Thomson Explains: SMPTE 2110 - Part 2

Tier 2: Intermediate Networking & Broadcast Basics

Tier 2 bridges general networking into the specialized context of broadcast media systems. Here we introduce concepts like multicast, VLANs for network segmentation, legacy SDI video knowledge, and how traditional broadcast timing works. These are critical intermediate skills because SMPTE 2110 builds on them heavily. Think of Tier 2 as the “glue” between IT and broadcast engineering.

IP Multicast – Distributing One Source to Many Destinations

Traditional video routers can send one camera feed to dozens of monitors. How do we replicate that in an IP network? The answer is multicast.

• What Multicast Is: In unicast IP, a source sends a separate stream to each receiver, which would be hugely inefficient if 20 receivers need the same video – 20 copies would clog the network. Instead, multicast uses special IP addresses that represent a group of receivers. The source sends one stream addressed to the multicast group, and the network (switches/routers) handles replicating that stream to all receivers who join the group.

• This way, “a single source can send data to multiple destinations without multiple transmissions”– exactly what we need for one video feed fanout.

• Multicast Addresses: IPv4 reserves 224.0.0.0 – 239.255.255.255 for multicast. In practice, SMPTE 2110 uses the 239.x.x.x range (administratively scoped addresses) for streams. Each stream (video or audio) is assigned a multicast IP and UDP port. For example, a camera might send video on 239.100.0.1:5000.

• IGMP (Internet Group Management Protocol): Here’s a critical networking piece: If multicast is not managed, a switch will flood the stream to every port (treating it like broadcast) – quickly overwhelming devices with data they don’t need.

• To prevent this, switches use IGMP snooping. When a receiver wants a stream, it sends an IGMP “Join” message for that multicast group. The switch hears this and only forwards that multicast traffic to that receiver’s port. This way, each stream goes only where it’s needed. As an engineer, you must ensure IGMP snooping is enabled on your switches for the VLAN carrying media, and that an IGMP querier is active (usually the router or switch sends periodic queries to maintain group memberships)

• Layer 2 vs Layer 3 Multicast: Multicast within one subnet/VLAN is handled by IGMP at Layer 2. But if you need streams to cross between subnets (or multiple switches/routed network), you enter the world of Layer 3 multicast routing (PIM – Protocol Independent Multicast). A larger facility might split networks by department or function, so to get a stream from one subnet to another, routers must be configured with PIM to forward multicast between them.

• Why you care: In a simple truck or studio with one big switch, you might live entirely in one subnet (no PIM needed). But as soon as you have multiple switches or networks (say separate video and audio networks, or an OB van connecting to a venue LAN), you need to understand PIM and multicast routing. At minimum, know that every separate network needs its own IGMP querier, and routing between them needs PIM Sparse Mode with a Rendezvous Point (RP). We won’t go deep into PIM here, but be aware it exists and that “layer 2 domains get too large” and must be broken up for scalability, using PIM to interconnect.

Real-World Example: If IGMP is misconfigured, subscribing one 4K video stream could unintentionally flood an entire switch, causing all devices to lag or drop packets. An engineer needs to quickly recognize “we’re seeing flooding, likely IGMP snooping is off on that switch.” Similarly, if two departments are on different subnets and a producer can’t get a feed from Studio A to Studio B, it might be because no PIM router is passing the multicast across – a clue that “Layer 3 multicast” was overlooked.

VLANs and Network Segmentation

In ST 2110 systems, it’s common to use separate networks or VLANs for different traffic types:

• Media vs Control vs Management: High-bandwidth media streams might live on one VLAN, while low-bandwidth control signals (like camera control, tally, or NMOS API traffic) are on another, to keep the heavy traffic isolated. PTP might even be on its own VLAN in some designs (though often PTP stays with media). VLANs let you simulate physically separate networks using one switch infrastructure.

• Redundancy (SMPTE ST 2022-7): A key concept (expanded in my Tier 3 and 4 articles) is dual-network redundancy for media streams. Typically this is implemented with two separate VLANs or switches (nicknamed “Red” and “Blue” networks). Each stream is sent in two identical copies over two networks, so if one fails, the other keeps things running. As a junior engineer, understand that devices will have two network interfaces for media in a 2022-7 system. This means you must configure and troubleshoot two parallel networks. We mention it here because you’ll see multiple VLANs or physical networks from the start in a 2110 facility.

• Routing and Access Control: Know which VLANs should talk to which. Often, the media VLANs are not routed to corporate networks for security. Sometimes a separate control PC network is allowed to reach the media devices (for management). It’s important to adhere to whatever network architecture is defined – plugging a device into the wrong VLAN can either isolate it or inadvertently expose the media network to outside traffic.

(Efficiency tip: Label your network ports and color-code cables for different VLANs (e.g. blue cables for “Blue” network). Many mistakes are simply plugging into the wrong network!)

SDI Fundamentals and Video/Audio Basics

Even though we are focusing on IP, a junior engineer must know SDI basics – partly to interface with legacy systems and partly to appreciate what ST 2110 is doing.

• What is SDI: SDI stands for Serial Digital Interface (e.g. SMPTE 259M for SD, 292M for HD, 424M for 3G-SDI, etc.). It’s a method of transporting uncompressed digital video, typically over coaxial cable in a point-to-point manner. An SDI cable carries one video signal, which may include embedded audio and ancillary data. Common SDI rates: 1.5 Gbps (HD 1080i/p30), 3 Gbps (1080p60), 12 Gbps (4Kp60).

