SIP headers (also called SIP fields or extra headers) carry message attributes to ensure that data packets travel along the correct path when communicating between devices on separate networks.
SIP headers are present for every HTTP request made by an outbound call. They can be categorized into four main types: record route headers, route headers, via headers, and contact headers. SIP headers are similar to HTTP header fields and always use the format
Follow these rules for header names:
- Write headers in the format: X-PH-Yourfield
- “Yourfield” must start with an uppercase letter. Other characters must be in lowercase.
- The header name can only contain alphanumeric characters (A-Z, a-z, 0-9).
- The header name can have a maximum length of 24 characters.
Following these rules for header values:
- The header value can only contain alphanumeric characters (A-Z, a-z, 0-9) and %.
- The header value can have a maximum length of 48 characters.
Header name-value pairs that don't follow these rules will not be sent by Plivo.