SMPTE ST 2110-21 - Traffic Shaping and Delivery Timing for Video

Specifies the timing model for senders and receivers of video RTP streams.

Two main types of Sender exist - Narrow Senders and Wide Senders. These names refer to the variability of their packet pacing:
Narrow Senders adhere much more tightly to narrow timing constraints, while Wide Senders can vary more widely in their packet pacing.

Narrow Senders
Narrow Senders are usually FPGA-based and are highly precise, adding a very minimal delay or jitter to the resulting IP stream. Narrow Senders can be divided into two sub-categories, namely Narrow Linear Senders (type NL) and Narrow Gapped Senders (type N - the "gapped" part is implied).

Narrow Linear< Senders space out the packets evenly, as shown on the right of the diagram below.

Narrow Gapped Senders
Do not send packets during blanking so will have a short gap during which no packets are sent.

Wide Senders (type W)
A Wide Sender can comprise a regular PC with some dedicated hardware that makes it capable of handling uncompressed video. Even with the dedicated hardware however, the transmitting PC can struggle to output packets at a steady pace. This variability in the rate of transmission places greater demands on the Receiver in terms of the buffering and memory required. As such, if there is a Wide Sender anywhere in your network, you will need a corresponding Wide Receiver.

Receivers In terms of receivers, the only classifications are Narrow or Wide. There is no distinction between linear and gapped for receivers.

Test methodology Testing for ST 2110-21 should assess resilience to:
Delay - usually due to physical link length or processing delays introduced by network elements. Introducing delay can also be useful for testing the essences' re-alignment mechanism. Constant delay should not affect anything, so we can use almost any value by default (within reason). Packet-by-packet delay value can range from 20µs to 10ms.

Packet loss - commonly caused by network congestion or as a result of packet corruption, since if the CRC becomes invalid, a store-and-forward switch will drop the packet. Packet Drop can be configured to almost anything; it really depends on the receiver and whether 2022-7 is being used (receivers that employ 2022-7 should be able to cope with any amount of packet loss).
ST 2022-7: Seamless Protection Switching of SMPTE ST 2022 IP Datagrams

Packet corruption - can be due to a dirty fiber or poor connection, among other causes. Cut-through switches do not perform any CRC error-checking, so error-checking needs to be performed by the receiver.

Bursty conditions - the Calnex SNE's Burst Packets mode can be very useful for testing that your buffer size is sufficient. The choice of value for the Burst Packets impairment will depend on the settings of your receiver - some receivers will not handle packet bursts well.

Reordered packets - on a LAN, the reordering of packets should be rarely seen, but over WANs there are more likely to be multiple routes that packets could take, making reordering more common.

Packet duplication - may occur as a result of misconfiguration (e.g. two streams of data being sent to the same destination by mistake) or some other network issue.

Jitter and packet delay variation (PDV) - this is usually introduced as a result of traffic passing through multiple routers in transit from the source to the destination. Each router will contain some amount of buffer, and these will vary between routers in each of the network "hops." When introducing Packet Corruption, packets should be considered dropped by the MAC layer of the decapsulator/receiver, so a clear correlation should be seen between Corruption introduced and packet loss observed. If the SDI video starts to flicker, this indicates that the buffer is not set to a high enough value. Increasing the buffer value should result in the video becoming smooth again.