Справочник Пользователя для Cabletron Systems EMM-E6 Ethernet
BRIDGES
EMM-E6 User’s Guide
1-17
1.6
BRIDGES
An Ethernet bridge is a device that allows the expansion of a network
beyond the limitations of the IEEE 802.3 specified limits for repeated
Ethernet networks. If an Ethernet network has a repeater hop of four
repeaters or a round trip propagation delay near the 51.2
beyond the limitations of the IEEE 802.3 specified limits for repeated
Ethernet networks. If an Ethernet network has a repeater hop of four
repeaters or a round trip propagation delay near the 51.2
µ
s maximum, a
bridge can be used to build an extended network. Ethernet bridges read in
packets and decide to filter or forward based on the destination address of
the packet. The simple forward/filter decision process allows a bridge to
segment traffic between two networks, keeping local traffic local. This
process increases the availability of each network while still allowing
traffic destined for the opposite side of the bridge to pass.
packets and decide to filter or forward based on the destination address of
the packet. The simple forward/filter decision process allows a bridge to
segment traffic between two networks, keeping local traffic local. This
process increases the availability of each network while still allowing
traffic destined for the opposite side of the bridge to pass.
Bridges can also connect similar networks together such as Ethernet,
Token Ring, and Fiber Distributed Data Interface (FDDI) together. Note
that similar networks means that the upper five layers of the OSI model,
see Figure 1-2, are the same but that different Data Link and Physical
layers may be used by the architecture. The Bridge operates at the Data
Link level of the OSI model. It stores packets and based on the packet
destination address, forwards or filters the packets. Because bridges work
at layer 2 of the OSI model, bridges are protocol independent. A bridge
must read the complete data frame, check for errors, and make forward or
filter decisions based on recognized addresses stored in its source address
table.
Token Ring, and Fiber Distributed Data Interface (FDDI) together. Note
that similar networks means that the upper five layers of the OSI model,
see Figure 1-2, are the same but that different Data Link and Physical
layers may be used by the architecture. The Bridge operates at the Data
Link level of the OSI model. It stores packets and based on the packet
destination address, forwards or filters the packets. Because bridges work
at layer 2 of the OSI model, bridges are protocol independent. A bridge
must read the complete data frame, check for errors, and make forward or
filter decisions based on recognized addresses stored in its source address
table.
Figure 1-2. OSI Model
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4
3
2
1
2
1
Bridge
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical
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5
4
3
2
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CH1Book Page 17 Wednesday, March 20, 1996 7:48 AM