Cisco uses RTP payload types from the values specified as dynamic and unassigned by RFC 3551 for signaling and also for designating RTP packets with certain types of data. This table is useful when you see unknown RTP payload types in a packet captur...

Fax passthrough is the transportation of fax communications over an IP network using a low compression codec like G.711. Fax passthrough occurs using one of two methods on Cisco voice gateways, NSE-based passthrough or protocol-based pass-through. Th...

Here is a listing of the basic T.30 message timers for G3 faxing. These  timers are used in error recovery and to make sure that the fax transaction  never gets stuck in a hung state. In calling scenarios involving international  connections or satel...

Fax machines may be capable of a few different modulations, and within each  of these modulations there are different speeds. Here are the common modulations  that are used in G3 fax calls.Common Modulations Used in G3 Fax CallsITU Standard Speeds (b...

Cisco utilizes proprietary NSEs or Named Signaling Events to handle  switchovers for a variety of different transport methods, especially for FoIP.  NSE messages are sent inband using an existing voice RTP stream. All NSE packets  use an RTP payload ...