Re: [CCAMP] Overlay model framework and context

Lou Berger <lberger@labn.net> Thu, 20 December 2012 14:39 UTC

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Date: Thu, 20 Dec 2012 09:39:28 -0500
From: Lou Berger <lberger@labn.net>
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To: Daniele Ceccarelli <daniele.ceccarelli@ericsson.com>
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Cc: CCAMP <ccamp@ietf.org>
Subject: Re: [CCAMP] Overlay model framework and context
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Daniele,

Just my opinion, but I see overlays as the (much) more generic term.  I
think LxVPNs are types of overlays, as are traditional layered networks,
as are the technologies that match/will result from discussions taking
place in the NVO3 context.

Lou

On 12/20/2012 5:22 AM, Daniele Ceccarelli wrote:
> I prefer using reference points instead of links.
> Access link and inter-domain links means tens of things in different
> contexts, while e.g. UNI means one single thing and clearly
> identifies the context. BTW it's just a preference, I don't mind how
> we'll finally call it.
> 
> There's one thing I would rather like to clarify and it's the
> relationship with VPNs. We have two options:
> 
> 1) Is a VPN a particular case of the overlay model?
> or
> 2) Is the overlay model a particular case of VPN?
> 
> I think this can help a lot with terminology. I've always assumed 1)
> but from what I read I tend to see that 2) has several supporters.
> 

