Direct connection via Local Link means working with the local telcos, i.e. SMS messages do not leave Singapore shores for the full delivery. It can be in the form of Shared / Dedicated Short Codes (5-digit numbers), Shared/Dedicated Long Codes or Caller ID.
Direct connection via International Link means working with the overseas aggregators, i.e. SMS messages (be they be sent to Singapore mobile numbers or non-Singapore numbers) do leave and route back to Singapore shores for the full delivery. It is usually in the form of Caller ID or long codes.