Version 4.0 Ethernet Network Fundamentals – Chapter 9 Sandra Coleman, CCNA, CCAI

 Identify the basic characteristics of network media used in Ethernet.  Describe the physical and data link features of Ethernet.  Describe the function and characteristics of the media access control method used by Ethernet protocol.  Explain the importance of Layer 2 addressing used for data transmission and determine how the different types of addressing impacts network operation and performance.  Compare and contrast the application and benefits of using Ethernet switches in a LAN as opposed to using hubs.  Explain the ARP process. Objectives

 Alohanet – 1970 – digital radio network to connect Hawaiin islands.  1 st LAN – Robert Metcalf – Xerox – 30 yrs. Ago Characteristics of Network Media used in Ethernet Ethernet operates at Layers 1 & 2 of OSI Model (Physical & Data Link) Ethernet operates at Network Access layer of TCP/IP model DIX (Digital Equipment, Intel, Xerox) – released stds. in 1980 IEEE 802.x – 1985

 Layer 1 – involves signals, bit streams that travel on the media, various topologies  Layer 2 – MAC sublayer – concerned w/physical components (802.3) Physical and Data Link Features of Ethernet LLC sublayer – (802.2) independent of physical equip. Concerned with upper layer transitions

 Know the IEEE numbers for Layer 1 & 2 protocols Physical and Data Link Features of Ethernet

 Logic Link Control – Connecting the Upper Layers  IEEE standard is represented here Physical and Data Link Features of Ethernet

 Media Access Control (MAC) Physical and Data Link Features of Ethernet

 Success of Ethernet is because of: simplicity/ease of maintenance, ability to adapt new technologies, reliability, and lower cost to install and upgrade Characteristics of Network Media used in Ethernet

 2 most common types of media are copper UTP and optical fiber. Physical and Data Link Features of Ethernet

 Migration from hubs to switches to increase throughput while minimizing collisions  Each port on a switch is a collision domain Characteristics of Network Media used in Ethernet

 DATA field contains the layer 3 (network layer) packet Layer 2 Addressing and Its Impact on Network Operation and Performance

 The Ethernet MAC Address Layer 2 Addressing (MAC)

MAC Address specifications Copied to RAM from ROM during POST (startup) 6 bytes (12 hex digits) long (3 bytes OUI, 3 bytes vendor assigned)

 Base 16 – 0-9, A-F.. Hexadecimal Numbering system

 MAC – used locally in the frame, layer 2 address  IP – used to cross a WAN in a packet, layer 3 address Another layer of addressing

 IP addresses NEVER change in a packet (layer 3)  MAC addresses DO change within a frame (layer 2)  If a device doesn’t know the MAC address for an IP address, it will broadcast an ARP request for this information. Addressing

Unicast – delivers a packet to ONE single destination host Broadcast – delivers a packet to all hosts on a single broadcast domain Multicast – delivers a packet to a group of hosts

 All devices have guaranteed access to the medium, but no prioritized claim on it. Explain CSMA/CD. MAC in Ethernet

 Random delay (backoff algorithm) is used to try to help prevent another collision. First expired timer gets to transmit data first.  Once a collision has occurred, devices return to listen before transmitting mode – THIS DECREASES network performance!  Devices DO NOT interrupt others that are in the process of sending data! Carrier Sense Multiple Access w/Collision Detection

Ethernet Timing  Every device that data travels (propagates) through adds delay (latency) because of the error checking, decision making involved.  This delay will actually cause some devices to transmit thinking there is NO signal on the wire, hence; collisions!

Interframe spacing Gives the media time to stabilize between frames. Allows slow devices time to process a frame and prepare for the next frame. All devices are required to wait 96 microseconds before transmitting again.

Overview of physical layer

 Created LOTS of collisions which will decrease network performance  Not scalable – just results in larger collision domains!  Increased latency Legacy Ethernet – Using Hubs

 Each port is its on collision domain; full bandwidth available to that port – full duplexing capabilities – virtually collision FREE!  Switch will isolate segments and limit collisions! Ethernet – Using Switches

 Purpose: resolve IPv4 addresses to MAC addresses  Maintained dynamically by monitoring traffic that occurs on that segment of the network or by broadcasting an ARP request packets with the desired IP address, looking for the MAC address. Address Resolution Protocol (ARP) Process Receiving device responds by sending an ARP reply back as a unicast frame with its MAC address. It can then be added to the ARP table.

YEAH… Only 2 more chapters!!! -Study Guide – Do this NOW and show me... -Pg Matching -Pg – Multiple Choice -Pg. 238 – Matching -Pg – Multiple Choice -Discuss online Test – take it before next class, open book. Will count as a test grade. -Labs…None