Internet DRAFT - draft-gcdrb-teas-5g-network-slice-application
draft-gcdrb-teas-5g-network-slice-application
TEAS Working Group X. Geng
Internet-Draft Huawei Technologies
Intended status: Informational L. Contreras
Expires: 9 September 2023 Telefonica
R. Rokui
Ciena
J. Dong
Huawei Technologies
I. Bykov
Ribbon Communications
8 March 2023
IETF Network Slice Application in 3GPP 5G End-to-End Network Slice
draft-gcdrb-teas-5g-network-slice-application-02
Abstract
Network Slicing is one of the core features in 5G, which provides
different network service as independent logical networks. To
provide 5G network slices service, an end-to-end network slice needs
to consists of 3 major types of network segments: Radio Access
Network (RAN), Mobile Core Network (CN) and Transport Network (TN).
This document describes the application of IETF network slice in
providing 5G end-to-end network slices, including the network slice
identification mapping, network slice parameter mapping and 5G IETF
Network Slice NBI.
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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Copyright Notice
Copyright (c) 2023 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
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described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 4
3. 5G End-to-End Network Slice . . . . . . . . . . . . . . . . . 5
3.1. IETF Network Slices in Distributed RAN deployment . . . . 6
3.2. IETF Network Slices in Centralized RAN deployment . . . . 6
3.3. IETF Network Slices in Cloud RAN deployment (C-RAN) . . . 7
3.4. Relationship between IETF network slice and 3GPP network
slice . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Overview of the mapping between 3GPP and IETF network
slices . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. VLAN Hand-off . . . . . . . . . . . . . . . . . . . . . . 13
4.2. SRv6 Label Hand-off . . . . . . . . . . . . . . . . . . . 13
4.3. MPLS Lable Hand-off . . . . . . . . . . . . . . . . . . . 14
4.4. Policy based routing (PBR) . . . . . . . . . . . . . . . 15
4.5. GTP Source Port-Based . . . . . . . . . . . . . . . . . . 16
4.6. Consideration of the Virtual Network Functions (VNF) . . 17
5. 3GPP Network Slice Mapping Parameters . . . . . . . . . . . . 18
6. 5G E2E Network Slice Mapping Procedure . . . . . . . . . . . 24
6.1. 5G E2E Network Slice Mapping in Management Plane . . . . 27
6.1.1. Mapping EP_transport to IETF NS CE endpoints . . . . 29
6.1.2. Mapping IETF NS CE to PE endpoints . . . . . . . . . 29
6.2. 5G E2E Network Slice Mapping in Control Plane . . . . . . 30
6.3. 5G E2E Network Slice Mapping in Data Plane . . . . . . . 31
6.3.1. Data Plane Mapping Considerations . . . . . . . . . . 31
6.3.2. Data Plane Mapping Options . . . . . . . . . . . . . 31
7. Example of IETF Network Slice request through IETF Network
Slice NBI . . . . . . . . . . . . . . . . . . . . . . . . 36
8. Gap Analysis . . . . . . . . . . . . . . . . . . . . . . . . 38
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
10. Security Considerations . . . . . . . . . . . . . . . . . . . 39
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11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 39
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 39
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 42
13.1. Normative References . . . . . . . . . . . . . . . . . . 42
13.2. Informative References . . . . . . . . . . . . . . . . . 44
Appendix A. An Appendix . . . . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44
1. Introduction
Driven by the new applications of 5G, the concept of network slicing
is defined to provide a logical network with specific capabilities
and characteristics. Network slice contains a set of network
functions and allocated resources(e.g. computation, storage and
network resources).
The IETF Network Slice (NS) service is defined in
[I-D.ietf-teas-ietf-network-slices] as a set of connections between a
number of CEs, with that connections having specific Service Level
Objectives (SLOs) and Service Level Expectations (SLEs) over a common
underlay network, with the traffic of one customer being separated
from another. The concept of IETF network slice is conceived as
technology agnostic.
The IETF NS service is specified in terms of the set of endpoints
(from CE perspective) connected to the slice, the type of
connectivity among them, and a set of SLOs and SLEs for each
connectivity construct.
In [I-D.ietf-teas-ietf-network-slice-nbi-yang], the endpoints are
described by an identifier, with some metrics associated to the
connections among them as well as certain policies (e.g., rate limits
for incoming and outgoing traffic).
The 5G network slice as defined in [3GPP TS 23.501] does not take the
transport network slice into consideration. This document introduces
the concept of 5G end-to-end network slice, which is composed of
three major types network segments: Radio Access Network (RAN),
Transport Network (TN) and Mobile Core Network (CN). Transport
network is supposed to provide the required connectivity between AN
and CN or inside AN/CN, with specific performance commitment. For
each end-to-end network slice, the topology and performance
requirement for transport network can be very different, which
requests transport network to have the capability of supporting
multiple different transport network slices.
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This document addresses the request of IETF Network Slice services
for 3GPP 5G Network Slices. The realization of such requested slices
is out of the scope of this document and addressed in other documents
such as [I-D.srld-teas-5g-slicing].
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].
Terminologies for IETF Network Slice go along with the definition in
[I-D.ietf-teas-ietf-network-slices].
The following terms are used in this document:
NSC: IETF Network Slice Controller
NSI: Network Slice Instance
NSSI: Network Slice Subnet Instance
S-NSSAI: Single Network Slice Selection Assistance Information
RAN: Radio Access Network
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
IOC: Information Object Class model, defined in 3GPP
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3. 5G End-to-End Network Slice
The scope of 5G End-to-End Network Slice discussed in this document
is shown in Figure 1. Transport network provides connectivity
between and inside RAN and CN. To support fully automated enablement
an assurance of 5G E2E network slices, multiple controllers are
needed to manage 5G E2E network slices in RAN, Core and Transport
domains. In addition, an E2E network slice orchestrator is needed to
provide coordination and control of network slices from an E2E
perspective.
+-----------------------------------------------------+
| +-----------------------------+ |
|-----+----------+----------------+ | |
| ****** +---+---+ ****** | +----+ | |
| * * | | * * | | | | |
| * RAN --- TN --- RAN --|-- | | |
| * NFs * | | * NFs * | | | | |
| ****** +-------+ ****** | | | | |
|---------------------------------+ | | +-+--+ +------+------+
RAN | | |IETF| | 5G E2E |
| +---+ NSC+--+Network Slice|
|TN | | | | Orchestrator|
| | +-+--+ +------+------+
+---------------------------------+ | | | |
| ****** +-------+ ****** | | | | |
| * * | | * * | | | | |
| * CN --- TN --- CN ---|-- | | |
| * NFs * | | * NFs * | | | | |
| ****** +---+---+ ****** | +----+ | |
+-----+----------+----------------+ | |
| CN| | |
| +-----------------------------+ |
+-----------------------------------------------------+
Figure 1: Scope of 5G End to End Network Slice
Depends on Radio Access Network (RAN) deployment, one or multiple
IETF network slice might be needed in 3GPP network. In the details
of various IETF network slices for following RAN deployment will be
discussed:
* Distributed RAN
* Centralized RAN
* Cloud RAN (C-RAN)
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3.1. IETF Network Slices in Distributed RAN deployment
Distributed RAN is the most common deployment of 3GPP RAN networks as
shown in Figure 2. The radio acess network (RAN) is connected to
Core network (CN) using the IETF transport network (TN1).
