> 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


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