ASCII Table

Char	Hex	Dec	Name	Char	Hex	Dec	Name
NUL	00	0	Null	@	40	64	Commercial At
SOH	01	1	Start of Header	A	41	65
STX	02	2	Start of Text	B	42	66
ETX	03	3	End of Text	C	43	67
EOT	04	4	End of Transmission	D	44	68
ENQ	05	5	Enquire	E	45	69
ACK	06	6	Acknowledge	F	46	70
BEL	07	7	Bell	G	47	71
BS	08	8	Backspace	H	48	72
HT	09	9	Horizontal Tab	I	49	73
LF	0A	10	Line Feed	J	4A	74
VT	0B	11	Vertical Tab	K	4B	75
FF	0C	12	Form Feed	L	4C	76
CR	0D	13	Carriage Return	M	4D	77
SO	0E	14	Shift Out	N	4E	78
SI	0F	15	Shift In	O	4F	79	Letter O
DLE	10	16	Data Link Escape	P	50	80
DC1	11	17	Device Control 1	Q	51	81	Letter Q
DC2	12	18	Device Control 2	R	52	82
DC3	13	19	Device Control 3	S	53	83
DC4	14	20	Device Control 4	T	54	84
NAK	15	21	Negative Acknowledge	U	55	85
SYN	16	22	Synchronous Idle	V	56	86
ETB	17	23	End of Transmission block	W	57	87
CAN	18	24	Cancel	X	58	88
EM	19	25	End of Medium	Y	59	89
SUB	1A	26	Substitute	Z	5A	90
ESC	1B	27	Escape	[	5B	91	Open Square Bracket
FS	1C	28	File Separator	\	5C	92	Back slash
GS	1D	29	Group Separator	]	5D	93	Close Square Bracket
RS	1E	30	Record Separator	^	5E	94	Circumflex/caret
US	1F	31	Unit Separator	_	5F	95	Underscore
SP	20	32	Space or Blank	'	60	96	Single Quote
!	21	33	Exclamation Point	a	61	97
"	22	34	Quotation Mark	b	62	98
#	23	35	Number sign (Pound sign)	c	63	99
$	24	36	Dollar Sign	d	64	100
%	25	37	Percent Sign	e	65	101
&	26	38	Ampersand	f	66	102
'	27	39	Apostrophe (Single quote)	g	67	103
(	28	40	Opening Parenthesis	h	68	104
)	29	41	Closing Parenthesis	i	69	105
*	2A	42	Asterisk (Star sign)	j	6A	106
+	2B	43	Plus Sign	k	6B	107
,	2C	44	Comma	l	6C	108
-	2D	45	Hyphen (Minus)	m	6D	109
.	2E	46	Dot (Period)	n	6E	110
/	2F	47	Forward Slash	o	6F	111	lower case o
0	30	48	Zero	p	70	112
1	31	49		q	71	113
2	32	50		r	72	114
3	33	51		s	73	115
4	34	52		t	74	116
5	35	53		u	75	117
6	36	54		v	76	118
7	37	55		w	77	119
8	38	56		x	78	120
9	39	57		y	79	121
:	3A	58	Colon	z	7A	122
;	3B	59	Semi Colon	{	7B	123	Open Curly Bracket
<	3C	60	Less Than	|	7C	124	OR (Pipe)
=	3D	61	Equality	}	7D	125	Close Curly Bracket
>	3E	62	Greater Than	~	7E	126	Equivalence (tilde)
?	3F	63	Question Mark	DEL	7F	127	Delete

Jacks and Modular Connectors

Jacks are called by various names RJ11, RJ45 etc. These terms are incorrect (though widely used by all of us -OK, OK we use them as well), they should be called Modular Connectors according to the following table:

Common Name	Correct Name	No of connectors	Notes
RJ11	4 Position Modular Connector	4	mostly used in analog (telephone) wiring
RJ11 or RJ12	6 Position Modular Connector	6	more commonly used these days in analog (telephone) wiring.
RJ45	8 Position Modular Connector	8	Used in telephone wiring (ISDN and T1), LAN (10baseT and 100BaseT) and RS232 (RS232D) wiring

NOTE: Male Modular connectors are numbered LEFT to RIGHT when viewed from the TOP (TOP is when the plastic lever is on the bottom). Female connectors are numbered from LEFT to RIGHT when viewed from the FRONT. An RJ45 (or 8 Position Modular Connector) example for both Male and Female connectors is shown below (the same principle applies to all modular connectors)

Male Connector Numbering	Female Connector Numbering

Telephone Wiring

Telephone Wiring is defined by USOC (Universal Service Order Code) which is now maintained by the TIA and uses the following conventions for cable pairing.

Analog Line Pair Numbering

The following diagrams show the various ways that single line pairs may be taken from a range of jacks.
NOTE: All numbering is viewed from the TOP (TOP on a Modular connector is when viewed with the lever/tab on the bottom). The diagrams show all possible types that will satisfy the Wiring Code.

USOC Code	No of Pairs	Diagram
USOC RJ11 or RJ11C	1
USOC RJ14C or RJ14	2
USOC RJ25 or RJ25C	3
USOC RJ48 or RJ48C	4

LAN Wiring

LAN Wiring is defined by EIA/TIA and uses the following two conventions for RJ45 (8 Position Modular Connector) pairing on UTP cable. See our LAN wiring page.

EIA/TIA wiring Code	Diagram	Notes
568A (colour diagram)
568B (colour diagram)

LAN and Telephones

If you mix LAN and Telephony on the same wiring it will be non-standard. Put simply this means that you may not be able to take advantage of certain new applications that use the currently unused pairs in 100base-TX. Increasingly we are seeing 'Power-over-Ethernet (PoE)' systems which can make use of both spare pairs in 1000base-TX wiring and will likely provide power for VoIP or other technologies. If you mix PoE systems with non-standard wiring you could destroy or damage equipment and have other unpleasant or harmful effects. 1000base-T (gigabit Ethernet) uses all 4 pairs (8 conductors) and cannot be used with mixed LAN and telephony wiring.

Electricity and Telephone Wiring: When the telephone rings, and depending on how close you are to the central office, there may be a hazardous voltage (up to 150 volts) on the line. Take sensible precautions such as:

1. Disconnect phone lines until the last possible moment.
2. If you can stop incoming calls using a 'class' service or a 'do-not-disturb' feature use it while you are actively working on the wiring.
3. Make sure your footwear has good insulation characteristics.
4. Make sure all your tools have insulated handles
5. Avoid touching bare wires
6. NEVER work near water
7. Never work on wiring during an electrical storm
8. If you smell gas stop and have it investigated immediately by an expert

FEASIBILTY - and more CAUTION

Many newer home and office cable installations use category 5 or 5e wiring. In many cases this carries just telephony or LAN traffic. We are frequently asked whether it can carry both LAN and Telephony since pulling additional wires can be a difficult, messy, expensive or downright impossible.
Since 10base-T or 100base-TX wiring uses 2 pairs (4 wires) and each analog phone connection uses a single pair (2 wires) you can, subject to limitations, run 2 telephone connections and LAN traffic on category 5(e) wiring but IF AND ONLY IF YOU CAN ANSWER YES TO ALL THE ITEMS BELOW.

1. The maximum speed of your LAN will be 100M bit/sec.
2. ALL the wiring that is planned to carry LAN or LAN and Telephony is Category 5 or 5e standard.
3. You have no equipment installed or planned to be installed that will use Power-over-Ethernet (802.3at) using Alternative B wiring (802.3at allows Alternative A wiring for PoE to use only the standard LAN signal pairs 1,2 and 3,6 so this is compatible with the mixed wiring here).
4. You have standard one pair (2-wire) analog phones throughout the premises.
5. Every access point that will carry LAN or LAN plus telephony traffic is wired as a Star or Home-run.

If you are NOT positive about the answers to the above STOP NOW and either find the definitive answers or take-up origami.
Note: If you are doing the wiring - pull two separate wires (one to carry telephony and one to carry LAN - both should be cat 5e or 6) to a single multi-use jack. This will save a lot of hassle. Only use these techniques if you have no other choice.

The configuration

These notes assume that you want one or more LAN connections and that you want to carry both telephony and LAN on the same cables.

