CoRE A. Bhattacharyya
Internet Draft S. Agrawal
Intended status: Standards Track H. Rath
Expires: April 2019 A. Pal
B. Purushothaman
TATA CONSULTANCY SERVICES LTD.
October 7, 2018
Adaptive RESTful Real-time Live Streaming for Things (A-REaLiST)
draft-bhattacharyya-core-a-realist-00
Abstract
This draft presents extensions to Constrained Application Protocol
(CoAP) to enable RESTful Real-time Live Streaming for improving the
Quality of Experience (QoE) for delay-sensitive Internet of Things
(IoT) applications. The overall architecture is termed ''Adaptive
RESTful Real-time Live Streaming for Things (A-REaLiST)''. It is
particularly designed for applications which rely on real-time
augmented vision through live First Person View (FPV) feed from
constrained remote agents like Unmanned Aerial Vehicle (UAV), etc.
These extensions provide the necessary hooks to help solution
designers ensure low-latency transfer of streams and, for contents
like video, a quick recovery from freeze and corruption without
incurring undue lag. A-REaLiST is an attempt to provide an
integrated approach to maintain the balance amongst QoE, resource-
efficiency and loss resilience. It provides the necessary hooks to
optimize system performance by leveraging contextual intelligence
inferred from instantaneous information segments in flight. These
extensions equip CoAP with a standard for efficient RESTful
streaming for Internet of Things (IoT) contrary to HTTP-streaming in
conventional Internet.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
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at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
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The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on April 7, 2019.
Copyright Notice
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Table of Contents
1. Introduction...................................................3
2. Revisiting CoAP................................................5
2.1. Some Interesting Aspects of CoAP..........................5
2.2. The Prevalent Approaches for Streaming over Internet......5
2.3. CoAP as the Best of Two Worlds............................6
3. The Approach behind A-REaLiST..................................6
3.1. Optional Context Aware Semantic Switch....................6
4. The Options Introduced.........................................7
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5. The Handshake and Exchange Semantics...........................8
5.1. Initial Negotiation.......................................9
5.2. Renegotiation............................................11
6. Some Design Guidelines........................................13
6.1. Implicit Congestion Avoidance............................13
6.2. Considerations for Consumer-side Rendering...............13
7. IANA Considerations...........................................14
8. Security Considerations.......................................14
9. References....................................................14
9.1. Normative References.....................................14
9.2. Informative References...................................15
1. Introduction
IoT emerged to facilitate exchange of frequent-but-small sensory
information amongst numerous constrained sensors [IOT-
ISOC][RFC7452]. However, recent trends in industry and research
community realize the importance of live visual data as important
sensory information. There are many discourses available to support
this observation [Murphy]. Live First Person View (FPV) from
Unmanned Aerial Vehicles (UAV) and dumb robot terminals are being
used for futuristic remote control and actuation applications for
Augmented Reality (AR), Visual Simultaneous Localization and Mapping
(VSLAM), UAV based surveillance, etc. Efficacy of these applications
depends on resource-efficient, low-latency, yet high QoE transfer of
the FPV over the Internet (or IP networks in general). Contrary to
the traditional video streaming applications, the UAV-like end-
points (henceforth referred as 'video producer') that capture and
transmit the FPV are resource constrained devices. Moreover, the
producer may work in a lossy environment marred with fluctuating
radio connectivity and disruptions due network congestion.
The QoE considerations of the video rendering unit (henceforth
referred as 'video consumer') for these applications are quite
different from traditional applications. For example, in case of
highly delay sensitive AR applications, a human brain may not
tolerate a noticeable video freeze or delayed reception, which might
have been overlooked for usual content delivery service like a
YouTube video. Such delay may result in wrong actuation. For
example, delayed FPV from a UAV may lead to wrong control commands
leading to catastrophic consequences. In addition, the communication
should be as light-weight as possible to optimize the usage of on-
board computing and energy resources of the UAV. So, real-time video
transmissions for IoT applications require special treatment
[Pereira]. However, as revealed through a detail analysis of the
state-of-the-art in the next section, the existing solutions do not
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address such special requirements. This draft attempts to bridge
this important gap by extending CoAP [RFC7252].
