ces that Cisco UCM controls are Cisco IP Phones that contain an operating system and respond to control messages in the format of SCCP packets, often called Skinny Packets, or respond to SIP packets when they run a version of code that contains a SIP User Agent. Call Control is considered the heart of any IP Telephony system because all signaling passes through the call control element, and calls fail if the central call control element does not completely understand the context and content of all messages. Other Physical Components of IP Telephony Some of the other physical components of an IP Telephony solution include LAN cabling and WAN connectivity. In today's modern solutions, the LAN connectivity is most often provided by a 10/100/1000 auto-sensing LAN Ethernet switch. Following are two items often deployed in Ethernet switches used for IP Telephony: Gigabit Ethernet (GigE) connectivity Power of Ethernet (PoE) GigE is deployed in less than 10 percent of the total number of physical Ethernet ports (as of late 2009), but most newly deployed Ethernet ports use Gigabit because of the low cost. PoE supplies electrical power to IP Telephony endpoints such as IP Phones and is a great solution because one cable provides power and a connection to the network, result- ing in fewer cables for the same number of IP devices. However, sending PoE cables is one of the definite determinations of the length of cable supported. PoE cables cannot generally extend past 1500 meters. 6 SIP Trunking IP Phones IP Phones vary widely in IP Telephony deployments from very basic phones that replicate the capability of POTS phones to complex phones that are closer to personal computing devices. The basic components of all IP Phones include a speaker, microphone, user agent, and DSP. IP-PBX An IP Public Branch Exchange (PBX) is the primarly call control agent for most IP Telephony deployments. Ethernet Switches An often overlooked component of IP Telephony is the Ethernet switches that connect all of the end devices together and provid