10 Gbps Symmetrical with XGS-PON
By Steven Harris
10 Gbps Symmetrical with XGS-PON
Many North American operators and other CableLabs members are working towards implementing a 10G initiative, a wired network for the future! Why is 10G essential? Video continues to apply pressure on the downstream and upstream spectrum of our access networks. Growth in shipments of next generation OLED and quantum dot displays will drive video bandwidth, subscriber streaming (i.e., OTT) and managed Internet protocol television (IPTV) requirements. Ultra HD (UHD) 4K shipments will continue to increase market penetration, while UHD 8K displays will ramp up next year. In addition, annual IP global traffic will reach zettabytes (ZB) in a few years, while global IP traffic will increase threefold over the next 5 years.1 10G is also essential to the future experiences our industry has not created yet!
To prepare future gigabit passive optical networks, or GPON, the family of standards is now featuring a new 10 Gbps symmetrical option for operators. Nowadays there are two symmetrical choices in the GPON roadmap for 10 Gbps: XGS-PON (ITU-T G.9807.1) and NG-PON2 (ITU-T G.989). In XGS-PON, the “X” refers to 10 Gbps while the “S” refers to symmetrical, however, the “S” is not available in XG-PON (ITU-T G.987). In fact, there is a 10 Gbps symmetrical standard already, NG-PON2, though the technology uses a more costly optics known as time and wavelength division multiplexing (TWDM). Using TWDM with NG-PON2 allows operators to supply a 40 Gbps symmetrical service with other added benefits like mobile backhaul/fronthaul. The focus here is on the features and benefits of XGS-PON in a residential, business, enterprise or a greenfield network. The reason is that XGS-PON addresses the cost issue of NG-PON2 optics by utilizing less expensive fixed optics for connectivity, lowering cost of ownership for an operator. In addition, the symmetrical optics found in XGS-PON extends the life and profitability of a PON while allowing for mass market adoption over a GPON infrastructure. Below is a table that compares the data rates of the GPON family of technologies and standards.
Table 1. Data rates of PON technologies
Since the physical (PHY) layer of XGS-PON is based on existing specifications, it operates within the same optical transmission windows, assuming wide operating optical splitters exist from 1260 nanometers (nm) to 1650 nm. The PHY compatible transmission convergence (TC) layer allows for co-existence of XGS-PON with the earlier XG-PON and NG-PON2 that uses TWDM. XGS-PON operates over a downstream wavelength of 1577 nm and an upstream wavelength of 1270 nm, allowing further compatibility over the optical distribution network (ODN) with existing GPON that uses different wavelengths. This allows operators to maintain existing GPON deployments as they progress to faster Internet deployments with PON. Furthermore, XGS-PON also has the ability to operate on GPON wavelengths, 1490 nm in the downstream and 1310 nm in the upstream. The XGS-PON PHY also leverages time division multiplexing (TDM) and time division multiple access (TDMA) methods to accommodate XG-PON compatibility. Using TDMA allows coexistence of XGS-PON and XG-PON. XGS-PON supports up to a 1:128 split ratio in the ODN, as well as 1:64, 1:32 and 1:16 split ratios.
Figure 1. Co-existence of wavelengths
The new XGS-PON standard is available today for production deployment. It is being piloted by a few cable operators in North America already, with a European operator (Orange Polska) piloting at 5 Gbps down and 2 Gbps up. XGS-PON allows operators like these to skip the non-symmetrical versions of PON. An optical line terminal (OLT) can be equipped with XGS-PON capabilities allowing simultaneous PON technologies to operate over an ODN. For example, a recommended primary optical power budget of 29 dB allows for both XGS-PON and NG-PON2 to co-exist for maximum flexibility in the future, as operators see themselves using more NG-PON2 in the next few years. In addition, the split ratio flexibility permits a single XGS-PON OLT interface to operate multiple PONs over an ODN. For example, XGS-PON may be deployed on a 1:64 split basis that is overlaid on an ODN with older GPON operating at a 1:32 split ratio, allowing XGS-PON to serving 2 Gbps, 5 Gbps or 10 Gbps subscribers. XGS-PON maintains flexibility for a future overlay of an additional fixed optics 10 Gbps/10 Gbps business PON and/or multiple TDWM NG-PON2 wavlengths using higher capability tunable optics.
In addition, as operators increase their fiber deep (FD) architecture deployments, XGS-PON is also a possibility for reaching the last mile using new hardware like remote OLTs (R-OLTs). Finally, DOCSIS provisioning of GPON, or DPoG, is a scalable operational support system interface (OSSI) used by operators to provision GPON, XG-PON and XGS-PON. DPoG additionally leverages the foundation of a well proven DOCSIS back office system while promoting multivendor interoperability, lowering the cost of ownership, leveraging the workforce knowledgebase, and supporting 10 Gbps services.
The ODN, or fiber optic access network, now has 10 Gbps fixed optic architectures for both XGS-PON and EPON. 10 Gbps reliable wired networks will be the platform for the next generation consumer services and future service possibilities. Believe it or not, work has begun on emerging 25 Gbps and 50 Gbps PON technology as well!
As a Society member keep current with SCTE·ISBE and the many resources designed to keep you in the know! Did you know SCTE·ISBE offers a PON certification? The certification is known as broadband fiber installer (SCTE.org/BFI), which is a comprehensive exam on RFoG, GPON and EPON FTTx architectures.
Figure 2. Co-existence GPON and XGS-PON
1. Cisco Visual Networking Index.
Steven Harris
Senior Director, Advanced Network Technology and Instruction, Learning and Development, SCTE•ISBE
Steve Harris is the Executive Director of Technical Education and Sales at SCTE·ISBE. He is a respected international telecommunications subject matter expert, sought-after presenter, and principle instructor. He responsible for the tremendous growth of SCTE·ISBE training curriculum, learning paths and certifications for 100,000+ telecommunication professionals. He also has responsibility for the client partnerships for the SCTE·ISBE Corporate Alliance Program (CAP) MSOs and vendors community.
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