D-Link Dsh8 Manual

							
 Chapter 8: Power Over Ethernet Overview 
GE-DSH-73/DSH-82 and DSH-82-PoE User Manual  167 
Figure 8-2 - Power Supplied over the Data Pins 
 
When to install PoE? 
Consider the following scenarios: 
•  • Youre planning to install the latest  VoIP Phone system to minimize cabling 
building costs when your company move s into new offices next month.   
•  • The company staff has been clamoring fo r a wireless access point in the picnic 
area behind the building so they can work on their laptops through lunch, but the 
cost of electrical power to th e outside is not affordable.  
•  • Management asks for IP Surveillanc e Cameras and business access systems 
throughout the facility, but they would ra ther avoid another electricians payment. 
 
 
References: 
IEEE Std 802.3af-2003 (Amendment to IEEE Std 802.3-2002, including IEEE\
 Std 
802.3ae-2002), 2003 Page(s):0_1-121 
White Paper on Power over Ethernet (IEEE802.3af) 
http://www.poweroverethernet.com/articles.php?article_id=52 
Microsemi /PowerDsine 
http://www.microsemi.com/PowerDsine/ 
Linear Tech 
http://www.linear.com/ 
  
						

							
Chapter 8: Power Over Ethernet Overview 
168  GE-DSH-73/DSH-82 and DSH-82-PoE User Manual 
The PoE Provision Process 
While adding PoE support to networked devices is relatively painless, it should be 
realized that power cannot simply be tran sferred over existing CAT-5 cables. Without 
proper preparation, doing so may result in  damage to devices that are not designed 
to support provision of power  over their network interfaces. 
The PSE is the manager of the PoE process.  In the beginning, only small voltage level 
is induced on the ports output, till a valid  PD is detected during the Detection period. 
The PSE may choose to perform classification , to estimate the amount of power to be 
consumed by this PD. After a time-contro lled start-up, the PSE begins supplying the 
48 VDC level to the PD, till it is physica lly or electrically disconnected. Upon 
disconnection, voltage  and power shut down. 
Since the PSE is responsible for the PoE proc ess timing, it is the one generating the 
probing signals prior to operating the PD  and monitoring the various scenarios that 
may occur during operation. 
All probing is done using voltage induction and current measurement in return. 
Stages of powering up a PoE link 
 
Stage Action Volts specified 
per 802.3af 
Volts 
managed 
by 
chipset  
Detection Measure whether powered device has the correct 
signature resistance of 15–33 k Ω 2.7-10.0 1.8–10.0 
Classification Measure which power level class the resistor indicates 14.5-20.5 12.5–25.0 
Startup Where the powered device will startup >42 >38  
Normal 
operation Supply power to device 36-57 25.0–60.0 
Line Detection 
Before power is applied, safety dictates that it  must first be ensured that a valid PD is 
connected to the PSEs output. This process  is referred to as line detection, and 
involves the PSE seeking a specific, 25 KO  signature resistor. Detection of this 
signature indicates that a valid PD is conne cted, and that provision of power to the 
device may commence.  
						

