what is use the parameter "adress_list" int the listener.ora

From: FreeDBA <p.hirth_at_gmail.com>
Date: 24 Aug 2006 06:44:11 -0700
Message-ID: <1156427051.620241.93800@m79g2000cwm.googlegroups.com>

Hi,
I would like understand the contains of listener.ora, partularly the Address-List parameter.
I have multiple database and so multiple listener.ora. In some listener there is the adress_list parameter and son other there is nothing abour adress_list !!!!!

Why ?

(DESCRIPTION_LIST =
    (DESCRIPTION =
(ADDRESS_LIST =

        (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC2))
      )


      (ADDRESS_LIST =

        (ADDRESS = (PROTOCOL = TCP)(HOST = 172.22.1.154)(PORT = 1521))
      )

    )
    (DESCRIPTION =
(PROTOCOL_STACK =

        (PRESENTATION = GIOP)
        (SESSION = RAW)
      )


      (ADDRESS = (PROTOCOL = TCP)(HOST = 172.22.1.154)(PORT = 2481))

    )
  )

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
(SID_NAME = PLSExtProc)
(ORACLE_HOME = d:\oracle8iserveur)
(PROGRAM = extproc)

    )
    (SID_DESC =
(GLOBAL_DBNAME = DGD)
(ORACLE_HOME = d:\oracle8iserveur)
(SID_NAME = DGD)

    )
  ) Received on Thu Aug 24 2006 - 08:44:11 CDT