Transcript 1. Optical networks: From point-to-point transmission to full

1
TTM 1: Access and core
networks, advanced
Based on paper:
“Optical networks: From point-to-point transmission to
full networking capabilities”
Presented by: Zekarias Teshome
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
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Introduction
 It was early realized that optical fiber has a
tremendous bandwidth and
 Also the low electromagnetic interference of the
medium makes it ideal for secure communication
 The main issue would be to find technically feasible
and economical ways to capitalize on this potential.
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
5
Transmission aspects
Transmission systems use WDM( method used to increase
the capacity of a single strand of fiber)
 From the transmitter side: many different colored lights combined
by the WDM multiplexing device and put in to the single strand of fiber.
 On the receiver side: each color is separated into its own color by
WDM Demultiplexing device
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Cont.
 Due to the characteristic attenuation curve of fiber, there
are two regions typically used for communications.
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Cont.
 Dense Wavelength Division Multiplexing(DWDM) and
 Coarse Wavelength Division Multiplexing (CWDM)
 The difference is the channel spacing.
 And the range of the optical spectrum they typically cover.
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DWDM Vs. CWDM
DWDM
 all frequencies spaced at multiples of 50 GHz
 with wavelengths in the 1530 – 1565 nm range,
 The tight spacing between these channels requires temperature
control of the lasers and increases cost.
CWDM
 Here the channel spacing is increased to 200 GHz,
– both the fabrication and the temperature control requirements of these
lasers are lower, and
– the overall cost dramatically reduced.
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
10
Opaque versus transparent
 A core optical network architecture can be opaque or
transparent.
 An opaque architecture implies that the optical signal carrying traffic
undergoes an optical to electronic to optical (OEO) conversion at
different places in the network.
 A transparent architecture implies that the optical signal carrying
traffic stays in the optical domain.
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
12
Re-configurable optical
networks
 The key NEs in order to realize re-configurable
optical networks are
 Reconfigurable optical add-drop multiplexer (R-OADM) and
 optical cross connects (OXC).
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OADM
 Typically close to 70 % of the traffic that arrives at a
node is through-passing traffic, i.e.
 traffic with destination another node.
 Instead of processing and switching/routing all traffic
an optical add-drop multiplexer (OADM) can allow
 some of the through-passing traffic to be forwarded optically,
directly through the node.
 The wavelengths that have been dropped may be added back in
the link.
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Cont.
• There are two main types of OADM that can be used
in WDM optical networks;
 Fixed OADMs: that are used to drop or add data
signals on dedicated WDM channels, and
 Reconfigurable OADMs: re-configurability refers to
the ability to select the desired wavelengths to be
dropped and added on the fly, as opposed to having
to plan ahead and deploy appropriate equipment.
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Cont.
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Optical cross connects
 Optical networks consist of a multiple of sub-networks.
 These will need to be interconnected by optical links in
an arbitrary topology, i.e. in a mesh topology
 In order to be able to realize mesh networks, optical
cross connects are required.
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Cont.
 An OXC performs in essence the same function as an R-OADM
but for a larger number of line ports and directions.
Schematic of an optical cross-connect; optoelectronic , all-optical
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Cont.
 An OXC provides several key functions in a large
network:
 Service provisioning
– An OXC can be used to provide end-to-end light paths in a large
network in an automated manner.
 Protection and restoration
– The OXC combined with monitoring equipment can provide swift
restoration of huge amounts of traffic by redirecting wavelengths
from the failed paths to alternative paths.
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Cont.
 Wavelength conversion
‒ Light paths need not use one single wavelength through the whole
network since this complicates wavelength management in the
network.
 Multiplexing and grooming
- in its purest form the OXC is all-optical. However, the OXC
comprises also an add-drop part where multiplexing and
grooming of ingress and egress signals can take place.
20
Cont.
 OXCs can be an opaque and employ an electrical
core.
 A large number of alternative all-optical solutions
have been explored,
 One of the most prominent OXC solutions is based
on: a two-dimensional or three-dimensional array of
miniature mirrors (MEMS based)
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Cont.
a) A picture of a miniature MEMS mirror, b) schematic of an OXC using miniature MEMS
mirrors
22
Cont.
