Cloud Computing: Business Trends and Technologies by Faynberg Igor & Lu Hui-Lan & Skuler Dor

Author:Faynberg, Igor & Lu, Hui-Lan & Skuler, Dor [Faynberg, Igor]
Language: eng
Format: azw3
ISBN: 9781118736142
Publisher: Wiley
Published: 2015-11-08T16:00:00+00:00

Figure 5.30 Different NATs for different paths.

Consequently, a process on a host within a given network may have different reflexive addresses depending on which TURN server it obtained them from.

Now we are ready to describe one definitive mechanism that uses STUN and TURN for NAT traversal. The name of this mechanism is Interactive Connectivity Establishment (ICE). It is by no means universal in that it applies only to a set of so-called offer/answer protocols, which allow two processes to arrive at a common view of a multimedia session using the SDP protocol. SIP is one such protocol, and it serves as the original inspiration for defining the common features of the offer/answer family. For the purposes of this book, we can assume that the protocol in question is indeed SIP.

ICE is defined in RFC 5245.84 The ultimate objective of ICE is to find two transport addresses best suited for establishing an RTP/RTCP session between two peers. With that, the peers are assumed to communicate between themselves through SIP, which knows how to traverse NAT. (Of course, the transport addresses used for this signaling are likely to be different from those best suitable for carrying the media stream over UDP.) These transport addresses are exchanged through SDP. ICE achieves this objective by accumulating the transport addresses, testing them for connectivity, and selecting the best-performing ones.

Altogether there are three types of addresses, as shown in Figure 5.31:

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