Network Working Group H. Khosravi
Request for Comments: 3604 Intel
Category: Informational G. Kullgren
S. Shew
Nortel Networks
J. Sadler
Tellabs
A. Watanabe
NTT
October 2003
Requirements for Adding Optical Support to
the General Switch Management Protocol version 3 (GSMPv3)
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This memo provides requirements for adding optical switching support
to the General Switch Management Protocol (GSMP). It also contains
clarifications and suggested changes to the GSMPv3 specification.
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 BCP 14, RFC 2119 [1].
1. Overview
This document details the changes to GSMP necessary for the support
of optical (non-transparent and all optical), SONET/SDH, and spatial
switching of IP packets, Layer 2 (L2) frames and TDM data. When
implemented, GSMP controllers will then be able to control: photonic
cross-connects (optical-optical), transparent optical cross connects
(optical-electrical-optical, frame independent), opaque cross
connects (optical-electrical-optical, SONET/SDH frames), and
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traditional TDM switches (all electrical). The resulting systems
could form IP based optical routers, optical label switches,
wavelength routers, and dynamic optical cross connects.
Several different generic models exist defining how to provide
control plane functionality in an optical network [2], [3], [4].
This document takes no position on which model is 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). Therefore, the requirements contained within are focused only
on the separation of control functions from data functions in order
to provide a more flexible network architecture.
GSMPv3 [5] is well suited for providing the control interface
necessary for allowing an IP based controller to direct the
activities of an optical switch. In order for GSMP to operate
between controllers and optical switches and cross connects, support
for optical labels and service and resource abstractions must be
added to GSMP.
This document also includes changes recommended by implementers that
will facilitate easier development of a GSMP implementation. These
changes consist of rearranging PDU formats, clarification of flags,
transaction identifiers, and response codes.
2. Requirements for Optical Support
2.1. Label
2.1.1. Label Types
New labels are needed to identify the entities that are to be
switched in the optical fabric. These are longer than the labels
defined in GSMPv3 as they have physical and structural context. As
GMPLS [2], [3] 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)
- Plesiochronous Data Hierarchy (PDH) labels [6]
- OTN G.709 labels
- Lambdas
- Fibers
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GSMP MUST include support for all label types list above, as well as
for label hierarchies and label lists as defined by GMPLS.
Therefore, the ability to perform operations on groups of the above
labels MUST also be supported (e.g., 5 OC-3s, contiguous wavebands).
2.1.2. Label Management Issues
An updated label range message MUST be provided. There MUST also be
support of multiplexing (e.g., no multiplexing, SONET, Gigabit
Ethernet multiplexing etc).
2.2. Statistics messages
Optical switches have a number of different statistics which are not
in common with ATM, or Frame Relay switches. Consequently, the
statistics messages SHOULD be updated to report Performance
Monitoring statistics defined for all new optical transport
technologies added to GSMP.
2.3. Configuration Issues
2.3.1. Switch Configuration
2.3.1.1. Layer Switching Identification
Since an Optical Switch may be able to provide connection services at
multiple transport layers (i.e., STS-3c, STS-1, VT-1.5, DS3, DS1),
and not all switches are expected to support the same transport
layers, the switch will need to notify the controller of the specific
layers it can support.
Therefore, the Switch Configuration message MUST be extended to
provide a list of the transport layers for which an optical switch
can perform switching.
2.3.2. Port Configuration
The port configuration message supplies the controller with the
configuration information related to a single port. Consequently,
extensive additions will need to be made to this command.
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2.3.2.1. Port Type extensions
Port types MUST be added to support the mix of optical signals that
can operate over a single fiber.
The port information that MAY need to be conveyed includes [7]:
- wavelengths available per interface
- bit rate per wavelength
- type of fiber
2.3.2.2. Supported Signal Type extensions
Since a port on an optical switch may support signals at multiple
transport layers, it is necessary to understand the signals
supported, as well as the possible ways that one signal can be
transported within another.
