ST 2110 Video Over IP
SMPTE ST 2110 is the broadcast-industry standard for sending professional, uncompressed video over IP networks. It is the modern replacement for baseband SDI coax. WATCHOUT can both send and receive ST 2110 video through a Deltacast ST 2110 IP board installed in a Runner node.
This page explains what ST 2110 is and how it fits with WATCHOUT. For step-by-step setup, see Setting Up ST 2110.
ST 2110 in WATCHOUT requires a Deltacast ST 2110 IP board. If your show does not have one, use SDI Output or NDI® Video Sources instead.
What ST 2110 is
ST 2110 is a family of SMPTE standards that carries video, audio, and metadata as separate IP streams over a standard Ethernet network. Each stream is sent as multicast UDP packets, timed against a shared PTP (Precision Time Protocol) clock.
Instead of one BNC cable per signal, you run one Ethernet cable. The same cable can carry many streams at once.
ST 2110 itself is bi-directional: the same network connection can send and receive video on the same wire. Specific hardware endpoints may be more limited — some boards or devices support both directions, others are playout-only or capture-only. Check the spec sheet of the board you have.
In WATCHOUT, each ST 2110 stream is addressed as a channel on the Deltacast IP board. A Display set to ST 2110 output is mapped to an output channel on its node. An ST 2110 capture source is mapped to an input channel on its node.
Essences
ST 2110 splits a single video signal into three independent streams, called essences:
| Essence | Carries |
|---|---|
| ST 2110-20 | Uncompressed video |
| ST 2110-30 | Uncompressed PCM audio |
| ST 2110-40 | Ancillary data (timecode, closed captions, etc.) |
WATCHOUT senders and receivers carry ST 2110-20 video only.
The rest of this page and the setup page refer to ST 2110-20 when they say "ST 2110".
ST 2110 compared to SDI
ST 2110 and SDI both carry uncompressed video. The difference is the transport:
| Aspect | SDI | ST 2110 |
|---|---|---|
| Cable type | Coax (BNC), one per signal | Ethernet over copper or fibre, shared |
| Per-cable carrying | One signal | Many streams, limited by link speed |
| One sender to many receivers | Distribution amplifier or matrix | IP switch (multicast) |
| Redundancy | Manual matrix routing | ST 2022-7 (see below) |
| Sync between senders | Genlock (analog reference) | PTP (network reference) |
Bandwidth and link speed
Uncompressed video bitrates are the same on both transports — the "G" in 3G-SDI and 12G-SDI is the actual bit rate in Gb/s. Plan ST 2110 networks against those numbers, plus RTP and Ethernet overhead, plus headroom.
| Format | Approximate bitrate | SDI carrier | What fits on one Ethernet link |
|---|---|---|---|
| 1080p60 | ~3 Gb/s | 3G-SDI | A 25 GbE link carries several streams. |
| 2160p60 | ~12 Gb/s | 12G-SDI or quad-link 3G-SDI | A 25 GbE link carries two streams. A 10 GbE link cannot carry one. |
For a WATCHOUT show, the two most useful ST 2110 properties are multicast and PTP sync.
One output, many receivers
An ST 2110 sender transmits as multicast UDP: one stream on one multicast address. Any number of receivers can join that group through the network switch, and the sender's bandwidth does not change.
In WATCHOUT, a Display set to ST 2110 output is such a sender.
This means:
- One Runner can send the same ST 2110 output to a video switcher, a recorder, and another Runner at the same time.
- Adding a receiver does not load the sender. It loads the switch.
- The switch must support IGMP snooping so it only forwards each stream to ports that asked for it. Without IGMP snooping the switch floods the stream to every port and the network collapses.
WATCHOUT's default output multicast address is 239.1.32.32 on UDP port 20000. You change both values per display.
Addressing streams: multicast and ports
Every ST 2110 stream is identified by a pair: a multicast address and a UDP port. The sender picks the pair when it starts the stream. Receivers subscribe to the same multicast group and listen on the same port. How you allocate that pair across many streams affects how much traffic each receiver actually sees.
Recommendation
Give every stream its own multicast address. Keep the UDP port at the default 20000 across streams. The switch's IGMP snooping then forwards each stream only to receivers that joined that specific group, and each receiver only sees the bandwidth it asked for. This is the standard practice in broadcast ST 2110 deployments.
Three strategies compared
| Strategy | Network behavior | Verdict |
|---|---|---|
| Same address, different ports | Every receiver on the group gets every stream's traffic. Port filtering happens only after the NIC. Wastes bandwidth and defeats IGMP snooping. | Avoid. |
| Different addresses, shared port | IGMP snooping forwards only the groups a receiver joined. Each receiver sees only the streams it wants. | Recommended. |
| Different addresses, different ports | Same network behavior as the recommended option. Just more numbers to track. | Use only if per-stream port labels help operators identify streams in tooling. |
What will not work
- Two senders publishing on the same multicast address and the same UDP port. Both streams arrive on every receiver's socket and the decoder produces garbage. WATCHOUT does not detect this. The operator must keep the (address, port) pair unique across all senders on the network.
