Introduction Chapter 1

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Introduction Chapter 1
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Outlines

• What is a WDM-enabled optical network?
• Why IP over WDM?
• What is IP over WDM?
• Next-generation Internet
• IP/WDM standardisation
• Summary and subject overview

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1.1 What is a WDM-enabled Optical Network?

• Conventional copper cables can only provide a
  bandwidth of 100 Mbps (106) over a 1 Km distance
  before signal regeneration is required.
• In contrast, an optical fibre using wavelength
  division multiplexing (WDM) technology can
  support a number of wavelength channels, each of
  which can support a connection rate of 10 Gbps
  (109).
• Long-reach WDM transmitters and receivers can
  deliver good quality optical signals without
  regeneration over a distance of several tens of
  kilometres. Hence, optical fibre can easily offer
  bandwidths of tens of Tbps (1012).

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What is a WDM-enabled Optical Network?

• In addition to high bandwidth, fibre, made of
  glass (which is in turn made mainly from silica
  sand), is cheaper than other conventional
  transmission mediums such as coaxial cables.
• Glass fibre transmission has low attenuation.
• Fibre also has the advantage of not being
  affected by electromagnetic interference and
  power surges or failures.
• In terms of installation, fibre is thin and
  lightweight, so it is easy to operate.
• An existing copper-based transmission
  infrastructure can be (and has been) replaced
  with fibre cables.

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What is a WDM-enabled Optical Network?

• In the fibre infrastructure, WDM is considered as
  a parallel transmission technology to exploit the
  fibre bandwidth using non-overlapping wavelength
  channels.
• An individual optical transmission system
  consists of three components
• the optical transmitter
• the transmission medium
• the optical receiver.

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WDM

• The transmitter uses a pulse of light to indicate
  the 1 bit and the absence of light to represent
  the 0 bit.
• The receiver can generate an electrical pulse
  once light is detected.
• A single-mode fibre transmission requires the
  light to propagate in a straight line along the
  centre of the fibre.
• a good quality signal,
• used for long-distance transmission.
• multimode fibre
• A light ray may enter the fibre at a particular
  angle and go through the fibre through internal
  reflections.
• The basic optical transmission system is used in
  an optical network, which can be a local access
  network (LAN),
• a metropolitan local exchange network (MAN), or a
  longhaul inter-exchange network (also known as
  Wide Area Network, WAN).

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TDM vs. WDM

• There is a continuous demand for bandwidth in the
  construction of the Internet.
• It is also relatively expensive to lay new fibres
  and furthermore to maintain them.
• Time Division Multiplexing (TDM)
• is achieved through multiplexing many lower speed
  data streams into a higher speed stream at a
  higher bit rate by means of nonoverlapping time
  slots allocated to the original data streams.
• Wavelength Division Multiplexing (WDM)
• is used to transmit data simultaneouslyat
  multiple carrier wavelengths through a single
  fibre, which is analogous to using Frequency
  Division Multiplexing (FDM) to carry multiple
  radio and TV channels over air or cable.
• TDM and WDM can be used together in such a way
  that TDM provides time-sharing of a wavelength
  channel, for example, through aggregating access
  network traffic for backbone network transport.

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TDM vs. WDM
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Cost of WDM

• Splitting the useable wavelength bandwidth into a
  number of slots (wavelength channels) not only
  demands sophisticated equipment but also
  increases the likelihood of inter-channel
  interference.
• As such, WDM equipment cost may dominate the
  total cost in a LAN and MAN environment.
• As of November 2001, commercial WDM optical
  switches are able to support 256 wavelength
  channels, each of which can support a data rate
  of OC-192 (10 Gbps).

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A point-to-point WDM-enabled optical transmission

• Wavelength Add/Drop Multiplexer (WADM)
• Wavelength Amplifier (WAMP)

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Double-ring WDM network

• A WDM-enabled optical network employs
  point-to-point WDM transmission systems and
  requires
• Wavelength Selective Crossconnect (WSXC) that is
  able to switch the incoming signal unto a
  different fibre possibly a different optical
  frequency.

