What is the difference between eap-mschapv2 and mschapv2 in EAP_TTLS?

With EAP-MS-CHAPv2, the data sent in tunnel will be encapsulated as EAP-MESSAGE AVP (attribute-value pair). In the case of MS-CHAPv2, there is no such extra encapsulation it is just the MS-CHAPv2 message.