Network Working Group X. Geng
Internet-Draft J. Dong
Intended status: Informational Huawei Technologies
Expires: August 17, 2020 T. Niwa
KDDI
J. Jin
LG U+
February 14, 2020
5G End-to-end Network Slice Mapping from the view of Transport Network
draft-geng-teas-network-slice-mapping-00
Abstract
Network Slicing is one of the core featrures in 5G. End-to-end
network slicing consists of 3 major types of network segments: Access
Network (AN), Mobile Core Network (CN) and Transport Network (TN).
This draft describes the procedure of mapping relationship between 5G
end-to-end network slice into and transport network slice defined in
IETF. This draft also intends to expose some gaps in the existing
network management plane and data plane to support inter-domain
network slice mapping. Further work may require cooperation between
IETF and 3GPP (or other standard organizations). The definition of
data model, signaling protocol extension and new encapsulation is out
of the scope of this draft.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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."
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This Internet-Draft will expire on August 17, 2020.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Network Slice Mapping Structure . . . . . . . . . . . . . . . 4
3.1. Requirements Profile . . . . . . . . . . . . . . . . . . 5
3.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Relevant functions . . . . . . . . . . . . . . . . . . . 6
4. Network Slice Mapping Procedure . . . . . . . . . . . . . . . 7
4.1. Network Slice Mapping in Management Plane . . . . . . . . 8
4.2. Network Slice Mapping in Control Plane . . . . . . . . . 9
4.3. Network Slice Mapping in data plane . . . . . . . . . . . 10
4.3.1. Data Plane Mapping Considerations . . . . . . . . . . 10
4.3.2. Data Plane Mapping Design . . . . . . . . . . . . . . 10
5. Network Slice Mapping Summary . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
9. Normative References . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
Driven by the new applications of 5G, the concept of network slicing
is defined to provide a logical network with specific network
capabilities and network characteristics. Network slice contains a
set of network functions and the required resources(e.g.
Computation, storage and network resources).According to [TS28530], a
5G end-to-end network slice consists of three major types network
segments: Radio Access Network (RAN), Transport Network (TN) and
Mobile Core Network (CN). Transport network is supposed to provide
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the required connectivity between AN and CN, which specific
performance commitment. For each end-to-end network slice, the
topology and performance requirement on transport network can be very
different, which requires transport network to have the capability of
supporting multiple different transport network slices.
A transport network slice is a virtual (logical) network with a
particular network topology and a set of shared or dedicated network
resources, which are used to provide the network slice consumer with
the required connectivity, appropriate isolation and specific Service
Level Agreement (SLA). A transport network slice could span multiple
technology (IP, Optical) and multiple administrative domains.
Depending on the consumer's requirement, a transport network slice
could be isolated from other, often concurrent transport network
slices in terms of data plane, control plane and management plane.
Transport network slice is being defined and discussed in IETF.
The procedure of end-to-end network slice instance creation, network
slice subnet instance creation and network slice instance termination
in management plane are defined in [TS28531]. The end-to-end network
slice allocation is defined in ETSI ZSM003. But there is no
specifications about how to map end-to-end network slice in 5G system
to transport network slice. This draft describes the procedure of
mapping 5G end-to-end network slice into transport network slice in
management plane, control plane and user plane.
2. Terminologies
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The following terms are used in this document:
NS: Network Slice
NSI: Network Slice Instance
NSSI: Network Slice Subnet Instance
NSSAI: Network Slice Selection Assistance Information
S-NSSAI: Single Network Slice Selection Assistance Information
AN: Access Network
RAN: Radio Access Network
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TN: Transport Network
CN: Mobile Core Network
DSCP: Differentiated Services Code Point
CSMF: Communication Service Management Function
NSMF: Network Slice Management Function
NSSMF: Network Slice Subnet Management Function
GST: General Slice Template
TNSII: Transport Network Slice Interworking Identifier
TNSI: Transport Network Slice Identifier
PDU: Protocol Data Unit
Editor's Note: Terminologies defined in 3GPP, e.g.,Network Slice
Subnet Management Function(NSSMF), Network Slice Subnet
Instance(NSSI) and Network Slice Selection Assistance
Information(NSSAI), is used in the end-to-end network slice mapping,
which may not be used necessarily within the transport network.
