How to determine if your network is ready to deliver high quality performance for voice and video.
This white paper addresses the challenges of VoIP/UC deployments and expansions with recommendations as to the appropriate processes, metrics and test methods to ensure the quality of user experience. In the examples, we illustrate the processes through the utilization of the NETSCOUT OptiView XG Network Analysis Tablet. While other tools can be used for these tasks (a network management system for SNMP-based information, or iPerf or other software tools for performance testing), the OptiView XG combines multiple functions in an integrated, high-performance platform.
- Network Readiness Assessment
- Network Infrastructure and Service Validation
- VoIP Traffic Assessment
- Estimate Call Bandwidth
- The NPT Test Failed – Now what?
Is your network ready for voice, video, and Unified Communications? Deploying or expanding these services onto the IP network improves productivity, cuts costs, and enables integration with other applications for most businesses. Many deploy these applications on their network infrastructure without first validating the readiness of their network to handle unique traffic demands. If your network is not ready for these business critical services, quality and availability will suffer, which is difficult to troubleshoot post-deployment. In addition to voice and video, IT departments are also responsible for supporting new critical applications including security camera systems and fire alarm systems, all while maintaining the high performance of business data applications.
When validating a network pre-deployment, it is easy to make assumptions about potential problem points based on previous experience or present network problems. It is important however to validate the impact that these expected problem points will have on voice and video quality before implementing any changes or upgrades. At times, engineers make significant changes and costly upgrades to the infrastructure, all before testing to determine if these were needed in the first place. Once a change has been implemented, it should be tested to ensure that it achieved the expected level of performance.
High quality delivery for voice, video, and UC services does not happen by accident. To ensure top performance, it is important to plan the implementation, including: baselining present network performance, validating carrier service level agreements, measuring traffic thresholds, validating QoS settings, and resolving underlying problems before they impact the users.
Если эти службы уже были развернуты в сети и работают плохо, этот опыт может также использоваться для оптимизации сети, чтобы повысить качество служб и опыт пользователей.
Network Readiness Assessment
A network assessment to prepare for voice, video, and UC traffic will require more than throughput tests and capacity planning on the network. For example, most VoIP calls generate under 100Kbps per call, so ensuring that the network can handle high throughput end to end doesn’t test the unique requirements of voice. Rather, metrics such as packet loss, jitter, and network delay have a major impact on call quality, and should be validated during the network assessment. Normal network traffic will compete with these services for bandwidth and forwarding priority, requiring a solid QoS configuration across the network. Testing and validating QoS settings with simulated traffic should be a part of the network assessment. Voice and video traffic may be transmitted across a service provider network to remote offices. While the provider may have a Service Level Agreement (SLA) for throughput, latency, and jitter, these should be tested to ensure the carrier is meeting their end of the agreement. While testing the provider network, the assessment should ensure that the provider is not modifying QoS markings and port numbers as packets pass through their system.
Network Infrastructure and Service Validation
Ensuring that the network is ready for voice, video and UC will require several key steps.
First, a full network inventory and physical connectivity map should be performed, which will serve as documentation during deployment. This step is made easier by using the automated discovery, reporting and mapping features of the NETSCOUT OptiView® XG. The creation of network maps in OptiView XG is instantaneous once discovery has completed. The benefit of this is that maps and reports can be instantly generated for up-to-the minute accuracy. After collecting a solid inventory, the following measurements should be included in the assessment:
- Router and Switch CPUs should be less than 30% sustained
- Interfaces should be completely clear of Ethernet errors, which cause packet loss
- Links handling voice and video traffic should have an average bandwidth utilization of less than 30%, with jitter measuring at less than 20ms.
- Packet loss on WAN connections should be less than 15 per hour.
Most of these tests can be viewed using the SNMP enabled discovery of the NETSCOUT OptiView® XG, focusing attention on the key switch and routers that will handle voice and video traffic. Measurements for throughput, jitter, delay, and packet loss can be made using the Network Performance Test (NPT) on the OptiView XG. This feature allows traffic to be defined and generated to a single remote endpoint or several remote endpoints. These endpoints measure the traffic stream to determine how the network handles and impacts quality, or they will reflect the stream back to the original OptiView for analysis. Thresholds can be configured in the test to monitor for degraded performance. We will discuss specific configurations for the NPT under the VoIP Traffic assessment section.
These network measurements will identify problem points in the infrastructure that should be resolved or upgraded prior to moving forward to the VoIP traffic validation steps. If these services are already deployed on the network, the OptiView NPT will identify specific areas of improvement for an optimized infrastructure.
