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Feb 27, 2009

Ethernet RJ45 Installation Cable Diagram

Fiber Optic Installation Diagram

Description :

(1). Ethernet Switch that support fiber optic module
(2). SC-SC style multimode ceramic connector
(3). Cable Assembly Multimode (Fiber Optic Patch Cords)
(3.a).FO Outdoor 4 Cores, Armored 50 micron
(4). Rack Mount Fibre Enclosure, 24 port (put in to the wallmound rack)
(5). Adapter Coupler Plate 6 Port
(6). Adapter Coupler SC Duplex
(7). Wall mount Enclosure 24 port (put on the wall)
(8). Fiber-Optic-Media-Converter-1000M-SC-Connector-External-Power-Supply
(9). Connector RJ45
(10).Lan Cable CAT5E UTP
(11).Catalysy 2900 XZ Series (Not Support FO Module)

Feb 19, 2009



USB Field allows you to use a standard USB 2.0 connection in harsh environments

  • Sealed against fluids and dusts (IP67)
  • Shock, Vibration and Traction resistant
  • No cabling operation in field and no tools required
  • Mechanical Coding / Polarization (2 positions)
  • Improved EMI protection

With USB Field, you can insert a standard USB 2.0 cordsetinto a metallic plug which will protect it from shocks, dust andfluids.No hazardous in-field cabling and grounding!

This metallic plug is connected into a receptacle, using a Tri Start Thread coupling mechanism (MIL-DTL-38999 series III type) with anti-decoupling device for high vibrations. On the receptacle side, one A USB receptacle is soldered onto a PCB allowing for the following back terminations:

  • another USB-A receptacle
  • solder : 4 tined holes on the PCB to solder your wires

The USB 2.0 cordset shielding is transmitted to the USB receptacle through grounding fingers. For an outstanding EMI protection, the conductive plated shells (Ni, Cd) with metallized receptacle inserts, transmit the shielding to the connector shells and finally to the panel.

Main Characteristics EnvironmentalProtection
  • Sealing(whenmated) : IP67 (Temporaryimmersion)
  • Salt Spray : 48 h with Nickel plating> 500 h with Olive DrabCadmium
  • FireRetardant / LowSmoke: UL94 V0 and NF F 16 101 & 16 102
  • Vibrations : 10 –500 Hz, 10 g, 3 axes : no discontinuity> 1micro s
  • Shocks: IK06 : weightof 250 g drop from40 cm [15.75 in] onto connectors(matedpair)
  • Humidity: 21 days, 43°C, 98% humidity
  • TemperatureRange : -55°C / +85°C

Data Transmission

  • USB Specification 2.0Data Rate : Up to 480 Mb/s for High Speed USB

  • Tri Start Thread coupling mechanism (MIL-DTL-38999 series III type) with anti-decoupling device
  • 2 mechanical Coding / Polarization possibilities by the user (receptacle insert rotation)
  • USBF TV plug retent° in the receptacle : 100 N in the axis
  • Mating cycles : 500 to 1500

Feb 17, 2009

Asterisk - WANPIPE® Echo Spike Generation: Debugging (Linux)

When a system suffers from an intractable echo, it is often very difficult to diagnose the origins and possible solutions to the echo problem. WANPIPE® has a utility that allows the echo from a unit impulse to be examined and analyzed.

If you have Sangoma Card with Hardware echo canceller, the echo spike is not very important or useful.
In this case we suggest using hardware echo canceller tools to determine the echo problem:

To debug Echo problem during the phone call:

1. Install WANPIPE version beta1w-2.3.4 or later, use the following command when installing:

./Setup install --echo-debug

The Setup script will patch Zaptel driver, so it will have to be recompiled/reinstalled after WANPIPE installation is complete. Software Echo canceller should be enabled on the span, where the test will be done (or on all spans).

2. Make the phone call and check if there is echo.

Find a number that shows consistent echo for this test. The test should be done from the side where the echo is heard. Ideally, mute the phone on the remote side during the test. Note the Zap channel number on which the test call is done, for example channel 12. The rest of this document assumes the test call is active on Zap channel 12.

3. Run the following command:

#>wanpipemon -zap -c ses -zapchan 12

A test impulse is sent on zap channel 12. The Finite Impulse Response (FIR) is saved to the file: /etc/wanpipe/span_1_chan_12_before_ec.spike as a set of linear samples taken 8000 times per second.

4. Copy the data from /etc/wanpipe/span_1_chan_12_before_ec.spike into a spreadsheet.

Asterisk - Debugging Asterisk/Wanpipe RBS

The wanpipemon utility provides the ability to debug RBS bits. The following command enables/disables WANPIPE RBS debugging and prints all debugging message into the /var/log/messages file. This feature is supported for all Sangoma digital AFT-series cards.

* To enable RBS debugging on reciever side (this command will print only changes to the RBS bit settings):
wanpipemon -i -c derr

* To disable RBS debugging on reciever side:
wanpipemon -i -c ddrr

* To enable RBS debugging on transmit side (this command will print only changes to the RBS bit settings):
wanpipemon -i -c dert

* To disable RBS debugging on transmit side:
wanpipemon -i -c ddrt

* Read the current RBS status bits from AFT-series cards:
wanpipemon -i -c drr

* Read the current RBS status from the Wanpipe driver:
wanpipemon -i -c dpr

In order to verify the RBS operations, you can run ./zttool utility and enable Sangoma RBS debugging at the same time. Zttoll shows what zaptel thinks is the RBS setting and the wanpipe utilities show what the sangoma driver thinks is the RBS setting. The two have to match at all times.

  1. In one window run: zttool
  2. In another window run: tail -f /var/log/messages
  3. Enable RBS debugging as stated above:
    wanpipemon -i -c derr #Enable rx rbs debugging
    wanpipemon -i -c dert #Enable tx rbs debugging
  4. Place a call on Asterisk with reproducable bad behaviour
  5. Compare zttool output versus the /var/log/messages
    If driver rbs changes are identical to zttool rbs changes problem is with the telco.
    If driver rbs changes differ from zttool rbs changes there could be a problem with the drivers.
  6. If zttool output doesnt match wanpipe rbs output please contact Sangoma Support.

Asterisk - Hardware echo canceler Fax/DTMF Debugging (AFT A101/2/3/8/Analog)

If you are experiencing ECHO or DTMF/Fax problems on your system using a card only when the hardware echo canceler is enabled, please follow the instructions below on how to capture an echo debug file.

The hardware echo canceler chip has a debug feature where a DEBUG Monitor will capture chip debug data during active calls. The captured debug binary file can be sent to Sangoma for further processing and analysis.

Before proceeding you should also confirm that Is my Hardware echo canceller running?

