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Chapter 1 Introduction Installation and Operation Manual

1-28 Functional Description Egate-100 Ver. 4.0

Figure

1-16. Management Traffic in a VLAN-Aware Application

Loop Detection

Egate-100 functions as a VLAN-aware bridge (L2 Ethernet switch) with PDH links

(E1/T1s) as the bridge ports.

E1/T1 loops are quite common in PDH networks (for diagnostic purposes, among

others). These can in turn produce Ethernet loops, resulting in Ethernet network

problems. Egate-100 features mechanisms to detect E1/T1 loops and avoid

Ethernet loops by disabling the bridge port. When the loop is released, Egate-100

automatically recovers.

The loop detection uses the following mechanisms according to the

encapsulation mode:

• For GFP VCAT mode, loop detection is performed on each channel using the

VCAT mechanism to detect a loop on the channel. In this mode, loops can

also be detected on the logical layer.

• Hardware loops can be detected on units that support single GFP and VCAT.

This mechanism requires units of Version 01-C or higher.

• For PPP and MLPPP modes, the PPP LCP mechanism is used for loop

detection.

• For other modes, the loop detection mechanism is based on the transmission

of periodic Ethernet frames over the link. If the frames are detected back at

the sending port, a loop is declared.

The loop detection frames are frames with SA=DA of the originating Egate-100

device, so they do not propagate in the network beyond the opposite

Ethernet/PDH bridge port (RICi-E1/T1 or other).

The loop detection frames are tagged with a VLAN ID that is predefined by the

user; This VLAN ID should not be used for a user traffic VLAN.

Loop detection frames are sent every five seconds. If a loop detection frame is

received back at the sending port, a loop is declared and transmission at the

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