Home | How Switches Work | Switching and Bridging | Methods | STP | Intro to Layer 2
Switching Notes
| Switching | |
| Cut-through | When a packet enters the switch its destination address is read and the leading edge of the packet is forwarded through the output port before the entire packet finishes entering the input port. |
| Faster than Store and Forward (Low Latency) | |
| Bad packets may be forwarded | |
| Store and Forward | When a packet enters the switch it is completely read into the switch, the cyclic redundancy check (CRC) is run, and it is forwarded out the appropriate output port. |
| Latency varies depending on frame size | |
| Bad packets are dropped | |
| Only available settings on Catalyst 5000 Switches | |
| Fragment Free | Instead of starting to forward a frame after the first 6 bytes have been received, a switch configured to use this method will wait to forward the frame until after the first 64 bytes are received. These 64 bytes are known as the "collision window," because a corrupted frame is usually recognized within the first 64 bytes. " height="39">Instead of starting to forward a frame after the first 6 bytes have been received, a switch configured to use this method will wait to forward the frame until after the first 64 bytes are received. These 64 bytes are known as the "collision window," because a corrupted frame is usually recognized within the first 64 bytes. |
| Faster than store and forward switching | |
| More reliable than cut-through switching | |
| The default method for Cisco switches | |
| Spanning Tree Protocol | Implemented to eliminate loops on a switched network |
| (STP) | Uses the Spanning Tree Algorithm (SPA) |
| IEEE specification is 802.1d | |
| ISDN | |
| BRI | Basic Rate Interface. Can carry voice, data, and video. |
| Otherwise known as 2B + 1D | |
| B channels have a bandwidth of 64 KBPS and are used for transmitting | |
| D channel has a bandwidth of 16 KBPS and is used for signaling | |
| PRI | Primary Rate Interface. Can carry voice, data and video. |
| US and Japan - 23B + 1 D | |
| Europe and elsewhere - 30B + 1D | |
| B channels have a bandwidth of 64 KBPS and are used for transmitting | |
| D channel has a bandwidth of 16 KBPS and is used for signaling | |
| ISDN Protocol Prefixes | |
| E | ISDN integration with existing telephone networks |
| Q | ISDN Switching and Signaling |
| I | ISDN Concepts, Terminology and Services |