To realize its purpose, the A-REaLiST architecture relies on
[RFC7967] and adds few new header options which, taken together, can
be conceived to form a conceptual 'Stream' extension on CoAP (Fig.
1).
+----------------------+
| Application |
+----------------------+ ----
| Stream | \
|----------------------| \ |CoAP
| Requests/Responses | | |extended
|----------------------| | CoAP |for
| Messages | | / A-REaLiST
+----------------------+ / ----
+----------------------+
| UDP |
+----------------------+
Figure 1: Abstract extended layering of CoAP for A-REaLiST with the
conceptual layer for streaming.
Though primarily designed for video streaming, these extensions can
also be used to allow streaming of time-series information on CoAP.
Note: Block-wise transfer [RFC7959] is a standardized extension to
CoAP for transferring large application data. The cited use case
for this is to perform firmware upgrade for a large number of
constrained devices. Block-wise transfer is primarily concerned
with reliable delivery of information. It works in synchronized
manner. If a message remains unacknowledged despite
retransmissions then the whole exchange is cancelled. So, it is
not suitable for real-time delivery [GIoTS] which is requirement
for many time-series information streams including video.
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2. Revisiting CoAP
2.1. Some Interesting Aspects of CoAP
( i) CoAP allows both confirmable (CON) and non-confirmable (NON)
messaging.
( ii) CON mode enables CoAP with an option for reliable RESTful
delivery like HTTP [RFC2616]on TCP. On the other hand,
intelligent use of No-Response option [RFC7967] along with NON
mode can create an RTP like best-effort messaging on UDP.
(iii) Context based switching between the reliable and best-effort
semantics can be executed from the end-application level. This
way an optimum balance between reliability delay-performance can
be maintained to improve the overall Quality of Experience (QoE).
( iv) The base CoAP specification is inherently designed for
resource constrained devices. Hence, a streaming protocol using
the stateless RESTful semantics on CoAP makes the solution
inherently lightweight. So, unlike conventional approach the
designers can use a single stack that is equally efficient for
sending the small data out of sensors, as well as, infinite
visual stream.
2.2. The Prevalent Approaches for Streaming over Internet
The two prevalent approaches for streaming over the Internet are as
below.
First approach is to send the information segment over HTTP which
uses the reliability feature of the underlying Transmission Control
Protocol (TCP) transport. In this case TCP state-machine puts more
emphasis on reliable delivery of segments rather than maintaining
the real-time deadlines. However, this is right now the prevalent
approach as it treats video and other streams as general Internet
traffic. So, streaming can seamlessly co-exist with the existing
Internet architecture. Also, since TCP takes care of ordered
delivery, the end-application does not need to worry about these
matters.
The other approach is to use a specialized protocol like Real-time
Transport Protocol (RTP) [RFC3550]. It treats video and other real-
time streams as a special type of traffic. To ensure real-time
delivery, the data is delivered in best-effort manner on top of UDP.
So, reliable delivery is undermined.
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2.3. CoAP as the Best of Two Worlds
It can be conjectured, tallying the above with previous section,
that CoAP inherently imbibes the functional features from HTTP-on-
TCP (reliable delivery) and RTP-on-UDP (best-effort delivery).
Further CoAP allows the switching between these two seamlessly just
by maneuvering the header options.
3. The Approach behind A-REaLiST
The design stems from the principles of ''progressive download'' on
top of the RESTful request/response semantics of CoAP. The
''producer'' chunks the continuous information stream into segments as
per the agreed maximum payload size suggested in [RFC7252]. Each
chunk is transmitted as a CoAP request to a given resource at the
''consumer''. This draft provides the necessary header extensions that
enable the ''consumer'' to maintain the sequence of the information
segments in time and space.