							
 Chapter 8: Power Over Ethernet Overview 
GE-DSH-73/DSH-82 and DSH-82-PoE User Manual  169 
The signature resistor lies in the PDs PoE fr ont-end, isolated from the rest of the PDs 
circuitries till detection is certified.  
Classification 
Once a PD is detected, the PSE may option ally perform classification, to determine 
the maximal power a PD is to consume. Th e PSE induces 15.5-20.5 VDC, limited to 
100 mA, for a period of 10 to 75 ms respon ded by a certain current consumption by 
the PD, indicating its power class.  
The PD is assigned to one of 5 classes: 0  (default class) indicates that full 15.4 watts 
should be provided. Classes 1-3 indicate  various required power levels and 4 is 
reserved for future use. PDs th at do not support classification are assigned to class 0. 
Special care must be employed in the defini tion of class thresholds, as classification 
may be affected by cable losses. 
Classifying a PD according to its power  consumption may assist a PoE system in 
optimizing its power distribution. Such a sy stem typically suffers from lack of power 
resources, so that efficien t power management based on  classification results may 
reduce total system costs. 
Start-up 
Once line detection and optional classifica tion stages are completed, the PSE must 
switch from low voltage to its full volt age capacity (44-57 Volts) over a minimal 
amount of time (above 15 microseconds). 
A gradual startup is required, as a sudden ri se in voltage (reaching high frequencies) 
would introduce nois e on the data lines. 
Once provision of power is initiated, it is  common for inrush current to be experienced 
at the PSE port, due to the PDs input capac itance. A PD must be designed to cease 
inrush current consumption (of over 350 mA)  within 50 ms of power provision startup. 
Operation 
During normal operation, the PSE provides  44-57 VDC, able to support a minimum of 
15.4 watts power. 
Power Overloads 
The IEEE 802.3af standard defines handling of  overload conditions. In the event of an 
overload (a PD drawing a higher power le vel than the allowed 12.95 Watts), or an 
outright short circuit caused by a failure in  cabling or in the PD, the PSE must shut  
						

							
Chapter 8: Power Over Ethernet Overview 
170  GE-DSH-73/DSH-82 and DSH-82-PoE User Manual 
down power within 50 to 75 milliseconds, while limiting current drain during this 
period to protect the cabling infrastructu re. Immediate voltage drop is avoided to 
prevent shutdown due to random fluctuations. 
Power Disconnection Scenarios 
The IEEE 802.3af standard requires that  devices powered over Ethernet be 
disconnected safely (i.e. power needs be s hut down within a short period of time 
following disconnection of a PD from an active port). 
When a PD is disconnected, there is a dange r that it will be replaced by a non-PoE-
ready device while power is still on. Im agine disconnecting a powered IP phone 
utilizing 48 VDC, then inadvertently plugging  the powered Ethernet cable into a non-
PoE notebook computer. Whats sure  to follow is not a pretty picture. 
The standard defines two mean s of disconnection, DC Disconnect and AC Disconnect, 
both of which provide the same functionality - the PSE shutdowns power to a 
disconnected port within 300 to 400ms. The upper boundary is a physical human limit\
 
for disconnecting one PD  and reconnecting another. 
DC Disconnect 
DC Disconnect detection involves measurem ent of current. Naturally, a disconnected 
PD stops consuming current, which can be  inspected by the PSE. The PSE must 
therefore disconnect power within 300 to  400 ms from the current flow stop. The 
lower time boundary is important to preven t shutdown due to random fluctuations. 
AC Disconnect 
This method is based on the fact that when a valid PD is connected to a port, the AC 
impedance measured on its terminals is sign ificantly lower than in the case of an 
open port (disconnected PD). 
AC Disconnect detection involves the induction  of low AC signal in addition to the 48 
VDC operating voltage. The returned AC sign al amplitude is monitored by the PSE at 
the port terminals. During normal operation,  the PDs relatively low impedance lowers 
the returned AC signal while a sudden disc onnection of this PD will cause a surge to 
the full AC signal level and will indicate PD disconnection. 
 
  
						

							
 
GE-DSH-73/DSH-82 and DSH-82-PoE User Manual  171 
Appendix A 
RJ-45 Pin Assignment  
Switchs RJ-45 Pin Assignments 
 
1000Mbps, 1000Base T 
 
Contact MDI MDI-X 
1 BI_DA+ BI_DB+ 
2 BI_DA- BI_DB- 
3 BI_DB+ BI_DA+ 
4 BI_DC+ BI_DD+ 
5 BI_DC- BI_DD- 
6 BI_DB- BI_DA- 
7 BI_DD+ BI_DC+ 
8 BI_DD- BI_DC- 
 
Implicit implementation of the crossover f unction within a twisted-pair cable, or at a 
wiring panel, while not expressly forbidden,  is beyond the scope of this standard. 
  