  1. Establish a call that has an echo problem noise or DTMF problem
  2. Determine the call channel number by running "show channels" on Asterisk CLI:
    CLI> show channels
  3. Run a echo canceler debug utility on that channel

    #>wan_ec_client wanpipe1 monitor

    Where is a channel number obtained in step 2.
  4. After 2 minutes of talk and noticeable echo, or 30 seconds of bad DTMF or noise.
    Obtain the debug statistics using:

    #>wan_ec_client wanpipe1 monitor

    The wan_ec_client will write a binary file in your local directory.

Feb 16, 2009

Asterisk - Configuring A500 BRI as Timing source for Asterisk

A500 BRI card can be used as Timing source for Asterisk , by adding following paramater in /etc/wanpipe/wanpipe1.conf .Note: This is the case when you have only A500 BRI card on the system.

Add TDMV_DUMMY_REF =YES inside [wanpipe1] section:

[trixbox1.localdomain ~]# cat /etc/wanpipe//wanpipe1.conf
# WANPIPE1 Configuration File
# Note: This file was generated automatically
# by /usr/local/sbin/setup-sangoma program.
# If you want to edit this file, it is
# recommended that you use wancfg program
# to do so.
# Sangoma Technologies Inc.
wanpipe1 = WAN_AFT_ISDN_BRI, Comment

w1g1 = wanpipe1, , TDM_VOICE_API, Comment

S514CPU = A
CommPort = PRI
MTU = 1500
UDPPORT = 9000
TTL = 255

MTU = 80


Make sure zaptel is installed before and also make sure to choose "SMG(BRI)+Zaptel Support" during the installation of the driver.

Feb 14, 2009

Asterisk - Sample Configuration files for a J1 implementation

Configuring your Sangoma A10x card for J1 is qute simple but it does require making some manul changes:

  1. First use the "wancfg_zaptel" script to quickly create a base wanpipeX.conf, zaptel.conf, and zapata.conf files. For now select the T1 line media and take the default line configuration options (B8ZS and ESF). Select the type of clocking to use; NORMAL, and the card will take the clocking from the line (select this for a telco connection) and MASTER if the card needs to act like the telco and generate the clocking for the line. Next select either PRI_NET (telco/master side of a PRI connection) or PRI_CPE (slave side of a PRI connection). Lastly direct the call to the Asterisk context of your choice.
  2. Once the configuration script has created all the files, the wanpipeX.conf files need to be modified so the driver correctly encodes the line. Open the file "/etc/wanpipe/wanpipeX.conf", where X is the port number. Add the line "FE_SUBMEDIA=J1" as per the following sample wanpipeX.conf file:

    #WANPIPE1 Configuration File
    # Date: Wed Dec 6 20:29:03 UTC 2006
    # Note: This file was generated automatically
    # by /usr/local/sbin/setup-sangoma program.
    # If you want to edit this file, it is
    # recommended that you use wancfg program
    # to do so.
    # Sangoma Technologies Inc.

    wanpipe1 = WAN_AFT_TE1, Comment

    w1g1 = wanpipe1, , TDM_VOICE, Comment

    S514CPU = A
    CommPort = PRI
    PCISLOT = 2
    PCIBUS = 7
    FE_MEDIA = T1
    FE_LINE = 1
    TE_REF_CLOCK = 0

    LBO = 0DB
    MTU = 1500
    UDPPORT = 9000
    TTL = 255
    TDMV_SPAN = 1
    TDMV_DCHAN = 24

  3. Save the file and confirm that Wanpipe, Zaptel, and Asterisk start properly. If you have any problems please following the debugging instructions at the following link: PRI Debugging

Sample Zaptel.conf File:

# Autogenerated by /usr/local/sbin/sangoma/setup-sangoma -- do not hand edit
# Zaptel Channels Configurations (zaptel.conf)

#Sangoma A102 port 1 [slot:2 bus:7 span:1]

Sample Zapata.conf file:

;autogenerated by /usr/local/sbin/config-zaptel do not hand edit
;Zaptel Channels Configurations (zapata.conf)
;For detailed zapata options, view /etc/asterisk/zapata.conf.orig




;Sangoma A102 port 1 [slot:2 bus:7 span:1]
channel =>1-23

Feb 13, 2009

Asterisk - Asterisk & Sangoma Hardware DTMF

Sangoma hardware DTMF is now supported starting from 3.3.0 wanpipe release. The Hardware DTMF is supported by the Octasic Hardware Echo/DTMF DSP. Therefore in order to take advantage of hardware DTMF you must have one of Sangomas AFT A200/A400,101/2/4/8 D cards (with onboard hardware echo cancelation)


  1. Download latest 3.3.X release or greater
  2. Install above wanpipe release:
    -> follow standard wanpipe installation instruction
  3. Configure wanpipe devices using wancfg_zaptel script.
    -> run: /usr/sbin/wancfg_zaptel
    -> follow standard wanpipe config instructions
    -> select hardware dtmf option
  4. Start wanpipe
    -> wanrouter start
  5. Configure zaptel
    -> ztcfg
  6. Start Asterisk
    -> asterisk

Feb 12, 2009

Asterisk - ZAPTEL with Adjustable Chunk Size

By default Zaptel runs with 8 byte chunk size. This equates to 1ms interrupt on TDM hardware! This causes congestion on the PCI bus and overal creates a bottle neck.

Sangomas hardware is able to automatically detect ZAPTEL chunk size and adjust accordingly. One can configure ZAPTEL for 8bytes (1ms - default)- 16bytes (2ms) - 40byte (5ms) or 80byte (10ms) chunk size. This would drastically reduce number of interrutps on your system and allow you to scale better with large number of ports.

To configure ZAPTEL for higher chunk size

./Setup install --zap-chunk=

Where CHUNK SIZE: 8, 16 , 40 or 80

Setup will patch zaptel source for selected chunk size and will remove wct4xxx (digium) driver out of zaptel Makefile. Reason for this is that digium wct4xxx driver does not support any chunk size other than 8bytes (1ms).

Once Setup recompiles zaptel and wanpipe drivers. There are no other configuration needed! Just start wanpipe and zaptel and Asterisk:

  1. wanrouter start
  2. ztcfg -vvv
  3. asterisk
  4. asterisk -c -r

In order to confirm that you are running with new zaptel chunk size. run:

  1. ifconfig w1g1
    -> confirm that MTU = configured chunk size.

This option has been tested in production and is SAFE for T1/E1 PRI Mode.
If running meetme chunk size of 40 is suggested.
Otherwise chunk size of 80 is most efficient..
Software echo cancelers are made for a chunk size of 8, so they may not function correctly.

This option does not work very well for ANALOG and T1/E1 E&M wink!
because zaptel hard codes the chunk size to 8 in some of the Analog/RBS
timing code. Sangoma is working on this problem.

If you are having trobule with this configuraiton please contact Sangoma Support.

Feb 11, 2009

A500 2 – 24 Port Scalable S/T BRI

Sangoma built its business by designing hardware that simply works, the fi rst time.

We have taken the time to ensure our BRI solution delivers.

