Alcatel-Lucent 7750 SR OS Interface Configuration Manual page 60

Ports
SLARP
An Alcatel-Lucent cHDLC interface will transmit a SLARP address resolution reply packet in
response to a received SLARP address resolution request packet from peers. An Alcatel-Lucent
cHDLC interface will not transmit SLARP address resolution request packets.
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, it
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.
There is interaction between the SLARP address resolution protocol and the SLARP keepalive
protocol. When one end of a serial line receives a SLARP address resolution request packet, it
assumes that the other end has restarted its serial interface and resets its keepalive sequence
numbers. In addition to responding to the address resolution request, it will act as if the other end
had sent it a keepalive packet with a sequence number of zero, and a returned sequence number the
same as the returned sequence number of the last real keepalive packet it received from the other
end.
SONET/SDH Scrambling and C2-Byte
SONET/SDH scrambling and overhead for cHDLC follow the same rules used for POS (RFC
2615, PPP over SONET/SDH).
The two key SONET/SDH parameters are scrambling and signal-label (C2-byte). Scrambling is
off by default. The default value of the C2-byte is 0xCF. These two parameters can be modified
using the CLI. The other SONET overhead values (for example, j0) follow the same rules as the
current POS implementation.
Page 60 7750 SR OS Interface Configuration Guide