
150
Agere Systems Inc.
Data Sheet
May 2001
and Packet Payload Engine
Ambassador T8110 PCI-Based H.100/H.110 Switch
14
Connection Control—Standard and Virtual Channel
(continued)
14.2.2.3.1 Subrate Switching Overview
Traditional byte-oriented TDM data switching provides 8 bits of data per time slot, or channel, regardless of the
TDM stream bit rate. A particular channel occurs once every 8 kHz frame, and there are 8K
frames per second.
This allows for a channel data propagation rate of (8 bits/frame * 8K frames/s = 64 Kbits/s).
Refer to Figure 50 and Table 113.
Figure 50. TDM Data Stream Bit Rates
Subrate refers to switching fractional portions of the byte-oriented TDM data streams. The T8110 allows the 8 bits
of a byte-oriented channel to be broken into multiple channels of fewer bits, either two 4-bit channels, four 2-bit
channels, or eight 1-bit channels. This lowers the data propagation rate per channel, but increases the overall
channel capacity for a given time-slot. Refer to Table 112 and Table 113.
Notes:
Bit subrate = 8 channels per time slot, 1 bit per channel.
Di-bit = 4 channels per time slot, 2 bits per channel.
Nibble subrate = 2 channels per time slot, 4 bits per channel.
Byte (no subrate) = 1 channel per time slot, 8 bits per channel.
.
Table 112. TDM Data Stream
Bit
7
6
5
4
3
2
1
0
Di-Bit
7:6
5:4
3:2
1:0
Nibble
Byte
7:4
3:0
7:0
0
1
2
3
4
5
6
7
0
1
2
3
0
1
124
125
126
127
62
63
31
ONE FRAME (8 KHz)
128 TIME SLOTS (CHANNELS) PER FRAME
TDM STREAM BIT RATE = 4 MBITS/S: EACH STREAM HAS
64 TIME SLOTS (CHANNELS) PER FRAME
TDM STREAM BIT RATE = 2 MBITS/S: EACH STREAM HAS
32 TIME SLOTS (CHANNELS) PER FRAME
EACH CHANNEL CONTAINS ONE 8-BIT
BYTE, REGARDLESS OF THE TDM
DATA STREAM BIT RATE
8 MBITS/S
4 MBITS/S
2 MBITS/S
TDM STREAM BIT RATE = 8 MBITS/S: EACH STREAM HAS
One Time-Slot (or Channel)