The Sangoma A500 S/T BRI Interface Card delivers superior audio quality and scalability. Expand from two to twenty-four ports of BRI with optional Octasic® Telco-grade, hardware echo cancellation.

A single PCI or PCI Express slot hosts the connection for up to 24 ports and ensures common synchronous clocking for all channels with no signaling issues. The card is 100% software confi gurable. Finally, a BRI card that upholds Sangoma’s high standards of quality in engineering and untiring product support.


1. From 2 to 24 ports are supported. Mix TE and NT modes, as required. Changing modes requires no jumpers — simply invert the colour-coded module.

2. Supports Asterisk®, Yate™, FreeSwitch™, CallWeaver™, PBX/ IVR projects, as well as other Open Source and proprietary PBX, Switch, IVR or VoIP gateway applications.

3. Single synchronous PCI and PCI Express interface for all 24 BRI interfaces.

4. Six ports per RemoraTM card.

5. Dimensions: 2U Form factor: 187 mm x 55 mm for use in restricted chassis.

6. Short 2U compatible mounting clips included for installation in 2U rackmount servers and high quality, tested 2 m 8-pin RJ45 port splitter cables included.

7. 32 bit bus master DMA data exchanges across PCI interface at 132 Mbytes/sec for minimum host processor intervention.

8. Autosense compatibility with 5V and 3.3V PCI busses.

9. Fully PCI 2.2 and PCI Express compliant, compatible with all commercially available motherboards, proper sharing of PCI interrupts.

10. Intelligent hardware: Downloadable FPGA programming with multiple operating modes. Add new features related to voice and/or data when they become available.

11. Power: 800 mA peak, operational 300 mA max at +3.3 V or 5 V.

12. Temperature range: 0 – 50 °C.

13. Optimized DMA stream and hardware-level HDLC handling unload the host CPU.

14. Raw bitstream interfaces can be used to support arbitrary non-standard line protocols, such as non-byte aligned monosynch or bisynch.

15. WANPIPE supports certifi ed, fi eld tested and reliable Frame Relay, PPP, HDLC and X.25.

Operating Systems

Linux (all versions, releases and distributions from 1.0 up).



Lifetime warranty on parts and labour. Plus a 30-day no questions asked return policy.

Certifi cation

FCC Part 15 Class A, FCC Part 68, CE, TBR3.

Diagnostic Tools

WANPIPEMON, SNMP, System logs.

Production Quality

ISO 9002


The A500 consists of a RemoraTM BRI daughterboard mounted on the AFT PCI card. The RemoraTM BRI card has three sockets, each of which can accept an S/T BRI module. One S/T BRI module has two S/T four wire interfaces, which support TE or NT modes of operation. Changing modes requires no jumpers — simply invert the module. Up to three additional RemoraTM daughterboards can be mounted in empty slot positions beside the A500 assembly. These are connected to the A500 by a special backplane bus connector.

Feb 10, 2009

USB - Sangoma's USBfxo

FXO :Analog FXO (Foreign Exchange Office) is the interface on a VoIP device for connecting to an analog PBX extension.

You will just simply have to plug the USB cable into the U100 and then into the server. Sangoma's USBfxo is a low-cost development tool kit, ideal for those just getting started with Asterisk® or those who just want a simple external solution.

The USBfxo is easy to install. There is no need to open up the computer to insert an interface card. Simply plug it in, and set up your Asterisk system; configure Sangoma's Wanpipe® drivers, as you would with any Sangoma card, and you're set to go. You can even connect multiple USBfxos in one system.

The USBfxo fully supports Asterisk on Linux systems and includes Zaptel/DAHDI drivers.

Ideal for OEMs, who want to offer low-cost PSTN access in appliances that do not have PCI or PCI express interfaces, developers who need an external solution, and even SOHO end users who are new to Asterisk.

  • Dual FXO ports
  • Easy installation, no need to open up computer to install PCI/PCIe card
  • Supports up to 2 simultaneous calls
  • Compact plastic enclosure
  • Low power consumption, takes power from USB bus
  • USB 2.0 compliant (compatible with USB 1.1)


  • USB 2.0 and USB 1.1 compliant.
  • 2 analog FXO ports for connecting to Telco, maximum 0.2 REN (Ringer Equivalence Number).
  • Industry standard USB type B connector.
  • Standard length type A to type B cable provided.
  • Compact plastic enclosure: 94 mm x 59 mm x 29 mm.
  • Low power consumption 200 mA: power drawn from USB bus.
  • Field upgradeable firmware.
  • Fully supports Asterisk and includes Zaptel/DAHDI drivers.
  • Sangoma Wanpipe® drivers and advanced diagnostics are included.
  • Connect multiple USBfxos in one system.
  • 5 year limited warranty.
  • RoHS Compliant.
  • Made in Canada.
more :

Feb 9, 2009

Blog can Publication your Idea

A blog can give your idea to publish in to the web. Blog is one place to collect anything about wathever and come out from the idea of someone, education, politics, social, science, technology, etc.

But, blog dominate by the people that only to organize them idea but the other maked the blog for to make the new information to support the other information that have found before in the world.

The motto : "Whatever that you want said, Blogger is the best choice to publication in the world".

Feb 8, 2009

RFID – Better Security Recommend by U.S. Officials

Organizations that use RFID devices should systematically evaluate potential security and privacy risks posed by the technology, U.S. government officials say in a new report detailing best practices for retailers, manufacturers, hospitals and federal agencies.

RFID raises unique security concerns because, unlike a desktop computer or most devices overseen by a company’s network security crew, a single RFID tag may be handled by multiple organizations.

“When you go into RFID, the chain of custody is different,” says Tom Karygiannis, lead author of a 154-page report released by the Department of Commerce’s National Institute of Standards and Technology (NIST). “We’re talking about a global supply chain. You’re working with suppliers, manufacturers, retailers; different organizations may have possession of the merchandise that has the RFID on it throughout the life cycle. This raises new privacy and security risks.”

The publication, titled “Guidelines for Security Radio Frequency Identification (RFID) Systems,” includes recommendations such as the following:

· Use firewalls that separate RFID databases from an organization’s other databases and IT systems.

· Encrypt radio signals when feasible.

· Authenticate approved users of RFID systems.

· Shield RFID tags or tag reading areas with metal screens or films to prevent unauthorized access.

· Use audit procedures, logging and time stamping to help detect security breaches.

· Implement procedures for tag disposal and recycling that permanently disables or destroys sensitive data.

The report was mandated by Congress under the Federal Information Security Management Act of 2002. In addition to usage in the retail industry, RFID devices are matching hospital patients to lab test results and helping track dangerous materials, raising concerns about eavesdropping or unauthorized use.

The federal report includes hypothetical case studies, including one in which a government agency oversees supply chain management of hazardous materials that are handled by a number of organizations during transport. The risks involving RFID are numerous: adversaries could identify and target vehicles containing hazardous materials; eavesdrop on tag transactions to learn the characteristics of the materials; damage or disable a tag, making it easier to steal; or alter sensor or manifest data stored on the tag to undermine business processes.

