Supporting Ethernet in OBS networks

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Supporting Ethernet in OBS networks

• Sami Sheeshia and Chunming Qiao
• Department of computer science and
  engineering
• State University of New York at Buffalo
• Jeffrey U.J.Liu
• Computer and Communications Research Lab
• Industrial Technology Research Institute,
  Taiwan
• 2002 Journal of Optical Computing

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Overview

• Abstract
• Introduction
• - various standards to enhance Ethernet
• 10GbE over SONET
• - disadvantages and quantifying its
  inefficiencies
• Ethernet over OBS
• - presenting a viable alterative which
  avoids the
  shortcomings of SONET.
• Ethernet over OBS specific integration issues-
• - such as OBS burst size
• - Multiprotocol Label Switching (MPLS) issues

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Abstract

• The paper introduces the likely role that OBS
  will play in the development of 10-Gbit Ethernet
  MAN.
• SONET (Synchronous optical networking) is being
  proposed for the same but its synchronous
  time-division multiplexing (TDM) is inefficient
  for transporting bursty traffic of the Ethernet.
• The author claims that OBS provides a better
  sharing of network resources and when coupled
  with generalized multiprotocol label switching
  (GMPLS) provides a robust Ethernet service.

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Introduction

• Recently network providers face new challenges at
  the MAN level due to the increased user
  requirements.
• Tremendous pressure to support broadband access
  and high speed WAN at low cost.
• So the above factors demands a flexible, proven
  MAN architecture combined with multi-vendor
  compatible implementations.
• 10GbE promises to play an important role,
  offering good speed, end-to-end protocol
  consistency for providers and users in a cost
  effective manner.
• 10GbE can operate over long link spans(40 km) and
  other transport layers such as SONET and DWDM.

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IntroSONET

• Historically, wide-area connectivity is been
  provided by SONET which were built to carry voice
  traffic.
• But it is not optimized for the bursty nature of
  the present time data traffic and is not able to
  scale itself to support the rapid growth of
  internet in a cost-effective manner (requires
  ADMs, hubs etc).
• Gigabit Ethernet has been popular in LAN and the
  MAN , however, Ethernet by itself cannot be
  considered to be a carrier class protocol as it
  does not provide what SONET guarantees.
• Standards such as Ethernet over WDM, resilient
  packet ring (RPR), packet over SONET (PoS) have
  been developed with carrier-grade qualities.

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Intro..1.Ethernet over WDM

• This provides a long haul connectivity(40 km)
  between two Ethernet switches.
• Point-point connections are done manually or via
  multiprotocol lambda switching.
• Disadvantage
• Total number of circuits that can be provisioned
  are limited.
• No traffic grooming or aggregation can be done.

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Intro2. Resilient packet ring (RPR)

• Combines the advantages of Ethernet and SONET to
  give traditional carrier class features.
• Has good MAC switching capabilities providing
  core fiber and ring operation.
• Controlled bandwidth allocation, 50-ms service
  restoration, bounded delay and jitters etc.
• Though RPR in conjunction with SONET and Ethernet
  can provide highly efficient MAN, carriers have
  opted to improve SONET transport instead.

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Intro3.Packet over SONET (PoS)

• PoS is a communication protocol for transmitting
  packets over SONET.
• PoS supports the sending of IP packets over WAN.
• Disadvantage
• It aggregates and encapsulates IP datagrams in
  Point-to-Point protocol (PPP) without any
  differentiation among different packet flows.
• So, lacks multicast and QoS capabilities.

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IntroNext-generation SONET

• Provides better bandwidth granularity than SONET
  and POS.
• Virtual Concatenation (VC) technique allows a
  better match between Ethernet data rates and
  SONET line rate improving circuit use.
• GFP is proposed to adapt multiservices to the
  SONET by a uniform mapping of Ethernet frames and
  client signals.
• LCAS provides bandwidth-on-demand capabilities.
• Disadvantage
• Does not address issues associated with using
  circuit-switching technology for data traffic.

