When we try to assess how well an IP video connection is working, one of the last things we seem to think about is the user’s method of accessing the network. Yet, if the performance of the video is poor, this is one of the most likely trouble spots. We’re going to investigate four different connection methods and discuss the problems that might be expected to arise. Looking at the table, you can see that we are imagining four users: A, B, C, and D. User A is connected to the network in a lab that is on the same subnet as the server that is streaming the video of the class. User B is receiving the streaming of the video of the class in her dorm room and is using campus Wi-Fi. User C is off campus at home and is connected though high-speed access supplied by a cable company. Finally, User D is also at home but is connected through the local phone company using DSL.
User A’s connection is probably a 100Mbps or 1Gbps connection, depending on the connection to the local switch port into which their cable is plugged. Network packet loss should be low but will have a bigger imapct on the IPTV delivery than on the ABR delivery. A common problem in such a situation is inadequate processing power in the play-out device.
[Byte-Sized Lesson: IP-Related Timing]
User B’s success should be analyzed with a focus on the physical level. The problem in this instance is often the wide variations in the available bandwidth when connected through Wi-Fi. Other Wi-Fi users, location of the access point, and even the orientation of the computer antenna can make a significant difference in the bandwidth available on an instantaneous basis. The typical transport delivery method in this instance would be MPEG transport, typically called IPTV, which is sensitive to variations in bandwidth. The bandwidth needed to deliver HD video is probably 4-8Mbps. We need to keep in mind that 100M or 1G Wi-Fi can routinely operate at one-tenth the nominal speed or less. ABR video, such as Microsoft Smooth Streaming or Apple HLS, could be used but will behave differently than IPTV. An ABR connection will be sensitive to the variations in network traffic that is created by other applications such as file transfers and uploads. Variations in bandwidth will increase network latency. This may or may not be perceived by the student.
Users C and D could receive the video as either ABR or IPTV. If Wi-Fi is being used, the caution about fluctuating bandwidth still applies. If the connection is wired, the cable connection should be adequate if the upstream and downstream speeds are symmetrical. However, DSL is most often asymmetrical—for example, 20M down and 2M up is common. In this case, IPTV could outperform ABR if the user has other applications using the uplink. A critical factor in ABR performance depends on the rate at which acknowledgements of delivery are received.
