2.
[ S N O M 4 S N A T F I L T E R ]
a=rtpmap:0 pcmu/8000 a=rtpmap:8 pcma/8000 a=rtpmap:3 gsm/8000 a=rtpmap:18 g729/8000 a=rtpmap:2
a=sendrecv a=silenceSupp:off - - - -
The NAT Filter changes the private address to a globally routable address and inserts the local port. It also inserts a hint that tells the other user agent that it should not do silence suppression. This reduces the risk that the connection is closed during a talk spurt of one of the parties.
2.4 Scaling and Redundancy
The NAT Filter product was designed to support distributed server farms. That means that the servers act stateless in principle; user agents may randomly pick a server in a server farm. This feature allows opera- tors to set up very large and robust networks.
Table 1: NAT conbimations
To/From | Public IP | Full Cone | Restricted | Symmetrical |
|
| NAT | NAT | NAT |
Public IP | Always | When | When STUN | When STUN |
|
| STUN | and ICE are | and ICE are |
|
| support is | available | available |
|
| available |
|
|
Full Cone NAT |
| When | When STUN | When STUN |
|
| STUN is | and ICE are | and ICE are |
|
| available | available | available |
Restricted |
|
| When STUN | When STUN |
NAT |
|
| and ICE are | and ICE are |
|
|
| available | available |
|
|
|
| and no port |
|
|
|
| checking |
Symmetrical |
|
|
| Needs filter |
NAT |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
18 • Architecture
