IBM SC30-3681-08 manual Frame Relay Frame, Hdlc Flags, Data Link Connection Identier Dlci

Using Frame Relay

If multiple PVCs are required and are not in a PVC group, the interface is not activated until all required PVCs are active.

If a required PVC belongs to a PVC group, the Frame Relay interface becomes inactive when all PVCs in the PVC group are inactive. If at least one PVC in the group is active, the interface becomes active following a successful exchange of LMI frames between the router and the FR switch. If there are multiple PVC groups, the interface does not become active until at least one PVC in each group is active.

A ªrequired PVC groupº is a group of circuits associated by name, where ªnameº is the name of the required PVC group.

These features can be used with WAN Reroute so that an alternate link can be brought up if all PVCs, required PVCs, or a group of PVCs become inactive on the primary FR link.

Frame Relay Frame

An FR frame consists of a ®xed size address ®eld with variable sized encapsulated user data. Figure 24 illustrates a Frame-Relay frame format.

	8	7	6	5	4	3	2	1
Octet	~‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡€
1	ˆ		HDLC Flag = 0x7e					ˆ
	…‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡ƒ‡‡‡‡ƒ‡‡‡‡†
2	ˆ	Data Link MSB/LSB (DL)					ˆC/R ˆ EA ˆ
	…‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡ƒ‡‡‡‡ƒ‡‡‡‡‚‡‡‡‡‚‡‡‡‡†
3	ˆ Connection ID (CI)				ˆFECNˆBECNˆ DE ˆ EA ˆ
	…‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡„‡‡‡‡„‡‡‡‡„‡‡‡‡„‡‡‡‡†
	ˆ							ˆ
	.		user					.
	.		data					.
	.							.
	ˆ							ˆ
	…‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡†
	ˆ		Frame Check					ˆ
	…‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡†
	ˆ		Sequence					ˆ
	…‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡†
N	ˆ		HDLC Flag = 0x7e					ˆ
	•‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡‡•

Figure 24. Frame-Relay Frame Format

HDLC Flags

Located in the ®rst and last octet, these ¯ags indicate the beginning and end of the frame.

Data Link Connection Identi®er (DLCI)

This 10-bit routing ID resides in bits 3 to 8 of octet 2 and bits 5 to 8 of octet three. The DLCI is the MAC address of the circuit. The DLCI allows the user and network management to identify the frame as being from a particular PVC. The DLCI enables multiplexing of several PVCs over one physical link.

392MRS V3.2 Software User's Guide