The suggested solutions include shielding vehicles and containers to prevent electromagnetic emissions, establishing a 100-meter perimeter around storage locations, and using password protection to prevent unauthorized parties from reading tags or changing the information they contain. As a general rule, the report says, tagged items should be identifiable only during embarkation, debarkation and storage, but not during transport.

“The technical challenge is for each person along the supply chain to be able to securely access information related to that particular tag. You have to be authorized and authenticated. It has to be done securely,” Karygiannis says.

Karygiannis, a senior researcher with NIST’s computer security division in Gaithersburg, Md., said the division is trying to stay ahead of the curve on RFID security. For example, its electromagnetics team in Boulder, Colo. is trying to develop ways to detect counterfeit RFID tags, a task that is difficult with today’s technology, he says.

Feb 7, 2009

Management Systems - ROI of Implementing CAPA, Audit and Document Management Systems

As business complexity and size grow, it is natural for quality managers to consider replacing existing paper-based systems, spreadsheets or isolated databases relied upon for managing critical quality and compliance processes, with integrated, centralized and workflow-driven systems.

However, architecting and implementing an enterprise-wide system for CAPA, Audit and Document Management requires investment and managers must justify the cost by demonstrating benefits of implementing a new system by analyzing the Return on Investment (ROI).

Here are three articles that provide a step-by-step approach for conducting the ROI analysis for the critical processes.

The framework includes elements like:

  • How much will the project cost
  • What can the company expect to gain in return
  • How many man-hours will be saved
  • Where will the process improve
  • What will be the quantifiable cost reductions
  • How will it impact the company's bottom line

Feb 6, 2009

The Twitter Hack Have 3 Way to Hurt You

Just days after popular social networking tool Twitter was hit was a phishing scam, the company is now trying to clean up a mess surrounding a separate hacking attack.

ver the weekend, some Twitter users received scam tweets, or direct messages, to visit certain sites or blogs. The URL in the message redirected users to a bogus login page in an attempt to steal login credentials for a phishing scheme.

"It appears someone gained access to the tools Twitter uses to control its millions of accounts," explained by senior technology consultant at security firm Sophos PLC. "Internal tools used by the tech support team were compromised. It's not clear if it was an inside job, or outside hacker. Twitter does say they think it was an individual."

he hack, according to Cluley, is much more serious than the earlier phishing attack because it was compromise of the system that potentially exposed all Twitter users to the following dangers.

Fraudalent password use If you gain access to someone's Twitter account, you might be able to gain access to their password, said Cluley.

"We know that 41 percent of people admit to using the same password on every web site and account that they access," he said.

Hackers, while gaining access to something seemingly simply like a username and password to one account may very well be able to use the information to gain access to more important information, such as your bank account.

Malware Infection Twitter officials said 33 accounts had been attacked in the latest hack. The hackers used their temporary access to send offensive messages.

The damage could have been much worse, said Cluley, if the hacker had decided to take a different approach.

"Imagine if instead, in the case of Britney Spears account for example, that the hacker had posted a link that said: 'Here's my new video. Click on this link.' Imagine how many people would have clicked on that and it could have pointed to malware? And Barack Obama is one of the most followed people on Twitter. If he said: 'I've just made a new speech. Check it out.' a lot of people would click on that link and get infected."

Identity theft Much like with Facebook and other Web 2.0 tools, it is always possible people are sharing too much information, said Cluley, which could be useful for the purpose of identity theft or other illegal activity.

"Imagine you have fraudulent access to an account and you have ex you are stalking? There may be information up there you don't want people to have."

Cluley said ultimately this news begs the question of why weren't Twitter systems more secure and what are the implications for the company.

"Some people are saying this ruins Twitter," said Cluley. "Twitter had been looking for a business model, a way to make money, and now that is no longer viable, according to some criticism. But I would say if that were the case, then e-mail and web sites would be no longer viable either. People are still going to carry on using Twitter. Twitter is becoming an enormous success story. This really is the first big headache they've had. But it's an appalling start of the year for them on the security side."

Feb 5, 2009

Safe of PC - How to protect against the Downadup worm

Security experts say it's the biggest worm attack in years, call it "amazing" and report that it infected nearly 9 million PCs in just two weeks.

Downadup is downright nasty. And that's even before it does much more than just spread.

But as analysts argue about how the compromised computers will be used -- to build a massive botnet, perhaps -- or how much information hackers will steal from infected machines, users like you have a more immediate concern: "How do I keep my PC from joining the ranks of the hacked?"

That's a simple question. Unfortunately, because of this worm's flexibility, the answers aren't.

What's the worm again? Thanks to the lack of an industry-wide labeling system, the worm goes by more than one name. Some companies dub it "Downadup," others call it "Conficker."

No matter the name, it's the same threat.

When did Downadup first appear? Security companies warned of the worm in late November 2008; Symantec Corp. was one of the first to sound the alarm when it raised its ThreatCon security alert level on Nov. 21. Within a week, Microsoft Corp. had added its voice to the chorus as it acknowledged a significant uptick in attacks.

However, the worm only really took off about a week ago as newer variations struck users and resulted in millions of infections.

How does it spread? One of Downadup's most intriguing aspects, say security researchers, is its multipronged attack strategy: It can spread three different ways.

The one that's gotten the most attention exploits a vulnerability in Windows that Microsoft patched nearly four months ago. The bug, which is in a file-sharing service that's included in all versions of the operating system, can be exploited remotely just by sending a malformed data packet to an unpatched PC.

But the worm can also spread by brute-force password attacks, and by copying itself to any removable USB-based devices such as flash drives and cameras. More on those two in a moment.

What machines are most vulnerable to Downadup attack? According to Microsoft, unpatched Windows 2000, Windows XP and Windows Server 2003 machines are at the greatest risk to exploits of the bug patched in October. That gibes with reports from security companies, which have highlighted the danger to PCs running Windows XP Service Pack 2 and XP SP3. Not coincidentally, those versions account for the bulk of Windows' market share.

Unpatched Windows Vista and Server 2008 systems, meanwhile, are less likely to fall victim to attack, since hackers must have authenticated access to the computer, or in other words, know the log-in username and password.

Any Windows-powered machines, however, can be compromised by the worm's password and USB attack strategies.

I'm running Windows 7 beta... am I safe? According to the Microsoft support document that details the October patch, yes you are.

Microsoft offered the fix as a security patch to users of the Windows 7 "pre-beta," the version it gave developers in late October and early November. It then integrated the patch into Windows 7 before it launched the public beta on Jan. 10.

OK, so how do I protect my PC? Because this thing is a triple threat, you'll need to take more than one defensive measure.

First of all, if you haven't already done so, apply the October fix that Microsoft tagged as MS08-067. If you have Windows Update set to automatically download and install patches, you should be protected, but it never hurts to double-check. You can verify that the patch has been installed by bringing up Windows Update, then clicking "Review your update history" and looking for a security update labeled as "KB958644."

