Two types of SIP network servers exist: proxy servers and redirect servers. Functional examples of these servers are provided in the section "Basic Operation of SIP," later in this chapter.
• Proxy server—Acts on behalf of other clients and contains both client and server functions. A proxy server interprets and can rewrite request headers before passing them on to other servers. Rewriting the headers identifies the proxy as the initiator of the request and ensures that replies follow the same path back to the proxy instead of the client.
• Redirect server—Accepts SIP requests and sends a redirect response back to the client containing the address of the next server. Redirect servers do not accept calls, nor do they process or forward SIP requests.
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