Frame Relay Frame Format - ZyXEL Communications Prestige 681 User Manual

Prestige 681 SDSL Router
Frames are "relayed" through switches in the network, creating basically a virtual private network (VPN)
between linked sites. This logical point-to-point circuit between customer sites is called a VC (virtual
circuit) of which there are two types. Permanent VCs (PVCs) have constant end points and need to be set up
in advance while switched VCs (SVCs) are set up on the fly as needed. The Prestige 681 supports PVCs
only.

3.1.1 Frame relay frame format

The frame format for frame relay is as follows.
Bytes
1 2-4
Flag Link Info
Lower DLCI (4 bits)
3-2
Figure 3-2 Frame Relay Solution
0-4,000
Data
Upper DLCI (6 bits)
FECN
Figure 3-3 Frame Relay Format
2
FCS
C/R EA 0
BECN DE EA 1
WAN Setup
1
Flag