WHITE PAPER. G.fast WHITE PAPER. G.fast promises to seriously boost signal speeds to customer premises. OVERVIEW

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1 G.fast Testing the new DSL technology that boosts speed over copper local loops OVERVIEW Telcos have offered customers Digital Subscriber Line (DSL) solutions for decades. DSL provides digital communication to the customer premises over copper local loops originally intended for analog telephony (POTS Plain Old Telephone Service). This was a big improvement compared to the analog alternatives. The first DSL solutions connected central offices and customer premises. However as FTTx (Fiber to the something ) solutions emerged, the telcos could deliver very high speed digital signals to the end point of the FTTx network - and then use DSL solutions to send the signal the rest of the way to the customer premises. This shortened the DSL part of the connection, enabling higher communication speeds. The latest DSL technology is G.fast ( fast is short for fast access to subscriber terminals ), which is defined for local loops up to 500 meters. The target communication speed is 150 Mbps to 1 Gbps depending on the loop length. G.fast technology will require new transmission equipment at the ends of the G.fast line, which of course will need to be tested. For this purpose the Broadband Forum is working on the certification test plan ID-337. A XenaBay chassis equipped with Odin- 1G-2S-6P 6-port 1Gbps test modules and the Odin-10G-1S-6P Wire-speed 6-port 10G L2-3 test modules provides powerful testing capabilities to test and verify G.fast transmission equipment in accordance with ID-337. G.fast promises to seriously boost signal speeds to customer premises. But how do you verify performance and conformance with Broadband Forum ID-337?

2 Contents G.fast - Testing the new DSL technology that boosts speed over copper local loops OVERVIEW... 1 Introduction... 3 G.fast deployment scenarios... 4 Future Development Amendment 2, 3 and XG-FAST... 5 G.fast Test Requirements... 5 G.fast Equipment... 7 Xena Networks G.fast Test Solutions... 7 Testing up to Layer Test Automation... 9 CONCLUSION... 9

3 INTRODUCTION The G.fast standard is the most recent DSL (Digital Subscriber Line) technology available for telecom operators to provide digital communication to their customers over legacy copper based local loops. G.fast is standardized in ITU-T G.9700 and G.9701, which were approved in April 2014 (G.9700) and December 2014 (G.9701). The G.fast standardization was coordinated with the Broadband Forum's work on FTTdp (Fiber To The distribution point). Earlier DSL systems include ADSL (Asymmetric Digital Subscriber Line) and ADSL2. These systems would provide a digital communication line between the Central Office and the Customers Premises. Many of the DSL systems would provide asymmetrical data transfer rates (higher rate from the central office to the customer s premises than the opposite way); the actual data rate would depend on the DSL technology and the distance between the central office and the customer premises. Figure 1: G.fast line terminated with DPU (Distribution Point Unit) and CPE (Customer Premises Equipment) Over the years FTTx (Fiber To The something ) solutions have emerged. They enabled network operators to lay down optical fibers to a location close to many customers and then use existing local loop copper cables the rest of the way to customer premises to provide digital communication services. VDSL (Very-High-bit-rate Digital Subscriber Line) and VDSL2 are DSL technologies developed for this purpose. VDSL systems normally require signals sent through a fiber network from the central office to a street cabinet from where customers are connected through VDSL lines. The FTTdp solution brings the end of the optical fiber line very close to the customer premises, typically leaving a distance shorter than 100 meters. G.fast is optimized for communication over this distance.

