Internet DRAFT - draft-beeram-ccamp-melg
draft-beeram-ccamp-melg
CCAMP Working Group Vishnu Pavan Beeram (Ed)
Internet Draft Juniper Networks
Intended status: Standards Track Igor Bryskin (Ed)
ADVA Optical Networking
Expires: August 12, 2014 February 12, 2014
Mutually Exclusive Link Group (MELG)
draft-beeram-ccamp-melg-03
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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. Virtual TE Link - Semantics....................................3
3. Mutually Exclusive Virtual TE Links............................3
3.1. Static vs Dynamic.........................................4
4. Static Mutual Exclusivity......................................4
5. Mutually Exclusive Link Group..................................7
6. Protocol Extensions............................................8
6.1. OSPF......................................................8
6.2. ISIS......................................................9
7. Security Considerations.......................................10
8. IANA Considerations...........................................10
8.1. OSPF.....................................................10
8.2. ISIS.....................................................10
9. Normative References..........................................10
10. Acknowledgments..............................................11
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 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 different types of mutual exclusivity (Static vs
Dynamic) that come into play and explains the need to advertise this
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information into the Client TEDB. It then goes onto introduce a new
TE construct (MELG) to carry static mutual exclusivity information.
2. Virtual TE Link - Semantics
A Virtual TE Link (as per existing definitions) represents the
potentiality to setup a server layer LSP, but there are currently no
strict guidelines imposed on how the underlying server layer LSP
would need to get set up. The characteristics of the underlying
server-path are not necessarily pinned down until the Virtual TE
Link gets actually committed. This means that some important
characteristics of the Virtual TE Link like shared-risk and delay
(and mutual exclusivity information) may not be known until the
corresponding server layer LSP is set up. This makes resource
planning (for example - pre-configuring network failure recovery
schemes) in a multi-layer network that includes Virtual TE Links a
very hard problem.
This document uses a slightly enhanced view of a Virtual TE Link. In
the context of this document, the Virtual TE Link (even when it is
uncommitted) is always aware of the key characteristics of the
underlying server-path. The creation and maintenance of this Virtual
TE Link is strictly driven by policy. Policy not only determines
which Virtual TE Link to create (What termination points?), but it
may also constrain how the corresponding underlying server layer LSP
(What path?) needs to get set up. The basic idea behind this
"enhanced view" is that it makes the "Virtual TE Link" get as close
as it can to representing a "Real TE Link".
Also, as per this document, a Virtual TE Link remains a Virtual TE
Link through-out its life-time (until it gets deleted by the
user/policy). It may get committed (underlying server LSP gets set
up) and uncommitted (underlying server LSP gets deleted) from time
to time, but it never really loses it "Virtual" property.
3. Mutually Exclusive Virtual TE Links
Mutual Exclusivity comes into play when multiple Virtual TE Links
are dependent on the usage of the same underlying server resource.
Since not all of these Virtual TE Links can get committed at the
same time, they are deemed to be mutually exclusive.
The existence of this "mutual exclusivity" property would need to be
advertised into the Client TE Domain. This is of relevance to Client
Path Computation engines; especially those that are capable of doing
concurrent computations. If this information is absent, there exists
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the risk of the Computation engine yielding erroneous concurrent
path computation results where only a subset of the computed paths
get successfully provisioned.
The "Mutual Exclusivity" property of a Virtual TE Link can be either
static or dynamic in nature.
3.1. Static vs Dynamic
Static Mutual Exclusivity: This type of mutual exclusivity exists
permanently within a given network configuration. It comes into play
when two or more Virtual TE Links depend on the usage of the same
non-shareable underlying server network domain resource. This
resource gets used up in its entirety by a single Virtual TE Link
when committed. Such resources exist only in the WDM layer.
Dynamic Mutual Exclusivity: This type of mutual exclusivity exists
temporarily within a given network configuration. It comes into play
when two or more Virtual TE Links depend on the usage of the same
shareable underlying server network domain resource. Mutual
Exclusivity exists when the amount of the server resource that is
available for sharing is limited; it ceases to exist when sufficient
amount of the resource is available for accommodating all
corresponding Virtual TE Links. Such resources exist in all layers.
