1 Version 3 Module 8 Ethernet Switching

2 Version 3 Ethernet Switching Ethernet is a shared media –One node can transmit data at a time More nodes increases the demands on the available bandwidth –The probability of collisions increases, resulting in more retransmissions A solution to the problem is to segment. Segmenting creates more collision domains

3 Version 3 Shared Media Environment Shared media environment – –multiple hosts have access to the same medium Extended shared media environment – –Using networking devices extends the environment to accommodate multiple access or longer cable distances Point-to-point network environment – –one device is connected to only one other device (ex. dialup network connections)

4 Version 3 Shared media environments

5 Version 3 Layer 1 Devices Layer 1 devices –repeaters and hubs Extend collision domains Primary function is extending cable segments Additional hosts increase the amount of traffic More traffic = greater chances of collisions –This results in diminished performance

6 Version 3 Collision Domains –Connected physical network segments where collisions can occur

7 Version 3 Collision domains

8 Version 3 Collision Domains The types of devices that interconnect the media segments define collision domains Classified as OSI Layer 1, 2 or 3 devices Layer 1 devices do not break up collision domains Layer 2 and Layer 3 devices break up collision domains –Increasing the number of collision domains is known as segmentation

9 Version 3 Segmentation

10 Version 3 Network segment

11 Version 3 Layer 2 Devices Layer 2 devices –Bridges and Switches –Segments collision domains –Controls frame propagation using the MAC address –Tracks the MAC addresses and segment they are on

12 Version 3 Layer 2 Bridging

13 Version 3 Bridges Has only two ports and divides a collision domain into two parts Entire network will share the same logical broadcast address space All decisions made are based on MAC or Layer 2 addressing No effect on the logical or Layer 3 addressing

14 Version 3 Layer 2 Switching

15 Version 3 Switches A switch is a fast, multi-port bridge Each port creates its own collision domain A switch dynamically builds and maintains a Content- Addressable Memory (CAM) table The CAM holds all of the necessary MAC information for each port

16 Version 3 Switch Operation Communication in both directions at once is known as full duplex Most switches are capable of supporting full duplex, as are most network interface cards (NICs) In full duplex mode, there is no contention for the media. –A collision domain no longer exists –Theoretically, the bandwidth is doubled when using full duplex

17 Version 3 Switch modes Store and Forward Cut through

18 Version 3 Switch Modes Cut-through switching –A switch transfers the frame as soon as the destination MAC address is received –lowest latency –no error checking

19 Version 3 Switch Modes Store-and-forward switching –Higher latency –The switch receives the entire frame before sending it out –Verifies the Frame Check Sum (FCS) –Invalid frames are discarded at the switch

20 Version 3 Switch Modes Synchronous switching –The source port and destination port must be operating at the same bit rate Asynchronous switching –The bit rates are not the same –The frame must be stored at one bit rate before it is sent out at the other bit rate –Store-and-forward must be used

21 Version 3 Switch Modes Asymmetric switching –Switched connections between ports of unlike bandwidths –Asymmetric switching is optimized for client/server –A server requires more bandwidth dedicated to the server port to prevent a bottleneck at that port

22 Version 3 Layer 2 Broadcasts Ethernet Broadcasts –When a node needs to communicate with all hosts on the network –A broadcast frame with a destination MAC address 0xFFFFFFFFFFFF is sent –The network interface card (NIC) of every host must respond

23 Version 3 Layer 2 Broadcasts The three sources of broadcasts and multicasts: –Workstations –Routers –Multicast Applications

24 Version 3 Layer 3 Devices Layer 3 devices –Routers –Do not forward collisions –Breaks up collision domains –Broadcast domains are controlled

25 Version 3 Broadcast domain

26 Version 3 Broadcast Domain –A grouping of collision domains –Broadcasts have to be controlled at Layer 3 devices –Layer 2 and Layer 1 devices do not control broadcasts

27 Version 3 Data Flow Layer 2 devices filter data frames based on the destination MAC address –A Layer 2 device will forward the frame unless something prevents it from doing so Layer 3 devices filter data packets based on IP destination address –A Layer 3 device will not forward the frame unless it has to –Layer 3 device creates multiple collision and broadcast domains

28 Version 3 Dataflow

29 Version 3 Latency The delay between the time a frame leaves the source device and the time the frame reaches its destination The following conditions can cause delays: –Physical media –Circuit delays Electronics that process the signal along the path –Software delays Decisions that must be made to implement switching and protocols –Delays caused by the content of the frame Destination MAC address has to be read

30 Version 3 Latency