Test Methodologies to Verify Transport Network SLAs

August 17, 2021 Anritsu Company

August 17, 2021

There has been plenty of conversation around 5G transport deployment and the challenges it poses as networks transition from 4G to 5G. Many 5G transport network operators and vendors agree architectural changes for radio and transport enables providers more control over their bandwidth utilization and complexity through the combination of virtualization and network slicing.

5G also introduces a new method to ensure network operation – service level agreements (SLAs). Mobile carriers establish SLAs with the goal of guaranteeing customers receive an optimum experience. For 5G, that translates to ultra-low levels of latency, jitter, and packet loss from the network. Proper standards-based testing can help operators monitor that SLAs are being met.  

Figure 1 displays a brief evolution of the Radio Access Network (RAN) from distributed architecture used in 3G, to a centralized configuration in 4G, and now the virtualized approach in 5G through the use of functional splits.

Evolution of the RAN from 3G to 5G.
Figure 1: Evolution of the RAN from 3G to 5G.

Why Network Virtualization

Network virtualization is a key network element for 5G to reach performance expectations. It relies on software to deliver networking and security services all the way from the data center to the cloud and to the network edge. By leveraging software, 5G networks can keep up with user demands for greater speed, agility, and security.

Network Slicing Benefits

Another major change in 5G is network slicing. Fundamentally, it is an end-to-end splitting of network resources and functions so selected applications, services, and connections can operate separately and with a specific purpose.

3GPP defines slicing procedures for the core network, directives for the access network and suggestions for the transport network. The global association states a network slice is a logical end-to-end network that can be dynamically created. Each slice may serve a particular service type with agreed upon SLA.

Network slicing is so appealing to operators because it allows each separate business operation to efficiently and reliably run on a designated slice. Infrastructure providers are responsible for managing these network slices end-to-end.

Supporting 5G Use Cases

So, let’s discuss the demand for SLAs within the new 5G virtual RAN architecture. Figure 2 displays the physical topology of the RAN, starting from the mobile devices through the 5G core network. Although the physical network path remains constant for the transport network, 5G services will be divided into different categories based on performance requirements.

Physical topology of the 5G RAN.
Figure 2: Physical topology of the 5G RAN.

One example is enhanced mobile broadband (eMBB). It utilizes a higher functional split for higher bandwidth but has increased latency. It is in contrast to Ultra reliable low latency communication (URLLC), which utilizes a lower split for greater intelligence at the RU+DU to reduce latency.

Massive Machine Type Communications (mMTC), with its predicted millions of cellular IoT devices, is slightly different. mMTC does not have the bandwidth or latency requirements of most eMBB or URLLC use cases. Plus, the intelligence can reside within the 5G core. 

As you can see by the above use case examples, the system complexity of 5G network slicing creates difficult challenges for the SLA management and verification lifecycle. Many are related to use of multiple layers and the variability of the definitions and computation methods of high-level Quality-of-Service (QoS) parameters.  

For operators, it raises an important question. “How can I verify multiple SLAs through the 5G transport network in the field?”

The answer can be explained referencing the physical transport topology shown in figure 2. Each 5G service application is segmented as it would appear as an SLA based on functional splits and network slicing to verify service performance. As shown in figure 3, the SLA requirements for each service differ and must be verified end-to-end – initially for connectivity and then for resiliency when other services are added.

Different SLA requirements for 5G use cases.
Figure 3: Different SLA requirements for 5G use cases.

Testing Based on ITU T Y.1564

Many operators rely on ITU T Y.1564 Service Activation testing to verify end-to-end SLA activation. With networks evolving so dramatically, the standard addresses the different network configurations and ensures quality across networks with multiple streams with different policing parameters. It also allows engineers to input Service Acceptance Criteria (SAC) information that is normally based on a subset of the user’s SLA. By inputting the SAC information before the test begins, it’s possible to set easy pass/fail criteria to simplify results and alleviate possible pain points for the engineer.

To simply test and address all areas, the standard has been written around two core components:

Service Configuration Test – During this stage, each Test Flow is completed in a sequential manner to confirm there are no network configuration issues.

Service Performance Test – Once the network configuration test is completed, confirming the network works under load over a configured duration of time is required. The Service Performance Test completes this phase by generating all Test Flows simultaneously at the CIR for 15 minutes, 2 hours, or an entire day, according to the standard. Custom time periods can also be selected by the user.  

This test methodology is commonly used in transport network SLA verification because it takes both physical and virtual network segments into account. The ITU-T Y.1564 test methodology is available in many network devices and field test equipment, such as those offered by Anritsu. Operators can use these solutions to share a common industry standard test result, so they can work with vendors and engineers to define how best to provision their network devices and functions.

You can learn more by visiting the Anritsu Resource Center and reviewing the Network Testing educational materials. You can also schedule a meeting with a solution expert at the Resource Center.

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