Network Working Group                         Luc Ceuppens (Chromisys)
Internet Draft                              Dan Blumenthal (Chromisys)
Expiration Date: September 2000                 John Drake (Chromisys)
                                     Jacek Chrostowski (Cisco Systems)
                                       W.L. Edwards (iLambda Networks)

              Performance Monitoring in Photonic Networks
                         in support of MPL(ambda)S


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet- Drafts
   as reference material or to cite them other than as "work in

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

1. Abstract

   Realizing the important role that photonic switches can play in
   data-centric networks, work has been going on within the IETF to
   combine the control plane of MPLS (more specifically traffic
   engineering) with the point-and-click provisioning capabilities of
   photonic switches [1]. This document outlines a proposal to expand
   this initiative to include DWDM, OADM and ATM systems. It also
   proposes to expand the work beyond simple establishment of optical
   paths and include optical performance monitoring and management. The
   combined path routing and performance information that will be
   carried and shared between these network elements will allow the
   elements or element management system (EMS) to adequately assess the
   "health" of an optical path (which can be a wavelength or fiber
   strand). The routers and/or ATM switches at the edges of the
   photonic network will then use this information to dynamically
   manage the millions of wavelengths available in the photonic layer.

Ceuppens/Blumenthal et al.                                    [Page 1]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

2. Introduction

   Over the last two years, DWDM has proven to be a cost-effective
   means of increasing the bandwidth of installed fiber plant. While
   the technology originally only served to increase the size of the
   fiber spans, it is quickly becoming the foundation for networks that
   will offer customers a new class of high-bandwidth and broadband

   Sales of DWDM systems will reach $6 billion in North America by the
   end of 2000. This roughly translates into tens of thousands of
   wavelengths deployed within optical networks, either as point-to-
   point connections or in ring topologies. In addition, several
   millions of wavelengths are projected to be deployed in enterprise,
   metropolitan, regional, and long haul networks by 2007 in the United
   States alone.

   These wavelengths will require routing, add/drop, and protection
   functions, which can only be achieved through the implementation of
   network-wide management and monitoring capabilities. Current-
   generation DWDM networks are monitored, managed and protected within
   the digital domain, using SONET and its associated support systems.
   However, to leverage the full potential of wavelength-based
   networking, the provisioning, switching, management and monitoring
   functions have to move from the digital to the optical domain.
   Efficiently managing (i.e., adding, dropping, routing, protecting,
   and restoring) the growing number of traffic-bearing wavelengths can
   only be achieved through a new breed of optical networking element.
   This network element is the photonic switch*.

   Photonic switching is the next logical step in a long history of
   switching technology that started with manual "plug board"
   operators, evolved to mechanical crossbar and finally digital
   switching. Photonic switching will enable transparent photonic
   networks. Photonic networks will greatly simplify the architecture
   of both the network and the network nodes by establishing end-to-end
   optical paths across the network. An end-to-end photonic path
   behaves as a transparent$  "clear channel", so that there is
   virtually nothing in the path to limit the throughput of the fibers.

*  Photonic switches are often referred to as optical cross-connects
  (OXC). However, today's OXCs are based on electrical rather than
  photonic switching fabrics, and therefore do not demonstrate the
  optical transparency required to grow photonic networks in the
  future. We use the term photonic switch to distinguish these classes.
$ Transparency implies that signals with any type of modulation schemes
  (analog or digital), any bit rate, and any type of format can be
  superimposed and transmitted without interfering with one another,
  and without their information being modified within the network.
  Opaque networks do not have this property.

Ceuppens/Blumenthal et al.                                    [Page 2]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

   A transparent channel essentially behaves like an ideal
   communications with almost no noise and very large bandwidth.
   Secondly, as the nodes in a photonic network have essentially no
   data processing to do, they can be made extremely simple and hence
   very cheap. Finally, optical node simplicity also means simplicity
   of control and management.

   Without any doubt, the next revolution in the telecommunications
   industry will occur within the optical domain. Now that the basic
   components are available to build photonic networks, the most
   important innovations will come from adding intelligence that
   enables the interworking of all the network elements (Routers, ATM
   switches, DWDM transmission systems and photonic switches). This new
   photonic internetwork will make it possible to provision high
   bandwidth in seconds, turning the new optical technology into a
   revenue spinner for the service provider rather than just a way of
   saving money.

