User Manual

ADCP-XX-XXX • November 2000 • Section 3: WMTS Functional Description
Page 3-13
 2000, ADC Telecommunications, Inc.
Ethernet protocol data units. This is then transmitted or received in each interaction prior to requiring
its IP address in the network. During the first connection of the WMU to the network and the CPE, an
entry is made in the address resolution table at the base station. This provides the relationship to the
MAC address and the IP address. The IP address is assigned to the user by the network administrator
when the user is added to the system. In addition to the addresses associated with the system, as
explained above, there are parameters directly associated with the WMU. Some examples are modem
serial number, frequencies of operation and power levels. It is important to keep databases with this
information current for both technical and administrative purposes. Parameters which are not field-
changeable, need to be entered only once. An example of this is the serial number which is set at the
time of manufacture. Other parameters are manually set at the time of installation. Examples of these
parameters are frequencies of operation and power levels. The system automatically negotiates these
parameters based on certain conditions. Finally, there are parameters associated with the user himself.
Examples are name, street; address, phone number, account number and type of transverter, WMU
and computer hardware. All these parameters are accounted during provisioning.
6.4 Channel Acquisition
The modem first scans for the downstream channel (frequency), then obtains QAM lock, and finds the
UCD (Upstream Channel Description) message with the channel characteristics to start upstream
transmission. A WMU may have to search several downstream channels before finding the one with
correct data. Channel acquisition is successful when the WMU decodes MPEG-2 frames in order to
decode the MAC frames (that bear the well known PID). The MAC frames are then passed to the
MAC layer, in the WMU, for processing.
6.5 Ranging
Ranging describes the following three processes that the WMU must accomplish. These include:
* Time reference fine adjustment
* Transmit frequency fine tuning
* Transmit power fine adjustment
Since each WMU in the network, is at a unique distance from the WMTS it contains unique settings
for these parameters. To begin the ranging process, the WMU transmits a ranging request message to
the WMTS during an Initial Maintenance opportunity (as described by the MAP messages), on the
upstream channel. The WMU begins to transmit this message at the starting boundary of the initial
maintenance opportunity, based on its rough time SYNC and its interpretation of the MAP. This
message is sent typically every 10 seconds, until answered. Upon receipt of this message, the WMTS
sends a ranging response message addressed to that WMU. If the WMU does not receive a ranging
response message from the WMTS within a time out period, one of two things may have happened.
First, as the initial maintenance opportunity is available to any WMU just attached to the network,
ranging request messages may collide. Second, the WMU transmit power level may be too low to be
detected by the WMTS. Consequently, if the WMU does not receive a ranging response message, it
increases the transmit power, and waits a random number of initial maintenance opportunities before
sending another ranging request. Initial ranging request is interrupted every 200msec, by a system
time-out. The WMU repeats the ranging request 16 times, each time changing the transmit power and