RAW                                                       J. Farkas, Ed.
Internet-Draft                                                  T. Dudda
Intended status: Informational                                 A. Shapin
Expires: 1 October 2020                                      S. Sandberg
                                                           30 March 2020

        5G - Ultra-Reliable Wireless Technology with Low Latency


   This document describes the features of 5G that make it a wireless
   technology providing ultra-reliability, high availability, and low
   latency; and looks out to possibilities on the application of 5G
   together with IETF Deterministic Networking (DetNet).

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 1 October 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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 Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Farkas, et al.           Expires 1 October 2020                 [Page 1]

Internet-Draft                   5G RAW                       March 2020

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Provenance and Documents  . . . . . . . . . . . . . . . . . .   2
   3.  General Characteristics . . . . . . . . . . . . . . . . . . .   4
   4.  Deployment and Spectrum . . . . . . . . . . . . . . . . . . .   5
   5.  Applicability to Deterministic Flows  . . . . . . . . . . . .   6
     5.1.  System Architecture . . . . . . . . . . . . . . . . . . .   6
     5.2.  Overview of The Radio Protocol Stack  . . . . . . . . . .   8
     5.3.  Radio (PHY) . . . . . . . . . . . . . . . . . . . . . . .   9
     5.4.  Scheduling and QoS (MAC)  . . . . . . . . . . . . . . . .  10
     5.5.  Time-Sensitive Networking (TSN) Integration . . . . . . .  12
   6.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   10. Informative References  . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   5G is a highly predictable scheduled wireless technology.  Equipped
   with Ultra-Reliable Low-Latency Communication (URLLC) features, 5G
   provides ultra reliability and high availability as well as low
   latency for critical communications.  That is, 5G is a Reliable
   Available Wireless (RAW) technology.  Its characteristics make 5G
   perfectly suitable to be part of deterministic networks, e.g.,
   industrial automation networks.  Furthermore, 5G already includes
   features and capabilities for integration with deterministic wireline
   technologies such as IEEE 802.1 Time-Sensitive Networking (TSN)
   [IEEE802.1TSN] and IETF Deterministic Networking (DetNet) [RFC8655].

2.  Provenance and Documents

   The 3rd Generation Partnership Project (3GPP) incorporates many
   companies whose business is related to cellular network operation as
   well as network equipment and device manufacturing.  All generations
   of 3GPP technologies provide scheduled wireless segments, primarily
   in licensed spectrum which is beneficial for reliability and

   In 2016, the 3GPP started to design New Radio (NR) technology
   belonging to the fifth generation (5G) of cellular networks.  NR has
   been designed from the beginning to not only address enhanced Mobile
   Broadband (eMBB) services for consumer devices such as smart phones
   or tablets but is also tailored for future Internet of Things (IoT)
   communication and connected cyber-physical systems.  In addition to
   eMBB, requirement categories have been defined on Massive Machine-

Farkas, et al.           Expires 1 October 2020                 [Page 2]

Internet-Draft                   5G RAW                       March 2020

   Type Communication (M-MTC) for a large number of connected devices/
   sensors, and Ultra-Reliable Low-Latency Communication (URLLC) for
   connected control systems and critical communication as illustrated
   in Figure 1.  It is the URLLC capabilities that make 5G a great
   candidate for reliable low-latency communication.  With these three
   corner stones, NR is a complete solution supporting the connectivity
   needs of consumers, enterprises, and public sector for both wide area
   and local area, e.g. indoor deployments.  A general overview of NR
   can be found in [TS38300].

                            Mobile Broadband
                                  / \
                                 /   \
                                /     \
                               /       \
                              /   5G    \
                             /           \
                            /             \
                           /               \
                       Massive          Ultra-Reliable
                     Machine-Type        Low-Latency
                    Communication       Communication

                       Figure 1: 5G Application Areas

   As a result of releasing the first NR specification in 2018 (Release
   15), it has been proven by many companies that NR is a URLLC-capable
   technology and can deliver data packets at 10^-5 packet error rate
   within 1ms latency budget [TR37910].  Those evaluations were
   consolidated and forwarded to ITU to be included in the [IMT2020]

   In order to understand communication requirements for automation in
   vertical domains, 3GPP studied different use cases [TR22804] and
   released technical specification with reliability, availability and
   latency demands for a variety of applications [TS22104].

   As an evolution of NR, multiple studies have been conducted in scope
   of 3GPP Release 16 including the following two, focusing on radio

   1.  Study on physical layer enhancements for NR ultra-reliable and
       low latency communication (URLLC) [TR38824].

   2.  Study on NR industrial Internet of Things (I-IoT) [TR38825].

Farkas, et al.           Expires 1 October 2020                 [Page 3]

Internet-Draft                   5G RAW                       March 2020

   In addition, several enhancements have been done on system
   architecture level which are reflected in System architecture for the
   5G System (5GS) [TS23501].

