CCNA3 Module 4 Brierley Module 4

CCNA3 Module 4 Brierley Topics LAN congestion and its effect on network performance Advantages of LAN segmentation in a network Advantages and disadvantages of using bridges, switches, and routers for LAN segmentation Effects of switching, bridging, and routing on network throughput Fast Ethernet technology and its benefits

CCNA3 Module 4 Brierley CSMA/CD detects multiple devices transmitting at the same time.

CCNA3 Module 4 Brierley The Ethernet/802.3 Interface Known as a shared-medium technology Uses a data frame broadcast method Uses Carrier Sense Multiple Access/ Collision Detection (CSMA/CD)

CCNA3 Module 4 Brierley Frame broadcast delivery nature of Ethernet/802.3 LANs Allows only one station to transmit at a time. Network congestion due to increased bandwidth demands. Normal latency Extending the distances Ethernet/802.3 LAN Performance can be negatively effected by several factors.

CCNA3 Module 4 Brierley Half-Duplex Design Loopback Tx Tx Rx Rx Collision Detection Ethernet Controller Tx Tx Rx Rx Collision Detection Ethernet Controller Transmit Receive Loopback Ethernet NIC Ethernet physical connector provides several circuits Most important are receive (RX), transmit (TX), and collision detection

CCNA3 Module 4 Brierley Half-Duplex Ethernet Design (Standard Ethernet) The transmit (TX) circuit is active at the transmitting station The receive (RX) circuit is active at the receiving station

CCNA3 Module 4 Brierley Both devices are contending for the right to use the single shared medium. The collision detection circuit contends for the use of the network When a collision occurs, a host will resume transmitting based on a back-off algorithm

CCNA3 Module 4 Brierley

Congestion and Bandwidth To relieve network congestion more bandwidth may be needed The problem could be broadcasts, chatty protocols, applications traffic, etc.

CCNA3 Module 4 Brierley

Propagation Delay Latency, also known as propagation delay. Propagation delay is the time a frame or packet takes to travel from the source node to its destination Adding hosts increases collisions, (increases jam signals)

CCNA3 Module 4 Brierley

Ethernet Transmission Times Each Ethernet bit has a 100ns window for transmission A byte is eight bits One byte takes a minimum of 800ns to transmit ( 8 bits at 100ns per equals 800ns )

CCNA3 Module 4 Brierley A 64 byte frame takes 51,200 ns or 51.2 microseconds to transmit –(64 bytes at 800ns = 51,200ns, –51,200ns/1000 = 51.2 microseconds)

CCNA3 Module 4 Brierley

Extending Shared Media LANs using Repeaters Signal attenuation – the signal weakens as it travels, from the resistance found in the medium. An Ethernet repeater can be used to extend the distance of a LAN

CCNA3 Module 4 Brierley

Improving LAN Performance  Segmenting the network using Bridges, Routers, or LAN Switches  Move to full duplex transmitting  Upgrade to Fast Ethernet

CCNA3 Module 4 Brierley

Why Segment LANs? Each segment uses (CSMA/CD) –Less devices are being shared –Each segment is considered to be its own collision domain

CCNA3 Module 4 Brierley Why Segment LANs? In a segmented LAN frames are passed between segments on the backbone using a bridge, switch, or router The backbone is its own collision domain and uses CSMA/CD to provide service between segments

CCNA3 Module 4 Brierley

Segmentation with Bridges Layer 2 devices, –independent of Layer 3 protocols data frames are passed along regardless of which Layer 3 protocol is being used –increase the latency (delay) in a network by 10-30% –Why?

CCNA3 Module 4 Brierley A bridge is a store and forward device –it must examine the destination address (MAC) to determine which interface to forward the frame If there is no match in the table, the frame is flooded out all other interfaces Bridges learn network’s segmentation by building address tables that contain the (MAC) address of each network device and which segment to use to reach that device Smaller collision domains are created, not broadcast domains

CCNA3 Module 4 Brierley

Segmentation with Routers Operates at the network layer and base all forwarding decisions on the Layer 3 protocol address Because routers perform more functions than bridges they cause additional latency

CCNA3 Module 4 Brierley Routers: Segment broadcast domains Forward packets based on network layer addresses Segment collision domains

CCNA3 Module 4 Brierley

More collision domains, but more bandwidth for each user

CCNA3 Module 4 Brierley

Segmentation with LAN Switches A switch segments a LAN into microsegments creating collision free domains from one larger collision domain, not broadcast domains With a switched Ethernet implementation the available bandwidth can reach closer to 100%.

