ZyXEL P-861H-G2 User Guide - Page 267
Interleave Delay, SNR Signal-to-Noise-Ratio
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Prestige 861H Series User's Guide nrt-VBR (non-real-time Variable Bit Rate) is commonly used for "bursty" traffic typical on LANs. PCR and MBS define the burst levels, SCR defines the minimum level. An example application is multimedia e-mail. Unspecified Bit Rate (UBR) does not guarantee bandwidth or throughput. Cells are dropped if there is not enough bandwidth. Only the PCR is set. An example application is background file transfer. Table 83 Service Characteristic CHARACTERISTIC Guaranteed Bandwidth Good for Real-Time Traffic Suitable for Bursty Traffic CBR Yes Yes No RT-VBR Yes Yes No NRT-VBR Yes No Yes UBR No No Yes 32.4 Interleave Delay Interleave delay is the wait (in milliseconds) that determines the size of a single block of data to be interleaved (assembled) and then transmitted. Interleave delay is used when transmission error correction (Reed- Solomon) is necessary due to a less than ideal telephone line. The bigger the delay, the bigger the data block size, allowing better error correction to be performed. This may sometimes be referred to as a "slow channel". An interleave delay of "0" means no interleaving takes place and transmission is faster (a "fast channel"). This would be suitable if you have a good line where little error correction is necessary. Reed-Solomon codes are block-based error correcting codes with a wide range of applications. The Reed-Solomon encoder takes a block of digital data and adds extra "redundant" bits. The Reed-Solomon decoder processes each block and attempts to correct errors and recover the original data. 32.5 SNR (Signal-to-Noise-Ratio) The Prestige uses SNR(Signal-to-Noise-Ratio) to determine line quality. SNR is the ratio of the amplitude of the actual signal to the amplitude of noise signals at a given point in time. A slow SNR indicates poor line quality. When SNR (upstream or downstream) falls below a predetermined threshold, the Prestige then uses rate adaptation. Chapter 32 VDSL Commands 266