Chapter 2 Networking

Chapter 2Chapter 2

Building a Network with the Building a Network with the OSI ModelOSI Model

ObjectivesObjectives• Describe models such as the OSI seven-layer

model• Explain the major functions of network

hardware with OSI Layers 1-2• Describe the functions of network software

with OSI Layers 3-7

OverviewOverview

The CompTIA Network+ ChallengeThe CompTIA Network+ Challenge

• Understand every aspect of networking– Use the Open Systems Interconnect (OSI)

model– Conceptualize the parts of a network

• The OSI Seven-Layer Model provides– A powerful tool for diagnosing

problems– A common language to describe

networks

Figure 2.1 Using the OSI terminology – Layer 3 – in a typical setup screen

Working with ModelsWorking with Models

Biography of a Model• What does “model” mean to you?

– Computer models that predict weather– Plastic model airplane– Fashion model

Figure 2.2 Types of Models

A model has all the major functions of the real item

Figure 2.3 Simple model airplane

• What functions define all networks?• What details can be omitted?• ISO (International Organization for

Standardization) proposed the OSI seven-layer model

The OSI seven-layer modelThe OSI seven-layer model

The OSI Model

Layer 7 - Application

Layer 6 - Presentation

Layer 5 - Session

Layer 4 - Transport

Layer 3 - Network

Layer 2 - Data Link

Layer 1 - Physical

The Seven The Seven Layers in ActionLayers in Action

A conceptual viewpoint of networking

– One of the workers has just completed a new employee handbook

– She needs to transfer the Word document to the other worker for review

Welcome to MHTechEd!Welcome to MHTechEd!

Figure 2.4 Janelle and Tiffany, hard at work

She could…• Copy the file to a flash drive and walk it

over to the other person (sneakernet)• Transfer the file using the network

Let’s Get Physical…Let’s Get Physical…and examine the network hardware and examine the network hardware components required for this transfercomponents required for this transfer

CablingCabling

• Most networks use a cable, like this one, as a physical channel to move the bits of data

Figure 2.5 UTP cabling

Unshielded Twisted Pair (UTP) cable

HubsHubs• Each computer system has

a cable leading to a device called a hub– Usually located in a closet

• The hub sends the data received from one system to all the other systems attached to it

Figure 2.6 Typical hub

Figure 2.7 The network so far, with the Physical layer

hardware

Network Interface Cards

• Network Interface Cards (NICs) are installed in PCs

• Network cables attach to the NICs

Figure 2.8 Typical NIC

NIC to Hub ConnectionsNIC to Hub Connections• Cables run from the

NIC in the PC to a jack on the wall

• Cables run through the walls to the closet where they connect to a hub

Figure 2.9 NIC with cable connect-ing the PC to the wall jack

Network Cabling SystemNetwork Cabling System

Figure 2.10 The MHTechEd network

The NIC• Each system must

have a unique identifier

• Media Access Control (MAC) address– A unique address burned

into a ROM chip on the network card

– Each MAC address is 12 hex characters or 48 bits in length

MAC address printed on surface of chip – and burned

inside the chip.

Figure 2.11 MAC address

MAC AddressesMAC Addresses• MAC addresses are 48-bits long• Usually represented using hexadecimal characters

(12 hex digits = 48 bits)– A typical MAC address:

004005-607D49

Organizationally unique identifier (OUI)

Device ID

No two MAC addresses are ever the same!

ipconfig /all

MAC address

Figure 2.12 Output from IPCONFIG/ALL

Moving DataMoving Data

Figure 2.13 Data moving along a wire

Figure 2-14: Oscilloscope of data

Moving DataMoving Data

Figure 2.15 Data as ones and zeroes

Moving DataMoving Data

Figure 2-16 Inside the NIC

Frames

Inside a frameInside a frame• Frames are made up of fields that contain

information• Frames contain the recipient’s MAC address, the

sender’s MAC address, the data itself, and a cyclic redundancy check (CRC) for error checking

Figure 2.17 Generic frame

Frame as a canisterFrame as a canister

Figure 2.18 Frame as a canister

Frame SizeFrame Size• Different networks use different sizes of

frames• Many frames hold about 1500 bytes of data• The sending software breaks up large

amounts of data into smaller chunks• The receiving station must then put the

chunks back together in the proper order

Processing FramesProcessing Frames• All devices on the network see the frame,

but only the device that it is addressed to will process it– Every frame is received by every NIC– The MAC address is used to decide if the frame

belongs to a given device

Getting Data on the LineGetting Data on the Line

• Since the cable is shared, only one system may speak at a time

• Processes are used to keep two NICs from talking at the same time

Figure 2.19 Incoming frame!

Incoming Frame!Incoming Frame!

