Q:

How to provide free tagging ability when saving nodes using services

A content type is going to be saved , this type contains a taxonomy term reference field named field_ucectgry .  I'm developing an app so the user can create new node types remotely.  Services module is used to provide a REST service for that. 
Now for filling field_ucectgry during node creation I must pass the term ID , but the problem is that this field must has free tagging ability which means new tokens for this field is accepted. 
So , how can I provide the ability of free tagging for my program? 
PS: this is the structure of the field in node :

A:

In D7, a taxonomy term reference field with the autocomplete widget uses JSON like this: 
"field_tags":{"und":"Foo,Bar"}" 
When it is an autocomplete, the term name needs to be used instead of the term id for free tagging it will simply create the term.