LONDON -- Ethernet Europe 2011 -- While operators are finally embracing and commercially deploying Ethernet backhaul in volume, they are not ready to give up their time division multiplex (TDM)-based circuits just yet because network synchronization is still a major challenge for them. That was one of the takeaways from an Ethernet backhaul panel discussion here on Wednesday.
It is common for operators to use a hybrid model for packet backhaul, whereby voice traffic is carried over E-1 links and high-speed data traffic is carried over Ethernet.
Despite the cost implications, Rob Thomas, director of product solutions at BT Wholesale , says the carrier still operates its TDM network along with its Ethernet connections to base station sites, and it will need to implement both new synchronization standards -- Synchronous Ethernet and Institute of Electrical and Electronics Engineers Inc. (IEEE) 1588v2.
"It's quite a significant cost to have Ethernet and SDH equipment squeezed into a nodeB [base station] rack," said Thomas. So, getting rid of the TDM circuit would not only free up the E-1, but also space in the equipment, he explained.
While the cost of running two different networks is incentive enough to do away with the old TDM networks, the vendor panelists agreed that operators are unlikely to have entirely removed TDM from their networks in the next three years.
Hossam Salib, VP of product management and marketing at Positron Inc. , said three years was "too aggressive" as a target for when operators will give up their TDM networks for backhaul transport.
According to Michael Ritter, VP of technical marketing at ADVA Optical Networking , three years from now is when operators will start to migrate away from TDM, but it will be different in different parts of the network. For example, that migration might happen first in urban areas rather than rural regions where "there is no incentive to invest there," he explained.
"It all comes down to economics," said BT's Thomas. "There are still many 2G sites out there. ... At what point do you switch off the TDM network? Running [BT's] 21CN and TDM is expensive."
Part of the reason for why operators need to hang on to their TDM networks is that there are still implementation challenges lurking for, in particular, the 1588v2 standard.
"[With] SyncE, everyone trusts that technology; it's a matter of bringing it to the network," said ADVA's Ritter. "[With] 1588v2, there is still a question about performance. There has to be a more common and versatile approach. There will be much more complex backhaul architectures because of all this."
"1588v2 is going to be the most simple way [for synchronization], assuming you know how to deploy it," said Ran Avital, VP of strategic and product marketing at Ceragon Networks Ltd.