Encoding 3GPP Slices for Interactive Media Services
draft-jiang-tsvwg-slice-media-service-00
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draft-jiang-tsvwg-slice-media-service-00
TSV Working Group T. Jiang
Internet-Draft D. Wang
Intended status: Informational China Mobile
Expires: 24 January 2024 23 July 2023
Encoding 3GPP Slices for Interactive Media Services
draft-jiang-tsvwg-slice-media-service-00
Abstract
Extended Reality & multi-modality communication, or XRM, is a type of
advanced service that has been studied and standardized in the 3GPP
SA2 working group. It targets at achieving high data rate, ultra-low
latency, and high reliability. The streams of an XRM service might
be comprised of data from multiple modalities, namely, video, audio,
ambient-sensor and haptic detection, etc. XRM service faces
challenges on various aspects, e.g. accurate multi-modality data
synchronization, QoS differentiation, large volume of packets, and
etc. While a new 3GPP network slice type, HDLLC, has been recently
introduced to handle the QoS requirements of XRM streams, the
ubiquitously-existed encryption of packet payload posts additional
challenges to the transport of encoded video packets via 5GS. We
have then discussed two potential IETF schemes, e.g., IP-DSCP based
or UDP-option extension, that could be applied to 'expose' XRM QoS
'metadata' to 5GS.
Status of This Memo
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. 3GPP Slices Mapping for Media Services . . . . . . . . . . . 4
2.1. 3GPP Network Slicing . . . . . . . . . . . . . . . . . . 4
2.2. 3GPP-defined Standardized SSTs . . . . . . . . . . . . . 4
2.3. Mapping Standardized SST for Encrypted XRM Service . . . 5
3. Possible IETF Schemes for Encrypted XRM Streams . . . . . . . 7
3.1. Using IP-DSCP to Map Encrypted XRM Streams . . . . . . . 7
3.2. Using UDP-option to Map Encrypted XRM Streams . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Extended Reality & multi-modality communication, or XRM, is a type of
advanced service that has been studied and standardized in the 3GPP
SA2 working group. With the objective of achieving economical
communication overhead, ultra-low latency, high reliability and top
security, it features multi-modal interactions among a group of
service entities that are distributed at the mobile network edges.
The benefits of seamlessly integrating multiple types of inputs
sourced via multiple channels make it widely applicable in fields,
like AR/VR, telepresence, gaming, education, etc.
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The XRM service can both consolidate the inputs from more than one
source and disseminate information to multiple destinations. That
is, input data from different kinds of devices/sensors or the output
data to different types of destinations are required for the same
task or application. This type of communication scheme possesses
intrinsic advantages of providing services that would be
complementary to each other, or even bearing progressive add-on
gains, so that redundant delivery and information accuracy could be
achieved effectively. In general sense, the streams of an XRM
service might be comprised of data from four modalities, namely,
video, audio, ambient-sensor and haptic detection.
Thanks to the unique nature and different requirements across
modalities, and especially to address the 5G service requirements of
different types of media steams with coordinated throughput, latency
and reliability, XRM service faces challenges on various aspects,
e.g. characteristics of generated data across modalities, accurate
multi-modality data synchronization, QoS differentiation, large
volume of small packets, and packet-size variation, etc. [_5G.TACMM]
XRM services use (multiple) IP PDU sessions to carry & transport data
frames. With a PDU session corresponding to one modality stream, the
coordinated transmission among multiple modality flows (or streams)
needs to be warranted. The application client(s) of the different
types of data of one application may be located at either one
destination (e.g., a UE), or multiple destinations (e.g. having VR
glasses, gloves, and more).
In current 5GS, the QoS Flow is the finest granularity of QoS
differentiation in the PDU Session, which implies that each packet in
a QoS flow is treated according to the same QoS requirements.
Specifically for the XRM service, a group of packets are used to
carry payloads of a PDU Set (e.g. a frame, video slice/tile). In
media layer, packets in such a PDU Set are decoded/handled as a
whole. For example, the frame/video slice may only be decoded in
case all or certain amount of the packets carrying the frame/video
slice are successfully delivered. For example, a frame within a GOP
(Group of Pictures) can only be decoded by the client in case all
frames on which that frame depends are successfully received. Hence
the groups of packets within the PDU Set have inherent dependency on
each other in media layer. Without considering such dependencies
between the packets within the PDU set, 5GS may perform a scheduling
with low efficiency. For example, the 5GS may randomly drop
packet(s) but try to deliver other packets of the same PDU set which
are useless to the client and thus waste radio resources [TS.23.501].
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The similar benefits are also applicable to audio samples, haptics
applications or remote control operations. The inter-dependency
among packets of a PDU Set (e.g. a frame/video slice) can possibly
help enhance the efficiency and promote user experience.
