Internet DRAFT - draft-farkas-raw-5g
draft-farkas-raw-5g
RAW J. Farkas, Ed.
Internet-Draft T. Dudda
Intended status: Informational A. Shapin
Expires: 1 October 2020 S. Sandberg
Ericsson
30 March 2020
5G - Ultra-Reliable Wireless Technology with Low Latency
draft-farkas-raw-5g-00
Abstract
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
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This Internet-Draft will expire on 1 October 2020.
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Copyright (c) 2020 IETF Trust and the persons identified as the
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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
availability.
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-
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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].
enhanced
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]
work.
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
aspects:
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].
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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
operator.
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.
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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.
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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).
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+----+ +---+ +---+ +---+ +---+ +---+
|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 |
+----+ +-----+ ++----++ +----+
| |
+-N9-+
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
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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
detection.
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.
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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
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multiple code rates including very low ones for the channel
robustness.
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.
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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
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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,
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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
components:
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
[IEEE802.1AS]
3. low latency, hence, can be integrated with Scheduled Traffic
[IEEE802.1Qbv]
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.
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+------------------------------+
| 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
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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
specifications.
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+.........+
. 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.
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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
submission",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3190>.
[TR38824] "3GPP TR 38.824, Study on physical layer enhancements for
NR ultra-reliable and low latency case (URLLC)",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3498>.
[TR38825] "3GPP TR 38.825, Study on NR industrial Internet of Things
(IoT)",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3492>.
[TS22104] "3GPP TS 22.104, Service requirements for cyber-physical
control applications in vertical domains",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3528>.
[TR22804] "3GPP TR 22.804, Study on Communication for Automation in
Vertical domains (CAV)",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3187>.
[TS23501] "3GPP TS 23.501, System architecture for the 5G System
(5GS)",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
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[TS38300] "3GPP TS 38.300, NR Overall description",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3191>.
[IMT2020] "ITU towards IMT for 2020 and beyond",
<https://www.itu.int/en/ITU-R/study-groups/rsg5/rwp5d/imt-
2020/Pages/default.aspx>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[I-D.ietf-detnet-ip-over-tsn]
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,
<https://tools.ietf.org/html/draft-ietf-detnet-ip-over-
tsn-02>.
[IEEE802.1TSN]
IEEE 802.1, "Time-Sensitive Networking (TSN) Task Group",
<http://www.ieee802.org/1/pages/tsn.html>.
[IEEE802.1AS]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Timing and Synchronization for Time-Sensitive
Applications", IEEE 802.1AS-2020,
<https://standards.ieee.org/content/ieee-standards/en/
standard/802_1AS-2020.html>.
[IEEE802.1CB]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Frame Replication and Elimination for
Reliability", DOI 10.1109/IEEESTD.2017.8091139, IEEE
802.1CB-2017,
<https://ieeexplore.ieee.org/document/8091139>.
[IEEE802.1Qbv]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Bridges and Bridged Networks -- Amendment 25:
Enhancements for Scheduled Traffic", IEEE 802.1Qbv-2015,
<https://ieeexplore.ieee.org/document/7440741>.
[IEEE802.1Qcc]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Bridges and Bridged Networks -- Amendment 31:
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Stream Reservation Protocol (SRP) Enhancements and
Performance Improvements", IEEE 802.1Qcc-2018,
<https://ieeexplore.ieee.org/document/8514112>.
[IEEE802.3]
IEEE, "IEEE Standard for Ethernet", IEEE 802.3-2018,
<https://ieeexplore.ieee.org/document/8457469>.
[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-
papers/ericsson-technology-review/articles/5g-tsn-
integration-for-industrial-automation>.
Authors' Addresses
Janos Farkas (editor)
Ericsson
Budapest
Magyar tudosok korutja 11
1117
Hungary
Email: janos.farkas@ericsson.com
Torsten Dudda
Ericsson
Ericsson Allee 1
52134 Herzogenrath
Germany
Email: torsten.dudda@ericsson.com
Alexey Shapin
Ericsson
Laboratoriegrand 11
SE-977 53 Lulea
Sweden
Email: alexey.shapin@ericsson.com
Sara Sandberg
Ericsson
Laboratoriegrand 11
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SE-977 53 Lulea
Sweden
Email: sara.sandberg@ericsson.com
Farkas, et al. Expires 1 October 2020 [Page 20]