3.  General Characteristics

   The 5G Radio Access Network (5G RAN) with its NR interface includes
   several features to achieve Quality of Service (QoS), such as a
   guaranteeably low latency or tolerable packet error rates for
   selected data flows.  Determinism is achieved by centralized
   admission control and scheduling of the wireless frequency resources,
   which are typically licensed frequency bands assigned to a network

   NR enables short transmission slots in a radio subframe, which
   benefits low-latency applications.  NR also introduces mini-slots,
   where prioritized transmissions can be started without waiting for
   slot boundaries, further reducing latency.  As part of giving
   priority and faster radio access to URLLC traffic, NR introduces
   preemption where URLLC data transmission can preempt ongoing non-
   URLLC transmissions.  Additionally, NR applies very fast processing,
   enabling retransmissions even within short latency bounds.

   NR defines extra-robust transmission modes for increased reliability
   both for data and control radio channels.  Reliability is further
   improved by various techniques, such as multi-antenna transmission,
   the use of multiple frequency carriers in parallel and packet
   duplication over independent radio links.  NR also provides full
   mobility support, which is an important reliability aspect not only
   for devices that are moving, but also for devices located in a
   changing environment.

   Network slicing is seen as one of the key features for 5G, allowing
   vertical industries to take advantage of 5G networks and services.
   Network slicing is about transforming a Public Land Mobile Network
   (PLMN) from a single network to a network where logical partitions
   are created, with appropriate network isolation, resources, optimized
   topology and specific configuration to serve various service
   requirements.  An operator can configure and manage the mobile
   network to support various types of services enabled by 5G, for
   example eMBB and URLLC, depending on the different customers' needs.

   Exposure of capabilities of 5G Systems to the network or applications
   outside the 3GPP domain have been added to Release 16 [TS23501].  Via
   exposure interfaces, applications can access 5G capabilities, e.g.,
   communication service monitoring and network maintenance.

Farkas, et al.           Expires 1 October 2020                 [Page 4]

Internet-Draft                   5G RAW                       March 2020

   For several generations of mobile networks, 3GPP has considered how
   the communication system should work on a global scale with billions
   of users, taking into account resilience aspects, privacy regulation,
   protection of data, encryption, access and core network security, as
   well as interconnect.  Security requirements evolve as demands on
   trustworthiness increase.  For example, this has led to the
   introduction of enhanced privacy protection features in 5G. 5G also
   employs strong security algorithms, encryption of traffic, protection
   of signaling and protection of interfaces.

   One particular strength of mobile networks is the authentication,
   based on well-proven algorithms and tightly coupled with a global
   identity management infrastructure.  Since 3G, there is also mutual
   authentication, allowing the network to authenticate the device and
   the device to authenticate the network.  Another strength is secure
   solutions for storage and distribution of keys fulfilling regulatory
   requirements and allowing international roaming.  When connecting to
   5G, the user meets the entire communication system, where security is
   the result of standardization, product security, deployment,
   operations and management as well as incident handling capabilities.
   The mobile networks approach the entirety in a rather coordinated
   fashion which is beneficial for security.

4.  Deployment and Spectrum

   The 5G system allows deployment in a vast spectrum range, addressing
   use-cases in both wide-area as well as local networks.  Furthermore,
   5G can be configured for public and non-public access.

   When it comes to spectrum, NR allows combining the merits of many
   frequency bands, such as the high bandwidths in millimeter Waves
   (mmW) for extreme capacity locally, as well as the broad coverage
   when using mid- and low frequency bands to address wide-area
   scenarios.  URLLC is achievable in all these bands.  Spectrum can be
   either licensed, which means that the license holder is the only
   authorized user of that spectrum range, or unlicensed, which means
   that anyone who wants to use the spectrum can do so.

   A prerequisite for critical communication is performance
   predictability, which can be achieved by the full control of the
   access to the spectrum, which 5G provides.  Licensed spectrum
   guarantees control over spectrum usage by the system, making it a
   preferable option for critical communication.  However, unlicensed
   spectrum can provide an additional resource for scaling non-critical
   communications.  While NR is initially developed for usage of
   licensed spectrum, the functionality to access also unlicensed
   spectrum was introduced in 3GPP Release 16.

Farkas, et al.           Expires 1 October 2020                 [Page 5]

Internet-Draft                   5G RAW                       March 2020

   Licensed spectrum dedicated to mobile communications has been
   allocated to mobile service providers, i.e. issued as longer-term
   licenses by national administrations around the world.  These
   licenses have often been associated with coverage requirements and
   issued across whole countries, or in large regions.  Besides this,
   configured as a non-public network (NPN) deployment, 5G can provide
   network services also to a non-operator defined organization and its
   premises such as a factory deployment.  By this isolation, quality of
   service requirements, as well as security requirements can be
   achieved.  An integration with a public network, if required, is also
   possible.  The non-public (local) network can thus be interconnected
   with a public network, allowing devices to roam between the networks.

