GSMP Working Group Avri Doria
Internet Draft Kenneth Sundell
Document: <draft-ietf-gsmp-reqs-00.txt> Stephen Shew
Category: WG Draft Nortel Networks
Hormunzd Khosravi
Intel
July 2001
Requirements for adding Optical Switch Support to GSMP
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 except that the right to
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Abstract
This memo provides an overview of the requirements on the GSMP
protocol for support of optical switching.
1. Overview
This draft is intended to describe the required changes to GSMP for
support of optical (non-transparent and all optical), SONET/SDH, and
spatial switching of IP packets, L2 frames and TDM data. The mix of
possible instantiations include GSMP controllers connected to:
photonic cross-connects (optical-optical), transparent optical cross
connects (optical-electrical-optical, frame independent), opaque
cross connects (optical-electrical-optical, SONET/SDH frames), and
traditional TDM switches (all electrical). These could form IP based
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Internet Draft Req. for Optical Support in GSMP July 2001
optical routers, optical label switches, wavelength routers, and
dynamic optical cross connects.
There are also several different generic models that might be
applied to running IP over WDM [1][2][11]. This document defines the
requirements for the separation of control functions from data
functions in order to provide a more flexible network
architecture.[3]
In this draft, no position will be taken about the eventual
architectural model that will be most appropriate (e.g., single or
multiple routing plane instances). The only assumption is that the
ability to separate the control mechanisms from the data switching
is as useful for the signaling of optical paths (e.g., GMPLS) as it
is for the signaling of L2 paths (e.g., MPLS).
GSMPv3[6] is well suited for providing the control mechanisms
necessary for allowing an IP based controller to direct the
activities of an optical switch. In order for GSMP to operate
between IP controllers and optical switches and cross connects,
support for optical labels and service and resource abstractions
must be added to GSMP.
2. Label Types
New labels are needed to identify the entities that are to be
switched in the optical fabric. These are longer than GSMPv3 labels
as they have physical and structural context. As GMPLS[1][2] has
had very similar requirements for label formats alignment with GMPLS
is proposed. This includes support for:
- Digital Carrier Hierarchy (e.g., DS-1, E1)
- SONET and SDH Hierarchy (e.g., OC-3, STM-1, VT1.5, VC-12)
- PDH labels [12]
- OTN G.709 labels
- Lambdas
- Fibers
GSMP MUST include support for all label types as well as for label
hierarchies and label lists as defined by GMPLS.
Bundles of the above labels SHOULD also be supported (e.g., 5 OC-
3s, contiguous wavebands)
3. Port and Label Management Issues
As with routers, it may be useful to recognize bundles of links [13]
between optical cross-connects. This goes beyond knowledge of
separate independent ports. If so, changes to the port management
message MAY be needed to describe ports which are part of a link
bundle.
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An updated label range message MUST be provided. There MUST also be
support of multiplexing (e.g. no multiplexing, SONET, Gigabit
Ethernet multiplexing etc).
4. Statistics messages
No changes are currently proposed for the statistics messages to
support optical switching.
5. Configuration Issues
5.1 Switch Configuration
No changes are currently proposed for the switch configuration
messages to support optical switching.
5.2 Port Configuration
The port configuration message supplies the controller with the
configuration information related to a single port. In order to
handle the specific port types in an optical switch, extensive
additions will need to be made to this command.
Port types MUST be added to support the mix of SONET/SDH signals
that can operate over a single fiber. Information that MAY need to
be conveyed includes[8]:
- wavelengths available per interface
- bit rate per wavelength
- type of fiber
Again, it MAY be useful to recognize bundles of links [13] between
optical cross-connects. If so, changes to the port configuration
message would be needed to describe ports which are part of a link
bundle.
5.3 Service Configuration
While new capability sets MUST be added to support quality
parameters in optical switches, no changes are foreseen to the
service configuration message as its role to carry the service
information as defined in the applicable service model. The changes
related to the service model will be discussed in section 0.
6. Service Model Issues
While one assumption of using optical media is that bandwidth is
plentiful, it should be expected that traffic engineering will be
necessary in any case[3]. GSMP provides the means for each
connection, or in this each light trail, to be created with specific
quality attributes. Capability to control re-timing and re-shaping
MUST be added.
