Internet DRAFT - draft-zu-nfvrg-elasticity-vnf
draft-zu-nfvrg-elasticity-vnf
Internet Research Task Force (IRTF) Z. Qiang
Internet Draft Robert Szabo
Intended status: Informational Ericsson
Expires: September 2015 March 2, 2015
Elasticity VNF
draft-zu-nfvrg-elasticity-vnf-01.txt
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Abstract
This draft is an analysis of Network Function Virtualization (NFV)
applications based on the NFV architecture, use cases and
requirements. The purpose of this analysis is to identify any NFV
characteristics related issues. The analysis is focusing on elastic
VNF with predicable performance, reliability and security. Only the
issues which are unique to NFV are discussed in this document.
Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................3
3. Terminology....................................................4
4. Network Function Virtualization................................5
4.1. NFV Requirements..........................................5
4.2. NFV Use Cases.............................................6
4.2.1. Network Function Virtualization Infrastructure.......6
4.2.2. Telecom Network Functions Migration..................7
5. Elasticity in a Distributed Cloud..............................7
5.1. NFV Infrastructure........................................8
5.2. Elastic VNF...............................................8
5.3. VNF Forwarding Graphs.....................................9
5.4. VNF scaling across multiple NFVI PoPs....................10
6. Elasticity with Predicable Performance........................10
6.1. Predicable Performance...................................10
6.2. Hardware virtualization features.........................11
6.3. Network Overlay..........................................12
7. Elasticity with Reliability...................................12
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8. Elasticity with Security......................................13
9. Security Considerations.......................................13
10. IANA Considerations..........................................13
11. References...................................................13
11.1. Normative References....................................13
11.2. Informative References..................................13
12. Acknowledgments..............................................14
1. Introduction
Network Functions Virtualization (NFV) is a network architecture
concept that proposes using IT virtualization related technologies,
to virtualize entire classes of network node functions into building
blocks that may be connected, or chained, together to create
communication services. NFV aims to transform the traditional
operator architect networks by evolving standard IT virtualization
technology to consolidate network equipment types onto industry
standard high volume services, switches and storage, which could be
located in a variety of NFV Infrastructure Point of Presences (NFVI
PoPs) including Data Center (DC), network nodes and in end user
premises. It is also indicated that an important part of controlling
the NFV environment should be done through automation network
management and orchestration.
This draft is an analysis of NFV applications based on the NFV
architecture, use cases and requirements. The purpose of this
analysis is to identify any NFV characteristics related issues. The
analysis is focusing on elastic VNFs with predicable performance,
reliability and security. Only the issues which are unique to NFV
are discussed in this document. The intention is to identify what is
missing, and what is needed to be addressed in terms of protocol /
solution specifications which may be the potential work for IETF.
The reader is assumed to be familiar with the terminology as defined
in the NFV document [nfv-tem].
2. Conventions used in this document
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].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
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3. Terminology
This document uses the same terminology as found in the NFV end to
end architecture [nfv-tem]:
Network Function Consumer: a Network Function Consumer (NFC) is the
consumer of virtual network functions. It can be either an
individual user, home user or the enterprise user.
NFV: network function virtualization. NFV technology uses the
commodity servers to replace the dedicated hardware boxes for the
network functions, for example, home gateway, enterprise access
router, carrier grade NAT and etc. So as to improve the
reusability, allow more vendors into the market, and reduce time to
market. NFV architecture includes a NFV Control and Management Plane
(orchestrator) to manage the virtual network functions and the
infrastructure resources.
NF: A functional building block within an operator's network
infrastructure, which has well-defined external interfaces and a
well-defined functional behavior. Note that the totality of all
network functions constitutes the entire network and services
infrastructure of an operator/service provider. In practical terms,
a Network Function is today often a network node or physical
appliance.
Network Function Provider: a Network Function Provider (NFP)
provides virtual network function software.
Network Service Provider (NSP): a company or organization that
provides a network service on a commercial basis to third parties. A
network service is a composition of network functions and defined by
its functional and behavior specification. The NSP operates the NFV
Control Plane.
NFV Infrastructure (NFVI): NFV Infrastructure indicates the
computing, storage and network resources to implement the virtual
network function. High performance acceleration platform is also
part of it.
VNF: virtual network function, an implementation of an executable
software program that constitutes the whole or a part of an NF that
can be deployed on a virtualization infrastructure.