4 Distance Target speed * < 100 m Mbps 100 m 500 Mbps 200 m 200 Mbps 250 m 150 Mbps 500 m 100 Mbps Table 1: G.fast target speed over a local copper loop without bridge taps * Target speed is the sum of the uplink and downlink speeds Table 1 shows the target speeds for G.fast at different distances. G.fast may be asymmetrical like for instance ADSL: Support for downstream/upstream ratios between 90/10 and 50/50 is mandatory while 50/50 to 10/90 is optional (a 90/10 ratio at target speed 1000 Mbps means 900 Mbps downlink and 100 Mbps uplink). To support simultaneous downlink and uplink traffic (duplex) on a line G.fast uses time-division duplexing (TDD); ADSL2 and VDSL2 use frequencydivision duplexing. DSL technologies send data traffic over copper cables originally intended for POTS (Plain Old Telephone Service). The copper cables support a much higher bandwidth that what is required for POTS (300 Hz to 3400 Hz) and this is utilized for the DSL technologies for sending the data traffic. To support higher data rates than other DSL technologies G.fast use higher frequencies 106 MHz and in 2017 also 212 MHz; highest frequency used for VDSL2 is 30 MHz. For G.fast, VDSL2 and other DSL technologies data is modulated using discrete multi-tone (DMT) modulation. The transport of high frequencies is very sensitive to Far End crosstalk (FEXT) between copper wire pairs in access network cables. To compensate for this Self-FEXT Cancellation (also known as Vectoring) is used. The signals are continuously monitored for crosstalk and compensated based on that. G.fast deployment scenarios G.fast will bring the fiber part of the line closer to the customer premises than other DSL solutions like VDSL2, which is associated with FTTN (Fiber To The Node). The FTTx systems normally associated with G.fast is FTTdp (Fiber To The distribution point). The FTTdp end node the DPU (Distribution Point Unit) will be connected to a limited number of customers at distances around 200 to 300 meters. For VDSL2 a FTTN end node a DSLAM (DSL Access Multiplexer) typically serves hundreds of customers within a distance of 1 km. An ADSL2 line will typically connect to a DSLAM in the central office and a customer up to 5 km away. FTTB (Fiber To The Basement) can be used in apartment buildings. The FTTB is terminated in the basement with a Multi-Dwelling Unit (MDU), which is equivalent to the DPU. G.fast is then used

5 to provide digital communication for the apartments in the building through the existing inbuilding telephone cabling. The connection between the DPU(/MDU) and the central office will normally use 1 Gbps or 10 Gbps optical lines. The Broadband Forum defines a number of FTTdp architecture options, including GPON, XG-PON1, EPON, 10G-EPON and point-to-point Ethernet. Future Development Amendment 2, 3 and XG-FAST Telecom network operators have for many years used DSL technologies to bring high speed digital communication to their customers. DSL specification work continues after the approval of G.9700 and G In July 2016 an amendment 2 to G.9701 was approved. New features in amendment 2 include increased maximum transmit power and support for increased bit loading. In 2017 an amendment 3 is planned. Amendment 3 will expand the frequency range from 106 MHz to 212 MHz boosting the communication speed to 2 Gbps for short loops. Amendment 3 will also improve vectoring (crosstalk interference cancellation) to support DPUs with more ports than today's 16 ports. The target is 48 port and 96 port DPUs to be used in street cabinets. The development continues as a 5th generation broadband (5GBB) technology has been proposed: XG-FAST. XG-FAST is expected to provide multi Gbps data speeds over distances up to 130 m and 10 Gbps data speeds over shorter local copper loops. G.fast Test Requirements The G.fast technology will require new transmission equipment at the ends of the G.fast line, which of course need will to be tested. This will be relevant for Development, Quality Assurance and Production at Network Equipment Manufacturers and G.fast component manufacturers. Also Network Operators verification/certification labs will require testing of the new G.fast equipment, in particular the devices located at the customer premises (i.e. the CPEs). For testing of G.fast transmission equipment the Broadband Forum works on defining a certification test plan ID-337 (Internal Document) for verification of interoperability between a DPU/MDU and one or more CPEs. ID-337 includes functional, stability and basic performance test cases for G.fast implementations. ID-337 includes single line and multiple line test setups. The setups are shown in figures 2 and 3.

6 Figure 2: Test setup for Ethernet/IP traffic single line test HON: High Order Node: First node on the path from the DPU into the network Data rate on the downstream and upstream data flows to/from the test equipment in the single line test (figure 2) will normally be 1 Gbps. The Physical Layer Test Setup shown in figure 2 and figure 3 should emulate the G.fast link using equipment like a wireline loop simulator and a noise generator. Figure 3: Test setup for Ethernet/IP traffic multi-line test Data rate on the downstream and upstream data flow to/from the test equipment in the multiline test (figure 3) will normally be 10 Gbps. If the Ethernet Switch is not used data rate on the upstream data flow should be N 1 Gbps streams. Table 2 and 3 show the test frame definition and size distribution that must be used for ID-337 test cases.