   In an alternative model, some countries are now in the process of
   allocating parts of the 5G spectrum for local use to industries.
   These non-service providers then have a choice of applying for a
   local license themselves and operating their own network or
   cooperating with a public network operator or service provider.

5.  Applicability to Deterministic Flows

5.1.  System Architecture

   The 5G system [TS23501] consists of the User Equipment (UE) at the
   terminal side, and the Radio Access Network (RAN) with the gNB as
   radio base station node, as well as the Core Network (CN).  The core
   network is based on a service-based architecture with the central
   functions: Access and Mobility Management Function (AMF), Session
   Management Function (SMF) and User Plane Function (UPF) as
   illustrated in Figure 2.

   The gNB's main responsibility is the radio resource management,
   including admission control and scheduling, mobility control and
   radio measurement handling.  The AMF handles the UE's connection
   status and security, while the SMF controls the UE's data sessions.
   The UPF handles the user plane traffic.

   The SMF can instantiate various Packet Data Unit (PDU) sessions for
   the UE, each associated with a set of QoS flows, i.e., with different
   QoS profiles.  Segregation of those sessions is also possible, e.g.,
   resource isolation in the RAN and in the CN can be defined (slicing).

Farkas, et al.           Expires 1 October 2020                 [Page 6]

Internet-Draft                   5G RAW                       March 2020

             +----+  +---+   +---+    +---+    +---+   +---+
             |NSSF|  |NEF|   |NRF|    |PCF|    |UDM|   |AF |
             +--+-+  +-+-+   +-+-+    +-+-+    +-+-+   +-+-+
                |      |       |        |        |       |
           Nnssf|  Nnef|   Nnrf|    Npcf|    Nudm|    Naf|
                |      |       |        |        |       |
                         |       |            |         |
                    Nausf|  Nausf|        Nsmf|         |
                         |       |            |         |
                      +--+-+   +-+-+        +-+-+     +-+-+
                      |AUSF|   |AMF|        |SMF|     |SCP|
                      +----+   +++-+        +-+-+     +---+
                               / |            |
                              /  |            |
                             /   |            |
                            N1   N2           N4
                           /     |            |
                          /      |            |
                         /       |            |
                     +--+-+   +--+--+      +--+---+      +----+
                     | UE +---+(R)AN+--N3--+ UPF  +--N6--+ DN |
                     +----+   +-----+      ++----++      +----+
                                            |    |

                      Figure 2: 5G System Architecture

   To allow UE mobility across cells/gNBs, handover mechanisms are
   supported in NR.  For an established connection, i.e., connected mode
   mobility, a gNB can configure a UE to report measurements of received
   signal strength and quality of its own and neighbouring cells,
   periodically or event-based.  Based on these measurement reports, the
   gNB decides to handover a UE to another target cell/gNB.  Before
   triggering the handover, it is hand-shaked with the target gNB based
   on network signalling.  A handover command is then sent to the UE and
   the UE switches its connection to the target cell/gNB.  The Packet
   Data Convergence Protocol (PDCP) of the UE can be configured to avoid
   data loss in this procedure, i.e., handle retransmissions if needed.
   Data forwarding is possible between source and target gNB as well.
   To improve the mobility performance further, i.e., to avoid
   connection failures, e.g., due to too-late handovers, the mechanism
   of conditional handover is introduced in Release 16 specifications.
   Therein a conditional handover command, defining a triggering point,
   can be sent to the UE before UE enters a handover situation.  A
   further improvement introduced in Release 16 is the Dual Active
   Protocol Stack (DAPS), where the UE maintains the connection to the

Farkas, et al.           Expires 1 October 2020                 [Page 7]

Internet-Draft                   5G RAW                       March 2020

   source cell while connecting to the target cell.  This way, potential
   interruptions in packet delivery can be avoided entirely.

5.2.  Overview of The Radio Protocol Stack

   The protocol architecture for NR consists of the L1 Physical layer
   (PHY) and as part of the L2, the sublayers of Medium Access Control
   (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol
   (PDCP), as well as the Service Data Adaption Protocol (SDAP).

   The PHY layer handles signal processing related actions, such as
   encoding/decoding of data and control bits, modulation, antenna
   precoding and mapping.

   The MAC sub-layer handles multiplexing and priority handling of
   logical channels (associated with QoS flows) to transport blocks for
   PHY transmission, as well as scheduling information reporting and
   error correction through Hybrid Automated Repeat Request (HARQ).

