2. MODEM CONFIGURATION
To configure a modem, there are five major components to be configured in it. They are,
- Framing
- Clock Source
- Mapping of timeslot
- Speed
- Timeslot start position
2.1 Framing
There are 2 modes of framing available to configure the modem. They are,
- Framed
- Unframed
2.1.1 Framed
When the modem is set to FRAMED, the user can select the required time slots and the speed. You can get a maximum of 1984 Kbps because; only 30x64 Kbps channels will be used for data transfer. Rest of 128 kbps will be used for signaling.
2.1.2 Unframed
When the modem is set to UNFRAMED, all the 32x64 Kbps channels are used for transmitting and receiving data. Hence you will get the entire 2.048 Mbps
2.2 Clock Source
Clock is a reference signal to synchronize both ends of a leased line. There are three ways to provide clock to a leased circuit. They are,
1. Generating the clock internal to the DCE and sending it to DTE.
2. Getting clock from the service provider equipment.
3. Both ends of the Leased line will synchronies with an external clock such as atomic clock.
Getting clock from the service provider equipment is the most preferred way of getting clock source. Based on the above, there are three types of settings. They are,
- Internal
- Line
- External
If a modem is set to Internal clock, it will produce the clock signals and will send it to the DTE.
If it is set to Line, the DCE equipment will receive the clock from the service provider end.
If it is set to External, the DCE equipment will receive the clock either from Service provider equipment or from an external clock source like atomic clocks.
2.3 Mapping of timeslot
When a modem is set to frame, it is required that the time slots need to be configured as per the required bandwidth. Bandwidth of each time slot is 64 Kbps. So if 256 Kbps of bandwidth is required, then you need to select 4 time slots.
Important thing to remember here is, if your selecting certain time slots, the same time slot has to be set in all the modems in the circuit.
For example, you are selecting TS1 to TS3 and TS5 for a 256 Kbps circuit, and then the same time slots have to be selected in all the modems in that circuit.
For selecting the time slot, there are two methods available. They are,
1. USER
2. SEQ
If User option is selected, the engineer who configures the modem has to select the time slots manually.
If SEQ option (short for sequential) is selected, then the sequence of time slots will be assigned starting from the time slot selected by the user.
2.4 Speed
Speed is the bandwidth requirement of the user. Starting from 64 Kbps to 2048 Kbps can be configured.
If a modem is set to unframe, then all the time slots of the circuit will be used. So, you will get a bandwidth of 2048 Kbps.
If it is set to Framed, the maximum bandwidth it can scale is based on the number of time slots selected. It can be a maximum of 1984 Kbps.
2.5 Timeslot start position
Time slot start position is a configuration, which tell the user from which time slot, the modem has to take for bandwidth calculations. This option is available only for frame option.
