Nokia 7705 SAR - 3.2.18.3 PTM Bonding

7705 SAR Interfaces
154
Interface Configuration Guide
3HE 11011 AAAC TQZZA Edition: 01
ATM bonding acts as an alternative to IMA as a method of logically combining
multiple lines transmitting ATM cells. ATM bonding differs from IMA in the following
ways:
• ATM links can run at different rates
• differential delay does not need to be constant, but should be controlled to
minimize buffering requirements
• the traffic header of transported ATM cells is modified to carry a sequence ID
• traffic is distributed to the links at the discretion of the transmitter, rather than
strict round-robin order
The 8-port xDSL module and the xDSL interface of the 6-port DSL Combination
module support 2-pair ATM bonding for ADSL2 and ADSL2+. When operating in
ATM bonded mode, the remaining 6 pairs on the 8-port xDSL module cannot be
used. Additionally, the only protocol stack supported is Ethernet over ATM with RFC
2684 LLC/SNAP bridged ATM packets. In ATM bonded mode, cell scrambling is
always enabled and ATM CLP is disregarded (it is not set or inspected for priority loss
indications). Any packet priority marking must be done at the Ethernet, MPLS, or IP
layers.
In ATM channel-bonding schemes, the end-user packets are split into 53-byte cells.
Each cell is tagged with a sequence ID by replacing bits in the ATM header with
sequence ID (SID) bits between bonding entities. The ATM bonding implementation
on the 7705 SAR-M currently only supports a 12-bit SID, although G.998.1 specifies
support for either an 8-bit or 12-bit SID bound by the aggregate rate, differential
delay, and number of links.
For ATM bonding, all bridged PDUs are sent without an FCS field. However, if an
attached DSLAM does send bridged PDUs with an FCS field attached, the FCS is
honored and is not removed or regenerated.
3.2.18.3 PTM Bonding
PTM bonding is specified by ITU-T G.998.2 and is supported on VDSL2, ADSL2, and
ADSL2+ interfaces on the 6-port DSL Combination module and 8-port xDSL module,
and on SHDSL on the 6-port DSL Combination module. The 7705 SAR-Wx variants
that support Ethernet and xDSL provide 4-pair xDSL PTM bonding (ADSL2+ or
VDSL2) on the RJ-45 xDSL port.