7 Ethernet Frame Header MAC Destination/Source Addresses etc. VLAN Tag IPv4 Header UDP Header Optional, downstream flow only Table 2: Ethernet/IP test frame definition Frame Size (bytes) Probability IPv4 Source/Destination Addresses etc. UDP Port etc. Data Payload Pseudorandom bit pattern Table 3: Ethernet Traffic Frame Size Distribution The target in ID-337 test cases is to verify that the DUT will not drop frames during the test. However if frame loss is detected, the Ethernet tester shown in figure 2 and figure 3 can t distinguish whether Ethernet frames are dropped by the DPU, the CPE, the HON or the Ethernet switch. Therefore a background Frame Loss Ratio (FLR) of 4e-7 is accepted in order to not disqualify the DUT for frames dropped by other network elements in the test setup. G.fast Equipment G.fast equipment is available from several vendors like: Adtran 508G G.fast DPU (8 port DPU) Adtran 516G G.fast DPU (16 port DPU) Nokia 7368 ISAM CPE F-240W-A ZINWELL [zgfs-1016d] FTTdp DPU ZINWELL [zgfs-1000c] CPE Xena Networks G.fast Test Solutions Two Xena test modules will be relevant for ID-337 testing of G.fast DPUs and CPEs: 10 Gbps optical Ethernet: Odin-10G-1S-6P Wire-speed 6-port 10G L2-3 test module 1 Gbps optical and electrical Ethernet: Odin-1G-2S-6P 6-port 1Gbps test module Using a XenaBay chassis provides up to 12 test modules for testing of G.fast DPUs and CPEs.

8 Figure 4: The powerful and versatile Xena Odin-1G-2S-6P Wire-speed 6-port 1GE L2-3 test module Testing up to Layer 3 Based on Xena s advanced architecture, the Odin-10G-1S-6P and Odin-1G-2S-6P are proven solutions for Ethernet testing at layers 2 and 3. Advanced test scenarios can be performed using the free test applications for the test modules: XenaManager-2G test software is used to configure and generate streams of Ethernet traffic between Xena test equipment and Devices Under Test (DUTs) and analyze the results. Flexible frame definition capabilities supporting the ID-337 frame definition requirements Multi-stream functionality to send traffic with the ID-337 Frame Size Distribution Xena2544 offers full support for the 4 test types specified in RFC 2544: Throughput Latency Frame loss Back-to-back frames Jitter (Frame Delay Variation) is also supported Xena2889 is an application for benchmarking the performance of Layer 2 LAN switches. The following RFC 2889 test types are supported: All Throughput and Forwarding rate tests (both Fully and Partially meshed) Congestion Control Address Caching Capacity Address Learning Rate Broadcast Frame Forwarding and Latency Forward Pressure and Maximum Forwarding Rate Xena3918 makes it easy to create, edit and execute all test types specified in RFC RFC 3918 describes tests for measuring and reporting the throughput, forwarding, latency and Internet Group Management Protocol (IGMP) group membership characteristics of devices that support IP multicast protocols.

9 Xena1564 provides full support for both the configuration and performance test types described in Y.1564 for complete validation of Ethernet Service Level Agreements (SLAs) in a single test. Test Automation G-.fast products will require testing during development and production. In both cases test scenarios are executed repeatedly to verify the quality and stability of the products. This is normally automated to ensure uniformity and reduce labor cost. XenaScripting is another free application for the Odin-10G-1S-6P and the Odin-1G-2S-6P. It is a powerful and easy-to-use command-line-interface (CLI) scripting API that makes test automation easier for test engineers: Ideal for test automation of e.g. production environments Controls XenaBay and XenaCompact chassis with installed test modules Powerful CLI approach from any TCP/IP capable tool environment Unified syntax for CLI- and GUI-generated test port configurations makes it easy to learn Script examples of Tcl, Perl, Java, Ruby, BASH and Python available Intelligent console tool bundled free with XenaManager-2G The XenaBay and XenaCompact chassis are typically controlled using XenaManager-2G, the free GUI application provided by Xena Networks. Everything you can do with XenaManager-2G can also be done via XenaScripting, using simple CLI text commands. CONCLUSION G.fast is the next DSL technology providing higher data rates than ever over copper wires to customer premises. Deployment has started and in a few years many network operators will offer services based on G.fast to their customers. Test of G.fast equipment is required to ensure the quality and proper functioning. This includes testing in accordance with the Broadband Forum certification test plan ID-337. For development and production automated tests are required to ensure uniformity and reduce labor cost. With the XenaBay equipped with 10 Gbps and 1 Gbps test modules the user gets powerful and versatile Ethernet test capabilities up to layer 3 to test and verify G.fast equipment like DPUs and CPEs testing in accordance with ID-337. Controlling tests with XenaScripting adds repeated testing of the G.fast DPUs and CPEs products required in development and production.