Re: [PWE3] draft-mohan-pwe3-mpls-eth-oam-iwk-00.txt as WG draft

[Maarten Vissers <[e-mail]>]

retry..

-----Original Message-----
From: Maarten Vissers [mailto:[e-mail]]
Sent: 14 July 2008 10:14
To: '[e-mail]'
Cc: '[e-mail]'
Subject: RE: [PWE3] draft-mohan-pwe3-mpls-eth-oam-iwk-00.txt as WG draft

Neil,

AIS/FDI OAM for all technologies is associated with configured
point-to-point, point-to-multipoint, rooted-multipoint and
multipoint-to-multipoint 'transport entities' (i.e.
PDH/SDH/OTN/ATM/MPLS(-TP)connections, Ethernet VLANs (inlcuding a standalone
802.1D network)). AIS will also be associated with the point-to-point and
point-to-multipoint PBB-TE connections.

COCS, COPS and CLPS are three types of forwarding mode within 'transport
entities'. 'Transport entities' itself **connection-oriented**, connection
admission controlled and traffic engineered; they are set up under
management plane control, with or without the help of a control plane.

- COCS is a forwarding mode in a 'transport entity' in which every traffic
unit is treated identically from a forwarding perspective in the switch
functions and link ingress points.
- COPS is a forwarding mode in a 'transport entity'in which every traffic
unit is treated identically from a forwarding perspective in the switch
functions (same as COCS case), but may be treated differently in link
ingress points. In link ingress points the CoS and Discard Eligibility of
the traffic unit determine the forwarding.
- CLPS is a forwarding mode in a 'transport entity' in which traffic units
may be treated differently from a forwarding perspective in switch functions
and link ingress points. In the link ingress points the CoS and Discard
Eligibility of the traffic unit determine its forwarding (same as in COPS
case). In the switch fucntions the value of a label within the traffic unit
(e.g. address label or demultiplexer label) determines the forwarding of a
traffic unit within the 'transport entity'.

CLPS forwarding behaviour within 'transport entities' is specified today for
Ethernet VLANs and IP VPNs. 
The label in the traffic unit that is used to determine which output port or
output ports of the VLAN/VPN 'transport entity' should receive this traffic
unit is the destination address label.

	Note that an 802.1D network is an Ethernet network with a single
VLAN (single 'transport entity'). 
	The 'internet' is an IP network with a single (public) 'IP VPN'
(signle 'transport entity').

In **theory** it is possible to specify CLPS forwarding also in e.g.
point-to-multipoint MPLS tunnels when those tunnels carry
point-to-multipoint MPLS PWs (with each PW carrying e.g. a TV channel).
Forwarding of a traffic unit within a MPLS tunnel connection in a MPLS
tunnel switch will - in a CLPS mode - depend on the value of the PW label
inside the traffic unit. For this purpose PW labels will be registered per
MPLS tunnel output port, and if a PW label value X is not assocaited with a
tunnel output port Y, then the MPLS tunnel traffic unit will not be
forwarded via this output port Y.

OAM mechanisms are specified to monitor these **connection-oriented**
'transport entities'. 
OAM mechanisms are not specified to monitor the individual traffic units or
streams of traffic units that are transported between ports of 'transport
entities'.

AIS/FDI, LCK, OCI/UNEQ are OAM maintenance signals that are generated within
the scope of the **connection-oriented** 'transport entity', including the
Ethernet VLAN 'transport entity'. That is why Ethernet AIS is specified in
Y.1731, G.8021 and G.8051. Without this Ethernet AIS OAM you will get alarm
storms in Ethernet VLAN and VPLS transport networks.

You need the AIS/FDI based alarm suppression mechanism as soon as you deploy
a 'transport entity' continuity check mechanism and you can not guarantee
that a broken 'transport entity' has its connectivity restored within 2
seconds. As PBB-TE tunnel connections are set up under management control,
PBB-TE AIS will be necessary to prevent PBB-TE tunnel Loss of Continuity
alarm storms after a cable with 96 fibers, each carrying e.g. 80 40G
wavelengths is broken.

Note that a Server MEP has nothing to do with TCM. A Server MEP is a MEP in
the server layer. Example of ETH Server MEP function: SDH VC-n termination
plus Sn/ETH adaptation function.

---

Every layer has three types of Maintenance Entity Groups (MEG) within a
'transport entity':
1) Network Connection (NC) MEG level
2) Tandem Connection (TC) MEG level
3) Link Connection (LC) MEG level.

The NC-MEG level is always present in a layer network supporting OAM. It is
however an operator's choice to deploy the available OAM at this NC-MEG
level.

TC-MEG and LC-MEG level presence depend of the layer network's role
(transport service layer, transport tunnel layer, transport link layer),
single/multi-owner status of the 'transport entity' and survivability
(protection) requirements.


