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Module 4. Introduction to LAN Switching. Objectives. 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

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Module 4

Module 4

Introduction to LAN Switching


Objectives
Objectives

  • 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



The ethernet 802 3 interface
The Ethernet/802.3 Interface same time.

  • Ethernet is known as a shared-medium technology – all the devices are connected to the same delivery media.

  • Ethernet media uses a data frame broadcast method of transmitting and receiving data to all nodes on the shared media.


  • Standard Ethernet same time. using Carrier Sense Multiple Access/ Collision Detection (CSMA/CD) and a shared medium can support data transmission rates of up to 10 Gbps (gigabits per second).

  • Goal of Standard Ethernet is to provide a best effort delivery service and allow all devices on the shared medium to transmit on an equal basis.


Performance of a shared media Ethernet/802.3 LAN can be negatively effected by several factors.

  • The data frame broadcast delivery nature of Ethernet/802.3 LANs

  • CSMA/CD access methods allow only one station to transmit at a time.

  • Network congestion due to increased bandwidth demands from multimedia applications such as video and the Internet.

  • Normal latency (propagation delay) of frames as they travel across the LAN layer 1 media and pass through layer 1, 2 and 3 networking devices.

  • Extending the distances of the Ethernet/802.3 LANs using Layer 1 repeaters.


Ethernet negatively effected by several factors.Controller

EthernetController

Transmit

Tx

Tx

Loopback

CollisionDetection

Loopback

CollisionDetection

Receive

Rx

Rx

Ethernet NIC

Ethernet NIC

Half-Duplex Design

  • Ethernet physical connector provides several circuits

  • Most important are TX (transmit), RX (receive), and CD (collision detection)


Half duplex ethernet design standard ethernet
Half-Duplex Ethernet Design (Standard Ethernet) negatively effected by several factors.

  • The most important of these circuits are the receive (RX), transmit (TX), and CD (collision detection0.

  • The transmit (TX) circuit is active at the transmitting station.

  • The receive (RX)circuit is active at the receiving station.


  • To the network this appears as a negatively effected by several factors.single one way bridge.

  • Both devices are contending for the right to use the single shared medium.

  • The CD (collision detection) circuit on each node contends for the use of the network when the two nodes attempt to transmit at the same time.

  • After a collision occurs, the hosts will resume transmitting based on the hold time calculated by a back-off algorithm.

  • Then the host will determine if the network is clear before attempting to retransmit.


Congestion and bandwidth
Congestion and negatively effected by several factors.Bandwidth

  • To relieve network congestion more bandwidth is needed or the available bandwidth must be used more efficiently.

  • “Throwing bandwidth at the problem”. This could be attacking the symptom and not the problem.


Propagation delay
Propagation Delay negatively effected by several factors.

  • Latency is also known as Propagation delay is the time a frame or packet requires to travel from the source to destination on the network.

    • The greater the number of devices the greater the latency or propagation delay

    • adding hosts simply increases collisions, increases jam signals decreasing throughput .


Ethernet transmission times
Ethernet Transmission Times negatively effected by several factors.

  • Each Ethernet bit uses a 100ns window for transmission.

  • A byte is equal to eight bits.

  • Therefore, one byte takes a minimum of 800ns to transmit (8 bits at 100ns = 800ns).


  • A negatively effected by several factors.64 byte frame requires 51,200ns or 51.2 microseconds to transmit

    • 1 Ethernet bit uses a 100ns window for transmission.

    • A byte is equal to eight bits.

    • Therefore, one byte takes a minimum of 800ns to transmit (8 bits at 100ns = 800ns).

    • 1 microsecond = 1000 nanoseconds

    • 1 byte = 8 bits

    • (64 bytes at 800ns) = 51,200ns

    • (51,200ns/1000) = 51.2 microseconds).


Extending shared media lans using repeaters
Extending Shared Media LANs using Repeaters negatively effected by several factors.

  • Signal attenuation –Signal weakens as they travels through the network due to resistance in the medium.

  • A repeater is used to extend the geography of a LAN allowing more users to share that same network.


Improving lan performance
Improving LAN Performance negatively effected by several factors.

  • The performance of a network can be improved in a shared media LAN by:

    • Segmenting the network using bridges, routers, or switches

    • Using full duplex transmitting

    • Upgrade to a faster Ethernet standard


Segment lans
Segment LANs? negatively effected by several factors.

  • Each segment uses the (CSMA/CD) protocol to manages traffic on the segment.

  • By segmenting a network - less devices are sharing the same bandwidth

  • Each segment is its own collision domain.


Segmented lans
Segmented LANs? negatively effected by several factors.

  • In a segmented Ethernet LAN messages passed between segments is transmitted on a network backbone using a bridge, switch, or router.

  • The backbone network is its own collision domain and uses CSMA/CD to manage between segments.


Segmentation with bridges
Segmentation with Bridges negatively effected by several factors.

  • Bridges are Layer 2 devices, independent of Layer 3 protocols used by routers

    • they transmit data frames regardless of which Layer 3 protocol is being used

    • They are transparent to the other devices on the network.

    • Bridges increase latency (delay) in a network by 10-30%.

      Why?


  • A bridge is by default a store and forward device negatively effected by several factors.

  • It examines the destination MAC address to determine through which interface the frame will be forward.

    • If there is no match in the CAM table, the frame is flooded out all other interfaces

  • Bridges “learn” network segments by building an address table, a CAM (Content Address Memory), containing the (MAC) address of each network device that accesses the bridge and pairs it with its network segment.