   The RLC sublayer handles sequence numbering of higher layer packets,
   retransmissions through Automated Repeat Request (ARQ), if
   configured, as well as segmentation and reassembly and duplicate

   The PDCP sublayer consists of functionalities for ciphering/
   deciphering, integrity protection/verification, re-ordering and in-
   order delivery, duplication and duplicate handling for higher layer
   packets, and acts as the anchor protocol to support handovers.

   The SDAP sublayer provides services to map QoS flows, as established
   by the 5G core network, to data radio bearers (associated with
   logical channels), as used in the 5G RAN.

   Additionally, in RAN, the Radio Resource Control (RRC) protocol,
   handles the access control and configuration signalling for the
   aforementioned protocol layers.  RRC messages are considered L3 and
   thus transmitted also via those radio protocol layers.

   To provide low latency and high reliability for one transmission
   link, i.e., to transport data (or control signaling) of one radio
   bearer via one carrier, several features have been introduced on the
   user plane protocols for PHY and L2, as explained in the following.

Farkas, et al.           Expires 1 October 2020                 [Page 8]

Internet-Draft                   5G RAW                       March 2020

5.3.  Radio (PHY)

   NR is designed with native support of antenna arrays utilizing
   benefits from beamforming, transmissions over multiple MIMO layers
   and advanced receiver algorithms allowing effective interference
   cancellation.  Those antenna techniques are the basis for high signal
   quality and effectiveness of spectral usage.  Spatial diversity with
   up to 4 MIMO layers in UL and up to 8 MIMO layers in DL is supported.
   Together with spatial-domain multiplexing, antenna arrays can focus
   power in desired direction to form beams.  NR supports beam
   management mechanisms to find the best suitable beam for UE initially
   and when it is moving.  In addition, gNBs can coordinate their
   respective DL and UL transmissions over the backhaul network keeping
   interference reasonably low, and even make transmissions or
   receptions from multiple points (multi-TRP).  Multi-TRP can be used
   for repetition of data packet in time, in frequency or over multiple
   MIMO layers which can improve reliability even further.

   Any downlink transmission to a UE starts from resource allocation
   signaling over the Physical Downlink Control Channel (PDCCH).  If it
   is successfully received, the UE will know about the scheduled
   transmission and may receive data over the Physical Downlink Shared
   Channel (PDSCH).  If retransmission is required according to the HARQ
   scheme, a signaling of negative acknowledgement (NACK) on the
   Physical Uplink Control Channel (PUCCH) is involved and PDCCH
   together with PDSCH transmissions (possibly with additional
   redundancy bits) are transmitted and soft-combined with previously
   received bits.  Otherwise, if no valid control signaling for
   scheduling data is received, nothing is transmitted on PUCCH
   (discontinuous transmission - DTX),and the base station upon
   detecting DTX will retransmit the initial data.

   An uplink transmission normally starts from a Scheduling Request (SR)
   - a signaling message from the UE to the base station sent via PUCCH.
   Once the scheduler is informed about buffer data in UE, e.g., by SR,
   the UE transmits a data packet on the Physical Uplink Shared Channel
   (PUSCH).  Pre-scheduling not relying on SR is also possible (see
   following section).

   Since transmission of data packets require usage of control and data
   channels, there are several methods to maintain the needed
   reliability.  NR uses Low Density Parity Check (LDPC) codes for data
   channels, Polar codes for PDCCH, as well as orthogonal sequences and
   Polar codes for PUCCH.  For ultra-reliability of data channels, very
   robust (low spectral efficiency) Modulation and Coding Scheme (MCS)
   tables are introduced containing very low (down to 1/20) LDPC code
   rates using BPSK or QPSK.  Also, PDCCH and PUCCH channels support

Farkas, et al.           Expires 1 October 2020                 [Page 9]

Internet-Draft                   5G RAW                       March 2020

   multiple code rates including very low ones for the channel

   A connected UE reports downlink (DL) quality to gNB by sending
   Channel State Information (CSI) reports via PUCCH while uplink (UL)
   quality is measured directly at gNB.  For both uplink and downlink,
   gNB selects the desired MCS number and signals it to the UE by
   Downlink Control Information (DCI) via PDCCH channel.  For URLLC
   services, the UE can assist the gNB by advising that MCS targeting
   10^-5 Block Error Rate (BLER) are used.  Robust link adaptation
   algorithms can maintain the needed level of reliability considering a
   given latency bound.

   Low latency on the physical layer is provided by short transmission
   duration which is possible by using high Subcarrier Spacing (SCS) and
   the allocation of only one or a few Orthogonal Frequency Division
   Multiplexing (OFDM) symbols.  For example, the shortest latency for
   the worst case in DL can be 0.23ms and in UL can be 0.24ms according
   to (section 5.7.1 in [TR37910]).  Moreover, if the initial
   transmission has failed, HARQ feedback can quickly be provided and an
   HARQ retransmission is scheduled.

