Mobile Networks
Mobile networks in this exam focus on transporting 4G and 5G traffic across Nokia SR OS networks: backhaul, midhaul, fronthaul, timing, QoS, and slicing. The exam tests whether you can map radio requirements to transport constructs rather than just name 5G features.
Transport segments and requirements
- Fronthaul (RU to DU) is latency- and jitter-sensitive; midhaul (DU to CU) and backhaul (CU to core) carry packet flows with different SLAs.
- 5G QoS flows map to transport CoS: DSCP at IP, EXP bits in MPLS, and queue scheduling at each hop.
- Timing uses SyncE for frequency and IEEE 1588 PTP for phase and time; boundary clocks and transparent clocks reduce error accumulation.
- Network slicing uses transport isolation: separate SR policies, VPNs, or Flex-Algo paths per slice.
Worked example
A gNB reports phase error after a transport upgrade. Verify PTP grandmaster priority and clock class, then check whether the boundary clock on the SR OS node is enabled on the correct port and whether SyncE is locked. If the path crosses an untrusted domain, PTP must not be allowed to traverse it without boundary or transparent handling. The fix is usually a timing-aware design, not a QoS change.
Traps
Do not treat all mobile traffic as one CoS; control-plane and timing traffic need protection. Do not assume more bandwidth fixes latency. Do not mix frequency sync (SyncE) with phase and time (PTP).