- A redundant SPS multicast address (Seamless Protection Switching, explained below) equal to the primary address on the same display. WATCHOUT blocks this in the UI with the message "SPS multicast address must differ from primary stream".
- Joining a group on a port the sender never uses. The receiver subscribes to the right multicast group but sees no packets.
Address range
Pick addresses from the administratively scoped IPv4 multicast range, 239.0.0.0 to 239.255.255.255. Avoid 224.0.0.0 to 224.0.0.255, which is reserved for control protocols including PTP. Avoid addresses already used elsewhere on the network for NDI, mDNS, or other multicast services.
PTP in brief
PTP (Precision Time Protocol, IEEE 1588) is a network clock. Every ST 2110 sender and receiver on the same network shares this clock so packets line up at the destination. Without PTP you cannot decode ST 2110 video reliably.
WATCHOUT uses the SMPTE ST 2059-2 PTP profile. You set a PTP domain number from 0 to 127. All nodes that should share the same clock must use the same domain.
WATCHOUT is a PTP follower only. It never advertises itself as a leader. Your network must have a separate PTP leader (often called the PTP grandmaster) — a dedicated PTP appliance, a PTP-capable switch, or another professional device. If no leader is present, no ST 2110 receiver locks.
PTP is separate from WATCHOUT's normal time sync between nodes, which uses NTP.
SDP in brief
SDP (Session Description Protocol) is a short text block that describes one ST 2110 sender's stream. It lists the multicast address, the UDP port, the video format, the timing model, and the RTP payload type.
A typical SDP looks like this (shortened for the page):
v=0
o=- 0 0 IN IP4 192.0.2.10
s=ST2110 sender
c=IN IP4 239.1.32.32/64
m=video 20000 RTP/AVP 96
a=rtpmap:96 raw/90000
a=fmtp:96 sampling=YCbCr-4:2:2; width=1920; height=1080; ...A WATCHOUT ST 2110 output generates its own SDP when the output starts. Copy that SDP and paste it into any receiver to configure it in one step.
Connection modes
WATCHOUT supports two ways to point a capture at a sender:
- Manual entry. You type the multicast address, port, and optional SPS settings into the capture form.
- SDP file. You paste or load the sender's SDP text, and WATCHOUT extracts the parameters from it.
SDP is the fastest and least error-prone path when the sender provides one. Manual entry works when no SDP is available, or when you want the show file to be self-contained. See Setting Up ST 2110 for the click-by-click procedure.
ST 2022-7 Seamless Protection Switching
SMPTE ST 2022-7 is a redundancy technique. The sender transmits two identical copies of the stream on two separate IP networks. The receiver listens to both networks and uses whichever packet arrives first. If one switch or one cable fails, no frames are dropped.
The Deltacast ST 2110 board has two Ethernet ports for exactly this purpose:
- The primary port carries the main stream.
- The secondary port carries the duplicate stream (the SPS stream).
WATCHOUT's UI calls this "ST 2022-7 Seamless Protection Switching (SPS)". Both names refer to the same feature.
The default SPS multicast address is 239.1.32.33 on UDP port 20002. The SPS multicast address must differ from the primary multicast address.
When SPS is on, WATCHOUT also joins the PTP multicast group on the secondary port. PTP keeps working even if the primary network goes down.
To use SPS you need two switches, or one switch with two VLANs that share no physical link. Running both ports through one switch gives you no protection.
NMOS in brief
NMOS (Networked Media Open Specifications) is a set of standards from the AMWA (Advanced Media Workflow Association) for managing ST 2110 systems on the control plane. NMOS does not carry video. It carries the catalogue of senders and receivers and the commands that connect them.
Two NMOS standards matter for ST 2110:
- IS-04 is for discovery. Every sender and receiver registers with an NMOS registry. A controller reads the registry and sees what is available on the network.
- IS-05 is for connection management. A controller tells a receiver to subscribe to a sender, and the receiver does it. This replaces hand-copying SDP files.
WATCHOUT includes its own NMOS Controller — it does IS-04 discovery and IS-05 routing. It runs as a service on a node, on port 3025, and opens in a web view from the Nodes window NMOS Controller action. WATCHOUT also interoperates with third-party NMOS controllers and registries. For a small fixed installation, route by pasting SDP files instead.
Put NMOS on a separate controller network (a dedicated VLAN or a separate switch) from the ST 2110 media networks. NMOS uses HTTP and mDNS, which are noisy and easy to misconfigure. Keeping them off the media network avoids confusing failures.
The NMOS Controller service uses the node's regular network adapters, not the board's two ST 2110 ports. Plan one extra network connection on the node for NMOS traffic.
Related
- Setting Up ST 2110 — step-by-step commissioning of a Deltacast ST 2110 board
- ST 2110 Output — per-display ST 2110 output configuration
- Time Synchronization — WATCHOUT's NTP node clock sync, separate from ST 2110's PTP
- Firewall Configuration — required ports for ST 2110 and PTP
- Deltacast VideoMaster — receive ST 2110 IP video as a capture source
- Capture Devices — other capture types (Generic Capture, NDI, Spout)
- SDI Output — the baseband alternative to ST 2110
NDI® is a registered trademark of Vizrt NDI AB.