Subject: [mpls-tp] MPLS-TP, existing transport networks and sections

From: Ben Niven-Jenkins <[email-masked]>
Date: Thu, 22 Jan 2009 16:39:05 +0000

Traditionally the section layer has provided the following functions: Frame
Alignment, Trail Trace, Path Identifier, Error monitoring, Parity/CRC,
Maintenance channels used for management, Automatic Protection Switching and
Synchronisation Status Message (SSM) for clock quality monitoring.
 
Some of these functions (Frame Alignment, Parity/CRC & Error Monitoring) are
not required to be implemented by MPLS as they are provided by the
underlying server layer that MPLS utilises.
 
The rest, with the exception of SSM, are provided by the MPLS label stack
(path identifier/multiplexing), the OAM tools available (Trace, APS), the
control plane/GACH (Maintenance channels) or a combination of OAM and
control plane (APS).

So the only thing a section layer provides that is not catered for in
MPLS-TP already is SSM messages.

So do we need a section layer for MPLS-TP at all?

Now I understand the desire to add MPLS-TP monitoring to the
"section"/"link" as a whole - i.e. Monitor all the LSPs across the
"section"/"link" using one ME Vs one ME per LSP. It seems to me that this
monitoring can be achieved more simply than creating a whole section layer
network? I think that others agree with me (but I wouldn't want to put words
in their mouths) and hence why MPLS-TP as specified today does not specify
an MPLS-TP Section layer network.

Ben

_______________________________________________
mpls-tp mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/mpls-tp

---

From: Maarten Vissers <[email-masked]>
Date: Thu, 22 Jan 2009 23:35:51 +0100

The first Section layer network we specified was the SDH Multiplex Section
and Regenerator Section layer networks. Frame alignment was not part of the
Section layer network functionality. The MS layer network provides
connection monitoring (bit error monitoring and maintenance signals) and
APS, DCC, OW and SSM communication channels. The RS layer network provides
connection monitoring (section trace and bit error) and DCC, OW and USR
communication channels.

The alignment function is part of the interlayer adaptation function; the
Section_CI related alignment is performed in the Physical Media to Section
Adaptation sink function. This is the case for SDH sections and for MPLS-TP
sections. Refer to e.g. Sn/TM_A_Sk function description in G.8121 where you
find the alignment function for sections.

A MPLS-TP Section layer network is a LSP layer network in your terminology,
of which a signle LSP is carried in a Physical Media layer network trail in
an "unlabelled" manner; i.e. as "unlabelled-LSP".

> Now I understand the desire to add MPLS-TP monitoring to the
"section"/"link"
> as a whole - i.e. Monitor all the LSPs across the "section"/"link" using
one
> ME Vs one ME per LSP. It seems to me that this monitoring can be achieved
more
> simply than creating a whole section layer network?

Your assumption is not correct. There is no simpler method than creating a
section layer network. Note that the section layer network does not have a
switching function. I.e G.805 specifies "It is possible to identify a set of
layer networks within the transmission media layer network which is likely
to be independently administered by a network operator by decomposing the
transmission media layer network. The connectivity of a transmission media
layer network cannot be directly modified by management action. Transmission
media layer networks are divided into section layer networks and physical
media layer networks.".

Note further that the section layer trail will exist prior to the existence
of a path/LSP layer connection. Only when the section layer trail indicates
that the section is performing according to the required performance, the
section layer trail will be resulting in the creation/advertisement of the
client layer link.

You do not need to support a MPLS-TP section layer trail in the following
cases:
1) you deploy an SDH interface port and the section trail is a signle hop
trail (no carrier-carrier); the VC-n layer trail will perform the MPLS-TP
transmission media trail monitoring
2) you deploy an OTN interface port and the section trail is a single hop
trail (no carrier-carrier); the ODUk layer trail will perform the MPLS-TP
transmission media trail monitoring
3) you deploy an Ethernet interface port and the section trail is a single
hop trail (no carrier-carrier); the ETH layer trail will perform the MPLS-TP
transmission media trail monitoring.

If however you have a "carrier-carrier application (II)" as described in
slides 17 and 21 in
http://ifa.itu.int/t/2009/sg15/exchange/wp3/q12/mpls-tp/layers-and-sublayers
-00.ppt you will need to support a MPLS-TP Section layer trail to monitor
the section from the transmitting MPLS-TP node via the fiber, MPLS-TP
carrier-carrier network and far end fiber, to the receiving MPLS-TP node.

Also to this carrier-carrier application (II) there is an alternative that
does not require an MPLS-TP Section layer trail, but instead uses an ETH
Section layer trail. I.e. when both MPLS-TP nodes have an Ethernet
interface, then it is possible to carry the ETH Section layer signal through
the MPLS-TP carrier-carrier network as an Ethernet LINE service.

I know that there are many options for the section layer functionality in
MPLS-TP. It would be nice if we could limit it to one type of section layer.
I have gone the direction to specify an MPLS-TP section layer as being
present in all types of physical media... i.e. I am ignoring that physical
media technology may have a layer that can perform the section layer
functionality.

But it is also possible to specify that MPLS-TP will only deploy ethernet
interfaces and that it will an ETH Section layer network (instead of an
MPLS-TP section layer network). This would also makes MPLS-TP simpler, as it
reduces the number of interface types we have to support on MPLS-TP
equipment.

If we can reach an agreement on a single section layer solution, then we can
document this in the framework. Otherwise it would be necessary to document
the different alternatives for the MPLS-TP transmission media layer network
(including the section and phy media layer netowrks). Such documentation is
a requirement to guarantee interworking between equipment of different
vendors and operators.

Regards,
Maarten

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Ben Niven-Jenkins
Sent: donderdag 22 januari 2009 17:39
To: [email-masked]
Subject: [mpls-tp] MPLS-TP, existing transport networks and sections

Maarten,

 

Ben