ART Area General Applications C. Perez-Monte, Ed.
Internet-Draft GridTICs - UTN FRM
Intended status: Informational March 21, 2016
Expires: September 22, 2016

SDCP: Streaming Distributed Control Protocol


This memorandum describes SDCP, a protocol to control multimedia streaming in cases where streaming generation should be distributed to improve performance. This is especially useful for Human-Things streams. Usually, real time applications such as virtual reality generate a user-controlled multimedia streaming. This is a time continuous data flux that could be divided spatially to distribute processing, memory or network resources. This protocol does not describe streaming communication, but the control of each single streaming generation in a best-effort by many nodes or things.

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Table of Contents

1. Introduction

Usually, the amount of information transmitted from human to computer is very small. Such is the case of information generated by input devices, for example, keyboards, mouses or touch screens. On the contrary, the amount of information transmitted from computer to human is big. This is increasing over time. Such is the case of information generated by output devices, for example, computer monitors or cellphone screens. Furthermore, the hardware resources such as data processing, network bandwidth or storage are too big. In many applications, human-to-computer control data is required to generate computer-to-human data, such as virtual reality. In this way, human-to-computer control data may be sending to many nodes in multicast method by best-effort delivery and processing.

Streaming Distributed Control Protocol (SDCP) is an application-level protocol for control of streaming distributed generation. SDCP is built on the User Datagram Protocol (UDP) [RFC0768], which provides a connection less transport mechanism. SDCP provides the complete information for proper streaming generation. Other mechanism have been specified to transmit multimedia streaming, including the Real Time Streaming Protocol (RTSP) [RFC2326]. The SDCP is not meant to displace this mechanism but rather complement it.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

1.2. Terminology

Some clarifications and additional definitions follow:

Integrator and Administrator nodes are the human-side and Processor nodes are the things-side of the communication system.

2. Distributed Scheme

Figure 1 shows scheme of a distributed stream generation system. Each processor node has processing, bandwidth or storing resources required for partial stream generation.

|Remote Administrator Node                                         |
                                 | Multicast SDCP data communication
|Local Proc Node||Local Proc Node||Local Proc Node||Local Proc Node|
                                 ||Uncompressed stream communication
| Local Integrator Node          || Local Integrator Node          |
                                 ||Compressed stream communication
| Remote Human Receptors                                           |

Distributed Scheme.

Figure 1

Administrator Node sends periodically SDCP multicast control datagrams to Processor Nodes. The use of multicast is mandatory to select processor group id. The amount of SDCP datagrams should be sufficient to compensate losses and to allow real-time operation. These losses may occur by delivery problems or ignored by processor nodes. Administrator Node MAY assign different Processor Node for processing each SDS.

Each unoccupied Processor Node receive SDCP datagrams. Occupied Processor Node SHOULD ignore SDCP datagrams. Each Processor Node generates stream portion through the use of more current SDCP control data. This generated stream is sent to appropriate Integrator Node.

Integrator Node receives stream portion unicast communication. All the stream portion received are integrated in a single stream that is sent to remote human receptors or locally visualized.

Administrator Node MAY assign different destination Integrator Node for each SDS. Each integrator node MAY receive multiple streams, a same DB or multiple/single SDS of multiple Processor Node. However, each SDS is assigned to only one Integrator node. While that different SDS of same stream MAY be assigned to send these to different integrator nodes, each SDS of same stream MUST NOT be sent to more than only one Integrator node.

3. SDCP Constant


3.1. Multicast Addressing


3.2. UDP Ports


4. SDCP Format

Main SDCP format is shown in figure 2.

| General DB Header | Specific SDS Header | Payload|

SDCP Format.

Figure 2

  • General DB Header: 224-bits length field. This header is required. Identifies fields from all the DB.
  • Specific SDS Header: 128-bits length field. This header is optional. Identifies fields from specific SDS. If this header is not present, all SDS of same DB SHOULD be treated equally.
  • Payload: Variable-length field. Stream Control Data.

4.1. General DB Header

DB Header is required.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|control data type|M| RD  |             Stream ID               |
|                                                               | 
|                    Time stamp (64 bits)                       |
|                                                               |
|                       SDCP Counter                            |
|                      Var DB Counter                           |
|                     No Var DB Counter                         |
| Payload plus opt header length|     Next Header Counter       |


DB Header Format.

