Hi

It is a Cisco proprietaryprotocol

Cisco Discovery Protocol (CDP) is primarily used  to obtain protocol addresses of neighboring devices and discover the  platform of those devices

Type Length Values (TLVs) are blocks of information embedded in CDP advertisements which gives details like address, device-id,platform...

http://www.cisco.com/en/US/docs/ios/12_1/configfun/configuration/guide/fcd301c.html

It is useful for Cisco Devices to discover the neighbors and its details.

Thanks

Raju