ETCP Packet Core and Service Continuity 1 — Questions and Answers
Question 1: In Ericsson's EPC, what does the SGW (Serving Gateway) do?
- Provides IP address allocation to UEs
- Acts as the mobility anchor for user plane data during intra-LTE handovers and idle-mode paging (Correct answer)
- Authenticates subscribers using AKA procedures
- Manages inter-PLMN roaming policy
Correct answer: Acts as the mobility anchor for user plane data during intra-LTE handovers and idle-mode paging
The SGW anchors the user plane bearers during handovers between eNBs, buffers downlink data during UE paging, and routes packets between the eNB and PGW.
Question 2: What is the purpose of the GTP (GPRS Tunneling Protocol) in Ericsson's packet core?
- Encrypting control plane messages between HSS and MME
- Tunneling user IP packets between EPC gateway nodes (SGW–PGW) and between eNB and SGW (Correct answer)
- Providing DNS resolution for subscriber domains
- Managing inter-RAT handover between LTE and Wi-Fi
Correct answer: Tunneling user IP packets between EPC gateway nodes (SGW–PGW) and between eNB and SGW
GTP-U tunnels encapsulate user plane IP packets over the S1-U (eNB–SGW) and S5/S8 (SGW–PGW) interfaces, providing subscriber-level tunnel isolation.
Question 3: In Ericsson's 5GC, which interface runs between the UPF and the Data Network (internet)?
- N3
- N6 (Correct answer)
- N9
- N4
Correct answer: N6
The N6 interface connects the UPF to external data networks (e.g., the internet or enterprise networks), carrying the unencapsulated subscriber IP traffic.
Question 4: What does 'UPF chaining' allow in Ericsson's 5G user plane architecture?
- Linking multiple UPFs in sequence so traffic passes through different processing functions (e.g., traffic inspection, NAT, firewall) in a service function chain (Correct answer)
- Bonding multiple physical UPF servers for higher throughput
- Routing voice and data to separate UPF instances by APN
- Synchronizing UPF clock sources across data centers
Correct answer: Linking multiple UPFs in sequence so traffic passes through different processing functions (e.g., traffic inspection, NAT, firewall) in a service function chain
UPF chaining (via Service Function Chaining) routes packets through a sequence of UPF instances or VNFs, each applying a specific processing function before forwarding.
Question 5: In Ericsson's packet core, what is PCRF (Policy and Charging Rules Function) responsible for in LTE?
- Providing radio resource allocation per TTI
- Defining and enforcing QoS policies and charging rules per bearer or subscriber session (Correct answer)
- Managing the physical transport between eNB and core
- Storing raw CDRs (Call Detail Records) for billing
Correct answer: Defining and enforcing QoS policies and charging rules per bearer or subscriber session
The PCRF dynamically sets QoS parameters (bandwidth, priority) and charging rules for each subscriber session, enforcing operator policies in real time.
Question 6: What does the term 'PDN Connection' refer to in Ericsson's LTE/EPC architecture?
- A physical fiber connection between the PGW and internet exchange
- The logical association between a UE and an external Packet Data Network (e.g., internet), anchored at the PGW (Correct answer)
- A dedicated signaling link between MME and HSS
- An inter-core interface between two operators' EPC nodes
Correct answer: The logical association between a UE and an external Packet Data Network (e.g., internet), anchored at the PGW
A PDN Connection is the end-to-end logical path from the UE through the EPC to an external data network, identified by an APN and maintained as long as the UE is active.
ETCP Packet Core and Service Continuity 1
In Ericsson's EPC, what does the SGW (Serving Gateway) do?