4 x.25 switching function, 5 x.25 load balancing, 4 x.25 switching function -6 – Nortel Networks 8000 User Manual
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7 LAPB and X.25 configuration
Nortel Secure Router 8000 Series
Configuration -WAN Access
7.1.4 X.25 switching function
The SR8000 also performs X.25 switching function, serving as a small-sized X.25 packet
switch to save the user’s investment in X.25. Figure 7-4 shows the interrelationship between
LAPB, X.25, and X.25 switching.
Figure 7-4 Interrelationship between LAPB, X.25 and X.25 switching
Internet Protocol
X.25
Switching
X.25
LAPB
X.25 and IP ( two directly connected routers without through X.25 network) can run over
LAPB.
The system contains a X.25 switch module that enables the router to function as a small-sized
packet switch and forward the packet directly instead of routing it through the upper layer.
In X.25 network, the router functions as DTE or DCE. If you adopt the X.25 switch function
the router functions as PSE.
7.1.5 X.25 load balancing
Using the hunt group property of the X.25 protocol, ISPs can provide load balancing function
on X.25 packet switching networks. X.25 load balancing can implement the load balancing in
different DTEs or different links of a single DTE, which guarantees no occurrence of link
overload when an address is accessed by a large number of subscribers.
DCEs provide X.25 load balancing. To implement the load balancing on X.25 networks, you
need the following:
•
A group of DTE or DCE interfaces (synchronous serial interfaces or XOT Tunnels) need
to be configured at the remote DCE on the network as a hunt group. It is necessary to
allocate an X.121 address to such a hunt group.
•
When the 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 selects a line in the hunt group,
according to diverse channel selection policies (round-robin or VC-number), and sends
the incoming call packets.
•
Different calls are allocated to the lines in the hunt group, thus achieving load balancing.
Note the following points:
•
The X.25 hunt group can dynamically select di^erent transmission lines only in the
process of the establishment of VC call. Once the whole VC is set up and enters the stage
of data transmission, the hunt group becomes ineffective and data transmission is
processed according to the normal VC.
7-6
Nortel Networks Inc.
Issue 5.3 (30 March 2009)