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Testing Times For Triple Play Networks

The term "Triple Play" is the popular name given to the provision of telephony, data and video services through the fixed telecommunications network, providing the ultimate (for the time being) in convergence. More specifically, it is the combination of high speed Internet data services, Internet telephony and video streaming over broadband access networks – all on a single delivery circuit. The next "big thing" that the network operators want to provide subscribers with is video (IPTV), and in particular "video-on-demand" – instant programme access to what you want to watch, when you want to watch it, and high definition television services (HDTV).

The quest for revenue and profit growth is driving carriers to implement Triple Play Services. The development of the telecommunications infrastructure from a telephony only service to a broadband service, allowing quality data communications for business and domestic purposes, has changed the fortunes of service providers since the collapse of the market at the turn of the century. The overcapacity built into networks for the "dot-com revolution" has been put to profitable use by giving the majority of subscribers higher speed and capacity, using ADSL in the access path. 

However, the growth is beginning to level off. The belief is that even broader band service provision will return the trend to growth, as subscribers avail themselves of the plethora of infotainment devices – all of which have insatiable appetites for data – so a single source of that data may bring back some loyalty to the service providers, and drive up the all important average revenue per user (ARPU). There is another driver, in that the method used to deliver such services will enable a dramatic simplification of network infrastructure with consequent cost savings.

The implementation of Triple Play services in the telecom network requires a major change in network architecture. Current networks are unable to deliver true bandwidth-on-demand as will be required for video-on-demand and interactive gaming. Circuit switched networks have run out of steam, and the next step has to be a fundamental change from a circuit switched to a packet switched network using Internet Protocol (IP). This change requires three fundamental changes in network technology. The first change is the move away from ATM to Ethernet networking technology.

Ethernet has long been established as the network technology of choice in the LAN, and will now be used, in carrier class version, in the WAN. The second change is a move from session based connectivity (e.g. PPP) to clientless connectivity which better suits the plug-and-play scenario in a domestic situation, using, for example, Dynamic Host Configuration Protocol (DHCP). The third change is in how the subscriber is connected to the network in order to be able to access such high speed services. Copper will still be used where appropriate (on short distances), but fibre and wireless will also be deployed to ensure that a quality service is experienced. Hybrid fibre and copper will also be used when distance from the DSLAM would otherwise degrade performance. The core network is, potentially, all that remains of the previous architecture, albeit with packet traffic using MPLS (Multi Protocol Labelling System.

There are a number of challenges in implementing Triple Play services. The single most important challenge is Quality of Service (QoS). Having said that, the technological and economic challenges underpin the ability of an operator to deliver a quality of service at a competitive price. The new services will have to deliver a large increase in bandwidth, support both multicast and unicast video, in an "always-on" mode, to meet readily scalable demand, both securely and economically! Ten years ago, we struggled with dial-up connections with 56kbps downstream bandwidths. Broadband has made download speeds of a few Mbps a reality. 

Video on Demand (VoD) will require at least 12Mbps. HDTV will require more still. Poor video quality is far less tolerable than poor voice quality. Even though the improved compression techniques offered by MPEG-4 will launch higher integral quality video content, and higher performance service delivery technology such as VDSL2 will be deployed, a well designed and managed network have to be prerequisites. Testing and service monitoring will be fundamental to quality service assurance.

Just as the network architecture is undergoing significant change, test techniques and test equipment also need radical change to assure the quality of the services provided. It is necessary for Quality of Service purposes to assure performance and quality of triple play service delivery from content / application provider through to the customer premises equipment. This is necessary because it is the dynamics of scalability that will stress the network to the limit. 

The Spirent AX 4000 will load the network from the Broadband Remote Access Server (B-RAS), through the router and Ethernet network and the IP-DSLAM. The IP-DSLAM in particular can become a bottleneck at peak viewing times. The Spirent AX 4000 with mAX-SLAM application is able to replicate user behaviour, simulating multiple subscribers’ channel hopping, ensuring that each channel requested is presented as seamlessly as is currently the case with terrestrial, satellite and coaxial cable TV services.

