Robert J. Sparks. The Session Initiation Protocol (SIP) Refer Method. RFC, 3515:1-23, April 2003. [doi]
@article{rfc3515, title = {The Session Initiation Protocol (SIP) Refer Method}, author = {Robert J. Sparks}, year = {2003}, month = {April}, doi = {10.17487/RFC3515}, url = {https://doi.org/10.17487/RFC3515}, researchr = {https://researchr.org/publication/rfc3515}, cites = {0}, citedby = {0}, journal = {RFC}, volume = {3515}, pages = {1-23}, }