Structured cabling plays a major role in audio-video systems today with Cat5e/6 being the most cost-efficient method to interconnect AV equipment in a multi-room or large venue environment. As more and more AV content is transmitted at HD resolution, there is a growing demand for the structured cabling system to support HD transmission over Cat5e/6 and therefore a greater need for HDMI over Cat5e/6 products. Furthermore the recent AACS Adopter Agreement pertaining to copy protection (“Analog Sunset”) and the gradual move away from unprotected component analog video is encouraging integrators to analyze future AV installations more closely in order to future proof them in support of HDMI. This article will focus on the key components needed to manage HDMI cabling over Cat5e/6.
In regard to HDMI systems a variety of sources may be found, ranging from cable boxes, PCs, DVD players, hard disk servers, audio-video receivers (AVR). Invariably, the system requires that they be connected to HDMI displays that may be located in another room or even on another floor. In regard to cabling, the obvious choice of cable is Cat5e/6 due to its lower cost and ease of installation. However, due to the fact that Cat5e/6 is not designed like HDMI cable, additional connectivity hardware is needed to interface between the HDMI equipment and the Cat5e/6 cabling system. This connectivity hardware comprises three main functions; Distance Extension, 1xN Distribution and Matrix Switching.
This function entails extending the HDMI display further from the source than would be normally feasible or practical if HDMI cable were used. For example, to connect a Blue Ray player from one room to the other side of the wall in the next room. Although distance is short, it would be more costly to break the wall to pass an HDMI cable versus connecting the devices via pre-existing Cat5e cable. Another example would be to connect an HD cablebox located at one end of an office to second location over 100 feet way where HDMI cable or midspan HDMI repeaters are not feasible.
This function entails distributing and extending a single HDMI source to multiple displays. For example, in an airline waiting lounge or hotel lobby. In a residential environment, it could be a DVD player or cablebox that plays out to different zones.
This function entails routing multiple HDMI sources to multiple displays. A non-blocking matrix allows one source to be sent to more than one display. Cable extension is also performed at the Cat5e/6 output of each HDMI port. This application comes into play in the hospitality industry where multiple HDMI sources are present and there are multiple zones selecting different sources. For example one HDMI source feeds the hotel lobby and another source feeds a conference room.
Issues – What to Look For
When looking for an HDMI cabling solution there are several issues that need to be considered in order to ensure success as described below.
Maximum Resolution – Cat5e Vs Cat6
In the HDMI environment, cable grade affects distance performance. Therefore, the first step is to verify whether application is feasible from the distance standpoint. Most HDMI connectivity hardware vendors specify the maximum distance based on resolution. Therefore, plan the cabling solution based on worst case scenario. If the HDMI source will never exceed 1080i resolution such as with cableboxes, then the maximum cable length could be based on 1080i. However, if it is possible that an HDMI source that outputs at 1080p or even 1080 Deep Color will be connected, then the cabling should planned based on the maximum distance at these higher resolutions. In regard to cable grade, Cat6 cable typically yields up to 50% more distance than Cat5e. Therefore, if the maximum cable length approaches the maximum distance specifications of the HDMI connectivity hardware, then it may be recommended to upgrade the cable to Cat6 instead of Cat5e to allow for a buffer.
Unshielded Twisted Pair versus Shielded Twisted Pair
HDMI transmission is typically more sensitive to external electromagnetic (EMI) and radio frequency interference (RFI) and therefore if the environment is electrically harsh, it may be wise to plan for shielded twisted pair (STP) cable to provide added EMI/RFI noise immunity. An example where EMI affect HDMI transmission is when lighting is turned on or off and the HDMI image flickers. If there is a doubt that some nearby appliances will interfere with the signal, it is better to install shielded twisted pair and avoid any surprises.
EDID (Extended Display Identification Data)
EDID (Extended Display Identification Data) is data that describes the capabilities of a display device to a source device. The EDID includes the resolutions and modes supported by the display device. In the context of HDMI distribution hubs, the source device consists of the HDMI source (typically a DVD player), and the display device consists of the remote & local displays (typically TVs), to which the distribution hub is connected. An HDMI distribution hub should have an EDID selector that allows the HDMI source to establish the right resolution and mode at which the HDMI source will send data to the display devices.
Support for 3D
Officially HDMI 1.4 specifies support for 3D. Furthermore, some datasheets state that the product is “3D Ready”. However, this does not guarantee that the device will work with 3D. Therefore, unless the connectivity devices comply with HDMI 1.4, support for 3D cannot be guaranteed. It is recommended to test the connectivity device with 3D in order to validate that it works.
Single Cat5e Vs Dual Cat5e
Currently there are two approaches to transmitting HDMI over Cat5e/6 cable. One approach requires two (2) Cat5e/6 cables and the other approach requires one Cat5 cable. Based on currently technology both approaches fully comply with HDMI standards. However, when building a complete system, one verifies that the extenders/switchers/distribution hubs use the same approach in order to avoid incompatibility issues.
Passive versus Active Extenders
There are HDMI extenders that are totally passive and do not require a power supply. They are designed to perform well at short distances and may not support all the higher resolutions. It is advisable to verify the application before using passive extenders to ensure that they will support your maximum distance/resolution requirements.
Some distribution hubs support cascading in order to build larger systems. However, not all hubs support this feature. Typically the hub is cascaded via the Local Monitor Out and is the recommended method of cascading. For example, this is a useful feature if the hub is only a 1×4 and there is a need to expand to 1×8.
In summary before purchasing HDMI-over-Cat5e/6 equipment verify the system requirements to see if they fall within the specifications of the products to be purchased.
The following are some useful links pertaining to HDMI over Cat5e/6.
AACS â€“ Final Adopter Agreement re: Analog Sunset
Extron â€“ Summary of Analog Sunset
HDMI Connectivity Vendors
The following is a partial list of vendors that provide a wide range of innovative HDMI connectivity hardware.
Kramer Electronics: www.kramerelectronics.com
MuxLab is a designer and manufacturer of security video and audio-video connectivity solutions for copper twisted pair cabling. Jeffrey Herman may be contacted at firstname.lastname@example.org.