VNC (Virtual Network Computing)

VNC is software that is used for remote desktop application. An engineer from JDSU introduced me to VNC. We can use VNC to control another desktop. It is very simple, just connect your desktop and remote desktop with cross cable and play your VNC. In VNC application you just need to fill IP address, Subnet, and DNS of your remote desktop. After that... you can control your remote desktop easily.

To install VNC it is very easy as well. It has its free edition.

I use VNC to control Optical DWDM Analyzer. I use JDSU. It is a kind of Optical spectrum analyzer that is specially designed for DWDM measurement. We an use USB memory stick to copy measurement result and process it in our desktop. But... it is very risky. Why? USB memory stick is potential to spead virus to our analyzer. So, i prefer to use VNC to display the result and capture the result by "print screen-ing" it.

About "print screen-ing" i will talk later. It uses a special software : SNAGIT.

Direct TV

DirecTV provides television and audio services to subscribers through satellite transmissions. Services include the equivalent of many local television stations, broadcast television networks, subscription television services, satellite radio services, and private video services. Subscribers have access to dozens or hundreds of channels, so its competitors are cable television service and other satellite-based services

Consumers who purchased DirecTV equipment subscribe to various packages of DirecTV programming for which the subscriber pays a monthly fee. A subscriber also can order pay-per-view events and movies. DirecTV contracts with and pays program providers such as cable networks, motion picture distributors, sports leagues, event promoters, and other programming rights holders, for the right to distribute their programming to its subscribers. All programming distributed by DirecTV is delivered to its broadcast centers in Castle Rock, Colorado, and Los Angeles, California, where it is then digitized and compressed. The resulting signal is encrypted, or electronically scrambled, by DirecTV to prevent its unauthorized reception. DirecTV then transmits these signals to several satellites located in stationary orbit approximately 22,300 miles above the equator

Blue Screen

Yesterday, i've got my laptop underwent 'blue screen'
Anybody knows what it is?

Let u s check the answer. I took this from wikipedia :

The Blue Screen of Death (also known as a stop error, BSoD, bluescreen, or Blue Screen of Doom) is a colloquialism used for the error screen displayed by some operating systems, most notably Microsoft Windows, after encountering a critical system error which can cause the system to shut down to prevent damage.

Bluescreens on NT-based Windows systems are usually caused by poorly-written device drivers or malfunctioning hardware. In the Win9x era, incompatible DLLs or bugs in the kernel of the operating system could also cause bluescreens. They can also be caused by physical faults such as faulty memory, power supplies, overheating of computer components, or hardware running beyond its specification limits. Bluescreens have been present in all Windows-based operating systems since Windows 3.1; earlier, OS/2 suffered the Black Screen of Death, and early builds of Windows Vista displayed the Red Screen of Death after a boot loader error.

IP Multicast to MAC Address Mapping

Map Multicast MAC address to IP Multicast Addresses

In the course of reading through the BSCI authorize self-study guide, I’ve come across a multicast example where the author talks about the concepts behind the multicast IP to MAC address mapping.

• In order to achieve the translation between a Layer 3 IP multicast address and Layer 2 multicast MAC address, the low-order 23 bits of the IP address (Layer 3) is mapped into the low-order 23 bits of the MAC address (Layer 2).
• The high order 4 bits of the Layer 3 IP address is fixed to 1110 to indicate the Class D address space between 224.0.0.0 through 239.255.255.255
  • Ethernet MAC addresses start with 01:00:5E, allowing for a range from 01:00:5E:00:00:00 through 01:00:5E:7F:FF:FF.
• With 32 total bits present in an IP address and 4 high order bits of it set at 1110, we are left with 28 bits of unique IP addresses we can use (32 - 4 = 28).
• But remember, 23 low-order bits out of the 28 available bits are mapped to the MAC address, giving us 5 remaining bits of overlap.
• With the 5 bits of extra overlap, there are 32 (2⁵ = 32) IP multicast address that map to one MAC multicast address.

The problem is, the book does not explain or show how it solved the mapping. So I went about researching how it was done. If you happened to be studying for BSCI, I am referring to the section of the BSCI: Authorized Self-Study Guide, by Teare and Paquet, that starts on page 598 - 600.

The following is an example of how we arrive with those 32 IP addresses that map to a single MAC address:

For reference, use the following conversion chart for converting hex to binary and vice versa

Let’s start by using the example MAC address given in the book :

01:00:5e:0a:00:01

1. Convert the hexadecimal MAC address 01:00:5e:0a:00:01 to binary
   • 0000 0001 : 0000 0000 : 0101 1110 : 0000 1010 : 0000 0000 : 0000 001
   • Here’s a breakdown of the conversion bit by bit:
     
