MoQ & MMT: Streaming Delivery Paths

MoQ (Media over QUIC) is Blockcast's low-latency delivery protocol for interactive streaming. Built on IETF MoQ drafts and WebTransport/QUIC, it delivers sub-500ms glass-to-glass latency — making it suitable for live sports, esports, auctions, and any use case where seconds of delay are unacceptable.

Unlike MAHP, which stores-and-forwards content through an encrypted cache, MoQ is a real-time pass-through protocol with no store-and-forward semantics. MoQ Relays forward media tracks directly from publishers to subscribers without caching.

The underlying container format is MPEG Media Transport (MMT) (ISO 23008-1) — the same format used by ATSC 3.0 broadcast, 5G MBS, and ISP multicast. By defining how MMT maps onto MoQ objects (draft-ramadan-moq-mmt), the same MMTP packets — identical bytes — can flow over any transport without transcoding.

---

How MoQ Works

1. Publishing (CAST → MoQ Relay)

FFmpeg on the CAST node publishes directly to the downstream MoQ Relay using the moq_mmt muxer — wrapping fMP4 fragments in MMTP packets and delivering them over WebTransport/QUIC (IETF MoQ draft).

There is no intermediate MoQ Server on the CAST node; FFmpeg acts as the MoQ publisher. This eliminates one hop of latency compared to architectures that require a local relay.

2. Relay Forwarding (RELAY → RELAY → BEACON)

MoQ Relays forward tracks from upstream publishers or parent relays to downstream subscribers and child relays. The relay implementation (hang-mmt-fec) is a Rust binary supporting:

• Dual-stack protocol: Both moqtail-00 (Draft-14 MoQ) and moqlite-00 protocols.

• Track registry: Cross-protocol forwarding with FEC metadata translation — a subscriber on moqlite can receive from a moqtail publisher.

• Pass-through forwarding: No caching, no transcoding. Packets arrive and leave in real time.

MoQ Relays can be chained (CAST → RELAY → RELAY → BEACON), same as MAHP, but the forwarding is purely real-time — there's no cache to warm up.

3. Playback (Relay → Player)

Each RELAY and BEACON exposes a MoQ ingress (ALPN moq-00 on port 443). Unmodified MoQ players connect here over standard QUIC/WebTransport and subscribe to tracks. The player is unaware of the multicast infrastructure upstream.

---

MoQ vs. MAHP Comparison

Aspect	MoQ	MAHP
Latency	Sub-500ms	Seconds (segment-based)
Transport	QUIC/WebTransport	Multicast UDP + HTTP
Caching	None (pass-through)	Encrypted edge cache
FEC	ALTA (Ed25519 per-packet)	TESLA + RaptorQ/Reed-Solomon
Best for	Interactive live, low-latency	High-throughput broadcast, file delivery
Player requirement	MoQ-capable (WebTransport)	Standard HTTP (DASH/HLS)
Offline resilience	None (real-time only)	Cache serves during disruptions

Both protocols run simultaneously on every RELAY and BEACON. The CAST node feeds both paths from the same FFmpeg process, so content is always consistent.

---

MMT: The Unified Container Format

MPEG Media Transport (MMT) is the unifying container across all Blockcast delivery paths. MMT is already the native container for ATSC 3.0 broadcast (Americas, South Korea), ARIB STD-B60 (Japan), and 5G Multicast-Broadcast Services (3GPP MBS).

Content ingested once at a CAST node reaches every device class through its optimal delivery path:

Delivery Path	Physical Medium	Receiver	Requirements
ATSC 3.0 broadcast	Over-the-air RF spectrum	TV with ATSC 3.0 tuner	Tuner hardware (Samsung, LG, Sony 2020+)
5G MBS	Cellular broadcast (3GPP)	5G phone/tablet	5G modem + MBS middleware
PIM-SSM + IGMPv3	ISP IP multicast	IWA browser, native app	Multicast-enabled ISP, UDP socket access
AMT unicast tunnel	UDP encapsulation (RFC 7450)	IWA browser, native app	Any network with UDP, DRIAD relay discovery
MoQ/QUIC unicast	WebTransport	Any browser, any app	None (universal fallback)

ATSC 3.0 (Broadcast TV)

ATSC 3.0 televisions receive MMTP streams natively over RF tuner hardware. These devices perform S-TSID parsing for FEC parameters and multicast group information, RaptorQ FEC decoding, and MMTP depacketization into MPU media segments — all in dedicated silicon.