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1.1.2 WDM Optical Network Evolution

• The first generation of WDM provides
• only point-to-point physical links that are
  confined to WAN trunks.
• configurations are either static or use manual
  configurations.
• only supports relatively low-speed end-to-end
  connectivity.
• The technical issues include design and
  development of WDM lasers and amplifiers, and
  static wavelength routing and medium access
  protocols.
• The WADM can also be deployed in MANs,
• To interconnect WADM rings, Digital Cross
  Connects (DCX) are introduced to provide
  narrowband and broadband connections.
• Generally these systems are used to manage voice
  switching trunks and T1 links.

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1.1.2 WDM Optical Network Evolution

• The second generation of WDM
• is capable of establishing connection-orientated
  end-to-end lightpaths in the optical layer by
  introducing WSXC.
• The lightpaths forma virtual topology over the
  physical fibre topology.
• The virtual wavelength topology can be
  reconfigured dynamically in response to traffic
  changes and/or network planning.
• The technical issues include
• the introduction of wavelength add/drop and
  cross-connect devices,
• wavelength conversion capability at
  cross-connects, and
• dynamic routing and wavelength assignment.
• network architecture begins to receive attention,
  
• In particular the interface for interconnection
  with other networks.
• Their cost efficiency in long-haul networks has
  been widely accepted.

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WDM Optical Network Evolution

• The third-generation of WDM
• offers a connectionless packet-switched optical
  network, in which optical headers or labels are
  attached to the data, transmitted with the
  payload, and processed at each WDM optical
  switch. Based on the ratio of packet header
  processing time to packet transmission cost,
  switched WDM can be efficiently implemented using
  label switching or burst switching.
• Pure photonic packet switching in all optical
  networks is still under research.
• The bufferless, all-optical packet router brings
  a new set of technical issues for network
  planning
• contention resolution
• traffic engineering
• over-provisioning
• over-subscription
• interoperability with conventional IP (Internet
  Protocol) routers destination-based routing).

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WDM Optical Network Evolution

• Examples of third-generation WDM devices are
• optical label switch routers
• optical Gigabit routers
• fast optical switches.
• Interoperability between WDM networks and IP
  networks becomes a major concern in
  third-generation WDM networks.
• Integrated routing and wavelength assignment
  based on MultiProtocol Label Switching (MPLS),
  also known as Generalised MPLs (GMPLS), starts to
  emerge.
• bandwidth management, path reconfiguration and
  restoration, and Quality of Service (QoS) support.

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Evolution
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Switching method

• Optical circuit switching
• is used for large-sized aggregated traffic (such
  as data trunks), so that once circuits are set
  up, the formed topology does not change often.
• This provides cost-efficiency in the long haul
  network because a few add/drop points are needed
  by the traffic and only physical transport link
  services are required.
• Optical packet switching
• is used for small-sized data packets. It offers
  efficient, flexible resource sharing by
  introducing complexity to the control system.
• Optical burst switching
• A compromise between packet and circuit
  switching,
• which switches traffic bursts over a
  packet-orientated network.

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cut-through paths

• Packet switching offers cut-through paths, known
  as layer 2 switching.
• The cut-through paths lower the network latency
  by avoiding intermediate node layer 3 functions.
• A packet routed network employs a
  store-and-forward paradigm, where each node
  maintains a routing table and a forwarding table.
  
• Once a packet arrives at the node, by comparing
  the packet header with the local forwarding
  table, the packet is sent to the next hop on the
  routing path.

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1.2 Why IP over WDM?

• IP provides the only convergence layer in the
  global and ubiquitous Internet.
• IP, a layer 3 protocol, is designed to address
  network level interoperability and routing over
  different subnets with different layer 2
  technologies.
• Above the IP layer, there are a great variety of
  IP-based services and appliances that are still
  evolving from its infancy.
• Hence, the inevitable dominance of IP traffic
  makes apparent the engineering practices that the
  network infrastructure should be optimised for
  IP.
• Below the IP layer, optical fibre using WDM is
  the most promising wireline technology, offering
  an enormous network capacity required to sustain
  the continuous Internet growth.