Planning - the Hard Work

If you thought this was going to be easy - forget it - go take-up floral arrangements, golf or watch paint dry.
Before you start you need to do three things

1. Invest in (or borrow) the right tools. You will need as a minimum:
   
   • A punch down tool (for the wall jacks and any cross-connects).
   • Labels for marking both ends of each connection/cable if this has not already been done.
   • If your cabling is not numbered (or otherwise clearly identified) or you are suspicious you may need cable detection equipment. This equipment normally has two parts. One part injects a tone onto a wire and the other end is like a wand and allows you to find the end that is carrying the tone. This type of equipment can vary enormously in price and quality ($100 to $500).
   • If you have to make up LAN or Telephone end cables then you will need a crimp tool suitable for RJ45 (8 wire - 4 pair) and RJ111/12 (6 wire) connectors. Get the best one you can afford. They typically come with a built-in cable-cutter and wire-stripper. Make a few practice cables and test them until you get it right - it's harder than it looks.
   • If you are pulling the cable - espcially in tight spots - get what is typically called a cable fisher. It's a roll of spring steel with a hook at the end for pushing and pulling wire. Indispensable.
   • Optional. LAN cable testers are available in a range of prices from $10s to $100s of dollars and if you are going to do a lot of wiring are well worth the investment since they let you check your work at each stage in the process.
2. Make a sketch plan of your current wiring and note the colours used at both ends of each connection and the equipment connected or to be connected. Now allocate, if it is has not already been done, a unique ID or number to each connection and then label both ends of the cable - preferably with the same number - as soon as you have found both ends of it! Remember you don't want to do this again.
   Finding both ends of an installed cable run is no easy task and you may need to use cable detection equipment to do so (see above). MAKE NO ASSUMPTIONS. Someone else, far less skilled than you, may have already installed non-standard features.
3. Document your new design on a new sketch plan, because:
   
   • In three days time YOU will have forgotten what you did.
   • You may sell or move from your premises and it's pretty unfriendly, if not dangerous, to leave your non-standard wiring undocumented.
   Your design should cover as a minimum the following elements:
   
   • YOUR COLOUR CODING STANDARD. Start with the LAN and select either 568A or 568B colour coding. This scheme defines the 2 pairs (4 wires) for the LAN. Select one spare pair to carry the first Telephony connection and the final pair to carry the second telephony connection. Stick to this standard everywhere EVEN IF IT MEANS RE-WIRING EXISTING CONNECTIONS. The alternate is that you will have non-non-standard wiring. Not even your mother will be able to help clean up that mess.
     The following is an example of such an allocation (based on 568B color coding) but it is not the only one possible.
     
     

     Pin No.	strand color	Name
     1	white and orange	LAN (TX_D1+)
     2	orange	LAN (TX_D1-)
     3	white and green	LAN (RX_D2+)
     4	blue	Telephone 1
     5	white and blue	Telephone 1
     6	green	LAN (RX_D2-)
     7	white and brown	Telephone 2
     8	brown	Telephone 2

   • 
     
     All the access points/jacks, to include the new ones you are installing, the connections to be supported, for example, kitchen - 2 telephones, den - 2 telephones and LAN and so on.

Gazing at Stars and 'Home Runs'

It's important that you understand the concept of Star Wiring topology (sometimes called home-run wiring) before you start. All LAN wiring uses a star topology.
Star (or home-run) wiring means that each access point (wall-plate) is directly run back to a central or home location (normally in the basement or where the telephone service enters the premises) with no breaks. Many, if not most, older premises and even quite recent ones use multi-drop telephone wiring which allows multiple phone access points on a single cable run.
This is perfectly permissible for phone systems (typically up to 5 such drops can be used) but, MULTI-DROP WIRING CANNOT SUPPORT LAN TRAFFIC. You must have STAR WIRING to each access point that will carry LAN traffic. Diagram 1 illustrates the differences in wiring topologies.

Diagram 1 - Star vs Multi-drop wiring

Equipment - Cables and Connectors

This section provides some notes about what type of cables and connectors you can use.

• Today (2006) you should be using Category 5e wiring which is typically competitively priced. You can however use category 5 for telephony and 100MB LANS but this may be flaky if you want to upgrade to GB LAN. If you want to invest for the future use Category 6 wiring.
• Cables (5, 5e or 6) come in two forms. Stranded - each conductor is made up of multiple smaller wires and Solid - each conductor has a single wire. Stranded cable is typically more expensive than solid cable. In general, cables that are rarely moved, such as runs inside walls or backbone wiring, use solid cabling. The exception to this is where you need to bend round very tight corners (the bend radius is less than 6 inches or 15cm) in which case you should use stranded cable for this purpose. Any cable which is moved or unplugged frequently, such as PC to wall plate cables, should use stranded cable.
• Stranded and solid cables MUST use the appropriate connectors. Do not be tempted to mix them. It is sometimes very difficult to tell from a connector description which is which. In general avoid these connectors because if the supplier does not know - what chance has the poor user. In general, connectors designed for wall plates assume solid cable.

Jacks, Access Points and Wall-plates

The next item on the agenda is getting the right connections at the room Access Point Wall-Plates (or Jacks - we're going to use the term Access Point from here on (AP for short)).
There is an enormous choice of Access Point wall-plates available today from reputable network suppliers with almost every combination of voice, data and video connections. The most flexible are called keystone wall-plates and provide blank plates with the right number of empty holes (available with typically 1, 2, 3, 4 and 6 holes). Recessed and surface mount options, as well as a whole range of colours, are typically available.

Keystone wall plate examples

Into these 'keystone' holes you plug the keystone jacks of the type that you need e.g. 1 RJ45 (for LAN) and 1 or 2 RJ11/12 (for Telephony), video etc. A wide range of colors is usually available. Both punch-down and 'tool-less' versions are now available.

Keystone jack example - punch-down

Keystone jack example - tool-less

End connections are critical and if poorly done can be a huge source of loss and poor performance. Use high quality and correctly rated connectors. DO NOT BE TEMPTED TO SKIMP COST AND USE EXISTING WALL-PLATES IF THEY ARE NOT SUITABLE JUST BECAUSE THEY ARE THERE. YOU WILL REGRET THIS WITHIN MINUTES. DO IT ONCE AND DO IT RIGHT.

Command Central

In a Star Network eveything interesting happens at our central or home location which is typically situated where the telephone wiring enters the home or premises. Here we will install our Hub/Switch and carry out all our cross connections using a Wiring or Punch-down block such as 110 type, BIX or Krone. We show a common 110 type below. They come in all sizes but each 'bar' typically has 25 punch-down slots - each 'bar' will take 3 incoming cables.

Hub vs Switch

The price difference between a Switch and a Hub is almost vanishly small these days. Unless budget really is a key issue we would suggest a Switch. They come in all kinds of sizes 4, 5, 8, 16 and 24 ports. Some have the ports at the back and leds at the front, others put both at the front (we illustrate both types below) Note: We show particular vendor products for illustration only. Any suitable Switch or Hub will do the job we do not endorse or recommend any particular vendor product.

RJ45 and LEDS at front

RJ45 at Rear LEDS at front

The general specification - irrespective of whether it's a switch or hub - is:

1. Minimum number of ports equal to the most systems you can think of connecting plus some (say 2) ('cos you are going to change your mind!)
2. 10/100 Mbit/s auto sensing
3. LINK LED for each port
4. 10/100 LED for each port

They typically come with lots of other features e.g. Full/Half Duplex, managed or unmanaged - your budget will figure out what else you want or can afford.

So let's Boogie

We are going to:

1. Run a cable from each room where we want to install multiple connections to our central location (typically where the telephones enter the house)
2. Add and wire the Access Point wall-plates in each required room
3. Install the Hub or Switch at the central location
4. Punch-down our incoming (from room) cables onto the puch-block
5. Cross-connect from the punch-block to the LAN and Telephone connections

Hang on a minute

This is a big job so spend a couple of minutes reading these notes:

1. If you get this wrong your telephone system may not work - is this acceptable?
2. It will probably take longer that you think - do you have the time?
3. Take one step at a time - test as much as you can when the step is complete.
4. If you need your phone system during the week - start on Friday evening - gives you Saturday to run round the stores to get everything you forgot!
5. Do all the LAN cross-connections before you touch your telephone system.
6. Do a single - least important - room first. Figure the time to finish the whole job and plan on that basis.
7. Read the troubleshooting hints before you start - you will probably need them at some point!

