One of the new features of 
is the backup feature. System version 3.2.0.0 (or higher) is recommended.
1. General
Backup means that establishes automatically a fail over line when the main line loses framing. Furthermore while fail over line is active still the main line is watched. switches automatically back to main line when it reaches framing state.
In backup mode runs two sub codecs whereas the first sub codec is responsible for the main line and the last sub codec (usually sub codec 2) is responsible for the fail over line.
Since backup feature runs two sub codecs it is similar to the gateway feature. However, the main difference is that at backup the last sub codec is active when the first sub codec is not(!) framed whereas at gateway feature the last sub codec is active when the first sub codec is framed.
X.21 satellite line with ISDN fail over
In the diagram above an X.21 satellite transmission using MPEG L2 with a bit rate of 256 kbps is backuped with an ISDN connection using AAC (MPEG 4) with a bit rate of 128 kbps. Since AAC (MPEG 4) is a much more efficient coding algorithm than MPEG L2 both main line and fail over line reaches nearly transparent quality.
2. Parameters to set
For Backup mode two parameters must be set:
2.1 Backup time
The backup time determines in ms how long the main line must be unframed since it is switched to the fail over line. Furthermore the backup time is also the fallback time from backup connection to main connection.
2.2 Backup connection
The backup connection can be:
| • | The last connection |
or
| • | A phone book entry (recommended) |
Note:
To prevent that any little framing toggle causes a switching to the backup line, it is recommendable to set the backup time to minimum 2,000 ms. This guarantees a stable backup behaviour.
Note 2:
When in the backup scenario a X.21/V.35 transmission is involved then the minimum backup time must be 3,000 ms.
3. Restrictions
Theoretically any kind of transmission can be backuped with any other kind of transmission. However, there are a few restrictions:
| • | If the backup line uses IP then IP/RTP must be used |
| • | X.21/V.35 connections cannot be backuped with another X.21/V.35 connection |
| • | Backup mode cannot be used if gateway mode, dual codec mode or point to multipoint (PMP) is active |
4. Considerations
In the following considerations it assumed that the backup line uses sub codec 2 (which is the case for CENTAURI II 300x; CENTAURI II 330x, MERKII and GANYMED 1102).
4.1 Last ISDN B-channels
Since there is no special parameter to determine which B-channels are assigned to sub codec 1 (main line) and sub codec 2 (backup line) in backup mode the last available B-channels are automatically assigned to sub codec 2. This means:
| • | At ISDN backup phone book entries the last ISDN numbers must be used e.g. with a CIM40 ISDN card and a bit rate of 128 kbps the numbers must be assigned to #8 and #7. |
| • | At a backup scenario using ISDN for fail over the ISDN cables must be connected to the last S0 ports e.g. at a CIM40 ISDN card and a bit rate of 128 kbps the ISDN cable must be connected to S04. |
4.2 Different IP ports at the sub codecs
At RTP different sub codecs use different RTP ports (see also chapter Necessary settings for framed connections/How to establish IP connections/IP Ports). This means that e.g. sub codec 2 uses port 5014 and 5015 by default (provided system software version >= 3.2.0.30).
However, when the backup connection should be established to sub codec 1 of another Mayah codec then the ports 5004 and 5005 must be used. Therefore at the backup phone book entry the IP address must be look like this:
<IP-address of other side codec>:5004
e.g. 88.217.252.72:5004
5. Useful hints
5.1 Independent testing of main line and backup line
It is strongly recommended to test independently the main line connection and the backup line connection i.e. test of both connections with inactive backup mode. However, the notes of item 3 and 4 should be considered.
5.2 Backup mode on both Mayah codecs
When backup line is established between the same two Mayah codecs which are responsible for the main line then even on the none establishing Mayah codec the backup mode should be switched on. The used backup phone book entry should be identical to the one of the establishing Mayah codec but with two changes:
| • | backup time should be about 1,000 ms less |
| • | no numbers or IP addresses in the backup phone book entry |
6. Configuration
The backup mode can be configured via menu item Settings/Others.
7. Looking of Remote main window
When backup mode is active the selected sub codec is also displayed in the main window. It can be switched between the sub codecs with the short cut key combinations <STRG><1> (sub codec 1) and <STRG><2> (sub codec 2).
