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Failure of Routes
Problem — With a single route to a destination point
code (DPC), service can be disrupted if all the links of the
link set used to reach that signaling node fail. Route
failover is a standard MTP3 operation which does not
require any specific action from the user application.
Solution — To eliminate this single point of failure, an
alternative link set can be provided in the SIU520 system
configuration to reach the same DPC. Route failover is a
standard MTP3 operation which does not require any
specific action from the user application.
Note: When an alternative route to a given DPC is
defined in an SIU520 configuration file, a choice must be
made between two different traffic modes: load sharing
or failover. In load-sharing mode, traffic sent towards the
remote signaling point is shared between the two link
sets. In failover mode, all traffic sent towards the remote
signaling point will normally be sent using the primary link
set, unless this link set fails, in which case the traffic will
use the alternative link set. See the Intel NetStructure
SIU520 Developer’s Manual for more information on the
selection of traffic mode in the MTP_ROUTE command.
Details — This example (see Figure 4) shows two link
sets (each containing one link) being used in load-sharing
mode to reach destination point code 0x400.
Building Fault-tolerant SS7 Systems Using the Intel
®
NetStructure™ SIU520 SS7 Signaling Gateway Application Note
5
Figure 4. SIU520 Connected to Mated STP Pair Providing Route Resiliency
SSP/SCP
A) Load sharing between link set 0 and link set 1 under normal
Link Set id 0
Point Code
0x200
Point Code
0x300
Point Code
0x400
Point Code
0x100
SSP/SCP
B) Traffic sent over link set 1 under failure of STP
Point Code
0x400
SIU520
Point Code
0x100
SIU520
STPA
STPB
Point Code
0x300
STPB
Link id 0, slc 0
L
ink id 1, s
lc 0
Link Set id 1
Link Set id 0
Link Set id 1
Link id 0, slc 0
L
ink id 1, slc 0
* MTP_LINKSET <linkset_id> <adjacent_spc> <num_links> <flags> <local_spc> <ssf>
MTP_LINKSET 0 0x200 2 0x0000 0x100 0x08
MTP_LINKSET 1 0x300 2 0x0000 0x100 0x08
* MTP_LINK <link_id> <linkset_id> <link_ref> <slc> <bpos> <blink> <bpos2>
*<stream> <timeslot> <flags>
MTP_LINK 0 0 0 0 0 0 0 0 16 0x0006
MTP_LINK 1 0 1 1 0 1 0 1 16 0x0006
MTP_LINK 2 1 0 0 0 2 0 2 16 0x0006
MTP_LINK 3 1 1 1 0 3 0 3 16 0x0006
* MTP_ROUTE <dpc> <linkset_id> <user_part_mask> <flags> <second_ls> <pc_mask>
MTP_ROUTE 0x400 0 0x0020 0x0003 1 0x00000000