nete0510: communication media and data communications 1 nete0510 optical networking supakorn...
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NETE0510: Communication Media and Data Communications
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NETE0510Optical Networking
Supakorn [email protected]
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Outline
History of Optical Networking SONET/SDH Standards DWDM
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History of Optical Networking
Optical telegraph was invented in the 1790s In 1880, Alexander Graham Bell patented the optical
telephone system Modern optical communications started in 1950s with the
development of pulsing-laser technology (light) across fiber (glass or plastic) with low loss rates to achieve high-speed data and voice communications transfer
SONET/SDH define basic transmission rates and characteristics, frame formats and testing, and an optical interface-multiplexing scheme Had been main WAN transport technology through 1990s
Now DWDM allows 160 wavelengths per fiber, each 2.5-10 Gbps
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Outline
History of Optical Networking SONET/SDH Standards DWDM
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SONET/SDH
SONET and SDH are U.S. and International standards, respectively, for optical telecommunication transport
Provide a technology that enables the major service providers to internationally standardize and control broadband network transport media through a common fiber interface called a “midspan meet”.
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SONET/SDH Advantages
Reduction of equipment needed and increase network reliability and availability
Centralized fault isolation and management of payload (traffic carried)
Synchronous multiplexing formats for DS1 and E1 allowing easy access for switching and multiplexing
International vendor interoperability Flexible architecture able to accommodate future
requirements
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Synchronous, Plesiochronous, Asynchronous
Synchronous All clocks are traceable to one Stratum 1 primary
reference clock (PRC) All digital transitions in the signals occur at exactly the
same rate Plesiochronous
Clocks are extremely accurate and almost exact, but small difference between them
Asynchronous The clocks do not have to match or be equal
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Layers in SONET
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Layers in SONET (cont’d)
Physical Layer Define physical fiber type, path, and characteristics Include many electrical interfaces which become virtual channels
within the Synchronous Transport Signal-1 (STS-1) frame – the base level building block of SONET
Section Layer Build SONET frames from either lower SONET interfaces or
electrical interfaces Line Layer
Provide synchronization, channel multiplexing, and protection switching
Path Layer Manage actual data transport across the SONET network
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SONET Network Structure
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SONET Network Structure (cont’d)
Path: information carried end-to-end Line: information carried for STS-n signals between
multiplexers Section: information carried for communication between
adjacent network equipment, e.g. regenerator Path-terminating equipment (PTE): user interface at
the CPE Line-terminating equipment (LTE): a terminal, switch,
add/drop multiplexer, or cross-connect Section-terminating equipment (STE): a regenerator
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SONET Structure
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SONET Structure (cont’d)
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Frame Format
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SONET Frame Format
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STS-1 Overhead
Section Overhead (9 bytes 3 columns x 3 rows) Performance monitoring Framing Messaging communication between STEs for control,
monitoring, administration, and other communication needs\ Voice communication between STE
Line Overhead (18 bytes 3 columns x 6 rows) Locating the SPE in the frame Multiplexing or concatenating signals Performance monitoring Automatic protection switching Line maintenance
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STS-1 Overhead(cont’d)
Path Overhead (9 bytes 1 column x 9 rows) Performance monitoring of the SPE Path signal label, which indicates the content of the SPE Path status, which conveys status and performance back to
the originating terminal Path trace, which allows verification of continues connection
with the originating terminal
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STS-1 Synchronous Payload Envelope (SPE) SPW is defined as 783 bytes 87 columns x 9 rows The first column is the path overhead Columns 30 and 59 are not used for payload, but
designated to fixed stuff columns So it remains 84 columns x 9 rows 756 bytes of
payload To support service that requires a payload larger than
STS-1, SONET allows concatenating STS-1s together to support
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Pointers
Located in the line overhead of each frameUsed for frame synchronizationIdentify subchannels down to the DS0
level within a SONET transmission
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Pointers
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Virtual Tributary (VT)
VTs are the building blocks of the SPE VTxx designates VTs of xx Mbps
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Virtual Tributary (VT)7 VT groups• 4 VT1.5s• 3 VT2s• 2 VT3s•1 VT6
•2 bit-stuffed unused columns•1 path overhead column
Locked mode: fix the VT structure within an STS-1 and is designed for channelized operation
Floating mode: allow these values to be changed by cross-connects and switches
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Multiplexing
SONET provides direct multiplexing of both SONET speeds and current asynchronous and synchronous services into the STS-n payload
Payload types range from DS1 and DS3 to OC-3c and OC-12c payloads
STS-1 supports direct multiplexing of DS1 and DS3 into single or multiple STS-1 envelopes, which are called VTs
Multiple STS-1 envelopes are multiplexed into an STS-n signal Each individual signal down to DS1 can be accessed without the
need to demultiplex and remultiplex the entire OC-n level signal use a SONET digital cross-connect (DXC) or multiplexer
SONET multiplexing requires an extremely stable clocking source with a stable reference point Frequency of every clock within the network must be the same as or
synchronous with the others The central clocking source is typically a Stratum 1 source
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Multiplexing
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SONET Hardware
Most common equipment term used is the SONET terminal equipments: SONET Terminating Multiplexer SONET Add/Drop Multiplexer (SADM) SONET Digital-Loop Carrier Systems (DLCs) SONET Digital Cross-Connects (SDXCs) SONET Regenerators and Optical Amplifiers
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SONET Terminating Multiplexer
Provide user or customer premises equipment (CPE) access to the SONET network
Aka terminal adapter, edge multiplexer, or terminal Similar to M13 multiplexer and allow low-speed access
to SONET backbone Turn electrical interfaces into optical signals by
multiplexing multiple DS1, DS3, or E1 VTs into the STS-n signals required for OC-n transport
Arranged in point-to-point configuration
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SONET Add/Drop Multiplexer (SADM)
Add/Drop Multiplexer Add one or more lower-bandwidth signal on to a high-
bandwidth stream Drop or extract other signals, removing them from the stream
and redirecting them to some other network paths Traditional ADM is asynchronous at DS3 and lower
speed. Require multiple equipments e.g. M13 MUX
SADM enables provider to drop and add not only the lower SONET rates, but also electrical interface rates sown to the DS1 level
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SONET Add/Drop Multiplexer (SADM)
Standard features: drop-and-insert: a process that diverts (drops) a portion of the
multiplexed aggregate signal at an intermediate point, and introduces (inserts) a different signal for subsequent transmission in the same position, e.g., time slot or frequency band, previously occupied by the diverted signal.