3.1. Optional Context Aware Semantic Switch
Before forming the CoAP message for each segment, the streaming
application may use a real-time analytics module (henceforth
referred as 'analytics module') which may provide inference to the
''Stream'' layer to decide the exchange semantics for the current
segment. The message is sent reliably (CON message) or as best-
effort (NON message with No-Response option) based on the segment's
information criticality. Criticality is measured in terms of
importance of the segment-content in reconstruction of the frames at
the consumer. However, determination of criticality can be done on
many aspects involving several application features like the source
encoding type, the rendering logic at the consumer, etc. This way
the over-all balance between QoE and resource-consumption may be
maintained. Fig. 2 explains the idea with conceptual blocks. The
overall concept and its efficacy has been explained with
experimental results in [Wi-UAV-Globecom]
+----------------------+
| Application | Information segment ---------
+----------------------+ ====================> |Real-time|
| Stream | <==================== |Analytics|
|----------------------| Reliable/ ---------
| Requests/Responses | Best-effort?
|----------------------|
| Messages |
+----------------------+
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Figure 2: Illustrating the concept for context aware switching
Some examples are:
Example-1: Temporally compressed videos like MPEG consist of Group
of Pictures (GoP) which comprises I-frames (Intra-frames) or key-
frames, P-frames (Predicted frames) and B-frames (Bidirectional
frames). Out of these 3 types of frames I-frames are most
critical in terms of synchronizing with the GoP at the receiver
end for successful rendering. So, an analytics module at the
''video producer'' end may infer each information segments of I-
frames as critical and send those segments reliably. The segments
corresponding to P and B frames may be transferred as best-effort
requests.
Example-2: Let us consider a Motion JPEG (MJPEG) stream. In this
case all the frames are independent JPEG frames and there is no
temporal compression. The analytics module may treat the segments
containing MJPEG meta-data for each frame as critical segments
and transfer them through reliable messaging. Rest of the
segments may be transferred as best-effort requests. An
intelligent rendering engine at the ''consumer'' application may
compensate for / conceal any possible loss of non-meta-data (non-
critical) segments using the reliably received meta-data and rest
of the non-meta-data segments received through best-effort. This
way high QoE can be ensured despite reduced resource usage.
4. The Options Introduced
To achieve the purpose of the Stream layer, three new protocol
header options have been proposed as below:
1) Stream_info: Consumes one unsigned byte. It maintains the stream
identity and indicates the present phase of exchange. It is both
a request and response option. It has two fields. The 3-LSBs
indicate the state of exchange (Stream_state) and 5-MSBs indicate
an identifier (Stream_id) for the stream. The identifier remains
unchanged for the entire stream. So,
Stream_id = Stream_info >> 3;
Stream_ state = Stream_info & 0x7.
Interpretation of Stream_state bits are :
000=> stream initiation (always with request);
001=> initiation accepted (always with response);
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010=> initiation rejected (always with response);
011=> stream re-negotiation (with request or response);
100=> stream ongoing.
2) Time-stamp: It consumes 32-bit unsigned integer. It is a request
option. It relates a particular application information segment
to the corresponding frame in the play sequence.
3) Position: It consumes 16-bit unsigned integer. It is a request
option and MUST be accompanied with the Time-stamp option. It is
a combination of two fields. The 15-MSBs indicate the ''offset'' at
which the present segment is placed in the frame corresponding to
the given timestamp. The LSB indicates if the current segment is
the last segment of the frame corresponding to the given
timestamp. Hence,
Last_segment = Position &0x01 ? True : False;
Offset = (Position >> 1).
+-----+---+---+---+---+--------------+--------+--------+---------+
| No. | C | U | N | R | Name | Format | Length | Default |
+-----+---+---+---+---+--------------+--------+--------+---------+
| TBD | X | | - | | Stream-info | uint | 1 | (none) |
+-----+---+---+---+---+--------------+--------+--------+---------+
| TBD | X | | - | | Time-stamp | uint | 4 | (none) |
+-----+---+---+---+---+--------------+--------+--------+---------+
| TBD | X | | - | | Position | uint | 2 | (none) |
+-----+---+---+---+---+--------------+--------+--------+---------+
Table 1: Option Properties
5. The Handshake and Exchange Semantics
As per the design considerations in view of the scenarios conceived
at present, video transfer is initiated by the ''producer'' which acts
as the client.
