By Rich Nesin, General Manager and Resident Philosopher, HomePNA
You probably heard that the P1901 draft just passed a sponsor ballot. Good news! The developers deserve a lot of credit for achieving a major milestone after five years of hard work. Like the ITU, the IEEE follows a multistep approval process and the group now has to sort through and resolve a stack of comments and then on to the next ballot.
One key to the progress is a coexistence mechanism that allows different powerline home networking technologies to share the same wires. This doesn’t mean they talk to each other. The coexistence mechanism, known by the catchy moniker of Inter-System Protocol or ISP, uses Time Division Multiple Access (TDMA), a proven medium sharing technique. TDMA let’s the different technologies share the wire by creating separate non-overlapping time slots for each one.
The IEEE along with HomePlug and HD-PLC are taking the next step and jointly developing a certification program for ISP. Where does that leave G.hn which also operates over powerlines (as well as coax and phone wires)? The ITU is working on a similar standard - only it’s called G.cx (for coexistence I guess). When it’s complete, G.cx should be identical to ISP allowing G.hn to coexist on the same wires with other home networking technologies.
Does this mean they will all provide the same throughput? Nope. The technologies are significantly different and will probably perform differently on the same wires. Since they share the wire, the maximum speed of each technology will be lower than if it was the only network present so throughput may be a concern – especially for demanding real time applications such as IPTV. As they say, time will tell and the market will decide, however at least we can hope that this path will lead to products that will at least work in a mixed technology environment and that may be good enough.