Ethernet%20Passive%20Optical%20Network%20(EPON)%20:%20Building%20a%20Next-%20Generation%20Optical%20Access%20Network

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Ethernet Passive Optical Network(EPON)
Building a Next- Generation Optical Access Network
Authors Glen Kramer and Gerry
Pesavento(AllOptic Inc.).

• COURSE CEG 790
• Instructor Dr. Bin Wang
• Presenter Ram Iyer

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Overview

• Introduction
• What are Passive Optical Networks ?
• Deployment Scenario of Next-Generation Access
  Networks
• Types of PON technologies
• Different types of PON topologies
• What are EPONs ?
• How does an EPON work ?
• Issues related to EPONs
• Benefits of using EPONs
• IEEE P803.3ah status
• The market for EPONs
• Conclusion

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Introduction

• Internet has spawned genuine demand for broadband
  services, leading to unprecedented growth in
  Internet Protocol (IP) data traffic. This
  humongous data traffic is putting pressure on
  carriers to upgrade their networks.
• An improvement over 56 kb/s is unable to provide
  enough bandwidth for emerging services such as
  the IP telephony, Video on Demand (VoD),
  interactive gaming, or two-way video
  conferencing.

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Per-user bandwidth requirements for new services
kept increasing as shown
A new technology is required which would be able
to handle the bandwidth hungry services.
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What is a Passive Optical Network (PON) ?

• Passive Optical Network (PON) is a high bandwidth
  Point-to-Multipoint (P2MP) optical fiber network
  based on the Asynchronous Transfer Mode protocol
  (ATM), Ethernet or TDM.
• Components used in Passive Optical Network
• PONs generally consist of an OLT (Optical Line
  Termination), which is connected to ONUs
  (Optical Network Units). OLT and ONUs are
  explained in the later slides of the presentation.

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Properties of PONs

• PONs rely on light waves for data transfer.
• Only passive optical components are used such as
  optical fiber, splices and splitters.
• PONs minimizes the fiber deployment in both the
  local exchange office and the local loop.
• PONs provides higher bandwidth due to deeper
  fiber penetration, offering gigabit per second
  solutions.

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Range of operation of PONs
PONs aim to break the First Mile (once called as
Last Mile) bandwidth bottleneck by targeting the
sweet spot between T1s and OC-3s that other
access network technologies do not adequately
address. PONs are capable of delivering high
volumes of upstream and downstream bandwidth (up
to 622 Mbps downstream and 155 Mbps upstream).
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Deployment scenario of Next-Generation Access
Network

• A logical way to deploy optical fiber in the
  local access network is using a point-to-point
  (P2P) topology, with dedicated fiber which runs
  from the local access network to each end-user
  subscriber (Figure a)

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Deployment of Next-Generation Access Network
contd..

• Second method is to deploy a remote switch
  (concentrator) close to neighborhood since it
  reduces the fiber deployment as shown in (Figure
  b). The main downside of this curb switch
  architecture is it requires electrical power as
  well as the backup power at the curb unit and
  currently, one of the highest cost for local
  exchange carriers is providing and maintaining
  electrical power in the local loop.

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Deployment of Next-Generation Access Network
contd..

• In the third we can see that a PON actually
  minimizes the amount of optical transceivers,
  central office terminations, and the fiber
  deployment. As stated earlier a PON is a
  point-to-multipoint (P2MP) optical network with
  no active elements in the signals path from the
  source to destination. PONs basically use passive
  optical components, such as optical fiber,
  splices, and splitters. This is show in the
  Figure c.