VM: virtual machines, a program and configuration of part of a host
computer server. Note that the Virtual Machine inherits the
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properties of its host computer server e.g. location, network
interfaces.
NFV Control and Management Plane (NFVCMP): a NFV Control and
Management Plane is operated by a NSP and orchestrates the NFV NFV
Overview
4. Network Function Virtualization
4.1. NFV Requirements
There are many virtualization requirements described by NFV in [nfv-
req]. The followings are highlights of a few NFV requirements which
are related to this document:
- Portability: VNF portability is a reasonable generic
virtualization requirement. It allows VNF mobility across
different but standard multi-vendor environment. However, moving a
VNF within the NFV framework with the Service Level Specification
(SLA) requirements including performance, reliability and security
could be a challenge.
- Performance: Virtualization adds additional processing overhead
and increases the latency. For latency-sensitive VNFs, it is a big
concern for NFV on how to achieve predictable low-latency
performance.
- Elasticity: NFV elasticity requirement allows the VNF to be scaled
within NFVI. Within the NFV framework, it is important to support
VNF scaling with the SLA requirements including performance,
reliability and security.
- Resiliency: NFV resiliency is a must requirement for NFV network,
including both the control plane and data plane. Necessary
mechanisms must be provided to improve the service availability
and fault management.
- Security: The traditional telecom network functions are developed
in dedicated hardware located in an isolated network. Security is
provided by underlay network. When moving VNF into a DC network
with shared Infrastructure, security becomes a big concern.
- Service Continuity: At VNF failure over, migration, mobility, and
upgrading, service downtime may not be avoided. In NFV, service
continuity must be supported which means the provided service must
be restored at the VNF instance updated / replaced / recovered.
This procedure includes the restoration of any ongoing data
sessions. And it shall be transparent to the user of NFV service.
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4.2. NFV Use Cases
Multiple use cases are described by NFV in [nfv-uc]. The followings
are a highlight of the NFV use cases.
4.2.1. Network Function Virtualization Infrastructure
Network Function Virtualization Infrastructure as a Service
(NFVIaaS), Virtual Network Function as a Service (VNFaaS) and
Virtual Network Platform as a Service (VNPaaS) are the NFV use cases
which describe how the telecom operators would like to build up
their telecom cloud infrastructure using virtualization.
Network Function Virtualization Infrastructure (NFVI) is the
totality of all hardware and software components which build up the
environment in which VNFs are deployed. The NFVI can span across
several locations. The network providing connectivity between these
locations is regarded to be part of the NFVI.
NFVIaaS is a generic IaaS plus NaaS requirement which allows the
telecom operator to build up a VNF cloud on top of their own DCs
Infrastructure and any external DCs Infrastructure. This will allow
a telecom operator to migrate some of its network functions into a
3rd party DC when it is needed. Furthermore, a larger telecom
operator may have multiple DCs in different geography locations. The
operator may want to setup multiple virtual data center (vDC), where
each vDC may cross several of its physical DCs geography locations.
Each vDC is defined for providing one specific function, e.g. Telco
Cloud.
VNFaaS is more focusing on enterprise network which may have its own
cloud infrastructure with some specific services / applications
running. VNFaaS allows the enterprise to merge and/or extend its
specific services / applications into a 3rd party commercial DC
provided by a telecom operator. With this VNFaaS, the enterprise
does not need to manage and control the NFVI or the VNF. However,
NFV Performance & portability considerations will apply to
deployments that strive to meet high performance and low latency
considerations.
With VNPaaS, the mobile network traffic, including WiFi traffic, is
routed based on the APN to a specific packet data service server
over the mobile packet core network. Applications running at the
packet data service server may be provided by the enterprise. And it
is possible to have an interface to route the traffic into an
enterprise network. But the infrastructure hosting the application
is fully under controlled by the operator. However, the enterprise
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has full admin control of the application and needs to apply all
configurations on its own, potentially via a vDC like management
interface with support of the hosting operator.
All the above use cases need solutions for the operator to share the
infrastructure resources with 3rd parties. Therefore cross domain
orchestration with access control is needed. Besides, the
infrastructure resource management needs to provide a mechanism to
isolate the traffic, not only based on the traffic type, but also
from different operators and enterprises.
