CBT - Certified Broadcast Technologist Broadcast Networking Basics Questions and Answers — Questions and Answers
Question 1: A broadcast facility is implementing a new IP-based video system to distribute a single live camera feed to 25 separate monitoring destinations within the plant. Which IP transmission method is the MOST efficient for this purpose?
- Unicast
- Multicast (Correct answer)
- Broadcast
- Anycast
Correct answer: Multicast
Multicast is the most efficient method because the source sends a single packet stream to a specific multicast group address. Network switches then intelligently replicate the stream only to the ports connected to devices that have requested to join that group, saving significant bandwidth compared to other methods.
Question 2: Which of the following statements best describes the fundamental principle of the SMPTE ST 2110 suite of standards for professional media over IP networks?
- It encapsulates the entire SDI signal, including video, audio, and data, into a single IP stream for simplified transport.
- It uses a proprietary compression algorithm to transmit 4K video over standard 1 Gigabit Ethernet networks.
- It separates video, audio, and ancillary data into individual, independently-timed essence streams over IP. (Correct answer)
- It is primarily designed for transmitting compressed video over the public internet to consumers.
Correct answer: It separates video, audio, and ancillary data into individual, independently-timed essence streams over IP.
The core concept of SMPTE ST 2110 is the separation of video, audio, and ancillary data into individual 'essence' streams. Each stream is independently packetized and timed using Precision Time Protocol (PTP), which provides immense flexibility in routing and processing signals within a production environment.
Question 3: In a broadcast IP network carrying real-time video and audio, what is the primary function of Quality of Service (QoS)?
- To scan all network traffic for viruses and malware.
- To assign priority to critical media traffic, ensuring low latency and minimizing packet loss. (Correct answer)
- To automatically assign IP addresses to new devices on the network.
- To encrypt all data packets to prevent unauthorized viewing.
Correct answer: To assign priority to critical media traffic, ensuring low latency and minimizing packet loss.
Quality of Service (QoS) is used to manage network traffic by prioritizing certain types of data over others. In a broadcast network, real-time video and audio streams are extremely sensitive to delays (latency) and packet loss. QoS ensures these critical media packets are handled before less time-sensitive traffic (like file transfers), guaranteeing the performance needed for a stable on-air signal.
Question 4: A broadcast engineer is setting up a new SMPTE ST 2110 facility. What is the critical role of the Precision Time Protocol (PTP / IEEE 1588) in this environment?
- To manage user access and security credentials for network equipment.
- To provide a high-accuracy, common time reference for synchronizing all separate media essence streams. (Correct answer)
- To compress video and audio streams to conserve network bandwidth.
- To monitor the network for hardware failures and send alerts.
Correct answer: To provide a high-accuracy, common time reference for synchronizing all separate media essence streams.
In an ST 2110 system, video and audio are separate IP streams. Precision Time Protocol (PTP) is essential for providing a highly accurate master clock reference to all devices on the network. This allows the separate essence streams to be precisely aligned and synchronized at their destination, which is the IP-based equivalent of traditional black burst or tri-level sync.
Question 5: When streaming live, real-time video over a managed IP network, why is the User Datagram Protocol (UDP) typically preferred over the Transmission Control Protocol (TCP) for transporting the media packets?
- TCP is an older protocol that is not compatible with modern video formats.
- UDP includes native, high-level encryption which is required for broadcast content.
- TCP's guaranteed delivery mechanism introduces latency that is unacceptable for live video. (Correct answer)
- UDP has a much larger packet size, allowing for higher video quality.
Correct answer: TCP's guaranteed delivery mechanism introduces latency that is unacceptable for live video.
TCP guarantees the delivery of every packet by requiring acknowledgements and retransmitting lost packets. This process of waiting for acknowledgements and retransmissions adds significant delay (latency), which would cause a live stream to pause or buffer. UDP, by contrast, sends packets without requiring acknowledgement, prioritizing speed and low latency over guaranteed delivery. For live video, it is better to have a momentary, imperceptible glitch from a dropped packet than to have the entire stream halt.
Question 6: Which network switch feature is most critical for efficiently managing multicast traffic in a media-over-IP environment by preventing streams from being sent to all network ports unnecessarily?
- IGMP Snooping (Correct answer)
- Power over Ethernet (PoE)
- Spanning Tree Protocol (STP)
- Link Aggregation (LACP)
Correct answer: IGMP Snooping
By default, a standard switch floods multicast traffic to all ports, which can overwhelm the network and connected devices. IGMP (Internet Group Management Protocol) Snooping allows the switch to 'listen' to the IGMP messages between devices and the router. The switch builds a table of which ports have devices that have requested a specific multicast stream and then forwards that stream only to those ports, drastically reducing unnecessary traffic.
