ZyXEL Communications Prestige 681 Guia do Utilizador descarregar pdf (Página 42)

Prestige 681 SDSL Router

3-2 WAN Setup

Figure 3-2 Frame Relay Solution

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 0-4,000 2 1

Flag Link Info Data FCS Flag

Upper DLCI (6 bits) C/R EA 0

Lower DLCI (4 bits) FECN BECN DE EA 1

Figure 3-3 Frame Relay Format

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 147 148

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ZyXEL Communications Prestige 681 Guia do Utilizador Página 42