It's all Twisted

Making good end connections is both the key to success and tougher than it looks. The following notes may help:

Wall Plate connections

1. Practice making connections until you get it right every time - especially before you destroy cables you just spend 2 hours fitting.
2. Make sure you have 6 - 8 inches of slack cable in case you make one or more mistakes.
3. If you make a mistake throw away the connector. Never be tempted to re-use connectors. They may work but one day they may stop and you will spend hours trying to find the problem.
4. When cutting the exterior cover of the cable be very careful not to cut the insulation cover of the conductors since this can cause shorts. Shorts are not good.
5. When making multiple connections in a keystone wall plate expose the MINIMUM amount of conductor necessary to complete the job.
6. Line up all the conductors according to the wiring standard you are using.
7. Punch-down or connect all the wires.
8. Carefully trim any excess conductors.
9. Test the connections before fitting the wall plate.

RJ45 End Connectors

1. Make and test practice cables until you get it right every time - especially before you destroy cables you just spend 2 hours fitting.
2. When cutting the exterior cover of the cable be very careful not to cut the insulation cover of the conductors since this can cause shorts.
3. Expose a maximum of 1 inch of individual conductors when preparing the cable for connection.
4. Line up all the conductors according to the wiring standard you are using.
5. Measure the cable and trim the conductor ends so they are are all the same length and no individual conductor wire is visible outside the plastic cover of the RJ45 connector.
6. Carefully slide the prepared cable into the RJ45 connector making sure the end of the conductors reaches the end of the RJ45 connector.
7. Using the crimp tool make the connection using one firm squeeze operation.
8. Test the cable before fitting if possible.
9. The RJ45 connector is the critical connection always use the highest quality connectors you can afford. The most common cause of connection faults is bad connectors.

Safety Information

Electricity and Telephone Wiring: When the telephone rings, and depending on how close you are to the central office, there may be a hazardous voltage (up to 150 volts) on the line. Take sensible precautions such as:

1. Disconnect phone lines until the last possible moment.
2. If you can stop incoming calls using a 'class' service or a 'do-not-disturb' feature use it while you are actively working on the wiring.
3. Make sure your footwear has good insulation characteristics.
4. Make sure all your tools have insulated handles
5. Avoid touching bare wires
6. NEVER work near water
7. Never work on wiring during an electrical storm
8. If you smell gas stop and have it investigated immediately by an expert

Now where did I put the telephone...

When you are wiring each access point be consistent and methodical. Either label each access point on the front cover (LAN, Telephone 1 etc) or use the same convention everywhere. Diagram 2 show one possible wall jack configuration.

Diagram 2 - Possible wall plate configuration

If you don't use a connection in a particular room - use a blank insert in its place don't change its position, for example, in EVERY room the second line is the bottom right position or whatever your stanard is.

We're starting to get a little Punchy

We are going terminate our 8 wire (4 pair) cat 5, 5e or 6 wires to the wiring block and then cross connect them to their destinations. Each LAN connection will go to a separate port on a HUB or Switch and the telephone pairs will go to our common telephone line(s). Diagram 3 shows this conceptually. Each pair is shown as single colored line to try and keep the level of detail as low as possible to give on overview of what we are trying to achieve. The REDs lines will connect from pairs 1,2 and 3,6 (using our suggested wiring scheme), the BLUE line represents Telephone Line 1 (pair 4,5) and the GREEN line represents Telephone Line 2 (pairs 7,8). Note: The color of the lines in diagram 3 should not be confused with the wire colors as shown in diagram 4. The colors were selected simply beause they provide the highest contrast on a white background and for no other reason. Diagram 4 shows the real wiring color as it appears on cat 5, cat 5e and 6 cables.

Diagram 3 - Cross Connect Overview

We have Lift-Off Houston

The following notes and diagrams assume that you are using the proposed color coding scheme. See diagram 4 below showing cat 5, 5e and 6 wiring colors.
Notes:

1. Punch all 8 conductors on each incoming (from rooms) wire onto the punch-block - use the same color sequence for every wire - most sensibly use the pin number sequence.
2. Keep the exposed conductor length as short as possible (max. 1", 2.5cm).
3. Make up the LAN-HUB/Switch 'pigtail' cables (straight) with an RJ45 connector on one end and separate exposed connectors on the other end. These cables should be long enough to go from the punch-down block to your HUB/Switch.
4. Trim the 4 unused conductors from this cable (blue, blue/white, brown, brown/white).
5. Punch each conductor of this cable onto the same colored conductor on the selected incoming cable - keep the exposed conductor length as short as possible (max. 1", 2.5cm).
6. Connect a PC into the LAN connection in the room from which the cable comes (you did remember to keep that diagram and you did label the cable ends didn't you?) and confirm you have a LINK on the Hub/Switch. If not stop and fix the problem before doing anything else.
7. Terminate each of the incoming telephone line wires on a SCREW terminal.
8. Punch one end of a JUMPER wire onto the relevant conductor of the incoming (from room) cable. Expose the metal of the conductor on the other end and connect it to the appropriate screw terminal of the telephone line. Note: In the diagram below the 'jumper wire' is shown as the same color as the conductor it is connected to, while this may be useful, it is not essential. Any wire color may be used.
9. Repeat the process above for each incoming (from room) cable.
10. Never try and punch more than two conductors into a single slot on the punch down block.
    

Diagram 4 - Detailed Color-Coded Wiring Diagram

We have (hopefully) Lift-off

Run around the house checking that everything works, rejoice and finish off watching that second TV program you almost missed. Phew!

And if it all goes Pear-shaped

Pear-shaped is a quaint British expression meaning ... well.. things are not so good.

Trouble Shooting Hints

Regretably there a lot of things that can go wrong - the following notes may help you:

1. Don't Panic - you can always make all your phone calls from the basement! Seriously: panic is not a very useful emotion - though perfectly natural. If you feel either panicky or tired: STOP. Go get some sleep or have a rest and something to eat - it really will be better when you start again.
2. Create and keep a 'gold standard', that is, use a single PC/laptop connect it directly to the hub via a cable that is long enough to strech from every room in the house to the hub - confirm that the Hub/Switch LINK led works every time and preferably use a PC that has a LINK led on its LAN card. Keep this configuration and move it to every room when you test the connection. At least you know something works. Plug this configuration into the wall connector under test and if you don't get LINK - it's your wall cable/punch-down cross-connect.
   The long cable and gold standard PC rig is designed to help isolate problems. An alternative strategy is to take the PC and its cable from the room in which it will be installed to the switch and confirm it works there. Depends on your own circumstances which stategy is more convenient or less exhausting. Of course before you do start dragging cables or lugging PCs around try the connection first. It may work first time. Then again it may not......
   LAN cable testers are available in a range of prices from $10s to $100s of dollars and if you are going to do a lot of wiring are well worth the investment.
   
3. Test every PC to wall LAN cable before you start by using them to connect to the Hub/Switch locally - you don't want to rip-up your installed cable until you are sure it's at fault.
4. Make no assumptions - test or check everything.
5. Buy a cheap magnifying glass - its almost impossible to do a visual check of punch-down connections (or any other for that matter) without one.
6. Use a 'continuity tester' or a volt-meter to check individual conductors in cables.

You can mail me to abhi.82@aol.in
Please  post any  suggestions or comments.

RS-232 Cables, Wiring and Pinouts

Brief tutorial and pinouts for RS-232, T1/E1 and V.35.

RS-232 standards(EIA-232) are defined by EIA/TIA (Electronic Industries Alliance /Telecommunications Industry Association). RS-232 defines both the physical and electrical characteristics of the interface. RS-232 is practically identical to ITU V.24 (signal description and names) and V.28 (electrical). RS232 is an Active LOW voltage driven interface and operates at +12V to -12V where:

Signal = 0 (LOW) > +3.0V (SPACE)
Signal = 1 (HIGH) < -3.0V (MARK)

DTE (PC) and DCE (Modem)

In serial communications the terminal end (PC) is called the Data Terminal Equipment (DTE) and the modem end is called the Data Communications Equipment (DCE) as shown in the diagram below.

