Mutually Exclusive Link Group (MELG)
draft-beeram-ccamp-melg-01
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Vishnu Pavan Beeram , Igor Bryskin | ||
| Last updated | 2013-07-15 | ||
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draft-beeram-ccamp-melg-01
CCAMP Working Group Vishnu Pavan Beeram (Ed)
Internet Draft Juniper Networks
Intended status: Standards Track Igor Bryskin (Ed)
ADVA Optical Networking
Expires: January 15, 2013 July 15, 2013
Mutually Exclusive Link Group (MELG)
draft-beeram-ccamp-melg-01.txt
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Abstract
This document introduces the concept of MELG ("Mutually Exclusive
Link Group") and discusses its usage in the context of mutually
exclusive Virtual TE Links.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
Table of Contents
1. Introduction...................................................2
2. Mutually Exclusive Virtual TE Links............................3
3. Mutually Exclusive Link Group..................................6
4. Protocol Extensions............................................6
4.1. OSPF......................................................6
4.2. ISIS......................................................7
5. Security Considerations........................................9
6. IANA Considerations............................................9
6.1. OSPF......................................................9
6.2. ISIS......................................................9
7. Normative References...........................................9
8. Acknowledgments................................................9
1. Introduction
A Virtual TE Link (as defined in [RFC6001]) advertised into a Client
Network Domain represents a potentiality to setup an LSP in the
Server Network Domain to support the advertised TE link. The Virtual
TE Link gets advertised like any other TE link and follows exactly
the same rules that are defined for the advertising, processing and
use of regular TE links [RFC4202]. However, "mutual exclusivity" is
one attribute that is specific to Virtual TE links. This document
discusses the need to advertise this information and the means to do
so.
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2. Mutually Exclusive Virtual TE Links
Consider the network topology depicted in Figure 1a. This is a
typical packet optical transport deployment scenario where the WDM
layer network domain serves as a Server Network Domain providing
transport connectivity to the packet layer network Domain (Client
Network Domain).
|
| +---+ /-\
| | | Router ( ) WDM
| +---+ Node \-/ node
|________________________________
+---+ /-\ /-\ /-\ +---+
| B |-------( E )--------( G )---------( J )---------| C |
+---+ \-/ \-/ \-/ +---+
/ \ / \
/ \ / \
/ \ / \
/ \ / \
/ \ / \
+---+ /-\ /-\ /-\ +---+
| A |---------( F )---------( H )---------( I )---------| D |
+---+ \-/ \-/ \-/ +---+
Figure 1a: Sample topology
------------- | [ ] Client TE Node
| Client TE | | +++ Client TE Link
| DataBase | |_____________________
-------------
[B] ++++++++ [E] [J] +++++++++ [C]
[A] ++++++++ [F] [I] +++++++++ [D]
Figure 1b: Client TE Database
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Nodes A, B, C and D are IP routers that are connected to an Optical
WDM transport network. E, F, G, H, I and J are WDM nodes that
constitute the Server Network Domain. The border nodes (E, F, I and
J) operate in both the server and client domains. Figure 1b depicts
how the Client Network Domain TE topology looks like when there are
no Client TE Links provisioned across the optical domain.
| ***** F-J WDM Path (lambda 192000)
| @@@@@ E-I WDM Path (lambda 192000)
|________________________________
+---+ /-\ @@@@@@@@ /-\ /-\ +---+
| B |-------( E )--------( G )---------( J )---------| C |
+---+ \-/ *\-/*@ @*\-/@ +---+
*/ \*@ @*/ \@
*/ \*@ @*/ \@
*/ \*@ @*/ \@
*/ \*@*/ \@
*/ \*/ \@
+---+ /-\ /-\ /-\ +---+
| A |---------( F )---------( H )---------( I )---------| D |
+---+ \-/ \-/ \-/ +---+
Figure 2a: Mutually Exclusive potential WDM paths
------------ | TE-Links E-I and F-J are mutually exclusive
| Client-TE| | Advertised with MELG-ID - 25/192000
| Database | | [SRLG-ID 25; Shared Resource ID 192000]
------------ |_____________________________________________
[B] ++++++++ [E] [J] +++++++++ [C]
++++ +++++
+++ +++
++++++
+++ +++
++++ +++++
[A] ++++++++ [F] [I] +++++++++ [D]
Figure 2b: Client TE Database - Mutually Exclusive Virtual TE Links
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Now consider augmenting the Client TE topology by creating a couple
of Virtual TE Links across the optical domain. The potential paths
in the WDM network catering to these two virtual TE links are as
shown in Fig 2a and the corresponding augmented Client TE topology
is as illustrated in Fig 2b.
