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Chapter 1
Overview
Interface Specifications
Figure 1-3
Time Slot Diagram
2,048 Mbps
32 time slots = 256 bits
64 kbps
8 bits
Time slot
0
1
2
3
28
29 30 31
Each of the 32 time slots is an 8-bit frame that transmits data at 64 kbps. Each of these time slots can be
configured to carry data or to remain empty. (The PA-4E1G inserts an idle pattern into empty time slots.)
Time slot 0, or the first 8 bits, is reserved as overhead. The remaining 248 bits (31 frames with 8 bits
each) are designated time slots 1 through 31. Time slot 16 is also designated as a framing slot when using
framed mode. When you use framed mode (G.704), you can configure time slot 16 to carry data and
operate as any of the other slots; therefore, in framed mode time slot 0 must be designated as a framing
signal; time slot 16 can be configured for either data or framing.
With framed mode (G.704) you can specify a bandwidth for the interface by designating 31 of the time
slots for data and reserving time slot 0 for framing (timing). When you use framed mode, you must
designate start and stop time slots; the slots within the start and stop boundaries are used for data, and
the remaining slots are left idle. For example, on an interface with framing set on time slots 1 through
8, the interface carries data within the specified 8 frames, and frames 9 through 31 remain idle. Because
each time slot transmits at 64 kbps, the interface operates at 512 kbps (8 frames x 64 kbps = 512 kbps).
By configuring 16 of the time slots to carry data and the other 16 to remain empty, you can essentially
configure the interface for 1.024 Mbps (by leaving half the time slots empty and unable to carry data).
The system inserts an idle pattern into unused time slots to identify them as overhead (unused for data).
Only one contiguous time slot range can be used. In Private Automatic Branch Exchange (PABX)
systems, time slot 16 is always left unused. By default, time slot 16 is not enabled for data in the
PA-4E1G interface. The command ts16 overrides the default and enables time slot 16 to carry data.
Unframed mode (G.703) uses all 32 time slots for data. None of the 32 time slots are used for framing
signals. This allows each of the 32 time slots to transmit at 64 kbps; therefore, 32 time slots x 64 kbps =
2.048 Mbps. While unframed mode is the default, you can also specify unframed mode with the
command timeslot 0-0, which specifies time slot 0 as the start slot with no stop (ending) time slot;
therefore, all slots are used for data. The no timeslot command restores the default of unframed mode.
Framed mode supports a 4-bit cyclic redundancy check (CRC4), which you enable with a software
command. The default is for no CRC.
Note
The E1-G.703/G.704 interface on PA-4E1G is compliant with BABT 221.
For more information about CRC4 with a PA-4E1G on a VIP, Cisco 7100 series router, Cisco 7200 series
router, or Cisco uBR7200 series router, refer to
Chapter 4, "Configuring the PA-4E1G."
PA-4E1G Serial Port Adapter Installation and Configuration
1-3
OL-3065-05
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