If you are only now installing the patch, you might want to take Microsoft's advice and also download and install the January edition of its free Malicious Software Removal Tool (MSRT), which was updated last week so that it can detect, and then delete, Downadup infections.

What's this about password attacks? Although most of the news about Downadup's spread has focused on its exploitation of a patched bug in Windows, the worm also propagates by trying to guess other machines' administrative passwords.

Once the worm penetrates a corporate network -- perhaps by infecting a single unpatched machine, say a laptop, that is later connected to that network -- it tries to break into other PCs, including those that have been patched with the October emergency fix.

"One of the ways in which the Conficker worm (also known as Confick or Downadup) uses to spread is to try and batter its way into ADMIN$ shares using a long list of different passwords," said Graham Cluley, a senior technology consultant at Sophos, in an entry to a company blog last Friday. Cluley included the list of passwords that Downadup tries, which range from the ubiquitous password and the moronic secure to the slightly-more-clever letmein and nimda, or admin spelled backward.

Cluley urged users to steer clear of what he called "poorly-chosen passwords," while other security companies recommended that users not only pick stronger passwords but change them periodically as well.

Obviously, if you're using a password that's on the Downadup list, you should change it immediately.

And the worm can spread from flash drives, too? Yes.

From the moment Downadup infects a PC, it copies a file, named "autorun.inf" to the root of any USB storage devices, typically flash drives, that are connected to the compromised computer. That file name takes advantage of Windows' Autorun and Autoplay features to copy the worm to any machine that a flash drive, camera or other USB device is plugged into. Downadup will infect that PC when the drive or device is connected, or when the user double-clicks the device's icon within Windows Explorer or from the desktop.

Security experts have recommended that users disable both Autorun and Autoplay in Windows.

A December blog post by Symantec researcher Ben Nahorney spells out how to disable Autoplay, while a separate post on the Hackology blog outlines how to turn off Autorun by editing the registry.

What are the signs that my PC has been hit? Microsoft's advisory about Downadup lists several symptoms of infection, including these:

-- Account lockout policies are being tripped (because your password's been hijacked, and changed, by the attacker).

-- Automatic Updates are disabled (because Downadup tries to keep the PC unpatched by turning off Windows Update's automatic update, as well as Background Intelligent Transfer Service (BITS), the Windows component used by Windows Update to actually deliver the updates).

-- Various security-related Web sites cannot be accessed (because Downadup blocks access to a whole host of security companies' sites in an effort to prevent antivirus software from being updated, which could result in the worm's detection and eradication).

If your PC is exhibiting any of these symptoms -- or the others that Microsoft spells out here -- the company recommends that you immediately use the MSRT to clean the machine.

You can download the MSRT from Microsoft's site, or follow these instructions, posted at its support site, that walk administrators through the steps to deploy the tool in enterprise environments.

Fiber Optic :: Glossary :: T - W

Tap loss - In a fiber optic cable coupler is the ratio of power at the tap port to the power at the input port.

Tap port - In a fiber optic cable coupler in which the splitting ratio between output ports is not equal it is the output port containing the lesser power.

TDM - Time Division Multiplexing.

Tee coupler - A 3 port optical coupler.

10Base-F - A fiber optic cable based version of an IEEE 802.3 network.

10Base-FB - That portion of a 10Base-F network that defines the requirements for the fiber optic cable backbone network.

10Base-FL - That portion of a 10Base-F network that defines the fiber optic cable link between a concentrator and a station.

10Base-FP - That portion of a 10Base-F network that defines a passive star coupler.

10Base-T - A twisted pair cable version of an IEEE 802.3 network.

10Base-2 - A thin coaxial cable version of an IEEE 802.3 network.

10Base-5 - A thick coaxial cable version of an IEEE 802.3 network; very similar to the original Ethernet specification.

Ternary - Made from 3 different elements.

Thermal noise - Noise resulting from thermally induced random fluctuation in current in the receiver's load resistance.

Thermal stability - A measure of the insertion loss variation as the device undergoes various environmental changes.

Throughput loss - In a fiber optic cable coupler it is the ratio of power at the throughput port to power at the input port.

Tight buffer - Type of cable construction whereby each glass fiber optic cable is tightly buffered by a protective thermoplastic coating to a diameter of 900 microns. High tensile strength rating achieved, providing durability, ease of handling and ease of connectorization.

Time Division Multiplexing - TDM. A transmission technique whereby several low speed channels share a given transmission medium, for example a fiber optic cable. With this technique they share it on a time basis. Each channel is given specific time slots to transmit during and can only transmit during these time slots.

Token ring - A ring based networking scheme. A token is used to control access to the network. Used by IEEE 802.5 and FDDI.

Total bandwidth - The combined modal and chromatic bandwidth.

Total internal reflection - Total reflection of light back into a material when it strikes the interface of a material having a lower index at an angle below the critical angle.

Transduce - A device for converting energy from one form to another, such as optical energy to electrical energy.

Transceiver - A combination of transmitter and receiver providing both output and input interfaces with a device.

Transmission loss - Total loss encountered in transmission through a system.

Transmitter - In the context of a fiber optic cable based communication link an electrical package, which converts an electrical signal to an optical signal.

Tree coupler - A passive fiber optical component in which power from 1-input is distributed to more than 2-output fiber optic cables.

TX - Transmitter.

UL - Underwriters Laboratories, Inc.

Ultraviolet - Optical radiation for which the wavelengths are shorter than those for visible radiation, that is approximately between 1 nm and 400 nm.

Uniformity - The maximum insertion loss difference between ports of a coupler.

UV - Ultraviolet.

VCSL - Vertical cavity semiconductor laser.

Velocity of light - The velocity of light is 300,000 km/sec in a vacuum. In a medium it depends in the refractive index and the wavelength.

WAN - Wide Area Network. A network of connected computers that cover a great geographical area.

Waveguide - A 2 dimensional substrate which carries light in channels inscribed in the material.

Wavelength - Distance an electromagnetic wave travels in the time it takes to oscillate through a complete cycle. Wavelengths of light are measured in nanometers (10-9 m) or micrometers (10-6 m).

Wavelength dependence - The variation in an optical parameter caused by a change in the operating wavelength.

Wavelength Division Multiplexer - A passive fiber optical device used to separate optical signals of different wavelengths carried on 1 fiber optic cable.

Wavelength Division Multiplexing - WDM. Simultaneous transmission of several optical signals of different wavelengths on the same fiber optic cable. It is a technique used so that several different communications channels can share the same fiber optic cable.

WDM - Wavelength Division Multiplexing.

WIC - Wavelength Independent Coupler.

mW - MicroWatt.

Feb 4, 2009

To Increase Traffic from Search Engines

Search engines scour the Internet to identify Web sites that are relevant to their users’ queries. They do this not only by reviewing pages’ visible content, but also by taking into account content hidden in HTML tags, e.g., META elements and image identifiers. By making a few small changes to your Web site’s HTML, you can significantly increase its chances of surfacing highly in users’ search results.

