Internet DRAFT - draft-ietf-teas-use-cases-sf-aware-topo-model
draft-ietf-teas-use-cases-sf-aware-topo-model
Network Working Group I. Bryskin
Internet-Draft Huawei Technologies
Intended status: Informational X. Liu
Expires: December 6, 2018 Jabil
J. Guichard
Y. Lee
Huawei Technologies
L. Contreras
Telefonica
D. Ceccarelli
Ericsson
J. Tantsura
Nuage Networks
June 4, 2018
Use Cases for SF Aware Topology Models
draft-ietf-teas-use-cases-sf-aware-topo-model-00
Abstract
This document describes some use cases that benefit from the network
topology models that are service and network function aware.
Status of This Memo
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This Internet-Draft will expire on December 6, 2018.
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Copyright (c) 2018 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Exporting SF/NF Information to Network Clients and Other
Network SDN Controllers . . . . . . . . . . . . . . . . . . . 4
4. Flat End-to-end SFCs Managed on Multi-domain Networks . . . 5
5. Managing SFCs with TE Constraints . . . . . . . . . . . . . . 6
6. SFC Protection and Load Balancing . . . . . . . . . . . . . . 7
7. Network Clock Synchronization . . . . . . . . . . . . . . . . 10
8. Client - Provider Network Slicing Interface . . . . . . . . . 11
9. Dynamic Assignment of Regenerators for L0 Services . . . . . 11
10. Dynamic Assignment of OAM Functions for L1 Services . . . . . 12
11. SFC Abstraction and Scaling . . . . . . . . . . . . . . . . . 13
12. Dynamic Compute/VM/Storage Resource Assignment . . . . . . . 13
13. Application-aware Resource Operations and Management . . . . 14
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
15. Security Considerations . . . . . . . . . . . . . . . . . . . 15
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
17.1. Normative References . . . . . . . . . . . . . . . . . . 16
17.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
Normally network connectivity services are discussed as a means to
inter-connect various abstract or physical network topological
elements, such as ports, link termination points and nodes
[I-D.ietf-teas-yang-te-topo] [I-D.ietf-teas-yang-te]. However, the
connectivity services, strictly speaking, interconnect not the
network topology elements per-se, rather, located on/associated with
the various network and service functions [RFC7498] [RFC7665]. In
many scenarios it is beneficial to decouple the service/network
functions from the network topology elements hosting them, describe
them in some unambiguous and identifiable way (so that it would be
possible, for example, to auto-discover on the network topology
service/network functions with identical or similar functionality and
characteristics) and engineer the connectivity between the service/
network functions, rather than between their current topological
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locations. The purpose of this document is to describe some use
cases that could benefit from such an approach.
2. Terminology
o Network Function (NF): A functional block within a network
infrastructure that has well-defined external interfaces and well-
defined functional behaviour [ETSI-NFV-TERM]. Such functions
include message router, CDN, session border controller, WAN
cceleration, DPI, firewall, NAT, QoE monitor, PE router, BRAS, and
radio/fixed access network nodes.
o Network Service: Composition of Network Functions and defined by
its functional and behavioural specification. The Network Service
contributes to the behaviour of the higher layer service, which is
characterized by at least performance, dependability, and security
specifications. The end-to-end network service behaviour is the
result of the combination of the individual network function
behaviours as well as the behaviours of the network infrastructure
composition mechanism [ETSI-NFV-TERM].
o Service Function (SF): A function that is responsible for specific
treatment of received packets. A service function can act at
various layers of a protocol stack (e.g., at the network layer or
other OSI layers). As a logical component, a service function can
be realized as a virtual element or be embedded in a physical
network element. One or more service functions can be embedded in
the same network element. Multiple occurrences of the service
function can exist in the same administrative domain. A non-
exhaustive list of service functions includes: firewalls, WAN and
application acceleration, Deep Packet Inspection (DPI), server
load balancers, NAT44 [RFC3022], NAT64 [RFC6146], HTTP header
enrichment functions, and TCP optimizers. The generic term "L4-L7
services" is often used to describe many service functions
[RFC7498].
o Service Function Chain (SFC): A service function chain defines an
ordered or partially ordered set of abstract service functions and
ordering constraints that must be applied to packets, frames, and/
or flows selected as a result of classification. An example of an
abstract service function is a firewall. The implied order may
not be a linear progression as the architecture allows for SFCs
that copy to more than one branch, and also allows for cases where
there is flexibility in the order in which service functions need
to be applied. The term "service chain" is often used as
shorthand for "service function chain" [RFC7498].
