de and decode the real-time signals. The benefits of a dedicated DSP for media processing are that the real-time encoding of the media streams do not have to compete against other processes for the resources, and as such, less jitter occurs in the signaling. The benefits of sharing the host processor are that the costs of the capability can be spread across the larger centralized components. Most HMP-based systems are either larger room-dedicated systems that utilize the central CPU as a replacement for the DSP, or much more commonly, HMP is used for software-based IP Telephony clients. Table 1-1 lists the strengths and weaknesses of DSPs versus HMPs. The next important component in IP Telephony is the user agent. The user agent is the software application that receives and interprets the signaling messages and determines how the various components of the system should be programmed to process the media. The signaling messages can come in a variety of formats, including MGCP, H.323, XMPP, and SIP. However, the protocol that has the most new features and highest amount of development focus today is SIP. User agents come in many forms according to the SIP standards (RFC-3261); however, they all perform some basic functions. A user agent must receive, interpret, and process SIP messages. As such, it must have, as a basic, minimum connectivity to and IP network and an IP stack. Table 1-1 Strengths and Weaknesses of DSPs Versus HMP for VoIP Call Processing Device Digital Signaling Processors (DSP) Host Media Processors (HMP) Strengths Real-time encoding of audio does not affect Flexible architecture to other processes. support new codecs. Unlimited scalability. High amount of processing Lower heat dissipation. power. Can be optimized for the type of decoding required. Weaknesses Embedded architecture makes implementation of Real-time encoding of new features more difficult. media affects other systems. Fewer programming tools. Cost of deployments is Higher initial costs for development. high. Not as flexible as host-b