• SDI vs IP Workflow: In an SDI router environment, to send a signal to multiple destinations, you need a video router or DA (distribution amplifier). Changing a routing requires a routing switcher or patch panel – it’s a physical or circuit-switched path. In IP (2110), the “router” is replaced by the network switch fabric and routing control software. SDI signals also had all essences together – video + audio embedded, ancillary data in the VANC – whereas IP separates them (more on that in Tier 3). This separation (video, audio, data as independent streams) is called “essence separation” and allows flexibility like audio breakaway (routing audio independently from video). As a new engineer, you should know that one big advantage of 2110 is precisely this flexible routing of each essence, which was not possible in SDI without specialized gear (embedders/deembedders). In summary, SDI was a one-cable-per-signal world; IP is many flows over one network.

• Legacy Gear: You’ll likely deal with SDI-to-IP gateways for equipment that hasn’t been replaced yet. For example, an older replay server might only have SDI outputs – so you use an IP gateway to encapsulate that into a 2110 stream on the network. Conversely, to feed an old SDI monitor from an IP stream, you use an IP-to-SDI converter. In one real IP station build, they “specified SDI-to-IP and IP-to-SDI converters” for devices lacking native 2110, converting their signals to ST 2110 RTP streams or back to SDI as needed

  • For more information, visit this link: smpte.org

• This means: even if your facility is IP-centric, a junior engineer will patch and troubleshoot these gateways, needing to understand both worlds.

• Audio Basics: SDI embedded audio is usually 16 channels per video. In IP, audio is separate streams (often using the AES67 standard in 2110-30). Know what AES and MADI are: AES3 (two-channel digital audio over XLR) and MADI (32 or 64-channel audio over coax/fiber) are common in audio plant. This helps because SMPTE 2110-31 can carry AES3 audio signals over IP (for things like Dolby E which are encoded in an AES3 pair). Also be aware of analog audio vs digital. An IP facility might still interface with analog audio in some cases (for comms or legacy).

• Timecode and Ancillary Data: In SDI, ancillary data lines carry things like timecode (LTC or VITC), closed captions, SCTE triggers, etc. ST 2110 has a separate essence (2110-40) for ancillary data. Just flag in your mind that “metadata doesn’t ride inside the video stream anymore, it’s its own stream.”

Why SDI knowledge matters: First, when something isn’t working in IP, a quick fix might be to fall back to SDI if possible (e.g. patch a cable directly). You need to know that option and how to do it. Second, when configuring IP systems, the format naming will reference traditional formats (1080i59, 1080p50, etc.) and you should know what those mean (frame rate, interlace vs progressive, color sampling). Third, a hybrid facility will have signal flows going between SDI and IP realms – you might have to trace a signal from a camera (2110) through a converter into an SDI waveform monitor, for example. If you don’t understand both, you can’t follow the signal.

Broadcast Timing & Sync (Legacy vs IP)

One concept that cannot be skipped is synchronization. In broadcast, all video and audio devices must lock to a common time base to avoid drifts and glitches (imagine one camera slightly out of sync – you’d get frames out of phase, tearing on switches, audio lip-sync issues, etc.).

• Black Burst and Tri-Level Sync: In a traditional SDI facility, there is usually a master sync generator providing an analog reference signal. Black burst (for SD/NTSC/PAL) or Tri-level sync (for HD) is distributed via coax to every video device’s reference input. These signals are basically reference “clock” pulses (black burst is essentially a color-black video signal with proper timing) that ensure each device’s video scanning is locked in phase with the others. For decades, this analog reference was the backbone of sync.

  • For more information, follow this link: telestreamblog.telestream.net

• Broadcast engineers are very familiar with concepts like genlock, house reference, etc. Audio equipment might lock to Word Clock or AES reference similarly. As a junior engineer, you should recognize the black burst waveform on an oscilloscope and know the purpose of the “REF IN” BNC on gear.

• Timing in IP (PTP introduction): When media goes IP, we can’t use analog waves over coax for sync. Instead, synchronization is achieved through Precision Time Protocol (PTP) packets over the network. PTP (defined by IEEE 1588) can sync devices to within sub-microsecond accuracy across the network.

• SMPTE ST 2059-2 defines the broadcast profile of PTP for use with video (essentially replacing black burst with PTP). We’ll dive deeper in Tier 3, but at this stage understand: PTP is the new “house sync”. If a device doesn’t lock to PTP, it’s the IP equivalent of not being plugged into house reference – you will get problems like mis-timed video switching or audio drift.

• Why Timing Matters Operationally: If an engineer doesn’t appreciate timing, they might chase ghosts. For example, without proper sync, a video mixer could have a jittery output or a frame sync might constantly drop/repeat frames. In SDI days, the first thing to check on a misbehaving source was “is it genlocked to house?” In IP, the first thing to check is often “is it locked to PTP?” This mindset carries over.

• System Phasing: In multi-camera productions, all cameras need to be phase-aligned for seamless switching. PTP ensures each device has the same time-of-day clock down to the microsecond. Using that, each video frame and audio sample can be timestamped (in ST 2110, senders put a timestamp in each RTP packet indicating the sampling time). If all devices share time, the receiver can align those essences perfectly (so audio stays locked to video, etc.). As a stepping stone, recall that in SDI, vertical interval switching was used to cut signals cleanly – requiring sources timed to the same frame rate and phase. The IP analog is using PTP time stamps to align frames.

To summarize Tier 2: you should now understand multicast and how networks carry many-to-many streams, how VLANs carve up a network, the essence of SDI/baseband video and audio signals, and the old vs new approach to sync. These are the everyday concepts bridging IT and video. By mastering Tier 2, you’ll avoid rookie mistakes like misusing unicast, flooding networks with multicast, or forgetting to sync sources. You’ll also be able to communicate with seasoned broadcast folks – when they say “Is that camera genlocked?”, you’ll answer “Yes, it’s PTP-locked to the Grandmaster” (and know what that means).