To find a great example of search-engine optimization, we didn’t have to look farther than the Share Helpful Tips section of the ADB. We had spent about five minutes searching when Mike Lepore, creator and Webmaster of, flew into view. He had provided helpful tips to other Associates for a long time, so we sat down and asked him to identify some of the key practices that could help Associates who wanted to improve their search-engine placements. Here’s what we found out:

  • Use META tags, which appear at the top of your HTML documents. They can either be hand-coded or inserted by most HTML editors. They allow you to precisely describe certain elements of your page.
  • Try to begin each Web page with phrases relevant to the page’s content. Avoid starting with a lot of navigation elements or advertisements that don’t contain keywords relevant to the page’s major topic.
  • Remember that no single tactic works for all search engines. Each one has its own way of ranking Web sites. For example, Google notes the “description” Meta tag and ignores the “keywords” one, while others take both into account.
  • First and foremost, create smart content. Mike provides lengthy, information-packed reviews of books that he’s read which gives his visitors a reason to come back often. Check out his review of here to see a great example of good content.
Optimize each page separately. Search engines don’t rank Web sites in their entirety, instead ranking each page individually. For example, even if your site mainly focuses on business software, if you have a children’s software page, be sure to include relevant keywords to that topic.

Feb 3, 2009

Fiber Optic :: Glossary :: S

SC - A connector type. It is primarily used with single-mode fiber optic cables. It offers low cost, simplicity and durability. Furthermore, it provides for accurate alignment by a ceramic ferrule. It is a push on -pull off connector with a locking tab. It is similar to the connector used for FDDI but is not compatible.

Scattering - A property of glass which causes light to deflect from the fiber optic cable and contributes to losses.

SDM - Space Domain Multiplexing

Semiconductor Laser - Same as a laser diode.

Sensitivity - For a fiber optic cable receiver it is the minimum optical power required to achieve a specified level of performance, such as BER. Alternatively, it is the minimum amount of energy required by a receiver for successful operation.

Shot noise - Noise caused by random current fluctuations arising from the discrete nature of electrons.

Signal to noise ratio - The ratio of signal power to noise power.

Silica - Glass material, nearly pure SiO2.

SI-POF - Step index plastic fiber optic cable.

Simplex - Transmission in only 1 direction.

Simplex cable - A term sometimes used for a single-fiber cable.

Single-mode - A small core, fiber optic cable that supports only 1 mode of light propagation above the cutoff wavelength. Typically, the diameter of the core is 9-10 mm. Dispersion and power loss through the cable walls are low with this type of cable. It is proper for long distance transmission.

SMA - A connector type. This was the predecessor of the ST connector. It features a threaded cap and housing. The use of the SMA connector has decreased markedly in recent years being replaced by the ST and SC connectors.

SNR, S/N - Signal to noise ratio. Usually expressed in dB.

Soliton - An optical pulse that does not suffer dispersion as it propagates over a distance.

SONET - Synchronous Optical Network. An international standard for fiber optic cable based telephony.

Source - There is 2 possibilities. First, it is a generator of information or data. Secondly, within the context of fiber optics it is a light emitter, either an LED or laser diode, for a fiber optic cable based link.

Spectral attenuation - Measure for the attenuation in dependence on wavelength.

Spectral bandwidth (Between half power points) - It is the wavelength interval in which a radiated spectral quantity is not less than half its maximum value. It is a measure of the extent of the spectrum. For a light source typical spectral widths are 20 to 60 nm for a LED and 2 to 5 nm for a laser diode.

Spectral width - The measure of the wavelength extent of a spectrum. It is usually based upon the 50% intensity points. When referring to the spectral width of sources, typical spectral widths are 20 to 60 nm for a LED and 2 to 5 nm for a laser diode.

Splice - An interconnection method for joining the ends of 2 fiber optic cables in a permanent or semi-permanent fashion. Thermal fusing may carry out splicing or it may be mechanical.

Splicing - The permanent joining of fiber optic cable ends to identical or similar fiber optic cables without using a connector. See also Fusion splicing and Mechanical splicing.

Splice box - Housing for 1 or more splice organizers. The changeable front panel can be equipped with different connector plugs.

Splice closure - A container used to organize and protect splice trays.

Splice organizer - An organizer panel that holds up to 12 splices with splice protectors and sufficient loops.

ST - A keyed bayonet connector type similar to a BNC connector. It is used for both multi-mode and single-mode fiber optic cables. Its use is wide spread. It has the ability both to be inserted into and removed from a fiber optic cable both quickly and easily. Method of location is also easy. There are 2 versions ST and ST-II. These are keyed and spring loaded. They are a push in and twist type.

Star coupler - A coupler for a fiber optic cable in which power at any input port is distributed to all output ports.

Star network - A network in which all terminals is connected through a single point, such as a star coupler.

Steady state - Equilibrium mode distribution.

Step index fiber - A fiber optic cable, either multi-mode or single-mode, in which the core refractive index is uniform throughout so that a sharp step in refractive index occurs at the core-to-cladding interface.

Step index profile - A refractive index profile in which the refractive index changes abruptly from the value n1 to n2 at the core cladding interface.

Strength member - That part of a fiber optic cable composed of Kevlar Aramid yarn, steel strands or fiberglass filaments that increases the tensile strength of the cable.

Stripping - Removing the coating from a fiber optic cable.

Fiber Optic :: Glossary :: Q - R

Quaternary - Made from 4 different elements.

Quantum efficiency - In a photodiode, the ratio of the primary carriers (electron-hole pairs) created to incident photons. A quantum efficiency of 70% means 7 out of 10 incident photons creates a carrier.

Rayleigh scattering - The scattering of light that results from small inhomogeneities in material density or composition. This causes losses in optical power. The losses vary with the 4th power of wavelength. This scattering sets a theoretical lower limit to the attenuation of a propagating lightwave as a function of wavelength. This varies from 10 dB/km at 0.5 microns to 1 dB/km at 0.95 microns.

RAYTELA® - Plastic, fiber optic cable manufactured by Toray Industries.

RB - Rhodamine B dopant.

Receiver - In the context of a fiber optic cable based communications link it is an electronic package, which converts optical signals to electrical signals.

Receiver sensitivity - The minimum acceptable value of average received power at the fiber optic cable receiver point, R, in order to achieve a BER of 10-12. It takes into account power penalties caused by the use of a transmitter with worst-case values of extinction ratio, jitter, pulse rise and fall times, optical return loss at the transmitter point, S, receiver connector degradations and measurement tolerances. The receiver sensitivity does not include penalties associated with dispersion, jitter or reflections from the optical path. These effects are specified separately in the allocation of maximum optical path penalty. Sensitivity takes into account worst-case operating and end-of life conditions. In the case of digital signals the optical power is usually quoted in Watts or dBm.