For OTN, SONET/SDH and PDH optical switches, the Port configuration
message MUST be extended to detail the different transport layer
signals that are supported by a port. Furthermore, this extension
MUST detail which signals may be transported by another signal.
This mechanism MUST also provide information about optional
capabilities (such as virtual concatenation and arbitrary
concatenation for SONET/SDH) available on a port.
2.3.2.3. Trace Mechanism support Identification
A number of transport layer signals include overhead channels that
can be used to identify the source of a signal. Since they are
embedded in the signal, only the network element has access to the
signals. However, not all network elements have the capability to
set or read the messages in these channels on every port.
Consequently, this port attribute needs to be reported to the
controller.
The Port Configuration message MUST be extended to report which trace
mechanisms are supported by a port.
2.3.2.4. Port Location Identification
Since contemporary Optical switches have the ability to support tens
of thousands of ports in hundreds of shelves located in as
potentially as many bays, the current "Slot/Port" location identifier
is inadequate.
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The Slot/Port Location Identifier MUST be extended to encode
Bay/Shelf/Slot/Port.
2.3.2.5. Port-related Partitioning Extensions
Partitioning can be done for any resource that exists in the network
element. The GSMP partitioning draft currently defines ports and
switching resources as partitionable resources. Since optical
switches may support multiple transport network layers, an additional
resource type is introduced: the transport layer signal.
The point where a transport layer signal is inserted into a lower
layer signal (called an "access point" by the ITU [8]), is very
similar to a port. Therefore, when partitioning is done on a
transport layer signal basis, the partition that is the user of the
access point MUST have a port that associated with the access point.
Labels will then be used in the to describe the subordinate signals.
2.3.3. 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.
2.4. 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 [5]. GSMP provides the means for each
connection to be created with specific attributes. Therefore,
service parameters will need to be defined for each of the Different
Optical technologies.
2.4.1. Transparent Optical
Capability to control re-timing and re-shaping on a per port level
MUST be added.
2.4.2. SONET/SDH and OTN
The capability to control the adaptation parameters used when a
transport signal is inserted into another transport signal MUST be
added. These parameters SHOULD be modifiable at times other than
adding a branch so that functions such as Tandem Connection
Monitoring can be configured. Currently, the default set of service
models in GSMP are all based on the services models defined
elsewhere, e.g., the Intserv model [9], [10], the Diffserv [11]
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model, ATM QoS models and the Frame relay forum QoS models. A
determination needs to be made of the applicable service models for
optical channel trails. These models MUST then be mapped to the GSMP
capability set mechanism.
2.5. 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).
A new encapsulation SHOULD be defined allowing the use of a non-IP
raw wavelength control connection.
Likewise, a new encapsulation SHOULD be defined allowing GSMP to be
used in legacy Data Communication Network (DCN) environments that use
OSI CLNP.
The security risks of additional non-IP encapsulations MUST be
described, since the mandatory to implement mechanism of IPsec is not
available for these control channels, as in the RFC 3293 Ethernet and
ATM cases. It is in scope to perform risk analysis and describe if
mechanisms for link-level security mitigate the risk.
2.6. MIB Issues
If a new encapsulation is defined, then the encapsulation group
SHOULD be updated. No other changes should be required.
2.7. OXC Transaction Model
2.7.1. 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 behavior.
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2.7.2. 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.
2.8. OXC Protection Capabilities
To achieve good 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 protection
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 behavior 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. Consequently, the GSMP port configuration command MUST
be extended to allow autonomous protection behaviors to be
provisioned into the Network Element.
Furthermore, the controller MUST be able to provide the parameters
for when reversion from a backup link to the original link is
allowed. This may take the form of hold-off timers, BER parameters,
or the requirement for controller directed reversion.
2.8.1. Non-Reserved Protection Links
An example of protection OXC behavior 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.
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When a backup link is used or the OXC reverts back to the original
link, the control plane (i.e., signaling) 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.
2.8.2. 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.
