Overview
The scope of testing telecommunications networks broadly covers the key aspects of functionality, reliability, performance, and security.
It spans various domains, including interoperability, conformance, and system evaluation. Core network testers require support to ensure:
- That the system under test conforms to 4G / 5G 3GPP protocol specifications and performs the correct message exchanges (behavior, sequences, and formats).
- Seamless interoperation across different vendors and systems compatibility. In the case of errors, the root cause or at least the responsible network function needs to be clearly determined in order to be able to write a meaningful error report.
Therefore, the test environment needs, besides traffic generators and simulators to create controlled test scenarios, to also include a specialized protocol analyzer to monitor and evaluate the protocol behavior.
Scope of protocol testing
Protocol testing includes:
- Verification of message structures to ensure that message formats (headers, payload, etc.) conform to protocol specifications, including correct length, encoding, and delimiters.
- Validation of the correct message responses / sequence. This can include also the behavior in error conditions, timeouts or the robustness when sending invalid data.
The most complex task in testing telecommunications networks, however, is to analyze the end-to-end logical message behavior across the network including control as well as user plane.
This means to examine protocol logs to identify anomalies or errors in the protocol sequence / interactions. The core network consists of several independent network functions (e.g. MME, S-GW, HSS, x-CSCF) which communicate with each other via a set of different standardized interfaces and protocols (including S1C via S1AP/NAS, S1U via GTP-U, S11 via GTPv2, S6a via Diameter, Mx via SIP).
Protocol analysis tool
Protocol testing needs to be supported by a flexible tool which can reduce the testing and analysis effort considerably. This means, a protocol analysis tool for the core network needs to provide:
- Support all protocols from 5G SA and EPC / 4G LTE & 5G NSA
- Filtering of the mass of irrelevant messages
- Automatic correlation of messages from different interfaces/protocols and automatic call type/message flow discovery
- Effective filter options
- Logical network function grouping (which means to automatically recognize network functions from network address identifiers)
- Easy to understand graphical representations of message flows, errors in different protocols, etc.
It is important to note that protocol testing in the scope of overall network function testing is not a clearly defined procedure of fixed steps. It requires knowledgeable experts, supported by efficient tooling, which can detect and flexibly drill down into protocol issues and relate to different network segments (RAN, EPC, IMS, backhaul/transport) and network functions in order to indicate respective root causes (e.g. state error, functional error / SW bug, insufficient computing resources or bandwidth, …).
Benefits of protocol testing
Through thorough protocol testing, correct and reliable protocol support are verified.
However, overall protocol testing also improves in general the recognition of other indirectly related network problems and bottlenecks, and the identification of vulnerabilities when network error and load conditions etc. are tested.
This means good protocol testing and analysis is a critical aspect of building reliable, secure, and performant telecommunication network solutions. It provides multiple benefits ranging from
- early error detection to
- better performance and interoperability, and
- long-term system stability.
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