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WDM

• WDM-based optical networks have been deployed not
  only in the backbone but also in metro, regional,
  and access networks.
• In addition, WDM optical networks are no longer
  just point-to-point pipes providing physical link
  services, but blend well with any new level of
  network flexibility requirements.
• The control plane is responsible for transporting
  control messages to exchange reachability and
  availability information and computing and
  setting up the data forwarding paths.
• The data plane is responsible for the
  transmission of user and
• application traffic. An example function of the
  data plane is packet buffering and forwarding.
• IP does not separate the data plane from the
  control plane, and this in turn requires QoS
  mechanisms at routers to differentiate control
  messages from data packets.

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IP over WDM

• A conventional WDM network control system uses a
  separate control channel, also known as a data
  communication network (DCN), for transporting
  control messages.
• A conventional WDM network control and management
  system, e.g.
• according to the TMN framework, is implemented in
  a centralised fashion.
• To address scalability, these systems employ a
  management hierarchy.
• Combining IP and WDM means, in the data plane,
  one can assign WDM optical network resources to
  forward IP traffic efficiently, and in the
  control plane, one can construct a unified
• control plane, presumably IP-centric, across IP
  and WDM networks. IP over WDM will also address
  all levels of interoperability issues on intra-
  and inter-WDM optical networks and IP networks.

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The motivation behind IP over WDM

• WDM optical networks can address the continuous
  growth of the Internet traffic by exploiting the
  existing fibre infrastructure. The use of WDM
  technology can significantly increase the use of
  the fibre bandwidth.
• Most of the data traffic across networks is IP.
  Nearly all the end-user data application uses IP.
  Conventional voice traffic can also be packetised
  with voice-over-IP techniques.
• IP/WDM inherits the flexibility and the
  adaptability offered in the IP control protocols.
• IP/WDM can achieve or aims to achieve dynamic
  on-demand bandwidth allocation (or real-time
  provisioning) in optical networks.
• By developing the conventional, centralised
  controlled optical networks into a distributed,
  self-controlled network, the integrated IP/WDM
  network can not only reduce the network operation
  cost, but can also provide dynamic resource
  allocation and on-demand service provisioning.

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The motivation behind IP over WDM

• IP/WDM hopes to address WDM or optical Network
  Element (NE) vendor interoperability and service
  interoperability with the help of IP protocols.
• IP/WDM can achieve dynamic restoration by
  leveraging the distributed control mechanisms
  implemented in the network.
• From a service point of view, IP/WDM networks can
  take advantage of the QoS frameworks, models,
  policies, and mechanisms proposed for and
  developed in the IP network.
• Given the lessons learned from IP and ATM
  integration, IP and WDM need a closer integration
  for efficiency and flexibility. For example,
  classical IP over ATM is static and complex, and
  IP to ATM address resolution is mandatory to
  translate between IP addresses and ATM addresses.

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What is IP over WDM?

• IP/WDM network is designated to transmit IP
  traffic in a WDM-enabled optical network to
  leverage both IP universal connectivity and
  massive WDM bandwidth capacity.
• IP, as a network layer technology, relies on a
  data link layer to provide
• framing (such as in SONET or Ethernet)
• error detection (such as cyclic redundancy
  check, CRC)
• error recovery (such as automatic repeat
  request, ARQ).

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All-optical network

• An objective of optical networking is to provide
  optical transparency frome nd to end so that the
  network latency is minimised.
• This requires all-optical interfaces and
  all-optical switching fabric for the edge and
  intermediate network elements.
• Transponders are used to strengthen the optical
  signal.
• all-optical transponders (tunable lasers) and
• Optical-Electrical-Optical (O-E-O) transponders.
• The figure shows two types of traffic, IP (e.g.
  Gigabit Ethernet) and SONET/SDH, which in turn
  requires Gigabit Ethernet and SONET/SDH
  interfaces.
• In the case of multiple access links, a sublayer
  of the data link layer is the Media Access
  Protocol (MAC) that mediates access to a shared
  link so that all nodes eventually have a chance
  to transmit their data.
• The definition of a protocol model to efficiently
  and effectively implement an IP/WDM network is
  still an active research area.

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(No Transcript)
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Possible approaches for IP over WDM
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IP/ATM/SONET/WDM

• transports IP over ATM (Asynchronous Transfer
  Mode), then over SONET/SDH and WDM fibre.
• WDM is employed as a physical layer parallel
  transmission technology.
• The main advantage of this approach by using ATM
  is
• to be able to carry different types of traffic
  onto the same pipe with different QoS
  requirements.
• its traffic engineering capability and the
  flexibility in network provisioning, which
  complements the conventional IP best effort
  traffic routing.
• Disadvantage
• offset by complexity, as IP over ATM is more
  complex to manage and control than an IP-leased
  line network.

