Information Technology Reference
In-Depth Information
•
Used on short run copper.
•
Runs over a pair of 150 ohm balanced coaxial cable (twinax).
•
Maximum length is 25 m.
•
Mainly for server connections.
•
Uses 8B/10B encoding with simple NRZ.
1000BaseT GE over UTP
The IEEE standard for 1000 Mbps Ethernet over Category 5 UTP is IEEE 802.3ab; it was
approved in June 1999. This standard uses the 4 pairs in the cable. (100BaseTX and 10BaseT
Ethernet only use 2 pairs.) The specifications are as follows:
•
Category 5, 4-pair UTP.
•
Maximum length is 100m.
•
Encoding defined is a 5-level coding scheme.
•
1 byte is sent over the 4 pairs at 1250 MHz.
10 GE
Although not a test topic, the CCIE candidate should be familiar with the developing IEEE
802.3ae 10 GE technology. The draft standard mentions that it only functions on optical fiber
and operates in full-duplex mode. It can provide media solutions for metropolitan-area
networks (MANS) and wide-area networks (WANS). The standard is to be adopted in mid
2002. More information is at the 10 Gigabit Alliance web site at www.10gea.org.
Token Ring
Token Ring was developed by IBM for the forwarding of data on a logical unidirectional ring.
Token Ring is implemented in the data-link layer. Token Ring networks move a small frame,
called a
token
, around the network. Possession of the token grants the right to transmit data.
After a station has the token, it modifies it into a data frame, appends the data for transmission,
and sends the frame to the next station. No token is on the ring until the data frame is received
by the source station marked as read and copied, and releases a token back into the ring.
The IEEE standard for Token Ring is IEEE 802.5; the differences with IBM's specification are
minor. Table 4-6 shows the similarity and difference between the specifications.
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