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., signaling) 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.
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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.
2.8.3. 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.
2.8.4. Protection Link Capabilities
When an OXC has the capability to perform protection switching
independently from the Optical Call Controller (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, signaling clients could define a
path protection scheme over multiple GSMP enabled OXCs. This is for
further study.
2.9. Controller directed restoration
Bi-directional Connection Replacement
Connections in the transport network are inherently point-to-point
bi-directional. Unfortunately, GSMPv3 currently does not allow for
the B and R flags to be set on an add branch message. This means
that it is not possible to do an atomic replacement of a bi-
directional connection -- an action that is desirable for controller
directed restoration. Consequently, the protocol MUST be changed to
allow these flags to be used at the same time.
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2.10. Support for optical burst switching
GSMP for Optical Switching should also support optical burst
switching. As described in [12], [13], and [14], part of burst
switching connection setup includes reserving time on the transport
medium for the client.
This time is characterized by two parameters: a start time and the
duration. These values MAY define a one-time reservation or a
repeating reservation. Upon a request for setup of a burst
connection, the GSMP controller MUST perform appropriate Connection
Admission Control for the time and duration specified and, if the
connection is allowed, MUST signal these parameters to the burst
switching device to reserve the exact bandwidth required [12], [14].
The burst switch MUST perform the switching operation autonomously,
using the synchronization methods prescribed for the burst network it
is operating in.
3. Requirements from Implementers
This section describes requirements to GSMP v3 based on some
implementation experience. They address areas of ambiguity, missing
semantics, and configuration recommendations.
3.1. GSMP Packet Format
The Basic GSMP Message Format in chapter 3.1.1 in [5] describes the
common fields present in all GSMP messages except for the Adjacency
protocol.
3.1.1. Message segmentation
If a message exceeds the MTU of the link layer it has to be
segmented. This was originally done with the "More" value in the
Result field. The addition of the I flag and the SubMessage Number
to the header has made the "More" value obsolete.
The I flag and SubMessage numbers should be used in all messages that
can be segmented.
3.1.1.1. SubMessage Number and I flag
It should be specified if the SubMessage Number starts on 0 or 1 in a
segmented message and what value the I flag should have in an message
that is not segmented.
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3.1.1.2. Message Length
Clarification of what value should be used in the Length field for
segmented messages. Specifically, does the Length field contain the
total length of the message or the length of the current segment.
3.1.1.3. Message Segmentation example
To avoid all ambiguity an example of message segmentation should be
provided.
3.1.2. Transaction Identifier
The Transaction Identifier in [5] does not distinguish between
replies from a request with "AckAll" and "NoSuccessAck". It also
does not provide any information about how to handle replies where
the Transaction ID doesn't match a Transaction ID from a previously
sent request.
If multiple controllers are connected to a single switch and the
switch sends an event message with "ReturnReceipt" set to all of
them, there is no way for the switch to identify which controller the
receipt is coming from.
The "ReturnReceipt" value should not be permitted for Events.
3.2. Window Size
The Switch Configuration Message defined in chapter 8.1 in [5]
defines a Window size to be used by the controller when sending
messages to the switch. It is not stated if this window should apply
to all messages or only to messages that will always generate a
reply.
If messages that may not generate a reply should be counted against
the window a time-out period when they are to be removed from the
window should be defined.
It is not defined if the window should be cleared when the adjacency
is lost and later recovered.
3.3. Retransmission
A retransmission policy with a well-designed exponential backoff
should be used if no reply is received for a message with "AckAll"
set.
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3.4. Delete Branches Message
The "Delete Branch Element" has a 4 bit Error field that should be
redefined to match the size of the "Failure Response Codes".
3.5. Adjacency
The chapter about how to handle a new adjacency and re-established
adjacencies should be clarified.
3.5.1. Loss of Synchronization
The switch must not reset the connection states if another adjacency
has already been established since this would destroy an already
valid state.