   Dynamic multiplexing of data associated with different services is
   highly desirable for efficient use of system resources and to
   maximize system capacity.  Assignment of resources for eMBB is
   usually done with regular (longer) transmission slots, which can lead
   to blocking of low latency services.  To overcome the blocking, eMBB
   resources can be pre-empted and re-assigned to URLLC services.  In
   this way, spectrally efficient assignments for eMBB can be ensured
   while providing flexibility required to ensure a bounded latency for
   URLLC services.  In downlink, the gNB can notify the eMBB UE about
   pre-emption after it has happened, while in uplink there are two pre-
   emption mechanisms: special signaling to cancel eMBB transmission and
   URLLC dynamic power boost to suppress eMBB transmission.

5.4.  Scheduling and QoS (MAC)

   One integral part of the 5G system is the Quality of Service (QoS)
   framework [TS23501].  QoS flows are setup by the 5G system for
   certain IP or Ethernet packet flows, so that packets of each flow
   receive the same forwarding treatment, i.e., in scheduling and
   admission control.  QoS flows can for example be associated with
   different priority level, packet delay budgets and tolerable packet
   error rates.  Since radio resources are centrally scheduled in NR,
   the admission control function can ensure that only those QoS flows
   are admitted for which QoS targets can be reached.

Farkas, et al.           Expires 1 October 2020                [Page 10]

Internet-Draft                   5G RAW                       March 2020

   NR transmissions in both UL and DL are scheduled by the gNB
   [TS38300].  This ensures radio resource efficiency, fairness in
   resource usage of the users and enables differentiated treatment of
   the data flows of the users according to the QoS targets of the
   flows.  Those QoS flows are handled as data radio bearers or logical
   channels in NR RAN scheduling.

   The gNB can dynamically assign DL and UL radio resources to users,
   indicating the resources as DL assignments or UL grants via control
   channel to the UE.  Radio resources are defined as blocks of OFDM
   symbols in spectral domain and time domain.  Different lengths are
   supported in time domain, i.e., (multiple) slot or mini-slot lengths.
   Resources of multiple frequency carriers can be aggregated and
   jointly scheduled to the UE.

   Scheduling decisions are based, e.g., on channel quality measured on
   reference signals and reported by the UE (cf. periodical CSI reports
   for DL channel quality).  The transmission reliability can be chosen
   in the scheduling algorithm, i.e., by link adaptation where an
   appropriate transmission format (e.g., robustness of modulation and
   coding scheme, controlled UL power) is selected for the radio channel
   condition of the UE.  Retransmissions, based on HARQ feedback, are
   also controlled by the scheduler.  If needed to avoid HARQ round-trip
   time delays, repeated transmissions can be also scheduled beforehand,
   to the cost of reduced spectral efficiency.

   In dynamic DL scheduling, transmission can be initiated immediately
   when DL data becomes available in the gNB.  However, for dynamic UL
   scheduling, when data becomes available but no UL resources are
   available yet, the UE indicates the need for UL resources to the gNB
   via a (single bit) scheduling request message in the UL control
   channel.  When thereupon UL resources are scheduled to the UE, the UE
   can transmit its data and may include a buffer status report,
   indicating the exact amount of data per logical channel still left to
   be sent.  More UL resources may be scheduled accordingly.  To avoid
   the latency introduced in the scheduling request loop, UL radio
   resources can also be pre-scheduled.

   In particular for periodical traffic patterns, the pre-scheduling can
   rely on the scheduling features DL Semi-Persistent Scheduling (SPS)
   and UL Configured Grant (CG).  With these features, periodically
   recurring resources can be assigned in DL and UL.  Multiple parallels
   of those configurations are supported, in order to serve multiple
   parallel traffic flows of the same UE.

   To support QoS enforcement in the case of mixed traffic with
   different QoS requirements, several features have recently been
   introduced.  This way, e.g., different periodical critical QoS flows

Farkas, et al.           Expires 1 October 2020                [Page 11]

Internet-Draft                   5G RAW                       March 2020

   can be served together with best effort transmissions, by the same
   UE.  Among others, these features (partly Release 16) are: 1) UL
   logical channel transmission restrictions allowing to map logical
   channels of certain QoS only to intended UL resources of a certain
   frequency carrier, slot-length, or CG configuration, and 2) intra-UE
   pre-emption, allowing critical UL transmissions to pre-empt non-
   critical transmissions.

   When multiple frequency carriers are aggregated, duplicate parallel
   transmissions can be employed (beside repeated transmissions on one
   carrier).  This is possible in the Carrier Aggregation (CA)
   architecture where those carriers originate from the same gNB, or in
   the Dual Connectivity (DC) architecture where the carriers originate
   from different gNBs, i.e., the UE is connected to two gNBs in this
   case.  In both cases, transmission reliability is improved by this
   means of providing frequency diversity.

