# Azure Service Bus Transport Upgrade Version 3 to 4


## Topic name configuration

The API to configure the [topic name used for publish and subscribe](/transports/azure-service-bus/configuration.md#entity-creation-topology) has been changed, instead of:

<!-- snippet: 3to4-asbs-topic-name-old -->

```cs
var transport = new AzureServiceBusTransport("my connection string")
{
    TopicName = "CustomTopicName"
};
```

<!-- endsnippet -->

Use:

<!-- snippet: 3to4-asbs-topic-name-new -->

```cs
var transport = new AzureServiceBusTransport("my connection string")
{
    Topology = TopicTopology.Single("CustomTopicName")
};
```

<!-- endsnippet -->

For more advanced topology configurations, see the [topology documentation](/transports/azure-service-bus/topology.md).