Real-time transport Object delivery over Unidirectional Transport

Description

Real-time transport Object delivery over Unidirectional Transport (ROUTE) is a protocol designed for the efficient, reliable delivery of discrete data objects over unidirectional IP multicast/broadcast networks. It is specified within the context of 3GPP's Multimedia Broadcast Multicast Service (MBMS) and evolved MBMS (eMBMS), particularly for delivering media content for services like LTE-based broadcast. ROUTE operates at the application layer, typically on top of the User Datagram Protocol (UDP), and is designed to work in conjunction with other protocols like FLUTE (File Delivery over Unidirectional Transport) and MPEG Media Transport (MMT).

ROUTE is fundamentally built for delivering objects, such as MPEG-DASH (Dynamic Adaptive Streaming over HTTP) media segments, manifest files (MPDs), and other associated metadata. Its architecture is session-oriented, where a ROUTE session consists of one or more source flows. Each source flow carries objects from a specific source, and these objects are fragmented into source blocks, which are then encapsulated into ROUTE packets for transmission. A key component is the Layered Coding Transport (LCT) building block, inherited from FLUTE, which provides congestion control and packet identification features. ROUTE also incorporates the Asynchronous Layered Coding (ALC) protocol instantiation for reliable delivery using Forward Error Correction (FEC).

How it works: A media server prepares DASH segments and their corresponding MPD. These are presented as objects to the ROUTE sender. The sender assigns each object to a source flow, fragments it, and can apply FEC encoding to generate repair symbols. The resulting source blocks (data and repair symbols) are packetized into LCT packets with specific headers containing transport session identifiers (TSIs) and object identifiers. These packets are then transmitted over the unidirectional broadcast channel. At the receiver, the ROUTE client reassembles the objects from the received packets, using FEC to recover from packet loss. Once an object (e.g., a video segment) is completely received, it is passed to the DASH client for playback. ROUTE's role is to provide a highly efficient, scalable, and reliable transport mechanism for delivering file-based and chunk-based media over broadcast networks, enabling services like live TV and large-scale file distribution.

Purpose & Motivation

ROUTE was developed to address the growing demand for efficient mass-media distribution over mobile broadcast networks like eMBMS. Traditional unicast streaming becomes inefficient and costly when delivering popular live events or linear TV to thousands of simultaneous users. Broadcast/multicast offers a spectrum-efficient solution, but it required a modern transport protocol optimized for contemporary media formats, specifically MPEG-DASH, which had become the industry standard for adaptive streaming.

Previous protocols like FLUTE were designed for reliable file delivery but were not inherently optimized for the real-time, continuous streaming of segmented media. ROUTE was created to fill this gap. It solves the problem of transporting DASH segments and their manifests in a timely and synchronized manner over a unidirectional channel. Its purpose is to enable broadcasters and mobile operators to deploy scalable linear and on-demand TV services, offloading traffic from congested unicast networks. The motivation was driven by the need for a standardized, interoperable protocol that could support both live and on-demand content delivery within the 3GPP eMBMS ecosystem, facilitating the convergence of broadcast and broadband services.