   In addition to licensed spectrum, a 5G system can also utilize
   unlicensed spectrum to offload non-critical traffic.  This version of
   NR is called NR-U, part of 3GPP Release 16.  The central scheduling
   approach applies also for unlicensed radio resources, but in addition
   also the mandatory channel access mechanisms for unlicensed spectrum,
   e.g., Listen Before Talk (LBT) are supported in NR-U.  This way, by
   using NR, operators have and can control access to both licensed and
   unlicensed frequency resources.

5.5.  Time-Sensitive Networking (TSN) Integration

   The main objective of Time-Sensitive Networking (TSN) is to provide
   guaranteed data delivery within a guaranteed time window, i.e.,
   bounded low latency.  IEEE 802.1 TSN [IEEE802.1TSN] is a set of open
   standards that provide features to enable deterministic communication
   on standard IEEE 802.3 Ethernet [IEEE802.3].  TSN standards can be
   seen as a toolbox for traffic shaping, resource management, time
   synchronization, and reliability.

   A TSN stream is a data flow between one end station (Talker) to
   another end station (Listener).  In the centralized configuration
   model, TSN bridges are configured by the Central Network Controller
   (CNC) [IEEE802.1Qcc] to provide deterministic connectivity for the
   TSN stream through the network.  Time-based traffic shaping provided
   by Scheduled Traffic [IEEE802.1Qbv] may be used to achieve bounded
   low latency.  The TSN tool for time synchronization is the
   generalized Precision Time Protocol (gPTP) [IEEE802.1AS]), which
   provides reliable time synchronization that can be used by end
   stations and by other TSN tools, e.g., Scheduled Traffic
   [IEEE802.1Qbv].  High availability, as a result of ultra-reliability,

Farkas, et al.           Expires 1 October 2020                [Page 12]

Internet-Draft                   5G RAW                       March 2020

   is provided for data flows by the Frame Replication and Elimination
   for Reliability (FRER) [IEEE802.1CB] mechanism.

   3GPP Release 16 includes integration of 5G with TSN, i.e., specifies
   functions for the 5G System (5GS) to deliver TSN streams such that
   the meet their QoS requirements.  A key aspect of the integration is
   the 5GS appears from the rest of the network as a set of TSN bridges,
   in particular, one virtual bridge per User Plane Function (UPF) on
   the user plane.  The 5GS includes TSN Translator (TT) functionality
   for the adaptation of the 5GS to the TSN bridged network and for
   hiding the 5GS internal procedures.  The 5GS provides the following

   1.  interface to TSN controller, as per [IEEE802.1Qcc] for the fully
       centralized configuration model

   2.  time synchronization via reception and transmission of gPTP PDUs

   3.  low latency, hence, can be integrated with Scheduled Traffic

   4.  reliability, hence, can be integrated with FRER [IEEE802.1CB]

   Figure 2 shows an illustration of 5G-TSN integration where an
   industrial controller (Ind Ctrlr) is connected to industrial Input/
   Output devices (I/O dev) via 5G.  The 5GS can directly transport
   Ethernet frames since Release 15, thus, end-to-end Ethernet
   connectivity is provided.  The 5GS implements the required interfaces
   towards the TSN controller functions such as the CNC, thus adapts to
   the settings of the TSN network.  A 5G user plane virtual bridge
   interconnects TSN bridges or connect end stations, e.g., I/O devices
   to the network.  Note that the introduction of 5G brings flexibility
   in various aspects, e.g., more flexible network topology because a
   wireless hop can replace several wireline hops thus significantly
   reduce the number of hops end-to-end.  [ETR5GTSN] dives more into the
   integration of 5G with TSN.

Farkas, et al.           Expires 1 October 2020                [Page 13]

