Does Cisco 3504 Wireless LAN controller have HA (High Availability) option ?

Does Cisco 3504 Wireless LAN controller have HA (High Availability) option ?

WLAN Controller HA

Many previous Cisco wilress LAN controller like 5508, 5520, 2504 have the HA SKU unit, which could be used for N+1 HA (or clustering on the 5508) without additional license fees – the HA unit supported the maximum amount of APs for 90 days. But datasheet of Cisco 3504 WLC does not show clearly on the HA availability.

Does Cisco 3504 Wireless LAN controller (AIR-CT3504-K9) have HA(High Availability) option ?

The answer is ‘YES’.  The 3504 WLC supports high availability (Client SSO + AP SSO), it also supports N+1 High Availability. It’s basically what we are used to in other WLCs, like the 5508 or 5520, one becomes the Active and the other becomes the Hot Standby, synchronization occurs through the Redundancy Port.  In terms of licensing, these controllers support Smart Licensing or RTU licensing.

How does it work ?

High Availability is for box-to-box redundancy. In other words, 1:1 where one WLC will be in an Active state and the second WLC will be in a Hot Standby state continuously monitoring the health of the Active WLC via a Redundant Port. Both the WLCs will share the same set of configurations including the IP address of the Management interface. The WLC in the Standby state does not need to be configured independently as the entire configuration (Bulk Configuration while boot up and Incremental Configuration in runtime) will be synced from the Active WLC to the Standby WLC via a Redundant Port. The AP’s CAPWAP State (only APs which are in a run state) is also synced, and a mirror copy of the AP database is maintained on the Standby WLC. The APs do not go into the Discovery state when the Active WLC fails and the Standby WLC takes over the network’s Active WLC.

There is no preempt functionality. When the previous Active WLC comes back, it will not take the role of the Active WLC, but will negotiate its state with the current Active WLC and transition to a Standby state.

Like on other WLC, WLC 3504 supports both AP SSO and Client SSO. Given below is how one would connect two WLC 3504 using the RP port(back to Back) in HA Setup.
CT3504 HA Configuration
*Note*:  One can also connect RP port through a L2 switch.
To connect a pair of WLC 3504 in HA Setup to the wired network, one can use the following deployment examples. Please note that only two links are shown from WLC3504 to the switch(s) but one can connect all four of the GE links + mGig link for LAG.
CT3504 HA connecting
WLC supports the same HA configuration as other WLC. To configure High Availability,  refer to the HA deployment guide at the link below:

How to choose between PoE, PoE+ and UPoE (POE++) switches ?

Differences between POE,  POE+ and UPOE (POE++)

PoE, the abbreviation of ‘Power over Ethernet’,is a technology that delivers power and data safely over the same Ethernet cable for the local area networks (LANs).   After many years’ evolving,  it developed several types of PoE standards.  Nowadays in market you can see POE switch, POE+ and UPOE switches.


What’s the differences between POE,POE+ and UPOE  ?   Here let’s give a brief summary:

POE was defined in the IEEE 802.3af standard in 2003, is the oldest standard for the devices which can be powered on from the switch.  Under this standard, the PoE allows a PD (powered device) like VoIP phones to receive up to 12.95W PoE wattage, utilizing just two out of the available four twisted pairs in Ethernet cabling. As power sourcing equipment, a POE switch under 802.3af supports max power consumption per PoE port up to 15.4W with a voltage range between 44V and 57V.

Later in 2009, POE+ standard (IEEE802.3at standard) was evolved.  Switches which are complied to POE+ standard can provide up to 30W of power to the connected devices, which can attend the power requirement of certian power devices like wireless access points.  Similar to a PoE network switch, the PoE+ switch also supplies power over two pairs.

Latest standard is POE++,  which was regulated under IEEE 802.3bt  in 2018.  Under this standard, PoE++ technology has two types. One is called type 3, which enables two or all four twisted pairs in a copper cable to deliver power at a PD up to 51W; and the other called PoE type 4 is up to 71W at a PD over four twisted pairs in an Ethernet cable.  UPOE (universal power over Ethernet) is not a universal standard but a cisco Proprietary, which works similar to the PoE type 3 (PoE++). It extends the IEEE PoE+ standard to double the power to a PD to 51 watts. In some cases, UPoE is also called as PoE++.

Below are more details:

Switch type PoE switch PoE+ switch PoE++ switch
IEEE standard IEEE 802.3af IEEE 802.3at IEEE 802.3bt
PoE type Type 1 Type 2 Type 3
(Cisco UPOE)
Type 4
Power to PD 12.95W 25.5W 51W 71W
Max. power per port 15.4W 30W 60W 100W
Voltage range (at PSD) 44–57V 50–57V 50–57V 52–57V
Voltage range (at PD) 37–57V 42.5–57V 42.5–57V 41.1–57V
Twisted pair used 2-pair 2-pair 2-pair; 4-pair 4-pair
Supported cables Cat3 or better Cat5 or better Cat5 or better Cat5 or better

PoE,  PoE+ and UPOE Switch: Which to Choose ?

