There are number of blogs already available on this topic of "Central Monitoring using CCMS Infrastructure". Dirk Jenrich already shared lot of information related to Central Monitoring through his blogs.

So, you must be thinking "What's the new information which will be shared through  this blog?". Answer is Nothing New :-) , however i would rather try to make this topic(concept) more clear for any beginner.

Central Computing Management System (CCMS) infrastucture provides the functionality to Centrally monitor all your resources, components & scenario (in some cases) in your entire landscape. 

You can configure any Double Stack system to act as as Central Monitoring System [CEN system] for your landscape. Generally, SAP Solution Manager (with latest release) is used as CEN system. This system will then collect the data from the shared memory segment of all monitored (or managed) system & throws alert based on defined threshold condition.

There are 2 known methods to perform Central Monitoring using CCMS infrastructure :

1. RFC Monitoring - which does not require any agent installation. However using this method would require an extra work process for data transfer. To perform RFC monitoring, just schedule the background dispatching job on monitored system (ofcourse after setting-up CEN system) & create remote monitoring entry (OR create collect & analyze RFCs using SM59) from your CEN system to monitored system. Using this method data is actually pulled by your CEN system from shared memory of managed system. <SID>_RZ20_COLLECT RFC will simply collect all the data from shared memory segment of Managed system using an user with limited authorization (CSMREG user). <SID>_RZ20_ANALYZE RFC will be used to perform further analysis (in case of any Alert) into the managed system from the CEN system. So this user would require login details of managed system.
2. CCMS Agent - which requires the installation of CCMS agent on the managed system (i.e, host). This method doesn't require any work process becoz in this case CCMS agent will push the data from Managed system to CEN system [ I prefer to use this method for monitoring purpose]. Depending on the type of managed system [ABAP or JAVA] you have to install CCMS agent [CCM4X or CCMSR]. CCMS Agent provide various features to enhance the monitoring functionality of managed system. Like, monitoring of log files, OS data monitoring, event log monitoring etc.
3. CCMSPING Agent - another type (CCM4X & CCMSR) agent mainly used to perform the availability monitoring in a landscape. CCMSPing works very similar to PING command (to check availability of system in network), to check the availability of any particular Message Server. This agent should be installed once per landscape ( ofcourse more than one installation is also possible), and it should point the Central Monitoring System (CEN) of your entire lanscape. Then from CEN system we can configure the CCMSPing monitoring (or availability) for other managed system using Tx : RZ21 > Technical Infrastructure > Availability monitoring > Configure CCMSPing Monitoring. 

   

   Also there is a possibility to have Multiple Central Monitoring System (CEN) for collecting the data from different (or same) managed system. Refer the link containing details about Registering with Multiple Central Monitoring Systems from help.sap.com.

    

   Further refer "Monitoring Setup Guide" for step by step description on Setting up Central Monitoring, available @ service.sap.com/instguides > SAP NetWeaver > SAP NetWeaver 7.0 (2004s) > Operations > Monitoring > Monitoring Setup Guide (CEN NW 7.0 SP Stack 18) 

   Cheers!!