Figure 3

Processor Node or Processor Node Group id is determined by multicast destination address of ip stack.

Control data type: 8-bit selector. Type of control streaming generation data. Types are defined in accordance with specific requirement of application. E.g. virtual reality, game or video streaming, drone controller application, etc.

Control data mode: 1-bit selector. Instant or Historical Mode.

0 - Instant Mode

1 - Historical Mode

RD: 3-bit selector. Reserved for future use.

Stream ID: 20-bit unsigned integer. Multimedia Stream data identificator.

Time stamp: 64-bits unsigned fixed-point. It includes a 32-bit unsigned seconds field spanning 136 years and a 32-bit fraction field resolving 232 picoseconds such as RFC 5905 [RFC5905]. This 64-bit timestamp format is used in General DB header and payload.

SDCP Counter: 32-bit unsigned integer. Total number of SDCP datagrams sent.

Var DB Counter: 32-bit unsigned integer. Total number of SDCP datagrams sent with control data changes.

No Var DB Counter: 32-bit unsigned integer. Total number of SDCP datagrams sent from last control data change.

Payload plus opt header length: 16-bit unsigned integer. Length of Payload, in 16-octet units.

Next Header Counter: 16-bit unsigned integer. Number of Optional SDS Headers.

4.2. Specific SDS Header

SDS header is optional. This header specifies SDS allocation to nodes. Two functions are defined. On the one hand, this header MAY determine which SDS data are assigned to generate by processor node. On the other hand, this header MAY determine which SDS data are assigned to send from processor node to integrator node.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|                                                               |
|                    SDS group ID (64 bits)                     |
|                                                               |
|                                                               |
|                    Node group ID (64 bits)                    |
|                                                               |

SDS Header Format.

Figure 4

SDS group ID: 64-bit selector. Identifies individual SDS or SDS group for allocation to nodes.

Node group ID: 64-bit selector. Identifies integrator or processor node for its interface identifier from IPv6 unicast destination address or identifies processor node group for its low-order 64 bits of an IPv6 multicast destination address such as IP Version 6 Addressing Architecture [RFC2373]. Allocated Processor Node MUST process all SDS assigned in SDS group ID and MUST NOT process SDS not assigned. Non-allocated Processor Node MAY process all SDS. SDS not assigned to any Integrator Node MUST be sent to Default Integrator Node. Similarly, SDS assigned more than one Integrator Node MUST be sent only to Default Integrator Node.

4.3. Payload

Payload data format is specified in control data type field of general header. This field determine in virtual reality applications variables such as camera positions, light positions, etc.

Two modes are supported.

Instant Mode: Last change control data is only sent.

Historical Mode: All changes control data are sent.

Types of control data: TO DO.

5. Identificators Format


5.1. SDS index


5.2. Node index


6. Payload types


7. Streaming considerations


7.1. Streaming protocols


8. Acknowledgements

I would like to thank the resources and support of GRIDTICS and LICPaD of the Universidad Tecnologica Nacional Regional Mendoza (UTN FRM), LIDIC of the Universidad Nacional de San Luis (UNSL), the Joint Laboratory for System Evaluation (JLSE) at Argonne National Laboratory and Dept. of Bioengineering, Dept. of Biomedical and Health Information Sciences to the University of Illinois at Chicago (UIC). Especially, I am deeply grateful to Gustavo Mercado, Christian O'Flaherty, Ines Robles and Gabriel Montenegro for their support.

9. IANA Considerations

This memo includes no request to IANA.

10. Security Considerations


11. References

11.1. Normative References

[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.

11.2. Informative References

[RFC2326] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, DOI 10.17487/RFC2326, April 1998.
[RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, DOI 10.17487/RFC2373, July 1998.
[RFC5905] Mills, D., Martin, J., Burbank, J. and W. Kasch, "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010.

Author's Address

Cristian Federico Perez-Monte (editor) GridTICs - UTN FRM Rodriguez 273 Cuarto Piso Bloque Dpto Electronica Ciudad de Mendoza, Mendoza M5502AJE AR Phone: +54 261 524 4563 EMail: