WinCC Client Configuration: Uni-Client vs Multi-Client Systems

Overview

Siemens WinCC supports two fundamentally different client/server topologies that govern how runtime data is shared between operator stations. Misunderstanding the distinction between a Uni-Client (client without an own project) and a Multi-Client (client with an own project) leads to licensing violations, broken package imports, and operator stations that silently fail to receive tag updates. This reference covers both the classic WinCC V7.x configuration model and the WinCC Runtime Professional path under TIA Portal, including the Central Archive Server (CAS) restrictions that force a separate project on otherwise "clientless" clients.

Architecture: Two Client Models

The WinCC documentation differentiates between two cases. The wording appears on page 14/15 of the WinCC V7 Information System under "Distributed systems" and "Multi-user systems", and is replicated in the TIA Portal help under Clients and servers (RT Professional):

• Multi-user system (Uni-Client topology): A single WinCC Server project is referenced by up to 32 clients. Each client has no of its own project; the client runtime loads the server's package at startup and renders pictures directly from the server's project database. Uni-Clients can only access the one server whose package they imported.
• Distributed system (Multi-Client topology): Two or more WinCC servers coexist on the network, each holding its own project (for example, one server per plant area). Each Multi-Client holds its own local project, which contains the server references, the local picture tree, and the locally configured user administration. At runtime the Multi-Client opens a session against any number of the configured servers and merges their tag namespace into its own display.

Why the Configuration Steps Look Identical

In TIA Portal the wizard that creates a "WinCC Client" looks the same in both cases. The divergence only appears in three places:

1. The Computer list on the server project (which clients are explicitly trusted).
2. Whether the client is configured to automatically import the server package (Uni-Client) or to export the server data and reference it from a local project (Multi-Client).
3. The client runtime license stamped on the client station (RT Client vs RT Multi-Client).

Feature Comparison: Uni-Client vs Multi-Client

Maximum System Limits

The 32-client cap is documented in the WinCC Information System under "Configuration of a distributed system / Limits" and applies per server in a distributed system, not in aggregate across servers. For TIA Portal V20, the same per-server limit holds; the difference is that each Multi-Client can subscribe to multiple servers, so the effective count of "client PCs" can exceed 32 if you count them per server.

Configuration Procedure: Multi-User System (Uni-Client)

Prerequisites

• WinCC Server project is compiled without errors.
• Client PC is a member of the same Windows workgroup or domain as the server, with name resolution working both ways (test with ping <servername> and ping <clientname> from the opposite side).
• WinCC RT Client license is installed on the client; WinCC RT Server license on the server.
• TCP port 139/445 (SMB) and the configured WinCC communication ports (default: 80/HTTP, 443/HTTPS, plus 3389/RDP if you tunnel picture previews) are open between client and server.

Step-by-Step (TIA Portal V20, WinCC Runtime Professional)

1. Open the server project in TIA Portal. In the project tree, expand WinCC Runtime Professional > Communication > Server data.
2. Right-click Server data and choose "Create server data". The export directory (typically \<servername>\WinCCProj\<project>\ServerData\<servername>\) is created.
3. Open the Computer list on the server project and add the client PC name. The default name is the Windows hostname; for redundancy later you can also add a virtual computer name. Confirm with OK.
4. On the client PC, start TIA Portal and create a new WinCC Client project (or open the project intended for the client). In the project tree, under Devices & Networks, add a WinCC RT Professional device with the device type "WinCC Client".
5. In the client's Runtime settings > Server tab, add the server by name. The client reads the package from \<servername>\<serverdata>\<servername> at runtime start.
6. Configure the automatic package import: on the client's Runtime settings > Package tab, enable "Import package on startup" and set the path. This is the mechanism that ships new server picture revisions to all Uni-Clients the next time they cycle runtime.
7. Compile the client project, download it to the client PC, and start WinCC Runtime. The client log (C:\ProgramData\Siemens\Automation\WinCCRTProfessional\Logs\) shows Package import successful if the import worked.

Verification

• From the client, open Server data diagnostics (Start > Programs > WinCC > Server data diagnostics). The server should appear in green with last-connection timestamp < 5 s old.
• Force a tag change in the server project (for example, toggle a binary tag in a faceplate) and confirm the value reaches the client picture within one second on a 1 Gbit LAN.
• Restart the client runtime and confirm that the package is re-fetched (look in the log for Importing package \<servername>\...).

Configuration Procedure: Distributed System (Multi-Client)

Prerequisites

• Two or more WinCC Server projects compiled, each with its own exported server data directory.
• One client PC that will hold the local Multi-Client project. This project is a fully fledged WinCC Runtime Professional project in its own right, with its own picture tree and user administration.
• Licenses: WinCC RT Client on the Multi-Client plus a Multi-Client upgrade license (sometimes sold as "WinCC RT Client (multi-server)" or "WinCC/Server + WinCC/Client" bundles, depending on the catalog number).

Step-by-Step

1. On each server, create the server data export (right-click Server data > Create server data). The server will then make its package available to clients under \<servername>\<serverproject>\ServerData\<servername>\.
2. On the Multi-Client PC, open TIA Portal with the local client project. In Runtime settings > Server, add every server that the client should reach. The list is comma-separated and the order is the connection-try order.
3. Open the server's project, and in its Computer list, do not add the Multi-Client as a Uni-Client. Only add other servers (for server-to-server tag exchange) and any pure Uni-Clients. The Multi-Client is not registered on the server, because the Multi-Client owns its project and explicitly imports the server's package.
4. On the Multi-Client, open Server data and choose "Import server data" for each server. The package is stored under the local project's Server data node. This is the equivalent of the package export step on the server side.
5. Compile and download the client. Start runtime and verify that all configured servers show green in the connection diagnostics.
6. For redundant server pairs, enable Server redundancy in the client's Runtime settings and add both redundant partners in the server list. The client fails over automatically; failover time is dominated by the configured redundant partner switch time (default 60 s in WinCC V7.x, configurable down to 5 s).

Verification

• In the client runtime, open the Server list diagnostics window. Every server should be Connected; redundant pairs should show Standby on the inactive partner.
• Trigger a picture change on Server A and on Server B. Both pictures must render in the same client session, in the same window tree, with no tag crossover.
• Stop the active server of a redundant pair. The client should fail over to the partner within the configured switch time, with one logged entry "Server failover: A -> B".

Computer List Semantics

The computer list is the trust mechanism WinCC uses to validate which clients may open a runtime session against the server. There are three cases:

When in doubt, open the server project's Computer editor: every name in the list corresponds to a configured runtime target. Any Uni-Client that is missing from this list will fail with error 0x800<...> at the first picture-open attempt.

Package Import vs Package Export

The package is a compiled subset of the server project – pictures, tag database, alarm configuration, and scripts – that the client needs to render the server's views. The two architectures handle the package differently:

Engineering implication: a Uni-Client station is essentially a thin client. If the server is down, the operator station is unusable. A Multi-Client can keep showing cached picture content for the servers that are still up, which is why a single-server plant with redundant operator stations usually picks the Uni-Client model (one source of truth) while a multi-area plant picks the Multi-Client model (graceful degradation).

Central Archive Server (CAS) Restriction

WinCC projects that participate in a Central Archive Server configuration cannot use the client-without-own-project model. According to the Siemens support entry "Step 4: Create client application and references - WinCC/Central archive server (CAS)", "clients without own project are not released in a WinCC CAS environment" – the CAS subscription requires a local project on the client so that archive segments can be stored locally and re-broadcast to the CAS. The workaround is to create a fully-fledged local project on the client (i.e. switch to the Multi-Client model) and then configure the archive forwarding from that local project to the CAS. This is a common reason a one-server plant ends up running a Multi-Client topology: the CAS requirement forces a local project onto every operator station.

Licensing Reference

The exact catalog numbers are version-specific and live in the Siemens Industry Online Support under the WinCC Runtime Professional delivery release. Verify against the current price list before ordering; the functional split between "Client (single-server)" and "Client (multi-server)" has remained stable from V7.x through TIA Portal V20, but the SKU suffix (e.g. 6AV2 1xx-...) changes with each release.

Decision Guide: Which Topology Should I Use?

Use this matrix when you have to choose:

Troubleshooting Matrix

Diagnostics Files to Capture Before Calling Support

When opening a Siemens support request for a WinCC client/server issue, attach the following artefacts to speed up triage:

• Server project .log file from \<servername>\<project>\Logs\.
• Client runtime log from C:\ProgramData\Siemens\Automation\WinCCRTProfessional\Logs\ on the affected client PC.
• Output of WinCC Server Data Diagnostics on the client (exported as .txt).
• Export of the server project's Computer list (CSV from the editor).
• Screenshots of the License analysis dialog from both server and client.

Field-Proven Tips

• Use the same Windows user account for the WinCC service on the server and for the logged-in user on the client. Mixed-account setups cause "access denied" on the package share that the configuration looks correct on paper.
• Set the server's computer name in DNS or hosts. The client runtime resolves the server name at every connection attempt; a one-second DNS timeout during failover turns into a ten-second picture blackout.
• Disable SMB signing on the WinCC package share if you are running WinCC V7.4 or older on Windows Server 2012. Newer versions negotiate signing correctly, but older clients occasionally fail package import with a generic "network error" that is in fact a signing mismatch.
• Plan the computer list growth. Adding a Uni-Client always requires a server re-compile to push the new client name into the runtime computer list. Schedule that step into your change-management window.
• Document the project topology in the plant's HMI network drawing. The difference between Uni-Client and Multi-Client is invisible from a Windows Explorer view of the share, and operators troubleshooting at 03:00 will not guess right.

FAQ