Nokia 7705 SAR - 3.2.3.1 SLARP; 3.2.4 Inverse Multiplexing Over ATM (IMA)

7705 SAR Interfaces
76
Interface Configuration Guide
3HE 11011 AAAC TQZZA Edition: 01
3.2.3.1 SLARP
The 7705 SAR supports only the SLARP keepalive protocol.
For the SLARP keepalive protocol, each system sends the other a keepalive packet
at a user configurable interval. The default interval is 10 seconds. Both systems must
use the same interval to ensure reliable operation. Each system assigns sequence
numbers to the keepalive packets it sends, starting with zero, independent of the
other system. These sequence numbers are included in the keepalive packets sent
to the other system. Also included in each keepalive packet is the sequence number
of the last keepalive packet received from the other system, as assigned by the other
system. This number is called the returned sequence number. Each system keeps
track of the last returned sequence number it has received. Immediately before
sending a keepalive packet, the system compares the sequence number of the
packet it is about to send with the returned sequence number in the last keepalive
packet it has received. If the two differ by 3 or more, it considers the line to have
failed, and will not route higher-level data across it until an acceptable keepalive
response is received.
3.2.4 Inverse Multiplexing Over ATM (IMA)
IMA is a cell-based protocol where an ATM cell stream is inverse-multiplexed and
demultiplexed in a cyclical fashion among ATM-supporting channels to form a higher
bandwidth logical link. This logical link is called an IMA group. By grouping channels
into an IMA group, customers gain bandwidth management capability at in-between
rates (for example, between DS1 and DS3 or between E1 and E3) through the
addition or removal of channels to or from the IMA group. The 7705 SAR supports
the IMA protocol as specified by the Inverse Multiplexing for ATM (IMA) Specification
version 1.1.
In the ingress direction, traffic coming over multiple ATM channels configured as part
of a single IMA group is converted into a single ATM stream and passed for further
processing to the ATM layer, where service-related functions (for example, Layer 2
traffic management or feeding into a pseudowire) are applied. In the egress direction,
a single ATM stream (after service functions are applied) is distributed over all paths
that are part of an IMA group after ATM layer processing takes place.
An IMA group interface compensates for differential delay and allows for only a
minimal cell delay variation. The maximum differential delay supported for IMA is
75 ms on 16-port T1/E1 ASAP Adapter cards and 32-port T1/E1 ASAP Adapter cards
and 50 ms on 2-port OC3/STM1 Channelized Adapter cards.