Monday, 26 March 2007

Stealing the Minutes

Stealing the MinutesThe Internet isn't as secure as a regular phone line. Businesses are now learning that the hard way.

By Benjamin SutherlandNewsweek

March 19, 2007 issue - The telephone industry has been in an upheaval ever since upstarts began competing with the big telecoms by sending voice calls over the Internet. Now even big firms are using so-called voice over Internet protocol. But VoIP is not as secure as old-fashioned phone lines—as carriers that rely on the Internet are finding out. They're increasingly falling prey to "phreakers," who steal their minutes and resell them on a thriving black market.
Of course, anybody with a PC and a Net connection can talk free of charge to another PC user. For the telecoms, the profit is in using VoIP to deliver calls from one phone to another. That requires a "gateway" server to connect a carrier's phone network to the Net. Phreakers break into these gateways, steal "voice minutes" and sell them to other, usually smaller, telecoms. Many of these firms then sell printed phone cards or operate call centers. "It's a great racket," says Justin Newman, CEO of BinFone Telecom of Baltimore, which has been stung by phreakers.

These thieves steal 200 million minutes a month, worth $26 million, according to Stealth Communications, a New York City telecom. With more than 5,000 wholesale-minutes markets worldwide—located mainly on Web sites—fraud is hard to track. Emmanuel Gadaix, head of TSTF, a Hong Kong firm that investigates VoIP thefts, says it's "very easy to set up a temporary link" through a hacked gateway. His company was recently hired by a Panamanian telecom that lost $110,000 to phreakers. TSTF followed tracks, in vain, that snaked through Bulgaria, Canada, Costa Rica, Hong Kong and the United States. Phreaker trails are "way too complicated" to track successfully, says Gadaix.

The hackers use one of hundreds of cheap, illicit phreaker programs. One South African, who requested anonymity out of legal concerns, says he wrote a program, Lesion, in a few weeks and sells it for $10,000. Small telecoms, lacking the money for secure gateways, are "constantly under attack," says Marco Ivaldi, an Italian telecom expert.

For protection, telecoms are turning to private VoIP networks, separate from the public Internet. More than 1,000 telecoms, including AT&T and China Telecom, now buy and sell minutes on a network owned by Stealth. It car-ried more than 10 percent of worldwide VoIP traffic last year, a sevenfold increase over 2005. That percentage is expected to keep growing, as the security threat isn't going away.

© 2007 Newsweek, Inc.

DRAM now and future

(photo quoted from
Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory. Its advantage over SRAM is its structural simplicity: only one transistor and a capacitor are required per bit, compared to six transistors in SRAM. This allows DRAM to reach very high density. Since DRAM loses its data when the power supply is removed, it is in the class of volatile memory devices.(Wikipedia)

What would make a good memory subsystem?
1. High bank counts aids multitasking in multi-core CPUs,
2. High memory bandwidth to keep up demands from CPU and graphic engines.
3. Low latency reduces stall time for CPU in case of Cache miss.
4. High memory capacity reduces HD access.
5. Low power to reduce cooling cost

Application oriented market segmentation in 10 years
1. Commodity DRAM: x16 graphic, x8 desktop, x4 enterprise server.
2. Low Power DRAM: Handset, mobile phone.
3. Graphic DRAM: high and graphic system

DRAM design trend and challenges
1. More features to accommodate system variation and requirements
2. More design facilities to accommodate signal skew
3. Future DRAM considerations
4. Power dissipation is number 1 DRAM design objective.1.
5. Challenge in high frequency design in bulk CMOS technology.
6. High efficiency voltage regulator design.
7. High speed clock tree with very low jitter spec under noisy environment
8. Keep same power with very low jitter spec under noisy environment.
9. Package design and electrical modeling1.

1. Memory design has to start from system perspective.
2. High speed and robust design requires design innovation
3. Low cost and higher density DRAM with constant power budget will continue to be the main deriving force.

Tuesday, 20 March 2007

Thermal Noise

An additional, stochastic source of electrons in a CCD well is thermal energy. Electrons can be freed from the CCD material itself through thermal vibration and then, trapped in the CCD well, be indistinguishable from "true" photoelectrons. By cooling the CCD chip it is possible to reduce significantly the number of "thermal electrons" that give rise to thermal noise or dark current. As the integration time T increases, the number of thermal electrons increases. The probability distribution of thermal electrons is also a Poisson process where the rate parameter is an increasing function of temperature. There are alternative techniques (to cooling) for suppressing dark current and these usually involve estimating the average dark current for the given integration time and then subtracting this value from the CCD pixel values before the A/D converter. While this does reduce the dark current average, it does not reduce the dark current standard deviation and it also reduces the possible dynamic range of the signal.

