The IEEE's initial attempt at wireless LAN security was Wired Equivalent Privacy. This turned out to be a quite unfortunate moniker, as WEP was quickly shown to provide very little of the privacy it advertised.
802.11i improves on WEP by using completely new encryption algorithms and key-derivation techniques. This wireless security standard, finalized in 2004, makes it possible to safeguard over-the-air communications at Layer 2.
A key called the Pairwise Master Key (PMK) is established between the wireless station and the access point. This key is typically generated using 802.1X, which is authentication of the user to a RADIUS or other authentication server using Extensible Authentication Protocol. Both the station and RADIUS server derive identical keys, and the RADIUS server returns that key to the access point.
Next, the station and access point exchange a sequence of four messages, called the "four-way handshake." In this exchange, the PMK and freshly generated rando…
DTMF tones are the tones that are generated when a telephone key is pressed on a touchtone phone. Sometimes the called endpoint needs to hear those tones, such as when you enter digits during the call in response to a menu. Low-bandwidth codecs can distort the sound, however. DTMF relay allows that tone information to be reliably passed from one endpoint to the other. By default, SIP uses in-band signaling, sending the DTMF information in the voice stream. However, you can configure it to use RTP-NTE, SIP INFO messages, SIP NOTIFY messages, or KPML for transmitting DTMF tone information.
RTP-NTE is an in-band DTMF relay method, which uses RTP Named Telephony Event (NTE) packets to carry DTMF information instead of voice. If RTP-NTE is configured, SDP is used to negotiate the payload type value for NTE packets and the events that will be sent using NTE.
RTP-NTE can cause problems communicating with SCCP phones, which use only out-of-band DTMF relay. In a CallManager 4.x network with SCCP…