1 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3 v3.0 Module 4 Switching Concepts

222 © 2003, Cisco Systems, Inc. All rights reserved. Objectives Introduction to Ethernet LANs Introduction to LAN switching Switch operation

333 © 2003, Cisco Systems, Inc. All rights reserved LAN Development: Today’s LANs

444 © 2003, Cisco Systems, Inc. All rights reserved. Switches Switches create a virtual circuit (vc) between connecting devices that want to communicate. When the vc is created, a dedicated communication path is established. The implementation of a switch on the network provides microsegmentation. This creates collision free environment between source and destination, allows maximum utilization of available bandwidth.

555 © 2003, Cisco Systems, Inc. All rights reserved. Devices Function at Layers

666 © 2003, Cisco Systems, Inc. All rights reserved. Factors that Impact Network Performance Network traffic (congestion). Multitasking desktop operating systems (Windows, UNIX, and Mac) allow simultaneous network transactions. Faster desktop operating systems (Windows, UNIX, and Mac) can initiate faster network activity. Increased number of client/server applications using shared network data. Typical Causes of Network Congestion

777 © 2003, Cisco Systems, Inc. All rights reserved. Ethernet Performance of a shared-medium Ethernet/802.3 LANs is negatively affected by factors such as the following: The broadcast delivery nature of Ethernet. Carrier sense multiple access collision detect (CSMA/CD) access method allows only one host to transmit at a time. Multimedia applications with higher bandwidth demand such as video and the Internet. The latency of additional devices added by the extension of LANs by using repeaters. The distance added by using Layer 1 repeaters.

888 © 2003, Cisco Systems, Inc. All rights reserved. Half-Duplex Ethernet Design

999 © 2003, Cisco Systems, Inc. All rights reserved. Network Congestion

10 © 2003, Cisco Systems, Inc. All rights reserved. Network Latency Latency, or delay, is the time a frame or a packet takes to travel from the source station to the final destination.

11 © 2003, Cisco Systems, Inc. All rights reserved. Ethernet 10BASE-T Transmission Times Bit time (or slot time) — The basic unit of time in which 1 bit can be sent. For electronic or optical devices to recognize a binary 1 or 0, there is a minimum duration during which the bit is "on" or "off. " Transmission time — Equals the number of bits being sent times the bit time for a given technology. Another way to think about transmission time is as the time it takes a frame to actually be transmitted. (Small frames take a shorter amount of time, large frames take a longer amount of time to be transmitted.)

12 © 2003, Cisco Systems, Inc. All rights reserved. Benefits of Using Repeaters

13 © 2003, Cisco Systems, Inc. All rights reserved. Full-Duplex Transmitting

14 © 2003, Cisco Systems, Inc. All rights reserved. LAN Segmentation Segmentation allows network congestion to be significantly reduced within each segment.

15 © 2003, Cisco Systems, Inc. All rights reserved. LAN Segmentation with Bridges

16 © 2003, Cisco Systems, Inc. All rights reserved. LAN Segmentation with Routers

17 © 2003, Cisco Systems, Inc. All rights reserved. LAN Segmentation with Switches

18 © 2003, Cisco Systems, Inc. All rights reserved. LAN Switch Operation

19 © 2003, Cisco Systems, Inc. All rights reserved. Ethernet Switch Latency Latency is the period of time from when the beginning of frame enters a switch to the time it takes the frame to exit the switch. Latency is directly related to the configured switching process and volume of traffic.

20 © 2003, Cisco Systems, Inc. All rights reserved. Layer 2 SwitchingLayer 3 Switching

21 © 2003, Cisco Systems, Inc. All rights reserved. Symmetric Switching

22 © 2003, Cisco Systems, Inc. All rights reserved. Asymmetric Switching

23 © 2003, Cisco Systems, Inc. All rights reserved. Memory Buffering Port-based memory buffering Packets are stored in queues that are linked to specific incoming ports. It is possible for a single packet to block all other packets because its destination port is busy (even if the other packets could be delivered). Shared-memory buffering All packets use a common memory buffer. Packets in the buffer are then linked (mapped) dynamically to the appropriate destination port. Helps balance between 10- and 100-Mbps ports.

24 © 2003, Cisco Systems, Inc. All rights reserved. Two Switching Methods

25 © 2003, Cisco Systems, Inc. All rights reserved. Store and Forward

26 © 2003, Cisco Systems, Inc. All rights reserved. Cut Through

27 © 2003, Cisco Systems, Inc. All rights reserved. Functions of Ethernet Switches - Isolate traffic among segments - Achieve greater amount of bandwidth per user by creating smaller collision domains

28 © 2003, Cisco Systems, Inc. All rights reserved. Frame Transmission Modes Minimum 64 bytes

29 © 2003, Cisco Systems, Inc. All rights reserved. Network Switch Using CAM Learn the address by: Read the source MAC address of the received frame. Record the port on which the MAC address was received. Store in addressing table Compare the received destination MAC address with address table. If match, port provided, forward the frame to the correct port and address. If not found, forward the frames to all ports except the port it was received.

30 © 2003, Cisco Systems, Inc. All rights reserved. How Switches and Bridges Filter Frames Bridges and switches only forward frames, which need to travel from one LAN segment to another. To accomplish this task, they must learn which devices are connected to which LAN segment. Bridges are capable of filtering frames based on any Layer 2 fields.

31 © 2003, Cisco Systems, Inc. All rights reserved. LAN Segmentation Using Bridges

32 © 2003, Cisco Systems, Inc. All rights reserved. Microsegmentation of the Network A switch employs “microsegmentation” to reduce the collision domain on a LAN. The switch does this by creating dedicated network segments, or point-to-point connections.

33 © 2003, Cisco Systems, Inc. All rights reserved. Switches and Collision Domains The network area where frames originate and collide is called the collision domain. All shared media environments are collision domains.

34 © 2003, Cisco Systems, Inc. All rights reserved. Three Methods of Communication one transmitter tries to reach one receiver. one transmitter tries to reach only a subset, or a group, of the entire segment one transmitter tries to reach all the receivers in the network

35 © 2003, Cisco Systems, Inc. All rights reserved. Switches and Broadcast Domains Broadcasting is when one transmitter tries to reach all the receivers in the network. The server station sends out one message, and everyone on that segment receives the message.

36 © 2003, Cisco Systems, Inc. All rights reserved. Communication Between Switches and Workstations