Free 600-212 sample questions

Correct answer: mme-service state maintenance

The `state maintenance` command within a service configuration (like mme-service) is the correct procedure for gracefully taking a service out of operation for maintenance. This command prevents the service from accepting new sessions and allows existing sessions to terminate normally or be handed over, ensuring a hitless transition in a redundant setup. The `shutdown` command is more abrupt, and `chassis switchover` forces a hardware state change which may not be as graceful.

Correct answer: Implementation of L2TP tunneling from the PGW to the customer's LNS.

Layer 2 Tunneling Protocol (L2TP) is a standard feature on the PGW (acting as an L2TP Access Concentrator, or LAC) designed for this exact purpose. It extends the UE's Layer 2 session to the customer's L2TP Network Server (LNS) located at the corporate site. This allows the corporate network to control authentication (often via RADIUS) and assign a trusted IP address directly to the UE, effectively placing the UE on the corporate network.

Correct answer: True

This statement is true. The Sv interface is the control plane interface between the MME and the MSC Server, used to facilitate the handover of the voice session from the packet-switched (PS) domain in LTE to the circuit-switched (CS) domain in UMTS/GERAN. The MSC Server is enhanced for SRVCC to manage the session transfer and control the media path switch.

Correct answer: Configuring a Diameter endpoint with primary and secondary peer priorities.

In Cisco StarOS, Diameter endpoints can be configured with multiple peers, each assigned a priority. The PGW will always attempt to send requests to the peer with the highest priority (e.g., priority 1). If that peer becomes unreachable (detected via watchdog messages or transaction timeouts), the PGW automatically fails over to the next highest priority peer (e.g., priority 2). This provides a simple and effective active/standby redundancy model for PCRF connectivity.

Correct answer: There is a database synchronization issue within a distributed HSS cluster.

The error 'IMSI unknown in HSS' indicates the HSS does not have a record for the subscriber the MME is querying. When this happens for multiple, otherwise valid subscribers, it strongly points to an internal HSS problem. In a distributed HSS architecture, a database synchronization failure or a partitioning event could make a subset of subscriber records unavailable to the HSS front-end handling the MME's requests, leading to this specific error.

Correct answer: IRI is generated by the MME for control plane events, while the SGW or PGW taps the user plane for CC.

This accurately describes the division of labor. The MME, as the primary control plane node, generates IRI for events like attaches, detaches, and handovers. The Call Content (the actual user data) is tapped from the user plane, which can be done at either the SGW or the PGW, depending on the network architecture and the location of the intercept point. Both streams of information are then sent to the LI Mediation Function.

Correct answers: The MME performs a DNS query based on the UE's Tracking Area Identity (TAI) to find a suitable SGW.; The MME performs a DNS query based on the Access Point Name (APN) requested by the UE to find a suitable PGW.

SGW selection is often geographically based to keep the user plane path optimal. The MME uses the TAI of the UE's current location to construct a DNS query (for S-NAPTR and A records) to find topologically appropriate SGWs.

The PGW is the gateway to a specific packet data network (like the internet or a corporate network), and this is identified by the APN. The MME uses the APN provided by the UE (or the default from the HSS) to construct a DNS query to resolve the IP address of the appropriate PGW.

Correct answer: The Final-Unit-Action (FUA) handling and credit-reauthorization thresholds.

When a subscriber's quota is exhausted, the OCS sends a Credit-Control-Answer with a Final-Unit-Indication. The PGW's action upon receiving this is determined by the Final-Unit-Action (FUA), which should be 'TERMINATE'. If there's a delay, it could be due to misconfigured credit-reauthorization thresholds (e.g., the PGW waits too long to ask for a new quota) or improper handling of the FUA, allowing a small amount of data to pass before the session is torn down. This is the most direct cause of revenue leakage in this scenario.

Correct answer: Polling schema-level and bulk statistics MIBs specific to the PGW service.

Cisco StarOS provides extremely detailed statistics via SNMP, but they are organized into schemas. To get granular data like specific drop reasons or failure causes, one must poll the schema-level MIBs (e.g., pgw-schema) and bulk statistics MIBs. This approach allows an NMS to retrieve thousands of specific counters related to session management, bearer handling, and protocol errors, which is far more detailed than high-level system MIBs or generic traps.

Correct answer: To transfer UE context between MMEs during an inter-MME handover.

The S10 interface is a control plane interface that connects two MMEs. Its primary purpose is to facilitate the transfer of UE context (such as security information and bearer details) from a source MME to a target MME when a UE moves between tracking areas that are served by different MMEs. This ensures a seamless handover process.