A) Transport Link (or Section) layer requires typically support of the
NC-MEG level only; i.e. case of I-NNI and E-NNI. 
Only when this link/section layer signal is treated as a port-based service
TC-/LC-MEG levels will become important; i.e. case of UNI.

B) Transport Tunnel (or Path) layer requires typically support of the NC-MEG
level only; i.e. case of I-NNI and E-NNI.
When this tunnel/path layer signal is treated as an individual or bundled
service entity, then TC-/LC-MEG levels will become important; i.e. case of
UNI and carrier-carrier.
Tunnel protection switching is assumed to be performed between PE nodes
using the NC-MEG level MEP functions to monitor for SF/SD status.

C) Transport service (or Channel) layer requires support for the NC-MEG
level and possibly for TC-MEG and LC-MEG levels as well.
When the service/channel layer 'transport entity' starts/ends inside the
transport network (at UNI-N ports) of a single network operator and if such
'transport entity' is not protected, then the NC-MEG will be the only active
MEG level. 
When protection of a 'transport entity' segment is required, a TC-MEG level
is necessary to monitor the segment.
When two or more network operators provide the 'transport entity', each
operator want to be able to monitor the status/performance of the 'transport
entity' segment in its network; this requires the presence of a TC-MEG
level.
When the 'transport entity' starts/ends in the customer domain, the NC-MEG
level is owned by the customer and the transport network must deploy a
TC-MEG level to monitor the status/performance provided by the transport
network between the UNI-N ports. For this case, the LC-MEG level may be used
to monitor the status/performance of the 'transport entity' segment on each
UNI (CE to T-PE) and E-NNI.

When the PBB-TE tunnel layer is a tunnel/path layer operated within the
administrative domain of a single network operator you will need only the
NC-MEG level. 
As soon as PBB-TE tunnel connections may start/end in the customer domains
or in two network operator domains, PBB-TE tunnel layer will need TC-MEG and
LC-MEG levels.

Regards,
Maarten



-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of
[e-mail]
Sent: 12 July 2008 10:16
To: [e-mail]
Cc: [e-mail]; [e-mail]; [e-mail]
Subject: Re: [PWE3] draft-mohan-pwe3-mpls-eth-oam-iwk-00.txt as WG draft

Thank you Jon....some attempted answers in-line: 
[e-mail] wrote 11 July 2008 18:22

> Hi Neil,
> 
> A quick query on the subject of AIS:
> 
> I understand your summary of the background of AIS, but there is 
> surely still a requirement for a triggered forward error indication of 
> some form?  ATM defined AIS cells for this function, so there is 
> already a precedent for this function in a co-ps network.
NH=> Yes, that is true.  However, it's not as obvious a requirement as you
might think.  FDI requires a persistent binding of a client and server layer
network, ie the sever, on failure, needs to be sure who its clients are in
order to inject FDI into them....it's not much good if those clients change.
This long-lasting client/server permanence has been a traditional truth in
nested PDH/SDH co-cs mode transport layer networks...which is of course
where the notion of AIS comes from as I explained.  But what if the clients
can change more dynamically?  Start by envisioning co-cs or co-ps mode SVC
clients (eg co-cs PSTN) which have shrinking holding times......in the limit
this become a single message of a cl-ps mode client layer network.  So if we
imagine a link connection in such a client layer network (ie a single hop
between 2 adjacent client layer nodes which is provided by a network
connection in some lower layer server network) it becomes quite clear that
we cannot assign any permanence between a specific client communications
instance and their use (or not) of that link (=server network connection).
Hopefully you can see that.  And this is why it makes no sense whatsoever to
carry over the idea of AIS/FDI into cl-ps mode layer networks and explains
why IEEE had the good sense to take AIS out of 802.1ag.

We discussed the issue of FDI within BT when considering the OAM we would
want for PBB-TE (co-ps mode based on using the original cl-ps Ethernet
traffic unit), and on balance we considered it was not a good idea.
However, the CV and BDI OAM functions are essential....but they should NOT
be piggybacked in order that we can properly address the p2mp connection
case.