3. Network Slice Mapping Structure
The following figure shows the necessary elements for mapping end-to-
end network slice into transport network slice. All these network
slice elements are classified into three groups: requirements/
capabilities, identifiers and relevant functions.
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+-----------------+
| CSMF |
+--------+--------+
|
+--------V--------+
| NSMF |
+-----------------+
+----------| NSI Identifier |----------+
| | Service Profile | |
| | TN Network- | |
| | -Slice Profile | |
| +-----------------+ |
| | |
+------V------+ +----------V----------+ +------V------+
| AN NSSMF | | TN NSSMF | | CN NSSMF |
+-------------+ +---------------------+ +-------------+
| AN-NSSI- | | TN-NSSI Identifier | | CN-NSSI- |
| -Identifier | | Function Management| | -Identifier |
| ... | | ... | | ... | Management
+-------------+ +---------------------+ +-------------+ Plane
| | | | -----------------
|<----------PDU session (S-NSSAI)---------->| Control
| | | | Plane
V V V V -----------------
/\ +-----+ +-----+ +-------+ Data
/AN\ -----| PE |-----...-----| PE |----| UPF | Plane
/____\ +-----+ +-----+ +-------+
|-->TNSII<--|------>TNSI<-------|-->TNSII<--|
TNSII: Transport Network Slice Interworking Identifier
TNSI: Transport Network Slice Identifier
3.1. Requirements Profile
In order to satisfy a tenant's request for a network slice with
certain characteristics, creating a new network slice or using
existing network slice instance is constrained by the customer's
requirement and the capability of the network slices.
o Service Profile: represents the properties of network slice
related requirement that should be supported by the network slice
instance in 5G network. Service profile is defined in [TS28541]
6.3.3.
o TN Network Slice Profile: represents the properties of transport
network slice related requirement that should be supported by the
transport network slice in a 5G network. Slice Profile is defined
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in [TS28541] 6.3.4. TN Network slice profile is newly defined in
this draft.
3.2. Identifiers
Network slice related identifiers in management plane, control plane
and user(data) plane play an important role in end-to-end network
slice mapping.
o Single Network Slice Selection Assistance Information(S-NSSAI):
end-to-end network slice identifier in control plane, which is
defined in [TS23501];
o Network Slice Instance(NSI) Identifier: end-to-end network slice
identifier in management plane, which is created in NSMF; NSI is
is set of Network Function instances and the required resources
(e.g. compute, storage and networking resources) which form a
deployed Network Slice, which is defined in [TS23501];
o Transport Network Slice Instance(TN-NSSI) Identifier: transport
network slice identifier in management plane, which is created in
TN NSSMF; TN-NSSI is newly defined in this draft.
o Transport Network Slice Interworking Identifier (TNSII): network
slice identifier which is used for mapping end-to-end network
slice into transport network slice in user plane. TNSII is newly
defined in this draft.
o Transport Network Slice Identifier(TNSI): transport network slice
identifier in data plane(user plane). TNSI is newly defined in
this draft.
The relationship between these identifiers are specifies in the
following sections.
3.3. Relevant functions
There are a set of slice relevant functions that are necessary for
transport network slice management:
o Topology management
o QoS management
o Resource management
o Measurement management
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o ...
Some of these functions are implemented inside the transport network
and independent from the end-to-end network slice, e.g., topology
management, QoS management, resource management; Some of the
functions are related to the end-to-end network slice and should
cooperate with other network elements from other domain, e.g.,
Measurement management.
4. Network Slice Mapping Procedure
This section provides a general procedure of network slice mapping:
+--------------------------------+
| Requirement Matching |
+---------------+----------------+
|
V
+--------------------------------+
| NSI<->NSSI Mapping |
+---------------+----------------+
|
V
+--------------------------------+
| S-NSSAI Selection |
+---------------+----------------+
|
V
+--------------------------------+
| S-NSSAI<->TNSII Mapping |
+---------------+----------------+
|
V
+--------------------------------+
| TNSII<->TNSI Mapping |
+--------------------------------+
1. NSMF receives the request from CSMF for allocation of the network
slice instance with certain characteristics.
2. Based on the service requirement , the Network Slice Management
Function(NSMF) acquires the properties of network slice related
requirement that should be supported by the network slice instance in
5G network, which is defined in Service Profile([TS28541] section
6.3.3).
