Transcript (EPON) : Building a Next

Ethernet Passive Optical Network
(EPON) : Building a NextGeneration Optical Access
Network
Authors : Glen Kramer and Gerry Pesavento(AllOptic Inc.).
COURSE – CEG 790
Instructor – Dr. Bin Wang
Presenter – Ram Iyer
Overview
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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
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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 twoway 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) ?
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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
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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 NextGeneration Access Network
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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..
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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..
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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-tomultipoint (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
Number of Transceivers
- 32
- 64
Curb-switched network - Number of Fibers
Number of Transceivers
-1
- 66
Passive Optical Network - Number of Fiber
Number of Transceivers
-1
- 33
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Types of PON technologies
PON
Asynchronous transfer mode
PONs (APONs)
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Ethernet PONs (EPONs)
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Passive Optical Networks
APONs
EPONs
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Data is transmitted in fixed  Data is transmitted in variablelength 53-byte cells as
length packets of up to 1,518
specified by ATM protocol.
bytes according to IEEE 802.3
protocol for Ethernet.
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APONs don’t deliver data,
video and voice over a single  EPONs deliver data, video and voice
platform.
over a single platform
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APONs offer insufficient
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EPONs offer higher bandwidth
bandwidth
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EPONS are less expensive than
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APONs are expensive
APONs
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APONs do not provide
 EPONs provide broader service
broader service capabilities
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 customer’s data, video,
and telephony networks and the PON. Its function is to receive traffic
in a optical format and convert it into customer’s 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
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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 enduser subscriber over a single network.
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What are EPONs?
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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 ?
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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
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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
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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
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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.
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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:
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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:
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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 ?
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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?
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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
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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
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More subscribers per PON
More bandwidth per subscriber
Higher split counts
Video capabilities
Better QoS
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Lower Costs
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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:
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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
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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
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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
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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
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Topics in Lightwave: Ethernet Passive Optical
Network (EPON): Building the NextGeneration Optical Access Network
Glen Kramer and Gerry Pesavento, Alloptic, Inc.
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http://www.iec.org/online/tutorials/ep
on/
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