MoQ integration happens at the gateway level, not on the TV itself. The MMT-MoQ draft defines bidirectional S-TSID ↔ MoQ Catalog conversion, so the same content is discoverable by both broadcast receivers (via S-TSID/SLT bootstrap signaling) and MoQ subscribers (via catalog JSON). An ATSC 3.0 broadcast station's S-TSID becomes a MoQ catalog, enabling a single content pipeline to serve both broadcast and IP-delivered audiences simultaneously.

5G Multicast-Broadcast Services

3GPP MBS (TS 22.246, Release 17) defines multicast-broadcast at the 5G modem level. 5G MBS can carry the same MMTP streams as ATSC 3.0, with the modem handling delivery and the CAS (Conditional Access System) stack handling decryption independently.

CAS muting enables simultaneous broadcast: the same encrypted MMTP stream serves ATSC 3.0 tuners over RF and 5G MBS devices over cellular. Each receiver's CAS stack decrypts independently — the content provider encrypts once, and both physical layers deliver the same protected bytes.

On Android, the receive path is provided by the Qualcomm LTE Broadcast SDK or the open-source 5G-MAG middleware. The modem delivers MMTP packets directly to the application layer — same bytes, different physical medium. Combined with the DePIN token incentive model, 5G MBS receivers can earn rewards simply by tuning in to multicast streams, contributing to network offload.

PIM-SSM + IGMPv3 (ISP Multicast)

When an ISP has enabled PIM-SSM on their routers, clients can receive multicast natively — the most bandwidth-efficient delivery path after broadcast.

1. The MoQ catalog includes SSM (S,G) endpoint addresses in its multicast extension field.

2. A native client or IWA browser app issues an IGMPv3 join for the source-specific group (e.g., (10.0.0.1, 232.1.1.10)).

3. PIM-SSM builds a shortest-path tree from the source through the ISP's routers to the subscriber's edge.

4. MMTP packets replicate in router silicon at each hop — not in software on x86 servers.

5. The client receives the identical MMTP packets that the CAST node produced.

SSM group allocation maps each ABR quality tier to a separate multicast group, so quality switches are IGMPv3 leave/join operations. FEC repair symbols are carried on dedicated groups. For browsers, this requires IWA with DirectSocket API (UDPSocket.joinGroup()). For native apps, Android provides MulticastSocket with MulticastLock, and iOS provides NWConnectionGroup (iOS 14+).

Hardware-Offloaded AMT Unicast Tunnel

AMT (RFC 7450) is the pragmatic fallback when PIM-SSM is not available on the subscriber's ISP. AMT encapsulates multicast packets inside a UDP unicast tunnel:

1. The client discovers the nearest AMT relay via DRIAD (RFC 8777) — a DNS reverse lookup on the multicast source IP.

2. The client establishes an AMT tunnel (UDP port 2268) to the relay.

3. The relay performs an IGMPv3 join on behalf of the client on its multicast-enabled upstream interface.

4. MMTP packets arrive at the relay via native multicast, get encapsulated in UDP, and tunnel to the client.

The critical advantage is hardware offload: thousands of ISP edge routers (Juniper MX) already have AMT relay capability built into their routing ASICs. A single router performs the packet replication function that previously demanded dedicated CDN server complexes — up to 500,000 concurrent tunnels at line-rate throughput per device. The marginal cost is a configuration change, not new hardware.

This is the path shown in the architecture diagram as FFmpeg → MMTP SSM → AMT Relay -.-> AMT tunnel -.-> IWA/SDK Player. For full details on AMT relay infrastructure, see AMT Relays & Multicast Backbone.

---

Transport Hierarchy (Graceful Degradation)

Clients attempt transports in preference order, starting with the highest-bandwidth path and falling back gracefully:

Native clients (TV, mobile SDK):

Priority	Transport	Availability
1	Native SSM (IGMPv3/MLDv2)	Multicast-enabled networks
2	AMT over UDP (RFC 7450)	Any network with UDP
3	MoQ over QUIC	Universal
4	HTTP DASH/HLS	Universal fallback

Browser clients:

Priority	Transport	Availability
1	SSM via IWA DirectSocket	IWA-enabled Chrome
2	AMT via IWA DirectSocket	IWA-enabled Chrome
3	MoQ over WebTransport	Chrome 97+, Firefox 115+
4	HTTP DASH via MSE/fetch	Universal fallback

Every client starts at Priority 3 or 4 (unicast), receives the MoQ catalog which includes the multicast endpoint discovery extension, then promotes itself to the highest available path. The catalog itself is the discovery mechanism — no separate signaling infrastructure is needed.

