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Politecnico di Milano - Academic Year 2012/2013 - Mario
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3. The Optical Transport Network, OTN
The enormous grown of the traffic due to IP pushes toward the
design of transport networks less opaque of SONET/SDH with respect
to WDM layer. In other term it becomes soon mandatory to have a
transport protocol suitable to manage the WDM colours. In fact,
SONET/SDH was born essentially grey, thus there are not native
information about the colours in the OH of both the protocols. In
the 1999 with the Reccomandation ITU G.872 the new protocol named
Optical Transport Network or OTN was born. The new protocol:
Is transparent for the client SONET/SDH as we ll as for the
G-Ethernet, ATM, IP and MPLS;
Delivers path with granularity 2.5,10, and 40 Gb/s; I mprove the
OAM function for all the clients.
The Optical Transport Module collects and organizes the vital
information to move safely the client traffic into the Transport
Net. It is divided in Analogic and Digital zones.
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN The most important entity
of the Optical Transport Module is the Optical Channel that can be
defined as a optical circuit (the Optical Channel Carrier OCC)
provided of frame (the Optical Transport Unit OTU). By means of the
OCh the information of the client can journey through the network
including the optical subsystems (Optical Amplifier, Optical
Add-Drop Multiplexer, Optical Cross-Connect, WDM and so on).
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
Convoy: the OTU
Rail: OCC or the or the colour
In the railway paradigm, the Optical Channel is like the
junction between the convoy and the rail
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Politecnico di Milano - Academic Year 2012/2013 - Mario
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3. The Optical Transport Network, OTN
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Politecnico di Milano - Academic Year 2012/2013 - Mario
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3. The Optical Transport Network, OTN
Optical channel green
Optical channelviolet
Optical channelblu
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
All the differentOch are merged In the same core of the optical
fiber
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN All the information about
the allocation (the OCC) , abse nce or presence of clients,
characteristic of the main sub-systems and components of the net,
are contained in the Non-Associated Over-Head (thus, over-head does
not associated to a par ticular ) and will be transmitted by
appropriated out-of-band signalling. Viceversa, the information
related to the specific OCh are allocated in the Associated Over
Head of the OTU. NAOH and AOH together form the Optical Transport
Module OTM. In the real networks, we are in presence of many
optical circuits and many electrical clients: the result is an
increasing of the OTM complexity which presents an analog and a
digital sub-section, both organized with the layers paradigm.
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
The analogical section of the OTM is organized like the SONET
OH. In fact we have three layers: Optical Transport Section, OTS,
that involves the optical fiber, the optical amplifier and the
optical tx/rx; Optical Multiplexing Section, OMS, that provide for
the function of the multiplexing/demultiplexing (the change of the
wavelength); Optical Channel that can be delivered or extracted by
menas the Optical Add/Drop Multiplexers, OADM.
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
O/EWC
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Politecnico di Milano - Academic Year 2012/2013 - Mario
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3. The Optical Transport Network, OTN
O/EWC
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Politecnico di Milano - Academic Year 2012/2013 - Mario
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3. The Optical Transport Network, OTN
In the Figure is shown the analogy between the layers of the
SONET and of the analog section of the OTM
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Politecnico di Milano - Academic Year 2012/2013 - Mario
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3. The Optical Transport Network, OTN
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
The Digital Section of the OTM must guarantee the correct
mapping of the synchronous as well as a-synchronous clinets. The
Frame organization of the digital section of the OTM is similar to
that of SONET with one main difference: the frames at different
bit-rate have different temporal length (while in SONET/SDH the
temporal length is always 125 s) Also the Digital Section of the
OTM is organized in three sub-layer: The Optical Payload Unit, OPU
The Optical Data Unit, ODU The Optical Transport Unit, OTU (that we
have seen is joint with the OCC)
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Politecnico di Milano - Academic Year 2012/2013 - Mario
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3. The Optical Transport Network, OTN
-OPU (Optical Payload Unit): adapts the different tributaries
(both synchronous as a-synchronous) ; -ODU (Optical Data Unit):
manages the electrical connection end-to-end; -OTU (Optical
Transport Unit): inserts the FEC and provides for the signal
monitoring.
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
The hierarchic levels of OTM are only three: 1 corresponding to
2,5 Gb/s 2 corresponding to 10 Gb/s 3 corresponding to 40 Gb/s In
correspondence we have the payload OPU-k where k=1,2,3
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
As example let us consider the OPU-1. The frame is constituted
by 3807 columns and 4 rows equivalent to 15228 bytes. The temporal
length is fixed in order to recovery exactly the bytes transported
by STM-16 (thus 90x9x3x16= 38880 bytes). Hence
!
152283888012510
"6 sec = 48.971 sec
The same rule is valid also for OPU-2 and OPU-3 with the sole
exception of more bytes added in OPU-2 (16x4=64) and in OPU-3
(16x4x2=128) in order to fill the frame. Hence we have for
OPU-2
!
15164155520125 sec =12.191 sec and for OPU-3 , 3,035 s.
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
Hence, the whole structure of the OTM involving both the Analog
and the Digital section looks like the figure below
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
In the figure below the frame of SONET is compared with the
frame of OTN
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Politecnico di Milano - Academic Year 2012/2013 - Mario
Martinelli - Optical Communication Course - Lecture Slide -Only for
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3. The Optical Transport Network, OTN
The whole vision of the traffic management in the OTN net is
schematized in the figure below. It can be noticed that the digital
information carried out by the optical channel in the network can
be associated to frame with different colours. In other terms, the
OTN allows the circuit switching of the colours.