SDP Descriptors for MMTP
draft-bouazizi-sdp-descriptors-mmtp-00

Abstract

This document specifies the use of SDP for the description of MPEG Media Transport protocol (MMTP) sessions. It defines the parameters required to begin, join, receive data from, and/or end MMTP sessions.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on April 3, 2015.

Copyright Notice

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Table of Contents

• 1. Introduction
• 2. MMTP Descriptors
• 2.1. MMTP Protocol Identifier
• 2.2. Object Flow Semantics
• 2.3. Object Flow Descriptors
• 3. SDP Syntax Examples
• 4. IANA Considerations
• 4.1. Transport Protocol
• 4.2. Media Formats
• 4.3. Attribute Names
• 5. Security Considerations
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Author's Address

1. Introduction

The MMTP protocol is an application layer transport protocol that is designed to transport different types of media objects under real-time delivery constraints. In particular, MMTP provides a delivery mode that is optimized for low-delay delivery of fragmented ISOBMFF media files. The Session Description Protocol (SDP) [RFC4566]) provides a general-purpose format for describing multimedia sessions in announcements or invitations. SDP uses an entirely textual data format (the US-ASCII subset of UTF-8 [RFC3629]) to simplify authoring and increase readability. SDP only defines the syntax to describe multimedia sessions with sufficient information to enable receivers to participate in the session. SDP does not restrict the way the session description is distributed to the receivers, so that potentially any transport protocol (e.g. HTTP [RFC2616], MMTP [draftMMTP], SAP [RFC2974], SIP [RFC3261]) may be used for this purpose. This document defines a new protocol identifier for the MPEG Media Transport Protocol (MMTP) as well as other SDP attributes for describing and initiating an MMTP session. The formal ABNF syntax [RFC5234] is used for defining the syntax of the new SDP attributes. The defined SDP descriptors apply independently of whether Any Source Multicast (ASM) or Source Specific Multicast (SSM) is used to route the media.

2. MMTP Descriptors

The MMTP specification [draftMMTP] describes the required and optional parameters for describing an MMTP session. This document specifies the SDP parameters for MMTP sessions that can be used for the discovery of MMTP sessions. The required SDP parameters for describing an MMTP session are:

• The destination information, consisting of the destination IP address and port number.
• An indication that the session is an MMTP session
• The version number of the MMTP protocol used in the current MMTP session

The optional SDP parameters are:

• The start and end time of the MMTP session
• Bandwidth specification
• Description of the object flows of the MMTP session

An MMTP session consists of one or more object flows, each of which is identified by a unique packet identifier. The packets that belong to the same object flow use the same packet identifier and build a sub-flow of the MMTP flow. The description of the SDP parameters is provided in the following sections.

2.1. MMTP Protocol Identifier

The ABNF syntax for the "m=" line as specified by [RFC4566] is defined as follows: media-field = "m=" media SP port {"/" integer] SP proto 1*(SP fmt) CRLF proto = "MMTP/UDP" The "MMTP/UDP" protocol identifier specifies that the the session being described will use the MMTP protocol [draftMMTP] on top of a UDP connection. The "fmt" list may be used to describe the object flows that are delivered as part of the MMTP session.

2.2. Object Flow Semantics

An MMTP session consists of an MMTP flow that is delivered during a designated period of time that is indicated by the session start and end time or through external means. Each MMTP sub-flow carries objects of an object flow. An object flow is composed of a set of related objects that are meant to be consumed together by the receiver. An object flow may carry objects of one of the following types:

• media objects that are formatted as fragmented ISOBMFF files and that are meant to be consumed sequentially. In MMT terms, MPUs would constitute the objects of such an object flow, which is named as Asset.
• the object flow consists of generic objects that are meant to be consumed simultaneously or in sequence.
• the object flow consists of objects that carry signaling messages that are relevant to the consumption of the MMTP flow.
• the object flow carries FEC repair packets.

The SDP descriptors enables providing basic descriptive information about the object flow. The related SDP parameters are described in the following section.

2.3. Object Flow Descriptors

This internet draft specifies a set of SDP descriptors to describe the content of an MMTP session. It uses the "fmt" to identify the relevant object flows of an MMTP session and indicate its type. In addition, a textual description of the object flow may be provided separately. The ABNF syntax of the object flow description is defined as follows: of-descriptor = "a=of:" fmt SP of-identifier SP type-indicator CRLF of-identifier = "flowid=" 1*DIGIT type-indicator = "type=" type ["/" subtype] type = "MPU" / "GF" / "Signaling" / "FEC" The flowid is set to the packet_id of the MMTP subflow that carries the objects of this object flow. The type of the object flow corresponds to one of the object flow types described in Section 2.2. The subtype field is a type specific optional field that can be used to indicate a more specific type of the object flow. As an example, a subtype "MP" of type "signaling" may be used to indicate that the object flow carries (possibly among others) the MP tables of this MMTP session.

3. SDP Syntax Examples

						v=0
						o=user  6431641313 1 IN IP4  10.10.52.13
						s=An MMTP session
						t=1411639200 1427277600
						a=source-filter: incl IN IP4 * 10.10.52.13
						m=application 12345 MMTP/UDP 100 101 102 103 104
						a=of:100 flowid=0 Signaling/PA
						a=of:101 flowid=7623 MPU
						a=of:102 flowid=7624 MPU
						a=of:103 flowid=7625 GF
						a=of:104 flowid=7626 FEC
					

						SDP Attribute ("att-field")
						Attribute name: 	of
						Long form:			MMTP Object Flow description
						Type of attribute:	media level
						Subject to charset: No
						Purpose:			See this document
						Reference:			This document
						Values:				See this document