Reflectance - Light that is reflected back along the path of transmission, from either the coupling region, the connector or the terminated fiber optic cable.

Reflection - The abrupt change in direction of light as it travels from one material to a dissimilar material. Some of the reflected power gets transmitted back to the source.

Refraction - The bending of a beam of light at an interface between 2 dissimilar media or a medium whose refractive index is a continuous function of position (i.e. a graded index medium).

Refractive Index - The ratio of the velocity of light in a vacuum to its velocity in the medium. It is a synonym of index of refraction. Its symbol in 'n.'

Regenerative repeater - A repeater designed for digital transmission that both amplifies and reshapes the signal. Sometimes called regenerator.

Repeater - An optoelectronic device that amplifies or boosts a signal. Basically, it returns a signal to its original strength.

Responsivity - The ratio of a photodetector's electrical output to its optical input in Amperes/Watt.

Return loss - Same as reflectance.

Return reflection - Reflected optical energy that propagates backward to the source in a fiber optic cable.

Return reflection loss - The attenuation of reflected light. High return loss is desirable, especially in single-mode fiber optic cables.

Ring network - A network topology in which terminals are connected in a point to point serial fashion in an unbroken circular configuration. Frequently used with a token passing access protocol.

Rise time - The time required for the leading edge of a pulse to rise from 10% to 90% of its amplitude. The time required for a component to produce such a result. Turn on time. Sometimes measured between the 20% and 80% points.

Riser - Application for indoor cables that pass between floors. It is normally a vertical shaft or space.

RX - Receiver.

RZ - Signaling code.

Feb 2, 2009

Fiber Optic :: Glossary :: P

Passive Star Coupler - Couples 1 or more input optical signals coming from fiber optic cables to 1 or more output fiber optic cables acting as receivers. It accomplishes this by using only passive optical components.

Patch Panel - Distribution area to rearrange fiber optic cable connections and circuits. A simple patch panel is a metal frame. One side of the panel is usually fixed. This means that the fiber optic cables are not intended to be disconnected. On the other side are plugs to connect other fiber optic cables.

PC - Physical contact.

PCM - Pulse Code Modulation.

PCS - Plastic clad silica.

PD - Photodiode

- Polyethylene. This is a type of plastic material used to make cable jacketing.

Peak Wavelength - The wavelength at which the optical power of a source is at a maximum.

PF - Perfluorinated

Photocurrent - The electrical current that flows through a photosensitive device, such as a photodiode as a result of exposure to radiant power.

Photodetector - An optoelectronic transducer, such as a pin photodiode or avalanche photodiode.

Photodiode - A semiconductor diode that produces current in response to incident optical power and used as a detector in a fiber optic cable data link.

Photon - A quantum of electromagnetic energy. A discrete unit which lends a particle nature to light in contrast to its wave nature. Photons come into play when one talks about energy exchanges using light.

Photonics - The technology of transmission of information using light.

Physical contact connector - A connector designed with a radiuses tip to assure physical contact of the fiber optic cables and thereby increase return reflection loss.

Pigtail - A short length of fiber optic cable, permanently fixed to a component. It is used to couple power between the component and the fiber optic cable used for transmission.

PIN - Positive intrinsic negative photodiode.

PIN Photodiode - A diode with a large intrinsic region sandwiched between p+ and n- doped semi-conducting regions. Photons absorbed in this region create electron-hole pairs that are then separated by an electric field. This generates an electric current in a load circuit.

PIN-PD - PIN-photodiode.

Pistoning - The movement of a fiber optic cable axially in and out of a ferrule end, often caused by changes in temperature.

Plastic clad silica fiber optic cable - A fiber optic cable having a glass core and a plastic cladding.

Plastic fiber optic cable - Fiber optic cables having a plastic core and plastic cladding.

Plenum - The air handling space between walls, under structural floors and above drop ceilings. This can be used to route intra-building cabling.

Plenum cable - Fiber optic cables whose flammability and smoke characteristic allows it to be routed in a plenum area without being enclosed in a conduit.

PMMA - Polymethylmethacrylate

POF Consortium - Over 60 Japanese companies, government agencies and universities organized to promote plastic optical fiber-plastic fiber optic cable.

POF - Plastic Optical Fiber-plastic fiber optic cable.

POFA - Plastic optical fiber amplifier.

POFIG - US based POF interest group.

Point-to-Point - A fixed link secured between 2 distinct nodes or stations in a network.

Polarization stability - The variation in insertion loss as the polarization state of the input light is varied.

Polishing - Preparing the end of a fiber optic cable by moving the end over an abrasive material.

POLO - Parallel Optical Link Organization.

POLYGUIDE® - Polymer optical waveguide developed by DuPont.

Power meter - Device used to measure attenuation of a plastic fiber optic cable.

Primary coating - The plastic coating applied directly to the cladding surface of the fiber optic cable during manufacture to preserve the integrity of the surface.

Preform - A solid rod of plastic material from with a plastic fiber optic cable is drawn or a glass structure for which glass fiber optic cable is drawn.

Prefusing - Fusing with low current to clean the fiber optic cable end. Precedes fusion splicing.

Primary coating - The plastic coating applied directly to the cladding surface of the fiber optic cable during manufacture to preserve the integrity of the surface.

PTFE - Poly-tetrafluoroethylene, a representative of perfluoropolymer by DuPont and manufactured under the name Teflon®.

Pulse coded modulation - PCM. A technique in which, a analog signal is converted to a digital signal. This is accomplished by sampling the signals amplitude and expressing the different amplitudes as a binary number. Sampling must be at the Nyquist rate - at least twice the highest frequency in the information signal bandwidth.

Pulse spreading - The dispersion of an optical signal with time as it propagates through a fiber optic cable.

PUR - Polyurethane. Material used in manufacture of a type of jacketing material.

PVC - Polyvinyl Chloride. Material used in manufacture of a type of jacketing material.

Fiber Optic :: Glossary :: N - O

NA - Numerical Aperture - The light gathering ability of a fiber optic cable. This defines the maximum angle to the fiber optic cable axis at which light will be accepted and propagated down the fiber optic cable. NA= SIN F, where F is the acceptance angle. NA is also used to describe the angular spread of light from the central axis - as in exiting from the fiber optic cable, emitting from a source of entering a detector.

NA mismatch loss - The loss of power at a joint that occurs when the transmitting half has an NA greater than the NA of the receiving half. The loss occurs when coupling light from a source to a fiber optic cable, from fiber optic cable to fiber optic cable or from fiber optic cable to a detector.

NM - Nanometer 1 billionth of a meter.

NEC - National Electrical Code. Defines building flammability requirements for indoor cables.

NEXT - Near End cross-talk.

NIR - Near Infrared.

NIU - Network Interface Unit.

NLO - Non-Linear Optics.

NRZ - On-Off signaling code.

Numerical Aperture - See NA-Numerical Aperture. This is the imaginary cone which defines the acceptance area for the fiber optic cable core to accept light rays.