Serial Communications with a modem

RS-232 signals have a direction (in or out) depending on whether they are with respect to a DTE or a DCE. In all the pinout diagrams below the signal direction is with respect to the DTE (PC) end.

NULL Modem Connections

When PCs are connected back-to-back each end is acting as a DTE (there is no DCE in this case) and consequently certain signals may have to be looped in the connection to satisfy any input signal requirement. This is called a NULL (no) modem configuration. For example, when the DTE raises Request to Send (RTS) it typically expects Clear to Send (CTS) from the DCE. Since there is no DCE to raise CTS, the outgoing RTS signal is looped in the NULL modem cable to the incoming CTS to satisfy the DTE's need for this signal. This is shown in the diagram below.

Serial Communications with a NULL modem configuration

DB9 and DB25 Male and Female Pin Numbering

These diagrams show the male (grey background) and female (black background) pin numbering for DB9 and DB25 sub-miniature connectors. Generally Pin 1 is marked on the front of the connector right next to the pin - though you may need a magnifying glass to read it. Some manufacturers mark each pin number on the plastic housing at the rear of the connector. The male connector has the pins sticking out!

DB25 Male and Female

DB25: View looking into male connector

DB25: View looking into female connector

DB9 Male and Female

DB9: View looking into male connector

DB9: View looking into female connector

RS232 on DB25 (RS-232C)

The use of each pin including methods for spoofing signals is described in our Signal/pin primer. The RS-232 DB25 connector is capable of supporting two separate connections - each with its own optional clock when used in Synchronous mode or Bit-Synchronous mode. If you are using the interface purely for Asynchronous communications then you only need those marked with (ASYNC) below or you can use even fewer (if you understand what is happening). The column marked Dir shows the signal direction with respect to the DTE.
Note: This is NOT the same as the DB25 Parallel port on a PC.

Pin No.	Name	Dir	Notes/Description
1	-	-	Protective/shielded ground
2	TD	OUT	Transmit Data (a.k.a TxD, Tx) (ASYNC)
3	RD	IN	Receive Data (a.k.a RxD, Rx) (ASYNC)
4	RTS	OUT	Request To Send (ASYNC)
5	CTS	IN	Clear To Send (ASYNC)
6	DSR	IN	Data Set Ready (ASYNC)
7	SGND	-	Signal Ground
8	CD	IN	Carrier Detect (a.k.a DCD).
9	-	-	Reserved for data set testing.
10	-	-	Reserved for data set testing.
11	-	-	Unassigned
12	SDCD	IN	Secondary Carrier Detect. Only needed if second channel being used.
13	SCTS	IN	Secondary Clear to send. Only needed if second channel being used.
14	STD	OUT	Secondary Transmit Data. Only needed if second channel being used.
15	DB	OUT	Transmit Clock (a.k.a TCLK, TxCLK). Synchronous use only.
16	SRD	IN	Secondary Receive Data. Only needed if second channel being used.
17	DD	IN	Receive Clock (a.k.a. RCLK). Synchronous use only.
18	LL	-	Local Loopback
19	SRTS	OUT	Secondary Request to Send. Only needed if second channel being used.
20	DTR	OUT	Data Terminal Ready. (ASYNC)
21	RL/SQ	-	Signal Quality Detector/Remote loopback
22	RI	IN	Ring Indicator. DCE (Modem) raises when incoming call detected used for auto answer applications.
23	CH/CI	OUT	Signal Rate selector.
24	DA	-	Auxiliary Clock (a.k.a. ACLK). Secondary Channel only.
25	-	-	Unassigned

NOTE: Leave all pins not specified above unconnected.

view - looking into male connector

(male and female connector diagrams)

RS232 on DB9 (EIA/TIA 574)

Signal functions are described in detail in our Signal/pin primer. The column marked Dir shows the signal direction with respect to the DTE.

Pin No.	Name	Dir	Notes/Description
1	DCD	IN	Data Carrier Detect. Raised by DCE when modem synchronized.
2	RD	IN	Receive Data (a.k.a RxD, Rx). Arriving data from DCE.
3	TD	OUT	Transmit Data (a.k.a TxD, Tx). Sending data from DTE.
4	DTR	OUT	Data Terminal Ready. Raised by DTE when powered on. In auto-answer mode raised only when RI arrives from DCE.
5	SGND	-	Ground
6	DSR	IN	Data Set Ready. Raised by DCE to indicate ready.
7	RTS	OUT	Request To Send. Raised by DTE when it wishes to send. Expects CTS from DCE.
8	CTS	IN	Clear To Send. Raised by DCE in response to RTS from DTE.
9	RI	IN	Ring Indicator. Set when incoming ring detected - used for auto-answer application. DTE raised DTR to answer.

DB9 (EIA/TIA 574): View - looking into male connector

(male and female connector diagrams)

RS232 on RJ45 (RS-232D)

More properly EIA/TIA - 561. Use when connecting to or from a serial port with a 8 position Modular Jack (RJ45). If you are cross-connecting from a DB9 or a DB25 use the signal names to cross connect the appropriate pins. To illustrate the process the equivalent pins used for cross-connecting a DB9 connector signals are shown (see DB9 pin-out above).

Signal/pin primer

RJ45 Pin No.	Name	DB9 Cross Connect	Notes/Description
1	DSR/RI	6,9	Data set Ready/ring indicator
2	DCD	1	Data Carrier Detect
3	DTR	4	Data Terminal Ready
4	SGND	5	Signal Ground
5	RD	2	Receive Data
6	TD	3	Transmit Data
7	CTS	8	Clear to Send
8	RTS	7	Request to Send

Note: Pin 1 is a multi-function pin sharing DSR (Data Set Ready) and RI (Ring Indicator). This means it is impossible to differentiate between a incoming ring signal (RI) and when the modem has finally connected and synched up (DSR). With local (null modem connections) or if the modem is run in auto-answer mode this is not normally a problem. If used with a modem and the DTE (the computer end) wants to control the connection the problem is more real. DSR would normally indicate the 'connected and synched-up' state following DTR from the DTE whereas RI simply indicates a ring voltage is present on the line and would normally be the trigger for the DTE to raise DTR if it wants to accept the call. DCD will indicate that a carrier has been received but does not indicate synchronization of both ends. In most cases however CTS (Clear To Send) in response to RTS (Request To Send) will not normally be returned until an end-to-end connection is available (equivalent to the DSR state).

RJ45 Male Connector Pin Numbering

RS232 DB25 NULL Modem Pinout

Use when connecting two systems (e.g. PCs) via their DB25 interfaces without a modem (i.e. back-to-back). See the full signal names in the DB25 sections.
If this pinout does not work for you then you could try our Signal/pin primer because you may need to SPOOF connections.
Note: This DB25 is NOT the same as the DB25 Parallel port on a PC which is defined here.

DB25	Signal	DB25	Signal
3	RD	2	TD
2	TD	3	RD
20	DTR	6,8	DSR, DCD
6,8	DSR, DCD	20	DTR
4	RTS	5	CTS
5	CTS	4	RTS
7	SGND	7	SGND
22	RI	22	RI

DB25: View - looking into male connector

(male and female connector diagrams)

NOTE:

1. Leave all pins not specified above unconnected.
2. We have received email suggesting that the above pinout looks like DTR from one side is driving into DSR/DCD on the other side - not normally a healthy situation. The emails miss the point that since this is a NULL modem connection both ends are DTEs. The two peer DTE's treat DSR/DCD signals as RX (INPUT) only. The INPUT DSR/DCD on one side is created by cross connecting the OUTPUT DTR signal for the other peer.

RS232 DB9 NULL Modem Pinout

Use when connecting two systems, for example two PCs, via their DB9 interfaces without a modem. Typically called a back-to-back or NULL modem connection. See the full signal names in the DB9 section.
If this pinout does not work for you then you could try our Signal/pin primer because you may need to SPOOF connections.

