From my experience till now and for my better understanding, I quote it something like below:
Deployment Server: Mainly used for OS Deployments rather than software installs.... However, in special cases we can use DS also for software install. Deployment Solution should be installed on a server to designate as Deployment Server and Deployment Console is used to work / manage OS Distributions and sometimes Software installs...
Yes, we can use only Deployment Server (Deployment Solution 6.9) without using Notification Server which is available directly as Deployment Solution 6.9...
However, if only Deployment Solution 7.1 is needed, we need to install only Altiris Client Management Suite (DS 7.1 is part of CMS) via SMP (SMP -> it is used only to manage solutions / suits you have installed)...
Notification Server now known as SMP: Is mainly used for planned / controlled / scheduled software distributions... SMP as said above, also includes many other solutions / suits that help you to manage your IT Infrastructure (Assets, Software Licensing, Mobile Management, Inventory, Patching / applying Software updates, etc...)
As said above NS is also known as SMP. However, SMP is kind of an application that manages suits / solutions installed.. In other words, Name SMP is used in two cases (to refer NS and to refer to an app that will help us to manage Solution / Suits)
Please feel free to pour in your thoughts / suggestions or correct me if I have missed something...
Hope this helps... :)