<-------------- 3GPP E2E Network Slice ------------->
<---- RS ----> <-------- CS ---------->
<- INS1 -> <- INS2 ->
................. .........................
: RAN : : CN :
: : ........ : ....... :
: |----| |----| : : : : |----| : : |----| :
: | NF1| | NF2| : : TN1 : : | NF | : TN2 : | NF | :
: |----| |----| : : : : |----| : : |----| :
: : :......: : :.....: :
:...............: :.......................:
Legend
INS: IETF Network Slice
RS: RAN Slice
CS: Core Slice
TN: IETF network
CN: Core Network
RAN:Access Neetwork (Radio)
Figure 2: IETF network slices in distributed RAN deployment
3.2. IETF Network Slices in Centralized RAN deployment
In general the RAN network consists of network functions NF1 and MF2.
NF1 processes the radio signal and is connected to the transport
network and NF2 transmits and receives the carrier signal that is
transmitted over the air to the end user equipment (UE). In
Centralized RAN as depicted in Figure 3, network functions NF1 and
NF2 are separated by a network called fronthaul network (FH).
In this deployment a 3GPP E2E network slice contains of RAN and Core
slices and IETF network slices INS1, INS2 and INS3. INS1 and INS2
are identical to Figure 2 and INS3 is a new IETF network slice across
access network between NF1 and NF2.
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<-------------------- 3GPP E2E Network Slice ----------------->
<-------- RS ---------> <---------- CS --------->
<- INS3 -> <- INS1 -> <- INS2 ->
......................... ...........................
: RAN : : CN :
: ....... : ........ : ....... :
: |----| : : |----| : : : : |-----| : : |-----| :
: | NF1| : TN3 : | NF2| : : TN1 : : | NF | : TN2 : | NF | :
: |----| : (FH): |----| : : : : |-----| : : |-----| :
: :.....: : :......: : :.....: :
:.......................: :.........................:
Legend
INS: IETF Network Slice
RS: RAN Slice
CS: Core Slice
FN: Fronthaul IETF network
TN: IETF network
CN: Core Network
RAN:Access Neetwork (Radio)
Figure 3: IETF network slices in centralized RAN deployment
3.3. IETF Network Slices in Cloud RAN deployment (C-RAN)
In Cloud RAN deployment, the network function NF2 is further
disaggregated into real-time and non-real-time components. As shown
in Figure 4, these disaggregated components are called CU (Central
Unit) and DU (Distributed Unit) where they are connected by a new
network called Midhaul network (MH).
In this deployment a single 3GPP E2E network slice contains not only
RAN and 5G Core slices but IETF network slices INS1, INS2, INS3 and
INS4. IETF network slices INs1, INS2 and INS3 are identical to their
counterparts in centralized RAN deployment case (Refer to Figure 3).
In this deployment a new IETF network slice INS4 connects the DUs to
CUs through F1 interfaces.
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<---------------------- 3GPP E2E Network Slice ------------------>
<-------------- RS --------------> <------- CS ------>
<- INS3 -> <- INS4 -> <- INS1 -> <- INS2 ->
..................................... .....................
: RAN : :CN :
: ....... ...... : ...... : ..... :
: |---| : : |---| : : |---| : : : : |---| : : |---| :
: |NF1| : TN3 : | DU| : TN4 : | CU| : :TN1 : : | NF| :TN2: | NF| :
: |---| : (FH): |---| : (MH): |---| : :(BH): : |---| : : |---| :
: :.....: :.....: : :....: : :...: :
:...................................: :...................:
Legend
INS: IETF Network Slice
RS: RAN Slice
CS: Core Slice
FN: Fronthaul IETF network
MN: Midhaul IETF bnetwork
BH: Backhual IETF network
TN: IETF network
DU: Distributed Unit
CU: Central Unit
CN: Core Network
RAN:Access Neetwork (Radio)
Figure 4: IETF network slices in cloud RAN deployment (C-RAN)
3.4. Relationship between IETF network slice and 3GPP network slice
For the sake of description, the descriptions below all take the TN
slice between RAN and CN as an example, and the other cases are
similar. Figure 5 shows the correspondence between network entities
in E2E 5G slices and IETF slices respectively
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+---------------------+
| CSMF |
+----------|----------+
| +------------------------+
+---------------------+ | 5G E2E Network Slice |
| NSMF | | Orchestrator |
+---------------------+ +------------------------+
/ | \ |
/ | \ NSC NBI |
/ | \ |
+---------++---------++---------+ +------------------------+
| AN || TN || CN | | IETF Network Slice |
| NSSMF || NSSMF || NSSMF | | Controller (NSC) |
| || || | +------------------------+
+---------++---------++---------+ NSC SBI |
| | | |
| | | +------------------------+
| | | | Network Controllers |
| | | +------------------------+
| | | |
| | | |
****** ****** ****** ******
* 5G * * IETF * * 5G * * IETF *
* RAN * * Network* * Core * * Network*
* * * * * * * *
****** ****** ****** ******
Legend
Figure 5: Relationship between 3GPP domain controllers and IETF
Network Slice Controller
An example of 5G E2E Network Slice is showed in Figure 6. Each e2e
network slice contains AN slice, CN slice and one or more IETF
network Slices. 3GPP identifies each e2e network slice using an
integer called S-NSSAI. In Figure 4 there are three instances of e2e
network slices which are identified by S-NSSAI 01111111, 02222222 and
02333333, respectively. Each instance of e2e network slice contains
AN slice, CN Slice and one or more IETF network slices. For example,
e2e network slice 01111111 has AN Slice instance 4, CN Slice instance
1 and IETF network slice 6. Note that 3GPP does not cover the IETF
network slice. See [I-D.ietf-teas-ietf-network-slices] for details
of IETF network slice.
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Note that 3GPP uses the terms NSI and NSSI which are a set of network
function and required resources (e.g. compute, storage and networking
resources) which corresponds to network slice Instance, whereas
S-NSSAI is an integer that identifies the e2e network slice.
+-----------+ +-----------+ +-----------+
| S-NSSAI | | S-NSSAI | | S-NSSAI |
| 01111111 | | 02222222 | | 03333333 |
+---|-------+ +---|---|---+ +----|------+
| +----------+ | |
V V V V
******* ******** ********
Core * NSSI 1 * * NSSI 2 * * NSSI 3 *
Network ******** ******** ********
\ \ /
\ \ /
+-----+ +-----+ +-----+
Transport | IETF| | IETF| | IETF|
Network | NS 6| | NS 7| | NS 8|
+-----+ +-----+ +-----+
\ \ /
\ \ /
Radio ******** ********
Access * NSSI 4 * * NSSI 5 *
Network ******** ********
Legend
Figure 6: 5G End-to-End Network Slice and its components
The following network slice related identifiers in management plane,
control plane and data(user) plane play an important role in end-to-
end network slice mapping:
* Single Network Slice Selection Assistance Information(S-NSSAI):
The end-to-end network slice identifier, which is defined in
[TS23501]; S-NSSAI is used during 3GPP network slice signalling
process.
* IETF Network Slice Identifier: An identifier allocated by IETF
Neetwork Slice Controller (NSC) in management plane. In data
plane, IETF Network Slice Identifier may be instantiated with
existing data plane identifiers and doesn't necessarily require
new encapsulation.
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* IETF Network Slice Interworking Identifier: Data-plane network
slice identifier which is used for mapping the end-to-end network
slice traffic to specific IETF network slice. The IETF Network
Slice Interworking Identifier is a new concept introduced by this
draft, which may be instantiated with existing data plane
identifiers and doesn't necessarily require new encapsulation.
