Packet-based dynamic de-skewing for network switch with local or central clock

• Main Authors: HUI; ALEX CHI-MING, LEE; RAYMOND K
• Format: Patent
• Language: English
• Published: 17.02.1998
• Edition: 6
• Subjects: CALCULATING; COMPUTING; COUNTING; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRIC DIGITAL DATA PROCESSING; ELECTRICITY; MULTIPLEX COMMUNICATION; PHYSICS; TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHICCOMMUNICATION

A network switch uses a simple switch core of analog MOS transistor switches. The switch core is surrounded by many media-access controllers (MAC's) which buffer the data through the switch core. Multiple connections through the switch core may be made between different pairs of MAC's. Just one signal path through the switch core is needed per connection as a second path through the switch core for the clock is not needed. The clock is not encoded with the data, so PLL's are not needed for clock recovery. Data skew is instead measured for each packet transmitted through the switch core. A start flag is added to the packet by a source MAC as a packet header before being transmitted through the switch core. The start flag is a unique sequence which is detected by the destination MAC and triggers measurement of the data skew of the received start flag to the local clock. The measured data skew is then used to compensate for the rest of the packet. Because dynamic de-skewing is performed for each packet, any packet from any source MAC can be received. This allows freedom in MAC placement and enables construction of larger switches. The switch may have the MAC's physically separated from each other by greater distances since clocks can be locally generated. The clocks are independent from each other except for having the same frequency.