 A new OXC architecture that uses tunable lasers and
Array Waveguide Gratings (AWG) as shown in Figure below.
A schematic of an OXC based on an Arrayed Waveguide Grating and tunable
wavelength converters
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Cont.
 The port a signal will exit the OXC from, is explicitly
determined by its wavelength and the AWG input it
arrives at.
 Hence the OXC is re-configured by tuning the wavelength of the signal in
a wavelength converter using tunable lasers
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
25
MPLS/GMPLS
 MPLS involves setting up a specific path for a given
sequence of packets by
 labeling every packet in order to figure out which outward path a packet
should be switched toward its destination.
 multiprotocol because it works with the Internet Protocol (IP),
Asynchronous Transport Mode (ATM), and frame relay network
protocols.
 GMPLS (Generalized Multiprotocol Label Switching),
 is a technology that provides enhancements to Multiprotocol Label
Switching (MPLS) to support network switching for time, wavelength, and
space switching as well as for packet switching.
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
27
Network architectures
 Traditional transport networks can be modeled as the
interaction of two operating planes:
 a transport plane and
 a management plane.
 In this model, the transport plane carries the user
data and comprises network equipment, such as line
 interface cards, switch fabrics, backplanes and fiber plant.
 Network OAM&P (operations, administration,
maintenance and provisioning) is fully handled by the
management plane.
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Cont.
 Now, we are beginning to see the deployment of
optical control planes
 sit between the management and transport planes. The control
plane moves some of the network intelligence down to the NEs.
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Cont.
 In the optical transport field, the control plane has
been called by the IETF as,
 Generalized Multi-Protocol Label Switching, or GMPLS.
 The IP and optical control planes can be loosely or
tightly coupled in terms of,
 firstly, the details of the optical network topology, resources, and
routing information that is revealed to the IP layer, and
 secondly, the degree of control IP routers have on optical network
elements and thus the degree to which they can determine the
exact paths through this optical network.
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Cont.
 Based on this:
 The overlay model
 The peer model
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The overlay model
 In this architecture option the optical network has full
control over its network resources
o by means of a fully independent optical control plane.
A schematic of the Automatically Switched Optical Network, according to the overlay
model
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The peer model
 In this architecture the control planes of the optical
network and IP are fully integrated.
 the optical part unintelligent and
 rely on IP intelligence to run the network.
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
34
Reference network
 The network can be seen as comprising three parts:
 The core and long-haul part,
 The metropolitan area network, and
 The access part.
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Cont.
 The core part
 is a national network connecting major cities.
 The metro network
 extends over a large city or a province, comprises less
aggregated traffic than the core as it is closer to customers
and end users, and involves lower capacities than the core.
 Access part
 is the part that provides a connection between an end user
(e.g. a home) or a business to the metro and core networks.
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
37
Future IP solutions
 IP routers do not appear to be able to scale gracefully
to meet the needs of multi-Terabit networks.
 Alternatively, better scalable large switching matrices
may be created using both electrical and optical
switches.
A schematic of a hybrid optical-electrical router, using both optical switching matrices and
electrical switches
38
Cont.
 A next step is optical packet or burst switching (OPS/
OBS) – or so-called optical routers.
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Contents




Introduction
Transmission aspects
Opaque versus transparent
Re-configurable optical networks
 OADM
 Optical cross connects
 MPLS/GMPLS
 Network architectures
 The overlay model
 The peer model
 Reference network
 Future IP solutions
 Summery
40
Summery
 Optical networks may well be the key to high capacity
intelligent networks that utilize
 their resources in an efficient way and can provide a range of
differentiated services.
 Optical switching provides an economical way to
handle large amounts of traffic and to build reliable
networks.
 Optical functionality can be introduced at a separate
layer and complement higher network layers, and/or it
can be directly integrated and controlled by IP routers.
 Optical technology can also be employed to realize
larger/higher throughput and more robust IP routers.