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o Connectivity Service: Any service between layer 0 and layer 3
aiming at delivering traffic among two or more end customer edge
nodes connected to provider edge nodes. Examples include L3VPN,
L2VPN etc.
o Link Termination Point (LTP): A conceptual point of connection of
a TE node to one of the TE links, terminated by the TE node.
Cardinality between an LTP and the associated TE link is 1:0..1
[I-D.ietf-teas-yang-te-topo].
o Tunnel Termination Point (TTP): An element of TE topology
representing one or several of potential transport service
termination points (i.e. service client adaptation points such as
WDM/OCh transponder). TTP is associated with (hosted by) exactly
one TE node. TTP is assigned with the TE node scope unique ID.
Depending on the TE node's internal constraints, a given TTP
hosted by the TE node could be accessed via one, several or all TE
links terminated by the TE node [I-D.ietf-teas-yang-te-topo].
3. Exporting SF/NF Information to Network Clients and Other Network SDN
Controllers
In the context of Service Function Chain (SFC) orchestration one
existing problem is that there is no way to formally describe a
Service or Network Function in a standard way (recognizable/
understood by a third party) as a resource of a network topology
node.
One implication of this is that there is no way for the orchestrator
to give a network client even a ball-park idea as to which network's
SFs/NFs are available for the client's use/control and where they are
located in the network even in terms of abstract topologies/virtual
networks configured and managed specifically for the client.
Consequently, the client has no say on how the SFCs provided for the
client by the network should be set up and managed (which SFs are to
be used and how they should be chained together, optimized,
manipulated, protected, etc.).
Likewise, there is no way for the orchestrator to export SF/NF
information to other network controllers. The SFC orchestrator may
serve, for example, a higher level controller (such as Network
Slicing Orchestrator), with the latter wanting at least some level of
control as to which SFs/NFs it wants on its SFCs and how the Service
Function Paths (SFPs) are to be routed and provisioned, especially,
if it uses services of more than one SFC orchestrator.
The issue of exporting of SF/NF information could be addressed by
defining a model, in which formally described/recognizable SF/NF
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instances are presented as topological elements, for example, hosted
by TE, L3 or L2 topology nodes (see Figure 1). The model could
describe whether, how and at what costs the SFs/NFs hosted by a given
node could be chained together, how these intra-node SFCs could be
connected to the node's Service Function Forwarders (SFFs, entities
dealing with SFC NSHs and metadata), and how the SFFs could be
connected to the node's Tunnel and Link Termination Points (TTPs and
LTPs) to chain the intra-node SFCs across the network topology.
The figure is available in the PDF format.
Figure 1: SF/NF aware TE topology
4. Flat End-to-end SFCs Managed on Multi-domain Networks
SFCs may span multiple administrative domains, each of which
controlled by a separate SFC controller. The usual solution for such
a scenario is the Hierarchical SFCs (H-SFCs), in which the higher
level orchestrator controls only SFs located on domain border nodes.
Said higher level SFs are chained together into higher level SFCs via
lower level (intra-domain) SFCs provisioned and controlled
independently by respective domain controllers. The decision as to
which higher level SFCs are connected to which lower level SFCs is
driven by packet re-classification every time the packet enters a
given domain. Said packet re-classification is a very time-consuming
operation. Furthermore, the independent nature of higher and lower
level SFC control is prone to configuration errors, which may lead to
long lasting loops and congestions. It is highly desirable to be
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able to set up and manage SFCs spanning multiple domains in a flat
way as far as the data plane is concerned (i.e. with a single packet
classification at the ingress into the multi-domain network but
without re-classifications on domain ingress nodes).
One way to achieve this is to have the domain controllers expose SF/
NF- aware topologies, and have the higher level orchestrator operate
on the network-wide topology, the product of merging of the
topologies catered by the domain controllers. This is similar in
spirit to setting up, coordinating and managing the transport
connectivity (TE tunnels) on a multi-domain multi-vendor transport
network.