Because of their inherent difference, the advertisement paradigm of
the TE construct required to carry static mutual exclusivity
information is quite different from that of the TE construct
required to carry dynamic mutual exclusivity information. Static
mutual exclusivity Information can get advertised per TE-Link using
a simple sub-TLV construct. There wouldn't be any scaling issues
with this approach because of the static nature of the information
that gets advertised. On the contrary, advertising dynamic mutual
exclusivity information per TE-Link poses serious scaling concerns
and hence requires a different type of construct/paradigm.
This document introduces a new TE construct for carrying static
mutual exclusivity information. The mechanisms to address dynamic
mutual exclusivity are discussed in a separate document [SRcLG].
4. Static Mutual Exclusivity
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
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transport connectivity to the packet layer network Domain (Client
Network Domain).
|
| +---+ /-\
| | | Router ( ) WDM
| +---+ Node \-/ node
|________________________________
+---+ /-\ /-\ /-\ +---+
| R1|-------( A )--------( C )---------( E )---------| R3|
+---+ \-/ \-/ \-/ +---+
/ \ / \
/ \ / \
/ \ / \
/ \ / \
/ \ / \
+---+ /-\ /-\ /-\ +---+
| R2|---------( B )---------( D )---------( F )---------| R4|
+---+ \-/ \-/ \-/ +---+
Figure 1a: Sample topology
------------- | [ ] Client TE Node
| Client TE | | +++ Client TE Link
| DataBase | |_____________________
-------------
[R1] ++++++++ [A] [E] +++++++++ [R3]
[R2] ++++++++ [B] [F] +++++++++ [R4]
Figure 1b: Client TE Database
Nodes R1, R2, R3 and R4 are IP routers that are connected to an
Optical WDM transport network. A, B, C, D, E and F are WDM nodes
that constitute the Server Network Domain. The border nodes (A, B, E
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and F) 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.
| ***** B-F WDM Path
| @@@@@ B-E WDM Path
|________________________________
+---+ /-\ /-\ @@@@@@@@@ /-\ +---+
| R1|-------( A )--------( C )---------( E )---------| R3|
+---+ \-/ @\-/ \-/ +---+
@/ \ / \
@/ \ / \
@/ \ / \
@/ \ / \
@/ \ / \
+---+ /-\ ********* /-\ ********* /-\ +---+
| R2|---------( B )---------( D )---------( F )---------| R4|
+---+ \-/ \-/ \-/ +---+
Figure 2a: Mutually Exclusive potential WDM paths
------------ | TE-Links B-F and B-E are mutually exclusive;
| Client-TE| | They depend on the usage of the same
| Database | | underlying non-shareable server resource
------------ |_____________________________________________
[R1] ++++++++ [A] [E] +++++++++ [R3]
+++++
++++
++++
++++
++++
[R2] ++++++++ [B] ++++++++++++++++++++ [F] +++++++++ [R4]
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 require the usage of the
same source transponder (on "Node B"). 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.
This document proposes the use of "Mutually Exclusive Link Group
(MELG)" for catering to this scenario.
5. 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.
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6. Protocol Extensions
6.1. 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
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.
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6.2. 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
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.
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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.
7. Security Considerations
TBD
8. IANA Considerations
8.1. OSPF
IANA is requested to allocate a new sub-TLV type for MELG (as
defined in Section 6.1) under the top-level TE Link TLV.
8.2. ISIS
IANA is requested to allocate a new IS-IS TLV type for MELG (as
defined in Section 6.2).
9. 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.
[SRcLG] Beeram, V., "Shared Resource Link Group",
draft-beeram-ccamp-srclg, February 2014
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10. 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
John Drake
Juniper Networks
Email: jdrake@juniper.net
Gert Grammel
Juniper Networks
Email: ggrammel@juniper.net
Wes Doonan
Email: wddlists@gmail.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
Juniper Networks
Email: cmargaria@juniper.net
Friedrich Armbruster
Coriant GmbH
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Email: friedrich.armbruster@coriant.com
Daniele Ceccarelli
Ericsson
Email: daniele.ceccarelli@ericsson.com
Fatai Zhang
Huawei Technologies
Email: zhangfatai@huawei.com
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