Note: the term "IETF Network Slice Interworking Identifier" is
proposed but requires further discussion.
4. Overview of the mapping between 3GPP and IETF network slices
Referring to Figure 2-1, 2-2 and 2-3, a 3GPP network slice might have
one or more IETF network slices. Figure 7 is a representation of any
of these networks where the IETF network slice provides the
connectivity between NF1 and NF2 for specific SLO/SLE. For example,
Figure 7 could represent Figure 2-3 where the IETF network slice
needed between network functions are CU and UPF or it could represent
the Figure 2-3 where the IETF network slice is between network
functions DU and CU.
AC .-------. AC
| ,' `. |
| ,' `. |
-------- V ------- ------- V --------
| | | | | | | |
| NF1 |-------| PE1 | | PE2 |-------| NF2 |
| |-------| | | | | |
-------- ------- Provider ------- --------
`. Network ,'
`. ,'
-------
Figure 7: Typical IETF Network Slice in 3GPP Network
To provide an overview of various IETF network slice realization
solutions, we focus on Figure 2-3 where the IETF network slide is
INS1 and NF1 and NF2 are CU and UPF, respectively. Figure 8 shows
Although the realization methods described below is related to INS1,
they are applicable to other IETF network slices of Figure 2-1, 2-2
and 2-3. The result is shown in Figure 5. Please note that the IETF
network slice INS1 is between SDP1 and SPD2 which are the N3
interfaces on CU and UPF, respectively. As shown in Figure 8(A) and
Figure 8(B), the SDPs could be the loopback interface or IP
interface. For simplicity only case (A) is considered for the rest
of the section although the various realization methods are
applicable to both cases.
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SDP1 INS1 SDP2
(N3 I/F) | (N3 I/F)
| .---|---. |
| ,' | `. |
v ,' V `. V
-------- ------- ------- --------
| o=============================================o |
| | | PE1 | | PE2 | | |
| CU | | | | | | UPF |
-------- ------- Provider ------- --------
`. Network ,'
`. ,'
-------
(A)
SDP1 INS1 SDP2
(N3 I/F) | (N3 I/F)
| .---|---. |
| ,' | `. |
v ,' V `. V
-------- ------- ------- --------
| *======================================* |
| | | PE1 | | PE2 | | |
| CU | | | | | | UPF |
-------- ------- Provider ------- --------
`. Network ,'
`. ,'
-------
(B)
Legend:
* SDP (N3 interface as CU IP interface)
O SDP (N3 as CU loopback interface)
Figure 8: Representation of a Typical IETF Network Slice in 3GPP
Network
To realize the INS1 shown in Figure 8(A), the IETF network slice
controller (NSC) can use the following techniques:
* VLAN handoff
* MPLS label handoff
* SRv6 label handoff
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* Policy Based Routing (PBR)
* GTP source port based
4.1. VLAN Hand-off
As shown in Figure 9, the IETF Network slice INS1 is realized between
network functions CU and UPF using the VLAN handoff. In this case
the VLAN is hand-off ID from the 3GPP network slice to provider
network. Refer to section 5 for details of this solution.
<-------------------- INS1 ------------------->
VLAN Handoff IP/MPLS Services
| |
| |
N3 I/F | .---|---. N3 I/F
| | ,' | `. |
V V ,' V `. V
-------- ------- ------- --------
| O..........+======================+...........O |
| | | PE1 | | PE2 | | |
| CU | | | | | | UPF |
-------- ------- Provider ------- --------
`. Network ,'
`. ,'
-------
(A)
Legend:
O SDP (N3 interface)
+ Access points to provider network
... VLAN hand-off
=== IP/MPLS transport service in provider network
Figure 9: VLAN hand-off based for IETF Network Slice Realization
4.2. SRv6 Label Hand-off
Figure 10 depicts the realization of the IETF network slice INS1
using the SRv6 label handoff method. In this case, an SRv6 label
which represents the 3GPP network slice is added by CU or UPF to IP
traffic. In this case, network function CU and UPF are the endpoint
of the realization of IETF network slice INS1 and PE nodes do not
have any context of the IETF network.
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In this solution the identification of the 3GPP network slice is
embedded into IPv6 label where the 32-bit 3GPP network slice
identification is mapped into 128 bit of IPV6 label. In this case
the SRv6 SID is hand-off ID from the 3GPP network slice to provider
network. Refer to section 5 for details of this solution.
<-------------------- INS1 ------------------->
SRv6 tunnel
|
|
N3 I/F | .-------. N3 I/F
| | ,' `. |
V V ,' `. V
-------- ------- ------- --------
| *=============================================* |
| | | PE1 | | PE2 | | |
| CU | | | | | | UPF |
-------- ------- Provider ------- --------
`. Network ,'
`. ,'
-------
(A)
Legend:
* Access points to SRv6 Tunnel. Also the SDP (N3 interface)
=== Realization of the INS1 using SRv6 tunnel
Figure 10: SRV6 hand-off based for IETF Network Slice Realization
4.3. MPLS Lable Hand-off
Similar to section 2.4.2, the MPLS label based method uses an MPLS
label as identification of the 3GPP network slice. Figure 11 shows
this solution where the IETF network slice INS1 is relaized by CU and
UPF using the MPLS label. In this case, network function CU and UPF
are the endpoint of the realization of IETF network slice INS1 and PE
nodes do not have any context of the IETF network. In this case the
MPLS is hand-off ID from the 3GPP network slice to provider network.
Refer to section 5 for details of this solution.
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<-------------------- INS1 ------------------->
MPLS label tunnel
|
|
N3 I/F | .-------. N3 I/F
| | ,' `. |
V V ,' `. V
-------- ------- ------- --------
| *=============================================* |
| | | PE1 | | PE2 | | |
| CU | | | | | | UPF |
-------- ------- Provider ------- --------
`. Network ,'
`. ,'
-------
(A)
Legend:
* Access points to MPLS Tunnel. Also the SDP (N3 interface)
=== Realization of the INS1 using MPLS lable
Figure 11: MPLS hand-off based for IETF Network Slice Realization
4.4. Policy based routing (PBR)
As shown in Figure 12, in some deployments of the 3GPP network
slices, it would be possible for provider edge (PE) nodes to infer
the 3GPP network slice identification from the information in the IP
packet. In these cases, the IETF network slice INS1 is identified by
provider edger (PE) routers by a policy which might use any
combination of the following attributes of the IP packet.
* Source N3 IP address
* Destination N3 IP address
* Ingress interface
* DSCP
* Other information in IP packet
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<-------------------- INS1 ------------------->
PBR IP/MPLS Services PBR
| | |
| | |
N3 I/F | .---|---. | N3 I/F
| | ,' | `. | |
V V ,' V `. V V
-------- ------- ------- --------
| O..........+======================+..........O |
| | | PE1 | | PE2 | | |
| CU | | | | | | UPF |
-------- ------- Provider ------- --------
`. Network ,'
`. ,'
-------
Legend:
O SDP ((N3 interface)
+ Access points of IP/MPLS Services when PBR is applied
=== IP/MPLS service
Figure 12: Policy based routing (PBR) label hand-off based for
IETF Network Slice Realization
4.5. GTP Source Port-Based
In some deployments of the 3GPP network slices, the IETF network
slice INS1 might be realized by multiple GTP tunnels. As shown in
Figure 13, this solution uses the source UDP port of the GTP tunnel
to carry the identification of 3GPP network slice. A mapping table
between the 3GPP network slice and the source UDP port is needed in
this solution and needs to be maintained by network functions CU, UPF
and PE nodes. Refer to section 2.5 of [draft-ietf-dmm-tn-aware-
mobility-04] for details of this solution.
