2005 (UTC)

text: * but on second thought, I don't like that table at all and wouldn't support a move. SchmuckyTheCat 21:17, 14 Mar 2005 (UTC)
thread_title: Move to Orders of magnitude (bandwidth)

message: "56K modem capacity of 57.6 kbit/s was limited to 53.3 kbit/s over telephone lines; speed in practice typically 45 kbit/s."
* I know this is (or was at one point) applicable in the United States, but, I am unsure this applies worldwide. I have never heard of a CRTC regulation placing such a limit. SD6-Agent 18:23, 2 August 2005 (UTC)
replies: text: I'd refer you to my comment above on observed modem speeds. UK providers didn't seem to levy such restrictions in a lot of cases, for their own reasons. Unless it was BT on a rural exchange at all. In the former case, connection speeds of 56000bps and transfer rates of 7kbyte/s were, if not guaranteed, then fairly common. My father falling into the latter category sees speeds in the 21600-28800 range with a similar modem, horrible transfer speed and poor line reliability. 82.46.180.56 00:26, 4 September 2007 (UTC)
thread_title: Telecom regulations