Panasonic NN46240-502 - Manual (Page 62)

Nortel Secure Router 8000 Series
Configuration - LAN Access and MAN Access 4 VLAN configuration
In summary, the traditional network has disadvantages in the following areas:
• collision area
• broadcast area
In addition, the traditional network cannot ensure information security.
Isolating collision areas from normal areas
The following two methods extend the traditional LAN to accommodate more computers,
while preventing collision:
• Bridge: A bridge connects two areas and isolates a collision area from another normal
area.
• Layer 2 switch: The Layer 2 switch is derived from bridge technology. It can isolate
multiple collision areas, as shown in Figure 4-2.
OQ NOTE
In the remainder of this document, the term switch refers to the Layer 2 LAN switch.
Figure 4-2 Networking diagram of the Layer 2 switch
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Data flow
Bridges and switches forward the information from an incoming interface to an outgoing
interface through the switching mode, restricting the collision area to the port level. Thus, the
collision on the shared media is removed.
Switches receive all the data frames on a network segment. After learning the source Media
Access Control (MAC) addresses in the frames, the switches set up the MAC address tables
that store the mapping between the MAC addresses and the ports.
For a received frame, if a switch finds the destination MAC address in the address table, the
switch forwards the frame on Layer 2. Thus, the collision is isolated.
If a switch cannot find the destination MAC address in the address table, the switch
broadcasts the frame to all the ports except for the receiving port, which can cause a broadcast
storm.
The introduction of switches into networking solves the problem of the collision area through
Layer 2 switching. However, the information insecurity caused by the broadcast still exists.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 4-3