But as I also noted in my mail, a key requirement on OAM (at least that used
for defect detection) is that it is super reliable, and that tends to mean
as sparse as possible of function with minimal configuration.
Anything that requires lots of config (and the TCM stuff factors heavily
here - see later comment) is really not a requirement.
> 
> The problem that I foresee is that, although ethernet is inherently 
> cl-ps, Ethernet will be extensively used in a p2p manner, especially 
> when ethernet is used as a tail circuit to an IP service.  In this 
> case, I think that an AIS function is valid.  If this is not 
> available, would we not need to have CCM enabled in all cases?
NH=> Please remember that CV and FDI are very different.  CV checks THIS
layer network, FDI is an indication of failure (possibly from a CV flow
detected defect) in a LOWER layer network.  I've seen folks try and 'do
away' with CV and just use FDI...it's a mistake.....as to get FDI SOME layer
network has to be able to detect it's failures, and it won't always be the
section layer, ie very bottom of stack, that can do this.
No CV means you are blind to defects in your layer network, you only see
server layer defects IFF they generate a FDI into your layer network across
the adaptation function...and as explained above, FDI/AIS is not such a
great idea as folks might think.
> 
> Maybe the problem stems from the fact that SPs are often trying to use 
> Ethernet, that is inherently connectionless, in a connection oriented 
> manner!
NH=> Well yes....but the mere fact that special topology consideration
exists (ie the p2p degenerate network case you mentioned above) is not the
general network case.  
> 
> > Quite.....need to start getting these things right (here a
> transparent
> > client/server layer network relationship).
> Yes, seems to be the root of a lot of issues we are running into!
NH=> It is rather important/fundamental....but it is violated all over the
place.  I'll say no more on the matter here.

> Is it worth noting that Y.1731 seems to have defined a server layer:
> "NOTE - A Server MEP needs to support ETH-AIS function, as described 
> in sub-clause 7.4, where the Server/ETH adaptation function is 
> required to issue frames with ETH-AIS information upon detection of 
> defect at the Server layer by the Server layer termination and/or 
> adaptation function."
NH=> This is all about TCM.  One might like to observe that in any general
layer network only the access points are fixed....intermediate points can
change, and indeed MUST change if we want to have resiliency.
(You may be struck here by the similarities to the point I made earlier
regarding FDI and how one can't assume a permanence between a client
communications instance and the links (=server layer connections) it is
using at any epoch).  Now try and get your head around how you would manage
the config of such (moveable) intermediate points, especially if you were
trying to get accurate perf mon (PM) data across failures and restorations.
TCM sounds good on paper, but show me the management solutions for PM across
dynamic changes of routing.  Hint=> I've looked quite closely at doing this
at end points that are time invariant/fixed in the past and this is not a
simple problem even here (eg pkts in-flight, clock differences) now
extrapolate that problem to a raft of nested TCM levels that are not
invariant/fixed....let me know when you have an answer for PM in TCM across
failures/restorations ;-)

