5
During periods of no data transmission, the device, and not the host software driver,
performs idle cell insertion and deletion, thus unloading this task from the host PC and
unburdening the USB bus with unnecessary traffic.
The Convergence Sub layer performs message identification and clock recovery.
Additionally, the CS of the AAL converts the user service information coming from the upper
layer into a protocol data unit (PDU), and also carries out the opposite process at the
receiver.
Unspecified Bit Rate (UBR) service is supported. It allows a connection to be established
without specifying the bandwidth expected from the connection. The network makes no
guarantees for UBR service: it establishes the route but does not commit bandwidth. UBR
can be used for applications that have no delivery constraints and do their own error and flow
control. Examples of potential uses of UBR are e-mail and file transfer, as neither application
has real-time characteristics.
Constant Bit Rate (CBR) service allows a connection to be established with a specified
expected bandwidth. CBR can be used for an application such as video delivery.
ADSL Operating Modes
Full Rate ADSL Modes
Both T1.413 and G.992.1 (G.dmt) line coding schemes are supported for downstream rates
up to 8 Mbps and upstream rates up to 1 Mbps in 32 Kbps increments. User selection of
mode is supported through the provided control panel; however, auto provisioning is
supported so that the appropriate modulation is automatically selected based on what is
supported by the DSL Access Multiplexes (DSLAM) at the Central Office.
When operating in one of the full-rate modes, the low (POTS) and high frequency (ADSL)
bands must be separated with a filter. This can be done with either a service
provider-installed splitter (known as “splittered ADSL”), or with the use of distributed
micro-filters in line with each POTS device on the circuit (known as “splitter less full-rate
ADSL”). Both deployment models are supported.
G.lite Splitter less Mode
G.992.2 (G.lite) splitter less mode is supported for downstream rates up to 1.5 Mbps and
upstream rates up to 512 Kbps in 32 Kbps increments. User selection of mode is supported
through the provided control panel; however, auto-provisioning is supported so that the
appropriate modulation is automatically selected based on what is supported by the DSLAM
at the Central Office.
When operating in splitter less mode, the low and high frequency bands do not need to be
separated with a filter, and neither a service provider. Neither installed splitter, nor distributed
micro-filters are required. G.lite mode supports power management by defining a set of
power management states for the link and the use of the Embedded Operations Channel
(EOC) to coordinate between the ATU-R and ATU-C.
