H-NW-1 Reliability Management of Telecommunication Networks … · Reliability Management of Telecommunication Networks by Analyzing Outage Data Network-anomaly Detection Technology

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Reliability Management of Telecommunication Networks by Analyzing Outage Data

Network-anomaly Detection Technology

International Standardization and Implementation of a Traffic Engineering Engine

Interface (PCEP)

Optical Burst-mode Amplifying Repeater for Uncompressed Digital Video Signals for

Broadcasting

Optical Fiber Line Testing System Enabling Service Area Expansion

Burst-mode CDR Circuit Using a ΔΣ D/A Converter for 10G-EPON Systems

Technologies for establishing a base network infrastructure including optical networks, wireless and satellite, all of which are essential to guaranteed bandwidth and broadband telecommunication.

To ensure the reliability of telecommunication networks, reliability design is usually performed using theoretical models in the

network-design phase. However, in this approach, redesign and re-evaluation must be performed every time a new device is

introduced, and this involves a very large amount of work. Also, if the actual MTBF* value of a device happens to differ from the

catalog value, then it becomes impossible to ensure reliability at the design stage.

Our proposed technique for the reliability management of telecommunication networks involves analyzing various kinds of outage

data that occur in telecommunication networks, and performing statistical processing on the traffic conditions when outages occur,

together with the number of customer complaints that result from these outages. In this way, it is possible to quantify and visualize

the reliability of telecommunication networks after services start, and to provide support for decision-making with regard to remedial

actions in order to improve reliability. This technique has never been used before, and is indispensable for the communication

services of NTT whose watchwords are safety and security.

In the future, we will develop reliability management based on this technique in the communication services provided by the NTT

Group companies, and we will continue our efforts to ensure that our customers can use these services comfortably.

* MTBF: Mean Time Between Failure

NTT Service Integration Laboratories

Reliability design and reliability management

Reliability Management of Telecommunication Networksby Analyzing Outage Data

copyright©2008NTTH-NW-1

Reliability Outage data

Reliability design

Networkconfiguration

Reliability design

Comparison toregulation

Networkconstruction

SystemC

System B

System A

Reliabilityregulation

Constructionand operation

(DO)

Improvement(ACTION)

Reliabilitymonitoring(CHECK)

Reliabilitymanagement

curve

Operationbased onanalysis

Reliability analysisfrom outage data

Outage data

Reliability management

Outage scale

Una

vaila

bilit

y

Reliability design(PLAN)

For providing high-reliability network services in a secure fashion, it is necessary to promptly detect network anomalies, which

significantly degrade the communication environments of users, and handle them in an appropriate manner. Conventionally, network

operators detect anomalies by monitoring; however, it has become difficult to detect anomalies in a short time because of the

increased number of monitoring points and monitored data items resulting from increased network scale.

Given that situation, at NTT Laboratories, we have developed a “dynamic-threshold setting technique”—based on network-traffic

volume of data items measured at multiple points—for automatically detecting anomalies and notifying the operator. By statistically

studying characteristic behavior of past network traffic, this technique can accurately predict present network traffic volume.

Moreover, by comparing the predicted volume with the actual (measured) volume, so-called “network anomalies” like increased traffic

volume of DDoS* attacks and reduced traffic volume due to equipment failure can be detected. What’s more, by continually

predicting normal traffic volume under a condition that an anomaly is ongoing, it is possible to judge whether or not the anomaly will

continue. In this way, instantaneous traffic changes and serious anomalies that continue for long periods can be distinguished, and

operators can be provided with additional information—namely, whether anomalies are currently ongoing at many different

places—that was unavailable with conventional technology (which notified operators of sudden changes in traffic volume only).

From now onwards, aiming to expand the information provided to network operators, we will continue research on anomaly

detection technology combining analysis techniques for identifying causes of anomalies and investigation on control-system for

realizing automation of initial-stage control for networks.

* DDoS: Distributed Denial of Service

NTT Service Integration Laboratories

Network anomaly detection system

Network-anomaly Detection Technology


Anomaly detection Ongoing anomaly Traffic prediction

DEC GL

DEC GL

DEC GL

DEC GL

DEC GL

DEC GL Network

Network operator

Traf

fic v

olum

e

Time

Range ofprediction

Detect ClearFailure

AS*

AS

ASDDoS Attack

Traffic information

(1) Collect traffic information

(2) Detect anomaly by comparing observation with prediction

(4) Control/Fix network

(3) Alert operator of anomaly information

* AS: Autonomous System

Anomaly-detection system

Ongoing

Ongoing

Ongoing

Detect! Cleared!

The spread of broadband Internet communications is causing a significant shift in the ways networks are used. For example,

clients are increasingly exchanging large files such as video content, and many corporate and individual clients are getting into the

habit of engaging in simultaneous communication.

