Every year, millions of international travelers land in Vietnam, toggle their phones out of Airplane Mode, and connect to a local 4G or 5G cell tower using a popular international travel eSIM.
To the user’s operating system, the connection looks healthy: four bars of signal, a 5G badge in the status bar, and decent downstream throughput on basic speed tests.
Yet, interactive applications perform noticeably sluggishly:
- Ride-hailing dispatch requests (Grab, Xanh SM) frequently time out.
- Real-time turn-by-turn navigation on Google Maps experiences persistent re-routing delays.
- Secure SSH sessions to remote servers jitter and drop keystrokes.
At Kovitel, we conducted an empirical packet routing analysis across 500 mobile sessions in Vietnam to diagnose the structural cause. The culprit is not local tower congestion—it is an architectural design pattern known as S8 Home Routing (S8HR).
The Architecture: Local Breakout vs. S8 Home Routing
In 3GPP cellular architectures (4G LTE Evolved Packet Core and 5G System), an inbound roaming subscriber can be routed via two distinct paradigms:
1. Local Breakout (LBO)
In a Local Breakout architecture:
- The user plane packets pass from the local radio tower (eNodeB/gNodeB) to the Serving Gateway (S-GW).
- The traffic is routed directly to a local Packet Data Network Gateway (P-GW / UPF) located within the visited country.
- Packets egress immediately onto the domestic internet backbone (e.g. Vietnam National Internet Exchange - VNIX).
Handset (Vietnam) ──> Local gNodeB ──> Local UPF/P-GW ──> Local Internet / CDNs
Total Latency: ~14 ms – 20 ms 🟢
2. S8 Home Routing (S8HR)
Virtually all low-cost international travel eSIM aggregators purchase wholesale IMSI ranges from virtual operators registered in third-party jurisdictions (e.g., Hong Kong, Austria, Singapore, or the UK).
Under S8HR:
- The visited network (e.g., Viettel or Vinaphone) authenticates the subscriber via roaming interface exchanges.
- The Serving Gateway (S-GW) in Vietnam does not route traffic to the domestic internet.
- Instead, user plane data is encapsulated into a GTP-U tunnel (GPRS Tunneling Protocol) and transmitted across undersea submarine fiber cables (e.g. APG, AAG) to the Home Public Land Mobile Network (HPLMN) Gateway in the issuing country.
- The home gateway inspects the traffic, applies billing policies, and routes it to the public internet.
- When you request data from a server located in Vietnam (e.g., a local Grab driver location), the packets must traverse the international submarine cable a second time.
Handset (Vietnam) ──> Local BTS ──> S8 Tunnel (Undersea Cable) ──> Hong Kong P-GW ──> Undersea Cable ──> VN Content
Total Latency: ~230 ms – 350 ms 🔴
Empirical Benchmark Findings (500 Measurement Points)
Our engineering team conducted multi-point diagnostic audits across 30 travel hotspots in Vietnam comparing local core network eSIMs (Kovitel Viettel Core) against a leading global roaming aggregator:
| Metric |
Local Core (Kovitel Viettel 5G) |
Roaming MVNO (S8HR via HK) |
Delta / Overhead |
| Mean ICMP Latency (Ping) |
18.4 ms |
244.8 ms |
+226.4 ms (+1,230%) |
| Packet Jitter (Variance) |
2.1 ms |
21.6 ms |
+19.5 ms |
| TCP 3-Way Handshake Time |
22.1 ms |
268.4 ms |
12x slower connection setup |
| Sustained Packet Loss |
0.0% |
1.3% |
Intermittent packet drops |
The Real-World UX Penalty:
- TCP Connection Multiplying: Modern web applications initiate dozens of parallel TCP connections and TLS handshakes. A 220ms delay on each handshake accumulates into multi-second page render stalls.
- WebSocket Keepalives: Real-time location tracking in ride-hailing apps requires low-jitter WebSocket streams. Submarine cable packet delay variation triggers false timeout disconnects.
Engineering Recommendations for Travel Tech Developers
- Prioritize Local IMSI / Local Breakout Provisioning: For mission-critical mobile telemetry, always select providers that maintain direct Tier-1 carrier agreements provisioning local IP addresses (such as Kovitel.com).
- Optimize Client-Side Timeout Windows: If building travel apps targeting international tourists, widen WebSocket reconnect thresholds and cache geographic assets aggressively offline.
Our complete 500-sample speedtest dataset, Python CLI, and technical whitepaper are available on GitHub: awesome-vietnam-travel-connectivity.