Proxying Session Initiation Protocol (SIP) communications in a load balancing device. An outgoing SIP message is received from a session border controller device. The received outgoing SIP message comprises a routing control parameter in the form of a Uniform Resource Identifier (URI). The received outgoing message comprises one or more additional outgoing routing control parameters different to the URI. The one or more additional outgoing routing control parameters have been originated at the session border controller device to control one or more outgoing routing characteristics at the load balancing device. The one or more additional outgoing routing control parameters are extracted from the received outgoing SIP message. The outgoing SIP message is forwarded to a peer device using the one or more outgoing routing characteristics on the basis of the one or more extracted outgoing routing control parameters.