Behind the OIF’s new OTN-over-packet-fabric implementation agreement

The Optical Internetworking Forum this week announced an implementation agreement for OTN-over-packet-fabric-protocol, a move aimed at eliminating or minimizing the need to deploy separate devices to handle packet and wavelength switching.

A product supporting this capability could be a critical element of a packet-optical transport platform, said Winston Mok, technical editor for the new interoperability agreement. Some network operators, including Verizon, envision the P-OTP underpinning their next-generation networks.

Packet switching is the key
An implementation agreement is not a standard, cautioned Karl Gass, vice chair of the physical and link layer working group at the OIF. Instead, he said, an IA defines “what you need to pay attention to” but is not focused on enabling products from one manufacturer to work with those from another.

“When you develop technology, you want to break it down into bite size pieces, to look at the block diagram and draw circles around certain functions and bring them in to a component,” explained Gass.

The new IA anticipates using a packet switching fabric for both packet and wavelength switching, said Mok.

“The IA says, ‘This is how you convert a TDM stream into a packet format,’” Mok explained. “Now that traffic is sent to the egress side, how do you convert it back? The important thing about the conversion process is to allow . . . [the] line card to send a constant bit rate stream at exactly the same frequency it came in on. If it came in at 10.1 gigabits per second and goes out at 10.0 you have a mismatch.”

The solution, he said, “is all about how often you turn on and off the laser in whatever wavelength you happen to like or need.”

Goals include cost-efficiency
The creation of the IA should enable manufacturers to build a device to support the P-OTP approach at the same cost as a device that would support only one type of switching—although it may add slightly to the cost of an OTN line card, said Mok.

“If it doesn’t cost extra, why wouldn’t you buy a box that would do both?” he asked.

Products built around the new IA could be used anywhere in the network, but are likely to be most useful at the network edge, Mok said.

“The closer to the edge, the more varied your traffic is,” he said. He cited the hypothetical example of a network operator having a financial customer, a cell tower and residential customers taking IPTV service in close proximity to one another. The fewer devices are required in the network to support these customers, the more efficiently the network will operate, he explained.

A P-OTP box based on the new IA could give network operators considerable flexibility in serving various customer types, even as requirements shift over time, said Mok.

Essentially the product should minimize the importance of the question, “How do you determine what will grow faster in this corner of the country?” he said.