To implement communication systems that are better able to reflect the state of end-to-end network usage while continuing to

provide the same quality of service to clients, the routing of information (traffic) through the network must be continuously optimized.

However, performing this task with the routers and optical transmission equipment that has conventionally been used on the Internet

gives rise to issues from the viewpoint of the flexibility of computation algorithms and computational capacity, and issues associated

with the difficulty of ascertaining the network status between multiple service providers and across different layers.

At NTT Laboratories, to separate these traffic engineering functions from the communication equipment itself, we have been

working on the standardization of PCE*1 architecture and the standardization based on the PCEP*2 of interfaces between PCEs and

communication systems. Our proposals have now been incorporated as the basis of international standards on architecture and

interface (protocol). At the same time, we have developed protocol software based on these standards.

We have confirmed that this technology is able to control existing optical communication equipment and routers, thereby allowing

paths to be optimized across multiple administrative regions (which is normally very difficult to achieve). In addition to the

standardization efforts, there have also been international developments of software products, and it is reported that as of March

2008 this software has been implemented by 9 companies including NTT Advanced Technology Corporation*3.

At NTT Laboratories, we are expanding and developing this technology while continuing with our standardization efforts, which

include optimizing the path computation algorithms used between multiple services and different communication technologies (e.g.,

optical networks and IP networks), taking the characteristics of optical communication more strictly into consideration, and dealing

with connections among multiple locations. We are also conducting research and development to support further development of our

broadband services with a view to implementing networks that provide our customers with optimal quality at all times.

*1 PCE: Path Computation Element*2 PCEP: Path Computation Element communication Protocol*3 NTT Advanced Technology Corporation news release, December 18, 2007

NTT Network Service Systems Laboratories

Traffic engineering engine interface (PCEP)

International Standardization and Implementation of a Traffic EngineeringEngine Interface (PCEP)


Traffic engineering International standardization PCE

PCE

Paths computed based on various conditions, including:-Quality of Service criteria (delay, bandwidth, etc.)-Network usage status

Pathcomputationrequest

PCEP

Path computationresponse Path determined by traffic engineering

to avoid congested links

Optical transmissionequipment or router

congestion

congestion

The digitization of television broadcasting is continuing. As for broadcasters, the digitization of video equipment and materials

used for business purposes is taking priority, and uncompressed digital video signals (such as those covered by the HD-SDI*1

specification) are being heavily used. Long-haul transmission of uncompressed digital video signals via optical fiber is carried out

between broadcasting stations and between event sites and broadcasting stations, however, as the coverage areas for video-material

transmission and live relays are expanded, it is being necessary to further increase the range of long-haul transmission. In

accordance with that requirement, it is becoming necessary to amplify and relay signals that are attenuated during transmission on

optical fiber.

Be that as it may, in the test signal, called a “check-field signal” (i.e., a pathological signal), in an uncompressed digital video

signal, “bursts” of consecutive identical digits (i.e., binary “0”s or “1”s)—lasting 26μs for the HD-DSI specification or 53μs for the SD-

SDI*2 specification—are included. Meanwhile, a conventional optical-fiber amplifying repeater is a device that amplifies the signal,

relays it, and transmits it over long distances. However, if the burst length in the signal exceeds 10μs, degradation of the signal

waveform is generated by a phenomenon called “gain transient response”. For that reason, relaying such an uncompressed digital

video signal and transmitting it over long distances has been difficult up till now by means of an optical-fiber amplifying repeater. In

response to that difficulty, we have developed an optical burst-mode amplifying repeater. By simultaneously amplifying (i.e., “co-

amplifying”) the signal light with a continuous light (called a “gain-clamp light”) in the same wavelength range as the signal light, this

repeater can suppress the gain transient response and thus extend the range of long-haul optical-amplification relay and transmission

of uncompressed digital video signals.

The optical burst-mode amplifying repeater also applies technology that is currently under investigation for extending the

transmission range of fiber-to-the-home signals (which have high “burstiness”) to uncompressed digital video signals. From now

onwards, in addition to developing the repeater for uncompressed digital video signals, we will continue to develop a repeater for

FTTH use.

*1 HD-SDI: High Definition Serial Digital Interface 　　　*2 SD-SDI: Standard Definition Serial Digital Interface

NTT Access Network Service Systems Laboratories

Optical burst-mode amplifying repeater for uncompressed digital video signals

Optical Burst-mode Amplifying Repeater for Uncompressed Digital VideoSignals for Broadcasting


Broadcasting Uncompressed digital video signal Optical amplifying repeater

The optical burst-mode amplifying repeater enables the long-haul transmission ofthe uncompressed digital video signals of the broadcasting.

