- Ethernet Frames Format
- MAC address Each NIC has a unique, 48-bit MAC address; The first 24 bits identify the manufacture while the 2nd half is assigned by the manufacture.
- Ethernet Access Before Gigabit Ethernet, CSMA/CD is designed to allow fair access on shared media: Listen to avoid collision before transmitting. If collision occurs, retransmission is necessary. In 1997 IEEE 802.3x introduces full-duplex Ethernet, MAC control protocol and PAUSE.
- Ethernet Equipment
- Hubs/Repeaters Hubs/Repeaters are the central devices in a star topology and enhance the incoming signals to avoid degradation before transmitting them out. Hubs/Repeaters also support SNMP.
- Bridges Bridges transfer MAC layer packets from one network to another; and help prevent collisions by creating separate collision domain. To control the traffic, bridges need to build MAC tables and prevent loops using Spanning Tree Protocol
- Switches Switches link multiple networks compared to Bridges. Two categories of switches are commonly in use today: Cut through and Store-and-forward. Cut through provide lower latency while store-and-forward provides more intelligent processing of MAC layer packets.
- Routers Routers filter out unnecessary traffic by looking up IP address instead of MAC address in bridges/switches. Routers works like firewall to some extent and provide security functionality.
| Field | DIX Frame | IEEE 802.3 Frame |
|---|---|---|
| Preamble | 8 bytes | 7 bytes |
| Start Frame Delimiter | 1 bytes | |
| Destination Address | 6 bytes | 6 bytes |
| Source Address | 6 bytes | 6 bytes |
| Length | 2 bytes | |
| Type | 2 bytes | |
| LLC | Yes | |
| Data | 1500 bytes | Yes |
| Pad | Yes | |
| CRC/FCS | 4 bytes | 4 bytes |
| Total | 1518 bytes | 1518bytes |
>>>NEXT
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