Internet-Draft                   5G RAW                       March 2020

                    | 5G System                    |
                    |                         +---+|
                    |     +-+ +-+ +-+ +-+ +-+ |TSN||
                    |     | | | | | | | | | | |AF |......+
                    |     +++ +++ +++ +++ +++ +-+-+|     .
                    |      |   |   |   |   |    |  |     .
                    |     -+---+---++--+-+-+--+-+- |     .
                    |          |    |    |    |    |  +--+--+
                    |         +++  +++  +++  +++   |  | TSN |
                    |         | |  | |  | |  | |   |  |Ctrlr+.......+
                    |         +++  +++  +++  +++   |  +--+--+       .
                    |                              |     .          .
                    |                              |     .          .
                    | +..........................+ |     .          .
                    | .      Virtual Bridge      . |     .          .
   +---+            | . +--+--+   +---+ +---+--+ . |  +--+---+      .
   |I/O+----------------+DS|UE+---+RAN+-+UPF|NW+------+ TSN  +----+ .
   |dev|            | . |TT|  |   |   | |   |TT| . |  |bridge|    | .
   +---+            | . +--+--+   +---+ +---+--+ . |  +------+    | .
                    | +..........................+ |     .      +-+-+-+
                    |                              |     .      | Ind |
                    | +..........................+ |     .      |Ctrlr|
                    | .      Virtual Bridge      . |     .      +-+---+
   +---+  +------+  | . +--+--+   +---+ +---+--+ . |  +--+---+    |
   |I/O+--+ TSN  +------+DS|UE+---+RAN+-+UPF|NW+------+ TSN  +----+
   |dev|  |bridge|  | . |TT|  |   |   | |   |TT| . |  |bridge|
   +---+  +------+  | . +--+--+   +---+ +---+--+ . |  +------+
                    | +..........................+ |

       <----------------- end-to-end Ethernet ------------------->

                       Figure 3: 5G - TSN Integration

   NR supports accurate reference time synchronization in 1us accuracy
   level.  Since NR is a scheduled system, an NR UE and a gNB are
   tightly synchronized to their OFDM symbol structures.  A 5G internal
   reference time can be provided to the UE via broadcast or unicast
   signaling, associating a known OFDM symbol to this reference clock.
   The 5G internal reference time can be shared within the 5G network,
   i.e., radio and core network components.  For the interworking with
   gPTP for multiple time domains, the 5GS acts as a virtual gPTP time-
   aware system and supports the forwarding of gPTP time synchronization
   information between end stations and bridges through the 5G user
   plane TTs.  These account for the residence time of the 5GS in the
   time synchronization procedure.  One special option is when the 5GS
   internal reference time in not only used within the 5GS, but also to

Farkas, et al.           Expires 1 October 2020                [Page 14]

Internet-Draft                   5G RAW                       March 2020

   the rest of the devices in the deployment, including connected TSN
   bridges and end stations.

   Redundancy architectures were specified in order to provide
   reliability against any kind of failure on the radio link or nodes in
   the RAN and the core network, Redundant user plane paths can be
   provided based on the dual connectivity architecture, where the UE
   sets up two PDU sessions towards the same data network, and the 5G
   system makes the paths of the two PDU sessions independent as
   illustrated in Figure 5.  There are two PDU sessions involved in the
   solution: the first spans from the UE via gNB1 to UPF1, acting as the
   first PDU session anchor, while the second spans from the UE via gNB2
   to UPF2, acting as second the PDU session anchor.  The independent
   paths may continue beyond the 3GPP network.  Redundancy Handling
   Functions (RHFs) are deployed outside of the 5GS, i.e., in Host A
   (the device) and in Host B (the network).  RHF can implement
   replication and elimination functions as per [IEEE802.1CB] or the
   Packet Replication, Elimination, and Ordering Functions (PREOF) of
   IETF Deterministic Networking (DetNet) [RFC8655].

              . Device . +------+      +------+      +------+
              .        . + gNB1 +--N3--+ UPF1 |--N6--+      |
              .        ./+------+      +------+      |      |
              . +----+ /                             |      |
              . |    |/.                             |      |
              . | UE + .                             |  DN  |
              . |    |\.                             |      |
              . +----+ \                             |      |
              .        .\+------+      +------+      |      |
              +........+ + gNB2 +--N3--+ UPF2 |--N6--+      |
                         +------+      +------+      +------+

                    Figure 4: Reliability with Single UE

   An alternative solution is that multiple UEs per device are used for
   user plane redundancy as illustrated in Figure 5.  Each UE sets up a
   PDU session.  The 5GS ensures that those PDU sessions of the
   different UEs are handled independently internal to the 5GS.  There
   is no single point of failure in this solution, which also includes
   RHF outside of the 5G system, e.g., as per FRER or as PREOF

Farkas, et al.           Expires 1 October 2020                [Page 15]

Internet-Draft                   5G RAW                       March 2020

             .  Device .
             .         .
             . +----+  .  +------+      +------+      +------+
             . | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+      |
             . +----+  .  +------+      +------+      |      |
             .         .                              |  DN  |
             . +----+  .  +------+      +------+      |      |
             . | UE +-----+ gNB2 +--N3--+ UPF2 |--N6--+      |
             . +----+  .  +------+      +------+      +------+
             .         .

                     Figure 5: Reliability with Dual UE

   Note that the abstraction provided by the RHF and the location of the
   RHF being outside of the 5G system make 5G equally supporting
   integration for reliability both with FRER of TSN and PREOF of DetNet
   as they both rely on the same concept.