4.2.2. Telecom Network Functions Migration
Virtualization of telecom network functions, including Mobile Core
Network functions, IMS functions, Mobile base station functions,
Content Delivery Networks (CDN) functions, Home Environment
functions, and Fixed Access Network functions, are described in the
NFV use case document [nfv-uc]. In additional, VNF forwarding Graphs
is another use case which describes how the user data packets are
forwarded by traversing more than one operator service chain
functions, such as DPI, Firewall, Content Filtering, before reaching
the service server.
Migrate the telecom functions includes moving the control plane,
data plane and service network into a cloud based network and using
cloud based protocol to control the data plane. Service continuity,
network security, service availability, resiliency in both control
plane and data plane must be ensured at this migration.
5. Elasticity in a Distributed Cloud
Today the usage of personal devices, e.g. smartphones, for internet
service traffic, telecom specific service access, and accessing the
corporate network, is increased significantly. At the same time,
telecom operators are under pressure to accommodate the increased
service traffic in a fine-grained manner. Services provided by
telecom network must be done in an environment of increased
security, compliance, and auditing requirements, along with traffic
load may be changed dramatically overtime. Providing self-service
provisioning in telecom cloud requires elastic scaling of the VNF
based on the dynamic service traffic load and resource management
e.g. computing, storage, and networking.
The existing telecom network functions may not be cloud technologies
ready yet. Most of the NFV functions are stateful and running on
either specific hardware or a big VM. It is not designed to tolerate
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any system failure in many VMs. The network functions are very
difficult in term of configuration, scale updating, etc.
Re-engineering may be needed for virtualization enabling, e.g.
software adaption for software and hardware decoupling. For cloud
technologies readiness, telecom network functions need to be re-
designed to run on small VMs with multiple instances which can
provide higher application availability. Such VMs may be stateless
in operations or may need to support state migration (e.g., OpenNF
http://opennf.cs.wisc.edu/). With cloud ready network functions,
applications' dynamic scaling can be achieved by adding more VMs
into the service.
Virtualization provides the elasticity ability to scale up / down,
scale out / in with guaranteed computational resources, security
isolation and API access for provisioning it all, without any of the
overhead of managing physical servers. However, there are still many
optimizations which can be used to avoid the increasingly overhead.
5.1. NFV Infrastructure
Virtualized Network Function (VNF) is an implementation of a network
function that can be deployed on Network Function Virtualization
Infrastructure (NFVI).
For a large telecom operator, multiple NFVI Point of Presences (NFVI
PoPs) may be created according to multiple physical data centers. As
NFVI PoPs may be located in different geography locations,
networking characteristics should be taken into account when
selecting an NFVI PoP to host a VNF.
5.2. Elastic VNF
In many cases, a VNF may not be designed for scaling up/down. As
scaling up/down may require a restart of the VNF which the state
data may be lost. In that case either stateless operation is needed,
or the support of state information migration procedure is required,
which will increase the complexities of the VNF implementation.
Normally a VNF may be capable for scaling in/out only. Such VNF is
designed running on top of a small VM and grouped as a pool of one
VNF function.
VNF capacity may be limited if it only can be scaled within one NFVI
PoP, e.g., within one DC in a geography location. As an NFVI which
may be crossing multiple NFVI PoPs (or data center)s, it is possible
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to scale an elastic VNF crossing different network zones if it is
needed. At cross DC scaling, the result is that the new VNF instance
may be placed at a remote cloud location. It is a must requirement
to provide the same level of SLA including performance, reliability
and security.
5.3. VNF Forwarding Graphs
In NFV network, a VNF Forwarding Graph (VNF FG) (an application) may
consist of multiple VNFs, where each VNF may consist of multiple VNF
instances. Normally the VNFs are working as such that the services
provided by the VNFs may need to process the user data packets with
several selected VNF instances before delivering it to its
destination
For instance, when mobile users setup a PDN connection for IMS
services, there are multiple network entities involved along the PDN
connection, including eNB, Serving GW, PDN GW, P-CSCF, S-CSCF, etc.
Another example is service function chaining, where a service chain
is referring to one or more service processing functions in a
specific order which are chained to provide a composite service.
In telecom cloud, a service session may traverse multiple stateful
and stateless VNF functions of a VNF set. And with an NFVI
consisting of multiple NFVI PoPs, it may be crossing multiple DCs.
In such cloud, an incoming data packet may be processed by multi-VNF
instance before delivering to the final destination. Therefore the
east-west traffic (i.e. data traffic between VNFs within the DC) is
much heavier comparing to the north-south traffic (i.e. data traffic
in/out from the DC).