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<-------------------- INS1 ------------------->
GTP tunnels
|
|
N3 I/F | .-------. N3 I/F
| | ,' `. |
V V ,' `. V
-------- ------- ------- --------
| *=============================================* |
| *=============================================* |
| | | PE1 | | PE2 | | |
| CU | | | | | | UPF |
-------- ------- Provider ------- --------
`. Network ,'
`. ,'
-------
Legend:
* SDP (N3 interfaces)
=== Realization of the INS1 using data plane GTP tunnels
Figure 13: GTP source port-based for IETF Network Slice Realization
4.6. Consideration of the Virtual Network Functions (VNF)
In some 3GPP network slice deployments, it might be beneficial to
deploy RAN and Core network functions such as DU, CU, UPF etc as
virtual network functions (VNF) inside a data center (DC). As an
example, consider Figure 14 where the CU and UPF have been deployed
as VNF. The definition of the IETF network slice INS1 is exactly
similar to previous use-cases, i.e., INS1 is an IETF network slice to
provides the connectivity between service demarcation points SDP1 and
SDP2 to satisfy certain SLO/SLE. However, the realization of INS1
might be different from previous use-cases. Figure 14 shows one
possible solution for realization of INS1 where a portion of
realization is inside provider's network and other portion is inside
data centers. As an example, L3VPN service technology could be used
inside the provider network between provider edge routers PE1 and PE2
and VXLAN could be used inside data centers towards PE1 and PE2.
Note that the choice of technology during the realization is
responsibility of IETF network slice controller (NCS) and is out of
scope of this draft
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<-------------------- INS1 ------------------->
Realization of INS1 Realization of INS1
in data center in provider network
| |
SDP1 | | SDP2
| | .---|---. |
V V ,' | `. V
|------------| ,' V `. |------------|
| -------- | ------- ------- | -------- |
| | O...........+======================+..........O | |
| | | | | PE1 | | PE2 | | | | |
| | CU | | | | | | | | UPF | |
| -------- | ------- Provider ------- | ------- |
| | `. Network ,' | |
|------------| `. ,' |------------|
DC1 ------- DC2
Legend:
DC Data Center
O SDP (N3 interfaces)
=== Realization of INS1 in Provider Networks
... Realization of INS1 in data centers
Figure 14: VNF Consideration for IETF Network Slice Realization
5. 3GPP Network Slice Mapping Parameters
The network slice concept was introduced in 3GPP specifications from
the first 5G release, corresponding to Release 15. As captured in
[TS23.501], a network slice represents a logical network providing
specific network capabilities and network characteristics.
To make slicing a reality, every technical domain is split into one
or more logical network partitions, each referred to as a network
slice subnet. The definition of multiple slice subnets on a single
domain allows each segment to provide differentiated behaviors, in
terms of functionality and/or performance, tailored to some specific
needs. The stitching of slice subnets across the RAN, CN and TN
results in the definition of 5G network slices in 3GPP.
From a management viewpoint, the concept of network slice subnet
represents an independently manageable yet composable portion of a
network slice. The rules for the definition of network slice subnets
and their composition into network slices are detailed in the 5G
Network Resource Model (NRM) [TS28.541], specifically in the Network
Slice NRM fragment. This fragment captures the information model of
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5G network slicing, which specifies the relationships between
different slicing related managed entities, which is represented as
Information Object Class (IOC). The IOC that have been defined
including: NetworkSlice IOC, NetworkSliceSubnet IOC, ManagedFunction
IOC and EP_Transport IOC.
Information Object Class EP_Transport [TS28.541 Clause 6.3.18]
represents logical interface parameters of 3GPP subsystems, providing
specific network capabilities and network characteristics.
Relationships of Transport slicing-related 3GPP IOCs and IETF domain
represented on the Figure X for NgU/N3 slices with traffic between
3GPP CU-UP (or ORAN) CU-UP and 3GPP UPF, while the Figure Y similarly
represents F1-U slices with traffic between 3GPP (or ORAN) DU and
3GPP (or ORAN) CU-UP .
+----------------------------------+
| Slices in 3GPP domain |
| Model defined in IOC TS 28.541 |
| NgU/N3 slices |
+----+--------------------------+--+
+-----------------|+ |
| 3GPP CU-UP / || +-|---------------+
| ORAN O-CU-UP #1 || .-----. | |3GPP (i)UPF #1 |
| +---------------V| ,' TN `. +-V--------------+|
| | EP_NgU link to | | domain | | EP_N3 link to ||
| | UPF #1 | ; : | CU-UP #1 ||
| |+---------------| ; .-------. : +---------------+||
| ||EP_Transport 10+------(Slice 10 )------|EP_Transport 10|||
| |+---------------| | `-------' | +---------------+||
| | | | | | ||
| |+---------------| : .-------. ; +----------------||
| ||EP_Transport 20+------(Slice 20 )------|EP_Transport 20 ||
| |+---------------|A : `-------' ; A+----------------||
| +----------------|| | | |+----------------+|
| . . . || | | || . . . |
| +----------------|| `. ,' |+----------------+|
| | EP_NgU link to || `---' || EP_NgU link to ||
| | UPF #N || || CU-UP #N ||
| +----------------|| |+----------------+|
+------------------+| |+-----------------+
| |
+------+---------------------+--------+
| logical transport interfaces |
| e.g. GTP-U, IPSec endpoint |
+-------------------------------------+
Figure 5-1 Slicing example on the NgU/N3 interface
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+----------------------------------+
| Slices in 3GPP domain |
| Model defined in IOC TS 28.541 |
| F1-U slices |
+-+-------------------------+------+
+--------------|+ +|-----------------+
| 3GPP DU / || || 3GPP CU-UP / |
| ORAN O-DU #1 || ||ORAN O-CU-UP #1 |
| || .-----. || |
|+-------------V| ,' TN `. +V---------------+ |
|| EP_F1-U link | | domain | |EP_F1-U link to | |
|| to CU-UP #1 | ; : | DU #1 | |
|+--------------| ; .-----. : +--------------+ | |
||EP_Transport 1+-------(Slice 1)-------|EP_Transport 1| | |
|+--------------| | `-----' | +--------------+ | |
|| | | | | | |
|+--------------| : .-----. ; +--------------+ | |
||EP_Transport 2+-------(Slice 2)-------|EP_Transport 2| | |
|+--------------|A : `-----' ; A+--------------+ | |
|+--------------|| | | |+----------------+ |
| . . . || | | || . . . |
|+--------------|| `. ,' |+----------------+ |
|| EP_F1-U link || `---' ||EP_F1-U link to | |
|| to CU-UP #N || || DU #N | |
|+--------------|| |+----------------+ |
+---------------+| |+------------------+
| |
| |
+------+---------------------+--------+
| logical transport interfaces |
| e.g. GTP-U, IPSec endpoint |
+-------------------------------------+
Figure 5-2 Slicing example on the F1-U interface
For the transport (i.e., connectivity) related part of a network
slice, the key focus is on the EP_Transport IOC. Instances of this
IOC serves to instantiate 3GPP interfaces (e.g., N3) which are needed
to support Network Slicing and to define Network Slice transport
resources within the 5G NRM. In a nutshell, the EP_Transport IOC
permits to define additional logical interfaces for each slice
instance of the 3GPP user plane.
