Re: [vnfpool] 答复: Updated VNFPool Charter

[Hidetoshi Yokota <[e-mail]>]

Hi Ning,

Thanks for your answer and clarification and sorry for my late response.

Please see inline:

(2014/06/17 10:36), Zongning wrote:

Hi, Hidetoshi,

Thanks for reviewing the new charter. Please see inline.

-----邮件原件-----
发件人: vnfpool [mailto:[e-mail]] 代表 Hidetoshi Yokota
发送时间: 2014年6月16日 22:58
收件人: [e-mail]
主题: Re: [vnfpool] Updated VNFPool Charter

Dear Ning,

Thanks a lot for updating the charter and congratulations on BoF approval! Allow me to ask a couple of clarification questions.

o Could you clarify what "service state synchronization" is and why it is out of scope in this phase?

[Ning] Service state related to a specific function, e.g., NAT translation table, is usually synchronized between a live and backup VNF instance for stateful failover. However, this seemed to be a controversial item during the last BoF in London IETF, where we could not find multi-vendor support to standardize the state synchronization interface among their VNFs. We certainly understand that this is still a very important item for VNF failover, and will keep looking for the multi-vendor support. As mentioned in the charter, we leave it out of scope in this phase, which means we don't exclude it but will treat it as a future work.

HY> State synchronization is already identified by the PS document, so it is not appropriate just to say "out of scope in this phase". It may be possible to provide some assisting functions to the VNF even if service state synchronization is done within VNFs. At least, it should be discussed what level of synchronization can be supported and when. My proposal is: "The support of service state synchronization (e.g., its level and timing) will be determined during the course of this work"
 

- Does this service state include "networking service"? If so, active/active redundancy cannot maintain the state information in, for example, virtual routers any more, which would be a significant degrade from the current physical networks.

[Ning] See above. We agree it is important to maintain service state, but leave it out of scope until we find enough multi-vendor support.

HY> The same discussion as the above. We should at least discuss it and potential requirement may be identified apart from when to fulfill it.

- What is the relationship between service state synchronization and pool state maintenance?

[Ning] Pool states could be operational information of VNF pool itself, e.g. redundancy settings (n+k, 1:n, etc.), backup location/status, etc. They are not related to service state.

HY> Ok. Thanks.

2) Is the service control entity the NFV Orchestrator or VNF Manager or none of them in NFV terminolgy?

[Ning] I would guess it is more like the NFV Orchestrator to orchestrate the whole service, although we don’t map the VNFPool terminology to NFV terminology by purpose. :-)

3) In the last paragraph just before Goals and Milestones, it says, "the information exchanged between the VNF Pool and the SFC may..." If some information is exchanged between them, they are not independent any more, which would contradict the first sentence of this paragraph.

[Ning] Well, "independent" means that the pooling mechanisms defined in VNFPool are not coupled/dependent to SFC. But "independent" doesn't mean that they are not communicating at all. :-) So we have "information exchanged ...".

HY> Ok, I think what is important is "complementary" and "independent" could be misleading. My proposal is: In particular, the WG will work closely with the SFC WG, which is expected to provide complementary functionality to VNF Pool.

Regards,

-- 
Hidetoshi Yokota

KDDI R&D Laboratories, Inc.
e-mail:[e-mail]

Could you clarify a bit more on them please?

Regards,

--
Hidetoshi Yokota

KDDI R&D Laboratories, Inc.
e-mail:[e-mail]

(2014/06/12 12:19), Zongning wrote:

Dear all,

Based on the list discussion since we posted the last version, I have 
made some (minor) revision of the charter. The main changes are:

1)State that service state synchronization is out of scope “in this
phase”;**

2)Include VNF Pool with both virtualized and non-virtualized network 
function for further study;**

3)Explicitly state that the reference solution & gap analysis is not 
limited to RSerPool, but open to any other solutions, although no 
decision on protocols will be made in this phase;**

4)State that the linkage between SFC and VNF Pool is just like a pool 
user and a pool – nothing specified (yet);**

5)Update bullet #4 under “Questions that are raised…”, to keep it 
consistent with the idea that pooling is not visible to the service 
control entity.**

======================================================================
====

Network functions such as firewalls, load balancers, and WAN 
optimizers are conventionally deployed as specialized hardware servers 
in both network operators' networks and data center networks as the 
building blocks of the network services. There is a trend to implement 
such network functions as software instances running on general 
purpose servers, via a virtualization layer (i.e., hypervisors). These 
virtualized functions are called Virtualized Network Functions (VNFs), 
which can be used to build network services.

