FLUTE and ROUTE, the one-way transports behind broadcast and multicast media delivery.
Overview
5G-MAG tracks FLUTE and ROUTE, the two unidirectional transport protocols that carry DASH, HLS and CMAF media over broadcast and multicast networks without a return channel. For the technical analysis of how these transports work, see the Tech page linked below. For acronyms used here, see the Glossary.
Technology & Analysis
The implementer-facing analysis of the FLUTE and ROUTE transports and how DASH, HLS and CMAF are carried over each.
Specifications by role
| Role | Protocol / format | Defining specification |
|---|---|---|
| Unidirectional transport (files) | FLUTE | IETF RFC 3926 (version 1, 3GPP-mandated) / RFC 6726 (version 2, reference only) |
| Unidirectional transport (real-time objects) | ROUTE | IETF RFC 9223 |
| Transport building blocks | LCT, ALC, FCAST | IETF RFC 3451 / RFC 5651, RFC 3450 / RFC 5775, RFC 6968 |
| Adaptive streaming format | DASH | ISO/IEC 23009-1 |
| Adaptive streaming format | HLS | IETF RFC 8216 |
| Segmented media container | CMAF | ISO/IEC 23000-19 |
| 3GPP DASH profile | 3GP-DASH | TS 26.247 |
| DVB DASH profile | DVB-DASH | ETSI TS 103 285 |
| 3GPP broadcast delivery (uses FLUTE) | MBMS | TS 26.346 |
FLUTE: which version, and why
5G-MAG's FLUTE implementation (the rt-libflute library) targets FLUTE version 1, not the newer version 2, because 3GPP's own profile mandates it. The applicable version is reached through this dependency chain:
- TS 26.517, clause 6.2.1 — if FLUTE realises the Object Distribution Method, the MBS Distribution Session shall conform to the MBMS Download Profile of TS 26.346 clause L.4.
- TS 26.346, clause L.4 — the Download Profile constrains the FDT parameters of clause 7.2, defined by RFC 3926 and the 3GPP FDT extensions.
- TS 26.346, clause 7.2.0 — clients and servers shall implement RFC 3926 (FLUTE), RFC 3450 (ALC) and RFC 3451 (LCT).
- RFC 3926 — "This document specifies FLUTE version 1"; every FDT-carrying packet MUST set the version field to 1.
FLUTE version 1 (RFC 3926 and its companion RFCs 3450/3451) is normative for all 3GPP uses of rt-libflute. The revised IETF generation (RFC 6726 FLUTE v2, RFC 5651, RFC 5775) is reference material only for 3GPP purposes, tracked here because it's still the current IETF text for non-3GPP FLUTE deployments.
Specifications in scope
Every specification behind FLUTE, ROUTE and the media formats they carry. The layer filter separates what is normative for 3GPP use from the revised IETF generation that is valid text but not the mandated profile, which is the distinction the section above turns on.
28 of 28 specifications
| Specification | Title | Layer |
|---|---|---|
| RFC 3926 | FLUTE - File Delivery over Unidirectional TransportCore protocol, FDT, version 1 | IETF (normative) |
| RFC 3450 | Asynchronous Layered Coding (ALC) Protocol InstantiationTransport building block | IETF (normative) |
| RFC 3451 | Layered Coding Transport (LCT) Building BlockHeader format, TSI/TOI, Close Session/Object flags | IETF (normative) |
| RFC 5052 | Forward Error Correction (FEC) Building BlockFEC OTI, EXT_FTI, source block partitioning | IETF (normative) |
| RFC 3695 | Compact No-Code FEC schemeFEC Encoding ID 0 | IETF (normative) |
| RFC 5053 | Raptor FEC schemeFEC Encoding ID 1; the MBMS FEC scheme per TS 26.346 clause 7.2.12 and Annex B | IETF (normative) |
| RFC 1952 | GZIP file formatContent encoding of files for transport (TS 26.346 clause 7.2.5) | IETF (normative) |
| RFC 4607 | Source-Specific Multicast (SSM)Reception filtered on the announced source address | IETF (normative) |
| RFC 4570 | SDP Source FiltersHow SSM sources are announced (SDP handled by consuming applications) | IETF (normative) |
| RFC 5905 | Network Time ProtocolTime base for FDT and Cache-Control expiry values | IETF (normative) |
