May 20, 2014

What do we send the information?

In computers, encoding is the process of putting a sequence of characters (letters, numbers, punctuation, and certain symbols) into a specialized format for efficient transmission or storage. Decoding is the opposite process -- the conversion of an encoded format back into the original sequence of characters. Encoding and decoding are used in data communications, networking, and storage. The term is especially applicable to radio (wireless) communications systems.
The code used by most computers for text files is known as ASCII (American Standard Code for Information Interchange, pronounced ASK-ee). ASCII can depict uppercase and lowercase alphabetic characters, numerals, punctuation marks, and common symbols.

May 18, 2014

How to use DHCP server Option 43 to discovery WLC


The Cisco IOS DHCP Server feature is a full DHCP server implementation that assigns and manages IP addresses from specified address pools within the router to DHCP clients. The following figure shows the basic steps that occur when a DHCP client requests an IP address from a DHCP server.

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 Option 43:  Option 43 is used to provide IP addresses to LAP and is required if the WLCが is in a different subnet than the DCHP server itself
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The example of option 43 on Cat6K

ip dhcp pool vlan368
   network 172.33.68.0 255.255.255.0
   default-router 172.33.68.254
   option 43 hex f104.ac21.430a

When DHCP servers are programmed to offer WLAN Controller IP addresses as Option 43 for other Cisco Aironet LAPs, the sub-option TLV block is defined in this way:
  • Type—0xf1 (decimal 241)
  • Length—Number of controller IP addresses * 4
  • Value—List of the WLC management interfaces, typically translated to hexadecimal values
As you can see from the example TLV: f104.ac21.430 (ac21.430a is IP address of WLC management interface)

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1876: a revolution in communications --- Bell and his legacy

It is such a common occurrence that no one ever wonders from whence it came. But the telephone has a fascinating story behind it, one that could be entitled. "The Conquest of Solitude." It is the story of Alexander Graham Bell

He was born in Edinburgh, Scotland. in 1847, the son of a man who was consumed,passionately consumed, with the workings of the human voice, how it produced and used, and especially, in teaching the deaf how to use it. For in those days, you see, the deaf lived in permanent solitude. Not only could they no hear, they could not speak. After all, how could they pronounce words, they couldn't hear? Perhaps this obsession of the elder Bell was one of the reasons he marred whom he did. For the woman who would give birth to the inventor of the telephone - was deaf.

Yong Alexander Graham Bell grew up with his father's passions. In 1870, because of poor health, he migrated to Canada. It was not long before his success in teaching the deal to speak brought him to the attention of a wealthy merchant in Boston who had a deaf daughter, Mabel. Would Mr. Bell please teach Mabel how to speak? Yes, he would. And did. And they fell in love. I year later, in 1877, he and Mabel were married. He later became an American citizen.



Alexander Graham Bell died in 1922: Mabel five months later. She loved him that much. His name is likely to live as long as man recalls history. After all, there is this constant reminder of how he brought the human family into closer touch.

The first voice to travel over a wire was even a surprise for its inventor. Alexander Graham Bell. He was experimenting in his laboratory late one night, and quit by accident he succeded in transmitting a message to his assistant in the next room. What Mr. Bell could not know at the time was that nigh in 1876 would mark the stat of a revolution in communications.