Expert Summary
"Sustained Multi-Week Network Stability Confirmed Under Mobility Stress Conditions."
Based on intensive field monitoring conducted during the fourth week of February, the SKT local network has demonstrated sustained stability and high-throughput performance across three consecutive reporting periods.
Daily Stability: Monitoring data collected from Monday through Friday (Feb 23–27) indicates consistent download speeds exceeding 100 Mbps, with low and stable latency maintained during peak weekday hours.
Transit Performance: This week's evaluation focused on high-speed transit scenarios within deep underground environments. Measurements conducted inside the AREX (Airport Railroad) and the GTX (Great Train eXpress) corridors showed stable throughput and responsive latency performance. Notably, network consistency in these transit environments was observed to be comparable to — and in certain intervals more stable than — some high-density surface-level urban zones.
Continuous Connectivity: Field observations confirm that the SKT local eSIM profile maintained uninterrupted connectivity across key transit routes, including airport-to-city transfers, supporting stable navigation, messaging, and streaming use cases during movement.
Weekly eSIM Performance Index
Download performance
Seamless
Upload performance
Seamless
7-day trend
Overall status
Seamless
Minor delay under heavy upload
Overall stability
High
Usage readiness
Routing behavior
Native-dominant
Traffic primarily handled within local network paths
Regional Average Performance
This table represents the average connectivity health across major hubs during the fourth week of February.
| Location | Status | Speed | Responsiveness | |||
|---|---|---|---|---|---|---|
|
Download (Mbps) |
Upload (Mbps) |
Idle (ms) |
Download (ms) |
Upload (ms) |
||
| Hapjeong Station | Seamless | 106 | 60.8 | 33.3 | 40 | 592.3 |
| Hongdae Red Road | Seamless | 104.4 | 63.4 | 32.7 | 111.3 | 602 |
| DMC Station (B3) | Seamless | 102 | 87.1 | 29 | 36 | 408 |
| Hongik Univ. Station (B2) | Seamless | 110 | 98.6 | 37 | 79 | 353 |
eSIM Connectivity Benchmarks by Day
Daily tracking results to show network stability. Monitoring is conducted during weekday peak hours to provide the most conservative and realistic performance data for travelers.
| Date | Location |
Download Speed (Mbps) |
Upload Speed (Mbps) |
Ping (ms) |
|---|---|---|---|---|
|
MON
02/23/2026
|
Hongdae Red Road |
🟢 105 | 🟢 94.2 | 🟢 39 |
|
Hapjeong Station |
🟢 104 | 🟢 46.3 | 🟢 40 | |
|
TUE
02/24/2026
|
Hongdae Red Road |
🟢 110 | 🟢 62.3 | 🟢 28 |
|
Hapjeong Station |
🟢 111 | 🟢 60.1 | 🟢 31 | |
|
WED
02/25/2026
|
DMC Station (B3) |
🟢 102 | 🟢 87.1 | 🟢 29 |
|
Hongik Univ. Station (B2) |
🟢 110 | 🟢 98.6 | 🟢 37 | |
|
THU
02/26/2026
|
Hongdae Red Road |
🟢 106 | 🟢 58.4 | 🟢 30 |
|
Hapjeong Station |
🟢 104 | 🟢 75.9 | 🟢 29 | |
|
FRI
02/27/2026
|
Hongik Univ. Station |
🟢 121 | 🟠 36.1 | 🟢 35 |
|
Hongdae Red Road |
🟠 96.4 | 🟠 38.6 | 🟢 34 |
121 Mbps
98.6 Mbps
28 ms
💡 Weekly Insight
Connectivity on the Move
Q. Do local eSIM profiles maintain stable connectivity during high-speed transit and river crossing?
A. Field measurements indicate that native local eSIM profiles maintain stable connectivity during high-speed transit, including deep underground rail environments and river crossings.
Across tested scenarios, download throughput remained consistently above 100 Mbps, while upload performance remained functionally stable. Although upload latency increased under certain mobility and structural conditions, no session drops or service interruptions were observed.
Observed latency variations did not materially impact typical traveler use cases, including map navigation, messaging, social media browsing, or high-definition video streaming.
Field Observation
GTX Train
A mobility-focused stress test was conducted to evaluate whether seamless connectivity could be maintained during rapid transit scenarios.
Test Conditions
Performance was evaluated under the following high-speed and structurally challenging environments:
1Surface Transit (Urban): Bus crossing the Han River (Seogang Bridge, max. 60 km/h)
2Deep Underground (High-Speed):
- GTX Train: High-speed transit at significant depth (max. 180 km/h, approx. B8 level)
- AREX (Airport Railroad): Rapid transit linking airport and city (max. 110 km/h, approx. B7 level)
Results
Across all tested scenarios, the network maintained stable performance despite wide river crossing and deep underground high-speed movement.
Average measured performance:
- Download: 106 Mbps
- Upload: 52 Mbps
- Idle Latency: 32 ms
No measurable connection drops were observed during high-speed transit.
