VOS3000 Callee Source Header Flexible To Request-Line Selection
Configuring the VOS3000 callee source header setting determines how VOS3000 extracts the destination (called) number from incoming SIP INVITE messages at the mapping gateway. The two available sources — the To header and the Request-Line (Request-URI) — can contain different values when a SIP proxy rewrites the destination during call routing. Choosing the correct source is essential for accurate dialed-number extraction, which directly affects routing prefix matching, billing rate lookups, and CDR recording of the called number. Get help with this configuration on WhatsApp: +8801911119966.
In SIP signaling, the called party number appears in two places: the To header and the Request-Line (also called Request-URI). Under normal conditions, both contain the same destination number. However, when calls pass through SIP proxies that perform number translation, load balancing, or routing decisions, the Request-Line may be rewritten to a different URI while the To header retains the original dialed number. Understanding which header contains the correct destination number for your deployment is the key to proper VOS3000 callee source header selection.
Table of Contents
To Header vs Request-Line — What Each Contains
The SIP To header and Request-Line serve different purposes in the SIP protocol. The To header identifies the logical recipient of the call (the originally dialed number), while the Request-Line specifies where the SIP message should actually be delivered (which may be a proxy-modified address). VOS3000 lets you choose which one to use for extracting the callee number.
| Header | SIP Purpose | Typical Content | Modified by Proxy? |
|---|---|---|---|
| To | Logical recipient identification | Original dialed number | Rarely (per RFC 3261) |
| Request-Line | Message delivery target | May be rewritten by proxy | Commonly rewritten |
When To and Request-Line Differ
Understanding the scenarios where the To header and Request-Line contain different values is critical for correct VOS3000 callee source header selection. These differences arise from SIP proxy behavior and can significantly impact routing accuracy if the wrong source is selected.
| Scenario | To Header Contains | Request-Line Contains | Best Source |
|---|---|---|---|
| Direct gateway connection | 12015551234 | 12015551234 | Either (same value) |
| SIP proxy with prefix injection | 12015551234 | 0012015551234 | To (original number) |
| Carrier with tech prefix stripping | 12015551234 | 9112015551234 | To (original number) |
| Proxy rewriting to internal URI | 12015551234 | [email protected] | To (original number) |
| Load balancer with rewritten URI | 12015551234 | [email protected] | To (original number) |
Configuration Steps for VOS3000 Callee Source Selection
To configure VOS3000 callee source header selection, navigate to the mapping gateway settings in the VOS3000 client. The callee source option is located under §2.5.1.2 of the mapping gateway configuration panel. For step-by-step gateway configuration guidance, see our gateway configuration guide. Need hands-on help? Message us on WhatsApp: +8801911119966.
| Step | Action | Detail |
|---|---|---|
| 1 | Open mapping gateway | Gateway > Mapping Gateway > select gateway |
| 2 | Locate Callee Source field | Under SIP header settings section |
| 3 | Select source header | Choose “To” or “Request-Line” based on upstream proxy behavior |
| 4 | Save configuration | Click Save to apply changes |
| 5 | Test with sample calls | Verify CDR callee number matches expected dialed digits |
Impact on Routing Prefix Matching
The extracted callee number is used for prefix matching in the VOS3000 routing table. If the wrong source is selected, the prefix may not match any routing entry, causing the call to fail with “No Available Router” or “Route Not Found” errors. For example, if a carrier prepends a tech prefix of 00 in the Request-Line, selecting Request-Line as the callee source would extract “0012015551234” instead of “12015551234”, which would fail to match the rate table entry for “1” prefix. For more on this, see our VOS3000 number transform guide.
| Callee Source | Extracted Number | Prefix Match | Routing Result |
|---|---|---|---|
| To (original) | 12015551234 | Matches prefix “1” | Successful routing |
| Request-Line (with tech prefix) | 0012015551234 | Matches prefix “00” or fails | Wrong route or no route |
Troubleshooting VOS3000 Callee Source Configuration Issues
When VOS3000 callee source header selection is misconfigured, the most common symptom is calls failing with “No Available Router” errors or CDRs showing incorrect called numbers. For broader routing troubleshooting, see our VOS3000 NoAvailableRouter guide and call routing reference.