						

							
Appendix A: RJ-45 Pin Assignment 
172  GE-DSH-73/DSH-82 and DSH-82-PoE User Manual 
10/100Mbps, 10/100Base-TX 
When connecting your 10/100Mbps Ethernet Switch to another switch, a bridge or a 
hub, a straight or crossover cable is nece ssary. Each port of the Switch supports 
auto-MDI/MDI-X detection. That means you  can directly connect the Switch to any 
Ethernet devices without making a crossover cable. The following table a\
nd diagram 
show the standard RJ-45 re ceptacle/ connector and their pin assignments: 
 
RJ-45 Connector pin assignment 
Contact MDI 
Media Dependant Interface 
MDI-X 
Media Dependant Interface-Cross 
1  Tx + (transmit)  Rx + (receive) 
2 Tx - (transmit)  Rx - (receive) 
3 Rx + (receive)  Tx + (transmit) 
4, 5 Not used 
6 Rx - (receive)  Tx - (transmit) 
7, 8 Not used 
 
The standard cable, RJ-45 pin assignment 
 
1
2
3 45
6 7 8
8
7
6 54
321
 
The standard RJ-45 receptacle/connector  
  
						

							
  AppendixAppendix AAppendix AAppendix A: RJ-45 Pin Assignment 
GE-DSH-73/DSH-82 and DSH-82-PoE User Manual  173 
There are 8 wires on a standard UTP/STP cable and each wire is color-coded. The 
following shows the pin allocation and colo r of straight cable and crossover cable 
connection: 
Figure A-1: Straight-Through and Crossover Cable  
 
Straight Cable    SIDE 1  SIDE2 
SIDE 11
12
23
3
4
45
56
67
7
8
8
SIDE 2 1 = White / Orange 
2 = Orange 
3 = White / Green 
4 = Blue 
5 = White / Blue 
6 = Green 
7 = White / Brown 
8 = Brown 
1 = White / Orange
2 = Orange 
3 = White / Green 
4 = Blue 
5 = White / Blue 
6 = Green 
7 = White / Brown 
8 = Brown 
    
Crossover Cable    SIDE 1  SIDE2 
SIDE 11
12
23
3
4
45
56
67
7
8
8
SIDE 21 = White / Orange 
2 = Orange 
3 = White / Green 
4 = Blue 
5 = White / Blue 
6 = Green 
7 = White / Brown 
8 = Brown 
1 = White / Green 
2 = Green 
3 = White / Orange
4 = Blue 
5 = White / Blue 
6 = Orange 
7 = White / Brown 
8 = Brown 
 
 
Please make sure your connected cables ar e with same pin assignment and color as 
above picture before deploying th e cables into your network.  
						

							
: RJ-45 Pin Assignment 
174  GE-DSH-73/DSH-82 and DSH-82-PoE User Manual 
 
  
						

							
 
  175  
Appendix B 
Troubleshooting  
• Verify that is using the right power cord /adapter (DC 24-48V), please dont use the 
power adapter with DC output higher than  48V, or it may damage this device. 
•  Select the proper UTP/STP cable to cons truct the user network. Use unshielded 
twisted-pair (UTP) or shield twisted-pair  (STP) cable for RJ-45 connections that 
depend on the connector type the switch  equipped: 100O Category 3, 4 or 5 cable 
for 10Mbps connections, 100O Category  5 cable for 100Mbps connections, or 
100O Category 5e/above cable for 1000Mbps  connections. Also be sure that the 
length of any twisted-pair connection does  not exceed 100 meters (328 feet). 
•  Diagnosing LED Indicators: To assist in  identifying problems, the switch can be 
easily monitored through panel indicators, which describe common problems the 
user may encounter and where the us er can find possible solutions. 
•  If the power indicator does not light on  when the power cord is plugged in, you 
may have a problem with power cord. Th en check for loose power connections, 
power losses or surges at power outlet.  If you still cannot resolve the problem, 
contact the local dealer for assistance. 
•  If the LED indicators are normal and the connected cables are correct but the 
packets still cannot be transmitted. Plea se check the user systems Ethernet 
devices configuration or status