Nortel Networks 8000 - Manual (Page 210)

Nortel Secure Router 8000 Series
Configuration -WAN Access 7 LAPB and X.25 configuration
• After being set up, PVC continues in the stage of data transmission without the process
of call establishment and call deletion. Therefore, X.25 load balancing is ineffective on
PVC and functions only on SVC.
Within a single X.25 hunt group, all DTEs hold the identical status and share the same X.121
addresses. The DTEs in a hunt group can call other DTEs outside the hunt group in the
normal mode. When devices outside the hunt group access the hunt group, they cannot learn
which equipment they access as the line selection is controlled by the DCEs configured with
the hunt group.
DTE addresses in a hunt group may be identical with or different from the hunt group
addresses.
X.25 hunt group supports:
• Substitution of source address: It hides the addresses of DTEs outside a hunt group.
Therefore, internal DTEs can learn only the substituted source address, instead of
learning the source address to which a call is connected. This protects the privacy of the
subscribers.
• Substitution of destination address: It hides the addresses of DTEs inside the hunt group.
Therefore, external DTEs learn only the hunt group address, which enforces the security
of the internal network of the hunt group.
Figure 7-5 Diagram of X.25 network load balancing
As shown in Figure 7-5:
• Server A and Server B concurrently provide identical services to the subscribers. The
servers are configured as a hunt group named "hg1".
• Server A and Server B have the same address of 9999 and the hunt group address is
8888.
• Enable the function of substituting the destination address on Router A for changing calls
connected to address 8888 to calls connected to address 9999.
• When a subscriber processes a service, the subscriber terminal sends a call to the
destination address 8888. The calls from various terminals are substituted on Router A
with the calls to 9999, and are transmitted to Server A and Server B respectively. Thus,
load balancing is realized between Server A and Server B, and the pressure on a single
server is decreased.
X.25 hunt group supports two types of call channel selection policies: round-robin mode and
VC-number mode, but a hunt group can only utilize one type of channel selection policy.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 7-7