From above table, you can find some differences over the power supply and work mode among PoE,  PoE+ and UPOE switches.  As result,  their applications are also different:

PoE vs PoE+ vs PoE++ Switch.jpg

802.3af switch is usually used to support devices that require the power delivery less than 15.4W, such as VoIP phones, sensors, meters, wireless access points with two antennas and simple, static surveillance cameras that don’t pan, tilt or zoom.

For PoE+ switch, it supports devices such as more complex surveillance cameras that pan, tilt or zoom, as well as wireless access points with six antennas, and video IP phones.

With a higher power wattage, type 3 of the PoE++ switch can support devices such as video conferencing system components and building management devices. And type 4 of the PoE++ switch can support devices such as laptops and TVs.

Active POE vs passive POE

Active POE vs. Passive PoE Switch

POE switch is designed to offer both network connection and power supply to one PoE powered device (PD) through one Ethernet cable. And as the demand for deploying PD devices such as IP phones, IP cameras and access points increases, PoE switch is commonly used in today’s enterprise and campus networks for it helps to reduce deployment complexity and cost. Now we can see there are both active PoE switch and passive PoE switch sold in the market. What exactly are they? Should we use active PoE or passive PoE switches for our network?

What Are Active PoE and Active PoE Switch?

Active PoE, short for active Power over Ethernet, is also known as standard PoE which refers to any type of PoE that negotiates the proper voltage between the power supply equipment (PSE) and the PD device. Active PoE switch is a device that complies with standard PoE, so it is also named standard PoE switch. This type of switch is rated to be IEEE 802.3af, IEEE 802.3at or IEEE 802.3bt compliant. Thus it can be further divided into PoE, PoE+ and PoE++ switches. Before powering up, the active PoE switch will test and check to ensure the electrical power is compatible between the switch and the remote device. If it isn’t, the active PoE switch will not deliver power, preventing any potential damage to the non-PoE device.

Active PoE switch application.jpg

What Are Passive PoE and Passive PoE Switch?

Passive PoE, also known as the passive Power over Ethernet, is a non-standard PoE. It can also deliver power over the Ethernet lines, but without the negotiation or communication process. Passive PoE switch does not adhere to any IEEE standard. The power is “always-on” when using passive PoE switch in networks, which means it always sends electric current out over the ethernet cable at a certain voltage regardless of whether the terminal device supports PoE or not. So using passive PoE switch may burn out the terminal devices if they’re not prepared for electrified Ethernet cables.

Passive PoE switch application.jpg

Active vs. Passive PoE Switch: What Are Their Differences?

As mentioned above, active PoE switch and passive PoE switch can both provide PoE connections but in very different ways. Besides that, they also differ in PoE power supply pinout, Ethernet support, cost, etc.

Active vs. Passive PoE Switch: PoE Power Supply Pinout

As we know, there are three methods for PoE switches to supply power: PoE Mode A, PoE Mode B and 4-pair PoE. In PoE Mode A, power is delivered simultaneously with data over pins 1, 2, 3, and 6. In PoE Mode B, power is injected onto pins 4, 5, 7, and 8. And 4-pair PoE delivers power over all 8 pins simultaneously. Active PoE switch can support all PoE Mode A, PoE Mode B and 4-pair PoE, while passive PoE switch can only support PoE Mode B.

10/100BASE-T Network 1000BASE-T Network
Pins at Switch PoE Mode A (Data & Mixed DC) PoE Mode B (DC on Spares) 4-pair PoE PoE Mode A (Bi-Data & DC) PoE Mode B (Bi-Data & DC) 4-pair PoE
Pin 1 Rx+ & DC+ Rx+ Rx+ & DC+ TxRx A+ & DC+ TxRx A+ TxRx A+ & DC+
Pin 2 Rx- & DC+ Rx- Rx- & DC+ TxRx A- & DC+ TxRx A+ TxRx A+ & DC+
Pin 3 Tx+ & DC- Tx+ Tx+ & DC- TxRx B+ & DC- TxRx B+ TxRx B+ & DC-
Pin 4 Unused DC+ DC+ TxRx C+ TxRx C+ & DC+ TxRx C+ & DC+
Pin 5 Unused DC+ DC+ TxRx C- TxRx C- & DC+ TxRx C- & DC+
Pin 6 Tx- & DC- Tx- Tx- & DC- TxRx B- & DC- TxRx B- TxRx B- & DC-
Pin 7 Unused DC- DC- TxRx D+ TxRx D+ & DC- TxRx D+ & DC-
Pin 8 Unused DC- DC- TxRx D- TxRx D- & DC- TxRx D- & DC-

Active vs. Passive PoE Switch: Ethernet Support

Active PoE switches can support 10/100/1000Mbps Ethernet up to 100m over Cat5/5e/6 cable. Passive PoE switches, however, commonly support 10/100 Mbps Ethernet up to 100m. Thus active PoE switches can be applied in both traditional 10/100BASE-T and modern 1000BASE-T PoE networks. While passive PoE switches are usually used in the past 10BASE-T and 100BASE-T PoE networks.