   However, the intelligent open photonic network can only be built if
   the currently vertically layered network migrates to a horizontal
   model where all network elements work as peers to dynamically
   establish optical paths through the network. The IETF has already
   addressed the interworking of routers and optical switches through
   the MPL(amda)S initiative [1]. We propose to expand this initiative
   to include DWDM systems and ATM systems. We also propose to expand
   the work beyond simple establishment of optical paths and include
   optical performance monitoring and management. The combined
   information that will be carried and shared between these network
   elements will allow the elements or element management system (EMS)
   to adequately assess the "health" of an optical path (which can be a
   wavelength or fiber strand). The routers and/or ATM switches at the
   edges of the photonic network will then use this information to
   dynamically manage the millions of wavelengths available in the
   photonic layer.

   As a summary, the following functions need to be covered

   1. Dynamic Bandwidth Provisioning
   2. Optical Performance Monitoring
   3. Signaling for 1 and 2.

   The remainder of this document discusses these functions into more

Ceuppens/Blumenthal et al.                                    [Page 3]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

3. Dynamic bandwidth provisioning

   As indicated above, the photonic network uses photonic switches and
   optical transmission equipment to provide point-to-point connections
   to attached internetworking devices. These connections will
   typically take the shape of dedicated wavelengths, but can also be
   SONET leased line services or gigabit Ethernet connections. While
   the photonic network will typically provide these bandwidth services
   to IP routers, the model should be extended to include ATM switches.

   While the idea of bandwidth-on-demand is certainly not new, existing
   networks do not support instantaneous service provisioning. Current
   provisioning of bandwidth is painstakingly static. Activation of
   large pipes of bandwidth takes anything from weeks to months.

   The imminent introduction of photonic switches in the transport
   networks opens new perspectives. Combining the bandwidth
   provisioning capabilities of photonic switches with the traffic
   engineering capabilities of MPLS [2], will allow routers and ATM
   switches to request bandwidth where and when they need it.

   To make this work, however, requires more than simply advertising
   the availability of routes by the photonic switches to the routers
   and/or switches. They will also need to provide information about
   the characteristics and performance of the paths. Adequately
   assessing the status and health of an optical path through the
   photonic network requires a detailed cooperation between the
   photonic switches and the transmission systems providing the basic
   transport capabilities in the long-haul network.

4. Performance Monitoring

   Service providers to date have limited the role of DWDM in the
   network to creating "virtual fiber", i.e., the straightforward
   increase in capacity of the fiber plant, even if this meant a
   dramatic increase in complexity since each virtual fiber required
   the deployment of its own SONET equipment. The reason behind this
   restricted role is the worry about network management, alarm
   monitoring and protection capabilities of DWDM systems and the
   photonic layer in general.

   Current performance monitoring in optical networks requires
   termination of a channel (wavelength) at an OEO (optical-electrical-
   optical conversion) point to detect bits related to BER of the
   payload or frame (e.g., SONET LTE monitoring). For example, one form
   of error checking can be carried out at the SONET level by
   monitoring the B1 and J0 overhead bytes of the SONET stream.
   However, while these bits indicate if errors have been received,
   they do not supply channel-performance data. This makes it very
   difficult to assess the actual cause of the degraded performance.

Ceuppens/Blumenthal et al.                                    [Page 4]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

   The premise of photonic networks requires the availability of tools
   to measure and control the smallest granular component of such
   networks --the wavelength channel. These functions include the
   monitoring of amplifiers and switches at add/drop sites, the
   deployment and commissioning of DWDM routes, as well as the
   restoration and protection of networks. This must be accomplished
   with speed and accuracy over an extended period of time.