3. NSMF needs to decide on the constituent NSSIs(including AN NSSI,
CN NSSI and TN NSSI) to be created using the information from service
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profile and the endpoint information(AN/CN edge nodes) . So NSMF
derives transport network slice related requirements from the Service
profile, and maintains them in Transport Network Slice Profile. So
as to CN Slice Profile and AN Slice Profile.
4. Transport Network Slice Profile is sent to TN NSSMF to request
allocation of the required TN NSSI(s).
5. TN NSSMF allocates TN network slicing subnet instance(TN NSSI)
which could satisfy the requirement between the specified endpoints
(AN/CN edge nodes) in Transport Network Slice Profile and sends the
TN NSSI Identifier to NSMF.
6. NSMF acquires the mapping relationship between NSI Identifier and
TN NSSI Identifier.
7. When a PDU session is set up between AN and CN, S-NSSAI is used
to choose network slice instance for the PDU session.
8. For a user packet in a particular network slice that to be sent
to transport network, the AN/CN edge nodes encapsulate the packet
using the transport network slice interworking identifier (TNSII)
according to the S-NSSAI or the NSI. Network Slice could also be
differentiated by physical interface, if different network slices are
transported through different interface;
9. The edge node of transport network parses the TNSII from the
packet and maps the packet to the corresponding transport network
slice. It may encapsulate a transport network slice identifier
(TNSI) into the packet. .
10. The nodes in transport network transit the packet inside the
corresponding transport network slice.
The procedure of end-to-end network slice mapping involves the
mapping in three network planes: management plane, control plane and
data plane.
4.1. Network Slice Mapping in Management Plane
The transport network management Plane maintains the interface
between NSMF and TN NSSMF, which 1) guarantees that transport network
slice could connect the AN and CN with specified characteristics that
satisfy the requirements of communication; 2) builds up the mapping
relationship between NSI identifier and TN NSSI identifier; 3)
maintains the end-to-end slice relevant functions;
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Service Profile defined in[TS28541] represents the requirement of
end-to-end network slice instance in 5G network. Parameters defined
in Service Profile include Latency, resource sharing level,
availability and so on. How to decompose the end-to-end requirement
to the transport network requirement is one of the key issues in
Network slice requirement mapping. GSMA(Global System for Mobile
Communications Association) defines the [GST] to indicate the network
slice requirement from the view of service provider.
[I-D.contreras-teas-slice-nbi] analysis the parameters of GST and
categorize the parameters into three classes, including the
attributes with direct impact on the transport network slice
definition. It is a good start for selecting the transport network
relevant parameters in order to define Network Slice Profile for
Transport Network. Network slice requirement parameters are also
necessary for the definition of transport network northbound
interface.
Inside the TN NSSMF, it is supposed to maintain the attributes of the
transport network slice. If the attributes of an existing TN NSSI
could satisfy the requirement from TN Network Slice Profile, the
existing TN NSSI could be selected and the mapping is finished If
there is no existing TN NSSI which could satisfy the requirement, a
new TN NSSI is supposed to be created by the NSSMF with new
attributes.
TN NSSI resource reservation should be considered to avoid over
allocation from multiple requests from NSMF (but the detailed
mechanism should be out of scope in the draft)
TN NSSMF sends the selected or newly allocated TN NSSI identifier to
NSMF. The mapping relationship between NSI identifier and TN NSSI
identifier is maintained in both NSMF and TN NSSMF.
4.2. Network Slice Mapping in Control Plane
There is no explicit interaction between transport network and AN/CN
in the control plane, but the S-NSSAI defined in[TS23501] is treated
as the end-to-end network slice identifier in the control plane of AN
and CN, which is used in UE registration and PDU session setup. In
this draft, we assume that there is mapping relationship between
S-NSSAI and NSI in the management plane, thus it could be mapped to a
transport network slice .
Editor's note: The mapping relationship between NSI defined in
[TS23501] and S-NSSAI defined in [TS23501] is still in discussion.
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4.3. Network Slice Mapping in data plane
If multiple network slices are carried through one physical interface
between AN/CN and TN, transport network slice interworking
identifier(TNSII) in the data plane needs to be introduced. If
different network slices are transported through different physical
interfaces, Network Slices could be distinguished by the interface
directly. Thus TNSII is not the only option for network slice
mapping, while it may help in introducing new network slices.