5. Managing SFCs with TE Constraints
Some SFCs require per SFC link/element and end-to-end TE constrains
(bandwidth, delay/jitter, fate sharing/diversity. etc.). Said
constraints could be ensured via carrying SFPs inside overlays that
are traffic engineered with the constrains in mind. A good analogy
would be orchestrating delay constrained L3 VPNs. One way to support
such L3 VPNs is to carry MPLS LSPs interconnecting per-VPN VRFs
inside delay constrained TE tunnels interconnecting the PEs hosting
the VRFs.
_
Figure 2: L3 VPN with delay constraints
Planning, computing and provisioning of TE overlays to constrain
arbitrary SFCs, especially those that span multiple administrative
domains with each domain controlled by a separate controller, is a
very difficult challenge. Currently it is addressed by pre-
provisioning on the network of multiple TE tunnels with various TE
characteristics, and "nailing down" SFs/NFs to "strategic" locations
(e.g. nodes terminating many of such tunnels) in a hope that an
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adequate set of tunnels could be found to carry the SFP of a given
TE-constrained SFC. Such an approach is especially awkward in the
case when some or all of the SFs/NFs are VNFs (i.e. could be
instantiated at multiple network locations).
SF/NF-aware TE topology model in combination with TE tunnel model
will allow for the network orchestrator (or a client controller) to
compute, set up and manipulate the TE overlays in the form of TE
tunnel chains (see Figure 3).
Said chains could be duel-optimized compromising on optimal SF/NF
locations with optimal TE tunnels interconnecting them. The TE
tunnel chains (carrying multiple similarly constrained SFPs) could be
adequately constrained both at individual TE tunnel level and at the
chain end-to-end level.
_
Figure 3: SFC with TE constraints
6. SFC Protection and Load Balancing
Currently the combination of TE topology & tunnel models offers to a
network controller various capabilities to recover an individual TE
tunnel from network failures occurred on one or more network links or
transit nodes on the TE paths taken by the TE tunnel's connection(s).
However, there is no simple way to recover a TE tunnel from a failure
affecting its source or destination node. SF/NF-aware TE topology
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model can decouple the association of a given SF/NF with its location
on the network topology by presenting multiple, identifiable as
mutually substitutable SFs/NFs hosted by different TE topology nodes.
So, for example, if it is detected that a given TE tunnel destination
node is malfunctioning or has gone out of service, the TE tunnel
could be re-routed to terminate on a different node hosting
functionally the same SFs/NFs as ones hosted by the failed node (see
Figures 6).
This is in line with the ACTN edge migration and function mobility
concepts [I-D.ietf-teas-actn-framework]. It is important to note
that the described strategy works much better for the stateless SFs/
NFs. This is because getting the alternative stateful SFs/NFs into
the same respective states as the current (i.e. active, affected by
failure) are is a very difficult challenge.
_
Figure 4: SFC recovery: SF2 on node NE1 fails
At the SFC level the SF/NF-aware TE topology model can offer SFC
dynamic restoration capabilities against failed/malfunctioning SFs/
NFs by identifying and provisioning detours to a TE tunnel chain, so
that it starts carrying the SFC's SFPs towards healthy SFs/NFs that
are functionally the same as the failed ones. Furthermore, multiple
parallel TE tunnel chains could be pre-provisioned for the purpose of
SFC load balancing and end-to-end protection. In the latter case
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said parallel TE tunnel chains could be placed to be sufficiently
disjoint from each other.
_
Figure 5: SFC recovery: SFC SF1-SF2-SF6 is recovered after SF2 on
node N1 has failed
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_
Figure 6: SFC recovery: SFC SF1-SF2-SF6 is recovered after node N1
has failed
7. Network Clock Synchronization
Many current and future network applications (including 5g and IoT
applications) require very accurate time services (PTP level, ns
resolution). One way to implement the adequate network clock
synchronization for such services is via describing network clocks as
NFs on an NF-aware TE topology optimized to have best possible delay
variation characteristics. Because such a topology will contain
delay/delay variation metrics of topology links and node cross-
connects, as well as costs in terms of delay/delay variation of
connecting clocks to hosting them node link and tunnel termination
points, it will be possible to dynamically select and provision bi-
directional time-constrained deterministic paths or trees connecting
clocks (e.g. grand master and boundary clocks) for the purpose of
exchange of clock synchronization information. Note that network
clock aware TE topologies separately provided by domain controllers
will enable multi-domain network orchestrator to set up and
manipulate the clock synchronization paths/trees spanning multiple
network domains.
