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Configure X.25 215
which guarantees no occurrence of link overload when an address is accessed by a
large number of subscribers.
X.25 load balancing is provided by DCEs. In order to implement the load balancing
in X.25 networks, a group of DTE/DCE interfaces (synchronous serial interfaces or
XOT Tunnels) need to be configured at the remote DCE on the network as a hunt
group. And it is necessary to allocate an X.121 address to such hunt group. When
other equipment in the network accesses the DTE inside the hunt group, they
need to call the hunt group address. After receiving the call request packets, the
remote DCE will, according to diverse channel selection policies (round-robin or
vc-number), select a line in the hunt group and send the incoming call packets.
Different calls will be allocated to the lines in the hunt group, thus achieving load
balancing.
It should be noted that X.25 hunt group can dynamically select different
transmission lines only in the process of the establishment of virtual circuit call.
Once the whole virtual circuit is established and enters into the stage of data
transmission, hunt group will be ineffective and data transmission will be
processed in accordance with the normal virtual circuit. After being established,
PVC stays at the data transmission stage 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 identical status and have the same
X.121 addresses. The DTEs in a hunt group can call other DTEs outside the hunt
group in a normal mode. When equipment outside the hunt group access the
hunt group, they cannot know which equipment they will access, because the line
selection is controlled by the DCEs configured with hunt group.
DTE addresses in a hunt group may be identical or different to the hunt group
addresses. X.25 hunt group supports the substitutions of source address and
destination address. The function of destination address substitution enables us to
hide the addresses of DTEs inside the hunt group, thus external DTEs only know
the hunt group address, which enforces the security of the internal network of
hunt group. The function of source address substitution can hide the addresses of
DTEs outside a hunt group, therefore internal DTEs can only know the substituted
source address instead of the source address a call is connected to, which protects
subscribers' privacy.