According to [TS28.541], the EP_Transport construct on 3GPP side has
the following attributes: ipAddress, logicaInterfaceInfo,
nextHopInfo, qosProfile and epApplicationRef In which, nextHopInfo
could be used for choosing PE node in transport network and
LogicalInterfaceInfo could be used for Transport Network Slice
mapping.
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nextHopInfo (optional): identifies the ingress transport node. Each
node can be identified by any combination of IP address of next-hop
router of transport network, system name, port name and IP management
addresses of transport nodes.
logicInterfaceInfo (mandatory): a set of parameters, which includes
logicInterfaceType and logicInterfaceId. It specifies the type and
identifier of a logical interface. It could be a VLAN ID, MPLS Tag
or Segment ID. This is assigned uniquely per slice.
From the Transport Network domain side, these parameters assist on
the definition of the CE transport interface configuration and shall
be taken as an input to the transport service model to create
coherent Network Slice transport service. Fig. Z illustrates how the
EP_Transport parameters can relate to the IETF ones for determining
the endpoint connectivity.
+-----------------------+ .-----. +-----------------+
| 3GPP CU-UP / | ,' TN `. | 3GPP (i)UPF #1 |
| ORAN O-CU-UP #1 | | domain | | |
|+----------------------| +-----------+ : +----------------+|
||EP_NgU link to UPF #1 | | PE 1 | : | EP_N3 link to ||
|| | | | : | CU-UP #1 ||
||+---------------------| | .-------. | | +---------------+||
||| EP_Transport for +--+(Slice 10 )+----+---| EP_Transport |||
||| S-NSSAI FWA | |A`-------' | ; +---------------+||
|||logicInterfaceType = | +|----------+ ; +----------------+|
||| Vlan ID | |: ; +-----------------+
||| logicInterfaceId = | | | |
||| Vlan 200 | | | |
|||ipAddress = 20.2.2.2 | | `. ,'
||+--------------A------| | `---'
|+---------------|------| +-+-------------------+
+----------------|------+ | nextHopInfoList |
| |NextHopInfo = IP/mask|
+--------------+------+ | of PE 1 |
| epApplicationRef = | | system name = PE 1 |
|EP_NgU link to UPF#1 | | port name = Gi1/1 |
+---------------------+ +---------------------+
Figure 5-3 Example of 3GPP EP_Transport IOC TS28.541 parameters with correlation
to IETF
Furthermore, that same parameters should be leveraged for
constituting the connectivity construct allowing endpoint
interconnection. That is, there is no additional information that
could be leveraged at service level that the one provided by
EP_Transport, which essentially reflects an endpoint view. Fig. W
represents this relationship between 3GPP and IETF parameters.
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3GPP subsystem - CE Transport Network node - PE
+----------------------+ +----------------------+
|InformationObjectClass| | IETF Slice Model |
| <-----------------> |
| EP_Transport | | LxSM + extensions |
+----------------------+ +----------------------+
Representation of connectivity:
EP_NgU/N3, link between (O)-CU-UP and UPF
F1-U, link between (O)-DU and (O)-CU-UP
Figure 5-4 Relationships of the 3GPP parameters with the IETF parameters
Leveraging on the EP_Transport information, the IETF NSC should be
instructed through its NBI on performing the slice connection. Fig.
Q graphically represents the slice connection (e.g., for Ng-U/N3) as
expected by 3GPP by using connectivity constructs (of a IETF Network
Slice service) to be configured by the IETF Network Slice Controller.
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Slices in 3GPP domain Slices in 3GPP domain
Model defined in IOC TS 28.541 Model defined in IOC TS 28.541
+------------------+ +------------------+
|3GPP CU-UP / ORAN | | 3GPP UPF #1 |
| O-CU-UP #1 | Slices in IETF domain | |
| | | |
|+-----------------| +----+ +----+ +-----------------+|
|| EP_NgU link to | |PE 1| |PE 2| | EP_N3 link to ||
|| UPF #1 | | | .-. | | | CU-UP #1 ||
||+----------------| | | | | | | +----------------+||
||| EP_Transport | | | | | | | |EP_Transport for|||
|||for S-NSSAI 100 o--------------PDU 1-------------o S-NSSAI 100 |||
||| Vlan 100 | | | | | | | | Vlan 100 |||
||| IP 10.1.1.2 |<--->| | ; : | |<-->| IP 10.1.1.2 |||
||+----------------| | |; :| | +----------------+||
||+----------------| | || || | +----------------+||
||| EP_Transport | | || || | |EP_Transport for|||
|||for S-NSSAI 200 o--------------PDU 2-------------o S-NSSAI 200 |||
||| Vlan 200 | | || || | | Vlan 200 |||
||| IP 20.2.2.2 |<--->| || TN || |<-->| IP 20.2.2.2 |||
||+----------------| | || || | +----------------+||
|| | | || |+----+ +-----------------+|
|+-----------------| | || | +------------------+
|+-----------------| | |: ;+----+ +------------------+
|| EP_NgU link to | | | : ; |PE 3| | 3GPP UPF #2 |
|| UPF #2 | | | | | | | +-----------------+|
||Serving S-NSSAI o--------------PDU 3-------------o EP_N3 link to ||
|| 100 |<--->| | : ; | |<-->| CU-UP #1 ||
|+-----------------| | | : ; | | | Serving S-NSSAI ||
+------------------+ +----+ `. ,' +----+ | 100 ||
' +-----------------+|
+------------------+
Figure 5-5 Example of CU-UP Slice in the 3GPP domain using an IETF Network Slice service
From the perspective of IETF Network Slice realization, some of these
options could be realized in a straightforward manner while other
could require of advanced features (e.g., PBR, SRv6, FlexE, etc).
IETF Network Slice service may be a set of techniques and underlaying
technologies, so multiple models may be used to define slice.
According to the [TS28.541] attributes in the EP_Transport, the IETF
Network Slice may be defined by the following combination of the
parameters:
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+------------------------------------------------------------------+
| EP_Transport attribute name |
| |
+---------------+----------------+----------------+----------------+
| ipAddress |logicInterfaceId| nextHopInfo | qosProfile |
+---------------+----------------+----------------+----------------+
| Different | Same for all |
| per slice | slices |
+---------------+---------------------------------+----------------+
| Same for all | Different | Same for all |
| slices | per slice | slices |
+---------------+----------------+----------------+----------------+
| Different | Same for all | Different | Same for all |
| per slice | slices | per slice | slices |
+---------------+----------------+----------------+----------------+
| Same for all | Different | Same for all |
| slices | per slice | slices |
+--------------------------------+----------------+----------------+
| Different |
| per slice |
+---------------+--------------------------------------------------+
| Same for all | Different |
| slices | per slice |
+---------------+--------------------------------------------------+
From the perspective of IETF Network Slice realization, some of these
options could be realized in a straightforward manner while other
could require of advanced features (e.g., PBR, SRv6, FlexE, etc).
IETF Network Slice service may be a set of techniques and underlaying
technologies, so multiple models may be used to define slice.