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8. Client - Provider Network Slicing Interface
3GPP defines network slice as "a set of network functions and the
resources for these network functions which are arranged and
configured, forming a complete logical network to meet certain
network characteristics" [I-D.defoy-netslices-3gpp-network-slicing]
[_3GPP.28.801]. Network slice could be also defined as a logical
partition of a provider's network that is owned and managed by a
tenant. SF/NF-aware TE topology model has a potential to support a
very important interface between network slicing clients and
providers because, on the one hand, the model can describe
holistically and hierarchically the client's requirements and
preferences with respect to a network slice functional, topological
and traffic engineering aspects, as well as of the degree of resource
separation/ sharing between the slices, thus allowing for the client
(up to agreed upon extent) to dynamically (re-)configure the slice or
(re-)schedule said (re-)configurations in time, while, on the other
hand, allowing for the provider to convey to the client the slice's
operational state information and telemetry the client has expressed
interest in.
9. Dynamic Assignment of Regenerators for L0 Services
On large optical networks, some of provided to their clients L0
services could not be provisioned as single OCh trails, rather, as
chains of such trails interconnected via regenerators, such as 3R
regenerators. Current practice of the provisioning of such services
requires configuration of explicit paths (EROs) describing identity
and location of regenerators to be used. A solution is highly
desirable that could:
o Identify such services based, for example, on optical impairment
computations;
o Assign adequate for the services regenerators dynamically out of
the regenerators that are grouped together in pools and
strategically scattered over the network topology nodes;
o Compute and provision supporting the services chains of optical
trails interconnected via so selected regenerators, optimizing the
chains to use minimal number of regenerators, their optimal
locations, as well as optimality of optical paths interconnecting
them;
o Ensure recovery of such chains from any failures that could happen
on links, nodes or regenerators along the chain path.
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NF-aware TE topology model (in this case L1 NF-aware L0 topology
model) is just the model that could provide a network controller (or
even a client controller operating on abstract NF-aware topologies
provided by the network) to realize described above computations and
orchestrate the service provisioning and network failure recovery
operations (see Figure 7).
_
Figure 7: Optical tunnel as TE-constrained SFC of 3R regenerators.
Red trail (not regenerated) is not optically reachable, but blue
trail (twice regenerated) is
10. Dynamic Assignment of OAM Functions for L1 Services
OAM functionality is normally managed by configuring and manipulating
TCM/MEP functions on network ports terminating connections or their
segments over which OAM operations, such as performance monitoring,
are required to be performed. In some layer networks (e.g.
Ethernet) said TCMs/MEPs could be configured on any network ports.
In others (e.g. OTN/ODUk) the TCMs/MEPs could be configured on some
(but not all network ports) due to the fact that the OAM
functionality (i.e. recognizing and processing of OAM messages,
supporting OAM protocols and FSMs) requires in these layer networks
certain support in the data plane, which is not available on all
network nodes. This makes TCMs/MEPs good candidates to be modeled as
NFs. This also makes TCM/MEP aware topology model a good basis for
placing dynamically an ODUk connection to pass through optimal OAM
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locations without mandating the client to specify said locations
explicitly.
_
Figure 8: Compute/storage resource aware topology
11. SFC Abstraction and Scaling
SF/NF-aware topology may contain information on native SFs/NFs (i.e.
SFs/NFs as known to the provider itself) and/or abstract SFs/NFs
(i.e. logical/macro SFs/NFs representing one or more SFCs each made
of native and/or lower level abstract SFs/NFs). As in the case of
abstracting topology nodes, abstracting SFs/NFs is hierarchical in
nature - the higher level of SF/NF-aware topology, the "larger"
abstract SFs/NFs are, i.e. the larger data plane SFCs they represent.
This allows for managing large scale networks with great number of
SFs/NFs (such as Data Center interconnects) in a hierarchical, highly
scalable manner resulting in control of very large number of flat in
the data plane SFCs that span multiple domains.
