R O U T I N G

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R O U T I N G

• in traditional and optical networks
• Dorota Woodbury

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What Is Routing?

• Moving information across the network from
• a source to a destination, typically through
• intermediate node(s). It consists of
• Determining optimal routing paths
• Transporting information (e.g. grouped in
  packets, cells in packet switching)

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Path Determination

• Routing protocols use routing algorithms to
  populate routing tables, which contain the route
  information such as
• destination/next hop association
• desirability of a path, and other
• Routers build a picture of network topology based
  on routing information received from other
  routers

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Routing Algorithms - Goals

• Optimality
• Simplicity and low overhead
• Robustness and stability
• Rapid convergence
• Flexibility

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Routing Algorithms - Types

• Static vs. dynamic
• Single path vs. multipath
• Flat vs. hierarchical
• Host-intelligent vs. router-intelligent
• Intradomain vs. interdomain
• Link-state vs. distance vector

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Routing Algorithms - Metrics

• Path length
• Reliability
• Delay
• Bandwidth
• Load
• Communication cost

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Routing Protocols

• Exterior Gateway Protocol (EGP)
• Border Gateway Protocol (BGP)
• Routing Information Protocol (RIP) dv
• Open Shortest Path First (OSPF) - ls
• Intermediate System-to-Intermediate System
  (IS-IS) ls
• Interior Gateway Routing Protocol (IGRP)

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BGP-4

• Is the current exterior routing protocol
• used for the global internet.
• Essentially a distance-vector algorithm
• Only changes are exchanged
• Loops at the AS level can be detected by
  reviewing the AS_PATH attribute received from
  neighbors
• Path selection policy is left up to individual
  implementations

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RIP-2

• Extension to RIP - the most widely
• used interior routing protocol
• Width restriction (16 hops infinity)
• Bandwidth consumptive (distance vector update
  every 30 sec)
• Difficult diagnosis of bugs

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OSPF-2

• It is intended as Internets preferred
• interior routing protocol (IETF).
• Scalability
• Full subnetting support
• Hello packets
• TOS (Type of Service) routing
• Tagged routes
• Password authentication
• Equal-cost multi-path routing

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IS-IS

• Link-state hierarchical routing protocol.
• Topology discovery through ESH and ISH messages,
  followed by updates
• Default metric (max path value 1024, with a max
  link value of 64)
• Optional metrics
• Delay
• Expense
• Error

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IGRP

• Developed for large networks with
• complex topology.
• Vector of metrics (topological delay time,
  bandwidth of the narrowest segment, channel
  occupancy, reliability of the path)
• Traffic split between several paths that fall
  within certain parameters
• Sophisticated techniques to maintain stability
  when topology is changing

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Transporting Information

• Circuit switching
• Packet Switching
• Virtual Circuit Packet Switching (X.25, Frame
  Relay)
• Datagram Switching (IP)
• Hybrid (ATM)

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Circuit Switching

• Communication lines are dedicated to passing
  messages from the source to the destination.
• Ideal when data must be transmitted quickly, must
  arrive in sequencing order and at a constant
  arrival rate (real time data, audio, video)
• Not efficient for bursty data traffic

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Virtual Circuit Packet Switching

• Initial setup phase
• Short packet headers
• Sequential arrival at destination
• Error-free guarantee
• Slower than Circuit Switching
• Competition for resources
• Setup phase

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X.25

• Popular in Europe
• Store-and-forward
• Excellent flow control
• Data integrity guarantee
• Full error correction
• Large inherent delay
• Large buffering requirement

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Frame Relay

• Popular in North America
• Reduced transmission delay
• Minimal storage requirement
• Variable packet length
• No guarantee of data integrity
• No flow control
• Not suitable for voice or video

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Datagram Packet Switching (IP)

• Each packet an independent entity its header
  contains full information about the destination
• Intermediate nodes examine the header of the
  packet, and decide to which node to send the
  packet
• Use the shortest way to the destination
• Find a free node to pass the packet to

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Datagram Packet Switching (IP)

• Router changes the physical address in the header
  to that of the next hop and retains the
  destination protocol address
• Requires re-sequencing at the destination
• Does not guarantee delivery
• Is time consuming (every router has to decide
  where to send each packet)

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ATM

• Connection-oriented like Frame Relay
• High bandwidth
• Superior (to FR) QoS
• Designed to support voice, data, video
• Higher speeds (1.544 Mbits/s - 10Gbits/s)
• Due to fixed cell size, network delays and
  latencies can be predicted
• Delivery of voice and data traffic at a fixed
  rate
• Protocol-independent

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MPLS

• Supports the forwarding of data packets based on
  a label that is prepended to each IP packet
• Label Switched Routers (LSR) forward packets
  according to the attached labels along a Label
  Switched Path (LSP)
• Implements virtual connections Labeled Switched
  Paths (LSPs)

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MPLS Control Plane

• Shared transmission medium for the control plane
  messages and data plane packets
• Shared reliability
• Restoration techniques allow sharing of
  pre-established during provisioning restoration
  LSPs, which do not use any bandwidth until
  utilized

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IP over MPLS

• Enhancement of the network capabilities (traffic
  engineering, Qos support)
• Makes the connectionless IP connection-oriented
• A peer network model tightly integrated IP/MPLS
  and optical layers for optimized optical networks

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GMPLS

• Standard defined in November 2001 by IETF
• Supports multiple types of switching
• Interfaces that recognize packet/cell boundaries
  and are able to process packet/cell headers
• Interfaces that forward data based on the datas
  time slot in a repeating cycle (TDM)
• Interfaces that forward data based on the
  wavelength on which the data is received (OXC)
• Interfaces that forward data based on a position
  of the data in the real world physical spaces
  (OXC that operate at the level of fibers)

