> For the complete documentation index, see [llms.txt](https://prosbcdocs.telcobridges.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prosbcdocs.telcobridges.com/telecom-references/parameter-reference/sip-user-to-user-encoding.md).

# SIP: User-to-User encoding

### Encoding options for SIP User-to-User header

#### Use hexadecimal encoding format

Each byte of the UUI is printed as a 2-digits hexadecimal value. This allows encoding any value in the UUI, including non-printable characters. User-to-User:303030303030312e5468697320697320612074657374205555492076616c7565;encoding=hex;purpose=isdn-interwork;content=isdn-uui

#### Use text encoding format

UUI is stored "as-is" (without any modification) into the SIP header.

**Note: If any illegal character is encounterd (non-printable, or illegal in a SIP header), the encoding will be forced to hexadecimal as shown above.** User-to-User:0000001.This is a test UUI value with only printable characters legal in a SIP header;encoding=text;purpose=isdn-interwork;content=isdn-uui

#### Use text encoding format with the escape illegal characters option

UUI is stored in the SIP header without modification (like with the text encoding format).

However, UUI bytes that do not corresponds to a printable ASCII character, or that corrsponds to an ASCII character that can't be used within a SIP header will be escaped.

Escaping is made by using character % followed by a 2-digits Hexadecimal value. User-to-User:This is a test UUI value with non-printable data here %00%00%00%00%00%00%03.;encoding=text;purpose=isdn-interwork;content=isdn-uui


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://prosbcdocs.telcobridges.com/telecom-references/parameter-reference/sip-user-to-user-encoding.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.