Last, the Network Services such as DNS and DHCP should be monitored for performance, as voice and video devices will put a higher demand on these systems. These tests can be run using the Network Services tests on the OptiView XG, which measures response time and availability.
VoIP Traffic Assessment
Once the network has been assessed for problems that will impact the performance of voice and video, a VoIP Audit should be run to simulate traffic streams and fully evaluate network readiness. This test will also bring to light any other unexpected issues that will impact these services before they are deployed. This assessment applies in principal to video and UC as well, and can be adjusted to simulate these services as well.
First, logical areas where voice and video traffic will travel should be identified. This will allow test endpoints to be strategically placed on the network to validate the connections where traffic will really travel. For example, if there are remote offices, branches, or buildings within a campus, traffic should be verified for these logical locations, giving a full picture of performance across key links for both local and remote users. The Graphical Path Analysis feature of the OptiView XG will graphically visualize these paths, showing all interfaces at both layer two and three between the endpoints. Any network errors or links with high utilization along the path will be flagged by this automated test.
Using the Network Performance Test on the OptiView, engineers can simulate the traffic load of multiple voice and video streams to remote endpoints throughout the network, while simultaneously measuring traffic performance with respect to loss, delay, jitter, and throughput. The NPT compares the actual performance of traffic against configured thresholds to provide a simple pass/fail summary result. This test will give engineers a clear picture of how real application traffic will perform once it is deployed, while unearthing problem which will impact performance.
To validate the network using the Network Performance Test, an OptiView is selected as the traffic generator and is connected at a central point on the network as discussed above. This test requires another OptiView XG, a OneTouch AT, or a LinkRunner AT to serve as an endpoint for the traffic stream. The test can generate up to eight simultaneous traffic streams which can be layered onto the network. For example, with VoIP, there is typically a call signaling conversation, the actual voice data, as well as background traffic. The OptiView can simulate all three of these traffic types at the same time, using three different streams. The streams can be directed to different endpoints distributed on the network to validate several locations at once. The source OptiView is configured with key parameters controlling the content and utilization of the simulation traffic stream. Endpoints will collect and measure the traffic, or will reflect it back to the source OptiView for measurement.
Estimate Call Bandwidth
Testing network readiness for voice and video differs from standard throughput testing on the network. Each call generates a relatively low amount of bandwidth, depending on the codec in use. The chart below gives the approximate Ethernet bandwidth in use for each codec and number of simultaneous calls.
|Codec - # Calls||1||10||50||100||500||1000|
Using the Network Performance Test (NPT), a new traffic stream can be configured to simulate these levels of call loads. The traffic can be configured using a packet size of around 200 bytes which accurately represents a RTP (real-time transport protocol) packet. In the test, settings for QoS can be configured, which will then validate both local and service provider infrastructure devices, ensuring they are being handled properly from end to end.
In addition to simulating RTP streams, additional traffic streams can be layered in by the NPT test which will simulate call setup traffic. If packet loss occurs during call setup, the call may not establish at all. The thresholds in this individual stream of the test can be configured to be more loss sensitive. A stream can also be configured that will simulate user traffic, loading the network to normal usage levels. This will create more realistic traffic levels for measuring simulated voice and video streams.
The NPT Test Failed – Now what?
If a performance problem is experienced with the NPT, it can often be traced to one or two links that are impacting the traffic. Since multiple devices and interfaces are involved in delivering the service, this is a challenge, especially in a production environment with contending traffic. The engineer needs a way to quickly identify the problem point in the traffic path which is causing the test to fail. The Graphical Path Analysis feature can be used to map the path between endpoints and visually display all interfaces and devices involved in delivering the traffic. The test will automatically flag errors, utilization spikes, and CPU problems, assisting network engineers in finding the root cause of the failed test.
To fully experience the benefits of voice, video, and UC on the IP network, care should be taken to validate the infrastructure before deployment. Problems affecting performance can be detected and resolved before they affect users, or impact a critical system. Using the Network Performance Test, the OptiView XG can simulate and measure voice and video traffic, revealing pain points such as packet loss, jitter, delay, and problems with QoS configurations. These tests can be used both in pre-deployment and in the optimization stage of service rollout. The NPT can also validate network changes to verify the effect of an upgrade or new configuration. Both the local network infrastructure and the carrier network between branches can be validated for VoIP and Video readiness. When problems are detected, the visual Path Analysis feature will assist in pinpointing the root cause. These features will ensure a tested, validated, and quantified network that is truly ready for voice, video and Unified Communications.