Note: The design considerations are driven by the experiences drawn
from the applications where live video feeds are transmitted from
battery operated constrained ''video producers'' like UAVs and dumb
robotic terminals, etc. For example, while a fixed infrastructure
system is using streamed FPV feed from UAVs, there may be situations
where each time a UAV is low on resources (energy and computation, a
new UAV with better state of resources (fresh battery, etc.) is
commissioned. The overall operation becomes simple if the newly
commissioned UAV readily starts its job by streaming to the same
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resource at the fixed infrastructure. It can be easily configured to
determine whether the consumer is up and watching by observing the
responses to the CON requests. In case the exchange is initiated by
the consumer then whenever a new UAV is commissioned, the consumer
has to re-initiate the request again.
Each segment is transmitted to the ''video consumer'' as a POST
request. The Time-stamp and Position options help sequential
ordering of the segments at the consumer.
5.1. Initial Negotiation
Initial negotiations for frame rate, video type, encoding details,
etc., are performed by exchanging configuration scripts (cbor or
json) over POST request. Exact format of the script is application
dependent and is not part of this draft.
Fig. 3 illustrates the exemplary exchanges related to handshakes for
connection initiation.
Note: All reliable transfers are in blocking mode. So, the producer
MUST wait to send any further segment (critical/ on-critical) till
the response is received for the critical segment. Please refer to
Section 6 for suggested behavior in case a reliable transfer fails.
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Client (Producer) Server (Consumer)
| |
| POST: CON; |
| URI=/video; |
| Stream-info = <5-bit ID>000; |
| Payload= CBOR or JSON |\
+------------------------------------------------->| |
| | |Stream
| ACK; | |negotiation
| Response = 2.04 CHANGED | |
| Steam-info = <5-bit ID>001 | |
|<-------------------------------------------------|/
: :
: :
|(First segment of an MJPEG frame. Contains |
| meta-data. Critical segment needs reliable |
| delivery.) |
| |
| POST: CON; |
| URI=/video; |
| Stream-info = <5-bit ID>100; |
| Time-stamp = <time_stamp_of_this_frame>; |
| Position = 0; |
| Payload= <Bytes_in_1st segment> |\
+------------------------------------------------->| |
| | |
| ACK; | |
| Response = 2.04 CHANGED | |
| Steam-info = <5-bit ID>100 | |
|<-------------------------------------------------| |
|(Second segment of an MJPEG frame. Contains | |
| non-meta-data. Non-critical segment- best effort | |
| transfer.) | |
| | | Stream
| POST: NON; | | ongoing
| URI=/video; No-response = 127 | |
| Stream-info = <5-bit ID>100; | |
| Time-stamp = <time_stamp_of_this_frame>; | |
| Position = 1024; | |
| Payload= <Bytes_in 2nd _segment> | |
+------------------------------------------------->| |
| | |
: : |
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Figure 3: Example showing successful negotiation of streaming
parameters followed by transmission of video information and
control. It is assumed that the segment size negotiated as 1024 at
the initiation. So, the position of the 2nd block is 1024. Note the
use of No-response option with NON request for the non-critical
segment.
5.2. Renegotiation
The renegotiation phase may occur when the ''consumer'' does not agree
to parameters proposed by the producer and proposes a modified set.
This may happen when the consumer application may need a less frame-
rate than what is proposed by the producer. So, the ''consumer'' may
request a lower frame-rate and thereby avoid unnecessary traffic in
the network. The reduction may also be driven by the processing load
on the producer which is anyway a constrained device. So, if a
consumer requests more frame-rate than what is initially proposed by
the producer, then the producer may insist on the lower frame-rate.
