One of the great things about the SCTE show is the program of technical sessions available. Unlike other shows where session attendance can be quite sparse, the sessions at SCTE are often standing room only. Such was the case this morning when I crammed in to one conference room for presentations on Engineering IP Video. Two Motorolans were presenting, John Ulm and Robert Howald out of the Motorola CTO office for the Home and Networks Mobility business. The goal of both presentations was to articulate some of the technical challenges for cable IP video delivery and then show, through modeling, some of the options for clearing those hurdles.
Of the things I learned during the session, one of the most interesting was the reality of variable bit rate (VBR) delivery for IP video. The capacity gains for VBR are often touted at 40-50% or more over use of a constant bit rate (CBR). (More capacity means greater ability to deliver more content.) However, realistically, according to Ulm, the gains are only about 25% for MPEG-2 SD video, and maybe 20% for MPEG-4 AVC HD video. That’s when you factor in packet recovery. You can use statistical multiplexing with VBR delivery, but it turns out that statmuxing provides much greater benefit when used with static IP multicasting.
Another nugget I picked up was the comparative value of bonded versus unbonded channels for IP video delivery. Bonding provides greater efficiency, giving operators room for roughly two additional HD streams. Using unbonded channels, however, provides greater flexibility. You know all of those set-tops out there with embedded DOCSIS? Well, they don’t support channel bonding yet. Operators can’t deliver IP video over bonded channels to those DOCSIS set-tops currently being shipped to consumer homes.
The migration to IP for cable operators will be fascinating as it starts to take place. And while a year ago I might have said we have a long time before that happens, the buzz at SCTE this year suggests the process could start sooner than many expected. Certainly there’s a lot of research and planning taking place now.