he users still get to use the interface they have grown accustomed to, but on the network side, every management system will talk to every other management system using a common and widely accepted form. Again, it's just like a canonical language: If people from five different language groups need to communicate, they have a choice. They can each learn everybody else's language (four additional languages per person) or they can agree on a canonical language (Esperanto), which reduces the requirement to a single language each. In network management, there are several canonical forms. The most common are ISO's Common Management Information Protocol (CMIP), the IETF's Simple Network Management Protocol (SNMP), and the Object Management Group's Common Object Request Brokered Archi- tecture (CORBA). As long as every manager device agrees to use one of these on the network side, every system can talk to every other system. Other canonical forms found at the Application Layer include ISO's X.400/X.500 Message Handling Service (Quiz: Where would you find these?) and the IETF's Simple Mail Transfer Protocol (SMTP) for e-mail applications; ISO's File Transfer, Access, and Management (FTAM), the IETF's File Transfer Protocol (FTP), and the Hypertext Transfer Proto- col (HTTP) for file transfer; and a host of others. Note that the services provided at this layer are highly specific in nature: They perform a lim- ited subset of tasks. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Protocols Protocols Layer Six: The Presentation Layer For our e-mail example, let's assume that the Application Layer converts the PC-specific information to X.400 format and adds a header that will tell the receiving device to look for X.400-formatted content. This is not a difficult concept; think about the nature of the information that must be included in any e-mail encodi