Distortion Testing of Broadband LAN Distribution Systems

Distribution systems for transporting multiplexed data are generally comprised of high-quality CATV-type amplifiers and equipment. CATV systems are designed and specified so that noise and distortion caused by amplifier nonlinearities will not be noticeable in a TV picture, or at least will be within acceptable limits. Specification and testing of these systems has become standardized in the CATV industry, and performance and limitations for multi-channel video are well understood. LAN distribution systems are specified in the same manner and may be tested likewise, but relating specifications and data performance is not as straightforward due to the wide variety of data services and modem characteristics. Data rates may vary from perhaps 56 Kb/sec (or lower) in a 100KHz bandwidth to 10 Mb/sec in a 12MHz bandwidth. Broadband T-1 modems, operating at 1.544 Mb/sec in a 750KHz bandwidth, are widely used. In addition, data and video services may coexist in a LAN network. Thus, the distribution system operational criteria are system dependent. However, certain basic measurements and tests are applicable to all systems, and these are reviewed in this paper.