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IP/ATM

• ATM uses a cell switching technology. Each ATM
  cell has a fixed 53-byte (5-byte header and
  48-byte user data) length, so application traffic
  has to be packetised into cells for transport and
  reassembled at destination.
• ATM cell packetisation is the responsibility of
  the ATM SAR (Segmentation and Reassembly)
  sublayer.
• SAR becomes technically difficult above OC-48.
• Having an ATM circuit layer between IP packet and
  the WDM circuit seems superfluous.
• The statement is strengthened by the emergence of
  the MPLS technique of the IP layer.

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key features of MPLS

• Use of a simple, fixed-length label to identify
  flows/paths.
• Separating control from data forwarding, control
  is used to set up the initial path, but packets
  are shipped to next hop according to the label in
  the forwarding table.
• A simplified and unified forwarding paradigm, IP
  headers are processed and examined only at the
  edge of MPLS networks and then MPLS packets are
  forwarded according to the label (instead of
  analysing the encapsulated IP packet header).
• MPLS provides multiservice. For example, a
  Virtual Private Network (VPN) set up by MPLS has
  a specific level of priority indicated by the
  Forwarding Equivalence Class (FEC).

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key features of MPLS (count.)

• Classification of packets is policy-based, with
  packets being aggregated into FEC by the use of a
  label. The packet-to-FEC mapping is conducted at
  the edge, for example, based on the class of
  service or the destination address in the packet
  header.
• Providing enabling mechanisms for traffic
  engineering, which can be employed to balance the
  link load by monitoring traffic and making flow
  adjustments actively or proactively. In the
  current IP network, traffic engineering is
  difficult if not impossible because traffic
  redirection is not effective by indirect routing
  adjustment and it may cause more congestion
  elsewhere in the network. MPLS provides explicit
  path routing so it is highly focused and offers
  class-based forwarding. In addition to explicit
  path routing, MPLS offers tools of tunneling,
  loop prevention and avoidance, and streams
  merging for traffic control.

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IP/SONET/WDM

• IP/MPLS over SONET/SDH and WDM.
• SONET/SDH provides several attractive features to
  this approach
• SONET provides a standard optical signal
  multiplexing hierarchy by which low-speed signals
  can be multiplexed into high-speed signals.
• SONET provides a transmission frame standard.
• the SONET network protection/restoration
  capability, which is completely transparent to
  upper layers such as the IP layer.

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IP/SONET/WDM

• SONET networks usually employ a ring topology.
  SONET protection scheme can be provided
• as 1 1 meaning data are transferred in two
  paths in the opposite direction and the better
  signal is selected at the destination
• as 11 indicating there is a separate signalled
  protection path for the primary path
• or as n1 representing where primary paths share
  the same protection path.
• The design of SONET also enhances OAMP
  (Operations, Administration, Maintenance, and
  Provisioning) to communicate alarms, controls,
  and performance information at both system and
  network levels.

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SONET/SDH

• However, SONET carries substantial overhead
  information, which is encoded in several levels.
• Path overhead (POH) is carried from end-to-end.
• Line overhead (LOH) is used for the signal
  between the line terminating equipment, such as
  OC-n multiplexers.
• Section overhead (SOH) is used for communication
  between adjacent network elements, such as
  regenerators.
• For an OC-1 pipe with 51.84 Mbps transmission
  rate, its payload has the capacity to transport a
  DS-3 with 44.736 Mbps digital bit rate.

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3G

• IP/MPLS directly over WDM,
• the most efficient solution among the possible
  approaches.
• It requires that the IP layer looks after path
  protection and restoration.
• It also needs a simplified framing format for
  transmission error handling.
• Several companies are developing a new framing
  standard known as Slim SONET/SDH, which provides
  similar functionality as in SONET/SDH but with
  modern techniques for header placement and
  matching frame size to packet size.
• adopt the Gigabit Ethernet framing format. The
  new 10-Gigabit Ethernet is especially designed
  for dense WDM systems. Using the Ethernet frame
  format, hosts (Ethernet) on either side of the
  connection do not need to map to another protocol
  format (e.g. ATM) for transmission.