> BR
> Daniele
> 
> 
> 
> 
>> -----Original Message-----
>> From: Fatai Zhang [mailto:zhangfatai@huawei.com] 
>> Sent: giovedì 20 dicembre 2012 2.44
>> To: Lou Berger; Igor Bryskin; BELOTTI, SERGIO (SERGIO); 
>> Daniele Ceccarelli
>> Cc: CCAMP
>> Subject: 答复: [CCAMP] Overlay model framework and context
>>
>> Hi all,
>>
>> Support.
>>
>> People are more familiar with the existing things like "access 
>> links" and "inter-domain links" (or E-NNI links).
>>
>>
>>
>>
>> Best Regards
>>
>> Fatai
>>
>> -----邮件原件-----
>> 发件人: ccamp-bounces@ietf.org [mailto:ccamp-bounces@ietf.org] 代表 
>> Lou Berger
>> 发送时间: 2012年12月20日 7:08
>> 收件人: Igor Bryskin
>> 抄送: CCAMP
>> 主题: Re: [CCAMP] Overlay model framework and context
>>
>> Igor,
>>
>> You said:
>> IB>> I like "access links" and "inter-domain links" better.
>>
>> This works for me.
>>
>> Lou
>>
>> On 12/19/2012 12:27 PM, Igor Bryskin wrote:
>>> Lou, please see my answers to your questions
>>>
>>> -----Original Message-----
>>> From: ccamp-bounces@ietf.org [mailto:ccamp-bounces@ietf.org] 
>> On Behalf 
>>> Of Daniele Ceccarelli
>>> Sent: Wednesday, December 19, 2012 5:57 AM
>>> To: Lou Berger
>>> Cc: CCAMP
>>> Subject: Re: [CCAMP] Overlay model framework and context
>>>
>>> Hi Lou,
>>>
>>> Plese find replies in line.
>>>
>>> BR
>>> Daniele
>>>
>>>> -----Original Message-----
>>>> From: Lou Berger [mailto:lberger@labn.net]
>>>> Sent: lunedì 17 dicembre 2012 20.45
>>>> To: Daniele Ceccarelli
>>>> Cc: CCAMP
>>>> Subject: Re: [CCAMP] Overlay model framework and context
>>>>
>>>>
>>>> Daniele,
>>>> 	Thanks for getting this on-list discussion going.  I have some 
>>>> comments and questions:
>>>>
>>>> - So what's a "client layer network" in this context?  Perhaps you 
>>>> mean OC or "(overlay) customer layer"?
>>>
>>> IB>> Client layer is where Overlay Network topology exists. 
>> It includes:
>>> a) access links (connecting OCs to OEs)
>>> b) virtual links (connecting OE / OVNs (Overlay Virtual 
>> Nodes) within 
>>> a given server domain)
>>> c) inter-domain links (connecting OE to OE that belong to 
>> neighboring 
>>> server domains) All three categories exist in the same client layer 
>>> and named from the same naming space
>>>
>>> Yes. The terms client layer and server layer are 
>> reminescences to be corrected.
>>>
>>>>
>>>> - So what's a "server layer network" in this context?  Perhaps you 
>>>> mean OE or "(overlay) provider layer"?
>>>
>>> IB>> It is the layer where the UNT (Underlay Network 
>> Topology) exists 
>>> IB>> (which may be in the same, lower or higher layer 
>> network than of 
>>> IB>> the ONT)
>>>
>>> Again correct
>>>
>>>>
>>>> - For OC, I'd thing referring back to a CE in the VPN context, and 
>>>> likewise to a PE for an OE, is helpful context.
>>> IB>> agree
>>>
>>> In the case of the interface we generally define the ONI as 
>> an overlay interface that in a particular case is called UNI. 
>> I would apply the same method: those nodes are called Overlay 
>> Customer and Overlay Edge and in the particular case of VPNs 
>> they are the CE and PE respectively. What about that?
>>>
>>>>
>>>> - As you mention in the Appendix, (from the OC perspective) 
>> there is 
>>>> no difference between a virtual and real node
>>> IB>> Agree
>>>
>>>  (and presumably link as
>>>> well).  Given this and your comment in 8, that the ONI can take the 
>>>> form of a UNI or include both signaling and routing (i.e., a 
>>>> peer/I-NNI or
>>>> E-NNI) what value is there in introducing the ONI term?  
>> Said another 
>>>> way, there's no specific term for the interface between a CE and PE 
>>>> in L3VPNs, so why do we need to introduce one in this context?
>>>
>>> We gave a name to the UNI, why don't giving to the ONI?
>>>
>>> IB>> As long as it allows for both or either signaling 
>> and/or routing 
>>> IB>> exchanges
>>>
>>>>
>>>> I think this same comment probably holds for the O-NNI 
>> (e.g., what's 
>>>> the name of the interface between providers which support L3VPN 
>>>> handoffs?)...
>>>
>>> I would suggest giving a name to that interface also in 
>> order to distinguish between an "internal" and an "external" 
>> link when multiple overlay provider network domains are present.
>>>
>>> IB>> I like "access links" and "inter-domain links" better. 
>> Note also that a "link" and "node" are TE topology concepts 
>> and orthogonal to CP interfaces (which are Signaling/Routing 
>> speakers). If you mean by "internal" and "external" links the 
>> CP connectivity, than I agree with you.
>>>
>>>>
>>>> Much thanks,
>>>> Lou
>>>>
>>>> On 12/17/2012 6:17 AM, Daniele Ceccarelli wrote:
>>>>> Dear CCAMPers,
>>>>>
>>>>> In the last weeks several off-line discussions on the
>>>> Overlay model framework and related works took place. Some 
>>>> discussions led to some sort of agreemet among a small group of 
>>>> people, some others to a set a viable options, some others 
>> to totally 
>>>> open issues. I tried to summarize the output of such discussions 
>>>> below so to progress the discussions into a single thread 
>> on the WG ML.
>>>>>
>>>>> Please note that the aim of this mail is not to present a
>>>> well shaped and conclusive idea to the WG but rather to provide the 
>>>> basis for starting a discussion from a barely shaped idea (step 1) 
>>>> instead of starting it from scratch (step 0).
>>>>>
>>>>> In addition you can find attached a slide depicting a
>>>> proposal of the overlay scenario.
>>>>>
>>>>> Thanks,
>>>>> Daniele
>>>>>
>>>>> + Disclaimer:
>>>>>  1. Packet opto integration is often considered but the work
>>>> can be extented to any type of SC. Eg. TDM over LSC.
>>>>>
>>>>> + Terminology:
>>>>>
>>>>>  1. Virtual Link: A virtual link is a potential path between
>>>> two virtual or real network elements in a client layer 
>> network  that 
>>>> is maintained/controlled in and by the server domain control plane 
>>>> (and as such cannot transport any traffic/data and protected from 
>>>> being
>>>> de-provisioned) and which can be instantiated in the data 
>> plane (and 
>>>> then can carry/transport/forward traffic/data) preserving 
>> previously 
>>>> advertised attributes such as fate sharing information.
>>>>>  2.  Virtual Node: Virtual node is a collection of zero or
>>>> more server network  domain nodes that are collectively represented 
>>>> to the clients as a single node that exists in the client layer 
>>>> network and is capable of terminating of access, inter-domain and 
>>>> virtual links.
