Specifications

MP-2100 HS-R Installation and Operation Manual Introduction
Functional Description 1-7
• EXT DCE (DTE1): the interface provides a receive clock signal to the user's
DTE, and accepts the transmit clock from the user's DTE. The user's DTE must
operate with loopback timing; that is, it must transmit at the rate of the receive
clock signal provided by the HS-R channel interface. This timing mode is
suitable for tail-end applications.
Timeslot Assignment
The HS-R module processes the payload data from all the channels in accordance
with the guidelines of ITU-T Rec. I.460. It then organizes the payload data for
transmission in the main link timeslots of the Megaplex, to achieve optimal packing
of data.
Data in the main link timeslots is formatted in 8-bit groups (octets). In accordance
with ITU-T Rec. I.460, channels carrying data rates lower than the B-channel rate
can be assigned 2, 4, or 8 bits in each octet. When necessary, rate adaptation is
performed to convert the data rate at which the users' DTE actually operates to the
rate corresponding to the number of bits that can be assigned in a main link
timeslot octet.
Table 1-1 lists the supported user's terminal data rates, the data rate obtained after
rate adaptation, the number of B-channel octet bits assigned by the HS-R module
to carry the channel payload data, and the corresponding fraction of main link
timeslots for each data rate.
Table 1-1 Utilization of Main Link Timeslots
User’s DTE Rate After Rate
Adaptation
Number of Bits
0.6 through 9.6 kbps 16 kbps 2 (¼ timeslot)
19.2 kbps 32 kbps 4 (½ timeslot)
38.4, 48, 56, and 64 kbps 64 kbps 8 (1 timeslot)
As shown in Table 1-1, the HS-R module uses minimum allocations of two bits
(16 kbps). The HS-R module can automatically multiplex the data rates obtained
after optimal adaptation, to fill the standard main link bandwidth allocation unit,
one timeslot (64 kbps). For example:
• When two channels operate at rates that require two bits (i.e., up to a
maximum 9.6 kbps per channel), the main link bandwidth allocated to the two
channels is ½ timeslot.
• When all four channels operate at rates up to a maximum 9.6 kbps per
channel, the main link bandwidth allocated to the four channels would be one
timeslot.
• When two channels operate at 9.6 kbps, one channel at 19.2 kbps, and one
channel at 56 kbps, the main link bandwidth allocated to the first two channels
would be ½ timeslot, another ½ timeslot for the third channel, and one