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Signal

• Conventional IP networks use in-band signalling
  so data and control traffic is transported
  together over the same link and path.
• A WDM optical network has a separate data
  communication network for control messages.
  Hence, it uses out-of band signalling.
• In the control plane, IP over WDM can support
  several networking architectures, but the
  architecture selection is subject to constraints
  on existing network environments, administrative
  authority, and network ownership.

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Signalling
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1.4 Next-generation Internet

• US Internet-related research and development
  partnerships include not only entities that are
  directly focused on Internet development such as
  IETF but also general standard organisations such
  as IEEE and ANSI and federal government agencies
  such as DARPA (Defense Advanced Research Projects
  Agency) (www.darpa. mil) and NSF (National
  Science Foundation) (www.nsf.gov).
• The Next Generation Internet (NGI) initiative
  (www.ngi.gov) was established in 1998 for the
  period of 5 years, through which government
  agencies will cooperate to create next generation
  Internet capabilities to allow for enhanced
  support for their core missions, as well as to
  advance the state-of-the-art in advanced
  networking.

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NGI initiative will

• develop new and more capable networking
  technologies to support Federal agency missions
• create a foundation for more powerful and
  versatile networks in the 21st century
• Form partnerships with academia and industry that
  will keep the US at the cutting edge of
  information and communication technologies
• enable the introduction of new networking
  services that will benefit businesses, schools,
  and homes.

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NGI goals

• conducting research in advanced end-to-end
  networking technologies, including differentiated
  services, particularly for digital media, network
  management, reliability, robustness, and
  security
• prototyping and deploying national-scale testbeds
  that are able to provide 100 to 1000 times
  current Internet performance
• developing revolutionary new applications
  requiring high performance networks.

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SuperNet testbed
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SuperNet streamline networking protocol stacks
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CANARIE

• the Canadian Network for the Advancement of
  Research, Industry, and Education, is a
  non-profit corporation supported by its members,
  project partners and the Canadian government to
  accelerate Canadas advanced Internet development
  and facilitate the widespread adoption of faster,
  more efficient networks and enable the next
  generation of advanced products, applications and
  services.
• In February 1998, the Canadian government
  provided CANARIE with a 55 million grant towards
  the 120 million project to develop a national
  optical RD Internet, known as CAnet III.
  Industry members provided the remaining part of
  the funding.

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Canada

• Using new fibre optic-based technology and Dense
  Wavelength Division Multiplexing (DWDM), CAnet 3
  intends to deliver unrivalled network capability
  with a potential for OC768 (40 Gbps) to Canadian
  research institutions and universities.
• Phase I was completed in October 1998, where an
  optical Internet backbone was set up between
  Toronto, Ottawa and Montreal. Currently Phase II
  is in progress,
• through which the optical Internet Backbone will
  be extended west from Toronto to Vancouver and
  east from Montreal to Atlantic Canada.

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European Asia

• European ACTS (Advanced Communications
  Technologies and Services) program.
• In addition, many European NRNs (National
  Research Networks) have established national
  high-performance advanced network
  infrastructures.
• In Asia Pacific, a number of countries have
  participated in the APAN (Asia Pacific Advanced
  Networking) initiative.

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1.5 IP/WDM Standardisation

• the Internet Engineering Task Force (IETF)
  (www.ietf.org) and
• the International Telecommunication Union,
  Telecommunication Standardisation Sector (ITU-T)
  (www.itu.org) respectively.

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• In particular, IETF has been focusing on these
  IP/WDM-related issues
• MPLS/MPl S (Multiprotocol Lambda Switching)/GMPLS
  (Generalized MPLS).
• Layer 2 and layer 3 functionalities within
  optical networks.
• NNI (Network to Network Interface) standard for
  optical network.

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ITU-T

• In particular, ITU-T has been focusing on these
  IP/WDM related issues
• Layer 1 features of the OSI model.
• Architectures and protocols for next-generation
  optical networks, also known as optical transport
  network (OTN), defined in G.872.
• Architecture for the automatic switched optical
  network, defined in G.ason.