NETE0510: Communication Media and Data Communications 1 NETE0510 Optical Networking Supakorn Kungpisdan [email protected].

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



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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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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 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



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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

NETE0510: Communication Media and Data Communications 1 NETE0510 Optical Networking Supakorn Kungpisdan [email protected].

Documents

communication media

data communicationslayers

highspeed data

data communicationssynchronous

adjacent network equipment

network reliability

common fiber interface

sonet networknete0510