Renegotiation may also occur if, during a stream, the producer
senses a change in the end-to-end channel condition and proposes a
new set of best possible parameters that can be served to the
consumer.
Note that, that the consumer is never allowed to exceed the limits
advertised by the producer.
Fig. 4 illustrates exemplary exchanges for re-negotiation.
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Client (Producer) Server (Consumer)
| |
| POST: CON; |
| URI=/video; |
| Stream-info = <5-bit ID>000; |
| Payload= CBOR or JSON |\ Initial
+------------------------------------------------->| |negotiation
| | |followed by
| ACK; | |renegotiation
| Response = 2.04 CHANGED | |request with
| Steam-info = <5-bit ID>010 | |revised
| Payload= CBOR or JSON | |params.
|<-------------------------------------------------|/
| |
| POST: CON; |
| URI=/video; |
| Stream-info = <5-bit ID>010; |
| Payload= CBOR or JSON |\ Successful
+------------------------------------------------->| |renegotiation
| | |as the
| ACK; | |consumer
| Response = 2.04 CHANGED | |agrees to the
| Steam-info = <5-bit ID>001 | |revised
|<-------------------------------------------------|/ proposal.
: :
: (Streaming starts) :
Figure 4: Example showing successful renegotiation of streaming
parameters. Note the maneuvering of the Stream-info bit patterns.
Fig. 5 illustrates exemplary exchanges when a stream negotiation is
unsuccessful. The accompanied script may provide hints to the reason
for unsuccessful negotiations. A simple case of unsuccessful attempt
may be observed if the resource on the ''consumer'' side is not ready.
The exact formatting of the script is not in the scope of this
draft.
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Client (Producer) Server (Consumer)
| |
| POST: CON; |
| URI=/video; |
| Stream-info = <5-bit ID>000; |
| Payload= CBOR or JSON |\ Unsuccessful
+------------------------------------------------->| |negotiation.
| | |The request
| ACK; | |is successful.
| Response = 2.04 CHANGED | |But consumer
| Steam-info = <5-bit ID>011 | |may reject
| Payload= CBOR or JSON | |for some
|<-------------------------------------------------|/ reason
| | mentioned in
Script.
Figure 5: Example showing unsuccessful renegotiation despite
successful response code against the initiation request.
6. Some Design Guidelines
6.1. Implicit Congestion Avoidance
The throughput and resource optimization for A-REaLiST depends
largely on the best-effort delivery on UDP. Despite that the
application designer can make A-REaLiST implicitly congestion aware
and proactively avoid congestion. CoAP has a basic congestion
avoidance mechanism which uses exponential back off to increase the
timeout for retransmissions. However, that works only for CON
messages.
The implicit congestion avoidance works like this: In case the
producer fails to successfully transfer a critical segment of a
frame within the MAX_TRANSMIT_SPAN as well as within MAX_RETRANSMIT
[RFC7252] attempts, the producer drops transmission of rest of the
segments in that frame and waits for the next frame to be ready. The
rationale is, since the critical segment is not delivered, the
consumer will fail to reconstruct this frame anyway. So, there is no
point in clogging the network with rest of the segments.
6.2. Considerations for Consumer-side Rendering
While the critical segments are delivered reliably in a sequential
manner, non-critical are delivered with best-effort in an open-loop
exchange. Also, the whole frame can be dropped to avoid congestion.
Hence, the application at the ''consumer'' end-point (server) needs to
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deal with issues like out-of-order delivery, frame/segment loss,
asynchronous segment arrival.
The issues mentioned above have been discussed in literatures
[Perkins]. So the basic approach should be: Buffer till a critical
time to iron out the jittery, out-of-order arrival of the segments,
play out from the appropriate buffer at a constant rate determined
by the frame-rate of the video. There may be intelligent algorithms
to play-out with high QoE despite non-arrival of non-critical
segments within the play-out deadline. This draft provides the hooks
to create such designs. Reference architecture of the play-out
mechanism is provided in [Wi-UAV-Globecom]. The play-out
architecture leverages on the design assumption about the 'less-
constrained' nature of the consumer in terms of memory and
processor.