Getting To Know You• Usually two devices have talked before, so

the destination MAC address is already known

• If the MAC address is not known, a broadcast message is sent over the network– The destination device will respond by sending

its MAC address– A MAC broadcast address is FF-FF-FF-FF-FF-FF

Figure 2.20 Building the frame

Figure 2.21 Adding the data and CRC to the frame

Figure 2.22 Sending the frame

Figure 2.23 Reading an incoming frame

After the frame is receivedAfter the frame is received• The receiving station checks the CRC value in

the frame– If the value matches what it should, then the NIC

sends the data portion to the network operating system for processing

– If the value does not match, the frame has errors and must be resent

The Two Aspects The Two Aspects of NICsof NICs

Figure 2.24 Layer 1 and Layer 2 are now properly applied to the network

Figure 2.25 LLC and MAC, the two parts of the Data Link Layer

Beyond the Single Wire – Beyond the Single Wire – Network SoftwareNetwork Softwareand Layers 3 – 7and Layers 3 – 7

SubnetsSubnets

Figure 2.26 Large LAN complete (left), and broken into two subnets (right)

Network Protocols• Network protocols define rules for how systems

are addressed, how to chop data up into chunks, how to deal with routers, and so on

• As a network grows, a more universal address-ing method than MAC addresses is needed

• TCP/IP: – Transmission Control Protocol (TCP)

– Internet Protocol (IP)

IP IP –– Playing on Layer 3, the Playing on Layer 3, the Network LayerNetwork Layer

• IP address: a unique numeric identifier

• An IP address is a logical address while a MAC address is a physical address

• IP uses a dotted-decimal notation

• Each 8-bit number ranges from 0 to 255– Example: 192.168.4.232

• No two systems on the same network share the same IP address

• Routers are used to chop large networks up into smaller ones

• Routers forward packets by logical address

• An IP router (most common) forwards IP packets

• Works at Layer 3, the Network layer

Figure 2.27 Typical small router

Figure 2.28 MHTechEd addressing

Figure 2.29 Router added to the OSI model for the network

Frames (packets) within FramesFrames (packets) within Frames

• Network software creates a packet that contains the sending and receiving IP addresses along with the data

Figure 2.30 IP packet

Figure 2.31 IP packet in a frame (as a canister)

• The packet is enclosed within a frame that contains the sending and receiving MAC addresses

Figure 2.32 IP packet in a frame

IP packet in a frame

Connecting to the Internet Connecting to the Internet

• A router connects a local network to the Internet

• The local hub is connected to the router

• The router is connected to the Internet through a cable or phone line

• The cable or phone line uses a different kind of frame, so the router strips the frame and creates a new one

Figure 2.33 Adding a router to the network

Figure 2.34 Router removing network frame and adding one for the cable line

Connecting Connecting to the Internetto the Internet

Figure 2.35 Router in action (notice addresses)

• The router replaces the MAC address with the type of address used by the cable or phone company

• The frame uses the IP address to guide it to the receiving system

• The receiving router strips off the cable or phone company frame and adds the MAC address for the receiving system

• The NIC strips off the MAC header and hands the frame off to the NOS

Assembly and Disassembly Assembly and Disassembly – – Layer 4, Layer 4, the the Transport LayerTransport Layer

• Most data is much larger than a single frame• Network protocols chop up the data into smaller

packets, and give each one a sequence number• The sequence numbers are used by the receiving system

to put the packets back in order, and to assemble them• This compares to the numbering of boxes by UPS

Figure 2.36 Labeling the boxes

• Transport layer is the assembler/disassembler• Transport layer also initializes requests for packets

that weren’t received in good order

Figure 2.37 OSI updated

• One system may be talking to many other systems simultaneously

• The software that handles these processes is called session software, working at Layer 5

Talking on a Network Talking on a Network –– Layer 5, Layer 5,the the Session LayerSession Layer

Figure 2.38 Handling multiple inputs

Figure 2.39 Each request becomes a session

Figure 2.40 OSI updated

Standardized Formats Standardized Formats –– or Why Layer 6, or Why Layer 6, Presentation, Has No FriendsPresentation, Has No Friends

• Presentation layer tasks solved an old problem

• Macintoshes and PCs use very different formats

• Standardized formats have been created that allow very different operating systems to exchange data

Figure 2.41 Different data formats were often unreadable between systems

Figure 2.42 Everyone recognized PDF files!

Figure 2.43 OSI updated

Network Applications Network Applications –– Layer 7, Layer 7, the the Application LayerApplication Layer

• Users use Application layer network applications to exchange data on a network– Network in Windows Vista (My Network Places in

earlier Windows)– Web browser like Internet Explorer or Netscape

Navigator– Outlook Express for e-mail

• All operating systems have APIs at the Application layer for network-aware applications

Figure 2.44 Network applications at work

Figure 2.45 OSI updated

How Tiffany Gets Her DocumentHow Tiffany Gets Her Document

• The next few slides illustrate a typical process that takes place to copy a file from one machine to another over a network

Figure 2.46 Network application showing computers on the MHTechEd network

Figure 2.47 Copying the Word document

Figure 2.48 Chopping the Word document

Figure 2.49 Creating and addressing packets

Figure 2.50 Creating frames

Figure 2.51 Tiffany’s system grabbing a frame

• The OSI seven-layer model is a troubleshooting tool

• Example: Jane can’t print to the networked printer– Layer 1 and 2: NIC shows activity?– Layer 3: Does computer have a proper IP

address?– Move up through the layers to discover problem

area