3Com MSR 50 Series Configuration Manual page 322

322 C 14: X.25 LAPB C
HAPTER AND ONFIGURATION
# Configure interface Ethernet 1/0.
<RouterB> system-view
[RouterB] interface ethernet 1/0
[RouterB-Ethernet1/0] ip address 196.25.231.1 255.255.255.0
[RouterB-Ethernet1/0] quit
# Configure interface Serial 2/0.
[RouterB] interface serial 2/0
[RouterB-Serial2/0] ip address 192.149.13.2 255.255.255.0
[RouterB-Serial2/0] link-protocol x25
[RouterB-Serial2/0] x25 x121-address 1004358902
[RouterB-Serial2/0] x25 vc-range bi-channel 9 1024
[RouterB-Serial2/0] x25 pvc 4 ip 192.149.13.1 x121-address 100435890
1 broadcast packet-size 512 512 window-size 5 5
[RouterB-Serial2/0] quit
# Enable RIP.
[RouterB] rip
[RouterB-rip-1] network 192.0.0.0
[RouterB-rip-1] network 196.0.0.0
As you go through the above configuration procedure, you may be probably
puzzled due to different PVC numbers (that is, 3 and 4 in this scenario) on Router
A and Router B. You should distinguish between "VC" and "logic-channel".
Virtual circuit refers to the end-to-end logic link between the calling DTE and the
called DTE, while logic channel refers to the logic link between two directly
connected devices (either between DTE and DCE, or between the ports of two
packet switching exchanges). A virtual circuit consists of several logic channels,
and each logic channel has a separate number. Hence, a VC between Router A
and Router B can be the one shown in the following figure (suppose this VC
passes four packet switches in the network).
Figure 75 One VC consisting of several logic-channels
X.25 network
LC 24
LC 243 LC 3
LC 3 LC 4
Router A Router B
Therefore, the PVC 3 and PVC 4 mentioned in the example actually refer to the
numbers of the logic-channels between the routers and the PBXs directly
connected. The two sides of the PVC can identify the same PVC by using their
logic-channel numbers, however, without the likelihood of causing any mistake.
This is why no strict distinction is made between "virtual circuit" and "logic
channel".