Preliminary Data Sheet

AL2100

11/11/02

Broa d c om Co rp o r a ti o n

Document

AL2100-DS01-405-R

100Base-TX to 100Base-FX Conversion

Secti on 3: Fu nction al Descri p ti on

The AL2100 contains a physical layer interface (PHY) for 100BASE-TX, and a PHY for 100BASE-FX networks. The PHY

contains all the necessary functions, such as elastic store, quantizer, and driver circuits, to complete a media converter

design. The device converts the MLT3 scrambled symbols from the twisted-pair (TP) input port into 4B5B NRZI encoded

data, and transmits it over the fiber media. The 4B5B NRZI encoded data from the fiber-input port is converted to a scrambled

MLT3 symbol stream for TP transmission.

The device also supports far-end fault detection (fiber-only), and links status propagation. If any port is in a link-fail state, the

device cease transmitting data, and disables the appropriate output port. In essence, the device is transparent in regard to

the connecting links. The media converter uses an elastic store to retime the received signal.

The AL2100 supports redundant link applications. A redundant link can be formed by either a switch with the 100BASE-FX

transceiver that supports far-end fault signaling or two AL2100s. In the event of a link failure, the redundant link is

automatically established.

The AL2100's 100BASE-TX receiver receives the scramble MLT3 signals, and passes them to the clock recovery circuit for

data/clock extraction.The device de-scrambles the signals, and decodes them into an NRZ data stream. The signal is then

passed through elastic-store circuitry for retiming. The resulting signal is converted into a serial NRZI data stream, and sent

to the 100Base-FX transmitter.

The AL2100's 100BASE-FX receiver receives the NRZI data stream through the PECL receiver inputs, and passes them on

to the clock recovery circuit for data/clock extraction. The device feeds the signals through elastic-store circuitry for retiming

and encoding the NRZI data, and conversion to scramble MLT3 signals. The signals are sent to the 100BASE-TX

transmitter.

The ideal function of a media converter chip provides a full-duplex transparent media link. The AL2100 supports full

IEEE 802.3-compliant auto-negotiation functions. Auto-negotiation can be enabled to negotiate with the link partner for full-

duplex applications.

The AL2100 provides an on-chip elastic store. With the elastic store in place, the device retimes the received signal, and

removes jitter. In order to reduce the latency, preambles are inserted to the packet.