Computer Networks - Lecture 6, p2

Computer Science & Software Engineering
Computer Networks (CITS3230) - Lecture 6

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Physical Properties

The original Ethernet proposal was for a 3Mbps network, connecting up to 256 stations (1975).

The IEEE-802.3 standard has since been introduced which at first supported up to 1024 stations at 10Mbps over a total length not exceeding 2.5km.

Each packet must be at least 64 bytes long to provide some reasonable chance of detecting collisions over long-ish propagation times.

Due to power losses within the Ethernet cables, each segment cannot exceed 500m, so repeaters were used to connect up to 5 segments in a single LAN.

Later additions to the 802.3 standard support increasingly faster twisted pair speeds: 100Base-T, 1000Base-T, and recently 10GBase-T.

Similarly, fiber optic speeds and segment lengths have increased: 10GBase-ER (extended range) allows 40km. 100Gbps is in the works.

Type	Cable	Max. Segment	Nodes/seg.	Advantages
10Base5	Thick coax	500m	100	Used for backbones
10Base2	Thin coax	185m	30	Cheaper
10Base-T	Twisted pair	100m	1024	Easy maintenance
10Base-F	Fiber optic	2000m	1024	Best between buildings
Computer Networks (CITS3230), Lecture 6, p2, 14th April 2008.