DB9	Signal	DB9	Signal
2	RD	3	TD
3	TD	2	RD
4	DTR	6,1	DSR, DCD
6,1	DSR, DCD	4	DTR
7	RTS	8	CTS
8	CTS	7	RTS
5	SGND	5	SGND
9	RI	9	RI

DB9 TIA/EIA 574: View - looking into male connector

(male and female connector diagrams)

NOTE:

1. We have received email suggesting that the above pinout looks like DTR from one side is driving into DSR/DCD on the other side - not normally a healthy situation. The emails miss the point that since this is a NULL modem connection both ends are DTEs. The two peer DTE's treat DSR/DCD signals as RX (INPUT) only. The INPUT DSR/DCD on one side is created by cross connecting the OUTPUT DTR signal for the other peer.

RS232 DB9 and DB25 Loopback Pinout

Loopback is a method of testing the RS232 connector and interface circuitry to ensure it is functioning correctly, that is, in layman's jargon - it ain't broke! If communication fails to occur between two machines the question that immediately arises is - which end is broken? In the worst case both ends could even be broken in which case ritual suicide may be the best solution. Loopback works by testing each end of the connection independently. Data is sent and received on the same RS232 connector - which may be either DB9 or DB25. The test normally consists of using some program to transmit data. The program then checks to ensure exactly the same data was received. Loopback testing gives you a binary result - it works, in which case the end under test is good, or it does not, in which case the end under test is broken. Pinouts are shown for both DB9 and DB25. The loopback is normally constructed in the DB shell or using a diagnostic light-box.

DB9 Loopback

DB9	Signal	Loopback to	Signal
2	RD	3	TD
3	TD	2	RD
4	DTR	6,1,9	DSR, DCD, RI
7	RTS	8	CTS
5	SGND	5	SGND

(DB9 male and female connector diagrams)

NOTE:

1. We show 4 (DTR) being looped to 6 (DSR), 1 (DCD) and 9 (RI). RI (9) is included because we understand that certain test programs use this to ensure a more complete test of the interface signal set.

DB25 Loopack

DB25	Signal	Loopback to	Signal
3	RD	2	TD
2	TD	3	RD
4	RTS	5	CTS
5	CTS	4	RTS
7	SGND	7	SGND
15	DB	17	DD
20	DTR	6,8,22	DSR, DCD, RI
23	CH/CI	23	CH/CI

(male and female connector diagrams)

NOTE:

1. For the sake of simplicity this loopback will only work for the primary channel. Full DB25 interfaces allow a secondary channel. If a complete interface loopback is required you will need to add pins 12, 13, 14, 16, 19, 24.
2. By looping the primary channel clocks (15 and 17) both synchronous and asynchronous capabilities can be tested. If only asynchronous tests are being performed omit this, and the pin 23 loopback
3. We show 20 (DTR) being looped to 6 (DSR), 8 (DCD) and 22 (RI). RI (22) is included because we understand that certain test programs use this to ensure a more complete test of the interface signal set.

RS232 DB9 NULL Modem Pinout on CAT5/CAT5(e)/CAT6

This is in response to a number of recent emails asking how to wire both ends of a DB9 connection using cat5, cat5(e) or cat6 cable. This must not be confused with DB9 to RJ45 (RS232D). We have shown a null modem (back-to-back PCs) only configuration. And if you want to use cat5, cat5(e) or cat 6 with a real modem (a DB25 connector)? Our advice - don't.
Warning:. There is, as far as we know, no standard to cover the use of cat5, cat5(e) or cat 6 (8 conductor) wiring when used with two DB9 connectors. Any such wiring scheme is therefore non-standard - that includes the wiring scheme below. Specifically this means that both ends of the cable must be wired in the same way and that no assumptions can be made about how the other end is wired. You will have to manually inspect both ends of the connection. Damage can result from mis-matched wiring.
A DB9 clearly has 9 connections and a cat5, cat5(e) and cat 6 cable has 8 conductors. RS232D has chosen to use Pin 1 as a multi-function pin (DSR/RI) to provide maximum flexibility with modems - in particular it allows for DCD which is a meaningful signal from a modem but not, we suggest, from a peer PC. We have chosen to use a minor variation on the normal DB9 Null modem pinout above - specifically we have allowed for RI which could be used from a peer PC to commence a transmission sequence. The colors used are unimportant but the suggested configuration is one way to provide the shortest use of the adjacent (twisted) pairs.
If this pinout does not work for you then you could try our Signal/pin primer because you may need to SPOOF connections.

PC1 Peer			PC2 Peer
DB9	Signal	cat5(e) Color	DB9	Signal	cat5(e) Color
2	RD	Brown	3	TD	Blue
3	TD	Blue	2	RD	Brown
4	DTR	Green	6,1	DSR, DCD	Brown-white
6,1	DSR, DCD	Brown-white	4	DTR	Green
7	RTS	Blue-white	8	CTS	Green-white
8	CTS	Green-white	7	RTS	Blue-white
5	SGND	Orange	5	SGND	Orange
9	RI	Orange-white	9	RI	Orange-white

DB9: View - looking into male connector

(male and female connector diagrams)

NOTE:

1. We have received email suggesting that the above pinout looks like DTR from one side is driving into DSR/DCD on the other side - not normally a healthy situation. The emails miss the point that since this is a NULL modem connection both ends are DTEs. The two peer DTE's treat DSR/DCD signals as RX (INPUT) only. The INPUT DSR/DCD on one side is created by cross connecting the OUTPUT DTR signal for the other peer.

RS232 DB9 to DB25 Pinout

Use when connecting a DB9 (e.g. a PC) to a DB25 (e.g. a modem) interface. See the full signal names in the DB9 and DB25 section.
Signal/pin primer

DB9	Signal	DB25
1	DCD	8
2	RD	3
3	TD	2
4	DTR	20
5	SGND	7
6	DSR	6
7	RTS	4
8	CTS	5
9	RI	22

View - looking into male connector

(male and female connector diagrams)

View - looking into male connector

(male and female connector diagrams)

NOTE: Leave all pins not specified above unconnected.

RS232 DB9 to DB25 NULL Modem Pinout

Use when connecting two systems (e.g. PCs) when one has a DB9 interface and the other a DB25 interface without a modem. Typically called a back-to-back or NULL modem connection. See the full signal names in the DB9 and DB25 sections.

Signal/pin primer

DB9	Signal	DB25	Signal
2	RD	2	TD
3	TD	3	RD
4	DTR	6,8	DSR, DCD
6,1	DSR, DCD	20	DTR
7	RTS	5	CTS
8	CTS	4	RTS
5	SGND	7	SGND
9	RI	22	RI

DB9: View - looking into male connector

(male and female connector diagrams)

View - looking into male connector

(male and female connector diagrams)

NOTE: Leave all pins not specified above unconnected.

EIA/TIA RS-530-A (DB25)

RS 530-A defines the pinout when using either balanced RS-422 (and RS-485) or unbalanced RS-423 electrical interfaces using a DB25 connector. By using a DB25 connector RS-530 is now frequently used to replace many older standards which defined hideously huge connectors such as V.35. (used a whopping 35 pin connector) and RS-449 (used a pretty serious 37 pin connector).

V.35 on DB25 (RS-530-A)

The original V.35 specification defined use of balanced signals over a huge 35 pin connector. V.35 has been obsolete for years (replaced with V.10 and V.11) though the term is still frequently used. Most modern systems that call themselves V.35 use a DB25 connector which has more modest dimensions. The A (+) and B (-) below refer to each signal pair used in balanced serial interfaces. When used with RS-423 (unbalanced) the B (-) are tied to a common ground. Signals marked U under Bal/Ubal are not balanced since they typically change very infrequently (for example once per session) and therefore do not affect TX/RX performance sensitivity - hence speed. BEWARE: RS-530 (without the A suffix) is an earlier standard and is wired differently. This is the 530-A pinout spec.

