ATSC 3.0 Primer

ATSC 3.0 (Advanced Television Systems Committee 3.0), also known as NextGen TV, is the next-generation broadcast television standard in the United States. It represents a complete redesign of over-the-air television broadcasting, built on an all-IP foundation.

Unlike its predecessor ATSC 1.0 (which has been in use since 1996), ATSC 3.0 uses modern Internet Protocol (IP) for all data delivery, enabling unprecedented flexibility and capabilities for broadcasters and viewers alike.

The ATSC 3.0 protocol stack is organized in layers, each responsible for specific functions in the broadcast chain. Understanding this stack is essential for stream analysis.

┌─────────────────────────────────────────────────┐
│            Application Layer                     │
│    (HTML5, HELD, DRM, Interactive Services)      │
├─────────────────────────────────────────────────┤
│            Presentation Layer                    │
│         (HEVC, AC-4, IMSC1 Captions)            │
├─────────────────────────────────────────────────┤
│            Transport Layer                       │
│           (ROUTE / DASH  or  MMT)               │
├─────────────────────────────────────────────────┤
│            Signaling Layer                       │
│    (LLS: SLT, RRT, SystemTime, AEA, CDT)        │
│    (SLS: USBD, S-TSID, MPD, HELD)               │
├─────────────────────────────────────────────────┤
│              Link Layer (ALP)                    │
│        (ATSC Link-layer Protocol)               │
├─────────────────────────────────────────────────┤
│            Physical Layer (PHY)                  │
│      (OFDM, LDPC/BCH, LDM, MIMO, PLP)          │
└─────────────────────────────────────────────────┘

The ATSC 3.0 physical layer uses OFDM (Orthogonal Frequency Division Multiplexing) with advanced error correction, enabling robust reception in challenging conditions.

Key PHY Technologies

The ALP (ATSC Link-layer Protocol) encapsulates IP packets and signaling for transmission over the physical layer. It's the bridge between IP-based content and the broadcast PHY.

ALP Packet Types

┌──────────────────────────────────────────────────┐
│ Packet Type (3 bits) │ Payload Config (5 bits)  │
├──────────────────────────────────────────────────┤
│              Length (variable)                    │
├──────────────────────────────────────────────────┤
│              Payload Data                         │
└──────────────────────────────────────────────────┘

ATSC 3.0 uses a two-tier signaling architecture: LLS (Low Level Signaling) for bootstrap information, and SLS (Service Layer Signaling) for detailed service descriptions.

LLS (Low Level Signaling)

LLS tables are carried in dedicated ALP signaling packets on a well-known multicast address (224.0.23.60:4937). They provide the entry point for service discovery.

SLS (Service Layer Signaling)

SLS provides detailed information about each service's components, delivery, and presentation. It's delivered via ROUTE/DASH or MMT on service-specific multicast addresses.

ATSC 3.0 supports two media delivery protocols: ROUTE/DASH (the primary method in the US) and MMT (used primarily in other regions).

ROUTE (Real-time Object Delivery over Unidirectional Transport)

ROUTE extends the FLUTE protocol for real-time streaming. It delivers DASH segments over UDP multicast using LCT (Layered Coding Transport).

ROUTE Session
    │
    ├── LCT Channel (TSI=0) ─── SLS Signaling
    │                              ├── USBD.xml
    │                              ├── S-TSID.xml
    │                              └── MPD.xml
    │
    ├── LCT Channel (TSI=1) ─── Video Segments
    │                              ├── init.mp4
    │                              ├── segment_1.m4s
    │                              └── segment_2.m4s
    │
    └── LCT Channel (TSI=2) ─── Audio Segments
                                   ├── init.mp4
                                   └── segment_1.m4s

MMT (MPEG Media Transport)

MMT is an alternative delivery protocol standardized by ISO/IEC 23008-1. It uses MPUs (Media Processing Units) instead of DASH segments.

Service discovery in ATSC 3.0 follows a hierarchical process, starting from the bootstrap signaling and drilling down to individual media components.

1. Tune to RF Channel
         │
         ▼
2. Receive ALP Packets on PLP0
         │
         ▼
3. Parse LLS on 224.0.23.60:4937
         │
         ├──► SLT (Service List Table)
         │        │
         │        ├── Service ID: 5001
         │        ├── Short Name: "WKBW"
         │        ├── Major.Minor: 7.1
         │        └── SLS Multicast: 239.255.1.1:5001
         │
         ▼
4. Join Service Multicast (239.255.1.1:5001)
         │
         ▼
5. Parse SLS (USBD → S-TSID → MPD)
         │
         ▼
6. Join Component Multicasts
         │
         ├──► Video: 239.255.2.1:5001
         └──► Audio: 239.255.2.2:5001

ATSC 3.0 mandates modern, efficient codecs to deliver high-quality content within available bandwidth.

Video Codecs

Audio Codecs

ATSC 3.0 supports interactive applications using standard web technologies (HTML5, JavaScript, CSS), enabling rich viewer experiences.

<HELD xmlns="tag:atsc.org,2016:XMLSchemas/ATSC3/AppSignaling/HELD/1.0/">
  <HTMLEntryPackage appContextId="app1" appRendering="true">
    <ContentInfo>
      <MediaUrl>app/index.html</MediaUrl>
    </ContentInfo>
  </HTMLEntryPackage>
</HELD>