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Decrease in the number of Fibers and Transceivers
used
Point to point network - Number of Fiber
- 32
Number of Transceivers - 64
Curb-switched network - Number of Fibers
- 1
Number of Transceivers - 66
Passive Optical Network - Number of Fiber
- 1
Number of Transceivers - 33
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Types of PON technologies
PON
Asynchronous transfer mode PONs (APONs)
Ethernet PONs (EPONs)
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Passive Optical Networks

• APONs
• Data is transmitted in fixed length 53-byte cells
  as specified by ATM protocol.
• APONs dont deliver data, video and voice over a
  single platform.
• APONs offer insufficient bandwidth
• APONs are expensive
• APONs do not provide broader service capabilities

• EPONs
• Data is transmitted in variable-length packets of
  up to 1,518 bytes according to IEEE 802.3
  protocol for Ethernet.
• EPONs deliver data, video and voice over a single
  platform
• EPONs offer higher bandwidth
• EPONS are less expensive than APONs
• EPONs provide broader service capabilities

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Components used in PON topologies
All transmission in a PON are performed between
an optical line terminal (OLT) and optical
network units (ONUs).
What is Optical Line Terminal (OLT) ?
An OLT resides in the local exchange (central
office), connecting the optical access network to
the metro back-bone.
What are Optical Network Units (ONUs) ?
The ONU provides the interface between the
customers data, video, and telephony networks
and the PON. Its function is to receive
traffic in a optical format and convert it into
customers desired format (Ethernet, IP
multicast, T1, etc.)
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Typical PON architecture
APONs
EPONs
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Different types of PON topologies

• Tree topology
• Bus topology
• Ring topology
• Tree with redundant trunk

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PON topologies
Figure 3
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Why do we require EPONs?

• We require EPON technology since it has the
  following qualities
• it is inexpensive,
• simple, scalable and
• capable of delivering bundled voice,
• it provides data and video services to an
  end-user subscriber over a single network.

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What are EPONs?

• Ethernet passive optical networks (EPON) are an
  emerging access network technology that provides
  a low-cost method of deploying optical access
  lines between a carrier office (CO) and customer
  site.
• We can say that, Ethernet Passive Optical
  Networks (EPONs) represents the convergence of
  low-cost Ethernet equipment and low-cost fiber
  infrastructure, to be the best candidate for the
  Next-Generation access network.

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How does an EPON work ?

• In a EPON the process of transmitting data
  downstream from the OLT to multiple ONUs is
  fundamentally different from transmitting data
  upstream multiple ONUs to the OLT.
• The different techniques used to accomplish the
  downstream and upstream transmission in a EPON
  are shown in Figure 4 and Figure 5.

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Downstream traffic in EPON
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Downstream Traffic flow in an EPON

• Consider the downstream traffic in EPON
• In the Figure 4, the data broadcasted downstream
  from OLT to multiple ONUs in variable-length
  packets of up to 1,518 bytes, according to IEEE
  802.3 protocol. Each packet carries a header that
  uniquely identifies it as data intended for
  ONU-1, ONU-2 or ONU-3.At the splitter the traffic
  is divided into three separate signals, each
  carrying all of the ONU specific packets. When
  the data reaches the ONU, it accepts the packets
  that are intended for it and discards the packets
  that are intended for other ONUs. For example, in
  figure 4, ONU-1 receives packets 1, 2 and 3
  however only two packets are delivered to end
  user 1.

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Downstream Frame Format in an EPON
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Upstream traffic in EPON
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Upstream Traffic flow in a EPON
Consider the downstream traffic in EPON

• Figure 5 shows the upstream traffic is managed
  utilizing TDM technology, in which transmission
  time slots are dedicated to ONUs. The time slots
  are synchronized so that upstream packets from
  the ONUs do not interfere with each other one the
  data is couple onto the common fiber. For
  example, ONU-1 transmits packet 1 in the first
  time slot, ONU-2 transmits packet 2 in the second
  non-overlapping time slot, and ONU-3 transmits
  packet 3 in a third non-overlapping time slot.

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Upstream Frame Format in an EPON
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Transceiver Issues

• There are number of issues which have surfaced
  by the use of transceivers (A transceiver is a
  device which is capable of transmitting and
  receiving signals)
• Due to the unequal distances between the central
  office and ONUs, optical signal attenuation in
  the PON is not same for each ONU i.e. the power
  level received at the OLT will be different for
  each ONU (this is also called as near-far
  problem)

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Transceiver Issues Contd.

• As shown in the Figure below, one ONUs signal
  strength is lower at the OLT, which is most
  likely due to the longer distance.

