Let take a classical example: you want email notification 24×7 but SMS only the night and for critical alerts only. How do this with contacts definitions? You have to duplicate the contact. One with notification_period of 24×7 and the email command, and one other with send-by-sms for the night. Duplicate contacts can be hard to manage in services definitions afterward !

That why notification ways are useful: you defined some notification ways (that look really like contacts) and you linked them to your contact.

For example, you can have the below configuration: your contact, a happy admin:

define contact{
    contact_name                    happy_admin
    alias                           happy_admin
    email                           admin@localhost
    pager                           +33699999999
    notificationways                email_in_day,sms_the_night
}

And now define our notification ways:

#Email the whole 24x7 is ok
define notificationway{
       notificationway_name            email_in_day
       service_notification_period     24x7
       host_notification_period        24x7
       service_notification_options    w,u,c,r,f
       host_notification_options       d,u,r,f,s
       service_notification_commands   notify-service
       host_notification_commands      notify-host
}

#But SMS only the night
define notificationway{
       notificationway_name            sms_the_night
       service_notification_period     night
       host_notification_period        night
       service_notification_options    c   ; so only CRITICAL
       host_notification_options       d   ; and DOWN
       service_notification_commands   notify-service-sms
       host_notification_commands      notify-host-sms
}

And you can call theses ways from several contacts :)

The contact is valid because he's got valid notificationways. For each notification, we ask for all notification_ways to give us the commands to send. If their notification options or timeperiod is not good, they just do not give one.

Of course, you can still have “old school” contact definition, and even with the notificationways parameters. The service_notification_period parameter of the contact will just be used to create a notificationways like the others, that's all.