Open Standard Interconnect - A 7-layer model defined by ISO for defining a data communication network. It provides means for executing the blue print of the network architecture.

Optical cable - An assembly of fiber optic cables and other material providing mechanical and environmental protection.

Optical fiber - Synonym for fiber optic cable.

Optical fiber coupler - This is used in 2 contexts. In the first it refers to a device whose purpose is to distribute optical power among 2 or more ports. In the second it refers to a device whose purpose is to couple power between a fiber optic cable and a source or detector.

Optical link - Any optical transmission channel designed to connect 2 end terminals or to be connected in series with other channels. Sometimes terminal hardware i.e. transmitter and receiver, is included in the definition.

Optical time domain reflectometry - A method of evaluating fiber optic cables based upon detecting backscattered (reflected) light. It is used to measure attenuation, evaluate splice and connector joints and locate faults.

Optical waveguide - Synonym for fiber optic cable.

Optical window - Wavelength range of a fiber optic cable with a very low attenuation. Fiber optic data links using LED sources work in the 1st window at 850 nm or in the 2nd window at 1300 nm. Fiber optic data links using laser sources work in the 2nd window at 1310 nm or in the 3rd window at 1550 nm.

OPTI-GIGA™ - Graded index plastic fiber optic cable developed by Boston Optical Fiber.

OPTI-LUX™ - Step index plastic fiber optic cable developed by Boston Optical Fiber.

OPTI-MEGA™ - Step index plastic fiber optic cable developed by Boston Optical Fiber.

Opto-electrical Converter - Converts an optical signal into an electrical signal.

Opto-electronics - The range of materials and devices that generate light (lasers and light-emitting devices), amplify light (optical amplifiers), detect light (photodiodes) and control light (electro-optic circuits). Each of these functions requires electrical energy to operate and depends upon electronic devices to sense and control this energy. In a broader sense it means pertaining to a device that responds to optical power, emits or modifies optical radiation or utilizes optical radiation for its internal operation. It is any device which functions as an electrical to optical transducer or optical to electrical transducer.

OSI - Open Standards Interconnect.

OTDR - Optical Time Domain Reflectometer. A method of characterizing a fiber optic cable wherein an optical pulse is transmitted down the fiber optic cable and the resulting backscatter and reflections are measured as a function of time. The OTDR is useful in estimating the attenuation coefficient as a function of distance and identifying defects and other localized losses.

Feb 1, 2009

Fiber Optic :: Glossary :: M

Macro bend - A large fiber bend that can be seen with the unaided eye.

Macrobendiing - Macroscopic axial deviations of a fiber optic cable from a straight line, in contrast to microbending.

MAN - Metropolitan Area Network. This is a network linking LANs and other networks at many sites within a city area. Dimensions are usually of the order to 10's of km.

Manchester - Balanced signaling code, used at lower data rates.

Material dispersion - Light pulse broadening caused by various wavelengths of light traveling at different velocities down a fiber optic cable. Material dispersion increases with the increasing spectral width of the source. It is attributable to the wavelength dependence of the refractive index of the material used to form the fiber optic cable. It is characterized by the material dispersion parameter, M (l).

Material scattering - In an optical waveguide it is that part of the total scattering attributable to the properties of the materials used for waveguide fabrication.

MAU- Medium Attachment Unit. This is an active component of an Ethernet LAN connecting peripheral devices with the electrical bus cable.

MBPS - Mega Bits Per Second - 1 million BPS.

MDPE- Medium density polyethylene jacketing.

Mechanical splice - A splice in which fiber optic cables are joined mechanically for example by being glued or crimped in place. However, they are not fused together.

MFD - Mode field diameter.

MHz. - Mega Hertz, 1 million Hz.

Microbend Loss - The loss attributed to microscopic bends in fiber optic cable.

Microbending - Curvatures of the fiber optic cable which involves axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Micro bends cause loss of light and consequently increase attenuation of the fiber optic cable.

Micrometer - 1 millionth of a meter, abbreviated mm. Also referred to a micron.

Micron - See micrometer.

Misalignment loss - The loss of power resulting from angular misalignment, lateral displacement and end - separation.

MM - Millimeter, 1 thousandth of a meter.

MMF - Multi-mode fiber optic cable.

Modal bandwidth - A bandwidth limiting mechanism in multi-mode fiber optic cables. It is also used in single-mode fiber optic cables when operated at wavelengths below cutoff. Modal bandwidth arises because of the different arrival times of the various modes. It is a synonym for intermodal dispersion.

Modal dispersion - The dispersion resulting from difference in the time it takes for different rays to traverse a fiber optic cable.

Modal noise - The fluctuation in optical power due to the interaction of the power traveling in more than 1 mode.

Mode coupling - The transfer of energy between modes. In a fiber optic cable, mode coupling occurs until the EMD is reached.

Mode field diameter - The diameter of optical energy in a single-mode fiber optic cable. Because the MFD is greater than the core diameter, MFD replaces the core diameter as a practical parameter.

Mode filter - A device used to remove high-order modes from a fiber optic cable and thereby simulate EMD.

Mode mixing - The numerous modes of a multi-mode fiber optic cable differ in their propagating velocities. As long as they propagate independently of each other, the fiber optic cable bandwidth varies inversely with the fiber optic cable length due to multi-mode distortion. As a result of inhomogeneities of the fiber optic cable geometry and the index profile, a gradual energy exchange occurs between modes with different velocities. Due to this mode mixing, the bandwidth of long multi-mode fiber optic cables is greater than the value obtained by linear extrapolation from measurements on short fiber optic cables.

Mode scrambler - A device composed of one or more fiber optic cables in which strong mode coupling occurs. Frequently used to provide a mode distribution that is independent of source characteristics.

Modem - An acronym for Modulator-Demodulator. This is a device that carries out both modulation and demodulation. With the modulation function the modem takes information, which is in digital form - usually, 0's and 1's, and represents it by signals, which can be sent (transmitted) over a transmission medium. With the demodulation function the modem takes signals out of the transmission medium (received) and determines which digits then represent, what sequence of 0's and 1's.

Modes - In guided wave propagation, such as that through fiber optic cable, it is the distribution of electromagnetic energy that satisfy Maxwell's equations and boundary conditions. Specifically, applied to optics and transmission down a fiber optic cable a mode is loosely equivalent to a light ray of classic ray optic theory. Sometimes used to denote a light path through a fiber optic cable.

Modulation - The process by which the characteristic of one wave (the carrier) is modified by another wave (the information signal). Examples include amplitude modulation (AM), and frequency modulation (FM).

Monochromatic - Consisting of a single wavelength. In practice, radiation is never perfectly monochromatic but, at best, displays a narrow band of wavelengths.

Multi-mode fiber optic cable - Type of fiber optic cable that support more than 1 propagation mode.

Multiplexing - The process by which 2 or more signals are transmitted over a single transmission medium. Examples include Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM).

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