6. 5G E2E Network Slice Mapping Procedure
This section provides a general procedure of network slice mapping:
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+-----------------+
| NSMF |
+-----------------+
+----------| S-NSSAI |----------+
| |(e.g. 011111111) | |
| +-----------------+ |
| | |
V V V
+-------------+ +---------------------+ +-------------+
| RAN NSSMF | | IETF NSC | | CN NSSMF |
+-------------+ +---------------------+ +-------------+
| RAN Slice | | IETF Network Slice | | CN Slice |
| Identifier | | Identifier | | Identifier |
| (e.g., 4) | | (e.g., 6) | | (e.g., 1) | Management
+-------------+ +---------------------+ +-------------+ Plane
| | | | -----------------
| | | |
V V V V -----------------
/ \ +-----+ +-----+ +-------+ Data
/RAN\ ----| PE |-----...-----| PE |----| CN | Plane
/-----\ +-----+ +-----+ +-------+
Figure-6 Relation between IETF and 3GPP Network Slice management
1. 3GPP NSMF receives the request from 3GPP CSMF for allocation of a
network slice instance with certain characteristics.
2. Based on the service requirement, 3GPP NSMF acquires requirements
for the end-to-end network slice instance, which is defined in
Service Profile([TS28541] section 6.3.3).
3. Based on Service Profile, 3GPP NSMF identified the network
function and the required resources in AN, CN and TN networks. It
also assigns the unique ID S-NSSAI.
4. 3GPP NSMF sends a request to AN NSSMF for creation of AN Slice,
out of the scope of this document.
5. 3GPP NSMF sends a request to CN NSSMF for creation of CN Slice,
out of the scope of this document.
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6. 3GPP NSMF sends a request to IETF Network Slice Controller (NSC)
(acting as an NSSMF for transport connectivity, or TN NSSMF, from the
perspective of the 3GPP Management System)) for creation of IETF
Network Slice. The request contains attributes such as endpoints
(based on the information from EP_Transport IOC), required SLA/SLO
along with other IETF network slice attributes. It also cotains
mapping informatin for IETF Network Slice Interworking Identifier.
Note: term "TN NSSMF" under discussion to ensure consistency with
3GPP specifications.
7. IETF NSC realizes the IETF network slice which satisfies the
requirements of the IETF network slice service requested between the
specified endpoints (RAN/ CN edge nodes). It may assign sliceID and
send it to 3GPP NSMF.
Note: Consistency with the YANG NBI model should be ensured on
parameters being passed between components
8. 3GPP NSMF mantains the mapping relationship between S-NSSAI and
IETF Network Slice Service ID;
9. When the User Equipment (UE) appears, and during the 5G
signaling, it requests to be connected to specific e2e network slice
identified by S-NASSI. Then a GTP tunnel (which is UDP/IP-based)
will be created.
10. UE starts sending traffic in context of e2e network slice for
specific S-NASSI.
11. The endpoints of the 5G network slice in AN encapsulates the
packet into a GTP tunnel, adds a Slice Interworking Identifier
according to the selected S-NSSAI and send it to the transport
network.
12. The transport network edge nodes parse the Slice Interworking
identifier in the received packet and maps the packet to the
corresponding IETF network slice. It may encapsulate the packet with
slice specific identifiers for enforcing the SLA of IETF Network
Slice service in the in transport network.
Note: steps 11 and 12 under discussion since they could depend on
specific realization mechanisms.
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6.1. 5G E2E Network Slice Mapping in Management Plane
The transport network management Plane maintains the interface
between 3GPP NSMF and TN NSSMF, which 1) guarantees that IETF 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 any other identifier
potentially used by the IETF NSC; 3) maintains the end-to-end slice
relevant functions.
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.ietf-teas-ietf-network-slice-use-cases] analyzes the parameters
of GST and categorize the parameters into three classes, including
the attributes with direct impact on the IETF 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 IETF NSC (playing the role of TN NSSMF in 3GPP scope), it
is supposed to be responsible of maintaining the attributes of the
IETF network slice. If the attributes of an existing IETF Network
Slice service could satisfy the requirement from the 3GPP Network
Slice Profile, an existing IETF network slice could be selected and
the mapping is then finished. In case there is no existing IETF
Network Slice which could satisfy the requirement, a new IETF Network
Slice is supposed to be created by the IETF NSC with the requested
attributes.
IETF Network Slice resource reservation should be considered to avoid
over allocation from multiple requests from 3GPP NSMF (but the
detailed mechanism is out of scope of this draft)
3GPP TN NSSMF will request the IETF Network Slice service adding in
the IETF Network Slice service request some slice identifier to the
IETF NSC. The mapping relationship between NSI identifier and IETF
Network Slice service identifier could be maintained in both 3GPP
NSMF and IETF NSC.
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Then, at the time of provisioning a 3GPP slice, it is required to
provide slice connectivity constructs by means of IETF network
slices. Then it is necessary to bind two different endpoints, as
depicted in Figure 2:
* Mapping of EP_Transport (as defined by [TS28.541]) to the endpoint
at the CE side o f the IETF network slice. This is necessary
because the IETF Network Slice Controller (NSC) will receive as
input for the IETF network slice service the set of endpoints at
CE side to be interconnected
* Mapping of the endpoints at both CE and PE side. The endpoint at
PE side should be elicited by some means by the IETF NSC, in order
to establish and set up the connectivity construct intended for
the customer slice request, according to the SLOs and SLEs
received from the higher level system.
3GPP concern
----------- ---------
/ /
/ /
O EP_Transport_left EP_Transport_right O
/A /A
/ | / |
----- | ---|-------
| |
| |
.......|............................................|..........
| |
| |
| |
-------|-- ---------- ---------- | -------
| / / / ____ / / | /
V/ / / ( ) / / V/
O<---->O 0==( )==0 O<---->O
/ / / (____) / / /
/ / / / / /
----- ---------- ---------- ----------
CE_left PE_left PE_right CE_right
IETF concern
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6.1.1. Mapping EP_transport to IETF NS CE endpoints
The 3GPP Management system provides the EP_Transport IOC to extend
the slice awareness to the transport network. The EP_Transport IOC
contains parameters as IP address, additional identifiers (i.e., vlan
tag, MPLS label, etc), and associated QoS profile. This IOC is
related to the endpoints of the 3GPP managed functions (detailed in
the EP_Application IOC).
The information captured in the EP_Transport IOC (as part of the 3GPP
concern) should be translated into the CE related parameters (as part
of the IETF concern). There will be cases where such translation is
straightforward, as for instance, when the 3GPP managed functions run
on monolithic, purpose- specific network elements, in the way that
the IP address attribute from the EP_Transport IOC directly
corresponds to the IP address of an interface of such network
element. In this case, the information on EP_Transport IOC can be
directly passed to the IETF NSC through the NBI, even though some
additional information could be yet required, not being defined yet
on 3GPP specifications (e.g., the mask applicable to the IP address
field on EP_Transport). Note that information gaps are further
detailed in a summary section at the end of this document.
However, there could be other cases where such a relationship is not
straightforward. This could be the case of virtualized 3GPP managed
functions that could be instantiated on a general-purpose bare-metal
server or in a data center. In these other cases it is necessary to
define additional means for eliciting the endpoint at the CE side
corresponding to the endpoint of the 3GPP-related function.
With solely EP_Transport characterization in 3GPP as today (i.e.,
according to 3GPP Release 16 specifications), we could expect the NS
CE endpoint being identified by a combination of IP address and some
additional information such as vlan tag, MPLS label or SR SID that
could discriminate against a certain logical interface. The next hop
router information is related to the next hop view from the
perspective of the 3GPP entity part of the slice, then providing
hints for determining the slice endpoint at the other side of the
slice boundary. Finally, the QoS profile, if present, helps to
determine configurations needed at the PE side to respect the SLOs in
the connection between CEs slice endpoints.