4. Security Considerations
The security of GSMP's TCP/IP control channel has been addressed in
[15]. Any potential remaining security considerations are not
addressed in this requirements document.
5. Acknowledgements
The list of authors provided with this document is a reduction of the
original list. Currently listed authors wish to acknowledge that a
substantial amount was also contributed to this work by: Avri Doria
and Kenneth Sundell
The authors would like to acknowledge the careful review and comments
of Dimitri Papadimitriou, Torbjorn Hedqvist, Satoru Okamoto, and
Kohei Shiomoto.
6. References
6.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
6.2. Informative References
[2] Berger, L., Ed., "Generalized MPLS - Signaling Functional
Description", RFC 3471, January 2003.
[3] Mannie, E., et al., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", Work in Progress, May 2003.
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[4] ITU-T Recommendation, "Architecture for the Automatically
Switched Optical Network (ASON)", G.8080/Y.1304, January 2003
[5] Doria, A., Sundell, K., Hellstrand, F. and T. Worster, "General
Switch Management Protocol V3", RFC 3292, June 2002.
[6] Sadler, J., Mack-Crane, B., "TDM Labels for GSMP", Work in
Progress, February 2001.
[7] Rajagopalan, B., et al., "IP over Optical Networks: A
Framework", Work in Progress, September 2003.
[8] ITU-T Recommendation, "Generic functional architecture of
transport networks", G.805, March 2000.
[9] Braden, R., Clark, D. and S. Shenker, "Integrated Services in
the Internet Architecture: An Overview", RFC 1633, June 1994.
[10] Wroclawski, J., "Specification of the Controlled-Load Network
Element Service", RFC 2211, September 1997.
[11] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z. and W.
Weiss, _"An Architecture for Differentiated Services", RFC 2475,
December 1998.
[12] C. Qiao, M. Yoo, "Choice, and Feature and Issues in Optical
Burst Switching", Optical Net. Mag., vol.1, No.2, Apr.2000,
pp.36-44.
[13] Ilia Baldine, George N. Rouskas, Harry G. Perros, Dan
Stevension, "JumpStart: A Just-in-time Signaling Architecture
for WDM Burst-Switching Networks", IEEE Comm. Mag., Fab. 2002.
[14] Sanjeev Verma, et al. "Optical burst switching: a viable
solution for terabit IP backbone", IEEE network, pp. 48-53,
Nov/Dec 2000.
[15] Worster, T., Doria, A. and J. Buerkle, "GSMP Packet
Encapsulations for ATM, Ethernet and TCP", RFC 3293, June 2002.
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7. Authors' Addresses
Hormuzd Khosravi
Intel
2111 NE 25th Avenue
Hillsboro, OR 97124 USA
Phone: +1 503 264 0334
EMail: hormuzd.m.khosravi@intel.com
Georg Kullgren
Nortel Networks AB
S:t Eriksgatan 115 A
P.O. Box 6701
SE-113 85 Stockholm Sweden
EMail: geku@nortelnetworks.com
Jonathan Sadler
Tellabs Operations, Inc.
1415 West Diehl Road
Naperville, IL 60563
Phone: +1 630-798-6182
EMail: Jonathan.Sadler@tellabs.com
Stephen Shew
Nortel Networks
PO Box 3511 Station C
Ottawa, ON
K1Y 4H7
EMail: sdshew@nortelnetworks.com
Kohei Shiomoto
EMail: Shiomoto.Kohei@lab.ntt.co.jp
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Atsushi Watanabe
Nippon Telegraph and Telephone Corporation
807A 1-1 Hikari-no-oka, Yokosuka-shi
Kanagawa 239-0847, Japan
EMail: atsushi@exa.onlab.ntt.co.jp
Satoru Okamoto
Nippon Telegraph and Telephone Corporation
9-11 Midori-cho 3-chome, Musashino-shi
Tokyo 180-8585, Japan
EMail: okamoto@exa.onlab.ntt.co.jp
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8. Full Copyright Statement
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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RFC, FYI, BCP