    • Collision domains are created, not broadcast domains.


Segmentation using routers
Segmentation using Routers negatively effected by several factors.

  • Routers operate at network layer and base routing decisions on the Layer 3 IP protocol address.

  • Routers perform higher level functions than do bridges consequently they operate at a higher latency.


Routers
Routers? negatively effected by several factors.

  • Segment broadcast domains

  • Forward packets based on destination network layer addresses, i.e. IP

  • Segment collision domains


More collision domains, but more bandwidth for each user negatively effected by several factors.


Segmentation with lan switches
Segmentation with LAN Switches negatively effected by several factors.

  • A switch segments a LAN into microsegments creating collision free domains from one larger collision domain, not broadcast domains.

  • Switched Ethernet available bandwidth can reach close to 100%.


Lan switch latency
LAN Switch Latency negatively effected by several factors.

  • Each switch on an Ethernet LAN adds latency to the network.

  • The type of switching used can help overcome the built in latency of some switches.


Full duplex ethernet overview
Full-Duplex Ethernet Overview negatively effected by several factors.

  • Full duplex Ethernet allows the transmission of a packet and the reception of a packet at the same time.

  • Requires two pairs of conductors and a switched connection between each node



Full bidirectional traffic (two-way) and on a 10Mbps circuit yields 20Mbps of throughput. DuplexEthernetController

TX

Full DuplexEthernetController

Tx

Tx

CollisionDetection

CollisionDetection

Loopback

Loopback

RX

Rx

Rx

Full-DuplexEthernet Design

  • Transmit circuit connects directly to receive circuit

  • No collisions

  • Significant performance improvement

  • Eliminates contention on Ethernet point-to-point links

  • Uses a single port for each full-duplex connection


HUB bidirectional traffic (two-way) and on a 10Mbps circuit yields 20Mbps of throughput.

Using Full Duplex

Half Duplex

Full Duplex

  • Nodes must

    • Be directly attached to a dedicated switched port

    • Have installed network interface card that supports full duplex


Full duplex ethernet design
Full-Duplex Ethernet Design bidirectional traffic (two-way) and on a 10Mbps circuit yields 20Mbps of throughput.

Standard Ethernet normally can only use 50-60% of the 100Mbps available bandwidth.

  • This is due to collisions and latency.

  • Full duplex Ethernet offers 100% of the bandwidth in both directions.

  • This produces a potential 200Mbps throughput – 100Mbps TX and 100Mbps RX.



Source MAC address is used to build this table to communicate this circuit is established within the switch.


How a lan switch learns addresses
How a LAN Switch Learns Addresses to communicate this circuit is established within the switch.

  • When messages are received by the switch their:

    • addresses are read and stored in the CAM (Content Address Memory).

  • Each time an address is stored it is time stamped.

    • This allows addresses to be stored for a set period of time.


But more domains to communicate this circuit is established within the switch.


Benefits of switching
Benefits of Switching to communicate this circuit is established within the switch.

  • A LAN switch allows many users to communicate in parallel :

    • through the use of virtual circuits

    • dedicated network segments

    • in a collision free environment.

  • Very cost effective.


Symmetric switching
Symmetric Switching to communicate this circuit is established within the switch.

  • A symmetric switch is optimized through even distribution of network traffic across the entire network .

  • All networks using the same bandwidth.


before forwarding to communicate this circuit is established within the switch.


Asymmetric switching
Asymmetric Switching to communicate this circuit is established within the switch.

  • Asymmetric switching is best exemplified in client-server network traffic flows where multiple clients are simultaneously communicating with a server.

    • Each usually at a lower bandwidth than the server


Memory buffering
Memory Buffering to communicate this circuit is established within the switch.

  • The area of memory where the switch stores the destination and transmission data is called the memory buffer.

  • This memory buffer can make use of two methods for forwarding packets:

    • port based memory buffering

    • shared memory buffering.


  • Port based memory buffering to communicate this circuit is established within the switch. 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. (Better!)


3 frame transmission modes in a switch one variation
3 frame transmission modes in a switch to communicate this circuit is established within the switch.(+one variation)


Three switching methods
Three Switching Methods to communicate this circuit is established within the switch.

  • Store and Forward - the entire frame is received before any forwarding takes place.

    • Latency occurs while the frame is being received; the latency is greater with larger frames because the entire frame takes longer to read.

    • Error detection is high because of the time available to the switch to check for errors while waiting for the entire frame to be received.


  • Cut-through to communicate this circuit is established within the switch. 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 and has poor error detection.


Fragment-Free Switching to communicate this circuit is established within the switch.

The switch reads only the 1st 64 bytes of the incoming frame and then forwards the frame to its destination port


Means the switch is in cut through mode to communicate this circuit is established within the switch.


Adaptive cut through
Adaptive Cut Through to communicate this circuit is established within the switch.

  • 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


Shared to Switched to communicate this circuit is established within the switch.

TheNewWiringCloset

HUB

TheOldWiringCloset

VLANSystem

HUB

HUB

HUB

LANCampusSwitch

HUB

The New Backbone

Emerging Trends: The Network Evolution


Benefits of Switches to communicate this circuit is established within the switch.

  • Number of collisions reduced

  • Simultaneous, multiple communications

  • High-speed uplinks

  • Improved network response

  • Increased user productivity


Module 41

Module 4 to communicate this circuit is established within the switch.

Switching Concepts

END


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