2. 3GPP Slices Mapping for Media Services
2.1. 3GPP Network Slicing
5G network slicing is a network architecture that enables the
multiplexing of virtualized and independent logical networks on the
same physical network infrastructure. Each network slice is an
isolated end-to-end network tailored to fulfil diverse requirements
requested by a particular application.
Network slices may differ between supported features and network
function optimisations. This technology assumes a central role to
support 5G mobile networks that are designed to efficiently embrace a
plethora of services with very different service level requirements
(SLR). The realization of this service-oriented view of the network
leverages on the concepts of software-defined networking (SDN) and
network function virtualization (NFV) that allow the implementation
of flexible and scalable network slices on top of a common network
infrastructure.
The business model adopted in Telco domain normally indicates that a
network slice is administrated by a mobile virtual network operator
(MVNO). The infrastructure provider (the owner of the Telco
infrastructure) leases its physical resources to the MVNOs that share
the underlying physical network. According to the availability of
the assigned resources, a MVNO can autonomously deploy multiple
network slices that are customized to the various applications
provided to its own users.
2.2. 3GPP-defined Standardized SSTs
As shown in the following Figure 1, 3GPP 5GS have defined 6 standard
SSTs, covering eMBB, URLLC MIoT and more. Standardized SST values
provide a way for establishing global interoperability for slicing so
that Public Land Mobile Networks or PLMNs can support the roaming use
case more efficiently for the most commonly used Slice/Service Types.
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+----------------------------------------------------------------+
| Types | Value | Characteristics |
+-------+-------+------------------------------------------------+
| eMBB | 1 | Slice for 5G enhanced mobile broadband |
+-------+-------+------------------------------------------------+
| URLLC | 2 | Slice for ultra-reliable low-latency comm. |
+-------+-------+------------------------------------------------+
| MIoT | 3 | Slice for Massive IoT |
+-------+-------+------------------------------------------------+
| V2X | 4 | Slice for V2X Services |
+-------+-------+------------------------------------------------+
| HMTC | 5 | Slice for High-performance Machine-type comm. |
+-------+-------+------------------------------------------------+
| HDLLC | 6 | Slice for High data-rate & low-latency comm. |
+-------+-------+------------------------------------------------+
Figure 1: 3GPP Standardized SSTs
Specifically, the 6th SST in the table, i.e., HDLLC or the slice for
High Data-rate & Low-Latency communication service, was just
introduced as a new SST for the handling of the XRM service in May,
2023. XR media service or XRM is characterized by high data rate and
low latency communication. As per [TS.23.501], the 5GS QoS framework
has been enhanced to support different QoS handling for PDU Set. It
supports differentiated QoS handling considering different importance
of PDU Sets, e.g. by treating packets (i.e. PDUs) belonging to less
important PDU Set(s) differently to reduce the resource consumption.
One add-on benefit is the reduction of the complexity of roaming
configuration between networks.
Similarly, another SDO, GSMA ENSWI, also believes that the Extended
Reality and Media Services are promising services, and a new
standardized SST can bring consistent user experience for XRM
Services and enhance the user experience, especially in the roaming
case. Currently, GSMA ENSWI is working on defining a new NEST
(NEtwork Slice Template) for Extended Reality and Media Services
[GSMAnewSSTforXRM].
2.3. Mapping Standardized SST for Encrypted XRM Service
Different SST maps to varied QoS requirements, e.g., guaranteed
bandwidth, max-allowed bandwidth, max-data-burst, min-latency, max-
latency, jitter variation, etc. Particularly for the 5G XRM service,
thanks to the diversified settings of framing, slicing, encoding of
video images, there invovle additional parameters like the relative
importance among different data packets (or PDUs in 3GPP SA2 term)
that are generated from differrent types of frames, e.g., the I, P, B
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frames which render tiered priorities among them.
Another factor impacting the transport of encoded video packets is
the ubiquitously-existed encryption of packet payload. For example,
supposing RTP is used to transport video data. If the data contents
in a packet are encrypted at the video source (i.e., the UDP source),
then the later-added UDP header would not be able to expose the
above-mentioned QoS parameters to the routing entities in underlay
transport networks until the same packet reaches the UDP destination.
However, this posts somewhat great challenges to the 5GS-based XRM
service.
...........................................
: /-----------\ :
: | 5GS(SBA) | :
: /\-----------/\ :
: / | \ :
: +-----+ +------+ +-----+ :
: | AMF |-----| SMF |----| PCF | :
: +-----+ +------+ +-----+ :
: / | | :
: N1 N2 N4 :
: / | | :
: / | +-------+ :
+----+ +-------+ N3 | | N6 (UP) : +-------------+
| UE |--| gNB |----| UPF |------------:---| IP-domain |
+----+ +-------+ | | : | Network(DNN)|
: +-------+ : +-------------+
: | | :
: +-N9-+ :
...........................................