Contrary to common assumptions regarding underground signal degradation, the results indicate consistent handover performance and stable signal continuity within deep tunnel environments.
Idle latency levels recorded in transit corridors were comparable to — and in certain intervals lower than — measurements from densely populated surface-level urban zones.
Test Video
Seogang Bridge
Airport Railroad (AREX)
📹 More tests:
• GTX
Test Result
| Condition | Region | Status | Speed | Responsiveness | |||
|---|---|---|---|---|---|---|---|
|
Download (Mbps) |
Upload (Mbps) |
Idle (ms) |
Download (ms) |
Upload (ms) |
|||
| On a bus crossing the Han River | Seogang Bridge, Hangang River | Seamless | 🟠 98.7 | 🟢 49.2 | 🟢 36 | 🟠 160 | 🔴 730 |
| Inside a high-speed GTX*train | NW Metropolitan Area | Seamless | 🟢 116 | 🟢 54.4 | 🟢 30 | 🟢 53 | 🔴 807 |
| Inside an AREX* Train | Mapogu, Seoul | Seamless | 🟢 102 | 🟢 51.8 | 🟢 31 | 🟢 54 | 🔴 701 |
| Average | 🟢 106 | 🟢 52 | 🟢 32 | 🟠 89 | 🔴 746 | ||
*GTX(Metropolitan Express): A high-speed rail linking Seoul's outskirts to the center in 30 mins, hitting 180 km/h at 40–50m deep.
*AREX(Airport Railroad): A dedicated link between Incheon/Gimpo Airports and Seoul Station, offering both Express and All-stop services.
🛠️ Technical Note: The Secret of Seamless Mobility
Stable network performance within South Korea's subway and metropolitan rapid transit systems (including GTX corridors) is supported by infrastructure designed to address the signal propagation challenges of enclosed underground environments.
📡 LCX (Leaky Coaxial Cable) Deployment
Underground transit tunnels commonly utilize Leaky Coaxial Cables (LCX) installed along the tunnel length.
Unlike point-source antennas, LCX functions as a distributed antenna system, emitting radio signals continuously along the cable through engineered slots.
This configuration enables:
- More uniform signal distribution
- Reduced coverage gaps in curved or deep tunnel sections
- Improved signal continuity in confined environments
🔄 Handover Optimization in High-Speed Transit
Maintaining connectivity at speeds exceeding 100 km/h requires efficient inter-cell handover performance.
As a train moves between coverage sectors, the network dynamically reallocates connections based on real-time signal conditions.
Field observations during high-speed testing indicated stable session continuity without measurable connection drops, suggesting effective handover coordination within transit corridors.
🚇 Waveguide Effect in Tunnel Environments
Tunnel structures can support a waveguide propagation effect, where radio signals reflect along the tunnel walls rather than dispersing in open space.
Under certain frequency bands and infrastructure configurations, this phenomenon can help maintain signal strength deeper into confined underground spaces.
🔗 Native Infrastructure Advantage
A native local eSIM connects directly to the domestic carrier's core network infrastructure.
Unlike roaming-based profiles that may route traffic internationally before returning to local endpoints, native routing minimizes unnecessary latency overhead and reduces cross-border path dependency.
This direct routing architecture contributes to the low idle latency observed during transit testing.
Lab Verdict & Recommendations
Based on measurements collected during the fourth week of February (Feb 23–27, 2026):
• Across three consecutive monitoring weeks, average download throughput has remained above 100 Mbps in primary urban test zones. No measurable performance degradation was observed during the February sampling window, indicating sustained network stability under varied environmental conditions.
• No connection drops or signal interruptions were recorded during high-speed transit testing. The local eSIM profile maintained continuous connectivity in deep underground tunnels and open-air bridge crossings, including peak velocity intervals.
• Within specific transit corridors (GTX, AREX), measured idle latency (~32 ms) was comparable to — and in certain intervals lower than — values recorded in densely populated surface-level urban zones. These findings suggest effective infrastructure optimization within tunnel and rapid-transit environments.
• While download throughput remained consistent across scenarios, elevated upload latency (avg. ~746 ms) was observed during rapid movement. However, no material degradation in general usability was detected across common traveler use cases.
Scope Note
This report reflects real-time measurements collected during weekday peak hours within selected transit and urban test zones. Although findings indicate high reliability under observed conditions, individual user performance may vary depending on device hardware, radio conditions, and real-time network traffic outside monitored windows.
Director of Connectivity Lab
Ian Hyukjong Yeo
"Empowering journeys with easy, reliable, and convenient traveler eSIM solutions"
Ian Hyukjong Yeo is the Director of Connectivity Lab and a telecommunications entrepreneur with over 20 years of experience in the global telecom industry. Today, he leads Connectivity Lab's research and field benchmarking initiatives evaluating real-world eSIM performance for international travelers.