Network Expansion: Up to 100G Testing
The combination of digital media, personal computing and global networking is creating a radical shift in the telecom industry. The key trend is towards IP-fixed/mobile network convergence for the delivery of voice, video and data applications with IP (and Ethernet) as a common universal platform fueled by the exponential growth of video, gaming, collaboration and cloud-computer applications. This trend significantly stresses the transport backbones, which have been built on 10G wavelengths, and is driving the need for upgrades to 40G and 100G.
Given that many carriers have begun mass deployment of their 100G networks, a couple of questions arise: first, is 100 Gigabit Ethernet (GigE) testing different than 10 GigE testing? Second, what needs to be tested during the deployment of a new 100 GigE network?
CFP / CFP2 Validation
CFP quality is improving, and as a result we are now seeing fewer and fewer issues due to incompatibility or electrical crosstalk. However, a quick validation test is still required before each deployment to analyze the main status of the CFP and ensure that there are no errors. The main tests involve analyzing the laser power to ensure that the laser’s transmitted and received optical power is within the specific range; as part of the same validation process, the received per-lane frequency will need to be tested.
In some cases, the CFP is considered the weakest link in the network; in such cases, it will be critical to ensure that the CFP is completely functional before conducting any CFP deployment. In some cases, a per-lane view may be required to identify any suspicious lanes that could eventually cause bit errors. For instance, lane 9 as shown in below picture is slightly out of range.
Per-lane Power Measurement
The above tests are also applicable to the upcoming CFP2 interface, which is backward-compatible with CFP technology. There is no gearbox in the CFP2—it was moved to the host, reducing the physical size and power consumption. However, this also introduces some new challenges, and at the same time new issues. EXFO’s CFP2 adapter, which can be inserted into a CFP interface, allows field technicians to validate CFP2 transceivers before deployment, thus minimizing risk. Given that more than 60% of deployment issues are related to CFP or CFP2, it is now critical to test each CFP. EXFO’s CFP health check supports both interfaces with a basic and advanced mode for quick pass/fail validation.
The use of multiwavelength CFP interfaces has led to the common misconception that dispersion does not present an issue on fiber infrastructure. This is not the case. When providing service to a CPE location, the use of the LR4 or ER4 CFP will generally depend on the required reach. The LR4 interface operates over 10 km, whereas the ER4 operates over 40 km. Even though both use multiple wavelengths, each individual wavelength has a higher signaling rate than previous service offerings — 28G baud per channel compared to 10G baud on a 10G Ethernet deployment. Since the interface still uses NRZ modulation, the intolerance to PMD is similar to previous generations.
PMD Tolerance in 100G and 10G Networks
Optical Signal-to-Noise Ratio (OSNR) Measurement
In order to meet the constantly increasing need for bandwidth, more and more telecommunications operators are now deploying 40G or 100G coherent systems on long-haul dense wavelength-division multiplexing (DWDM) networks. These new technologies are certainly beneficial, but they also bring about new test and measurement challenges, in particular for optical spectrum analyzers (OSAs), versatile test instruments that are key to successful DWDM system commissioning and troubleshooting. Indeed, recent 40G/100G coherent systems featuring polarization multiplexing have made some traditional OSA measurements, such as optical signal-to-noise ratio (OSNR), impossible to carry out.
The International Telecommunication Union is a standards agency that establishes guidelines in the telecom industry. Their ITU-T Recommendation G. 697 (optical monitoring for DWDM networks), sets out the most common optical impairments.
Optical impairments from ITU-T Recommendation G. 697
OSAs can also be used to predict bit-error-rate (BER) results at turn-up. Indeed, we know that the OSNR must be greater than 15 to 18 dB at the receiver to ensure proper signal detection. While a BER test usually takes over 24 hours, an OSNR test (IEC or in-band) takes only 5 minutes. If the first BER fails, a second BER test will be needed after the issue is fixed, resulting in a very lengthy turn-up procedure. A smarter and faster way to proceed, commonly used by operators in Europe, is to run a short 5-minute OSNR test before the BER test. If the OSNR result is higher than 15 to 18 dB at the receiver, the BER test will most likely pass. If the OSNR is lower than 15 to 18 dB, the technician can proceed directly to troubleshooting, thus saving a full >24h BER test that would have failed anyway.