Active vs. Passive PoE Switch: Cost

All active PoE switches are equipped with the built-in PoE power controller which performs the function of PD device detection and classification. While the passive PoE switch has no such component and functions. Therefore it is reasonable to see the price of active PoE switch is higher than that of the passive PoE switch.

To sum up, active and passive PoE switches mainly differ from each other from the following aspects:

Active PoE Switch Passive PoE Switch
Standard IEEE 802.3af/at/bt N/A
Power Injection After Negotiation Immediately
Power Supply Mode PoE Mode A/PoE Mode B/4-Pair PoE PoE Mode B
Ethernet Support 10/100/1000BASE-T 10/100BASE-T
Max. Distance 100m 100m
Safety High Low
Cost Medium Low

Active vs. Passive PoE Switch: Which to Choose?

From the above content, we can say that for safety concerns, active PoE switches should always be our top choice for powering up remote IP phones, IP cameras, wireless access points, and other PD devices. However, you may also consider passive PoE switches if there is a tight budget. But remember that the passive PoE switch has no power detection function. So it is important to make sure you buy a passive PoE switch that matches the power specifications exactly to the PD device you are trying to power on. Otherwise, you can easily burn up your PD device. In addition, you should never connect computers and other non-PoE devices to the passive PoE switch.

Blog - How to choose Fiber optic transceivers

How to choose a right optical transceiver ?


A fiber optical transceiver is a photonic and electronic device that transmits and receives data over optical fibers rather than electrical wire. It is also called as an optical module or fiber optic module. Choosing a right fiber optic transceiver for your use is very important. Today’s main local carriers are major efforts to develop residential campus network and enterprise system, so that the number of fiber optic transceiver products is consistently improved to fulfill the needs of the access network building.

How to choose a right fiber optical transceiver when you don’t know the exact part number from equipment manufacturer ?

Blog -Cisco optical transceiver

You should consider following 7 key points before you place the order :

Form Factors

The multi source agreement (MSA) defines the different transceiver form factors. The MSA is an agreement between multiple vendors to manufacture optical transceivers that are used for different networking equipment. There are various types of Form Factors available in the market today. The most popular types include SFP, SFP+, QSFP, and some other types that are uncommonly used such as  CFP, CFP2, CFP4, 1×9, SFF, GBIC, XFP, SFF, X2, XENPAK, CSFP and so on. You should choose the right form factors based on your platform and real needs.

Blog - How to choose Fiber optic transceivers

Data Rate

Optical fiber’s bandwidth determines the data rate. The transceiver accommodates data rate on the basis of the standards such as Ethernet, Fibre Channel, SONET, SDH and InfiniBand. The emergence of the dual-rate optical transceiver is typical because of the cost consideration from 1G to 10G, 10G to 40G, 40G to 100G and it can be at a higher data rate that means Gigabit Ethernet is very fast. Dual-rate optical transceiver is a cost-effective solution to solve this query.

Transmission Distance or link budget

Fiber optic system is continuously restoring copper network, due to its different favorable circumstances such as high speed, high bandwidth, high density, and etc. Fiber optic cable can support much further distance than that of traditional copper cable like twisted pair wire or coax cable. However, in practice, the exact distance that fiber optic can support is limited by many factors. Transmission distance has become one of the biggest problems in the super fast optical communication. You have to make sense of the maximum distance or link budget needed in your fiber connection systems.

Fiber Mode

There are two modes to choose from in Fiber Optical Transceiver. Single Mode and Multimode, it is usually designed for systems of moderate to long distance like Metro or any other Long haul networks while on another hand Single mode optical fibers have a small core size which permits single mode or ray of light to be transmitted. Multimode transceiver usually cost less but give a short transmission distance (< 2km), while single mode transceiver allows a much longer distance of 160km at a higher cost.


It is very important to understand Wavelength while choosing fiber optical transceiver, our eyes are sensitive to lights of which wavelength is in the range of 400 nm to 700 nm. But in the fiber optics, lights are used in the infrared region which has wavelengths longer than visible light. Common wavelength usually comes from the range 850 nm to 1610 nm. Multimode fiber is specially designed that operate at 850 nm and 1310 nm, while single mode operates 1310 nm to 1550 nm.

Operating Temperature

Fiber optic transceivers have different operating temperatures when it is in use. For commercial fiber optic transceivers, it usually works at 0°C to 70°C, while for industrial usage, it works at -40°C. to 85°C.


There are so many brands of networking equipment, such as Cisco, Huawei, HP, Juniper, Fortinet, etc..,  they all have their own optical transceivers.  For most cases,  you will be recommended to use corresponding optical transceivers to prevent connection failure.  But you may also choose a compatible transceiver from OEM manufacturer or 3rd party when there is a budget limit. Then it’s very important to check the compatibility, which is a crucial part to check before you buy Fiber Optical Transceiver. It is essential to test the interoperability and compatibility of each fiber optic transceiver.  Because these networking equipment producers,  lock the third party transceivers and not allow non-certified module works with their switches. The compatibility is always an issue you face, you have to make an extensive research and ask the vendor to guarantee the same function as brand genuine one.