6.1.2. Mapping IETF NS CE to PE endpoints
As described in [I-D.ietf-teas-ietf-network-slices], there are
different potential endpoint positions for an IETF NS.
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|<---------------------- (1) ---------------------->|
| |
| |<-------------------- (2) -------------------->| |
| | | |
| | |<----------- (3) ----------->| | |
| | | | | |
| | | |<-------- (4) -------->| | | |
| | | | | | | |
V V AC V V V V AC V V
+-----+ | +-----+ +-----+ | +-----+
| |--------| | | |--------| |
| CE1 | | | PE1 |. . . . . . . . .| PE2 | | | CE2 |
| |--------| | | |--------| |
+-----+ | +-----+ +-----+ | +-----+
^ ^ ^ ^
| | | |
| | | |
Customer Provider Provider Customer
Edge 1 Edge 1 Edge 2 Edge 2
Figure 7: IETF Network Slice endpoints
The information that is passed to the IETF NSC in terms of endpoints
is the information relative to the CE side, which is the one known by
the slice customer (i.e., the 3GPP Management system, that
corresponds to the 3GPP managed functions). From that information,
the IETF NSC needs to infer the corresponding endpoint at the PE
side, in order to setup the desired connectivity constructs with the
SLOs indicated in the request.
Being the IETF slice request a technology-agnostic procedure, the
identification of the slice endpoints at the PE side should leverage
on generic information passed through the NBI to the IETF NSC.
6.2. 5G E2E 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, it is assumed that there is a correspondence between
S-NSSAI and the IETF Network Slice service identifier in the
management plane.
Note: to ensure consistency with NBI YANG model (i.e., service tag)
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6.3. 5G E2E Network Slice Mapping in Data Plane
If multiple network slices are carried through one physical interface
between AN/CN and TN, IETF Network Slice Interworking ID in the data
plane needs to be defined. If different network slices are
transported through different physical interfaces, Network Slices
could be distinguished by the interface directly. Thus IETF Network
Slice Interworking ID is not the only option for network slice
mapping, while it may help in introducing new network slices.
6.3.1. Data Plane Mapping Considerations
The mapping relationship between AN or CN network slice and an IETF
Network Slice will be based on a IETF Network Slice Interworking
identifier based on the information provided by the EP_Transport IOC.
When the packet of an uplink flow goes from AN to TN, the packet is
delivered according to the information provided by the EP_Transport
IOC (e.g., the information provided in the logicalInterface field);
then the encapsulation is read by the edge node of transport network,
which maps the packet to the corresponding IETF network slice.
6.3.2. Data Plane Mapping Options
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:
(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 unnecessary complexity.
The following picture shows the user plane protocol stack in end-to-
end 5G system.
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+-----------+ | | |
|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.
+------------------------+
| Application Protocols |
+------------------------+
| IP (User) |
+------------------------+
| GTP |
+------------------------+
| UDP |
+------------------------+
| IP |
+------------------------+
| Ethernet |
+------------------------+
6.3.2.1. 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.
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+------------------------+-----------
| 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:
* 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.;
* 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.
* Option fields/headers: It requires that both AN and CN nodes can
support the encapsulation and decapsulation of the options.
Ethernet header
* 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
ID can be supported by AN nodes is typically limited, which
effects the number of IETF 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.
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Two or more options described above may also be used together as the
IETF Network Slice Interworking ID, 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 IETF Network Slice
Interworking ID.
If the AN or CN could support SRv6, the protocol stack is as follows:
+------------------------+-----------
| Application Protocols | ^
+------------------------+ |
| IP (User) | Invisible
+------------------------+ for
| GTP | TN
+------------------------+ |
| UDP | V
+------------------------+------------
| SRH |
+------------------------+
| IPv6 |
+------------------------+
| Ethernet |
+------------------------+
The following field could be considered to identify a network slice:
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SRH:
* SRv6 functions: AN/CN is supposed to support the new function
extension of SRv6.
* Optional TLV: AN/CN is supposed to support the extension of
optional TLV of SRH.
6.3.2.2. 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:
UDP Header:
* 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.
A similar approach to this is followed in
[I-D.ietf-dmm-tn-aware-mobility]
6.3.2.3. Summary
From all the options overviewed, it should be noted that current 3GPP
Release 16 only supports through EP_Transport IOC the following slice
handoff identifier: vlan tag. MPLS or SID labels. Thus, the
consideration of more options as the ones here reported is a gap on
3GPP specifications.
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7. Example of IETF Network Slice request through IETF Network Slice NBI
As discussed in [I-D.ietf-teas-ietf-network-slices], to fulfill IETF
network slices and to perform monitoring on them, an entity called
IETF Network Slice Controller (NSC) is required to take abstract
requests for IETF network slices and realize them using suitable
underlying technologies. An IETF Network Slice Controller is the key
building block for control and management of the IETF network slice.
It provides the creation/modification/deletion, monitoring and
optimization of transport Slices in a multi-domain, a multi-
technology and multi-vendor environment.
Figure 8 shows the NSC and its NBI interface for 5G. Draft
[I-D.ietf-teas-ietf-network-slice-nbi-yang] a addresses the service
yang model of the NSC NBI interface for all network slicing use-
cases.
+------------------------------------------+
| 5G Customer (Tenant) |
+------------------------------------------+
A
|
V
+------------------------------------------+
| 5G E2E Network Slice Orchestrator |
+------------------------------------------+
A
| NSC NBI
V
+------------------------------------------+
| IETF Network Slice Controller (NSC) |
+------------------------------------------+
A
| NSC SBI
V
+------------------------------------------+
| Network Controller(s) |
+------------------------------------------+
Figure 8: IETF Network Slice Controller NBI for 5G
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As discussed in [I-D.ietf-teas-ietf-network-slices], the main task of
the IETF Network Slice Controller is to map abstract IETF network
slice requirements from NBI to concrete technologies on SBI and
establish the required connectivity, and ensure that required
resources are allocated to IETF network slice. There are a number of
different technologies that can be used on SBI including physical
connections, MPLS, TSN, Flex-E, PON etc. If the undelay technology
is IP/MPLS/Optics, any IETF models can be used during the realization
of IETF network slice.
There are no specific mapping requirements for 5G. The only
difference is that in case of 5G, the NBI interface contains
additional 5G specific attributes such as customer name, mobile
service type, 5G E2E network slice ID (i.e. S-NSSAI) and so on (See
Section 6). These 5G specific attributes can be employed by IETF
Network Slice Controller during the realization of 5G IETF network
slices on how to map NBI to SBI. They can also be used for assurance
of 5G IETF network slices. Figure 9 shows the mapping between NBI to
SBI for 5G IETF network slices.
| (1) NBI: Request to create/modify/delete
| 5G IETF Network Slice
V
+----------------------+
| IETF Network Slice | (2) Mapping between technology
| Controller (NSC) | agnostics NBI to technology
+----------------------+ specific SBI
^ ^ ^
| | |
|---| | |---| (3) SBI: Realize 5G IETF Network Slice
| | | by using various IETF models for
V V V services, tunnels and paths
+----------------------+
| Network |-+
| Controller(s) | |-+
+----------------------+ | |
+----------------------+ |
+----------------------+
Figure 9: Relationship between transport slice interface and IETF
Service/Tunnels/Path data models
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8. Gap Analysis
The way in which 3GPP is characterizing the slice endpoint (i.e.,
EP_Transport) is based on Layer 3 information (e.g., the IP Address).
