Many of the recent IT trade magazines and communications exhibition, cabling system performance of data transmission network transmission bit error rate as the focus of attention. In general, due to impedance mismatch caused by the channel return loss is the result of high bit error rate of the main reasons, and return loss performance of all have some effect, even the impact of near-end crosstalk attenuation serious.
Standard specifies the design and test requirements of the letter has to get consistent application performance, and these channels are likely to provide sufficient surplus Wufa amount to pay for the high-bandwidth Wangluoxuqiu Xuduoweilai application. In order to compare and verify the new Category 6 cabling options than the standard category 5e enacted to provide better quality and faster transmission speed of the network, Avaya Labs has recently using three high-speed, high-intensive applications, the amount of information transmitted to the experiment. Selected applications is 270 Mb / s serial digital video signals, 100BASE-TX and 100BASE-TX video stream data file transfer. And to share with the jacket large number of cable access on
Experiment, the simulation under the worst conditions of near-end crosstalk interference network transmission environment.
These experimental results show that the standard requirements, the use of a large excess amount of high-performance cabling systems can significantly improve network speed. In addition, the experiment also proved that the use of Category 6 cabling systems can now market the application of the existing transmission system and provide better performance.
Background
Channel throughput is defined as the channel through a certain period of time or the amount of transmitted data. Maximum transmission channel capacity only in the ideal channel conditions, be achieved, but in the real environment can not achieve. All channels are there different loss, so the channel can only be less than the maximum amount of working capacity or transmission conditions. In the communication system or a particular local area network, the channel must be designed to take into account to be able to compensate for these losses.
System components and environmental factors surrounding the transmission channel characteristics to bring to a certain extent, thereby affecting the structured cabling system transmission performance. Number of intervening factors to the structured cabling system channel negative impact on transmission performance, these disturbances were recorded in the IEEE 802.3ab 1000BASE-T Gigabit Ethernet standard, now the list is as follows:
* Scattering
* Interference
* Delay deviation
* Decay
Impedance mismatch * / return loss
* Near-end crosstalk and far-end crosstalk
All of these potential interference factors that may cause the channel bit error, thereby reducing the structured cabling system, the channel throughput. Bit error rate refers to the receiver bit error ratio and the total transmission bit. The use of high-speed information transmission network bandwidth and intensive applications, the minimum required to ensure the highest transmission bit error performance. In data applications, higher bit error rate, slow network performance will lead to signal retransmission. In video applications, higher bit rate lead to poor image interruption, loss of binding or produce white (snow). In any applications, higher bit error rate would result in unsatisfactory performance. The following sections will discuss some of the bit error rate and the factors that influence the amount after the transfer.
Scattering:
Scattering is a pulse generated when the adoption of the spread of the channel. It causes adjacent bits of each bit and superposition of the channel leading to the terminal receives the transmission bit error. Scattering within the interference is often called, can use visible graphics to reflect, to beat to measure. Cables and cable channel matching is the main produce scattering. For as 270Mb / s serial digital video applications, digital transmission, scattering will increase the bit error rate and reduce the performance of the channel, resulting in lower image resolution receiver. Usually adaptive equalizer circuit to join the communication hardware interfaces to compensate for scattering.
Interference:
Noise through the channel in the vicinity of the external electric and magnetic fields into the channel, which is outside interference. Non-directional ESD or EFT launch is a source of outside interference. Need to pay attention to yes, even the perfect design and installation of structured cabling system channel, the external electromagnetic field of the transformation will continue their work, affect the bit error rate, and lead to the imbalances You Yuan You Ying Jian circuit and communication cable line interfaces channel invasion, which caused adverse effects on system performance.
Delay deviation:
Delay deviation is different in many of the cable wrap on the cable transmission rate resulting from differences in stranding rates of change and limit line on the deviation in the insulation structure, and in seconds. Some applications need to transmit the signal in the composite twisted pair, and also reached the end of the receiver channel. So the delay is very important to minimize bias.
Twisted pair transmission site using a typical case is within the stock exchange of financial information sent to the high-resolution display. Such displays require more than 100 MHz of available bandwidth and simultaneous analog RGB video signals. Excessive delay may result in deviation of pigment dispersion, with the length of the channel will produce ghosting. 1000BASE-T (Gigabit Ethernet) is another need to use UTP twisted pair for transmission of the case. Delay standard deviation IEEE802.3ab agreement was defined as the frequency of 2MHz to 100MHz between the combination of all of the deviation between the difference in duplex channel shall not exceed 50ns.