>>>>>  3.Virtual Topology: Virtual topology is a collection of one
>>>> or more virtual or real server network domain nodes that 
>> exist in the 
>>>> client layer network and are interconnected via 0 or more virtual 
>>>> links.
>>>>>  4. Overlay topology:  is a superset of virtual topologies
>>>> provided by each of server network domains, access and inter-domain 
>>>> links.
>>>>>  5. Access Link: Link between OC and OE. GMPLS runs on that
>>>> link. It can support any of the SCs supported by the GMPLS.
>>>>>  6. Overlay Customer (OC): Something like the CN in RFC4208
>>>> teminology  but (i) receiving virtual topology from the 
>> core network 
>>>> and requesting the set up of one of them or (ii) requesting the 
>>>> computation and establishment of a path accordingly to gien 
>>>> constraints in the core network and receiving the parameters 
>>>> characterizing such path. (ii) == UNI.
>>>>>  7. Overlay Edge (OE): Something like the EN in RFC4208 but
>>>> able to deal with (i) and (ii) above.
>>>>>  8. ONI : Overlay network interface: Interface allowing for
>>>> signaling and routing messages exchange between Overlay and Core 
>>>> network. Routing information consists on virtual topology 
>>>> advertisement. When there is no routing adjacency across the 
>>>> interface it is equivalent to the GMPLS UNI defined in 4208.
>>>> Signaling messages are compliant with RFC4208. Information 
>> related to 
>>>> path carachteristics, e.g. TE-metrics, collected SRLG, path delay 
>>>> etc, either passed from OE to OC via signaling after the LSP 
>>>> establishment in the core network or from OC to OE to be 
>> used as path 
>>>> computation constraints, fall under the definition of 
>> signaling info 
>>>> and not routing info).
>>>>>  9. O-NNI (name to be found,maybe reused): Interface on the
>>>> links between different core networks in the overlay model 
>>>> environment, i.e. Between border OEs. Same features of the 
>> ONI apply 
>>>> to this interface. Could it be an E-NNI? A ONI? A new name 
>> is needed?
>>>>>
>>>>> + Statements
>>>>>  1. In the context of overlay model we are aiming to build
>>>> an overlay
>>>>> topology for the client network domains  2. The overlay
>>>> topology is comprised of:
>>>>>     a) access links (links connecting client NEs to the
>>>> server network domains). They can be PSC or LSC.
>>>>>     b) inter-domain links (links interconnecting server
>>>> network domains)   
>>>>>     c) virtual topology provided by the server network
>>>> domains. Virtual Links + Virtual Nodes (TBD) + Connectivity Matrix 
>>>> (with a set of parameters e.g. SRLG, optical impairments, delay etc 
>>>> for each entry) describing connectivity between access links and 
>>>> virtual links.
>>>>>  3. In the context of overlay model we manage  hierarchy  
>> of overlay 
>>>>> topologies with overlay/underlay relationships  4. In the 
>> context of 
>>>>> overlay model multi-layering and inter-layer relationships
>>>> are peripheral at best, it is all about horizontal network 
>>>> integration 5. The overlay model assumes one instance for 
>> the client 
>>>> network and a separate instance for the server network and 
>> in the ONI 
>>>> case the server network also surreptitiously participates in the 
>>>> client network by injecting virtual topology information into it.
>>>>>  6. L1VPN (and LxVPN) in general is a service provided over
>>>> the ONI (it falls under the UNI case as no routing adjacency is in 
>>>> place between OC and OE).
>>>>>
>>>>> + Open issues/questions
>>>>>  
>>>>>  1. PCE-PCEP - do we need to include considerations about
>>>> PCE and PCEP into the overlay framework context?
>>>>>  2. BGP-LS needs to be considered
>>>>>  3. Should potentials be included? E.g. I2RS?
>>>>>
>>>>> + Appendix:
>>>>> Some notes on the Virtual Node:
>>>>> 1.      Virtual Link Model along, sadly, does not scale 
>>>> because of N**2 problem. IP over ATM and single-segment PWs 
>> have the 
>>>> same issue, that's why people invented multi-segment PWs
>>>>> 2.      The only way to avoid full-mesh of Virtual Links is 
>>>> by having intermediate nodes interconnecting Virtual Links in the 
>>>> middle of the virtual topology
>>>>> 3.      These intermediate nodes cannot be real server 
>>>> domain switches, because, generally speaking:
>>>>>   a)Real switches belong to different layer network;
>>>>>   b)Real switches are named from different naming space
>>>>>   c)real switches individually may not have sufficient
>>>> resources to terminate virtual links (while a group of real 
>> switches 
>>>> collectively will have)
>>>>>   d)Presenting a group of real switches as a single virtual
>>>> node have better scalability qualities
>>>>> 4.      Even if you map a virtual node on a single real 
>>>> node, you need to keep in mind that real server domain 
>> switches are, 
>>>> generally speaking, blocking switches and as such must expose their 
>>>> connectivity matrices
>>>>> 5.      If you want to compute SRLG-disjoint paths that 
>>>> could potentially go through a real server domain switch, the 
>>>> latter's connectivity matrix must expose "internal" SRLGs, so that 
>>>> the two services traversing the switch will not simultaneously fail 
>>>> if a single internal element shared by the services fails
>>>>> 6.      If you walk through all cases that need to be 
>>>> addressed when you are traffic engineering topologies with blocking 
>>>> switches, you will understand that there is absolutely no 
>> difference 
>>>> between a virtual node and real blocking real node.
>>>>> 7.      Even in case of pure VL model, client NEs connected 
>>>> to server network domain must be upgraded so that they could 
>>>> understand the connectivity matrices advertised by the border nodes 
>>>> describing connectivity constraints between access links 
>> and virtual 
>>>> links they terminate.
>>>>>
>>>>>
>>>>>  
>>>>> ===================================
>>>>> DANIELE CECCARELLI
>>>>> System & Technology - PDU Optical & Metro
>>>>>
>>>>> Via E.Melen, 77
>>>>> Genova, Italy
>>>>> Phone +390106002512
>>>>> Mobile +393346725750
>>>>> daniele.ceccarelli@ericsson.com
>>>>> www.ericsson.com
>>>>>
>>>>> This Communication is Confidential. We only send and receive
>>>> email on
>>>>> the basis of the term set out at www.ericsson.com/email_disclaimer
>>>>>
>>>>>
>>>>>
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>>>>
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