3Com MSR 50 Series Configuration Manual page 301

Configuring X.25 301
vc-number). Different calls will be distributed on various lines in hunt group to
implement load sharing.
Note that X.25 hunt group selects different transmission lines only during VC call
establishment. Once the whole VC completes the establishment and enters data
transfer phase, X.25 hunt group will not function any longer and data transfer will
be processed based on the normal VC. Since PVC is in data transfer phase after
establishment and experiences no call establishment and call clearing processes,
X.25 load sharing can function only on SVC, and not on PVC.
In an X.25 hunt group, the position of all DTEs is identical, and they have the same
X.121 address. DTEs inside hunt group can call other DTEs outside hunt group
according to the normal mode. When accessing hunt group, the devices outside
hunt group can not know which device they are accessing, and the line selection is
controlled by the DCE configured with hunt group.
The DTE address in hunt group can either be the same as the hunt group address,
or different from that. X.25 hunt group supports the substitution between the
source address and the destination address. You can use the destination address
substitution function to hide the DTE address inside hunt group, and the DTE
outside hunt group only knows the hunt group address, to strengthen the
network security inside hunt group. You can use the source address substitution
function to hide the DTE address outside hunt group, because the DTE inside hunt
group cannot know the source address of a call connection but the substituted
address, thus protecting users' privacy.
Figure 63 X.25 network load sharing
HG 1
8888
Terminal A
9999
Server A
X.25 packet
switching
network
Router A
Terminal B
9999
Server B
Terminal C
As shown in the above figure, server A and server B, which be configured with a
hunt group HG 1, provide users with the same service. Server A and server B
addresses are 9999, and the hunt group address is 8888. Enabling the destination
address substitution function on Router A means that the address 8888 is replaced
by the address 9999. When a user transacts a service, the user terminal will send a
call to the destination address 8888. Such calls from any terminal are directed
towards the address 9999, which is transmitted to server A or server B via Router
A. The load sharing between server A and server B is implemented to lower the
pressure on a single server.