Regards, Neil


> 
> Cheers,
> ~Jon.
> 
> 
> > -----Original Message-----
> > From: [e-mail] [mailto:[e-mail]]
> On Behalf
> > Of [e-mail]
> > Sent: 09 July 2008 20:18
> > To: [e-mail]; [e-mail]
> > Cc: [e-mail]; [e-mail]
> > Subject: Re: [PWE3] draft-mohan-pwe3-mpls-eth-oam-iwk-00.txt
> > as WG draft
> > 
> > Hi Dinesh and Ali,
> > 
> > A few observations on the draft and the subject of OAM in
> general that
> > you might like to take into account:
> > 
> > 1	Despite what some folks having been trying to do in ITU the OAM
> > required for each of the 3 network modes (cl-ps, co-ps and
> > co-cs) is not the same.  For example, AIS is mentioned in
> the draft.  
> > AIS has its roots in co-cs mode PDH/TDM networks.
> > AIS is about alarm suppression (in co mode clients *above* a server
> > failure) not generating alarms.  It was a direct consequence of old 
> > TTL logic when, on failure, the logic 'floated' to +5V (ie binary 
> > 1).....so a binary all 1s signal was the natural indication
> of failure
> > here.  Note in particular it is a passive signal....in the
> sense that
> > we don't have to actively create special traffic units to
> mimic it as
> > we would in any packet network.  Further, since the co-cs mode is 
> > characterised by a constant bit rate signal AIS is naturally a 
> > constant stream of binary all 1s (when replacing the
> traffic signal).
> > 
> > AIS is however not a natural signal in packet networks.  
> And whilst it
> > is understandable to want to have an AIS/FDI OAM function in co-ps 
> > mode layer networks (on the assumption they have proper
> single source
> > connections, ie p2p or p2mp constructs only) it has no meaning in 
> > cl-ps mode networks, eg IP, Ethernet.  And this, of course, is why 
> > IEEE saw fit to deprecate AIS in 802.1ag for Ethernet OAM.
> > 
> > My view is that IETF should align its position with that of
> the IEEE
> > standards when dealing with Ethernet OAM.
> > 
> > 
> > 
> > 2	I note that the BDI (or RDI) function has been piggy-backed in
> > CC messages in both Y.1731 and 802.1ag.  In the case of
> co-cs or co-ps
> > mode layer networks this only works for symmetrical bidirectional 
> > connections, ie p2p constructs only.  It does not work for p2mp 
> > connection constructs (as these cannot be bidirectionally
> symmetric)
> > and so a CC message and a BDI message need to be
> distinct/independent
> > OAM messages here.
> > This is something to bear in mind for GMPLS (controlled co-cs mode 
> > layer network connections), MPLS and PWs (assuming the case of both 
> > these supporting proper single source co-ps connections).
> > 
> > Now of course Ethernet is a cl-ps mode technology so we don't have 
> > connections. However, if we make the OAM CC message a broadcast 
> > function between MEPs then we force a condition of symmetry
> here and
> > so one can, in principle, piggyback BDI in CC
> messages.....the traffic
> > of course can be, and usually is, unicast (once SA MAC learning has 
> > taken place).  So the first observation here is that the OAM is not 
> > exercising exactly the same processing path as the traffic.
>  Further,
> > the indiscriminate broadcasting of BDI to N far-ends wrt to
> an unknown
> > number of incoming failures is hardly good practice (see
> section 7.5
> > in Y.1731).
> > 
> > However, the key point I am making here is the former one,
> ie when we
> > are dealing with proper co-cs or co-ps mode p2mp
> connections we cannot
> > piggyback BDI in CC messages.
> > 
> > 
> > 3	It is a very, very bad idea to have client layer defects
> > reflected in a server layer network (be this DP/CP/MP).  I
> just noted
> > Yaakov also allude to this point in his mail 09 July 2008
> 17:31, viz:
> > 
> > "However, I would like to reiterate what I said in Philadelphia.
> > I am not a great fan of OAM mapping at all, and wouldn't
> care if the
> > present oam-msg-map draft died a natural death.
> > Ethernet to Ethernet PW OAM interworking is an evil, but
> frequently a
> > necessary one.
> > Work on it needs to be expedited."
> > 
> > Quite.....need to start getting these things right (here a
> transparent
> > client/server layer network relationship).
> > 
> > 
> > 4	Final, and far more general, point....OAM needs to be uber
> > reliable...far more so than the intrinsic failure rate of
> the network
> > it resides in.  So defect detection/handling OAM needs to be as 
> > simple/sparse as possible.  Collecting OAM (esp Perf Mon OAM) 
> > information also has a real opex cost.
> > Ops folks will turn-off as much OAM as they can...esp
> bloated/bad OAM
> > (Y.1731 is bloated IMO).  I've just noticed TCM (Tandem Connection
> > Monitoring) has been added to the
> > PWE3 charter.  I would strongly advise IETF *not* to go here just 
> > because others have included this in their standards.
> > This idea has been around for many years in ITU and there are very 
> > good reasons why very little of it is used in practice (I can spell 
> > this out if not obvious).
> > 
> > Regards, Neil
> > 
> > 
> > 
> > > -----Original Message-----
> > > From: [e-mail] [mailto:[e-mail]]
> > On Behalf
> > > Of Dinesh Mohan
> > > Sent: 08 July 2008 16:08
> > > To: [e-mail]; pwe3
> > > Subject: Re: [PWE3] draft-mohan-pwe3-mpls-eth-oam-iwk-00.txt
> > > as WG draft
> > > 
> > > Stewart, of course as an author I support this as a WG draft :-)
> > > 
> > > FYI...an updated version of the document is also
> available based on
> > > feedback during the meeting and some further offline
> > > discussions:
> > > http://www.ietf.org/internet-drafts/draft-mohan-pwe3-mpls-eth-
> > > oam-iwk-01
> > > .txt
> > > 
> > > If we agree, this could be the version that can be accepted for 
> > > working group draft.
> > > 
> > > ---
> > > Dinesh
> > > 
> > > -----Original Message-----
> > > From: [e-mail] [mailto:[e-mail]]
> > On Behalf
> > > Of Stewart Bryant
> > > Sent: Tuesday, July 08, 2008 7:35 AM
> > > To: pwe3
> > > Subject: [PWE3] draft-mohan-pwe3-mpls-eth-oam-iwk-00.txt
> as WG draft
> > > 
> > > We have a request to accept MPLS and Ethernet OAM Interworking
> > > 
> > > http://tools.ietf.org/id/draft-mohan-pwe3-mpls-eth-oam-iwk-00.txt
> > > 
> > > as a working group draft.
> > > 
> > > The authors thought that PWE3 had already agreed to this, but the 
> > > minutes of the last meeting do not say that, and in any
> case we did
> > > not do a list poll.
> > > 
> > > Please can we have views on whether to accept as WG draft
> > by COB 15th
> > > July.
> > > 
> > > Thanks
> > > 
> > > Stewart/Danny
> > > 
> > > 
> > > _______________________________________________
> > > pwe3 mailing list
> > > [e-mail]
> > > https://www.ietf.org/mailman/listinfo/pwe3
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> > > pwe3 mailing list
> > > [e-mail]
> > > https://www.ietf.org/mailman/listinfo/pwe3
> > > 
> > _______________________________________________
> > pwe3 mailing list
> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/pwe3
> > 
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