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 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). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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 reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 24 January 2024. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. Jiang & Wang Expires 24 January 2024 [Page 1] Internet-Draft Slice-Media-Service July 2023 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. 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. Jiang & Wang Expires 24 January 2024 [Page 2] Internet-Draft Slice-Media-Service July 2023 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]. Jiang & Wang Expires 24 January 2024 [Page 3] Internet-Draft Slice-Media-Service July 2023 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. Jiang & Wang Expires 24 January 2024 [Page 4] Internet-Draft Slice-Media-Service July 2023 +----------------------------------------------------------------+ | 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 Jiang & Wang Expires 24 January 2024 [Page 5] Internet-Draft Slice-Media-Service July 2023 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. Jiang & Wang Expires 24 January 2024 [Page 6] Internet-Draft Slice-Media-Service July 2023 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 Jiang & Wang Expires 24 January 2024 [Page 7] Internet-Draft Slice-Media-Service July 2023 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, . [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 Jiang & Wang Expires 24 January 2024 [Page 8] Internet-Draft Slice-Media-Service July 2023 [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 Jiang & Wang Expires 24 January 2024 [Page 9]