When placing VNF Forwarding Graphs, it is better spread the VNF
components across many NFVI PoPs, which may give a better
availability. However, multiple NFVI PoPs may also increases the
network latency, which can be considerably big compared to latencies
within a single NFVI PoP. Therefore, the whole VNF Forwarding Graph
should be taken into account instead of a single VNF component
during orchestration. Furthermore, during VNF scaling, dependencies
(interconnection) with other service instances of the VNF Forwarding
Graph shall also be considered.
When scaling, VNFs are not scaled only in relation to compute and
storage PoPs. VNF instances may need to be grouped together
according to the VNF FG and subjected to auto-scaling techniques to
the entire group. The scaling policies, e.g., ratio between the
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different VNFs, need to be applied on the VNF FG in aggregate to
control the scaling process.
5.4. VNF scaling across multiple NFVI PoPs
Since in general, a VNF is part of a VNF Forwarding Graph (or a
service function chain), meaning the data traffic may traverse
multiple stateful and stateless VNF functions in sequence. When some
VNF instances of a given service function chain are placed / scaled
out in a distant cloud execution, the service traffic may have to
traverse multiple VNF instances which are located in multiple
physical locations. In the worst case, the data traffic may ping-
pong between multiple physical locations.
Therefore it is important to take the whole service function chain's
performance into consideration when placing and scaling one of its
VNF instance. Network and cloud resources need mutual considerations
[unify1].
| Incoming traffic
+-----+------------+ +--------------------+
| | NFVI-PoP1 | | NFVI-PoP2 |
| V | | +-------+ |
| +-------+ +----+ +----+ | VNF-2 | |
| | VNF-1 +----->| GW |----->| GW |----->| | |
| +-------+ | | | | | | |
| +--| |<-----| |<-----| | |
| +-------+ | +----+ +----+ +-------+ |
| | VNF-3 | <-+ | | |
| +-------+ | | |
| | | | |
+-----+------------+ +--------------------+
|
V outgoing traffic
Figure 1 a data traffic flow traversing distributed VNF cloud
6. Elasticity with Predicable Performance
6.1. Predicable Performance
High performance with low-latency VNF is expected in the NFV
framework. The NFVI metrics are related to any kind of metrics
generated by the NFVI, including not only CPU load on a VM, CPU load
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on a host, but also interrupt rate handled by the hypervisor or
network latency/packet loss.
Virtualization adds additional overhead which impacts the
performance. This additional extra distortion shall be avoided or,
at least, minimized. It is a big concern for NFV on how to achieve
predictable and low-latency performance, not only at placing a VNF
into the DC, but also at VNF scaling.
Operator may wish to run standard test and use the result to provide
KPIs of the VNF. A significant part of a VNF vendor's performance
guarantees will depend on the choice of the virtualization
technology.
Network latency may not be at the same level if the physical
connections between the servers are various. Furthermore, geography
location of the physical servers also increases the network latency.
When placing or moving a VNF, the location of other VNFs of the same
VNF set shall be considered to avoid network latency issue. For
instance, VNF-a, VNF-b, and VND-c are grouped as one VNF set. When
moving VNF-b into a new location, the network connection between the
new location and the existing location may be a concern. As the
traffic may traverse from VNF-a to VNF-b, then VND-c, moving the
VNF-b into a new location may create Ping-Pong type of traffic,
which the network latency may be doubled. The best choice would be
to move the whole VNF set into the new location instead of only one
VNF.
6.2. Hardware virtualization features
Virtualization layer adds minimal overhead and delivers a
predictable performance between a minimum and maximum threshold for
latency and jitter which are far more important. Light weight
virtualization, e.g. container or bare metal, may be considered for
performance sensitive VNF applications. In additional, hardware
virtualization features (e.g. SR-IOV) are important to be supported
in order to provide some performance improvement. Many VNF requires
direct access to the device hardware so that they can offload
functionality with throughput rates of millions of packets a second.
Another alternative, which may be more attractive for latency-
sensitive applications, is using and non-hypervisor virtualization,
including bare metal and Linux container.
Optimization to drive high-throughput network workloads associated
with such functions as traffic filtering, NATing and firewalling.
Avoiding performance bottleneck, the virtualization layer shall have
a suitably-architected I/O stack.
