Question: When a Serving GPRS Support Node (SGSN) activates APN-based congestion control for Mobile Stations (MSs) with a specific subscribed Access Point Name (APN), what action may the SGSN take upon receiving a subsequent Attach request from an MS before its stored back-off time has expired, if the initial request was rejected without a low access priority indicator?
Option 1: The SGSN will process the request normally, ignoring the back-off time.
Option 2: The SGSN may immediately reject the subsequent request until the stored back-off time is expired.
Option 3: The SGSN will prompt the MS to change its APN before proceeding with the Attach request.
Option 4: The SGSN will automatically downgrade the MS's service quality for a specified period.
Explanation: This is because, as per the described congestion control mechanism, if an SGSN maintains an MS context and rejects a request without a low access priority indicator, it may store a back-off time per MS. To prevent overwhelming the network with simultaneous re-requests, the SGSN has the capability to reject any subsequent requests from the MS until the stored back-off time has elapsed, thereby managing network congestion more effectively.