Monday, 19 March 2007


What is required to build a successful telecom business?

Need to understand competition, and regulation and win market share. Need to keep customers by satisfying them early and win new ones. On the financial side, need to keep investors satisfied by having good margins: this can be done by increasing revenues and/or reducing costs. Revenues come from services. New service time to market is important. Existing services quality, billing, price, ordering, customer support will influence their success. Examples of services that a carrier can offer with an optical network: dark fiber; wavelength service; bandwidth (E1 to 2.5G) leasing;
Hierarchy in a Network: found in all networks. Logical structure to interconnect Network Elements. Connect local equipment to higher level equipment. Idea is not to interconnect all the local NEs together (not transmission resource efficient and not scalable approach) but to connect to a higher level (say regional) NE, themselves connected via a connection to a higher level NE. Equipment at different levels have different function. For example a Central Office/Telephone exchange at the local level will have connections to customers whereas the higher level will do connections between CO only and to the higher level.

A hierarchy brings order to the way interconnections are made and also creates different functions – in the same way as people in an organization hierarchy have different responsibilities and the hierarchy allows people to understand how of how people communicate.
Where transmission fits: the first or last mile is called Access – the rest is transmission. Transmission is what connect Network Elements such as Switches (telephone or data) together.

Switch functionality – example: a telephone switch connects 2 ports under the end user command. The difference between a tel switch and a cross connect is in the control of this element: the end user controls/activates the telephone switch (and the future intelligent optical switch!) whereas the management system for a cross connect allows its control. The logic of connecting a telephone call: all the COs talk to each other with signaling to set-up the call – same principle as we are going to have with the future intelligent optical network!
Analog and digital signals: an analogue signal is continuous in time. A digital signal is a series of on/off signals or ‘1’ and ‘0’.

Types of networks: Circuit switching, Packet switching

In circuit switching, a circuit across the network is established before data can flow from one point to another. This circuit can be seen as a pipe (like plumbing) and the data will flow on it. The data does not need to have any indication of where it is going. It just flows on the stablished pipe. In packet switching, the data to be sent is chopped into packets, each packet has a destination address and the switch examines it to decide where to send it. In connectionless networks, there is no predetermined route for the data to flow along (such as in IP or Ethernet networks). Each switch does its own analysis of where the data needs to go to send it on. In connection oriented packet switching networks (such as MPLS or ATM), a route is established once for all and the switches are setup to recognize the data to go on one route. Hence all the packets follow the same route.
ISO 7 Layer Model
Complex function is split into layers to simplify the tasks and allow a modular implementation: A client layer simply uses the service of a server layer. This allows the implementation of the server layer to be hidden – just the service is visible, not how the job is done.
The transport layer segments the info to be transmitted into pieces, numbers them (and can do checking on this number to ensure they all get through) and pass them on to the Network layer.
The network layer has a view of the whole network and can see which hop a packet needs to go next and passes the packet to the data link layer.
The data link layer ensure the point to point communication and passes the data to the physical layer for actual transmission onto the physical medium..
IP is layer 3
ATM, Frame Relay are layer 2
SONET/SDH is layer 1/2
A synchronous transmission pipe at the physical layer is has a fixed size and is present whether data flows or not.
Nortel Networks

Saturday, 17 March 2007

Flexible Electronics

(quoted from
Flexible electronics, also known as flex circuits or flex circuit boards, is a technology for building electronic circuits by depositing electronic devices on flexible substrates such as plastic. In the simplest case, flexible electronics can be made by using the same components used for rigid printed circuit boards. The only thing that needs to change is the substrate, being made flexible, rather than rigid. Typically, in LCD fabrication for example, glass is used as a substrate. If thin flexible plastic or metal foil is used as the substrate instead, the entire system can be flexible, as the film deposited on top of the substrate is usually very thin, on the order of a few micrometres. (Wikipedia)

In our group seminar this week, our department invited a professor who are good at the flexible electronics region to deliver a speach. I was very impressed on this topic. It's so-called future technology. The important features are urer-friendly, moblie and personalized life. He showed us many new concept photos and a short video about future life. The conclusion is that flexible electronics is the world wide trend, which will change our daily life eventually.

Friday, 16 March 2007


NoMachine NX is a Terminal Server and Remote Access solution based on a comprising set of enterprise class open source technologies. Thanks to the outstanding compression, session resilience and resource management developed on top of the X-Window system, and the integration with the powerful audio, printing and resource sharing capabilities of the Unix world, NoMachine NX makes it possible to run any graphical application on any operating system across any network connection as if you were sitting in front of your computer.

downloads When you install the NXserver, please remember to install client and node first.