Module 03: Essence Flows: SDI to IP Encapsulation
This stage represents the "Great Partition." Here, the traditional SDI signal is decomposed into its constituent parts—Video, Audio, and Metadata—and mapped into independent RTP streams. If you have PTP lock but a black screen, the failure is likely occurring in this translation.
The SDI Foundation
- SDI IN: Before troubleshooting the network, verify the physical source. Check the Gateway’s input statistics for CRC Errors. If the incoming BNC feed is unstable, the IP encapsulation will be inconsistent. Digital 101
- Gateway (The Encapsulator): Ensure the gateway is in
TX/Encapsulate
Verification of TX/Encapsulate Mode
Before the first packet hits the wire, the gateway's internal logic must be provisioned for outbound traffic:- NMOS Direction: Verify via your NMOS controller that the device is registered as a Sender. If the UUID is pinned as a receiver, the SDI-to-IP engine remains dormant.
- Port Provisioning: In high-density blades, ensure the SFP port is explicitly set to TX Mode. Mismatched provisioning often results in "Link Up" status but zero data throughput.
- Administrative State: Check that the Flow Admin State is toggled to 'Up' or 'Enabled'. If it shows 'Down' despite being enabled, verify the physical SDI lock.
In a multicast environment, the Gateway may be ready to send, but the Switch won't move the traffic without a Querier. If you see "No Traffic" on the destination side, check the following:
The Check
Use the switch CLI (show ip igmp snooping querier) to ensure an active Querier exists on the VLAN. Without a Querier, the IGMP Join from the receiver never reaches the gateway.
The Symptom
If the gateway is set to IGMP V3 but the switch is only running V2, the "Join" will be dropped, and the essence flow will remain stuck in the buffer.
Note: Some gateways require a "Static Multicast" force-toggle to bypass IGMP for initial testing. If you see packets after forcing TX, your issue is 100% IGMP/Querier related.
Another note - The "BNC Toggle" Rule: If the software shows TX mode is active but there is no traffic on the switch port, physically toggle the SDI input. Many older gateways require a "clean" SDI lock before the FPGA will initiate the RTP encapsulation process. mode. The Gateway’s primary job is assigning unique Multicast IP addresses and Port numbers to each essence. Encoding 101
The Three Pillars of ST 2110
SMPTE ST 2110 standards (including -20, -30, and -40) primarily specify the media transport over IP:
- How uncompressed video is packetized (ST 2110-20).
- How PCM digital audio is transported (ST 2110-30, referencing AES67).
- How ancillary data (e.g., captions, timecode, VANC data per ST 291-1) is carried (ST 2110-40).
They also cover timing/synchronization (via PTP in ST 2110-10), RTP/UDP/IP transport, traffic shaping, and session description via SDP files.
These are the essence flows themselves — the actual video, audio, and data packets on the network.
ST 2110-20 (Uncompressed Video):
The largest bandwidth consumer (approx. 1.1 Gbps for 1080i). Verify that the resolution and frame rate in the
SDP file
match the receiver's capabilities. A common fail point is an Interlace vs. Progressive mismatch.
ST 2110-30 (PCM Audio):
Verify Packet Time (1ms vs. 125µs). If the sender pushes Level C (125µs) and the receiver only supports Level A (1ms), you will encounter silence or distorted "metallic" audio.
ST 2110-40 (Ancillary Data):
Handles Closed Captions (CEA-708), Timecode, and AFD. Ensure the Gateway is configured to pass specific DID/SDIDs; unlike SDI, IP gateways often require manual "allow" lists for ancillary data.
NMOS's role in all this
What NMOS Defines (Control Plane)
NMOS (Networked Media Open Specifications from AMWA) provides the control and management layer on top of ST 2110. It does not define the media formats or transport rules — that's ST 2110's job.
Key NMOS specifications relevant here:
IS-04: Device discovery and registration (devices advertise themselves and their capabilities, including available senders/receivers for 2110 flows).
IS-05: Device connection management (routing connections between senders and receivers, often by exchanging or activating SDP files).
Others like IS-08 (audio channel mapping, especially useful for ST 2110-30), IS-09 (system parameters), etc.
NMOS makes large-scale ST 2110 systems practical by enabling automated discovery, dynamic routing, and orchestration — instead of manual SDP configuration or static multicast setups.
What NMOS Controls for These Streams
NMOS does control or influence the following for ST 2110-20, -30, and -40 flows:
Discovery — Finding devices and the flows they can send or receive.
Connection management — Setting up which sender connects to which receiver (including multicast/unicast addressing, ports, and SDP parameters).
Routing and switching — Dynamically patching video, audio, or ANC flows (similar to a router or matrix in traditional SDI).
Some stream parameters — Via connection APIs, such as activating a flow, updating SDP details, or (with IS-08) mapping specific audio channels in ST 2110-30 streams.
Redundancy (e.g., ST 2022-7) and basic monitoring.
In practice, many modern ST 2110 devices support NMOS IS-04/IS-05 out of the box for these essence types.
What NMOS Does Not Fully Control
Intrinsic media parameters defined by the 2110 standards themselves (e.g., exact video resolution/framerate/color space in 2110-20, sample rate/bit depth/channel count in 2110-30 PCM, or specific ANC packet types in 2110-40). These are set in the device's configuration or SDP and must comply with the standard.
Low-level device settings (e.g., PTP clock selection, network interface QoS/DSCP markings, hardware-specific encoding options, or deep format conversions). These are usually handled by the device's own web UI, API, or proprietary control system.
Manual/static setups — You can still run 2110 flows without NMOS by directly using SDP files, IGMP for multicast, etc. NMOS is optional but highly recommended for scalable, multi-vendor environments.
| Aspect | Controlled by ST 2110? | Controlled via NMOS? | Notes |
|---|---|---|---|
| Media transport & packetization | Yes | No | Core of -20/-30/-40 |
| Timing & synchronization (PTP) | Yes | Partial (system params via IS-09) | ST 2110-10 |
| Session description (SDP) | Yes | Yes (via IS-05 connection) | NMOS often activates SDP |
| Device discovery | No | Yes (IS-04) | Essential for large systems |
| Routing / connections | No | Yes (IS-05) | Main strength of NMOS |
| Audio channel mapping | No | Yes (IS-08 for -30) | Useful for PCM audio |
| Device-specific config | Partial | Limited | Usually via vendor API/UI |
In real-world 2110 deployments (as of 2026), NMOS is the standard way to manage and control ST 2110-20, -30, and -40 flows at a system level, especially in broadcast facilities. However, it complements rather than replaces the underlying 2110 standards.
Quick-Fix: Essence Troubleshooting
| Symptom | Probable Cause | Diagnostic Step |
|---|---|---|
| "Invalid Format" on Receiver | SDP File Mismatch | Compare Sender SDP vs. Receiver capabilities. |
| Video OK, Audio Silent •! | 2110-30 Level Mismatch | Match Packet Time (1ms is baseline). |
| Intermittent Video Flashing | Packet Pacing Issues | Check Gateway for Narrow vs. Wide pacing. |
| No Captions/Timecode | 2110-40 DID Mapping | Verify Gateway is "listening" for correct Ancillary IDs. |