However the information provided seems not to be sufficient for
instructing the IETF Network Slice Controller for the realization of
the IETF NEtwork Slice. For instance, some basic information such as
the mask associated to the IP address of the EP_Transport is not
specified, as well as other kind of parameters like the connection
MTU or the connectivity type (unicast, multicast, etc). More
sophisticated information could be required as well, like the level
of isolation or protection necessary for the intended slice.
In the case in which the 3GPP managed function runs on a purpose-
specific network element, the IP address specified in the
EP_Transport IOC serves as reference to identify the CE endpoint,
assuming the endpoint of the CE has been configured with that IP
address. With that information (together with the logical interface
ID) should be sufficient for the IETF NSC to identify the counterpart
endpoint at the PE side, and configuring it accordingly (e.g., with a
compatible IP address) for setting up the slice end-to-end.
Similarly, the next hop information in EP_Transport can help validate
the end-to-end slice between PE endpoints.
In the case in which the 3GPP managed function is instantiated as a
virtualized network function, the direct association between the IP
address of EP_Transport and the actual endpoint mapped at the CE is
not so clear. It could be the case, for instance when the
virtualized network function is instantiated at the internal of a
data center, that the CE facing the PE is far from the point where
the function is deployed, being that connectivity extended through
the internals of the data center (or by some internal configuration
of a virtual switch in a server). In these situations additional
information is needed for accomplishing the end-to-end connection.
At the same time, [TS28.541] IOC contains useful parameters to be
used in IETF Network Slice creation mechanism and enreaching IETF
Network Slice model. The following parameters may be suggested as a
candidates to the correlation of the IETF Network Slice parameters
and IETF Network Slice model enreachments:
* For the latency, dLThptPerSliceSubnet, uLThptPerSliceSubnet,
reliability and delayTolerance attributes, the following NRM apply
(with reference to the section in that specification):
- CNSliceSubnetProfile (section 6.3.22 in [TS28.541])
- RANSliceSubnetProfile (section 6.3.23 in [TS28.541])
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- TopSliceSubnetProfile (section 6.3.24 in [TS28.541])
* For the qosProfile attribute, the NRM which applies is
EP_Transport (detailed in section 6.3.17 in [TS28.541])
9. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
10. Security Considerations
11. Acknowledgements
The work of Luis M. Contreras has been partially funded by the
European Commission under Horizon 2020 project Int5Gent (grant
agreement 957403.
Thanks to Philip Eardley (philip.eardley@bt.com) for his contribution
to this document.
12. Contributors
Jose Ordonez-Lucena
Telefonica
Ronda de la Comunicacion,
s/n Sur-3 building,
3rd floor Madrid 28050 Spain
Email: joseantonio.ordonezlucena@telefonica.com
Ran Pang
China Unicom
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Email: pangran@chinaunicom.cn
Liuyan Han
China Mobile
Email: hanliuyan@chinamobile.com
Jaehwan Jin
LG U+
Email: daenamu1@lguplus.co.kr
Jeff Tantsura
Microsoft
Email: jefftant.ietf@gmail.com
Shunsuke Homma
NTT 3-9-11,
Midori-cho Musashino-shi,
Tokyo 180-8585 Japan
Email: shunsuke.homma.ietf@gmail.com
Xavier de Foy
InterDigital Inc.
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Canada
Email: Xavier.Defoy@InterDigital.com
Kiran Makhijani
Futurewei Networks
US
Email: kiranm@futurewei.com
Hannu Flinck
Nokia
Finland
Email: hannu.flinck@nokia-bell-labs.com
Rainer Schatzmayr
Deutsche Telekom
Germany
Email: rainer.schatzmayr@telekom.de
Ali Tizghadam
TELUS Communications Inc
Canada
Email: ali.tizghadam@telus.com
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Christopher Janz
Huawei Canada
Canada
Email: christopher.janz@huawei.com
Henry Yu
Huawei Canada
Canada
Email: henry.yu1@huawei.com
13. References
13.1. Normative References
[GST] "Generic Network Slice Template",
<https://www.gsma.com/newsroom/all-documents/generic-
network-slice-template-v2-0/>.
[I-D.ietf-dmm-tn-aware-mobility]
Chunduri, U., Kaippallimalil, J., Bhaskaran, S., Tantsura,
J., and P. Muley, "Mobility aware Transport Network
Slicing for 5G", Work in Progress, Internet-Draft, draft-
ietf-dmm-tn-aware-mobility-05, 19 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-dmm-tn-
aware-mobility-05>.
[I-D.ietf-teas-ietf-network-slice-definition]
Rokui, R., Homma, S., Makhijani, K., Contreras, L. M., and
J. Tantsura, "Definition of IETF Network Slices", Work in
Progress, Internet-Draft, draft-ietf-teas-ietf-network-
slice-definition-01, 22 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slice-definition-01>.
[I-D.ietf-teas-ietf-network-slice-nbi-yang]
Wu, B., Dhody, D., Rokui, R., Saad, T., Han, L., and J.
Mullooly, "IETF Network Slice Service YANG Model", Work in
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Progress, Internet-Draft, draft-ietf-teas-ietf-network-
slice-nbi-yang-03, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slice-nbi-yang-03>.
[I-D.ietf-teas-ietf-network-slice-use-cases]
Contreras, L. M., Homma, S., Ordonez-Lucena, J. A.,
Tantsura, J., and H. Nishihara, "IETF Network Slice Use
Cases and Attributes for the Slice Service Interface of
IETF Network Slice Controllers", Work in Progress,
Internet-Draft, draft-ietf-teas-ietf-network-slice-use-
cases-01, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slice-use-cases-01>.
[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
K., Contreras, L. M., and J. Tantsura, "A Framework for
IETF Network Slices", Work in Progress, Internet-Draft,
draft-ietf-teas-ietf-network-slices-19, 21 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slices-19>.
[I-D.srld-teas-5g-slicing]
Szarkowicz, K. G., Roberts, R., Lucek, J., Drake, J.,
Boucadair, M., Contreras, L. M., Bykov, I., Rokui, R.,
Jalil, L., Setyawan, B. D., Dhamija, A., and M. Amani, "A
Realization of IETF Network Slices for 5G Networks Using
Current IP/ MPLS Technologies", Work in Progress,
Internet-Draft, draft-srld-teas-5g-slicing-05, 13 January
2023, <https://datatracker.ietf.org/doc/html/draft-srld-
teas-5g-slicing-05>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[TS23501] "3GPP TS23.501",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
[TS28530] "3GPP TS28.530",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3273>.
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[TS28531] "3GPP TS28.531",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3274>.
[TS28541] "3GPP TS 28.541",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3400>.
[ZSM003] "ETSI ZSM003",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
13.2. Informative References
[InfRef] "", 2004.
Appendix A. An Appendix
Authors' Addresses
Xuesong Geng
Huawei Technologies
Email: gengxuesong@huawei.com
Luis M. Contreras
Telefonica
Email: luismiguel.contrerasmurillo@telefonica.com
Reza Rokui
Ciena
Email: rrokui@ciena.com
Jie Dong
Huawei Technologies
Email: jie.dong@huawei.com
Ivan Bykov
Ribbon Communications
Email: Ivan.Bykov@rbbn.com
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