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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
ΔΣD/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 Networks
by Analyzing Outage Data
Reliability Outage data
Reliability design
Network configuration Reliability design Comparison to regulation Network construction System C System B System A Reliability regulation Construction and operation (DO) Improvement (ACTION) Reliability monitoring (CHECK) Reliability management curveOperation
based on
analysis
Reliability analysis
from outage data
Outage data
Reliability management
Outage scale Unavailability 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 T raf fic volume Time Range of prediction Detect Clear Failure AS* AS AS DDoS 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 Anomaly-detection system Ongoing Ongoing Ongoing 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 Engineering
Engine 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
Path computation request
PCEP
Path computation
response Path determined by traffic engineering
to avoid congested links
Optical transmission equipment or router
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 26
μ
s for the HD-DSI specification or 53μ
s 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 10
μ
s, 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 Video
Signals for Broadcasting
Broadcasting Uncompressed digital video signal Optical amplifying repeater
The optical burst-mode amplifying repeater enables the long-haul transmission of
the uncompressed digital video signals of the broadcasting.
Uncompressed digital video signal
(burst part)
Optical fiber amplifying repeater (waveform is distorted)
Optical burst-mode amplifying repeater (waveform distortion is suppressed) Long-haul transmission Optical fiber Broadcast facility Event site Optical burst-mode amplifying 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 center
Measuring bending loss using OTDR Loss Distance CO*1 OLT*2 FTM*4 IDM*3 Large-scale FS VPN
Central office (Metropolitan area)
Central office (Rural area)
Trunk line optical cable
Water sensor module Small-scale
FS
*1 CO: Central Office *2 OLT: Optical Line Terminal *3 IDM: Integrated Distribution Module *4 FTM: Fiber Termination Module
Normal condition With water
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 ɺʈ 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 ɺʈ 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 Input data Recovered clock Recovered data Reference clock Digital block 10 Delay Gating circuit Gated VCO ΔΣ D/A converter Up/Down counter Frequency detector D-FF*
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