4.3.1. Data Plane Mapping Considerations
The mapping relationship between AN or CN network slice identifier
(either S-NSSAI in control plane or NSI/NSSI in management plane) and
TNSII needs to be maintained in AN/CN network nodes, and the mapping
relationship between TNSII and TNSI is maintained in the edge node of
transport network. When the packet of a uplink flow goes from AN to
TN, the packet is encapsulated based on the TNSII; then the
encapsulation of TNSII is read by the edge node of transport network,
which maps the packet to the corresponding transport network slice.
Editor's Note: We have considered to add "Network Instance" defined
in [TS23501]in the draft. However, after the discussion with 3GPP
people, we think the concept of "network instance" is a 'neither
Necessary nor Sufficient Condition' for network slice. Network
Instance could be determined by S-NSSAI, it could also depends on
other information; Network slice could also be allocated without
network instance (in my understanding) And, TNSII is not a
competitive concept with network instance.TNSII is a concept for the
data plane interconnection with transport network, network instance
may be used by AN and CN nodes to associate a network slice with
TNSII
4.3.2. Data Plane Mapping Design
The following picture shows the end-to-end network slice in data
plane:
+--+ +-----+ +----------------+
|UE|- - - -|(R)AN|---------------------------| UPF |
+--+ +-----+ +----------------+
|<----AN NS---->|<----------TN NS---------->|<----CN NS----->|
The mapping between 3GPP slice and transport slice in user plane
could happens in:
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(R)AN: User data goes from (radio) access network to transport
network
UPF: User data goes from core network functions to transport network
Editor's Note: As figure 4.7.1. in [TS28530] describes, TN NS will
not only exist between AN and CN but may also within AN NS and CN NS.
However, here we just show the TN between AN and CN as an example to
avoid unncessary complexity.
The following picture shows the user plane protocol stack in end-to-
end 5G system.
+-----------+ | | |
|Application+--------------------|------------------|---------------|
+-----------+ | | +-----------+ |
| PDU Layer +--------------------|------------------|-| PDU Layer | |
+-----------+ +-------------+ | +-------------+ | +-----------+ |
| | | ___Relay___ |--|--| ___Relay___ |-|-| | |
| | | \/ GTP-U|--|--|GTP-U\/ GTP-U|-|-| GTP-U | |
| 5G-AN | |5G-AN +------+ | +------+------+ | +-----------+ |
| Protocol | |Protoc|UDP/IP|--|--|UDP/IP|UDP/IP|-|-| UDP/IP | |
| Layers | |Layers+------+ | +------+------+ | +-----------+ |
| | | | L2 |--|--| L2 | L2 |-|-| L2 | |
| | | +------+ | +------+------+ | +-----------+ |
| | | | L1 |--|--| L1 | L1 |-|-| L1 | |
+-----------+ +-------------+ | +-------------+ | +-----------+ |
UE 5G-AN | UPF | UPF |
N3 N9 N6
The following figure shows the typical encapsulation in N3 interface
which could be used to carry the transport network slice interworking
identifier (TNSII) between AN/CN and TN.
+------------------------+
| Application Protocols |
+------------------------+
| IP (User) |
+------------------------+
| GTP |
+------------------------+
| UDP |
+------------------------+
| IP |
+------------------------+
| Ethernet |
+------------------------+
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4.3.2.1. Layer 3 and Layer 2 Encapsulations
If the encapsulation above IP layer is not visible to Transport
Network, it is not able to be used for network slice interworking
with transport network. In this case, IP header and Ethernet header
could be considered to provide information of network slice
interworking from AN or CN to TN.
+------------------------+-----------
| Application Protocols | ^
+------------------------+ |
| IP (User) | Invisible
+------------------------+ for
| GTP | TN
+------------------------+ |
| UDP | V
+------------------------+------------
| IP |
+------------------------+
| Ethernet |
+------------------------+
The following field in IP header and Ethernet header could be
considered :
IP Header:
o DSCP: It is traditionally used for the mapping of QoS identifier
between AN/CN and TN network. Although some values (e.g. The
unassigned code points) may be borrowed for the network slice
interworking, it may cause confusion between QoS mapping and
network slicing mapping.;
o Destination Address: It is possible to allocate different IP
addresses for entities in different network slice, then the
destination IP address could be used as the network slice
interworking identifier. However, it brings additional
requirement to IP address planning. In addition, in some cases
some AN or CN network slices may use duplicated IP addresses.
o Option fields/headers: It requires that both AN and CN nodes can
support the encapsulation and decapsulation of the options.
