Application Notes

Switched Digital Video, or SDV, is a technology that enables increased efficiency of network bandwidth for service providers. Studies show that 80 percent of video subscribers watch the same 20 percent of programming channels.

Cable service providers face an increasingly competitive landscape with the growth of video offerings from telcos and satellite service providers. Successful, reliable high quality delivery of thousands of video streams through dozens of

Cable MSOs across North America and Europe are already aware of the potential benefits and rewards of implementing Switched Digital Video (SDV) networks. By implementing SDV, cable MSOs will be better positioned to compete against the telcos and their promise of advanced services which will be delivered to the home at bandwidths greater than 50Mbs.

This memo defines a set of supplementary tests for networking interconnection devices (switches) that can be used to evaluate and
compare their performance when used with streaming media. The Media Delivery Index (MDI) [i3] measurement is employed as a convenient stream quality indicator of input and output streams to indicate cumulative stream jitter and packet loss under test load conditions.

This memo defines a Media Delivery Index (MDI) measurement that can be used as a diagnostic tool or a quality indicator for monitoring a network intended to deliver applications such as streaming media, MPEG video, Voice over IP, or other information sensitive to arrival
time and packet loss. It provides an indication of traffic jitter, a measure of deviation from nominal flow rates, and a data loss at-a-glance measure for a particular flow. For instance, the MDI may be used as a reference in characterizing and comparing networks

Data switches are increasingly being deployed in cable and Telco transport environments with large numbers of streams of voice and video over IP (streaming media). Owing to their real time nature, streaming media applications are particularly sensitive to packet arrival time jitter and loss. Due to a wide variety of possible network application uses, using traditional data application oriented tests often do not reflect the performance experienced of a network when it is used in a streaming media application. This note proposes and describes the following plan for network evaluation:

MPEG video transport streams undergo time distortions known as jitter when being transported by packet switched networks such as Ethernet. Identifying and measuring jitter and packet loss in such networks is key to maintaining high quality video delivery. The Media Delivery Index (MDI) is a set of measurements used for monitoring and troubleshooting networks carrying any streaming media type. The MDI can be used to warn or alarm on impairments that result in unacceptable video delivery and on conditions that result in unacceptable network margin before video quality is impacted.

Forward Error Correction (FEC) technology is often used to improve reliability of data transport and loss characteristics on links with loss pattern metrics that do not measure up to those needed for streaming media applications. The loss patterns and distribution encountered on links are key to determining how much redundant FEC overhead may, or may not, be required to provide acceptable performance for an application.

Recent releases of firmware for the IneoQuest Technologies, Inc. Singulus G1-T include new, powerful features that allow line-rate packet modification as well as selective packet drop capabilities while in network TAP mode. User selected packet fields can be modified as the packets are forwarded through the G1-T from the one port to the other port or modified as they are received from one of these ports and transmitted from the same port. In addition, user specified packet criteria can be used to identify packets to selectively forward or to selectively filter traffic.