For general consumer web applications, MoQ/WebTransport (Priority 3) is effectively the highest available transport. IWA DirectSocket (Priorities 1–2) is available to enterprise-managed Chrome, DePIN participants with token-incentivized IWA installation, and technical users who side-load the IWA.

---

Direct Multicast via IWA & Mobile SDK

For clients that want to bypass the relay infrastructure entirely and receive multicast directly, Blockcast provides optional browser and mobile extensions through the PIM Multicast Gateway.

Chrome IWA (Isolated Web App)

An optional in-browser gateway with Direct Sockets API access:

• Manages multicast subscriptions, AMT tunnel lifecycle, and DRIAD relay discovery.

• Enables direct multicast data path without a local BEACON.

• WASM Modules: Rust-compiled AMT protocol (RFC 7450 state machine, IGMP/MLD report generation) and ALTA authentication (Ed25519 verification).

Chrome Extension

Message router bridging the webpage and IWA, handling tab lifecycle and origin-based security.

Mobile SDK

Optional native AMT gateway for Android and iOS applications — same direct multicast capability as the IWA, for native apps.

Transport Modes (when IWA or Mobile SDK is active)

Mode	Behavior	Latency	Throughput
Native	Direct Sockets API → OS multicast join	~1ms	10Gbps+
AMT Tunnel	DRIAD discovery → UDP tunnel via WASM	~2ms	5Gbps+
Auto (default)	Try native → fallback to tunnel if no packets in N seconds	Adaptive	Adaptive

Without the IWA or Mobile SDK, the client simply connects to the nearest BEACON or RELAY as a standard MoQ player over WebTransport.

Browser Compatibility

For browsers without IWA support (Firefox, Safari), the MoQ BEACON can bridge to non-IWA clients via:

• mDNS advertisement (_moq-gateway._tcp.local): Local network IWA discovery

• WebTransport bridge: Forwards multicast to secondary browsers over QUIC

• Standalone Node.js gateway: Docker-deployable for headless environments

---

IWA Home Gateway

An IWA node running on a wired-connected device (Chromebox, desktop, mini-PC) can serve as a local multicast anchor, bridging ISP multicast to household wireless devices:

Internet (SSM/AMT)
       │
       ▼
 [ISP Router w/ AMT Relay]
       │  wired Ethernet
       ▼
 [Chromebox / Desktop IWA]  ← DirectSocket multicast rx
       │  WebTransport (local)
       ▼
 [Phone] [Tablet] [Smart TV] [Laptop]

Advantages:

• Wired reception avoids Wi-Fi jitter and supports higher bitrates than wireless multicast (most consumer APs do not relay multicast).

• A single multicast stream serves the entire household regardless of the number of local viewers.

• Wireless clients use standard MoQ/WebTransport with no IWA requirement, no special permissions, and full browser compatibility.

• Local FEC repair reduces retransmission round trips to the origin.

---

Authentication

MoQ streams use a different authentication mechanism than MAHP:

• ALTA (Asymmetric Loss-Tolerant Authentication): Ed25519 per-packet verification for MoQ-MMT streams. Integrated into the PIM multicast gateway. Unlike TESLA's time-delayed disclosure, ALTA provides immediate verification — important for low-latency use cases.

---

End-to-End Flows

Multicast Publishing Flow

Relay & Coverage Flow

Playback Flow

---

Standards & References

Standard	Role
IETF MoQ (Draft-14)	Core protocol for media delivery over QUIC
ISO 23008-1 (MMT)	Universal container format across all delivery paths
draft-ramadan-moq-mmt	MMT packaging for MoQ — maps MMTP packets to MoQ objects
draft-ramadan-moq-multicast	Multicast delivery and catalog endpoint discovery for MoQ
draft-ramadan-moq-fec	Forward Error Correction for MoQ (RaptorQ, LDPC, Reed-Solomon)
ATSC 3.0	Over-the-air broadcast standard (Americas, South Korea)
ARIB STD-B60	Japanese broadcast standard using MMT
3GPP TS 22.246 (5G MBS)	5G Multicast-Broadcast Services
RFC 7450 (AMT)	Tunneling for IWA/SDK direct multicast path
RFC 8777 (DRIAD)	Relay discovery for IWA/SDK direct multicast path