Having stated the need to test the service overall, to ensure that the end to end performance standards are met, it is essential that the individual elements of the network are adequately tested during installation and commissioning. Starting at the subscriber premises the connection into the network will be either copper (if the distance from the DSLAM is less than about 1km), or fibre (as in Fibre To The Home (FTTH) or Business (FTTB), or a combination of both (as in Fibre To The Curb (FTTC) or Cabinet (FTTCab). For testing the copper connection, there are a number of one-box solutions available that will determine the physical quality of the pair. Products such as the Fluke NetDSL or the JDSU (Acterna) SmartClass will perform this task, and the Spirent Tech-X Plus will also perform DSL tests as well as key triple play service tests such as IP ping, route tracing, end-to-end IP throughput, emulate VoIP call set-up and receive, emulate sending and receiving video, call placing and clear-down signalling and packet statistics.

If the customer connection circuit includes fibre, the fibre integrity will be tested with an OTDR (Optical Time Domain Reflectometer). A product such as the EXFO AXS-100 OTDR is specifically designed for FTTx applications and can have additional functionality for fault location and repair, such as power meter, fibre inspection, and visual fault location. The device will store many hundreds of measurements, or a particular trace or footprint can be hard-copied onto a local printer. Where problems are encountered in the passive optical network (PON) that may exist in a FTTH application, individual components such as optical splitters can be tested with an optical source and power meter such as the JDSU (Acterna) OLS and OLP series of devices.

In the Transport Network, the fibre in the core of the network carries the highest density traffic, and the utmost care is taken when commissioning. An Optical Time Domain Reflectometer (OTDR) such as the Anritsu 9076B is used to check the end-to-end integrity of all joints (splices). Long fibre runs are checked for Chromatic Dispersion (CD) (phase distortion), and compensation inserted if out of tolerance. A NetTest CMA-5000 analyser with CD and PMD capability would be most suitable for this task. Setting up the Wave Division Multiplexer (WDM) requires the use of an Optical Spectrum Ananlyser, for example the Anritsu 9710C. 

This testing scenario is even more critical if repeater amplifiers are deployed in long haul fibres. In the access and aggregation part of the network, the primary networking technology, Carrier Ethernet, will be tested in one of two ways. In installation and commissioning situations, active (intrusive) testing techniques will be employed to check continuity and configuration, throughput, frame loss, burstability, and latency. Traffic will be generated to stress the network to capacity. When live traffic is on the network, passive (non-intrusive) testing will be employed to monitor the network to observe what is causing impairments. The NetTest CMA5000 can be configured in both active and passive modes.

Legacy circuits may still exist in the network to support enterprise customers’ applications for many years to come. These circuits are likely to be carried on SDH transport infrastructure. Interfacing to the IP network will be achieved by using a General Framing Protocol (GFP) which will allow the traffic to be injected into the MPLS (Multi Protocol Labelling System) core. Suitable products for testing SDH/GFP circuits are the Agilent Technologies J7230B, the Anritsu MP1590B, the JDSU (Acterna) ONT 5xxx, or the NetTest CMA 5000.

Communications in the 21st century means living with the myriad of security issues associated with the internet and a network that is based on IP is just as vulnerable to viruses, Trojans and worms unless suitable and robust resilience is built in, enabling the network to operate even when it is under attack. Products such as the Agilent Technologies N2X NetworkTester will run performance tests on triple play service networks whist injecting simulated Denial of Service (DoS) attacks, spam, and virus attachments to the traffic mix.

Signalling in the network, required to create, modify and terminate VoIP calls, is normally achieved using Session initiation Protocol (SIP). The Agilent Technologies J7830A Signalling Analyser with J7844A VoIP option performs real time analysis of all aspects of a VoIP call and can trace the call through multiple telephony technologies including SS7 and mobile 2G, 2.5G and 3G, to identify where failures occur.

Testing the capabilities of the video servers used in multicast and unicast IPTV applications can be achieved using products such as the Spirent Avalanche or the Ixia IxLoad. The test configuration can be either a single streaming server or a bank of streaming servers. The testing involves simulating demand for the various types of content available, by up to several millions of users to stress the server or servers to the limit of acceptable quality, expressed in terms of server response time, packet loss and jitter. The statistics provided will determine the exact number of users that can access the server within quality tolerance parameters set by the operator.

With the need for new test and assurance technology to test the new network technology, Triple Play looks like changing the fortunes of the test equipment vendors as well as the telecommunications market vendors and service providers.

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