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Approaches suggested to solve the attenuation
problem

• There are couple of approaches which are
  suggested in this paper but they have not been
  implemented since they have their own drawbacks
• One of the approaches suggested is
• To allow ONUs to adjust their transmitter power
  such that power levels received by the OLT from
  all the ONUs becomes the same.
• Drawback of this approach
• This method is not favored by the transceiver
  designers because it makes the ONU hardware more
  complicated, requires special signaling protocol
  for feedback from the OLT and ONU and most
  importantly degrades the performance of the all
  the ONUs to that of the of the most distant unit.

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Security
Is Encryption mechanism necessary in Passive
Optical Network ?

• Encryption mechanism is necessary since a
  malicious ONU if placed in promiscuous mode would
  be able to read all the downstream packets.

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On which layer of the OSI model the encryption
must be placed?

• If the encryption is placed in the MAC layer then
  it will encrypt the MAC frame payload only, and
  leave the headers in plain text. This method
  prevents malicious ONUs from reading the payload,
  but they may still learn other ONUs MAC address.
• Implementing the encryption scheme on the
  physical layer would encode the entire bit
  stream, including the frame headers and CRC. In
  this scheme no information is learned by a
  malicious ONU. But the difficulty is the physical
  layer is a connectionless layer. Requiring the
  Physical layer in a OLT to apply different keys
  for different ONUs will make it connection-aware.
  
• So encryption in EPON still remains an open
  question.

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Benefits of Ethernet PONs

• Higher bandwidth up to 1.25 Gbps symmetric
  Ethernet bandwidth
• Lower Costs lower up-front capital equipment and
  ongoing operational costs
• More revenue broad range of flexible service
  offerings means higher revenues

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Higher bandwidth

• More subscribers per PON
• More bandwidth per subscriber
• Higher split counts
• Video capabilities
• Better QoS

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Lower Costs

• Cost reduction in the case of EPONs are
  achieved by simpler architecture, more efficient
  operations, and lower maintenance needs of an
  optical IP Ethernet network.
• Eliminate complex and expensive ATM and SONET
  elements and dramatically simplify the network
  architecture
• Long-lived passive optical components reduce
  outside plant maintenance
• Standard Ethernet interfaces eliminate the need
  for additional DSL or cable modems
• No electronics in outside plant reduces need for
  costly powering and right-of-way space

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More Revenue
Revenue opportunities from EPONs include

• EPONs support for legacy TDM, ATM and SONET
  services.
• Delivery of new Gigabit Ethernet, fast Ethernet,
  IP multicast and dedicated wavelength services.
• Provisioning of bandwidth in scalable 64 Kbps
  increments up to 1 Gbps.
• Tailoring of services to customer needs with
  guaranteed SLAs (Service License Agreement).
• Quick response to customer needs with flexible
  provisioning and rapid service reconfiguration.

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IEEE P802.3ah status

• The standards work for Ethernet in the local
  subscriber access network is being done in the
  IEEE P802.3ah Ethernet in the First Mile (EFM)
  Task Force.
• In order to evolve Ethernet for local
  subscriber networks, P802.3ah is focused on four
  primary standards definitions
• Ethernet over copper
• Ethernet over P2P fiber
• Ethernet over P2MP fiber
• Operation, administration, and maintenance (OAM)

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• IEEE 802.3ah has been approved. Materials
  concerning the
• P802.3ah standards effort and the presentation
  materials
• can be found at
• http//www.ieee802.org/3/efm/index.html
• http//www.ieee802.org/3/efm/public/index.html

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The Market for EPONs

• Analysts expect the optical access market to grow
  rapidly.
• CIBC (Canadian Imperial Bank of Commerce)
  forecasts the market for PON access system to
  reach 1 billion by 2004 from 23 million in
  2000.
• P2P optical Ethernet offer the best possibility
  of a turnaround in the telecom sector.

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Conclusion

• The future of broadband access network is likely
  to be a combination of point-to-point and
  point-to-multipoint Ethernet, optimized for
  transporting IP data, as well as time critical
  voice and video.

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References

• Topics in Lightwave Ethernet Passive Optical
  Network (EPON) Building the Next-Generation
  Optical Access Network
• Glen Kramer and Gerry Pesavento, Alloptic,
  Inc.
• http//www.iec.org/online/tutorials/epon/