2. Isolate the 23 low-order binary bits from the converted MAC address:
   • 0000 0001 : 0000 0000 : 0101 1110 : 0000 1010 : 0000 0000 : 0000 0001
3. Take the low order 23 bits from step 2 and plug it into the low-order 23 bits of the IP address (do this in binary):
   • 1110 xxxx : x000 1010 : 0000 0000 : 0000 0000
     • 1110 - First 4 high-order bits of the IP address for the multicast address space (224.x.x.x).
     • xxxx x - 5 remaining bits after the 23bits of the IP address is mapped to the MAC address plus the 4 high order bits 1110. This is equal to 32 total IP addresses.
4. Convert the binary equivalent of the IP addresses to decimal, replacing the x variables with all the values to get all 32 possible IP addresses:
   • 1110 0000 : 0000 1010 : 0000 0000 : 0000 0001 = 224.10.0.1
   • 1110 0001 : 0000 1010 : 0000 0000 : 0000 0001 = 225.10.0.1
   • 1110 0010 : 0000 1010 : 0000 0000 : 0000 0001 = 226.10.0.1
   • 1110 0011 : 0000 1010 : 0000 0000 : 0000 0001 = 227.10.0.1
   • 1110 0100 : 0000 1010 : 0000 0000 : 0000 0001 = 228.10.0.1
   • 1110 0101 : 0000 1010 : 0000 0000 : 0000 0001 = 229.10.0.1
   • 1110 0110 : 0000 1010 : 0000 0000 : 0000 0001 = 230.10.0.1
   • 1110 0111 : 0000 1010 : 0000 0000 : 0000 0001 = 231.10.0.1
   • 1110 1000 : 0000 1010 : 0000 0000 : 0000 0001 = 232.10.0.1
   • 1110 1001 : 0000 1010 : 0000 0000 : 0000 0001 = 233.10.0.1
   • 1110 1010 : 0000 1010 : 0000 0000 : 0000 0001 = 234.10.0.1
   • 1110 1011 : 0000 1010 : 0000 0000 : 0000 0001 = 235.10.0.1
   • 1110 1100 : 0000 1010 : 0000 0000 : 0000 0001 = 236.10.0.1
   • 1110 1101 : 0000 1010 : 0000 0000 : 0000 0001 = 237.10.0.1
   • 1110 1110 : 0000 1010 : 0000 0000 : 0000 0001 = 238.10.0.1
   • 1110 1111 : 0000 1010 : 0000 0000 : 0000 0001 = 239.10.0.1
   • 1110 0000 : 1000 1010 : 0000 0000 : 0000 0001 = 224.10.0.1
   • 1110 0001 : 1000 1010 : 0000 0000 : 0000 0001 = 225.138.0.1
   • 1110 0010 : 1000 1010 : 0000 0000 : 0000 0001 = 226.138.0.1
   • 1110 0011 : 1000 1010 : 0000 0000 : 0000 0001 = 227.138.0.1
   • 1110 0100 : 1000 1010 : 0000 0000 : 0000 0001 = 228.138.0.1
   • 1110 0101 : 1000 1010 : 0000 0000 : 0000 0001 = 229.138.0.1
   • 1110 0110 : 1000 1010 : 0000 0000 : 0000 0001 = 230.138.0.1
   • 1110 0111 : 1000 1010 : 0000 0000 : 0000 0001 = 231.138.0.1
   • 1110 1000 : 1000 1010 : 0000 0000 : 0000 0001 = 232.138.0.1
   • 1110 1001 : 1000 1010 : 0000 0000 : 0000 0001 = 233.138.0.1
   • 1110 1010 : 1000 1010 : 0000 0000 : 0000 0001 = 234.138.0.1
   • 1110 1011 : 1000 1010 : 0000 0000 : 0000 0001 = 235.138.0.1
   • 1110 1100 : 1000 1010 : 0000 0000 : 0000 0001 = 236.138.0.1
   • 1110 1101 : 1000 1010 : 0000 0000 : 0000 0001 = 237.138.0.1
   • 1110 1110 : 1000 1010 : 0000 0000 : 0000 0001 = 238.138.0.1
   • 1110 1111 : 1000 1010 : 0000 0000 : 0000 0001 = 239.138.0.1
5. All the 32 IP addresses on step 4 map to MAC address 01:00:5e:0a:00:01

Convert IP Multicast Address to Multicast MAC Address

Conversely, a multicast IP address can be converted to its equivalent MAC address. Once you’ve figured out how to convert from Layer 2 MAC to Layer 3 IP, doing the reverse is easy.

To start, we can pick any address from the 32 IP addresses we converted above. Let’s pick a random one like 227.138.0.1

1. First convert the address 227.138.0.1 to binary:
   • 11100011 : 10001010 : 00000000 : 00000001
   • We’re only concerned with the red colored portion which represents the low-order 23bits of the IP address.
     
   • Notice that we are dropping the high order bit of the second octet.
     
2. Convert those 23 bits to hexadecimal:
   • 0A:00:01
3. We already know that the first 3-bytes (24 bits) of the MAC address is 01:00:5E. This was established earlier in the article. Simply append the result on step 2 to the first 3-bytes and you have your MAC address:
   • 01:00:5E:0A:00:01
   • *You can pick any of the 32 Ip addresses we have on the list above and you will always get 01:00:5E:0A:00:01 as your MAC address following the steps just mentioned.

To summarize:

• 1^st octet - Notice that the first octet is left alone.
• 2^nd octet - You only need to convert the last 7 bits to hex. The second octet in decimal is 138. But if you drop the highest order bit, it becomes a decimal 10 or hex 0A.
• 3^rd octet - Convert it directly to hex.
• 4^th octet - Convert it directly to hex.

taken from : http://routemyworld.com/2009/03/04/ip-multicast-to-mac-address-mapping/