   Fast and accurate determination of the various performance measures
   of a wavelength channel implies that measurements have to be done
   while leaving it in optical format. In the remainder of this
   document we will refer to this as "optical performance monitoring"
   (OPM). One possible way of achieving this is by tapping a portion of
   the optical power from the main channel using a low loss tap of
   about 1%.  In this scenario, the most basic form of OPM will utilize
   a power-averaging receiver to detect loss of signal (LOS) at the
   optical power tap point. Existing DWDM systems use OTDRs (Optical
   time-domain reflectometers) to measure the parameters of the optical

   As photonic networks mature, it will be desirable to generate a more
   detailed picture of the channel "health" in a manner that can be
   communicated to the EMS and other network control entities, as well
   as between other network elements. By monitoring various OPM
   parameters, one can attempt to estimate the BER, detect gradual or
   sudden performance degradation, and report these to local or global
   NMS entities, and to attached internetworking devices. Also, fiber
   spans are typically characterized, or calibrated, during the
   provisioning process on DWDM systems, as fiber manufacturer, fiber
   type etc. all have a bearing on how the various DWDM spectrums
   should be populated. It would be useful to have the calibrated data
   for each fiber span available as part of the overall information on
   the photonic layer. All the available information can then be
   correlated across the network to make decisions on fault isolation
   and take appropriate actions such as rerouting the connection or
   adaptively downgrading or upgrading the bit-rate of a channel.

   When deploying an optical network it is common practice to document
   the baseline for all operating parameters, such as signal power,
   bit-error rate, OSNR, etc., prior to network turn-on. During normal
   operation, network elements equipped with OPM capabilities can
   report any degradation events of the optical channel to the network
   operations center (NOC) and to the other network elements. The
   element management system (EMS) can document the degradation of the
   photonic layer in time by saving optical performance monitoring data
   in an archival database. As channels are added, removed or rerouted,
   the NOC can continuously monitor and analyze the status as channels
   are dynamically managed.

   With the advent of an open photonic network, we can envision a trend
   of leasing channels or wavelengths that span multiple networks. This
   will require optical interconnects between various networks.

Ceuppens/Blumenthal et al.                                    [Page 5]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

   Invariably, as channels are handed off between carriers, problems
   can occur which require monitoring to resolve conflicts. Most of
   these issues occur at network boundaries. In addition, if service
   providers offer various levels of QoS, both networks will have a way
   of negotiating the end-to-end QoS of the channels and both service
   providers will need a way to ensure that the other party lives up to
   the service contract. Here again, independent monitoring is needed
   to ensure quality and continuity of service.

   The issue of effective OPM sensitivity will impact how pervasive
   each technique is used in a network due to cost and complexity.
   Certain techniques may require an optical amplifier at the tap point
   resulting in OPM module sensitivity equivalent to that of the final
   path termination point. Other issues that need to be addressed
   include definition of OPM at the section, line and path levels.
   Since monitoring can be in principal performed at any point within
   the network, traditional use of LTE points does not carry over.

   Another problem related to transparency lies in determining the
   threshold values for the various parameters at which alarms must be
   declared. Very often these values depend on the bit rate on the
   channel and should ideally be set depending on the bit rate.
   However, in a truly transparent network, one may have to set alarms
   to correspond to the highest possible bit rate that can be present
   on a channel. In addition, since a signal is not terminated at an
   intermediate node, if a wavelength fails, all nodes along the path
   downstream of the failed wavelength could trigger an alarm. This can
   lead to a large number of alarms for a single failure, and makes it
   somewhat more complicated to determine the cause of the alarm (alarm

   We see as potential candidates, the following OPM functions:

   1. Dispersion (chromatic and polarization mode):
      The distortion or spreading of bits due to variations in
      propagation velocity of different wavelengths and polarization
      modes in the fiber and other network elements.

   2. Optical signal-to-noise ratio (OSNR):
      The ratio of optical power in a primary data channel to the power
      in optical background noise accumulated during transmission and
      switching. This ratio is usually specified within some optical
      bandwidth of a receiver filter. The OSNR of a channel at the
      destination receiver will set the limit of the final detected SNR.

   3. Bit-rate
      The data rate of the channel in a transparent system will be
      necessary to make decisions on other performance metrics.

   4. Q-Factor
      A measure of the signal-to-noise ratio (SNR) assuming Gaussian
      noise statistics.

Ceuppens/Blumenthal et al.                                    [Page 6]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

   5. Wavelength registration
      The determination of which wavelengths are present on a given

   6. Wavelength selective component drift
      The drift of a laser, filter, mux or other wavelength selective
      component relative to the ITU grid.