The use of VNFs introduces additional challenges to the reliability of 
the provided network services. A single VNF instance would typically 
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 can make a VNF 
instance unreliable.

In order to achieve higher reliability, a VNF may adopt a pooling 
mechanism, where a number of VNF instances with the same function can 
be grouped as a pool to provide the function. We call such a pool a 
VNF Pool.Conceptually, a Pool Manager is used to manage a VNF Pool, 
e.g., selects active/standby VNF instances, and potentially interacts 
with a service control entity. Such a service control entity is an 
entity that orchestrates a set of network functions to build network 
services. The major benefit of using VNF Pool is that reliability 
mechanisms such as redundancy model are achieved by the VNF Pool 
inside the VNF and thus not visible to the service control entity. A 
VNF Pool-enabled VNF still appears as a normal VNF when orchestrated 
by a service control entity.

Questions that are raised by the addition of a pooling mechanism to 
VNF include:

·How to manage the redundancy model, e.g., select active/standby VNF 
instances in a VNF Pool?

·What pool states need to be maintained to support the pooling 
mechanism itself, and how are such states maintained?

·What information is exchanged between a VNF and a service control 
entity? For example, how can a VNF Pool be addressed by the service 
control entity?

·After a VNF instance failover, how does the Pool Manager notify the 
service control entity some characteristic changes of the VNF, e.g., 
capacity change, but without disclosure of the pooling procedure?

The WG initially focuses on several reliability mechanisms that are 
mainly associated with a redundancy model based on a VNF Pool.
Additional mechanisms may include pool state maintenance only for 
pooling purpose. Service state synchronization is out of scope for 
this phase. The WGassumesthat a VNF Pool contains redundant VNF 
instances of same functional type. Different types of VNFs are 
envisioned to be held in separate VNF Pools. VNF Pool composed by both 
virtualized and non-virtualized functional instances may be included 
after further use case and requirements study. The WG will address the 
reliability of an individual VNF, but not the reliability related to 
the control or the routing between adjacent VNFs that can form a 
network service.

Specifically, the WG will work on the following technical aspects:

·Redundancy management within a VNF Pool, such as the signaling 
between the Pool Manager and the instances in the pool for instance 
registration, backup instances selection, and switching between active 
and standby instances.

·The protocol between the Pool Manager and the underlying network to 
collect the network information required for appropriate 
placement/selection of backup instances.

·The protocol between a VNF and the service control entity to exchange 
operational information between a VNF Pooland the service control entity.

·Identify and analyze reliable interfaces, such as transport protocol 
like MPTCP and SCTP for reliable delivery of the messages associated 
with the redundancy management within a VNF Pool.

·Analysis of pooling security characteristics and requirements to 
identify and mitigate threats against the pooling mechanism.
Identification of an appropriate trust model between pool members, and 
between pool members and the Pool Manager.

The WG plans to deliver a problem statement, a set of use cases, 
requirements and an architecture covering the aforementioned technical 
aspects, and applicability and gap analysis of existing technologies 
including but not limited to RSerPool. We will rely heavily on 
existing IETF technologies, but that gaps will be found around 
problems like redundancy mechanisms, state maintenancesolely for 
pooling purposes, reliable transport, and trust/security, all of which 
will need to be considered and addressed. Although no decision on 
protocols will be made in this phase, we will keep open for candidate 
protocols for VNF Pool. The WG will seek re-chartering before adopting 
any work to develop new, or extend existing, protocols.

In particular, we will work closely with the SFC WG, as we believe 
that SFC and VNF Pool are independent but complementary. SFC would 
essentially see aVNFPool-enabled VNFas a normal service function and 
therefore be able to merge it into an SFC just like any other service 
functions. Just like the communication between any pool users and VNF 
Pool, the information exchanged between the VNF Pool and the SFC may 
include some operational information of the VNF Pool.

Goals and Milestones:

December 2014 - Submit VNFPool Problem Statement to IESG for 
publication as an Informational document.

April 2015 - Submit VNFPool Use Cases to IESG for publication as an 
Informational document.

August 2015 - Submit VNFPool Requirements, including the manageability 
of VNF Pool to IESG for publication as an Informational document.

August 2015 - Submit VNFPool Architecture to IESG for publication as 
an Informational document.

December 2015 - Submit one or more Applicability and Gap Analysis of 
existing protocols to VNFPool to IESG for publication as Informational 
document(s).

======================================================================
====

Your comments and suggestions to the charter are ALWAYS highly 
appreciated!

Thanks.

-Ning



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