Attenuation:
Attenuation is the signal amplitude when the channel energy through the reduction. And scattering similar to cable and connectors to connect the main factors that contributed to attenuation. IEEE 802.3 protocol on the 1000BASE-T standard requirements, attenuation is the loss of access, the maximum attenuation duplex channel using the following formula:
Access loss (f) = 2.1 f (0.529) + 0.4 / f (dB) [f = 1MHz to 100MHz]
The adverse effects of channel attenuation can study the transmission of analog video signals to prove the effect. Decay leading to the video stream over the low-frequency luminance signal intensity lower than the high-frequency part of the chroma signal part of the received image dark, low contrast.
Impedance mismatch / Return Loss:
Impedance mismatch / return loss and equipment in the internal impedance of the load impedance falls. On the structured cabling systems, such losses were mostly in the form of components channel where there is no appropriate match. This will affect the energy and the maximum transmission power between the load. The interface circuit using a hybrid feature 1000BASE-T system, the imbalance will be reduced to the minimum impedance matching is very important. Mixed function used to achieve full-duplex data transmission.
Hybrid circuit to provide four pairs of terminals, the signal from a terminal, after entering, out of distribution from the two adjacent, but not reach the corresponding terminal line right. Equipment, impedance matching circuit and channel is very important, otherwise generate echo, that is, the transmission of energy will be reflected in the form of noise occurs at the receiving end. Will echo compensation circuit into the 1000BASE-T interface circuit, the purpose is to create an effective boycott of blending the echo effect.
1000BASE-T, IEEE 802.3ab standard impedance mismatch that the same as the return loss in decibels, ie a specific frequency for each segment of the relevant impedance (100 ohms). Return loss is due to impedance mismatch resulting from the application of signal reflection, the ratio is a numerical score. IEEE 802.3ab standard recording channel influence of impedance mismatch, and use the following formula impedance mismatch tolerance range.
Return Loss (f) = 15 (dB) (f = 1MHz to 20MHz)
Return Loss (f) = 15 - 10log (f/20) (dB)
(F = 20MHz to 100MHz)
The second formula to allow for value in return loss there is a wide margin. For example, the tolerance range is the standard requirements of the 100 MHz frequency 8dB return loss. The return loss is equal to 100 ohms (-57 ohm to 133 ohm) impedance mismatch. Such as 1000BASE-T applications like the ability to allow a wide range of impedance mismatch. This suggests that factors such damage not as threatening as other factors, cabling transmission performance.
Near-end crosstalk and far-end crosstalk:
From one or more pairs of wire to the other adjacent line on the signal coupling is called crosstalk. Near-end crosstalk loss is defined as: coupling signal and the original transmission signal from the same channel side by measurement situations, transmission signal size and coupling ratio of the signal size. FEXT loss is defined as: signal coupling the other end of the original transmission signal to measure the relative circumstances, the transmission signal size and coupling ratio of the signal size. Near-end crosstalk and far-end crosstalk loss is also in decibels (dB) for statements.
For 1000BASE-T and many other lines in terms of the transmission system to minimize the near-end crosstalk is critical. 1000BASE-T full-duplex per channel receivers and four from the channel connected to the feelings of near-end crosstalk between adjacent transmitters. Therefore, 1000BASE-T transmission system, the introduction of near-end crosstalk compensation in order to reduce near-end crosstalk interference. The same way, the far-end crosstalk compensation for the introduction of 1000BASE-T transmission system can also reduce the far-end crosstalk interference. However, if the far-end crosstalk and near-end crosstalk for the impact of comparison, very little on the obvious, so can be ignored.
In addition, the near-end crosstalk interference arises between adjacent cables, these cables are not the same jacket. Near-end crosstalk generally refers to the near-end crosstalk from external interference, when the cable bundle together tightly when being produced. Outside the near-end crosstalk is generally regarded as outside interference.
In short, structured cabling system transmission performance of the channel were a number of potential interference factors. Whether near-end crosstalk, far-end crosstalk noise generated by crosstalk or external, on the bit error rate are very important influence, followed also bring disaster to the structured cabling system channel transmission performance. Crosstalk effects as other structured cabling systems, like the damage to the channel, it can be difficult to control the point spread and affect more applications.
Demonstrate
Laboratory experiments show that Avaya made of three different large-scale high-bandwidth-intensive applications, the near-end crosstalk (NEXT) is the main factor affecting the transmission performance of the damage. Experiments were conducted on two four-connector channel to the assessment, one channel with a common market over five related products CAT5e, the other channel on the common use of market SYSTIMAX GigaSPEED? Six types of wiring systems.
