Chapter 2
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Agenda
 Internetworking Basics
 Internetworking Model
 The OSI Reference Model
 Ethernet Networking
 Wireless Networking
 Data Encapsulation
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Possible causes of LAN traffic congestion are
 Too many hosts in a broadcast domain
 Broadcast storms
 Multicasting
 Low bandwidth
 Adding hubs for connectivity to the network
 A large amount of ARP or IPX traffic (IPX is a
Novell
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Network Segmentation
 Collision domain
 Broadcast domain
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Two advantages of using routers in your network are

They don’t forward broadcasts by default.
 They can filter the network based on layer
3
(Network layer) information (i.e., IP address).
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Four router functions in your network can be listed as
 Packet switching
 Packet filtering
 Internetwork communication
 Path selection
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Internetworking Model

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The Layered Approach
Advantages of Reference Models
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It divides the network communication process into smaller and simpler components, thus aiding component development, design, and troubleshooting.
It allows multiple-vendor development through standardization of network components.
It encourages industry standardization by defining what functions occur at each layer of the model.
It allows various types of network hardware and software to communicate.
It prevents changes in one layer from affecting other layers, so it does not hamper development.
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The OSI Reference Model
 The upper layers
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The lower layers
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Layer functions
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Application Layer


The Application layer of the OSI model marks the spot where users actually communicate to the computer.
Sample ->
 World Wide Web (WWW)
 E-mail gateways
 Electronic data interchange (EDI)
 Special interest bulletin boards
 Internet navigation utilities
 Financial transaction services13
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The Presentation Layer
 It presents data to the Application layer and is responsible for data translation and code formatting.
 This layer is essentially a translator and provides coding and conversion functions.
A successful data-transfer technique is to adapt the data into a standard format before transmission.
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The Session Layer
 The Session layer is responsible for setting up, managing, and then tearing down sessions between Presentation layer entities.
 This layer also provides dialogue control between devices, or nodes. It coordinates communication between systems, and serves to organize their communication by offering three different modes: simplex
, half duplex , and full duplex
.
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The Transport Layer


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The Transport layer segments and reassembles data into a data stream.
Services located in the Transport layer both segment and reassemble data from upper-layer applications and unite it onto the same data stream.
They provide end-to-end data transport services and can establish a logical connection between the sending host and destination host on an internetwork.
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 The Transport layer is responsible for providing mechanisms for multiplexing upper-layer applications, establishing sessions, and tearing down virtual circuits.
 The Transport layer can be connectionless or connection-oriented.
 Some of you are probably familiar with
TCP and UDP already.
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Flow Control
 Data integrity is ensured at the Transport layer by maintaining flow control and by allowing users to request reliable data transport between systems.
 The segments delivered are acknowledged back to the sender upon their reception.
 Any segments not acknowledged are retransmitted.
 Segments are sequenced back into their proper order upon arrival at their destination.
 A manageable data flow is maintained in order to avoid congestion, overloading, and data loss.
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Connection-Oriented Communication
 a call setup , or a three way handshak e
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Transmitting segments with flow control
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Windowing
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Acknowledgments

It guarantees that the data won’t be duplicated or lost.
 This is achieved through something called positive acknowledgment with retransmission a technique that requires a receiving machine to communicate with the transmitting source by sending an acknowledgment message back to the sender when it receives data.
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Transport layer reliable delivery
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The Network Layer

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The Network layer (also called layer 3) manages device addressing, tracks the location of devices on the network, and determines the best way to move data, which means that the Network layer must transport traffic between devices that aren’t locally attached.
Two types of packets are used at the Network layer:
 Data packets : routed protocol
 Route update packets : routing protocol
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Routing table used in a router
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Here are some points about routers that you should really commit to memory:
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Routers, by default, will not forward any broadcast or multicast packets.
Routers use the logical address in a Network layer header to determine the next hop router to forward the packet to.
Routers can use access lists, created by an administrator, to control security on the types of packets that are allowed to enter or exit an interface.
Routers can provide layer
2 bridging functions if needed and can simultaneously route through the same interface.
Layer
3 devices (routers in this case) provide connections between virtual LANs (VLANs).
Routers can provide quality of service (QoS) for specific types of network traffic.
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The Data Link Layer
 The Data Link layer provides the physical transmission of the data and handles error notification, network topology, and flow control.
 The Data Link layer formats the message into pieces, each called a data frame , and adds a customized header containing the hardware destination and source address.
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Data Link layer with the Ethernet and IEEE specifications.
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The IEEE Ethernet Data Link layer has two sublayers:


Media Access Control (MAC)
802.3
Defines how packets are placed on the media.
Contention media access is “first come/first served” access where everyone shares the same bandwidth —hence the name. Physical addressing is defined here,
Logical Link Control (LLC)
802.2
Responsible for identifying Network layer protocols and then encapsulating them.
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Switches and Bridges at the Data Link Layer
 Layer
2 switching is considered hardware-based bridging because it uses specialized hardware called an application-specific integrated circuit
(ASIC)
.
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The Physical Layer


 we find that the Physical layer does two things: It sends bits and receives bits. Bits come only in values of 1 or
0 —a Morse code with numerical values.
The Physical layer specifies the electrical, mechanical, procedural, and functional requirements for activating, maintaining, and deactivating a physical link between end systems.
This layer is also where you identify the interface between the data terminal equipment (DTE) and the data communication equipment (DCE)
.
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Hubs at the Physical Layer
 A hub is really a multiple-port repeater. A repeater receives a digital signal and reamplifies or regenerates that signal, and then forwards the digital signal out all active ports without looking at any data.
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Lecture 2-2
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The success of Ethernet is due to the following factors:
 Simplicity and ease of maintenance
 Ability to incorporate new technologies
 Reliability
 Low cost of installation and upgrade
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802.3 Ethernet in Relation to The OSI Model
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IEEE 802.x Standards
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Ethernet Technologies Mapped to the OSI model
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Ethernet Addressing
 We get into how Ethernet addressing works. It uses the Media Access Control (MAC) address burned into each and every Ethernet Network
Interface Card (NIC).
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MAC Address Format
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Generic Frame Format
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IEEE 802.3
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Ethernet II Frame Format
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Ethernet II and IEEE 802.3 Frame Format
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Media Access Control (MAC)
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MAC Rules and Collision
Detection/Backoff
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MAC Rules and Collision
Detection/Backoff
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Ethernet Timing
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Interframe Spacing
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Backoff
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Error Handling
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Types of Collisions
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The effects of having a CSMA/CD network sustaining heavy collisions include
 Delay
 Low throughput
 Congestion
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Ethernet Errors
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Ethernet Errors
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FCS Errors
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Parameters for 10 Mbps Ethernet
Operation
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Manchester Encoding Examples
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Parameters for 100-Mbps
Ethernet Operation
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MLT-3 Encoding Example (100Base-TX)
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NRZI Encoding Examples (100Base-FX)
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Parameters for Gigabit Ethernet
Operation
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Actual 1000Base-T Signal
Transmission
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Gigabit Ethernet Layers
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Gigabit Ethernet Media
Comparison
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Parameters for 10-Gbps
Ethernet Operation
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10GBASE LX-4 Signal Multiplexing
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Benefits of WLANs
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Evolution of Wireless LANs
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Unlicensed Frequency Bands
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Wireless Technologies
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Distance Versus Speed
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Wireless Technologies
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In-Building WLANs
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The IEEE 802 Standards
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IEEE 802.11 Protocols
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IEEE 802.11 Standards
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Data Encapsulation
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Summary
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OSI model —the seven-layer model used to help application developers design applications that can run on any type of system or network. Each layer has its special jobs and select responsibilities within the model to ensure that solid, effective communications do, in fact, occur.
Remember that hubs are Physical layer devices and repeat the digital signal to all segments except the one it was received from.
Switches segment the network using hardware addresses and break up collision domains.
Routers break up broadcast domains (and collision domains) and use logical addressing to send packets through an internetwork.
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