The MPLS WG Archive

[Maarten Vissers <mvissers@lucent.com>]

All:

As both G.805 and GMPLS are describing the same physical network, there
must be a unique relation between the terminology in the two cases. I
see it as our duty to discover and describe this relation; otherwise I
foresee problems when the transport plane (derived from G.805) and the
control plane (derived from GMPLS) are to interconnect.

A) Transport view 

When you look at today's transport network, you can identify the
following:
- user network (might be as small as a single network element)
- network operator network.

From the network operator's perspective, the user connects via a fiber
(let's limit to this medium for this purpose). The network operator will
now transport the complete or only a part of the signal on this fiber. 

In either case, the network operator doesn't provide the trail or
network connection. The trail and network connection start in the user
network.
As such, the network operator provides transport via a subnetwork
connection.

	Example of complete signal transport: transport of an 
	STM-N/OC-N signal including all of its overhead. E.g. STM-N
	signal is mapped into the payload of the ODUk.
	Other example is the transport of a DS1 via the payload of 
	a VT1.5 signal, or an E1 via the payload of a VC-12 signal.
	As the ODUk, VT1.5 and VC-12 start in the operator's network,
	the ODUk, VT1.5 and VC-12 trail and network connection start
	in the operator's network. These are the server layer trails
	and network connections.

	Example of transport of a part of the signal: transport of
	a VC-4 or STS-1; in this case the STM-N/OC-N signal on the
	fiber is terminated and the VC-4 or STS-1 is extracted and
	passed through.

In network management these DS1 and E1 subnetwork connections are often
referred to as DS1 and E1 circuits.
We could formalise this terminology, allowing us to start talking about
VC-4 circuit, STS-1 circuit, STM-N/OC-N circuit. Something to consider?

B) Monitoring view

A network operator may decide that the transport of the signal through
his subnetwork connection ("circuit") has to be monitored. The
subnetwork connection can therefore be extended with tandem connection
(ATM: segment) monitor functionality. 

For SDH/SONET and ATM one tandem connection level is defined. 
For OTN, 6 levels of tandem connection are defined in G.709. 
For MPLS, ... levels of tandem connection are proposed in the MPLS OAM
activity (Neil can you provide the number here) in draft Y.17oam.1.

Tandem connections can be nested, and perhaps even overlapping (under
discussion at the moment in Q.11/15).

-----

What has helped me in the past, is to formalize the relationships. I
have used BNF for this (refer e.g. to Annex C/EN 300 417-1-1
(http://webapp.etsi.org/pda/home.asp?wki_id=7959)).

Perhaps we can use BNF (or similar tool) again to formalise the
relationships in GMPLS.


Regards,

Maarten

---- copy of annex C/EN 300 417-1-1 --------

Annex C (informative):	Network "production rules"

The relationship between trails, (sub-)network connections, link
connections, atomic functions, and reference points can be described by
means of the "production rules" of a network. This kind of formalism can
also be found in software language specifications. One of the methods
used to describe a language is the Backus-Naur Form (BNF) 23) . This
shows the decomposition and partitioning processes described in § 3 of
ITU-T Recommendation G.803 [28].

<trail>			::=	AP <termination> <network connection>
					<termination> AP

<network connection>	::=	TCP <sub-network connection *> TCP

<sub-network connection *>	::=	<sub-network connection *> CP <link
connection> CP
					<sub-network connection *>
				| <simple connection>
				| <tandem connection>

<link connection>		::=	<adaptation> <trail> <adaptation>
				| Transmission_Medium

<simple connection>		::=	Degenerate_Connection
				| Matrix_Connection (C)

<adaptation>			::=	Adaptation (A)

<termination>		::=	Trail_Termination (TT)

<tandem connection>	::=	<Dadaptation> AP_D <Dtermination> TCP_D
					<sub-network connection *> TCP_D
					<Dtermination> AP_D <Dadaptation>

<sub-network connection *>	::=	<sub-network connection * > CP <link
connection>
					CP <sub-network connection *>
				| <simple connection>

<Dadaptation>		::=	Domain_Monitoring_Adaptation (D_A)

<Dtermination>		::=	Domain_Monitoring_Trail_Termination (D_T)

		AP_D:		Domain Monitoring Access Point
		CP_D:		Domain monitoring Connection Point
		TCP_D:	Domain Monitoring Termination Connection Point
		TM:		Transmission_Medium

The <sub-network connection> shows the recursion, which terminates when
the <simple connection> is selected. This <simple connection> represents
the cross-connection on an individual matrix, or an inflexible (fixed)
connection for the case where a matrix is not present. It is represented
by the (flexible) connection function or an (inflexible) line.

The <link connection> shows the layering process, which terminates when
the Transmission_Medium is selected.

The concept of the <tandem connection> is introduced here because it is
considered to provide a rigid way of describing the property that is
required for the so-called tandem connection i.e. a sub-network
connection that can be monitored via an overhead dedicated for this
purpose.
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