| RFC 6726 | FLUTE version 2Revises RFC 3926; not the 3GPP-mandated profile | IETF (reference only) |
| RFC 5651 | LCT (revised)Revises RFC 3451 | IETF (reference only) |
| RFC 5775 | ALC (revised)Revises RFC 3450 | IETF (reference only) |
| RFC 6330 | RaptorQ FEC schemeFEC Encoding ID 6; not part of the TS 26.346 FEC scheme set | IETF (reference only) |
| RFC 9223 | ROUTE - Real-time Object delivery over Unidirectional TransportThe real-time object transport, alongside FLUTE | IETF (normative) |
| RFC 6968 | FCAST object deliveryTransport building block | IETF (reference only) |
| RFC 8216 | HTTP Live Streaming (HLS)Adaptive streaming format carried over these transports | IETF (normative) |
| TS 26.346 | MBMS; Protocols and codecsThe central specification for FLUTE-based delivery. Clause 7.2 covers FLUTE usage for MBMS download (header specializations, FDT schema and 3GPP FDT extensions, FEC schemes, content encoding); clause 7.2.12 and Annex B the MBMS FEC scheme (Raptor, RFC 5053); clause 7.3 SDP for the download delivery method; clause 9 associated delivery procedures, file repair and reception reporting; Annex L the MBMS Download Profile and User Service profiles. | 3GPP |
| TS 26.347 | MBMS URLs and APIsMBMS client interface towards applications (consumer scope) | 3GPP |
| TS 23.246 | MBMS; Architecture and functional descriptionContext | 3GPP |
| TS 26.517 | 5G MBS; User Services and ProtocolsClause 6.2 defines the Object Distribution Method over FLUTE and binds it to the MBMS Download Profile of TS 26.346 | 3GPP |
| TS 26.502 | 5G MBS; User service architecture | 3GPP |
| TS 23.247 | Architectural enhancements for 5G MBSDefines the N3mb/GTP-U transport context served by rt-libflute's UDP tunnel mode | 3GPP |
| TS 29.581 | 5G System; MBSTF servicesThe service APIs of rt-mbs-transport-function, the main 5G MBS consumer of rt-libflute | 3GPP |
| TS 26.247 | 3GP-DASH; Transparent end-to-end packet-switched streaming serviceThe 3GPP DASH profile carried over these transports | 3GPP |
| ISO/IEC 23009-1 | Dynamic Adaptive Streaming over HTTP (DASH)Adaptive streaming format | Media formats |
| ISO/IEC 23000-19 | Common Media Application Format (CMAF)Segmented media container | Media formats |
| ETSI TS 103 285 | DVB-DASHThe DVB DASH profile | Media formats |
References to verify
One link on this page needs a maintainer check: the ISO/IEC 23009-1 (DASH) link points to the catalogue page for the 2022 (5th) edition (iso.org/standard/83314.html). A 2026 (6th) edition of ISO/IEC 23009-1 appears in the IEC catalogue, which would make the linked edition superseded, but iso.org blocks automated access so the current-edition page could not be confirmed; update the link to the current edition before publication. The ISO/IEC 23000-19 (CMAF) link is confirmed as the current 2024 (3rd) edition, and the ETSI TS 103 285 (DVB-DASH) link is confirmed against the ETSI publication listing (latest published version v1.4.1; this page deliberately links the version directory rather than one version). The protocol-to-RFC mappings (FLUTE = RFC 3926/6726, ROUTE = RFC 9223, HLS = RFC 8216, and the LCT/ALC/FCAST building blocks), the TS 26.346/26.517 normative chain, and the FEC scheme identifiers were confirmed against primary spec text.
5G-MAG tracking and contribution focus
5G-MAG tracks these transport and format specifications and their use across its 5G Broadcast and 5G MBS work. See Tech: Multimedia Delivery Protocols for the implementer-facing analysis. Contributions to this documentation are made through the 5G-MAG Standards repository.
Related Standards Work
- Standards: 5G Broadcast
- Standards: 5G Multicast Broadcast Services (MBS)
- Standards: DVB-I over 5G
- Tech: Multimedia Delivery Protocols
- Feedback and Requirements: how 5G-MAG submits feedback and requirements to SDOs
Refer to the Standards repository to contribute to this documentation.