Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-02-24
2003-08-05
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C359S199200
Reexamination Certificate
active
06603112
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to network management systems and more particularly to techniques for detecting malfunctions in communications networks.
BACKGROUND OF THE INVENTION
As is known in the art, an all-optical network (AON) refers to a network which utilizes exclusively lightwave communication. In particular, an AON system refers to a system in which: all network-to-network interfaces are based on optical transmission, all user-to-network interfaces use optical transmission on the network side of the interface, and all switching and routing within AON network nodes is performed optically. One important advantage of maintaining an optical network core in comparison to using electro-optic components at nodes or in transmission systems is higher bandwidth. Typically, optical bandwidths are generally one hundred fold those of electronic bandwidths. Thus, avoiding optical/electronic/optical conversions can provide in some instances roughly one hundred times greater data rates than possible with electro-optic networks.
An optical network that allows routing and switching of data within the network without interpretation or regeneration of the individual data streams is referred to as a transparent network or as a network having a transparency feature. Within this context of transparency, we do not include all-optical techniques for data regeneration. Such techniques may be faster than electro-optic regeneration methods, but may be modulation or format dependent and, hence non-transparent. While transparent networks have many desirable features (e.g. terminal upgrades do not require network upgrades), transparency has important ramifications for security.
Although contemporary AONs are still largely in the research arena, commercial providers are beginning to provide limited AON functions in their networks. Those AONs in the research arena may be generally classified into two types: wavelength division multiplexed (WDM), which separate multiple channels of traffic each onto its own wavelength, and time-division multiplexed (TDM), which separate multiple channels of traffic each into its own time slot. Code Division Multiple Access (CDMA) networks also exist. CDMA networks provide a multiple access scheme by using code sequences as traffic channels in a common optical channel. CDMA permits more than one signal to simultaneously utilize the channel bandwidth in a noninterfering manner. TDM networks to date have often employed soliton transmission and other features that will likely require further development to reach commercial maturity. Therefore, WDM AONs are more likely to be exploited in the near term than are TDM AONs.
Existing AONs are generally architected as circuit-switched networks. Circuit-switched networks are compatible with (1) existing telecommunication installations (long haul), (2) asynchronous transmission mode (ATM) networks, and (3) some multiplexing equipment often used with Internet networks. Fully operational packet-switched AONs have not been implemented, in part owing to the lack of a desirable optical memory.
AON architecture can generally be divided into optical terminals (which are the user-network interface), network nodes (which switch, route, and sometimes perform multiplexer/demultiplexer functions), and optically amplified fiber optic links. A separate control network (not always all-optical) is usually used for signaling purposes. The switching and routing may be done via mechanical switches, opto-electronic switches, passive optical routers, or splitter/combiners. Common network topologies include star, ring, and mesh. Some network architectures allow a hybrid mixture of network topologies.
Although there are a large number of possible architectures, most contemporary WDM
AONs are built using a combination of a relatively small set of devices or components each of which has a security property. Some commonly used AON components are shown in Table 1.
TABLE 1
Component
Component Function
Example
Combiner
Combine optical signals
Star Coupler
from N fibers to 1 fiber
Splitter
Split signal from
Star Coupler
1 fiber to N fibers
Demultiplexer
Separate multiple signals on one
Waveguide
fiber each onto its own fiber
Grating Router
Multiplexer
Combine individual signals from
Waveguide
multiple fibers onto one fiber
Grating Router
Optical
Increases the signal strength
Erbium Doped Fiber
Amplifier
(amplitude) of an input signal
Amplifier (EDFA)
Spatial
Let pass or dump particular
LiNbO
3
Switch
Switch
signals, or switch it
between fibers
Lasers
Transmit a signal
Many
Optical
Receive a signal
PINFET, Avalanche
Receivers
Photo-diodes
Fiber Cable
Transport
Many
One component of relative importance in AONs, as well as in other networks including but not limited to electro-optic networks, is the optical amplifier. Optical amplifiers are used in both nodes and links of AONs. Some optical amplifiers work by using a pump laser and a gain medium to amplify optical signals without converting them to electronic signals. One artifact of the amplification is amplified spontaneous emission (ASE) noise, which is added to the output of a signal exiting the amplifier.
Each of the components listed in Table 1 above. is susceptible to some form of malfunction. As used herein, the term “malfunction” refers to any abnormal operational change, including but not limited to a degradation. A malfunction may cause a failure at one or more links or nodes and may have various causes, such as a security attack. A malfunction may affect signal channels having signal paths or routes which share devices with a nefarious user's channel. An understanding of the security properties of each component provides a reasonable foundation for predicting network vulnerabilities and suggesting robust architectures.
The above components have been integrated into testbeds to show the operations and limitations of AONs. AON demonstrations to-date have taken place mostly in government-funded testbeds or testbeds funded by consortia. In the United States, there are consortia involving academia, industry, and government. In particular, the AON, MONET, and NTONC consortia have multiple participating organizations and have all developed testbeds. In addition, the European RACE consortium, and the Japanese efforts have also developed testbeds. Various testbeds and laboratory experiments have demonstrated aggregate throughputs of over 1 Tbit/s. The traffic carried has consisted of Asynchronous Transfer Mode (ATM), Internet Protocol (IP), Synchronous Optical Network (SONET), Frame Relay, and digitized video.
The components of AONs and other networks including non-AON networks are each vulnerable to some form of denial of service or eavesdropping-type attack. Some attack methods of concern include jamming (i.e. the overpowering of legitimate network signals with illegitimate or attack signals) which can be used to degrade or deny service, and the exploitation of device crosstalk. Device crosstalk exists within a number of different optical devices, and is the phenomenon in which signals from one portion of the optical device leak into another portion of the same device. The crosstalk phenomena can be used to implement service denial or eavesdropping attacks. It should be noted that signal interception and traffic analysis are both included under the eavesdropping heading as that term is used herein. It is thus desirable to detect malfunctions including attacks such as eavesdropping attacks in AON's and other networks but not limited to electro-optic networks.
There are may reasons for which, in AONs, malfunctions must be detected and identified at all points in the network where malfunctions may occur, and the speed of detection should be commensurate with the data transmission rate of the network. One reason why the high data rates of AONs have an important consequence for malfunction detection, is because large amounts of data can be affected in a short time. When a fixed duration malfunction disrupts service, the amount of data affected is linearly proportional to the
Chinn Stephen R.
Medard Muriel
Le Que T.
Luu Thanh X.
Massachusetts Institute of Technology
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