Implementing Cisco Service Provider Mobility Lte Networks Free Sample Questions

In many VoLTE implementations that use SIP preconditions (RFC 3312), the network waits for a Provisional Response Acknowledgement (PRACK) message from the UE before committing to the establishment of the dedicated bearer. The PRACK confirms that the UE has received the 183 Session Progress message with the SDP answer. If the PRACK is not received by the P-CSCF/PGW, the resource allocation for the QCI 1 bearer will not proceed, even if the PCC rule has been received from the PCRF.

DPI is required to identify traffic at the application layer, such as distinguishing video streams from a specific partner from other general internet traffic. This identification is the first step in applying a special charging policy.

Once the traffic is identified by DPI, a Policy and Charging Control (PCC) rule must be applied. This rule maps the sponsored traffic to a unique Service-Identifier or Rating-Group, which the OCS/OFCS can then use to apply the correct charging logic (i.e., charge the partner instead of the subscriber).

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.

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.

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.

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.

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.

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.

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.

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.