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Currently, the default set of service models in GSMP are all based
on the services models defined elsewhere, e.g. the Intserv
model[5][7], the Diffserv[4] model, ATM QoS models and the Frame
relay forum QoS models. A determination needs to be made of the
applicable quality models for optical channel trails. These models
MUST then be mapped to the GSMP capability set mechanism.
7. Encapsulation issues
The working group needs to decide whether a new encapsulation is
required. In other words, will all optical switches used in either
the MPLS over Optics and the IP over optics applications require
that IP be implemented on the control channel connecting the GSMP
controller and Optical switch (the GSMP target). If a raw
wavelength control connection is to be allowed, a new encapsulation
SHOULD be defined.
8. MIB Issues
If a new encapsulation is defined, then the encapsulation group
SHOULD be updated. No other changes should be required.
9. OXC Transaction Model
9.1 Serial Transactions
Many existing OXCs use a command interface which assumes a serial
transaction model. That is, a new command cannot be issued or
processed until the existing command is completed. Under
provisioning control via a network management application, and with
non-dynamic path setup, this model has been adequate.
Moving to a dynamic path setup capability with a distributed control
plane, a parallel transaction model is likely required for
performance. This is particularly helpful when the performance of
setting up a TDM style connection is much slower than setting up an
L2 connection table. If the OXC is not able to support a parallel
transaction model, a GSMP controller MUST be informed of this and
adopt serial transaction behaviour.
9.2 Bulk Transactions
Again due to the time it may take some OXCs to setup TDM connections
relative to L2 fabrics (e.g., VC-4/STS-1 SPE fabric in an HOVC/STS
switch), support for sending multiple transactions in the same
message is a useful optimization. When an OXC receives a bulk
message, the individual transactions are acted upon and a single
reply is sent. If parallel transactions are not supported, bulk
messages can improve performance by reducing transaction overhead.
Bulk transactions SHOULD be supported.
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10. OXC Restoration Capabilities
To achieve fast link protection performance (e.g., 50 ms after
failure detection), SONET/SDH and some OXC systems use hardware
based protection schemes (e.g., ring protection). Achieving this
level of performance solely using a data control plane such as GMPLS
is a serious challenge. An alternate approach is to utilize fast
restoration capabilities of an OXC with a dynamic control plane.
An implication of this hybrid approach is that extensions are needed
to GSMP to provision the behaviour of an OXC in anticipation of a
link failure.
This differs from the strict master-slave relationship in GSMP for
Layer 2 switches in that here the OXC is capable of taking an action
independent of the GSMP controller and then informing the controller
afterwards.
10.1 Non-Reserved Protection Links
An example of protection OXC behaviour is that when a link fails, a
backup link may be used to protect traffic on. This backup link
could be selected from a set of links, none of which are pre-
reserved. A backup link could be shared with one or more "working"
links which is a form of 1:n shared protection. Specifying the set
of possible backup links SHOULD be done as an option to the Add-
Branch message.
When a backup link is used or the OXC reverts back to the original
link, the control plane (i.e., signalling) may need to know about
the new path state in order to notify the operator, or take some
other OAM action (e.g., billing, SLA monitoring). An additional
GSMP message to inform the controller SHOULD be added to do this.
10.2 Dedicated Protection Links
A more specialized form of restoration called "1+1" defines a
(usually node disjoint) protection path in a transport/optical
network for a given working path. At the ingress node to the path,
the traffic signal is sent simultaneously along both working and
protection paths. Under non-failure conditions at the egress node,
only the last link of the working path is connected to the client.
When any link in the working path fails, traffic on the working path
ceases to be received at end of the path. The egress OXC detects
this condition and then switches to use the last link of the
protection path without the controller having to issue a Move-Input-
Branch message. At no time is the ingress node aware which link the
egress node is using. Selection of the protection path and all of
its links is outside the scope of GSMP.
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Specification of the two output branches at the ingress node can be
done with the usual Add-Branch semantics. The ingress node
protection link is not shared with any other working link.
Specification of the two input branches at the egress node should be
done when the Add-Branch message is sent. This SHOULD be an option
to that message. The egress node protection link is not shared with
any other working link.
When a protection link is used or the OXC reverts back to the
working link, the control plane (i.e., signalling) may need to know
about the new path state in order to notify the operator, or take
some other OAM action (e.g., billing, SLA monitoring). An
additional GSMP message to inform the controller SHOULD be added to
do this.