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6.3. Network Overlay
Network overlay adds additional overhead when forwarding the data
packets. Reference [vxlan-p] is a VXLAN performance testing report
which indicates the overlay performance is a concern. Avoiding
overlay connections may be one option which is more attractive for
latency-sensitive applications.
Furthermore, additional network latency may be added when traversing
the cross-DC overlay connections. To avoid any additional network
latency, all the functions of a VNF set may be placed in the same
low-latency network zone, e.g. same host or same DC. However, when
the capacity limitation the network zone is reached, scaling-out one
VNF into another network zone may be needed. In this case, as the
service session has to traverse the same path, the Ping-Pong traffic
between the network zones cannot be avoided. Depends on the network
overlay technologies used for the cross network zone connection, the
overhead network latency can be various. In another words, the
network performance may become unpredictable.
7. Elasticity with Reliability
NFV resiliency is a must requirement for NFV network, including both
the control plane and data plane. Necessary mechanisms must be
provided to improve the service availability and fault management.
With virtualization, the use of VNFs can pose additional challenges
on the reliability of the provided services. For a VNF instance, it
typically would not have built-in reliability mechanisms on its host
(i.e., a general purpose server). Instead, there are more factors
of risk such as software failure at various levels including
hypervisors and virtual machines, hardware failure, and instance
migration that may make a VNF instance unreliable. Even for cloud
ready NFV applications, a HA may still be needed as the storage,
load balancer may be failure. Service restoration solution is still
needed.
One alternative to improve the VNF resiliency is to take snapshot of
the VM periodically. At VNF failure, the network can restore the VM
at same or different host using the stored snapshot. However, there
is a downtime of the provided service due to the snapshot
recovering. And the downtime is much longer than the expected value
which could be tolerated by NFV. NFV has a completely different
level of reliability requirements, e.g. recovering time, comparing
to enterprise cloud applications.
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To improve the network function resiliency, some kind high
availability (HA) solutions may be needed for NFV network, which has
the potential to minimize the service downtime at failure. However,
in most of the telecom use cases, there are application level
restoration procedures available which makes the high availability
solution less important.
The VNF reliability can be achieved by eliminating any single points
of failure by creating a redundancy of resources, normally,
including enough excess capacity in the design to compensate for the
performance decline and even failure of individual resources; that
is, a group of VNF instances providing the same function works as a
network function cluster or pool, which provides protection (e.g.
failover) for the applications and therefore an increased
availability.
8. Elasticity with Security
TDB
9. Security Considerations
This is a discussion paper which provides inputs for NFV related
discussions and in itself does not introduce any new security
concerns.
10. IANA Considerations
No actions are required from IANA for this informational document.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and Overell, P.(Editors), "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, Internet Mail
Consortium and Demon Internet Ltd., November 1997.
11.2. Informative References
[nfv-arch] Network Functions Virtualization Infrastructure
Architecture Overview; GS NFV INF 001.
[nfv-rel] Network Function Virtualization (NFV) Resiliency
Requirements; ETSI GS NFV-REL 001.
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[nfv-uc] Network Function Virtualization (NFV) Use Cases; ETSI GS
NFV 001
[nfv-req] Network Function Virtualization (NFV) Virtualization
Requirements; ETSI GS NFV 004
[nfv-sec] Network Function Virtualization (NFV) NFV Security Problem
Statement; ETSI NFV-SEC 001
[nfv-tem] Network Function Virtualization (NFV) Terminology for Main
Concepts in NFV; ETSI GS NFV 003
[vxlan-p] Problem Statement for VxLAN Performance Test, draft-liu-
nvo3-ps-vxlan-perfomance, (working in progress)
[unify1] Szabo, R., Csaszar, A., Pentikousis, K., Kind, M., and D.
Daino, "Unifying Carrier and Cloud Networks: Problem
Statement and Challenges", draft-unify-nfvrg-challenges-00
(work in progress), October 2014.
12. Acknowledgments
Many people have contributed to the development of this document and
many more will probably do so before we are done with it. While we
cannot thank all contributors, some have played an especially
prominent role. The following have provided essential input: Suresh
Krishnan.
Authors' Addresses
Zu Qiang
Ericsson
8400, boul. Decarie
Ville Mont-Royal, QC,
Canada
Email: Zu.Qiang@Ericsson.com
Robert Szabo
Ericsson Research, Hungary
Irinyi Jozsef u. 4-20
Budapest 1117
Hungary
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Email: robert.szabo@ericsson.com
URI: http://www.ericsson.com/
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