Page 22 - Security Today, November 2017

side the camera. There are several compres- sion technologies available, and they each have their advantages and disadvantages. Some compression technologies use what’s called a predictive frame approach. This means that if nothing changes from frame to frame, the CODEC only transmits what has changed in order to minimize the band- width required. The other main type of CODEC uses a transformative approach. In this approach, the CODEC chops the images into manageable chunks before actually compressing it. Some of the most popular compression technologies include MPEG-1, MPEG-2, MPEG-4, and H.264, with H.264 being the most popular for IP video surveillance applications.
It is beyond the scope of this article to elaborate in detail about each CODEC. However, it is worth noting that the CO- DEC used can have a big effect on the bandwidth required. Changing the CO- DEC from MPEG to H.264, for example, can reduce bandwidth requirements more than 50 percent. Incorporating compres- sion technologies over IP networks can re- duce bandwidth requirements, but it also means that each frame is critically impor- tant. Frame errors can have devastating consequences for an application like video surveillance, so a robust network infra- structure is very important.
Network protocols. When transmitting information over IP networks, there is al- ways a balance to be struck between latency and reliability. In applications that are not as time-sensitive, like data transmission for instance, typically employ a protocol like Transmission Control Protocol (TCO/ IP). With TCP/IP, if the receiving device determines there are packet errors, it will buffer the data and request a resend from the transmitting device. Upon successful delivery of the resent packets, the receiving device will reconstruct the packet transmis- sion and display the information.
Therefore, the TCP/ IP protocol priori- tizes reliable delivery over latency. In other applications, like VoIP and video, where there is extreme time sensitivity, then pro- tocols like Real Time Protocol (RTP), or User Datagram Protocol (UDP) are used. When using RTP or UDP, packet errors are simply dropped until error free pack- ets are delivered. The user will notice the dropped packets as the image or audio will be distorted or turn off temporarily until error free packets are received again. RTP and UDP prioritize latency over reliabil-
ity. The compression technology H.264 for example is usually transmitted with UDP or RTP protocols. Again, a high- quality network infrastructure is critical to video surveillance application and can contrib- ute to minimizing packet errors.
IP Video Application Testing
The TEK Center at Berk-Tek conducted testing to determine how well different structured cabling infrastructures sup- ported high definition and ultra-high defi- nition video in various conditions. TEK Center engineers prepared bundles of several different cables: LANmark-XTP (Cat 6A), LANmark-10G FTP (Cat 6A), LANmark 10G2 (Cat 6A), and Generic
Figure 1.
Cat 6 cables.
The bundles were set up in a 6-around-1
configuration, as illustrated in Figure 1. Each bundle was made up of seven cables, and the cable in the middle (called the vic- tim cable) experiences the worst case alien crosstalk possible. The surrounding six cables are called the “disturbers.” The ca- ble bundles were then configured into 100 meter, four-connector channels. Please see
Every cable of every bundle was first tested with a Fluke DSX-5000 field test unit to ensure each met the Cat 6 or Cat 6A performance accordingly. After successful performance testing, the TEK Center be- gan testing by energizing only the victim cable while transmitting in either 1080p or 4K UHD. Each test was repeated 12 times for statistical confirmation. Then, the test was repeated, but the six disturbers were also energized with 10GBASE-T traffic (similar frequency to UHD) to find what happens when alien crosstalk develops within the 6-around-1 cable bundle. This testing was also repeated 12 times. Table 1
Figure 2.
illustrates the test results.
The TEK Center used Quantum Data’s
780C Multi-Interface Interoperability Tes- ter (seen in Figure 2), which was originally released in June 2014. The test unit pro- vides “Results of Confidence” which is a near-instantaneous measurement used to determine if the channels under test will provide satisfactory performance. Both 1080p and 4KUHD transmissions were tested. Please note that Quantum Data states that the 780C has a maximum reach of 75 meters when measuring 4K trans- missions. Therefore, the 100m 4K test re- sults are not considered relevant because they are beyond the distance capabilities of the test unit at the time of the testing (February 2016).
In order to compensate for the test unit, the TEK Center shortened the channel to 75 meters, and two-connector channels were used for 4K transmissions. The re- sults of the 75-meter, two-connector chan- nel testing can be seen in Table 2 below.
Then, the TEK Center turned up the heat. In environments like hot plenum spaces (think Arizona summertime), com- bined with up to 100W of PoE, the cables toward the center of the bundle especially will get hot. Heat creates higher attenua- tion that will negatively impact perfor- mance. The TEK Center tested all bundles in the two-connector 75 meter channel test configuration at 75-degree C (167-degree F), to which all Berk-Tek cables are listed. The results can be seen in Table 3.
Two solutions, LANmark-XTP and LANmark-10G FTP, are listed to 90-de- gree C (194-degree C), so the TEK center tested both to that temperature as well. The results are shown here in Table 4.
Structured Cabling Recommendation
An important point to note is that, while Category 6 and 5e are installed today to support IP video surveillance, the prob- ability for success decreases significantly
NS8
1117 | NETWORKING SECURITY