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Migration from TDM to IP Networks

A traditional communications network uses Plesiochronous Digital Hierarchy (PDH) and/or SDH/SONET-based TDM technologies. Many carriers and enterprises are modernizing their TDM-based network infrastructure to IP to support increased traffic volume, speed, and benefit from the convergence of voice, data, and video. The TDM-to-IP transition minimizes overall operational costs, resources, and quickly roll out new services. However, most enterprises still have a mix of TDM, and VoIP infrastructure to support a variety of customer needs.

Integrated Test Platforms for Migration from TDM-to-VoIP

A migration to Voice over Internet Protocol (VoIP) and converged IP networks is inevitable but poses challenges, which requires significant testing, and troubleshooting. As communications network evolve, test and measurement solutions are key to successful transition. Typical test cases that arises during migration of services from TDM to IP are outlined below.

Hybrid TDM-IP Network Testing

Simulate various elements in a hybrid TDM VoIP network, and test inter-operability of different network elements, be it VoIP to VoIP,  TDM to TDM,  VoIP-TDM, and/or Analog-VoIP.

GL’s MAPS™ (Message Automation and Protocol Simulation) platform is designed for simulating and testing ’Multiple Protocols’ and ‘Multiple Interfaces’. MAPS™platformscan easily simulate and test TDM end points, Analog end points, SIP end points, Signalling/Media Gateways, and the entire core-network. Complex scenarios can be easily setup to perform end-to-end testing of signalling, call flows and traffic.
GL also offers integrated mTOP™ platforms (Multiple TDM Optical and Packet rack systems) that can house any combination of USB based TDM, Optical, and Packet equipment - PacketExpert™, tProbe™ (T1/E1), USB T3/E3Dual UTAs, and LightSpeed1000™ to support multiple interfaces in a compact rack space.

Test High Speed WAN Services (T3, E3, DS3, T1, E1)

Use Case Examples: Emulate SS7-to-SIP via soft switch, SS7-to-SS7 (same SSP), SS7-to-SS7 (different SSP's), Continuity Check call flows, Fax/Voice/Tones call flows, loss of connectivity tests and SNMP trap notification,  and many others.

End-to-end Assessment of Network Performance

End Users perceive quality in a practical way. When networks perform poorly, users may experience service disruption, poor audio quality, delay in call setup, or echo during calls, resulting lowered productivity. For end users - reliable connectivity, quality of heard speech, none or imperceptible echo, low delay, low noise, and good volume are generally considered important. Service Providers assess quality through Service Level Agreements (SLA) that assess long term service reliability, quality of service, and traffic volume capacity.  Service coverage area, its features and functions, and consistent call quality are also important.

Equipment Manufacturers address quality through equipment characteristics such as conformance to protocol specifications, meeting throughput, latency, blocking / congestion requirements, and to reliability and availability specifications over time.

End-to-End Quality Testing Across Networks

During and post migration from traditional TDM-IP networks calls for periodic end-to-end testing for call quality and media delivery. Ability to simulate calls being the end point and test variety of networks intrusively for voice, data, and video quality is one of the critical requirements for carriers.

GL’s VQuad™ Probe HD or VQuad™ mTOP™ platform uses a combination of telephony devices (FXO, T1/E1, SIP/RTP, Bluetooth®, Balanced Audio I/O, PTT) to support multiple interfaces to objectively evaluate Signal Strength, Voice, Video, & Data Quality on Cellular networks, Land Mobile Radios, and Wired networks. It can simulate calls being the end point and test core network issues. VQuad™ Probe HD can connect to practically any end-point, including Wireless (Bluetooth®, Wi-fi, 3G, 4G, LTE, PTT), VoIP, Analog, and TDM, independent of underlying network type and perform automated voice, video and data testing.

Various associated analytical applications (Voice QualityVideo QualityData testsEcho and Delay testsFax testsVoice Band Analysis) work with the base VQuad™ software to provide "end-to-end assessment" of the network performance.

Use Case Examples: Call Quality in a Hybrid TDM-VoIP Network, Audio Quality Testing of LMRs (PESQ, POLQA), Measure Signal Strength (RSSI), Smartphone/Handset Benchmark Testing

Testing Gateways

The transition to All-IP requires “Gateways” that convert legacy signalling and traffic carried over TDM to new IP signalling / traffic carried over IP/Ethernet. The gateways must achieve synchronization between TDM circuits and IP networks and cope with impairments of the underlying networks.  Therefore, the need to test and emulate elements within both sides of gateways is important. GL’s MAPS™ (Message Automation and Protocol Simulation)platforms are capable of connecting to any PSTN, ATA, and next generation Gateways and simulate all the elements surrounding the Gateways (DUT) to test the all functionalities.

Use Case Examples: Emulate Trunking Gateway (TGW) in digital network and Residential Gateway (RGW) in analog network, and thus perform inter-operability tests in a hybrid TDM-IP network.

Testing Gateways TDM-to- VoIP Networks

Echo Cancellation

Echo can be as simple as sidetone, or more complex such as line, and acoustic echo. Typically, voice gateways provide many value-added services such as echo cancellation, Voice Activity Detection (VAD), comfortable noise generation and encoding/decoding. Acoustic Echo Cancellers (AEC) are used in phones or in the network to minimize this distortion. Acoustic echo, unlike line echo, is dynamic during a call as people and speakers move about and reflections change.

