Mitel 5560 IPT none Specifications download pdf (Page 354)

Engineering Guidelines

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When the data is encrypted, it is simply replaced with a scrambled version. This is a 1 for 1

transformation, so there are no additional bytes. As a result, the bandwidth is the same for

encrypted or non-encrypted information. This is NOT true for Secure RTP (SRTP) which

appends either 4 or 10 bytes to the voice payload depending on the cipher mode used. See

“Voice streaming security (SRTP)” on page 341.

For the signalling information, there are some additional messages related to setting up the

secure connections. However, these are minimal when compared to the remainder of the

signalling bandwidth, which is already quite low. For voice information the bandwidth remains

the same for both encrypted and unencrypted payloads.

As an analogy, the encryption can be considered as simply another voice CODEC or an

additional process in the voice-streaming path. For voice streaming, G.711 and G.729 CODECs

are often used. The encryption merely makes these secure, so the result is a secure-G.711 and

a secure-G.729 CODEC. The bit rate remains the same, as does the network bandwidth

requirements.

Figure 59: Unsecured vs Secured Connection

Signalling and media paths

Media and signalling path encryption is supported for all of Mitel's IP phones on the 3300 ICP.

Media path encryption is accomplished with Secure RTP using 128-bit Advanced Encryption

Standard (AES). Encryption is backwards compatible to support both currently shipping

desktops and previously deployed Mitel IP desktops. Mitel provides encryption of the media

path between multiple 3300 ICPs using the Secure Sockets Layer (SSL) protocol. This allows

scalability of applications by configuring 3300 ICPs into clusters or deploying them as part of

a centrally managed but distributed architecture.

The signalling path is generally between the controller and the IP Phone or other end-device.

This path is established as a secure connection. Signalling information is interpreted within the

controller. Where a message needs to be sent to another controller, such as with IP-Networking,

or to another end device, an independent secure connection is used. Thus a call between two

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Mitel 5560 IPT none Specifications Page 354