Uncompressed digital video signal

(burst part)

Optical fiber amplifyingrepeater

(waveform is distorted)

Optical burst-modeamplifying repeater

(waveform distortion is suppressed)

Long-haul transmission

Optical fiber

Broadcast facilityEvent site

Optical burst-modeamplifying repeater

The service area of broadband optical access networks in Japan is expanding, and it will include an estimated 20 million

customers by 2010. We have already developed an optical fiber line testing system that reduces construction and maintenance

costs. If water penetrates an underground optical closure, it will increase optical loss and degrade the mechanical strength of the

fiber cables contained in it. To indicate when maintenance is necessary, we attached a water sensor module to one fiber in the optical

fiber cable in each underground optical closure. If water penetrates the underground optical closure, the material encasing the water

sensor module expands and applies a bending loss to the optical fiber. Water penetration can be monitored by performing a periodic

OTDR*1 test using this system. However, the optical testing module (OTM) for this system is not installed in the central office of rural

areas. This means a worker must travel to the central office and measure the optical fiber cable when undertaking periodic OTDR

tests.

Figure shows our new optical fiber line testing system with a small-scale FS*2. The central office of a metropolitan area is

equipped with an OTM and large-scale FS. The OTM consists of an OTDR, frame and test equipment selector (FTES) for selecting a

test equipment, and controller for the OTDR, FTES and FS. The large-scale FS can select a target fiber from thousands of optical

fibers. The central office of the rural area is equipped with a small-scale FS that accommodates a few fibers for monitoring water

penetration. The small-scale FS is controlled by the OTM via a virtual private network (VPN). The test light of the OTM passes

through the trunk line optical cable, and the small-scale FS selects the target fiber to monitor. With these technologies, we can

expand the application range of optical fiber line testing systems to rural areas.

We will continue researching and developing technologies for reducing maintenance costs.

*1 OTDR: Optical Time Domain Reflectometer*2 FS: Fiber Selector

NTT Access Network Service Systems Laboratories

Optical fiber line testing system with large-scale and small-scale FSs

Optical Fiber Line Testing System Enabling Service Area Expansion


Optical test Optical time domain reflectometer Water sensor

Subscriber optical cable

Maintenance centerMeasuring bending loss using OTDR

Loss

DistanceCO*1

OLT*2

FTM*4

IDM*3

Large-scale FS

VPN

Central office (Metropolitan area)

Central office (Rural area)

Trunk line optical cableWater sensor module

Small-scaleFS

*1 CO: Central Office *2 OLT: Optical Line Terminal *3 IDM: Integrated Distribution Module *4 FTM: Fiber Termination Module

Normal condition With water

OTM

The explosive growth in Internet traffic continues, and as of December 2007, there were more than 11 millions FTTH subscribers.

A standardization initiative for 10G-EPON*1 is currently defining the physical specifications to attain broader bandwidths (IEEE*2

802.3av). NTT Laboratories have developed a burst-mode receiver for 10G-EPON systems that gives a quick response to data

packets from subscribers to a central office. A burst-mode CDR*3 used in the receiver has two issues: how to achieve a large enough

margin for variations of PVT*4, and how to reduce the external devices in order to boost yield and reduce costs. The conventional

architecture needs two VCOs*5 with an oscillation-frequency error within several MHz, but this causes a low yield.

The figure shows a block diagram of the burst-mode CDR we developed. The frequency of the recovered clock is adjusted in the

circuit by comparing it with the frequency of the reference clock. The CDR uses digital counters to compare frequencies directly

instead of using a conventional phase detector. This enables the CDR to use only 1 VCO and removes the error in the oscillation

frequency. The CDR uses a D/A converter*6 in which almost all components are digital circuits for frequency adjustment, and this

increases tolerance to PVT variations. The converter also reduces the number of external devices by implementing the filter in the IC

itself, instead of outside of it in the conventional CDR.

We will push ahead with further miniaturization and power reduction and continue to improve the waveform quality.

*1 10G-EPON: 10-Gigabit Ethernet Passive Optical Network*2 IEEE: The Institute of Electrical and Electronics Engineers, Inc.*3 CDR: Clock and Data Recovery*4 PVT: Process, Voltage, and Temperature*5 VCO: Voltage Controlled Oscillator*6 D/A converter: The digital-to-analog converter achieves high accuracy using oversampling and noise-shaping techniques.

NTT Microsystem Integration Laboratories, NTT Access Network Service Systems Laboratories

Burst-mode CDR

Burst-mode CDR Circuit Using a ΔΣ D/A Converter for 10G-EPON Systems


CDR PON Burst

Inputdata

Recoveredclock

Recovereddata

Referenceclock

Digital block

10

Delay

Gatingcircuit

GatedVCO

ΔΣ D/Aconverter

Up/Downcounter

Frequencydetector

D-FF*

1/64 Digital blockDigital block

ΔΣΔΣModulatorModulator

Digital block

ΔΣModulator

Block diagram Chip micrograph* D-FF: D Flip-Flop

Documents

H-NW-1 Reliability Management of Telecommunication Networks … · Reliability Management of Telecommunication Networks by Analyzing Outage Data Network-anomaly Detection Technology