7. IANA Considerations
The IANA is requested to assign numbers to the three options
introduced in this draft for inclusion in the ''CoAP Option Numbers"
registry as shown below.
+--------+--------------+-------------+
| Number | Name | Reference |
+--------+--------------+-------------+
| TBD | Stream-info | Section 4 |
+--------+--------------+-------------+
| TBD | Time-stamp | Section 4 |
+--------+--------------+-------------+
| TBD | Position | Section 4 |
+--------+--------------+-------------+
8. Security Considerations
This draft presents no security considerations beyond those in
Section 11 of the base CoAP specification [RFC7252].
9. References
9.1. Normative References
[RFC7252]
Shelby, Z., Hartke, K. and Bormann, C.,"Constrained Application
Protocol (CoAP)", RFC 7252, June, 2014.
[RFC7967]
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Bhattacharyya, A., Bandyopadhyay, S., Pal, A., Bose, T.,
''Constrained Application Protocol (CoAP) Option for No Server
Response'', RFC 7967, August, 2016.
9.2. Informative References
[IOT-ISOC]
Rose, K., Eldridge, S., Chapin, L., ''The Internet of Things: an
overview'', Internet Society, pp.1-50, October, 2015.
[RFC7452]
Tschofenig, H., Arkko, J., McPherson, D., "Architectural
Considerations in Smart Object Networking", RFC 7452, March, 2015.
[Murphy]
Murphy, C., ''Internet of Things: Are you underestimating video?'',
Available online:
http://www.informationweek.com/bigdata/bigdataanalytics/internetofth
ingsareyouunderestimatingvideo/a/d-id/1269508, June, 2014.
[Pereira]
Pereira, R., Pereira, E. G., ''Video Streaming Considerations for
Internet of Things'', International Conference on Future Internet of
Things and Cloud, pp. 48-52, August, 2014.
[RFC7959]
Bormann, C., Shelby, Z., ''Block-Wise Transfers in the Constrained
Application Protocol (CoAP)'', RFC 7959, August, 2016.
[GIoTS]
Dey, S., Bhattacharyya, A., Mukherjee, A., "Semantic data exchange
between collaborative robots in fog environment: Can CoAP be a
choice?", Global IoTS, pp. 1-6, June, 2017.
[RFC2616]
Fielding, R., Irvine, U.C., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., ''Hypertext Transfer
Protocol -- HTTP/1.1'', RFC 2616, June, 1999.
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[RFC3550]
Schulzrinne, H., Casner, S., Frederick, R., Jacobson, V., ''RTP: A
Transport Protocol for Real-Time Applications'', RFC 3550, July,
2003.
[Wi-UAV-Globecom]
Bhattacharyya, A., Agrawal, S., Rath, H., Pal, A., ''Improving Live-
streaming Experience for Delay-sensitive IoT Applications : A
RESTful Approach'', accepted in Globecom (Wi-UAV workshop), Dec.,
2018.
[Perkins]
Perkins, C., ''RTP: Audio and Video for the Internet'', Addison-
Wesley, 2003.
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Authors' Addresses
Abhijan Bhattacharyya
Tata Consultancy Services Ltd.
Kolkata, India
Email: abhijan.bhattacharyya@tcs.com
Suvrat Agrawal
Tata Consultancy Services Ltd.
Bangalore, India
Email: suvrat.a@tcs.com
Hemant Rath
Tata Consultancy Services Ltd.
Bhubaneswar, India
Email: hemant.rath@tcs.com
Arpan Pal
Tata Consultancy Services Ltd.
Kolkata, India
Email: arpan.pal@tcs.com
Balamurali Purushothaman
Tata Consultancy Services Ltd.
Bangalore, India
Email: arpan.pal@tcs.com
Bhattacharyya, et al. Expires April 7, 2019 [Page 17]