The PrimeFaces.ab function is a shortcut function for PrimeFaces.ajax.AjaxRequest.

//ajax shortcut  
ab: function(cfg, ext) {  
    return PrimeFaces.ajax.AjaxRequest(cfg, ext);  
}

The PrimeFaces.ajax.AjaxRequest can be asynchronous or synchronous. The AjaxRequest uses the AjaxUtils, which handles all send, process, response, and update.

PrimeFaces.ajax.AjaxRequest = function(cfg, ext) {
cfg.ext = ext;

if(cfg.async) {  
    return PrimeFaces.ajax.AjaxUtils.send(cfg);  
}  
else {  
    return PrimeFaces.ajax.Queue.offer(cfg);  
}  

}

Passing a cfg (configuration) object to the PrimeFaces.ajax.AjaxUtils.send(cfg), this cfg object has:

• cfg.global: a boolean value used to trigger p:ajaxStatus if it's a true.
• cfg.onstart: to be called when the request is to be send.
• cfg.async: a boolean value, where if this call is asynchronous or not.
• cfg.source: can be a client id or an element defined by this keyword
• cfg.formId: if an explicit form is defined, or it would look into a parent source
• cfg.resetValues
• cfg.ignoreAutoUpdate
• cfg.fragmentId: used for the process of the components
• cfg.fragmentUpdate
• cfg.event: behaviour event, like click or change
• cfg.params: request params
• cfg.partialSubmit: if partial submit is enabled, there are components to process partially
• cfg.onerror: to be called when the request had an error status.
• cfg.onsuccess: to be called when the request had a success status.
• cfg.oncomplete: to be called when the request is completed.

Note: I came up with this explanation based on my understanding of the source code.

Also you can refer to this answer, might be helpful.

http://stackoverflow.com/questions/23031582/primefaces-ab-function