Signal/pin primer

Pin No.	Name	Bal/Ubal	Notes/Description
1	Shield		Cable Shield, connected at DTE only.
2	BA		Transmit Data (A+) (a.k.a TxD)
3	BB		Received Data (A+) (a.k.a. RxD)
4	CA/CJ		RTS (A+) Request To Send
5	CB		CTS (A+) Clear To Send
6	CC	U	Data Communications Equipment Ready (modem/CSU) (a.k.a DSR)
7	AB		Signal Ground
8	CF		Data Carrier Detect (A+) (a.k.a DCD, CD or RLSD)
9	DD		Receiver Signal Element Timing (B-) RX Clock
10	CF	-	Data Carrier Detect (B-) (a.k.a DCD, CD or RLSD)
11	DA	-	Ext. Transmit Clock (B-)
12	DB		Transmit Signal Element Timing (B-) TX CLOCK
13	CB		CTS (B-) Clear to Send
14	BA		Transmit Data (TD) (B-) (a.k.a TxD)
15	DB		Transmit Signal element Timing (A+) TX CLOCK
16	BB		Received Data (B-) (a.k.a RxD)
17	DD		Receiver Signal Element Timing (A+) RX CLOCK
18	LL	U	Local Loopback
19	CA/CJ		RTS (B-) Request to Send
20	CD	U	DTE Ready (a.k.a DTR)
21	RL	U	Remote Loopback
22			RI Ring Indicator
23	AC		Signal Ground
24	DA		Ext TX Clock (A+)
25	TM	U	Test Mode

NOTES:

• Leave any pins not specified above unconnected.
• In balanced mode signals with the same name are the paired set, for example, pins 2 and 14 are both named BA and form the Transmit Data pair. Each signal of the pair is either a high (A+) or low (B-)
• When used with RS-485 in half-duplex, multi-dropped environments a simple three signal arrangements is frequently used - one pin is used as a GND and RX/TX is alternately switched onto a balanced pair of wires which can be either the BA (TX) or BB (RX) pair.

View - looking into male connector

(DB25 male and female connector diagrams)

DB - Designations for D-subminiature Connectors

This lists the designations for DB connectors (supplied by Rob Recny - Thanks). Any errors in this list are ours not Rob's.

• A - 15-pin 2-row joystick connector.
• B - 25-pin 2-row serial or parallel connector - also 44-pin high-density 3-row.
• C - 37-pin connector - sometimes found on multi-port serial or data acquisition boards.
• D - 50-pin connector - a little longer than C, but three rows using the same pins as the 2-row connectors.
• E - 9-pin 2-row serial - also 3-row VGA.

So a DB9 is more properly a DE-9P. Isn't knowledge a wonderful thing!
The thread size on an RS232 receptacle (the jackscrew) is UNC 4-40.

T1/E1 Pinout (RJ-48C)

T1/E1 wiring may use either a RJ45, DB15 or BNC connectors. The pinout shown uses RJ45 connectors - its formal name is USOC RJ-48C and is defined in ANSI T1-403-1989. T1 is a North America (primarily) digital service providing 1.544 Mbps. E1 is a European/Rest of World standard providing digital service at 2.048 Mbps. CATegory 5(e) cabling is used to provide balanced pairs. The color coding for Cat 5(e) cabling may be 568A or 568B.

RJ45 Pin	Signal	Notes
1	RX1 (Ring - negative)
2	RX2 (TIP - positive)
3	FGND (RX GND)	Ground/Shield
4	TX1 (Ring - negative)
5	TX2 (TIP - positive)
6	FGND (TX GND)	Ground/Shield
7	NC	Unused
8	NC	Unused

NOTES:

1. NC = Not connected.
2. There are a confusing number of pinouts for use with an RJ45/48C connector. Some specs show use of pins 7,8 for Grounds. Always consult any equipment specification if available.
3. The telecom world loves its Tip and Ring designations. Tip is assumed to carry a positive voltage (and would carry the transmission signal), Ring a negative voltage (and would carry the inverted transmission signal)

 You can mail me to abhi.82@aol.in
Please  post any  suggestions or comments.

LAN Wiring & Pinouts - 10base-T, 100base-TX/T4, 1000base-T, 10Gbase-T

LAN Wiring & Pinouts - 10base-T, 100base-TX/T4, 1000base-T, 10Gbase-T

Crossed and Straight cables - when to use them

The following diagram shows the Normal use of Crossed and Straight cables (see also the notes below).

Notes:

1. We show Straight cables as BLUE and Crossed as RED. That is our convention. The cable color can be anything you choose or, more likely, the vendor decides.
2. To avoid the need for Crossed cables many vendors provided UPLINK ports on Hubs or Switches - these were specially designed to allow the use of a STRAIGHT cable when connecting back-to-back Hubs or Switches. Read the manufacturers documentation carefully.
3. Increasingly vendor hubs (can you still buy them) and switches will auto-detect the connection type and internally switch the connectors so that STRAIGHT cables can be used everywhere.

Standards Summary

The various standards can get a tad complicated and messy. We get occasional email requesting a summary of the standards - this is our attempt to provide a quick overview.

Standard	Required Pairs	10M	100M	1000M	10G	Cable	Notes
10base-T	2 (1/2 and 3/6)	yes	yes	no	no	cat 5, 5e, 6	100m support only if no cat 3/4 in run
100base-TX	2 (1/2 and 3/6)	yes	yes	no	no	cat 5, 5e, 6	100m support only if no cat 3/4 in run
100base-T4	4 (1/2, 3/6, 4/5 and 7/8)	yes	yes	yes	yes	cat 3, 4, 5, 5e, 6	max of 100m if cat 3 or 4 in network
1000base-T	4 (1/2, 3/6, 4/5 and 7/8)	yes	yes	yes	yes	cat 5e, 6	Functionally identical to 100base-T4. Some cat cables may be acceptable.
10Gbase-T	4 (1/2, 3/6, 4/5 and 7/8)	yes	yes	yes	yes	cat 6a	cat 6 cables may be used but have distance limitations.

Category 5(e) (UTP) colour coding table

The following table shows the normal colour coding for category 5 cables (4 pair) based on the two standards supported by TIA/EIA (see also our primer on this topic)
We get occasional email about the difference between 568A and 568B wiring. Which one you use is a matter of local decision. These standards apply to the color code used within any SINGLE cable run - BOTH ENDS MUST USE THE SAME STANDARD. However, since they both use the same pinout at the connectors you can mix 568A and 568B cables in any installation.

 

10baseT Straight Cable (PC to HUB/SWITCH)

Straight cables are used to connect PCs or other equipment to a HUB or Switch. If your connection is PC to PC or HUB to HUB you MAY need to use a Crossed cable with older equipment. Most modern Hubs and Switches provide auto-sensing which means a straight cable can always be used.
The following cable description is for the wiring of both ends (RJ45 Male connectors) with the 568B category 5(e) wiring colors you could, of course, use the 568A colour scheme.

Pin No.	strand color	Name
1	white and orange	TX+
2	orange	TX-
3	white and green	RX+
4	NC	*
5	NC	*
6	green	RX-
7	NC	*
8	NC	*

NOTE: Items marked * are not necessary for 10M LANs (10base-T) but since you will be moving shortly to 100MB or Gigabit LANs (won't you) you will save yourself a LOT OF TIME finding crappy cable (that you made) that does not work. Instead we suggest you wire to 100Base-T4 standards. After all you gotta stick the ends somewhere man.
We use BLUE for 10base-T straight cables. NOTE: All our wiring is now done to the 100base-T4 spec which you can use with 10base-T networks - but NOT necessarily the other way around.

10baseT Crossed cable (PC to PC or HUB to HUB)

Crossed cables are used to connect PCs to one other PC or to connect a HUB to a HUB. Crossed cables are sometimes called Crossover, Patch or Jumper cables. If your connection is PC to HUB you MUST use a Straight cable.
The following description shows the wiring at both ends (male RJ45 connectors) of the crossed cable.

One end RJ45 Male	Other end RJ45 Male
1	3
2	6
3	1
4 *	5 *
5 *	4 *
6	2
7 *	8 *
8 *	7 *

NOTES:

1. Items marked * are not necessary for 10M LANs but since you will be moving shortly to 100MB or Gigabit LANs (won't you) you will save yourself a LOT OF TIME finding crappy cable (that you made) that does not work. Instead we suggest you wire to 100BaseT standards.
2. We use RED for crossed cables (or more commonly now a red heat-shrink collar at each end).
3. All our crossed wiring is done to the 100base-T4 spec which you can use with 10baseT networks - but NOT always the other way around.

