Pipeline Profile: John Downey

SCTE member since 1996 Title: Broadband Network Engineer, Cisco Systems Broadband Background: Prior to joining Cisco Systems in 2000, Downey worked in Acterna’s Multimedia Division in Indianapolis as a broadband training manager. He also gained telecom experience at C-COR Electronics where he was an applications and training engineer. Why are MSOs now interested in DOCSIS 2.0? DOCSIS 2.0 was a pure physical upgrade to provide "speed" for all the services that DOCSIS 1.1 introduced such as VoIP and maybe commercial services. There wasn’t a rush to upgrade modems in the field because of lack of competition, and VoIP had a slow start. VoIP also worked fine with existing DOCSIS 1.1 modems because of the beginning low penetration. Now that Verizon is knocking at the door of many systems, it’s becoming apparent that cable systems need to offer faster speeds. Some systems like the idea of a more robust upstream layer in the CMTS to upgrade from QPSK to 16-QAM, but DOCSIS 2.0 adds much more than this. Advanced time division multiplexing (ATDMA) allows a modulation as high as 64-QAM and 6.4 MHz wide channel width giving about 27 Mbps of usable rate for 1 upstream port. There is also a nice MAC management message 29 sent on the downstream that 1.x cable modems won’t understand, which keeps older modems from ever ranging on an ATDMA-only channel. On the flip side, if a customer buys their own DOCSIS 2.0 cable modem, the modem can be given a config file to set TLV 39 to 0 to make it essentially a 1.x cable modem. What does an operator have to do to activate this service? Using DOCSIS 2.0 requires a CMTS linecard to support ATDMA and in some cases SCDMA to be fully qualified. tComLabs recognized the need for an ATDMA qualification for EuroDOCSIS since most MSOs aren’t looking at SCDMA unless intending to use the frequency below 20 MHz. Cable modems need to be replaced, but most EMTAs installed for VoIP are DOCSIS 2.0 certified. The next question is, can the upstream lasers carry multiple upstream frequencies and/or some of those upstream frequencies at very high modulation schemes such as 64- QAM? Laser clipping could be a very real concern. Are there any hurdles or other technical issues involved? One issue with implementing DOCSIS 2.0 is the migration from older cable modems to a node area with all DOCSIS 2.0 cable modems. There will be a transition period for quite a while before all the legacy cable modems are replaced. DOCSIS 2.0 allows a mixed mode with one limitation—the channel width is dictated by the weakest link. In this case, that will be the legacy modems that cannot go any wider than 3.2 MHz. The advantage of doing mixed mode then becomes the fact that DOCSIS 2.0 cable modems can burst with 64-QAM on the same channel as the 1.x cable modems that can burst with 16-QAM. The modulation profiles allow multiple bursts for different information such as requests, station maintenance, short and long grants for 1.x cable modems and advanced short, long and UGS grants for 2.0 cable modems. Another nice feature in DOCSIS 2.0 may be the inclusion of logical channels. This feature was a way to allow SCDMA and ATDMA to share the same upstream port/frequency/channel. Another idea is to allow maybe 1.0 cable modems to use logical channel 0 and DOCSIS 1.1 cable modems to use logical 1. Logical channel 0 would have parameters suited for 1.0 cable modems such as QPSK, no fragmentation or pre-equalization since 1.0 cable modems don’t support it, maybe no concatenation, etc. Logical channel 1 would allow the DOCSIS 1.1 modems to use pre-equalization, concat, different mod profiles, etc. Another issue with all this upstream speed is the downstream now becomes a bottleneck. Hence the need for DOCSIS 3.0! Have you been speaking or doing any technical training lately? After the SCTE Expo in San Antonio in June where I presented VoIP Capacity and Troubleshooting Info, I presented at the Southern California Vendors Day and a few local chapters. Most of my time has been dedicated to providing training and troubleshooting at customer sites. Is advanced RF modulation a topic of interest at chapter meetings/vendors days? Not specifically. Believe it or not, upstream/return path issues are still the topic du jour as Ron Hranac can attest. I find that chapter meetings will always get a good showing for new technology, but it must include "Back to the Basics" training as well. We still have lots of churn in the industry, and it behooves us to offer "101" courses constantly. You entered another bodybuilding competition, I hear. How did that go? I entered one in May in Wilmington, N.C., and won Junior class overall. I have another in Greensboro, N.C., on Nov. 5. Eight-time Mr. Olympia, Ronnie Coleman, is the guest poser so it should be a packed house.