Agilent Measurement Journal - Issue 4 - 2008 - (Page 32)

ﬁnd the point at which devices reach their limits. To provide a deterministic stimulus, Agilent recommends — and provides — hardware-based high-scale TCP load generators (Figure 2). of network-induced impairments on real TVs and set-top boxes. It’s also very compelling to provide video and sound decode to allow selective subjective assessment of quality from either real or simulated video channels. All network devices introduce delay, and its effect varies according to the type of service. For phone service, absolute delay must be signiﬁcantly less than one second or else conversation is difﬁcult. For broadcast TV, absolute delay is relatively unimportant (other than its effect on channel-change times) — but delay variation should be tightly controlled because the TV receiver must ultimately remove such variations by using buffer memory with a ﬁnite — and cost-sensitive — capacity. It’s worth noting that delay measurements averaged over many user trafﬁc streams are of little use. What’s needed are detailed per-user measurements of packet delay characteristics (Figure 3). Making meaningful measurements Testing IP performance requires more than just the blasting of devices with a realistic mix and scale of trafﬁc types. It is equally important to make measurements that are per-user and sensitive to all aspects of network performance that affect user QoE. Measures of simple packet loss and delay are certainly central but they aren’t enough. In the case of video QoS, which goes beyond the channel-change measurements described earlier, it is vital to measure factors such as media delivery index (MDI) at large scale. Though based on packet loss and delay, MDI is optimized to relate directly to the effect Figure 2. Varying the load dynamically over tens of thousands of active TCP connections allows accurate determination of device limits. Figure 3. Simultaneous per-user measurement of delay variation and packet loss provides a true picture of IPTV delivery quality. 10010010001110101110100100011010111010110011100010101001110101011010100101101001110100101101101001 10100100100011101011101001000110101110101100111000101010011101010110101001011010011101001011011010 32 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 4 - 2008

Agilent Measurement Journal - Issue 4 - 2008 Delivering Confidence through Compliance with Standards Contents Emerging Innovations Trying Early Device Implementations at the IEEE 1588 PlugFest Achieving Greater Confidence in Measurement Accuracy through Consistency in Calibration Services Overcoming the Challenges of RFID Component Testing 3GPP LTE: Introducing Single- Carrier FDMA Ensuring Reliable Operation and Performance in Converged IP Networks Testing Storage Area Networks and Devices at 8.5-Gb/s Fibre Channel Rates Choosing an Appropriate Calibration Method for Vector Network Analysis Making Traceable EVM Measurements with Digital Oscilloscopes Exploring Terahertz Measurement, Imaging and Spectroscopy: The Electromagnetic Spectrum’s Final Frontier Interpreting Quoted Specifications when Selecting Digitizers

Agilent Measurement Journal - Issue 4 - 2008

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