demand drafts are actually a specific type of bank drafts. they are categorized under bank drafts. when ever you are demanded to make a payment, your bank makes a draft on behalf of you, against the funds you provided, so that you can make a "demanded" payment anywhere else in the world with this draft that is backed by authenticity and reliability of your issuing bank. it is also a proof that you have that much funds available with you.
you can chose multinational bank for this purpose, as they have more contacts worldwide as compared to local banks, they can help your dd get cashed faster then the local ones.