Ethernet BER Test
Once the physical-layer test complete, the next step is to ensure that an Ethernet packet can be transmitted in an error-free manner over the entire network. This could be considered a basic test, but is helpful in validating that all of the traffi c is able to transition to the far end and loopback without any errors. Failing this would result in bit errors. The same test can also provide complete Ethernet statistics and protection switching time data from both paths (working and protection). This data helps qualify Ethernet switches or routers that identify end-to-end connectivity issues from the MAC layer and up.
Typical 100G Ethernet BER Test Topology
Testing Multiple Types of Services
The BER test is primarily based on pseudo-random traffic, whereas in reality, live traffic tends to be based more on different types of services, thereby driving the need for more multiservice tests in which the user can simulate multiple streams with predefined data, voice and video traffic profiles, or user-configurable profiles. These tests make it possible to simulate all of the types of services that will be running on the network while simultaneously qualifying all the key service-level agreement (SLA) parameters for each of these services. Moreover, these tests validate the quality of service (QoS) mechanisms provisioned in the network for prioritization of the different service types, which results in better troubleshooting, more accurate validation and much faster deployment. This capability includes the generation, shaping and monitoring of Ethernet and IP traffic with throughput, frame loss, sequencing, packet jitter, latency, frame size, traffic type and flow control.
Network Performance Validation : RFC2544 and Y.1564 Testing
To ensure that a 100 Gigabit Ethernet network is capable of supporting a variety of services (such as VoIP and video), an RFC 2544 test can be executed, whereby the 100G pipe will be tested and confi rmed for 100% throughput and low-latency frame loss by testing at different frame sizes. The predefi ned frame sizes will simulate various traffi c conditions, because small frame sizes increase the number of frames transmitted, thereby stressing the network device. Because carriers are currently faced with stressful constraints in terms of time to deployment, the industry can now initiate a shift toward ITU-T Y.1564 (EtherSAM) for turn-up testing. This test offers simultaneous tests (as opposed to RFC 2544’s sequential tests), and validates multiple services at the same time, thereby qualifying the services as defined in the SLA. ITU-T Y.1564 is a crucial test that must be executed, and is based on two phases. The first phase, which is called the network configuration test, consists of validating the QoS mechanisms and limits based on the key performance indicator (KPI) threshold: the committed information rate (CIR), the excess information rate and the discard traffic conditions.
As part of the process of minimizing test times and reducing the amount of truck rolls, a dual test set (DTS) configuration can measure the performance of the system under test (SUT) by measuring both transmission directions. Additionally, this test (which is also known as a head-to-toe test) offers a lot of value when the networks feature multiple routers.
EXFO Solution for 100G commissioning, turn-up and troubleshooting
A Powerful Combo: Agile OSA and Multiservice Test Solution in One Supertech Platform
Combining the FTB-88100NGE 100G multiservice module and the FTB-5240S-P OSA in EXFO’s FTB-500 portable platform provides a unique testing solution for commissioning 100G links and turning up legacy and packet-based services.
The FTB-88100NGE/5240S-P is a powerful duo for a simplified and streamlined field-testing experience.
Use the FTB-5240S-P OSA module to commission 100G links, and then activate the FTB-88100NGE Power Blazer Multiservice Test Module to address client-service turn-up testing requirements.
- Simultaneous 100G bit-error-rate testing and Pol-Mux OSNR measurement 100G
- Supports all possible rates up to 100G, as well as a wide range of technologies, including legacy TDM and new packet-based services
- Features multitesting capabilities, including SONET/SDH BERT and ITU-T Y.1564 EtherSAM for Ethernet service activation