CCNA3 Module 4 Brierley

LAN Switch Latency Each switch used on an Ethernet LAN adds latency to the network However, the type of switching used can help overcome the built in latency of some switches

CCNA3 Module 4 Brierley Types of Transmission Half-duplex Host checks medium for signal – if clear host transmits Only 1 host can transmit at a time Collisions – jam signal generated, back-off algorithm before retransmission 50-60% bandwidth available Full duplex Host can transmit immediately 2 hosts can transmit simultaneously No collisions 100% bandwidth available Requires dedicated connection to a switchport

CCNA3 Module 4 Brierley

Full-Duplex Ethernet Overview Full duplex Ethernet allows the transmission of a packet and the reception of a different packet at the same time Requires two pairs of conductors and a switched connection between each node

CCNA3 Module 4 Brierley Simultaneous transmission and reception of frames is called bidirectional traffic (both directions) and yields 20Mbps of throughput The network interface cards (NICs) on both ends need full duplex capabilities

CCNA3 Module 4 Brierley Full-Duplex Ethernet Design Transmit circuit connects directly to receive circuit No collisions Significant performance improvement Eliminates contention on Ethernet point-to-point link Uses a single port for each full-duplex connection TX Full Duplex Ethernet Controller Loopback Tx Tx Rx Collision Detection RX Full Duplex Ethernet Controller Loopback Tx Tx Rx Collision Detection

CCNA3 Module 4 Brierley Using Full Duplex Node must –Be directly attached to a dedicated switched port –Have installed network interface card that supports full duplex Full Duplex Half Duplex HUB

CCNA3 Module 4 Brierley Full-Duplex Ethernet Design Standard Ethernet normally can only use 50-60% of the 10Mbps available bandwidth This is due to collisions and latency. Full duplex Ethernet offers 100% of the bandwidth in both directions This produces a potential 20Mbps throughput – 10Mbps TX and 10Mbps RX

CCNA3 Module 4 Brierley

This virtual network circuit exists only when two nodes need to communicate This is why it is called a virtual circuit it exists only when needed and is established within the switch Allows multiple users to communicate in parallel via these virtual circuits

CCNA3 Module 4 Brierley

Source MAC address is used to build this table

CCNA3 Module 4 Brierley

How a LAN Switch Learns Addresses New addresses are read, learned and stored in Content Address Memory (CAM) –Each time an address is stored it is time stamped –This allows addresses to be stored for a set period of time.

CCNA3 Module 4 Brierley But more domains

CCNA3 Module 4 Brierley Benefits of Switching Allows many users to communicate in parallel –through the use of virtual circuits –in dedicated network segments –in a collision free environment Cost effective

CCNA3 Module 4 Brierley

Symmetric Switching A symmetric switch is optimized through even distribution of network traffic across the entire network

CCNA3 Module 4 Brierley before forwarding

CCNA3 Module 4 Brierley Asymmetric Switching Asymmetric switching is optimized for client-server network traffic flows

CCNA3 Module 4 Brierley

Memory Buffering The area of memory where the switch stores the destination and transmission data is called the memory buffer –It can make use of two methods for forwarding packets port based memory buffering or shared memory buffering

CCNA3 Module 4 Brierley Port based memory buffering –Packets are stored in queues that are linked to specific incoming ports Problem: One port may fill while another is empty Shared memory buffering –Deposits all packets into a common memory buffer that is shared by all the ports on the switch

CCNA3 Module 4 Brierley 3 frame transmission modes in a switch (+ 1 variation)

CCNA3 Module 4 Brierley Three Switching Methods Store and Forward - the entire frame is received before forwarding –Latency occurs while the frame is being received; the latency is greater with larger frames –Error detection is high due to the time available to check for errors waiting for the entire frame to be received

CCNA3 Module 4 Brierley Cut-through –The switch reads the destination address before receiving the entire frame –The frame is then forwarded before the entire frame arrives –This mode decreases the latency of the transmission BUT has poor error detection

CCNA3 Module 4 Brierley Fragment-Free Switching Switch reads only the 1st 64 bytes of the incoming frame before forwarding

CCNA3 Module 4 Brierley Adaptive Cut Through Combines cut through with store and forward The switch uses cut-through until there are a given number of errors Then the switch will change to store and forward method

CCNA3 Module 4 Brierley Means the switch is in cut through mode

CCNA3 Module 4 Brierley The Network Evolution Shared Switched The New Wiring Closet VLAN System LAN Campus Switch The New Backbone The Old Wiring Closet HUB

CCNA3 Module 4 Brierley Benefits of Switching Number of collisions reduced Simultaneous, multiple communications High-speed uplinks Improved network response Increased user productivity

CCNA3 Module 4 Brierley Switching Routing What’s the difference? Routing network Layer 3 Switching network Layer 2

CCNA3 Module 4 Brierley Module 4 Switching Concepts The End