   Note also that TSN is the primary subnetwork technology for DetNet.
   Thus, the DetNet over TSN work, e.g., [I-D.ietf-detnet-ip-over-tsn],
   can be leveraged via the TSN support built in 5G.

6.  Summary

   5G technology enables deterministic communication.  Based on the
   centralized admission control and the scheduling of the wireless
   resources, licensed or unlicensed, quality of service such as latency
   and reliability can be guaranteed. 5G contains several features to
   achieve ultra-reliable and low latency performance, e.g., support for
   different OFDM numerologies and slot-durations, as well as fast
   processing capabilities and redundancy techniques that lead to
   achievable latency numbers of below 1ms with reliability guarantees
   up to 99.999%.

   5G also includes features to support Industrial IoT use cases, e.g.,
   via the integration of 5G with TSN.  This includes 5G capabilities
   for each TSN component, latency, resource management, time
   synchronization, and reliability.  Furthermore, 5G support for TSN
   can be leveraged when 5G is used as subnet technology for DetNet, in
   combination with or instead of TSN, which is the primary subnet for
   DetNet.  In addition, the support for integration with TSN
   reliability was added to 5G by making DetNet reliability also
   applicable, thus making 5G DetNet ready.  Moreover, providing IP
   service is native to 5G.

Farkas, et al.           Expires 1 October 2020                [Page 16]

Internet-Draft                   5G RAW                       March 2020

   Overall, 5G provides scheduled wireless segments with high
   reliability and availability.  In addition, 5G includes capabilities
   for integration to IP networks.

7.  IANA Considerations

   This document does not require IANA action.

8.  Security Considerations

   5G includes security mechanisms as defined by 3GPP.

9.  Acknowledgments

   The authors acknowledge the work of all from Ericsson Research who
   contributed to the subject in any form.

10.  Informative References

   [TR37910]  "3GPP TR 37.910, Study on self evaluation towards IMT-2020

   [TR38824]  "3GPP TR 38.824, Study on physical layer enhancements for
              NR ultra-reliable and low latency case (URLLC)",

   [TR38825]  "3GPP TR 38.825, Study on NR industrial Internet of Things

   [TS22104]  "3GPP TS 22.104, Service requirements for cyber-physical
              control applications in vertical domains",

   [TR22804]  "3GPP TR 22.804, Study on Communication for Automation in
              Vertical domains (CAV)",

   [TS23501]  "3GPP TS 23.501, System architecture for the 5G System

Farkas, et al.           Expires 1 October 2020                [Page 17]

Internet-Draft                   5G RAW                       March 2020

   [TS38300]  "3GPP TS 38.300, NR Overall description",

   [IMT2020]  "ITU towards IMT for 2020 and beyond",

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,

              Varga, B., Farkas, J., Malis, A., and S. Bryant, "DetNet
              Data Plane: IP over IEEE 802.1 Time Sensitive Networking
              (TSN)", Work in Progress, Internet-Draft, draft-ietf-
              detnet-ip-over-tsn-02, 6 March 2020,

              IEEE 802.1, "Time-Sensitive Networking (TSN) Task Group",

              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Timing and Synchronization for Time-Sensitive
              Applications", IEEE 802.1AS-2020,

              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Frame Replication and Elimination for
              Reliability", DOI 10.1109/IEEESTD.2017.8091139, IEEE

              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Bridges and Bridged Networks -- Amendment 25:
              Enhancements for Scheduled Traffic", IEEE 802.1Qbv-2015,

              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Bridges and Bridged Networks -- Amendment 31:

Farkas, et al.           Expires 1 October 2020                [Page 18]

Internet-Draft                   5G RAW                       March 2020

              Stream Reservation Protocol (SRP) Enhancements and
              Performance Improvements", IEEE 802.1Qcc-2018,

              IEEE, "IEEE Standard for Ethernet", IEEE 802.3-2018,

   [ETR5GTSN] Farkas, J., Varga, B., Miklos, G., and J. Sachs, "5G-TSN
              integration meets networking requirements for industrial
              automation", Ericsson Technology Review, Volume 9, No 7,
              August 2019, <https://www.ericsson.com/en/reports-and-

Authors' Addresses

   Janos Farkas (editor)
   Magyar tudosok korutja 11

   Email: janos.farkas@ericsson.com

   Torsten Dudda
   Ericsson Allee 1
   52134 Herzogenrath

   Email: torsten.dudda@ericsson.com

   Alexey Shapin
   Laboratoriegrand 11
   SE-977 53 Lulea

   Email: alexey.shapin@ericsson.com

   Sara Sandberg
   Laboratoriegrand 11

Farkas, et al.           Expires 1 October 2020                [Page 19]

Internet-Draft                   5G RAW                       March 2020

   SE-977 53 Lulea

   Email: sara.sandberg@ericsson.com

Farkas, et al.           Expires 1 October 2020                [Page 20]