If an alternate input port is not specified with an original Add-
Branch message, it MAY be specified in a subsequent Add-Branch
message. In this case, it is useful to include information about
existing users of the output port in that Add-Branch message. This
helps the OXC immediately learn of the association between the new
input port and an existing one. The association is used to enable
OXC protection procedures. This capability MUST be added to the add-
branch message.
Similar contextual information is needed for a Delete-Branch message
so that the OXC can determine if a path becomes unprotected. This
capability MUST be added to the Delete-branch message.
10.3 Protection Triggers
Aside from link or equipment failures, there are a variety of
maintenance conditions that could cause the backup/protection
link(s) to be used. These may include:
-
Scheduled maintenance of the working link. Here the network
operator deliberately takes a link out of service to perform
maintenance.
-
Reconfiguration of fiber/node/network which causes temporary need
to use backup links.
It may be useful to specify these triggers when the
backup/protection links are defined with the Add-Branch message.
This depends on how the OXC is implemented to be aware of such
triggers. This is for further study.
10.4 Protection Link Capabilities
When an OXC has the capability to perform protection switching
independently from the OCC, it may be useful for the OCC to be
informed of these capabilities at switch and/or port configuration.
Applications in the GSMP controller could use this information. For
example, signalling clients could define a path protection scheme
over multiple GSMP enabled OXCs. This is for further study.
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11. Security Considerations
The security of GSMP's TCP/IP control channel has been addressed in
[10]. Any potential remaining security considerations are not
addressed in the current revision of this draft.
12. Acknowledgements
The authors would like to thank Dimitri Papadimitriou for his
valuable comments on this draft.
13. References
[1] Ashwood-Smith, D., et. al., "Generalized MPLS - Signaling
Functional Description", Internet Draft draft-
ietf-mpls-generalized-signaling-04.txt (work in
progress), May 2001.
[2] Mannie, E., et. al., _Generalized Multi-Protocol Label
Switching (GMPLS) Architecture_, draft-ietf-
ccamp-gmpls-architecture-00.txt (work in
progress), June 2001
[3] Awduche, D, Rekhter, Y, et. al., "Multi-Protocol Lambda
Switching: Combining MPLS Traffic Engineering
Control with Optical Crossconnects," draft-
awduche-mpls-te-optical-02.txt (work in
progress), July, 2000
[4] Blake, S., et. al., _An Architecture for
Differentiated Services_, RFC2475, December 1998
[5] Braden, R., _Integrated Services in the Internet
Architecture: An Overview_, RFC1633, June 1994
[6] Doria, A, Sundell, K, Hellstrand, F, Worster, T, "General
Switch Management Protocol V3," Internet Draft
draft-ietf-gsmp-08.txt (work in progress),
December 2000
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[7] J. Wroclawski, "Specification of the Controlled-Load
Network Element Service," RFC2211, Sep 1997.
[8] Rajagopalan, B., et. al., _IP over Optical Networks: A
Framework_, draft-many-ip-optical-framework-
02.txt (work in progress), November 2000
[9] Sjostrand, H, et al, Definitions of Managed Objects for the
General Switch Management Protocol (GSMP),"
Internet-Draft draft-ietf-gsmp-mib-04 (work in
progress), December 2000.
[10] Worster, T, et al, "GSMP Packet Encapsulations for ATM,
Ethernet and TCP," Internet-Draft draft-ietf-
gsmp-encaps-03 (work in progress), December 2000.
[11] G.ASON _Architecture for the Automatic Switched Optical
Network_, Draft v0.5.1, June 2001
[12] Sadler, J., Mack-Crane, B., "Generalized Switch Management
Protocol", draft-sadler-gsmp-tdm-labels-00.txt
(work in progress), February 2001
[13]
Kompella, K., et. al., _Link Bundling in MPLS Traffic
Engineering_, draft-kompella-mpls-bundle-05.txt
(work in progress), February 2001
14. Author's Addresses
Avri Doria
Nortel Networks
600 Technology Park Drive
Billerica MA 01821
avri@nortelnetworks.com
Kenneth Sundell
Nortel Networks AB
P.O. Box 6701
SE-113 85 Stockholm Sweden
ksundell@nortelnetworks.com
Stephen Shew
Nortel Networks
PO Box 3511 Station C
Ottawa, ON
K1Y 4H7
sdshew@nortelnetworks.com
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Hormuzd Khosravi
Intel
2111 NE 25th Avenue
Hillsboro, OR 97124 USA
Phone: +1 503 264 0334
hormuzd.m.khosravi@intel.com
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