Introduction to Data Communications
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Backbone Networks

In a Backbone Network, there is no Master Hub. The Level 1 Hubs are connected through their AUI port to a Coax Backbone. For Thin Coax, up to 30 Hubs can be connected together. For Thick Coax, up to 100 Hubs can be connected to the backbone. The Backbone is considered to be a populated segment.

Level 2 Hubs are allowed to be connected to the Level 1 Hubs' 10BaseT ports. This connection between the 2 Hubs is considered an unpopulated segment or link segment. Up to 1024 stations or nodes can be attached to the Level 2 Hubs' 10BaseT ports.

All stations and segments would appear as 1 Logical segment with 1 Network Number. In the real world, you would never attach 1024 stations to 1 segment, the resulting traffic would slow the network to a crawl.

40d. Hub's Addressing

Again, because a Hub is just many repeaters in the same box, any network traffic between nodes is heard over the complete network. As far as the stations are concerned, they are connected on 1 long logical bus (wire).

40e. Half-Duplex & Full-Duplex Ethernet Hubs

Normal Ethernet operation is Half-Duplex: only 1 station or node talking at a time. The stations take turns talking on the bus (CSMA/CD -bus arbitration).

Full-Duplex Ethernet Hubs are Hubs which allow 2 way communication between Hubs thus doubling the available bandwidth from 10 Mbps to 20 Mbps. Full duplex Hubs are proprietary products and normally only work within their own manufacturer's line.

If A wanted to talk to C, a direct 10 Mbps line would be connected through the 2 switching hubs. Simultaneously, if D wanted to talk to B, another direct 10 Mbps line in the opposite direction would be connected through the 2 switching Hubs thus doubling the available bandwidth to 20 Mbps.

There are no official standards for Full-Duplex Ethernet just proprietary ones.

40f. Switching Hubs

Switching hubs are hubs that will directly switch ports to each other. They are similar to full duplex hubs except that they allow dedicated 10 Mbps channels between ports.

If A wanted to communicate with B, a dedicated 10 Mbps connection would be established between the two. If C wanted to communicate with D, another dedicated 10 Mbps connection would be established.

Introduction to Data Communications
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