> For the complete documentation index, see [llms.txt](https://guides.clickatell.com/ussd-user-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://guides.clickatell.com/ussd-user-guide/getting-started/service-codes.md).

# Service codes

The USSD channel relies on one of three service codes: 

1. **Dedicated service code**: A code typically owned by one account and used by only one user for their company or service. It only has one segment, for example, \*111#. You can add as many sub-codes (extensions) as you want. 
2. **Semi-dedicated service code**: A code dedicated to one account but shared among other accounts. 
3. **Shared service** **code**: A code that is shared and used by multiple companies or services. Each company is allocated a channel on Clickatell's dedicated sub-code but the dedicated parent code is shared. You can add as many sub-codes (extensions) as you want, for example, \*111\*01\*xxx#. 

{% hint style="info" %}
The USSD bearer is accessed by calling a number that starts with the asterisk "\*" or hash/pound sign "#", followed by a combination of numerals, asterisks, and finally the hash/pound sign. 
{% endhint %}