In this particular example, the potential paths in the WDM layer
network supporting the Virtual TE Links not only intersect, but also
require the usage of the same resource (lambda channel 192000) on
the intersection. Because the Virtual TE Links depend on the same
uncommitted network resource, only one of them could get activated
at any given time. In other words they are mutually exclusive. This
scenario is encountered when the potential paths depend on any
common physical resource (e.g. transponder, regenerator, wavelength
converter, etc.) that could be used by only one Server Network
Domain LSP at a time.
For a Client Network Domain path computation function (especially a
centralized one) that is capable of concurrent computation of
multiple paths, it is important to know the existence of mutually
exclusive relationship between Virtual TE Links. Absent this
information, there exists the risk of yielding erroneous concurrent
path computation results where only a subset of the computed paths
can get successfully provisioned. This document introduces the
concept of Mutually Exclusive Link Group to address this problem.
The Virtual TE Link mutual exclusivity attribute can be either (a)
Static or (b) Dynamic.
In case (a), the Virtual TE Link mutual exclusivity exists
permanently within a given network configuration. This type of
mutual exclusivity comes into play when two or more Virtual TE Links
depend on a Server Network Domain resource that could be used in its
entirety by only one Virtual TE Link (when committed).
In case (b), the Virtual TE Link mutual exclusivity exists
temporarily within a given network configuration. This type of
mutual exclusivity comes into play when two or more Virtual TE Links
depend on a Server Network Domain resource that could be shared
simultaneously in some limited capacity by several Virtual TE Links
(when committed). Consider, for example, a situation when three
Virtual TE Links depend on a Server Domain WDM link that currently
has two lambda channels available. Consider further that each
Virtual TE Link (in order to be committed) requires one lambda
channel to be allocated on said WDM link. Obviously, under these
conditions only two out of three Virtual TE Links could be
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concurrently committed. Such Virtual TE Link mutual exclusivity is
dynamic and temporary because as soon as additional lambda channels
become available on the WDM link, the Virtual TE Link mutual
exclusivity will cease to exist - it will become possible to commit
all three Virtual TE Links concurrently.
This revision of the draft discusses only the Static Virtual TE Link
mutual exclusivity. Dynamic Virtual TE Link mutual exclusivity will
be addressed in later revisions.
3. Mutually Exclusive Link Group
The Mutually Exclusive Link Group (MELG) construct defined in this
document has 2 purposes
- To indicate via a separate network unique number (MELG ID) an
element or a situation that makes the advertised Virtual TE Link
belong to one or more Mutually Exclusive Link Groups. Path
computing element will be able to decide on whether two or more
Virtual TE Links are mutually exclusive or not by finding an
overlap of advertised MELGs (similar to deciding on whether two or
more TE links share fate or not by finding common SRLGs)
- To indicate whether the advertised Virtual TE Link is committed or
not at the moment of the advertising. Such information is
important for a path computation element: Committing new Virtual
TE links (vs. re-using already committed ones) has a consequence
of allocating more server layer resources and disabling other
Virtual TE Links that have common MELGs with newly committed
Virtual TE Links; Committing a new Virtual TE Link also means a
longer setup time for the Client LSP and higher risk of setup-
failure.
