User's Manual

X.25 Overview
117377-B Rev. 00 1-13
Transmitting Data
After Router B establishes the circuit, data travels between end stations 1.1.1.2
and 3.1.1.2 as follows:
1. Router A begins processing the packets it receives from IP end station 1.1.1.2
across the X.25 network to Router B.
2. Router B removes the X.25 packet headers and trailers and forwards only the
IP data to IP end station 3.1.1.2 (F
igure 1-8).
3. IP end station 3.1.1.2 transmits data to end station 1.1.1.2.
Note that other IP end stations (for example, 1.1.1.3) can use the virtual
circuit to transmit data in the direction of end station 3.1.1.2 until the call is
cleared.
The call request and call accept packets specify the logical channel numbers
(LCNs) assigned to the virtual connections between each router and its
corresponding DCE. As a result, subsequent X.25 data packets contain only
the logical channel numbers, rather than the complete X.121 destination
addresses.
Figure 1-8. Routing IP Traffic across the X.25 Network
2.1.1.22.1.1.1
1.1.1.2
1.1.1.1
3.1.1.2
3.1.1.1
10000 20000
DCE DCE
X.25 PDN
Router A Router B
IP network
IP network
1.1.1.3
X250009A