Based on the configuration and performance of Echo Canceller (EC) in the gateways and other equipment, echo exists in voice, and it is essential to test for echo characteristics. Echo Measurement Utility, G.168 EC Test Suite, Echo/Delay Compensation and Measurement applications across various networks.

EC Test Solutions
Use Case Examples: Line (Hybrid) Echo and Acoustic Echo scenarios using EMU , Automated G.168 EC Compliance Testing of Gateways, G.168 EC Compliance Testing of ATAs and Gateways with 2-Wire Interfaces, Acoustic Echo Tests conforming to ITU-T P.340, Echo/Delay Compensation System

Impairment Generation

Testing system performance under realistic network conditions requires the introduction of impairments that can be expected on real-time networks.

Circuit and packet (VoIP) networks introduce impairments such as delay and loss to speech traffic. Latency, CRC Errors, and Bit errors are the impairments that could be seen on T1 E1 bearers or signaling links. Latency, jitter, out-of-order packets, duplicate packets, and network congestion are other types of packet impairments expected on IP networks. Quantifying these impairments is an important first step to providing quality voice communications. All impairments can be simulated, quantified and compensated to study network behaviours under realistic conditions.

Impairment Simulation and Measurement

GL provides various simulation tools such as WAN IP Emulators, HDLC/PPP/Frame Relay Simulators, EC Test Tools, and VQuad Probe™ HD, that can introduce variety of impairments across IP, Optical, TDM and PSTN networks. In addition, MAPS™ supports low level impairment capability by manipulating select protocol fields in the forward and backward signalling messages (on a per call basis) before sending over transport. Impairment can be applied at any position in the given frame using byte offset value.

Use Case Examples: Satellite signal propagation, impairments and mitigation , Inserting Bulk Delay and Errors (single, fixed, automatic, random, and burst error) into the incoming bit stream, Emulating congestion in a IP network, Impairing protocol fields to study signalling responses.

Voice Feature Tests, IVR Tests, Codec Combability Tests

NGN advanced voice features are similar to but more sophisticated than CLASS (Custom Local Area Signalling Service) features PSTNs offer. These features include three way calling, call waiting, call hold, caller id, call waiting with caller id among others. In many cases, these features involve detection and generation of tones and dual tones with varying cadences. Capability for testing higher quality voice (any codec support), inband and out-of-band digit transmission, and DSP are just some necessary functions of a test tool used for testing NGNs. 

GL offers complete test solutions across ALL networks, both intrusive as well as passive. GL’s MAPS™ (Message Automation and Protocol Simulation) platforms offers in-depth functionality tests to be scripted and run repeatedly to test and verify voice features of NGNs. VQuad™ Probe extends the ability to perform detail QoS measurements and reporting. The architecture provides for complete and integrated lab management, network element functionality, device provisioning, and automation solutions, whether its end-to-end or within the core network infrastructure -- of Wireless, NextGen IP, and TDM networks.

Functionality Testing of Voice Features – Migration to NGNs

Use Case Examples: Voice Feature Testing for Legacy and Next Generation Networks, IVR Testing, Speech quality within VoIP and PSTN networks, Active QoS testing, SLA testing, TCP-UDP Throughput Testing,  Audio and Video MOS

Delay Measurements

Rigorous methods are needed to precisely measure the delay introduced by each network element as events  propagate end-to-end. Precise timing equipment are necessary for detecting, capturing, timestamping, and correlating events at Analog, TDM and IP interfaces.  Delay measurements should be conducted repeatedly  to ensure  that the device and network under test is performing as expected  consistently over time.

GL tools provide highly precise non-intrusive and intrusive timing measurements, accurate to the nano-second level. It includes all necessary hardware and software to identify, capture, timestamp, and correlate events at Analog, TDM and IP interfaces. These report Round Trip Delay, One-Way Delay measurements, Jitter, and Echo Measurements.

Echo Delay Compensation and Measurement

Use Case Examples: Critical Timing Measurements in Air Traffic Control networks, Delay Compensation to eliminate the varying delay/echo in TDM Networks, Emulate packet delays that occur over SONET/SDH carrying ATM/PoS traffic.

Testing Fax Transmission Quality

Successful deployment and migration of fax services requires extensive network design, test and traffic engineering. Test equipment that can generate and receive fax signals prove valuable in this process, especially when a bulk fax calls are required to be simulated over wired and wireless networks

GL provides comprehensive Fax Testing Solutions over IP, TDM and PSTN networks using its products. The tools help emulate, monitor and analyze fax signals in real time for traffic engineering, network design purposes, and for troubleshooting failed or poorly handled calls. Both MAPS™ as well as VQuad™ Probe HD can simulate bulk fax calls end-to-end over a variety of networks. In other words, one can follow the fax session from start to finish on both the send and receive sides.

Use Case Examples: Bulk fax call generation, Analysis of TDM-to-VoIP fax through media gateways

Fax Testing across TDM and IP
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