4. Protocol Extensions
4.1. OSPF
The MELG is a sub-TLV of the top level TE Link TLV. It may occur at
most once within the Link TLV. The format of the MELGs sub-TLV is
defined as follows:
Name: MELG
Type: TBD
Length: Variable
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLV Type | Sub-TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTE-Flags (16 bits) |U | Number of MELGs (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MELGID1 (64 bits) |
| MELGID2 (64 bits) |
| ........................ |
| MELGIDn (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Number of MELGs: number of MELGS advertised for the
Virtual TE Link;
VTE-Flags: Virtual TE Link specific flags;
MELGID1,MELGID2,...,MELGIDn: 64-bit network domain unique numbers
associated with each of the advertised
MELGs
Currently defined Virtual TE Link specific flags are:
U bit (bit 1): Uncommitted - if set, the Virtual TE Link is
uncommitted at the time of the advertising (i.e. the server layer
network LSP is not set up); if cleared, the Virtual TE Link is
committed (i.e. the server layer LSP is fully provisioned and
functioning). All other bits of the "VTE-Flags" field are
reserved for future use and MUST be cleared.
Note: A Virtual TE Link advertisement MAY include MELGs sub-TLV with
zero MELGs for the purpose of communicating to the TE domain whether
the Virtual TE Link is currently committed or not.
4.2. ISIS
The MELG TLV (of type TBD) contains a data structure consisting of:
6 octets of System ID
1 octet of Pseudonode Number
1 octet Flag
4 octets of IPv4 interface address or 4 octets of a Link
Local Identifier
4 octets of IPv4 neighbor address or 4 octets of a Link
Remote Identifier
2 octets MELG-Flags
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2 octets - Number of MELGs
variable List of MELG values, where each element in the list
has 8 octets
The following illustrates encoding of the value field of the MELG
TLV.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| System ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| System ID (cont.) |Pseudonode num | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+
| Ipv4 interface address/Link Local Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ipv4 neighbor address/Link Remote Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTE-Flags (16 bits) |U | Number of MELGs (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MELGID1 (64 bits) |
| MELGID2 (64 bits) |
| ........................ |
| MELGIDn (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The neighbor is identified by its System ID (6 octets), plus one octet
to indicate the pseudonode number if the neighbor is on a LAN
interface.
The least significant bit of the Flag octet indicates whether the
interface is numbered (set to 1) or unnumbered (set to 0). All other
bits are reserved and should be set to 0.
The length of the TLV is 20 + 8 * (number of MELG values).
The semantics of "VTE-Flags", "Number of MELGs" and "MELGID Values" are
the same as the ones defined under OSPF extensions.
The MELG TLV MAY occur more than once within the IS-IS Link State
Protocol Data Units.
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5. Security Considerations
TBD
6. IANA Considerations
6.1. OSPF
IANA is requested to allocate a new sub-TLV type for MELG (as
defined in Section 4.1) under the top-level TE Link TLV.
6.2. ISIS
IANA is requested to allocate a new IS-IS TLV type for MELG (as
defined in Section 4.2).
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4202] K.Kompella, Y.Rekhter, "Routing Extensions in Support
of Generalized Multi-Protocol Label Switching (GMPLS)",
RFC4202, October 2005.
[RFC6001] D.Papadimitriou, M.Vigoureax, K.Shiomoto, D.Brungard
and JL. Le Roux, "GMPLS Protocol Extensions for Multi-
Layer and Multi-Region Networks", RFC 6001, October
2010.
8. Acknowledgments
Chris Bowers [cbowers@juniper.net]
Authors' Addresses
Vishnu Pavan Beeram
Juniper Networks
Email: vbeeram@juniper.net
Igor Bryskin
ADVA Optical Networking
Email: ibryskin@advaoptical.com
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John Drake
Juniper Networks
Email: jdrake@juniper.net
Gert Grammel
Juniper Networks
Email: ggrammel@juniper.net
Wes Doonan
ADVA Optical Networking
Email: wdoonan@advaoptical.com
Manuel Paul
Deutsche Telekom
Email: Manuel.Paul@telekom.de
Ruediger Kunze
Deutsche Telekom
Email: Ruediger.Kunze@telekom.de
Oscar Gonzalez de Dios
Telefonica
Email: ogondio@tid.es
Cyril Margaria
Coriant GmbH
Email: cyril.margaria@coriant.com
Friedrich Armbruster
Coriant GmbH
Email: friedrich.armbruster@coriant.com
Daniele Ceccarelli
Ericsson
Email: daniele.ceccarelli@ericsson.com
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