Briefing: Next-Generation PON
Part 1: XG-PON1 goes commercial
Alcatel-Lucent is making available what it claims is the first broadband access platforms that support XG-PON1, the 10 Gigabit GPON standard. The company has developed an XG-PON1 line card for use in its latest ISAM-FX as well as its existing ISAM-FD access platforms. The ISAM platforms support copper and fibre-based broadband access.
“First [XG-PON1] deployments will likely be in Asia Pacific but we are seeing strong interest from other regions"
Stefaan Vanhastel, Alcatel-Lucent
Why is this significant?
System vendors and operators have been trialling 10 Gigabit GPON technology. Now Alcatel-Lucent has signalled that the technology is ready for commercial deployment. The vendor says operator deployments will start later this year, a claim backed by Infonetics Research. However, the market research firm forecasts 10 Gigabit GPON global deployments will only reach two million ports by 2014.
What has been done?
XG-PON1 is the asymmetrical version of the 10 Gigabit GPON standard delivering 10 Gigabit-per-second (Gbps) data rates downstream (to the user) and 2.5Gbps upstream. This compares to GPON, which delivers 2.5Gbps downstream and 1.25Gbps upstream.
The Alcatel-Lucent XG-PON1 line card has four 10 Gigabit GPON ports, and is available on the existing ISAM-FD products as well as the latest ISAM-FX high-capacity shelves.
There are three ISAM-FX shelves that accommodate four, eight and 16 line cards. The ISAM-FX shelves have a dual-100Gbps backplane capacity, compared to the ISAM-FD which has a 2x10Gbps capacity. The ISAM-FX shelves house up to two controllers, and the role of the backplane is to connect each line card to each controller. The 100Gbps is the capacity linking each line card to each of the two controllers. Since the XG-PON1 line card has four 10Gbps ports, the backplane will clearly support future denser line cards.
The controller acts as a central processing unit taking traffic from the line cards and packaging it for the network uplink. Each controller has a 480Gbps switching matrix, four 10 Gigabit Ethernet uplinks and service intelligence to handle the traffic flows. “You can have two controllers per shelf and then they work in a load sharing mode,” says Stefaan Vanhastel, marketing director wireline access at Alcatel-Lucent. “This gives you a total of eight uplinks and you can add more if needed.”
The PON architecture
The XG-PON1 standard allows operators a straightforward way to upgrade existing GPON networks. “The operator can put the two technologies on the same optical network, with some subscribers on GPON and others on 10 Gig GPON,” says Vanhastel.
Source: Alcatel-Lucent
Moving to XG-PON1 not only provides greater bandwidth but also supports more subscribers on the one fibre. According to Alcatel-Lucent the maximum number of PON end terminals or optical network units (ONUs) that GPON supports is 128, dubbed a split ratio of 1:128. In contrast, 1:128 is the starting split ratio for XG-PON1 while the maximum is 1:512.
Source: Alcatel-Lucent
What next?
Vanhastel admits that existing GPON provides more than enough bandwidth to subscribers. To ensure that a GPON subscriber gets sufficient bandwidth, the average split ratio operators use is 1:18. “With the higher-capacity XG-PON1, the average split ratio could go up significantly,” says Vanhastel.
Alcatel-Lucent says initial deployments of XG-PON1 will start in the second half of this year with more widespread deployments occurring in 2012. “The first deployments will likely be in Asia Pacific but we are seeing strong interest from other regions,” says Vanhastel.
Initial XG-PON1 deployments will likely be for backhauling traffic from fibre-to-the-building (FTTB) deployments. Here one fibre has a split ratio of 1:16 or 1:32 but each FTTB node supports 24 subscribers typically.
Meanwhile, the company announced in October 2010 trials with operators Verizon and Portugal Telecom involving the symmetrical (downstream and upstream) 10 Gigabit GPON variant known as XG-PON2. XG-PON2 has yet to become a standard.