drop-and-continue: drop some signals while allowing others to pass
Used for distributed point-to-point network connectivity A CO device forming the building blocks of the SONET network Enable easy expansion and are often used in SONET ring
architectures Operate at the higher transmission speeds of OC-3 through OC-
192
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SONET Add/Drop Multiplexer (SADM)
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SONET Digital-Loop Carrier Systems (DLCs)
Concentrate multiple DS0 traffic from remote terminals into a single OC-3 signal
Situated at local service providers and handle both voice and data traffic providing a SONET network interface for non-SONET equipment
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SONET Digital Cross-Connects (SDXCs)
Act as a gateway to SONET network
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SONET Regenerators and Optical Amplifiers
Both perform optical signal regeneration over fiber optics
Optical amplifiers just amplify the signal and noise
Regenerators reshape, retime, and retransmit signals that have incurred dispersion or attenuation over long transmission distances
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SONET Network Configurations
Point-to-point Two PTE pieces of equipment are connected directly
together with a STE/regenerator in line Point-to-multipoint
The PTE equipment is connected to a LTE/SADM that enables circuits to be added or dropped along the way
Ring Are deployed in most large-scale service provider
networks
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SONET Ring Architecture
Working pair outage
Normal operation
Fiber cut of both pairs
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SONET Advantages
Reduced network complexity and cost through SADM and SDXC capabilities
Ability to transport all forms of traffic: voice, data (ATM, IP), and video
Capability to build optical interconnects between carriers Efficient management of bandwidth at the physical layer Aggregation of low-speed data channels into common high-
speed backbone trunk transport Standard optical interface and format specification providing
vendor interoperability Increased reliability and restoration over electrical systems Increased bandwidth management through logical path
grooming Smart OAM&P features with uniformity
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SONET Disadvantages and Challenges
Strict synchronization schemes required Complex and costly SONET equipment contrast
to chapter optical Ethernet and other alternate MAN technologies
High percentage of SONET protocol overhead Fiber laying unutilized in a ring architecture,
waiting on a failure
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Outline
History of Optical Networking SONET/SDH Standards DWDM
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Dense Wavelength Division Multiplexing (DWDM)
Three methods to relieve capacity shortage: Increase the bit rate of existing systems, such as
moving OC-48 systems to OC-192 systems Install new fiber Optimize the use of existing fiber using methods like
increasing the number of wavelengths (and thus bandwidth available) per fiber
DWDM
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WDM
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DWDM VS WDM
Similar enable more than one wavelength to be added to a single-mode fiber Increased capacity depends on the number of
wavelengths added Current systems support 160 wavelengths per fiber
DWDM spaces the wavelengths closer than WDM and therefore has a greater overall capacity than WDM
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Advantages of DWDM
Every wavelength is independent of the others Can transport SONET, gigabit Ethernet, or
native ATM on the same optical fiber cable Do not require a large amount of overhead as
that of SONET Optical amplifier can apply to all wavelengths
cost savingsHaving 160 wavelengths on a DWDM fiber will
save amplifier 160:1
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DWDM Hardware
DWDM multiplexer/demultiplexer Combine multiple optical signal into a single optical fiber Separate optical wavelengths into a single wavelength fiber
Optical add/drop multiplexer (OADM) Like SADM, but in the optical domain Allow wavelengths to be split or added to a DWDM fiber
OXC A cross-connect between n-input ports and m-output ports Perform management of wavelengths at the optical layer
Optical amplifier Amplify signal strength to travel over long distances
Regenerator Same functionality as amplifier with resharing and retiming
capabilities
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Optical Amplifiers/Regenerators
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Interfaces
DWDM supports many different types of interfaces: SONET Ethernet (1Gbps, 10Gbps, and fast) Fiber channel ATM
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DWDM Network Configuration
Point-to-point The network must have the characteristics of ultra high-speed
channels (10-40Gbps), high signal integrity and reliability, and fast path restoration
Distance btw transmitters and receivers can be several hundred kms with less than 10 amplifiers
Ring SONET rings can be built with the combination with DWDM
Mesh (partial or full) Mesh architectures connect all-optical nodes together with two
routes, and implement intelligence in the notes to reroute wavelengths on faults
Extremely expensive to implement andmanage
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Advantages of DWDM
Support 160 wavelengths over 1 Tbps of traffic to be carried
Each wavelength can be a different traffic type e.g. SONET, gigabit Ethernet, IP over PPP, and can operate at different speeds
Optical amplifiers provide cost saving
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Disadvantages of DWDM
Some fiber plant are not suitable for DWDM and do not support DWDM
Difficult to troubleshoot, manage, and provision. Need to manage DWDM-specific equipment
Vendor interoperability issues
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Questions?
Next LecturePhysical Layer Protocols and
Access Technologies