100base-T Straight Cable (PC to HUB/SWITCH)

Straight cables are used to connect PCs or other equipment to a HUB or Switch. If your connection is PC to PC or HUB to HUB you MAY need to use a Crossed cable with older equipment. Most modern Hubs and Switches provide auto-sensing which means a straight cable can always be used.
The following cable description is for the wiring of BOTH ends (RJ45 Male connectors) with your category 5 wiring colors (TIA/EIA 568A or 568B though the example uses 568B colors).

Pin No.	conductor color	Name
1	white and orange	TX_D1+
2	orange	TX_D1-
3	white and green	RX_D2+
4	blue	BI_D3+ **
5	white and blue	BI_D3- **
6	green	RX_D2-
7	white and brown	BI_D4+ **
8	brown	BI_D4- **

We use BLUE for 100baseT straight cables.
NOTES:

1. Wires marked ** are ABSOLUTELY NECESSARY for 100Base-T4 networks - used when any combination of category 3/4/5 cables are present, when using 1000base-T (GigE) and MAY be required for Power-over-Ethernet (PoE) - see below.
   
2. Wires marked ** are not essential for 100Base-TX (using cat 5/5e6/6a ONLY cables) and CAN be used for other purposes, for example, telephony but, .. beware .. read this FAQ and our LAN plus Telephony article before you wire your entire neighbourhood for surround sound.
3. The Power-over-Ethernet spec (802.3af) allows three schemes where power may be supplied. Two of these schemes use pairs 4,5 and 7,8 (marked ** in above table) for power (called Midspan PSE and Alternative B or Mode B), one scheme uses ONLY pairs 1,2 and 3,6 (Endpoint PSE, Alternative A or Mode A) for both signals and power. Depending on which scheme you use pairs 4,5 and 7,8 may be required. See Power over Ethernet (PoE).
4. Gigabit Ethernet requires all 4 pairs (8 conductors).
5. All our wiring is now done to the 100base-T4 spec which you can use with 1000base-T and even 10baseT networks - but NOT the other way around.

100base-T Crossed cable (PC to PC or HUB to HUB)

Crossed cables are used to connect PCs to one other PC or to connect a HUB to a HUB. Crossed cable are sometimes called Crossover, Patch or Jumper cables. If your connection is PC to HUB you MUST use a Straight cable. Most modern Hubs and Switches provide auto-sensing which means a straight cable can always be used.
The following description shows the wiring at both ends (male RJ45 connectors) of the crossed cable. Note: The diagrams below shows crossing of all 4 pairs and allows for the use of cat3/4 cables with 100m LANs (100base-T4). Pairs 4,5 and 7,8 do not NEED to be crossed in 100base-TX wiring. See notes below.

We use RED for crossed cables (or more commonly now a red heat-shrink collar at each end).
NOTES:

1. All our crossed wiring is now done to the 100base-T4 spec (uses all 4 pairs, 8 conductors) which you can use with 1000base-T and even 10base-T networks - but NOT necessarily the other way around.
2. Many commercial 100m LAN patch cables seem not to cross pairs 4,5 and 7,8. If there is no cat3/4 wiring in the network this perfectly acceptable.
3. Gigabit Ethernet uses all 4 pairs so requires the full 4 pair (8 conductor) cross configuration (shown above).
4. If you are using Power-over-Ethernet (802.3af) then Mode A or Alternative A uses pairs 1,2 and 3,6 for both signals and power. Mode B or alternative B uses 4,5 and 7,8 to carry power. In all cases the spec calls for polarity insensitive implementation (using a diode bridge) and therefore crossing or not crossing pairs 4,5 and 7,8 will have no effect. See Power over Ethernet (PoE).

1000base-T Gigabit Ethernet

1000base-T is the copper based version of the gigabit Ethernet standard defined by 802.3ab which, since it is over 12 months old, is available free of charge from the enlightened IEEE. Great work. In passing, if you want to see sophistry raised to an art form read the EIA's justification for charging for their specifications. (Note: The original EIA statement is, unfortunately, no longer available on-line. This is a great loss to the development of the English language in general, and comedy writing in particular.) The following notes apply to the 1000base-T spec:

1. The standard defines auto-negotiation of speed between 10, 100 and 1000 Mbit/s so the speed will fall to the maximum supported by both ends - ensuring inter-working with existing installations.
2. The cable specification base-line is ANSI/TIA/EIA-568-A-1995 (which you have to pay for). This means that if you know your cat5 cable was manufactured to this standard (there was a lower rated 1991 version of this specification) then it will support Gigabit Ethernet. Cat5 cable manufactured to the old specification may work or it may not - you need to run some tests. Cat 5e and cat 6 being higher spec cables will support Gigabit Ethernet.
3. Maximum runs are the standard 100m (~330ft).
4. Gigabit Ethernet uses all 4 pairs (8 conductors). The transmission scheme is radically different from 10 and 100 Mbit/s standards (PAM-5: a 5 level amplitude modulation scheme) and each conductor is used for send and receive.
5. Crossed Gigabit Ethernet cables must cross all 4 pairs however it should be noted that since all 1000base-T equipment includes automatic crossover detection, crossed 1000base-T cables are extremely rare.
6. Because of the higher speeds everything about a Gigabit cable must be correct. Specifically the connectors must be rated for Gigabit operation with minimal untwisting of the cable when adding the connector. See also cabling hints.
7. When Cat6 cables are used these will also support 10 Gbit/s operation up to 55m. When Cat6a cables are used these will support 10 Gbit/s operation up to 100m.
   

10Gbase-T 10 Gigabit Ethernet

This is serious stuff only for server-server installations at this time - most PCs have a hard time even driving Gigabit networks. 10Gbase-T defines 10 gigabit Ethernet over copper cables (multiple other PHYs also exist within the 10G Ethernet ecosystem). Originally defined in 802.3an (2006) this has now been consolidated into the base 802.3-2008 spec (available at no cost from the IEEE). The followings notes apply to 10Gbase-T:

1. The standard allows for auto-negotiation and thus 10Gbase-T will interwork with 10base-T, 100base-TX/T4 and 1000base-T networks but default, obviously, to the highest common speed supported on any given point-to-point connection.
2. All 4 pairs - 8 connectors are required - it uses 1000base-T (or 100base-T4) wiring.
3. 10Gbase-T requires category 6a wiring defined by ANSI/TIA-568-C.2 (ISO 11801 amendment 2) to support 100m (~330ft) runs. Category 6a wiring is bigger (standard allows up to 0.35 inch cable diameter vs ~0.20 for cat 5e and ~0.23 for cat 6) and currently (2011) around 30% more expensive than cat 6 which is around 50% more expensive than cat 5e.
4. Category 6 wiring will support 10Gbase-T at up to 55m (~185ft) in electrically quiet environments and up to 37m (~81ft) in electrically noisy environments (such as in cable bundles, elevator shafts, proximity to flourescent lights). The measurement of electrical noise threshold levels (especially cross-talk) for cat 6a cables is defined by TIA-155-A (and ISO TR 24750) both of which you will have the dubious pleasure of paying for - handsomely.
5. To maintain 10G speeds needs serious attention to all wiring practices. Minimum bending radii, careful attention to connectors and minimum untwisting of pairs are all crucial - this is not amateur stuff. STP may be a safer option (a view not always shared by the cable suppliers) or optical.
   

Power over Ethernet (PoE)

The original PoE specification was 802.3.af (2003) which has been superseded by 802.3at (2009). The primary differences are that the new 802.3at specification includes support for Gigabit LANs and raises the power levels available when using certain cable types. The following notes apply:

1. The power available at each end-point with 802.3af is 13.0 Watts (W). The maximum input voltage is 44V DC at a current of 350ma which gives a figure of 15.4 W (44 x 350/100) but due to power losses in cables the 13.0 W value is guaranteed even at maximum (100m - ~330ft) runs on category 5, 5e and 6 wiring.
2. The current 802.3at standard spilts systems into two categories for PoE levels based on the cable type. Type 1 covers cat 5 cables and these remain limited to the 802.3af limits of 13 W. Type 2 covers cat 5e (the actual minimum spec is ANSI/TIA/EIA-568-A-1995 which does cover some late cat 5 cables which only became available some time after 1995) and cat 6 cables and increases the maximum current to 600ma giving a maximum power figure of 44 x 600/100 = 26.4 W. Again due to losses over distance (lower than with Type 1 systems) this gives a figure of 25.5 W which is available even at maximum (100m - ~330ft) runs.
3. Power Wiring: 802.3at defines two Alternatives (A and B) depending on your wiring system.
   
