Introduction to Tandem X.25 Capabilities

Data-Link-Layer Components
What is X.25?
1–28 065307 Tandem Computers Incorporated
Figure 1-19 shows the location of the address field within the frame format, and
indicates the how the frame address identifies the frame as a command or response.
Figure 1-19. Frame Addressing
DTE
03
DCE
01
Address
03
Flag FlagFCSControl
Information
(Optional) *
Address
03
Flag Control
Address
01
Flag Control
FlagFCS
Address
01
Flag FlagFCSControl
Information
(Optional) *
Commands
Commands
Responses
FlagFCS Responses
015
* Generally, only an Information Frame, which is a command frame, can contain
an information field. The only exception is a FRMR, which is a response frame
with a 3-octet information field.