Re: [CCAMP] Overlay model framework and context

Daniele Ceccarelli <daniele.ceccarelli@ericsson.com> Thu, 20 December 2012 10:22 UTC

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From: Daniele Ceccarelli <daniele.ceccarelli@ericsson.com>
To: Fatai Zhang <zhangfatai@huawei.com>, Lou Berger <lberger@labn.net>, "Igor Bryskin" <IBryskin@advaoptical.com>, "BELOTTI, SERGIO (SERGIO)" <sergio.belotti@alcatel-lucent.com>
Thread-Topic: [CCAMP] Overlay model framework and context
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Date: Thu, 20 Dec 2012 10:22:46 +0000
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Cc: CCAMP <ccamp@ietf.org>
Subject: Re: [CCAMP] Overlay model framework and context
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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
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>>>>
>>>>
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