Introduction to Tandem X.25 Capabilities

Packet-Layer Components

What is X.25?

065307 Tandem Computers Incorporated 1–15

Figure 1-10. Logical Channel Assignments

Logical Channel Numbers

LCN

Restart/Diagnostic/

Registration

Permanent

Virtual Circuit

One-Way

Incoming Virtual

Circuit

One-Way

Outgoing

Virtual Circuit

Two-Way

Virtual Circuit

0 Reserved

4095 Maximum LCN

Only incoming calls from the network

Only for calls originating from the DTE

For shared use by DTE

and DCE during peak

traffic flow.

DCE

DTE

Order of LCN

Selection

for Virtual Calls

010

Packet Structure Every packet transferred across the DTE/DCE interface consists of at least three octets

(Figure 1-11) of packet header. These three octets may be followed by additional octets

of user data or by other control information.