Introduction to Tandem X.25 Capabilities

Packet-Layer Components

What is X.25?

1–18 065307 Tandem Computers Incorporated

Figure 1-12. CUD in Call Setup Packets

Legend

Logical

Channel Identifier

Facility Length

Facility Fields

Call User Data 1–16 Octets

(in Call Request and

Incoming Call Packets only)

Bits

876543 21

0D SN

Packet Type Identifier (PTI)

Calling DTE Called DTE

DTE Addresses

Octet

0 = The initial bit (Q bit) is set to zero in call-setup packets.

D = The delivery bit (D bit).

SN = Sequence numbering information (either modulo 8 or modulo 128).

012