The SCTE Autumn Lecture Meeting, 2003.

The Society held its Autumn Lecture Meeting on 25th September. SCTE President, Dr. Roger Blakeway reports.

	Summary of Presentations The Sixteenth SCTE full day lecture programme was held in the Council Chambers of the IEE on Thursday 25th September. Over 80 people attended the event which had the theme Recent Advances in High Speed Data over Cable Delivery Solutions . The meeting was chaired by Dr Mark Burns, Chairman of the Papers Committee, who, after welcoming everyone and setting the scene for the day, introduced the speakers.

Presentations Now Available We are very pleased to be able to offer you the chance to see the presentations, again. Please right click on the lecturers' pictures to download a zip file of the slides used. Please be aware that these are very large files.

	'DOCSIS 2.0 - An Essential Guide to the Technology and its Benefits' Presented by Mr Serge Francois, Senior Product Manager at Terayon. In his paper, Mr Francois outlined the progress made since the DOCSIS system was introduced. The presentation began with detailed outline of DOCSIS 1 and 1.1. The basic limitations were outlined and this led on to a detailed description of the new and improved features available in DOCSIS 2. The use of direct sequence spread spectrum was described and the performance gains quantified. Trellis coding was also very clearly outlined by Serge. Altogether a very well presented lecture on a very complex subject.

'An Investigation Into RF Impairments Found In Real World Plant; Characterisations And Advances In DOCSIS Solutions To Combat Their Effect' Presented by Jack Moran of Motorola BCS. Jack Moran gave us some of his very considerable practical experience acquired whilst investigating problems in the return paths of Cable networks. Jack particularly honed in on the causes and effects of micro reflections which, as he explained, are caused by RF mismatches and, due to the low cable losses in the return path, such mismatches are hardly attenuated by the cable and can cause severe distortion of the digital bitstream. Jack also showed the results of experiments carried out back at his Lab verifying his findings in the field. The reaction from the audience showed that Jack had highlighted a very relevant and neglected aspect of return path operation.

	'Optimising DOCSIS Networks' presented by Robert F Cruickshank III, Co-Founder and VP Account Management for Stargus Inc. Robert drew on his considerable DOCSIS background gained from his involvement in the formulation of the DOCSIS standards to demonstrate how the many operational parameters can be tweaked to optimise the channel capacity of the reverse path. There is a tendency for operators to set up their systems using 'safe' defaults for the reverse path (e.g. QPSK, FEC settings). Robert emphasised the enormous amount of data that existed within CMTS and STBs which, with care, could be extracted without a significant load on the reverse path network and which could then be analysed to see where potential problems were occurring (e.g. in the RF or software domains) or where additional capacity could be gained. An iterative fine tuning to the operating parameters can result in better speed and reduced downtime. Robert showed a number of examples taken from live networks, which showed how adjustments could be made and then further fine-tuned resulting in significant additional channel capacity. This well presented and comprehensive paper completed an excellent morning session.

'More for Less, Better Business from Fewer Bits' After an excellent lunch, with the opportunity to discuss the topics raised by the morning session, the afternoon began with a paper by Colin Phillips, Manager TV Solutions at ntl. Colin's paper dealt with the choice and optimisation of bitrate for their envisaged VOD service. With 8M homes and 2M existing digital subscribers it was essential that MPEG2 was used for VOD transmission. They envisaged a distributed VOD playout using their 40 regional headends and transmission over GigE using DWDM down to the Hub level. Here they had to optimise the trade off of node size/concentration ration/bit rate using sensitivity analysis. This paper concentrated on the bitrate aspects with the overriding factor that the linear sensitivity meant that a 10% saving in bitrate would mean 10% cost saving in stream playout and transmission. Colin then presented a series of video clips to show the results of a double blind trial using subjective testing with non-expert viewers to ITU-R BT.500 guidelines. The baseline was chosen as 3.6Mbits/sec, which corresponds to their existing NVOD service. The net result was that, with modern encoders, 2.9Mbit/sec seemed to provide adequate results over the range of content types used, from sport to talking heads. This is a 20% reduction in bitrate and cost with the added bonus that 13 streams could be carried in a multiplex rather than the 10 with NVOD. In closing, Colin commented that a significant reduction in bitrate could be obtained with MPEG4 (currently giving good results at 1.25 to 1.75 Mbits/sec) but that would mean a new STB and problems with legacy boxes.

	'Etth: The Next Generation Data Over Cable' Presented by Reinaart Bryssink, VP Business Development at Teleste and Jan Ariesen of Tratec. Reinaart presented the current trend in data requirements to the home, which showed a 10Mbit/sec need by 2010 and 100Mbit/ec by 2020. Delivering 10Mbit/sec with DOCSIS led to small node sizes of less than 280 homes and subsequent network cost in subdividing the access network. An alternative solution was to provide Ethernet to the home, which covers all requirements from simple 'dial up' equivalence up to VDSL. In the Teleste solution, 500Mbit/sec chunks of bandwidth are delivered to the nodes using QAM modulated Ethernet. At the node a multitap with Ethernet switch is used to deliver 10BaseT at baseband to the home where a new outlet plate would be needed. Jan continued the presentation with a description of the hardware needed to use the coaxial drop for baseband 10BaseT. The problems were significant with different impedance requirements (75ohm for TV and 100ohm for Ethernet) and vastly different levels (typically 65dBuV for TV and 127dBuV for Ethernet). To ensure that spurii from the data did not exceed CENELEC specified levels in the video band an isolation of over 80dB in any diplexor would be needed, with a balun arrangement ensuring that the Ethernet was delivered as balanced twisted pair. The normal 5Mhz lower limit of galvanic isolators also had to be addressed since Ethernet needs a lower limit of 0.5Mhz; the use of a larger capacitor making leakage requirements difficult to meet. The system is entering a trial phase in The Netherlands.


The applause for all the speakers and the comments afterwards showed that the papers were well appreciated and had provoked a great deal of thought in those attending. Mark Burns, Chairman for the day and Chairman of the Papers Committee is to be congratulated, along with the speakers, for providing such an excellent programme.


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