   • If you are using 10base-T or 100base-TX (both only need 2 pairs - 4 connectors) then Alternative A wiring sends power over the signal pairs 1,2 and 3,6 since these may be the only ones connected. Alternative B wiring uses the unused pairs 4,5 and 7,8 for power and will clearly only work for systems which have connected all 4 pairs (and are therefore using 100base-T4 wiring!).
   • If you are using 100base-T4 or 1000base-T (both need 4 pairs - 8 connectors) then Alternative A wiring sends power over the signal pairs 1,2 and 3,6. Alternative B wiring uses the signal pairs 4,5 and 7,8. Since 100base-T4 and 1000base-T need all 4 wires connected there is no functional difference between Alternative A and B in this case.
     

RJ45 Connector (Plug and Receptacle) Pin Numbering

RJ45 Male Connector (Plug) and Female Connector (Receptacle)

Notes:

1. Today the male connector is more normally called a plug and the female connector a receptacle. Historically the term Jack was frequently used to describe what is now called a plug and Wall-Jack, or even just Jack, to describe the receptable. It's complicated.
2. While most commonly referred as an RJ45, it is a modular connector with the catchy name of 8P8C (8 Positions, 8 Connections). RJ - in case you were wandering - means Registered Jack.
3. The receptacle numbering is shown using a FRONT view (left to right, pin 1 - 8). Beware however, receptacles are wired from the REAR and hence the numbering will be inverted. Viewed from the REAR the numbering will be left to right, pin 8 - 1.
   

RJ45 Connections - some hints

We get mail saying 'Help. I've wired it correctly but it does not work'. Here are some simple notes that may help. Remember: it's more difficult that you think.
Use the best crimp tool you can afford or borrow. A cheap magnifying glass can sometimes help enormously. LAN cable testers are available in a range of prices from $10s to $100s of dollars and if you are going to do a lot of wiring are well worth the investment.

1. The RJ45 connector is the critical connection. Always use the highest quality connectors you can afford and rated for the cable category (using category 5e rated connectors with categeory 6/6a cable is a stupid economy). The most common cause of connection faults are bad connectors.
   
   There are different connectors for stranded and solid cable and manufacturers do not always do a good job at differentiating them. Spend the time to make sure you have the right connector type. Category 6/6a cables have higher rated (read - more expensive) connectors - always use them - don't penny-pinch. If you use the wrong type of connector the cable may work initially but it will almost certainly fail very quickly - then you'll spend hours debugging the problem. It will all end in tears as mothers throughout the world used to say, and probably still do.
2. Make and test practice cables until you get it right every time - especially before you destroy a cable you just spent 2 hours fitting.
3. When installing cable runs ensure the bend radius is within the cable specification and avoid kinks and excessive cable twisting. While the bend radius for Cat5/5e/6 is defined to be approximately 1 inch, in general this should be avoided and a more generous 3 - 6 inches should be allowed unless absolutely necessary.
4. When cutting the exterior cover of the cable be very careful not to cut the insulation cover of the conductors since this can cause shorts. Bottom line: the cable won't work.
5. Expose a maximum of 1 inch of individual conductors when preparing the cable for connection.
6. Untwist the pairs and line up all the conductors according to the wiring standard you are using. Only untwist the exposed connector pairs that lie outside of the exterior cover. Do not allow the untwisting operation to propagate under the exterior cover.
7. Measure the cable end by placing it beside the RJ45 and trim the conductor ends so they are are all the same length and no conductor wire is visible outside the plastic cover of the RJ45 connector. This procedure also ensures the absolute minimum of untwisted cable is used. Untwisting too much cable can easily cause reduced speed - especially when running Gigabit connections.
8. Carefully slide the prepared cable into the RJ45 connector making sure the end of the conductors reaches the end of the RJ45 connector.
9. Place the crimp tool carefully over the connector and make the connection with a single firm squeeze operation.
10. Visually inspect the connection and test the cable before fitting if possible.

Note: If you are having problems, throwing the crimp tool accross the room or beating your head against the nearest wall rarely improves the situation. Inspect the connection with a magnifying glass to see what is going wrong and then go and sit down in a dark room for 30 minutes (aka take a break) before trying again. This sometimes works.

Shielded Twisted Pair

Shielded Twisted Pair (STP) comes in a variety of formats. It is typically used in three applications:

1. Where there is significant EMI (Electro-Magnetic Induction) in the environment such as that caused by high-powered electric motors (for example, in elevator shafts), flourescent lighting, heavy industrial equipment, etc. In this case the ethernet signals in the cable require protection against external interference from either adjacent pairs or the environment.
2. Where there is extremely sensitive electrical/electronic equipment in the surrounding environment or where security requirements demand elimination of eavesdropping possibilities from radiated LAN signals (TEMPEST). In this case the ethernet signals in the shielded cable are contained and prevented from polluting, or escaping into, the external environment.
3. Where maximum performance - either speed or distance - is required. The problem here is normally Alien Crosstalk (ANEXT) such as can occur in very high speed (gigabit and 10gb) LANs. As Ethernet speeds continue to increase either fiber or Shielded Twisted Pair is becoming increasingly common. For instance, to reach 100m distances at 10Gb speeds on copper cables will require shielded cable (limited to 55m for UTP).

Shielded cable comes in three broad types with a confusing range of terminology:

1. Where there is a single foil (FTP - Foil Twisted Pair) or braided (ScTP - Screened Twisted Pair) shield inside the jacket covering all four pairs. Suitable for applications 1 and 2 above.
2. Where there is a foil shield covering each pair. This is frequently refered to as PiMF (Pairs in Metal Foil) and is designed primarily to eliminate Alien Cross-talk (ANEXT) from adjacent pairs. Suitable for application 3 above.
3. Where there is a foil shield covering each pair and a (Foil or Braided) shield covering the whole cable. This is frequently refered to as SSTP (Double Shield Twisted Pair) or even PiMF - since many manufacturers also add a jacket shield to foil covered pair cables. Suitable for applications 1, 2 and 3 above.

In almost all cases there is a single ground wire (called a drain) which allows for connection to secondary grounding sources.
The diagram below illustrates the differences:

Notes:

1. Shielded cable of any variety has a greater diameter than UTP and will therefore occupy more space in cable ducting and raceways.
2. Connecting shielded cable is more complex and time consuming - but not execessively so - than conventional UTP. Manufacturers specifications vary enormously, expecially with respect to grounding, and should be followed closely.
3. In shielded cable installations the jacks and receptacles are typically made of metal and the cable shield (foil or braid) is connected electrically to the connector and thence through the metal receptable to a suitable ground provided by the end equipment.
4. Foil covered pairs are typically not connected to ground and thus provide only alien crosstalk immunity from adjacent pairs (ANEXT).
5. Manufacturers specifications and measurements suggest that shielded cables do NOT create antenna effects - indeed experiments show that UTP creates a substantially greater antenna effect (~40db) over correctly grounded shielded cables.
6. Even ungrounded shielded cables provide better performance (by ~20db) than conventional unshielded twisted pair (UTP).
7. The drain wire provides a secondary or auxiliary ground method in cases where metallic path grounding is provided by the connectors and, as such, is optional. In cases where metal connectors are not being used (there is no grounding via the connectors) the drain wire may be used as the primary grounding method and needs to be routed independantly to a suitable ground. The drain wire (cable ground) needs to be exposed before the connector is added. This process could require a considerable length of exposed drain wire depending on the location of the ground source. A plastic insulating sheath should be placed over the drain wire to minimize electrical hazards.
8. In all cases where both ends of a shielded cable are grounded this should be done using a common (building) ground to avoid ground potential loops which if they exceed 1V will have serious effects on cable performance. It is also important to note that 'grounding both ends' means final equipment terminations. Intermediate jacks or faceplates must maintain electrical continuity throughout the cable run but are not themselves grounded. This app note from AMP provides a detailed explanation.

  

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