   7. Optical cross talk
      Two types of cross talk are of interest, in-band and out-of-band.
      In-band cross talk is seen as at the same wavelength as the
      primary channel and appears as cross talk in the electronic
      domain. Out-of-band cross talk appears as a different wavelength
      in the presence of the primary wavelength and appears as cross
      talk in the optical domain.

   8. Optical power transients
      Changes in the optical powers that are not due to normal bit
      transitions. May be due to optical amplifier gain transients or
      other transient non-linearity in the system.

   9. Bit-error-rate
      In a SONET environment BER can be directly measured on the channel
      using means to look at bits within the data stream. However, in a
      purely photonic network there will typically not be access to the
      data streams carried over the channel. However, by interpreting
      the other optical parameters, the system should be able to
      estimate the BER with relatively good accuracy, as well as
      guarantee bit error rate performance to the users of the channel.

      Random fluctuations in the location of rising and falling edges of
      bits relative to a local or recovered clock reference. As line
      speeds continue to increase, jitter will become a critical
      performance parameter.

   11.Insertion loss
      Indicates the input to output loss of a network element. When
      examining excessive power loss along the path of a channel the
      ability to measure insertion loss of individual network elements
      is very useful, specifically when compared against an archival

   12.Optical power level

   In addition to verifying the service level provided by the network
   to the user, performance monitoring is also necessary to ensure that
   the users of the network comply with the requirements that were
   negotiated between them and the network operator. For example, one
   function may be to monitor the wavelength and power levels of

Ceuppens/Blumenthal et al.                                    [Page 7]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

   signals being input to the network to ensure that they meet the
   requirements imposed by the network.

   To make any Performance Measurement metrics meaningful, major effort
   should be on conducting serious testing to draw correlation between
   the proposed Optical measurement metrics with the quality of the
   signals (electrical).

5. Signaling

   The vast majority of existing communications networks uses framing
   and data formatting overhead as the means to communicate between
   network elements and management systems.

   It is clear however, that truly transparent and open photonic
   networks can only be built with transparent signaling support.
   Arguments in favor of transparency include, but are certainly not
   limited to:

   - Framing and formatting makes the network opaque and as such
     inhibits the creation of bit rate and protocol transparent
     networks. As overhead information is processed in the digital
     domain, it requires an optical-to-electrical and electrical-to-
     optical conversion at every point in the network where traffic is
     inserted or dropped and at each point where management and
     monitoring is required. This imposes severe limitations and is
     probably the single biggest inhibitor of growth in current optical
     networks. That is why "digital wrappers" are not a viable
     solution. In fact, an all-optical network using digital wrappers
     is a contradiction in terms!

   - Attached internetworking equipment and customer equipment may not
     support the framing overheads.

   - In today's optical network (I.e., SONET) the service and
     infrastructure layer are inseparable. As a result, "optical-
     network-ignorant" protocols such as (ten) gigabit Ethernet, fiber
     channel or ESCON cannot be transported without being translated to
     the infrastructure layer. Hence the need for adaptations such as
     "gigabit Ethernet over SONET", "packet over SONET" etc.

   In contrast, separate control plane techniques# supports flexible
   control and management of multi-vendor networks and will pave the
   way for truly open and transparent photonic networks.

#  There may be instances where some "embedded" wavelength routing
   information is required. One such instance is in existing networks
   where DWDM junctions are "hard-wired" and the end-to-end path may
   consist of different wavelengths.