| Problem | Likely Cause | Solution |
|---|---|---|
| No Available Router errors | Request-Line has tech prefix, extracting wrong number | Change callee source to To header |
| Wrong rate applied | Extracted number has extra prefix digits | Switch to To header or strip prefix in dial plan |
| CDR shows internal URI | Request-Line rewritten by proxy to internal address | Use To header for original dialed number |
| Calls to some numbers fail | Partial prefix match due to extra digits | Analyze CDR to see actual extracted callee format |
Related Resources – VOS3000 Callee Source
- VOS3000 Gateway Configuration Routing Mapping
- VOS3000 Number Transform Guide
- VOS3000 Call Routing Guide
- RFC 3261 – SIP Protocol Specification
Frequently Asked Questions About VOS3000 Callee Source Header
What is the difference between To header and Request-Line in SIP?
The SIP To header identifies the logical recipient of the call — the party the caller intended to reach, which is typically the original dialed number. The Request-Line (Request-URI) specifies the actual network destination where the SIP message should be delivered, which may differ from the To header if a SIP proxy has rewritten it during routing. Under RFC 3261, the To header is generally not modified by proxies, while the Request-Line is commonly rewritten for routing purposes.
When should I use Request-Line as the callee source?
Use Request-Line as the VOS3000 callee source when the Request-URI contains the actual dialed number you need for routing, and there is no intermediate SIP proxy that modifies it. This is common in simple point-to-point SIP trunk configurations where the gateway sends INVITEs directly to VOS3000 without proxy intervention. If the Request-Line contains a different value than the To header due to proxy rewriting, you should typically use the To header instead to extract the original dialed number.
How do I know if my SIP proxy is rewriting the Request-Line?
You can determine whether your SIP proxy is rewriting the Request-Line by capturing SIP traffic using tcpdump or Wireshark and comparing the To header and Request-Line values in incoming INVITE messages. If they differ, a proxy is modifying the Request-Line. You can also check VOS3000 CDRs — if the CDR callee number shows unexpected prefixes or internal URIs, the Request-Line may contain modified values that are not suitable for routing or billing.
Does callee source affect the CDR called number field?
Yes, the VOS3000 callee source header selection directly determines what value appears in the CDR called number field. If To is selected, the CDR records the number from the To header. If Request-Line is selected, the CDR records the number from the Request-URI. Changing the callee source configuration can therefore change your CDR data, which affects billing reports, traffic analysis, and dispute resolution records. Always verify that the CDR called number matches the actual dialed number after changing this setting.
What happens if both To and Request-Line contain the same value?
If the To header and Request-Line contain the same value, the VOS3000 callee source header selection does not matter — either source will extract the same destination number. This is the case for direct gateway connections without intermediate SIP proxies. In such deployments, you can safely use either setting. However, it is still good practice to select “To” as the default because it is more stable and less likely to be modified by future network changes.
Can callee source and caller source be configured independently?
Yes, VOS3000 callee source header selection and caller source header selection are configured independently per mapping gateway. You can set the callee source to “To” while setting the caller source to “Remote-Party-ID”, or any other combination that matches your carrier’s SIP header conventions. This flexibility allows you to optimize CLI and DN extraction independently based on how each identity is delivered in your specific SIP trunk configuration.
Professional VOS3000 Gateway Configuration Support
Correct VOS3000 callee source header selection ensures that dialed numbers are extracted accurately for routing, billing, and CDR recording. Misconfigured callee source settings cause routing failures and billing discrepancies that are difficult to diagnose without understanding the SIP header structure.
Contact us on WhatsApp: +8801911119966
Our VOS3000 experts can analyze your SIP traffic, identify the correct callee source for each trunk, and configure your mapping gateways for optimal accuracy. Reach out today at +8801911119966 and eliminate routing failures caused by incorrect dialed-number extraction.
📞 Need Professional VOS3000 Setup Support?
For professional VOS3000 installations and deployment, VOS3000 Server Rental Solution:
📱 WhatsApp: +8801911119966
🌐 Website: www.vos3000.com
🌐 Blog: multahost.com/blog
📥 Downloads: VOS3000 Downloads
 | | |