Figure 2: A 5GS Logical DetNet Node
For example, as shown in the Figure 2, the network function(NF) UPF
is similar to an IP-domain router, which sends/receives IP packets
off the N6 interface to/from the IP domain network DNN. In the XRM
scenario, when a downlink packet (from the DNN) with encrypted video
contents arrives at the UPF from the N6 interface, the UPF would
generally only use the IP 5-tuple (or at most 6-tuple) for packet
classfication and prioritization (i.e., PDR in the 3GPP 5G term
[TS.23.501]). Unfortunately, the 5-tuple cannot expose all the QoS
related information, or so-named 'metadata' for XRM in this draft,
that would be required for the effective data processing of an XRM
stream. The existence of encryption prevents a UPF from diving
further into the data contents.
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3. Possible IETF Schemes for Encrypted XRM Streams
The challenges, revolving around the encrypted XRM service as
described in Section 2.3, lead to the exploration of novel IETF
mechanisms to convey these critical 'metadata' to a UPF (and then to
the 5GS).
3.1. Using IP-DSCP to Map Encrypted XRM Streams
One scheme is to use the 6-bit DS field in an IP header [RFC2474].
The fundamental advantage is that the IP-DSCP bits are not normally
subject to the encryption hurdle. However, the 6-bit DS field has
only 64 DSCP combinations that could not provide better granularity
which is an equal important factor for the further evolution of 5G
advanced services. Another disadvantage is the DSCP does not have
good hierarchy among its 6 bits. For example, while the objective to
promote the just-standardized HDLLC (SST=6) was initially targetting
at the XRM service, it could also be customized & applied later to
Metaverse service, i.e., another type of HDLLC service. Metaverse
service is being discussed in the 3GPP SA2 WG for the Rel-19
planning. Therefore, in this scenario (of HDLLC), any candidate
novel scheme should have the capability and extensibity to
accommodate the mappings for both the main SST, e.g., HDLLC itself,
and the more granular sub-types, e.g., XRM, Metaverse, etc., as
discussed previously.
3.2. Using UDP-option to Map Encrypted XRM Streams
Another novel scheme is to use the being-standardized UDP-option
[transportUDPoption]. Actually, when compared to the requirements of
encryption-handling, more-granular capability, as well as the
extensibility that could be achieved via the new UDP-option
structure, we think using UDP-option is a better alternative (than
using the IP-DSCP). For example, according to [transportUDPoption],
we may get a code from the 'Kind' range [10...126] to identify the
main type being the '3GPP network slice'. Then, we could further
define the sub-structure for more concrete SSTs as per the table in
Figure 1.
Another advantage is that UDP is a layer-4 protocol and its header
will normally not be processed by IP routers. Not only does this
relieve the processing burden off IP transport devices, but also
gives a clear demarcation of the TCP/IP layer structure.
Of course, though we do agree UDP datagrams should best be processed
in the end-to-end way, i.e., encapsulated at UDP sources and
decapsulated at UDP destinations, the 5GS-based XRM service is unique
in that the 5GS is a composite system which owns abundant and
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powerful functionalities that might grant a 5GS UPF to
'intelligently' break the IP-UDP demarcation rule by peeking at the
XRM 'metadata' in the UDP option field.
4. Security Considerations
Generally, this function will not incur additional security issues.
5. IANA Considerations
A new authentication option or other signaling message option may be
used based on the specific implementation.
6. References
6.1. Normative References
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[transportUDPoption]
Touch, J., "Transport Options for UDP", draft-ietf-tsvwg-
udp-options-22, June 2023.
[TS.23.501]
"3GPP TS 23.501 (V17.0.0): System Architecture for 5G
System; Stage 2", 3GPP TS 23.501, March 2021.
[TS.24.501]
"3GPP TS 24.501: Non-Access-Stratum (NAS) protocol for 5G
System (5GS)", 3GPP TS 24.501, September 2022.
[_5G.TACMM]
Jiang, T., Shi, X., Gao, J., and P. Liu, "On the 5G Edge
Network Challenges of Providing Tactile and Multi-modality
Communication Services", International Conference on Edge
Computing - EDGE'2021 , December 2021.
6.2. Informative References
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[GSMAnewSSTforXRM]
GSMA, "LS reply on a new SST value for Extended Reality
and Media Services",
https://www.3gpp.org/ftp/tsg_sa/WG2_Arch/
TSGS2_157_Berlin_2023-05/Docs/S2-2306269.zip, February
2023.
[_3GPPnewSSTforXRM]
3GPP, "Introduction of a new standard SST for Extended
Reality and Media Services",
https://www.3gpp.org/ftp/tsg_sa/WG2_Arch/
TSGS2_157_Berlin_2023-05/Docs/S2-2308186.zip, May 2023.
Authors' Addresses
Tianji Jiang
China Mobile
San Jose, CA
Email: tianjijiang@chnamobile.com
Dan Wang
China Mobile
Email: wangdanyjy@chinamobile.com
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