1. 100BASE-TX LAN large data file transfer:
Bit error rate performance of the local area network to transfer large files the time, and even affect the efficiency.
Demonstrate
a) 100BASE-TX LAN transfer large data files
b) 100BASE-TX LAN streaming video signal transmission
c) serial digital video (SDV)
Using Norton Ghost multicast server software, to a 248 MB video file from the server to the client. Monitoring transmission during the transmission speed and time spent. Using HP 8112A pulse generator, in 4 of the channel adjacent to the channel within the Department, the introduction of the proximal interference signal pulse.
Category 5e cable channel using the experimental results:
When connecting the LAN client PC manufacturers use general CAT5e type channel, the file transfer needs 129 seconds, the average transmission rate per minute for the 115 MB.
GigaSPEED six cable channels using the experimental results:
Channel using GigaSPEED 6 class, file transfer and 72 seconds, an average transfer rate per minute for the 206 MB. Crosstalk interference in the same condition, the same amount of information, with the GigaSPEED 6 class channel transmission time is category 5e channel transmission with a time of 80%.
2. 100BASE-TX LAN video streaming:
Transmission of multimedia content in the LAN need to have adequate transmission capacity. For the user's real-time view, the end user from the multimedia server to transfer large amounts of data capacity and error correction capabilities are critical. Both the received digital signals of video and audio quality to make subjective assessments, but also can determine the number of bit error.
A 56MB, 40 seconds of video files between server and client with a 4 by a pair of structured cabling connector channel 15 Jen / second transmission speed, channel the other manufacturers were using the cable and GigaSPEED category 5e Category 6 cable. Typically, the computer video format Zhen Zhen transmission speed is 15 / sec. File using Microsoft's multimedia device to transmit Multicast mode. The document is a boarder in the snow ski slopes of the image. Using HP 8112A pulse generator, in 4 of the channel within a channel adjacent to the proximal Department to introduce pulse interference. The introduction of pulse size, period, rise / fall time is different, thus simulating the worst of the near-end crosstalk environment. Cable is not used with the end section of 100 ohm to terminate the thread. Use of statistical software to measure the distribution and packet loss, network usage and the CRC bit error.
Other manufacturers use CAT5e type cable channel results:
CAT5e type cable hang in the letter, CRC bit error led to the video image distortion, such as images appear stagnant. Each error will cause the packet is invalid, resulting in the loss of image Zhen, causing screen jitter receiver.
Use GigaSPEED 6 cabling channel results:
Near-end crosstalk in the same environment, using the GigaSPEED cable will not produce bit error, so the received video image quality is very good.
3. Serial digital video (SDV):
SDV transmission is based on SMPTE 259M standards. This standard is widely used in the field of animation, the film digitization and to 270Mb / s transfer rate of non-compressed. The system can also be 45Mb / s compressed video transmission speeds to send important images to 143Mb / s non-compressed video transmission rate to transmit television images. Only 270Mb / s non-compressed video can be used to deliver high-quality movie images. 270Mb / s bit stream is edited and sent to the radio front-end used for live broadcasts. Cable length is less than or equal to 100 meters.
SDV from the analog baseband video and audio signals require 4.2MHz and 20KHz independent, digital, and can be combined bandwidth. In a single 75 ohm coaxial cable to 270Mb/sNRZI serial bit stream transmission. Video signal in the brightness and color elements are separated. Requirements of embedded digital audio bandwidth of 3MHz. Generally beat the 0.2UI (unit interval), is about 0.5ns. SMPTE 259M standard allows more than 18 dB return loss. SDV synthesized baseband signal peak to peak voltage value of 0.8V (+ / -10%), the minimum bandwidth required for the 135MHz, but the following lines in the effective energy spectrum analysis diagram can be extended to 270MHz.
SDV demo configuration can achieve bit error number and jump measurements, subjective assessment of the received signal can also be video and audio quality. Experiment was conducted by Sony and Tektronix manufactures audio and video equipment, used subjective assessment and the number of independent measurements. It includes transmission / reception to UTP adapter SDV, SDV signal 75 ohm unbalanced coaxial cable transmission for the 270 Mb / s, more than four pairs of balanced 100 ohm UTP cable. 2 SDV signal transmission in the opposite direction on that four pairs of cables in the 2 and 3 lines right, the purpose of the channel at each end crosstalk. Standard adaptive equalizer adapter to complete, according to state and deformation amount of the length of the channel within the cable, providing automatic compensation for services. Standard is designed to connect the adapter plug wire / plug the 15 pin device connector. The role of multi-pin connector cable and the current role of test equipment similar. It can be measured by any channel connectors minimize crosstalk. Not the cable channel in the end with the adapter, and each adapter is set to "Y" form.