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GMPLS

• Translates the label encoded as a time slot, or
  a wavelength, or a position in the real world
  physical space into a link
• Requires that an LSP starts and ends on a similar
  type of an LSR
• Formalizes possible separation of control and
  data channels

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GMPLS

• Support for waveband switching
• Waveband a set of contiguous wavelengths
• It may be desirable to switch multiple
  wavelengths as a unit
• Support for bidirectional optical LSPs
• A single set of signaling messages establishes
  downstream and upstream data paths (reduced setup
  latency and overhead)

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Optical Networks Control Plane

• Data and control planes in optical networks are
  not so tightly coupled control messages between
  OXCs can be sent
• Out of band
• Via overhead bits in a TDM channel
• Via a dedicated wavelength on a fiber
• Embedded in a Digital Wrapper
• Restoration bandwidth cannot be shared and
  allocated before failure

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Optical Networks Control Plane

• Topology (both data and control plane) and
  resource discovery (routing)
• Reliable delivery (IP)
• Scalable
• Bundled link
• Hierarchical routing (eg OSPF)
• Abstract topology representation (summarization)
• Additional overhead due to explicit management of
  network resources (link state) (not addressed)

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Optical Networks Control Plane

• Connection provisioning, maintenance and deletion
  (signaling)
• In GMPLS LSPs are maintained using a soft state
  protocol (refresh/timeout)
• In optical networks, control plane failure should
  not disrupt established data plane connections
  hard state approach
• Packet/circuit restoration schemes
• Graceful connection deletion (two-phase)

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Routing in Optical Networks

• IP/MPLS directly over transport network
• Virtual Circuit Switching optical
  cross-connects (OXC) switch and reconfigure
  wavelength channels
• Research on intelligent packet switching
  providing
• Aggregate efficiency
• Capacity utilization

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Optical Circuit Switching

• OXCs opaque devices that convert the signal to
  electronic domain small improvement over packet
  switches
• PXCs transparent to bit rate, protocol and
  wavelength order of magnitude in improvement

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Current Technologies

• Dominant technology for core networks is
  wavelength routing with permanent or
  semi-permanent circuits set up between endpoints
  for data transfer
• Emerging technologies optical packet switching
  with various approaches applied to allow parsing
  headers electronically

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Routing in Optical Networks

• Lightpath a fully optical transmission path
  between two nodes in a network, implemented by
  assigning a unique wavelength through the path
• Semilightpath a transmission path constructed
  by chaining several lightpaths together, using
  wavelength conversion at their junctions

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Wavelength Routing with Burst Switching

• Network capable of switching data in
  variable-sized parcels
• Just-in-time (JIT) signaling signaling messages
  travel slightly ahead of the data they describe
  signaling is out-of-band, with electro-optical
  conversion at every hop
• No buffering inside the network
• Data travels transparently

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Wavelength Routing with Burst Switching

• JET (Just-Enough-Time)
• Resources reserved for the shortest amount of
  time possible, based on start/end prediction
• Qos
• varying the delay between the signaling and the
  burst
• JIT (Just-in-Time)
• Explicit setup and explicit release
• Explicit setup and estimated release
• Estimated setup and explicit release
• Estimated setup and estiamted release

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Signaling schemes for optical burst switching.
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Optical Packet Switching

• Lack of technology to read the packet headers in
  the optical domain
• Cumbersome multiplexing and demultiplexing of
  wavelengths with dedicated hardware also
  necessary signal amplification (optical)
• One proposed solution Photonic Slot Routing
  (PSR) /in access and metro/
• Contention resolution in the form of optical
  storage or delay

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Sources

• G. Bennett, Tutorial. The Laypersons Guide to
  Optical Networking, DRCN 2001 3rd Intl Wkshp
  Design of Reliable Communication Networks, Oct.
  2001
• P. Ashwood-Smith et al., Generalized MPLS
  Signaling Functional Description, Nov. 2001
  
• M. Ford (ed.), Internetworking Technologies
  Handbook, Cisco Press, 1997.
• http//www.freesoft.org/CIE/Topics
• http//www.employees.org/kessler/words/thesis.htm

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Sources

• Caspian Networks white papers, Evolution of the
  Optical Internetwork. Building the intelligent
  optical packet network, Dec. 2000.
• E. A. Medova, Network flow algorithms for
  routing in networks with wavelength division
  multiplexing, IEE Proc.-Commun., Vol. 142, No.
  4, August 1995
• W. Liang, X. Shen, Improved Lightpath
  (Wavelength) Routing in Large WDM Networks, IEEE
  Trans. Comm., Vol. 48, No. 8, Sept 2000.
• G. Li, J. Yates, D. Wang, C. Kalmanek, Control
  Plane Design for Reliable Optical Networks, IEEE
  Comm. Mag., Feb 2002

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Sources

• I. Baldine, G. N. Rouskas, H. G. Perros, D.
  Stevenson, JumpStart A Just-in-Time Signaling
  Architecture for WDM Burst_Switched Networks,
  IEEE Commun. Mag., Feb. 2002.
• V. Elek, A. Fumagalii, G. Wedzinga, Photonic
  Slot Routing A Cost-Effective Approach to
  Designing All-Optical Access and Metro Networks,
  IEEE Commun. Mag., Nov. 2001
• A. R. Moral, P. Bonenfant, M. Krishnaswamy, The
  Optical Internet Architecures and Protocols for
  the Global Infrastructure of Tomorrow,, IEEE
  Commun. Mag., July, 2001.

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Sources

• D. Awduche, Y. Rekhter, Multiprotocol Lambda
  Switching Combining MPLS Traffic Engineering
  Control with Optical Crossconnects, IEEE Comm.
  Mag., March 2001.