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A new proposal

• Since the standards mentioned either lack
  end-to-end optical transparency or do not offer
  efficient use of core resources, OBS technology
  is taken advantage of to transmit Ethernet frames
  over WDM links.
• The author explains this provides a scalable and
  data optimized alternative to SONET-based
  connectivity.

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Ethernet over SONET(EoS)

• SONET was designed primarily for voice
  applications and is based on circuit oriented
  technology.
• Dual ring and equipment topology enables SONET to
  implement fast protection mechanisms.
• 10GbE physical layer is compatible with SONET.
• ( OC-192 link speed, use of SONET framing).
• Costly aspects like TDM support, performance and
  management functions have been avoided.

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Disadvantages of using SONET rings for data
transport

• Basically SONETs point-to-point design,
  circuit switch applications give rise to its
  limitations.

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1.Fixed circuits

• SONET provisions point-to-point circuit between
  ring nodes gt allocated a fixed amount of
  bandwidth.
• In Fig.1(a) each node in the ring is allocated
  only one quarter of the total bandwidth.
• Thus a limit is put on the maximum data burst
  traffic rates and increases the queuing delay.
• To create a logical mesh as in Fig.1(b) requires
  N(N-1) circuits which is time consuming and also
  waste ring bandwidth.

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2.Muticast Traffic

• Layer 2 muticast requires each source to allocate
  a separate circuit for each destination.
• Thus, a mesh has to be created in which separate
  copies of the packet are sent to each
  destination.
• Obviously, result multiple copies traveling
  around the ring, wasting bandwidth.

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3.Wasted Protection Bandwidth

• 50 of ring bandwidth and equipment is reserved
  for protection.
• SONET does not give the provider the choice of
  when and how much bandwidth to reserve for
  protection.
• Thus SONET does not provide protection in a
  cost-effective manner.

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4.Added Overhead

• SONET overhead (TDM capabilities, physical layer,
  management functions) for STS-192c frames
  resulting from the transportation of 10GbE frames
  over circuits built from SONET links is 3.7.
• But , at low traffic loads, efficiency worsens as
  large bursts of Ethernet frames are delivered in
  a fraction of SONET time slot.
• Carrying increasing data traffic over manually
  provisioned circuit-switched networks makes it
  difficult to develop new services thus increasing
  cost.

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Ethernet-over-SONET Efficiency

• Due to the burstiness and variable frame size
  of Ethernet traffic there is inefficiency in
  SONET framing.
• Efficiency of EoS is given by
• ?EoS ?SONET ?PE
  (1)
• where ?PE packing efficiency of Ethernet
  frames into SONET payload (SPE).

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• g - interarrival gaps
• r - unused remainder (due to low traffic load,
  size of incoming frame gtgtremainder in time slot)
• Let the Ethernet frame size be modeled with an
  exponential distribution with parameter ?
  frame/Byte.

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• The packing efficiency of the Ethernet frames
  into a SONET Tspe is given by
• Where M- maximum number of Ethernet frames that
  SPE can hold.
• B size of the burst.
• Y Sum of the first frame to the
  last frame.
• Due to the bursty nature, the time intervals (g)
  gtgtgtTspe
• Thus as g varies , ?PE becomes proportional to
  the offered load.

(2)
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Ethernet over OBS

• MP?S Lack of statistical multiplexing, leads to
  poor flexibility.
• Recent arrival of optical cross connects (OXC)
  can be used to extend 10GbE over long distances-
  point to point permanent resource reservation-no
  longer shared among different 10GbE.
• OBS is a new technology that exploits the large
  bandwidths of DWDM by avoiding electronic
  processing of optical packets.
• No O-E-O conversions in OBS.
• Burst- basic data block, collection of data
  frames with same destination address and QoS
  parameters.

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EoS

• Optical burst is switched by a predetermined path
  by a control packet.
• Improves backbone efficiency and offers excellent
  scalability.