Ethernet header
o VLAN ID: It is widely used for the interconnection between AN/CN
nodes and the edge nodes of transport network for the access to
different VPNs. One possible problem is that the number of VLAN
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ID can be supported by AN nodes is typically limited, which
effects the number of transport network slices a AN node can
attach to. Another problem is the total amount of VLAN ID (4K)
may not provide a comparable space as the network slice
identifiers of mobile networks.
Two or more options described above may also be used together as the
TNSII, while it would make the mapping relationship more complex to
maintain.
In some other case, when AN or CN could support more layer 3
encapsulations, more options are available as follows:
If the AN or CN could support MPLS, the protocol stack could be as
follows:
+------------------------+-----------
| Application Protocols | ^
+------------------------+ |
| IP (User) | Invisible
+------------------------+ for
| GTP | TN
+------------------------+ |
| UDP | V
+------------------------+------------
| MPLS |
+------------------------+
| IP |
+------------------------+
| Ethernet |
+------------------------+
A specified MPLS label could be used to as a TNSII.
If the AN or CN could support SRv6, the protocol stack is as follows:
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+------------------------+-----------
| Application Protocols | ^
+------------------------+ |
| IP (User) | Invisible
+------------------------+ for
| GTP | TN
+------------------------+ |
| UDP | V
+------------------------+------------
| SRH |
+------------------------+
| IPv6 |
+------------------------+
| Ethernet |
+------------------------+
The following field could be considered to identify a network slice:
SRH:
o SRv6 functions: AN/CN is supposed to support the new function
extension of SRv6.
o Optional TLV: AN/CN is supposed to support the extension of
optional TLV of SRH.
4.3.2.2. Above Layer 3 Encapsulations
If the encapsulation above IP layer is visible to Transport Network,
it is able to be used to identify a network slice. In this case, UPD
and GTP-U could be considered to provide information of network slice
interworking between AN or CN and TN.
+------------------------+----------
| Application Protocols | |
+------------------------+ Invisible
| IP (User) | for
+------------------------+ TN
| GTP | |
+------------------------+------------
| UDP |
+------------------------+
| IP |
+------------------------+
| Ethernet |
+------------------------+
The following field in UDP header could be considered:
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UDP Header:
o UDP Source port: The UDP source port is sometimes used for load
balancing. Using it for network slice mapping would require to
disable the load-balancing behavior.
5. Network Slice Mapping Summary
The following picture shows the mapping relationship between the
network slice identifier in management plane, control plane and user
plane.
AN/CN | TN
Management +---------+ | +---------+
Plane | NSI |<--------|------->| TN NSSI |
+---------+ | +---------+
| | |
| | |
Control +-----V-----+ | +----------+----------+
Plane | S-NSSAI | | | |
+-----------+ | | |
| +----V----+ +----V----+
+----------->| TNSII |<--------->| TNSI |
User | /Port |<--------->| |
Plane +---------+ +---------+
|
6. IANA Considerations
TBD
Note to RFC Editor: this section may be removed on publication as an
RFC.
7. Security Considerations
TBD
8. Acknowledgements
The authors would like to thank Shunsuke Homma for reviewing the draft and
giving valuable comments.
9. Normative References
[GST] "Generic Network Slice Template", 2016,
.
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[I-D.contreras-teas-slice-nbi]
Contreras, L., Homma, S., and J. Ordonez-Lucena,
"Considerations for defining a Transport Slice NBI",
draft-contreras-teas-slice-nbi-00 (work in progress),
November 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[TS23501] "3GPP TS23.501", 2016,
.
[TS28530] "3GPP TS28.530", 2016,
.
[TS28531] "3GPP TS28.531", 2016,
.
[TS28541] "3GPP TS 28.541", 2016,
.
[ZSM003] "End to end management and orchestration of network
slicing", 2016,
.
Authors' Addresses
Xuesong Geng
Huawei Technologies
Email: gengxuesong@huawei.com
Jie Dong
Huawei Technologies
Email: jie.dong@huawei.com
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Tomonobu Niwa
KDDI
Email: to-niwa@kddi.com
Jaewhan JIN
LG U+
Email: daenamu1@lguplus.co.kr
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