Ceuppens/Blumenthal et al.                                    [Page 8]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

   As already mentioned, the approach proposed by the MPLS/TE [1] task
   force of IETF propose to combine recent advances in MPLS traffic
   engineering control plane with emerging photonic switching
   technology to provide a framework for real-time provisioning of
   optical channels and allow the use of uniform semantics for network
   management operations control in hybrid networks consisting of
   photonic switches and label switching routers (LSRs). While the
   proposed approach is particularly advantageous for data-centric
   optical internetworking systems, it can easily be expanded to
   include basic transmission services. Similarly, it can be expanded
   beyond simple bandwidth provisioning to include optical performance

   It is worth mentioning that while the signaling is used to
   communicate all monitoring results, the monitoring itself is done on
   the actual data channel, or some range of bandwidth around the
   channel. Therefore, all network elements must be guaranteed to pass
   this bandwidth in order for monitoring to happen at any point in the

   Several signaling flows have to be supported:

   - between the internetworking equipment and the photonic cross-
   - between the photonic cross-connect and the DWDM transmission
   - between the DWDM systems and optical amplifiers
   - between the DWDM systems and optical add/drop multiplexers
   - between the internetworking devices and optical add/drop
     multiplexers or DWDM transmission systems (if this connection does
     not run through a PXC)

   We propose that the connection signaling be limited to exchanges
   between the internetworking device and the transmission network
   element it is directly connected to. This transmission element
   (e.g., a photonic cross-connect) then interfaces with the DWDM
   systems (if present) and so forth. This allows for the photonic
   switches to discover the transmission network topology and
   characteristics prior to attached devices asking for connections. It
   also caters for the continued support of any proprietary signaling
   that may already exist between DWDM and/or other transmission
   systems (whether in-band or out-of-band). All that is required is
   support of the standard external signaling interface.

   We also propose these signaling flows be supported on a dedicated
   wavelength, configured throughout the network. Whether this
   wavelength is part of the standard ITU grid or not, is beyond the
   scope of this document. We recommend however, that the signaling
   wavelength be a standard ITU channel, considering that the
   combination of existing C-band (1530- to 1560-nm) and the emerging
   S- (upper 1400-nm region) and L- (1570- to 1625-nm) transmission
   bands will leave little room for suitable non-ITU wavelengths.

Ceuppens/Blumenthal et al.                                    [Page 9]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

   Since dedicating an entire wavelength might not always be viable, we
   should envision the possibility of using this wavelength also for
   data traffic and envisage a way of sending the non-time-critical
   traffic in between the management traffic.

   The signaling protocol can easily be based on existing protocols. A
   slightly modified OSPF can be used for optical network topology
   discovery and distribution, as well as for route computation and
   path selection. Topology advertisement includes not only the nodes
   and the links to the nodes, but also characteristics of the links.
   The actual signaling protocol can be RSVP as extended for MPLS/TE.
   Finally, path management includes monitoring the path for failures,
   knowledge of failure restoration policies, and path teardown.

6. Summary

   This document outlined a proposal to expand Multi-Protocol Lambda
   Switching in two areas:

   - Include network elements such as DWDM, OADM and ATM switches to
     create a versatile transparent and open photonic network.
   - Expand the work beyond basic connection establishment and include
     performance-monitoring capabilities

   Work in this area should be closely coordinated with activities in
   the T1 committee, ITU and OIF to ensure a consistent industry-wide

8. Security Considerations

   This document raises no new security issues.

9. References

   [1] Awduche, D., Y. Rekhter, J. Drake and R. Coltun, "Multi-Protocol
       Lambda Switching: Combining MPLS Traffic Engineering Control
       With Optical Crossconnects", work in progress, November 1999.

   [2] Awduche, D., J. Malcolm, J. Agogbua, M. O'Dell and J. McManus,
       "Requirements for Traffic Engineering Over MPLS", RFC 2702,
       September 1999.


   We would like to thank Curtis Brownmiller (MCI WorldCom) for his
   review and comments.

Ceuppens/Blumenthal et al.                                   [Page 10]

Internet Draft    draft-ceuppens-mpls-optical-00.txt        March 2000

11.Author's Addresses

   Luc Ceuppens                      W.L. Edwards
   Chromisys                         iLambda Networks
   1012 Stewart Drive                Aspen, CO
   Sunnyvale, CA 94086               970.948.7104
   Email:    Email:

   Dan Blumenthal                    Jacek Chrostowski
   Chromisys                         Cisco Systems
   421 Pine Avenue                   365 March Rd
   Goleta, CA 93117                  Canata, Ontario K2K2C9
   Email:         Email:

   John Drake
   1012 Stewart Drive
   Sunnyvale, CA 94086

Ceuppens/Blumenthal et al.                                   [Page 11]