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EOS

• The GMPLS labels are used to identify the
  destination edge switch and are mapped to
  available wavelengths at each OBS switch.
• 1.Switched paths
• LOBS do not reserve the resources permanently
• LOBS are set up dynamically to support required
  QoS and torn down once burst are transmitted.
• Bandwidth allocated dynamically-burst by burst
  basis.

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• 2. Peer-to-Peer Networking
• GMPLS extends WAN connectivity into the
  MAN-simplifies interface
• Complex optical UNI interfaces not required.
• 3. Multicast traffic
• OBS provides multicast at WDM layer using
  light-splitting techniques-require additional
  hardware-complicate switch controls
• GMPLS-based multicast provides simplification and
  scalability at no cost.

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• 4.Protection and Restoration
• GMPLS fast reroute mechanism can be used to
  provide protection and restoration by
  automatically rerouting traffic on an alternate
  LOBS.
• Accomplishes by precomputing number of LOBS paths
  at the same time the primary LOBS paths are
  established.
• Integrating 10GbE over GMPLS enabled OBS requires
  specific details to burst size and GMPLS
  extensions.

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Ethernet-over-OBS efficiency

• OBS efficiency depends on the fraction of time
  the reserved bandwidth along a LOBS path is used
  by the burst .
• ts- time at which the bandwidth
  reservation starts
• T- burst time (burst size L/output
  data rate bo)
• To - offset time

(3)
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• End-to-end queuing delay depends whether fixed or
  variable size bursts are used.
• Fixed size burst allows paths to be set up as the
  burst is being assembled.
• In the fixed size the data burst encounters no
  edge delay as long as the offset time time
  taken to assemble the burst.
• In the variable-size, control packet can only be
  sent after entire burst is assembled minimum
  edge delay is To.

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Ethernet-over-OBS Burst Size

• For better efficiency, the OBS burst must be
  gtgtTo-ts but not so large to cause significant
  queuing delays.
• High bandwidth, full-duplex operation requires a
  flow control mechanism 10GbE source and
  destination exchange flow control packets- to
  prevent data loss, throttle frame transmission
  rate.
• Flow-control packets are typically 64 bytes, not
  assembled into bursts since it affects
  efficiency.
• Elasticity of OBS burst unlike SONET fixed frame
  slot size allows it to adapt to the bursty nature
  of Ethernet.
• Ethernet adaptor requires a minimum IFG between 2
  successive frames at 10GbE IFG 9.6ns or 12
  Bytes.
• IFG provides receiving station time to update
  counters, check CRC of previous frame, mange the
  buffers.

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• Two ways to implement IFG-
• Insert the 12 Byte spacing at the 10GbE receiving
  interface
• - places new requirements on the processing
  at the destination switch to seek the
  start of each frame.
• Incorporate the IFG within the burst
• - maintains the integrity of Ethernet
  transmission at the expense of wasted bandwidth
  within each burst.
• Since the IFG, preamble, frame check
  sequence (FCS) constitute a large overhead for
  the 1500 Byte Ethernet frame, 9000 Byte frames
  can be used to improve efficiency.
• For e.g.. 155,520-Byte(SONET slot) carrying
  1500 Byte frames incurs 1 overhead whereas
  9000-Byte frame requires fewer IFG, preamble
  resulting in 0.1, a reduction of ten fold.

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Performance comparison of EoS and EoB under
different traffic conditions.
EoB, Tg1
EoS
EoS
EoB, Tg5
EoB, Tg1
Ti burst aggregation time
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Ethernet-over MPLS issues

• What is Multi-protocol Label Switching (MPLS) ?
• A data mechanism to provide a unified service for
  both circuit-based clients and packet-switching
  clients.
• Supports various network technologies like ATM,
  IP etc.
• MPLS sets up label-switched paths (LSP) for
  packets , thus saving time for a LSR (router) to
  look up the next node for forwarding the packet
  to.
• Does not have common control and traffic
  engineering for wavelength , TDM and fiber
  switching.
• Forwarding Equivalence class (FEC)
• Set of packets with similar characteristics is
  forwarded the same way.