A pair of four connector channel is structured cabling market, other manufacturers use common CAT5e classes and SYSTIMAX GigaSPEED 6 categories related components composition. Tektronix TSG601 SDV optional signal generator to 16 among a SDV test samples to 270 Mb / s rate, with embedded AES / EBU digital audio, CRC data is transmitted to the waveform monitor Tektronix WFM601M SDV. Monitor performance real-time digital error detection, and according to SMPTE RP-165 standard reports CRC errors.
When detected between past and present video frame the CRC bit value has not also immediately report the error. Beat can be accurately measured and displayed as a graphic eye. Superposition of all possible channels to reach the receiving end of the transmission pulse sequence, constitute the graph. The shape of an eye image effect. The graphic is to assess the eye such as SDV baseband signal performance approach. In the channel, when the noise, interference, or beating increases, the degree will open their eyes reduced, opened the height that the noise environment in the degree of margin there. Tektronix WFM601M SDV waveform monitor can also provide a passive closed loop, allowing high-resolution NTSC Sony 20 "monitor to display the received video signal. Sony DVW-510 Digital Betacam? Player with embedded AES / EBU digital audio mode through a 3.5 minutes Digital Betacam format tapes to digital video transmission to high-resolution SDV Sony 20 "monitor. Display is especially equipped with video and audio serial digital interface to facilitate the automatic evaluation of the two.
Other manufacturers use CAT5e type cable channel results:
The first one-way transmission with a single SDV video and audio signals without significant problems. However, when the channel by adding a second near-end crosstalk SDV signal generator, the video and audio quality to become poor. A lot of white images (snow). The cause of this spot is due to bit-error-induced loss of picture elements or pixels results. Transmission of the audio part of the obvious, is dissatisfied with the static interference. Tektronix WFM601M waveform monitor display red alert to indicate that CRC bit error occurred. Beat is shown as graphic eye, the result of determination is 962 picoseconds. When from Tektronix TSG601 Signal Generator or the Sony Digital Betacam Player of the transmission signal is canceled, all visible and audible interference terminated, beating down to 592 pico seconds. CRC bit error, white or static electricity will no longer appear.
Use GigaSPEED 6 cabling channel results:
Use Category 6 GigaSPEED two-way transmission channel, there is no monitoring to any visual and audible interference, there is no record to the CRC bit error. The result is 592 beats measured picosecond, and only one channel in 5e class SDV signals recorded when the same beat. Obviously, the near-end crosstalk margin GigaSPEED designed for Category 6 channel to bring very good transmission performance.
Summary
When the file transfer in structured cabling channels, many interfering factors affecting high-speed, high-bandwidth intensive network applications, transmission performance, test clearly revealed the existence of near-end crosstalk severely affected. Other manufacturers are currently using CAT 5e cable for two types of application class - file transfer and LAN video streams, near-end crosstalk in the poor environment, the use of GigaSPEED 6 type cable made significant superior operating results. Near-end crosstalk of 10 dB additional surplus capacity, to a large extent, improved data transmission category 6 channel performance. Additional margin improved signal to noise ratio, In addition, when the channel crosstalk generated decreases, more signals can be transmitted.
Final argument also pointed out that there are some like the 270 Mb / s serial digital video applications well beyond the category 5e channel performance. Standard clear that the category 5e channel performance up to 100 MHz, which, significantly enough, because the application required by SDV channel performance to achieve 250 MHz, which is category 6 channel GigaSPEED can provide. Such as file transfer applications like the occasional packet loss can be allowed, and may spend time waiting for data packets re-sent. However, such as video streaming, and 270 Mb / s SDV application simply does not allow any delay. Video streaming program at a time transmission and processing of a packet.
Structured cabling within the transmission channel is an irreparable loss. As Chen and the pixel image is lost, the original transmission image quality noticeably declined. Therefore, channel losses transmission performance very much restricted. With high-speed bandwidth applications and growing future, this impact will become increasingly evident. Structured cabling system channel need to provide adequate margin to boycott the channel loss, in order to support the next generation beyond the current level of data rates, achieve good transmission performance.
1) Other manufacturers CAT5e type cable channel results: As the bit error produces many white
2) Avaya GigaSPEED 6 type cable channel results: there is no bit error caused by pixel loss