12. Dynamic Compute/VM/Storage Resource Assignment
In a distributed data center network, virtual machines for compute
resources may need to be dynamically re-allocated due to various
reasons such as DCI network failure, compute resource load balancing,
etc. In many cases, the DCI connectivity for the source and the
destination is not predetermined. There may be a pool of sources and
a pool of destination data centers associated with re-allocation of
compute/VM/storage resources. There is no good mechanism to date to
capture this dynamicity nature of compute/VM/storage resource
reallocation. Generic Compute/VM/Storage resources can be described
and announced as a SF, where a DC hosting these resources can be
modeled as an abstract node. Topology interconnecting these abstract
nodes (DCs) in general is of multi-domain nature. Thus, SF-aware
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topology model can facilitate a joint optimization of TE network
resources and Compute/VM/Storage resources and solve Compute/VM/
Storage mobility problem within and between DCs (see Figure 8).
13. Application-aware Resource Operations and Management
Application stratum is the functional grouping which encompasses
application resources and the control and management of these
resources. These application resources are used along with network
services to provide an application service to clients/end-users.
Application resources are non-network resources critical to achieving
the application service functionality. Examples of application
resources include: caches, mirrors, application specific servers,
content, large data sets, and computing power. Application service
is a networked application offered to a variety of clients (e.g.,
server backup, VM migration, video cache, virtual network on-demand,
5G network slicing, etc.). The application servers that host these
application resources can be modeled as an abstract node. There may
be a variety of server types depending on the resources they host.
Figure 9 shows one example application aware topology for video cache
server distribution.
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_
Figure 9: Application aware topology
14. IANA Considerations
This document has no actions for IANA.
15. Security Considerations
This document does not define networking protocols and data, hence is
not directly responsible for security risks.
16. Acknowledgements
The authors would like to thank Maarten Vissers, Joel Halpern, and
Greg Mirsky for their helpful comments and valuable contributions.
17. References
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17.1. Normative References
[RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
Service Function Chaining", RFC 7498,
DOI 10.17487/RFC7498, April 2015, <https://www.rfc-
editor.org/info/rfc7498>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015, <https://www.rfc-
editor.org/info/rfc7665>.
[ETSI-NFV-TERM]
ETSI, "Network Functions Virtualisation (NFV); Terminology
for Main Concepts in NFV", ETSI GS NFV 003 V1.2.1,
December 2014.
[I-D.ietf-teas-yang-te-topo]
Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
O. Dios, "YANG Data Model for Traffic Engineering (TE)
Topologies", draft-ietf-teas-yang-te-topo-15 (work in
progress), February 2018.
[I-D.ietf-teas-yang-te]
Saad, T., Gandhi, R., Liu, X., Beeram, V., Shah, H., and
I. Bryskin, "A YANG Data Model for Traffic Engineering
Tunnels and Interfaces", draft-ietf-teas-yang-te-14 (work
in progress), March 2018.
17.2. Informative References
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
DOI 10.17487/RFC3022, January 2001, <https://www.rfc-
editor.org/info/rfc3022>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[I-D.ietf-sfc-hierarchical]
Dolson, D., Homma, S., Lopez, D., and M. Boucadair,
"Hierarchical Service Function Chaining (hSFC)", draft-
ietf-sfc-hierarchical-08 (work in progress), April 2018.
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[I-D.defoy-netslices-3gpp-network-slicing]
Foy, X. and A. Rahman, "Network Slicing - 3GPP Use Case",
draft-defoy-netslices-3gpp-network-slicing-02 (work in
progress), October 2017.
[_3GPP.28.801]
3GPP, "Study on management and orchestration of network
slicing for next generation network", 3GPP TR 28.801
V2.0.0, September 2017,
<http://www.3gpp.org/ftp/Specs/html-info/28801.htm>.
[I-D.ietf-teas-actn-framework]
Ceccarelli, D. and Y. Lee, "Framework for Abstraction and
Control of Traffic Engineered Networks", draft-ietf-teas-
actn-framework-15 (work in progress), May 2018.
Authors' Addresses
Igor Bryskin
Huawei Technologies
EMail: Igor.Bryskin@huawei.com
Xufeng Liu
Jabil
EMail: xufeng.liu.ietf@gmail.com
Jim Guichard
Huawei Technologies
EMail: james.n.guichard@huawei.com
Young Lee
Huawei Technologies
EMail: leeyoung@huawei.com
Luis Miguel Contreras Murillo
Telefonica
EMail: luismiguel.contrerasmurillo@telefonica.com
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Daniele Ceccarelli
Ericsson
EMail: daniele.ceccarelli@ericsson.com
Jeff Tantsura
Nuage Networks
EMail: jefftant.ietf@gmail.com
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