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MPLS network
IP 2
B
IP 1
3

• Working of a Label Switched Path

IP 2
3
C
IP 1
IP 3
A
IP 2
IP 3
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Generalized Multi-protocol Label Switching (GMPLS)

• Extends the MPLS functionality for TDM
  (labels-time slots) and FDM (labels
  electromagnetic frequency of light waves).
• Ethernet tunnels provisioned dynamically to
  create wide-area- VLANs.
• Peer-to-peer networking where CPE is part of the
  MPLS cloud.
• Establishes space division multiplexed paths
  where labels indicate the position of the data.
• Establishes common control plane between IP
  service management and optical layers.

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VLL Virtual Leased Lines or Ethernet
tunnels. CPE Customer Premise
Equipment. PE Providers Edge
switch. VLAN (Virtual LAN) a group of
end-stations on multiple LAN segments and can
communicate as if they were on a single LAN.
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• CPE exchanges tables with the providers edge
  (PE) switches using GMPLS signaling.
• Ethernet frame arriving at the CPE from local
  LANS carry the original Ethernet fields and
  802.1p/q headers (p- covers traffic class
  expediting and dynamic multicast filtering part
  of MAC bridges, q-defines services provided in
  Virtual LANs).
• Frame is mapped to a FEC. FEC lookup yields the
  outgoing port and virtual circuit (VC) label,
  which is added to the frame and forwarded on the
  outgoing port toward PE switch.

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• The PE switch maps the Ethernet frame into an OBS
  burst and provides the required signaling by
  GMPLS label assignment in one of the following
  two addressing schemes,
• 1. Flat assignment scheme
• PE constructs a label forwarding base as shown
  below.
• Like CPE label assignment , each label designates
  a unique LAN-MAC-FEC, one for each frame.
• Only provides simple point to point connection.
• Increases amount of labels and signaling.

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• 2. Hierarchical assignment scheme
• Here each VLAN is assigned one VLL or LOBS label
  as shown in below.
• So labels with same LOBS label aggregated in to
  the same burst.
• Allows easy rerouting of VLAN traffic in event of
  failure.
• Additional processing overhead.

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• PE looks up the incoming label, determines the
  VLAN, adds a LOBS label as shown below.
• Frames with same LOBS label are aggregated into
  the same burst.

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EoB path protection and restoration

• 1. At WDM level
• At optical layer, schemes match that of
  SONET but inflexible, subjects of current
  research.
• 2. At Ethernet level
• Spanning Tree Protocol (STP ) is used to provide
  redundant paths.
• Long convergence time not suitable gtLOBS
  constantly setup and torn down.
• 3. At GMPLS level
• Head end - when path fails, OBS switch signals
  head-end switch to use a backup LOBS path.
• Local reroute makes a local decision to
  redirect the burst.

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• Timely detour path is needed.
• So, preestablished paths is essential in burst
  traffic.
• Shortest reroute time gtdecision made as close to
  the failure point.
• Since it takes time to inform the head node,
  local reroute mechanism is preferred.
• Impossible to predict where failure may occur.
• Every switch and link along the path is
  protected, detour paths setup dynamically at the
  same time primary paths are set up.

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• Local reroute requires establishing (N-1) detour
  paths as shown.
• where N- number of OBS switches that the LOBS
  traverses.

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Conclusion

• Extending Ethernet services over OBS provides
  better scalability and bandwidth efficiency than
  with SONET.
• SONET is limited by its TDM nature and by MP?S
  which does not provide statistical multiplexing.
• As DWDM evolves more and more wavelength will be
  supported on each fiber.
• Ethernet is best for LAN-MAN connectivity.
• OBS provides efficient sharing of backbone
  resources.
• GMPLS provides standard control mechanism to
  bridge distant MANs, provides protection with no
  permanent reservation of resources.
• Providers improve their revenue stream and
  consumers reduce their network operational cost.

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Questions?