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Topic2-PacketSwitchingNetworkingModels1.pptxITECH1102 Networking and Security
Week 2 – Packet Switching & Network Models
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Last week
Assessment:
Course Description
Expectations (10 – 12 hours per course per week)
Good idea to create a deadline calendar (Include all assessment tasks)
Type A/B assessments [Students must get an overall pass in Type B assessments]
Hence all students need to fully understand content to be able to answer test/exam questions.
Investigated simple eBay purchase
Significant technologies involved (we just looked at technology of Cat 6 cables).
Number systems
Decimal, Binary, Hexadecimal, Octal
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This week – overview of content
Discuss operation of basic networking hardware:
Network Interface Card
Hubs/switches/routers
Investigate different networks:
Home network
Campus network (Example: University type network)
The Internet
Investigate two reference models of networking:
The Internet Model (TCP/IP model)
OSI Reference Model
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Circuit switches vs Packet Switched networks
In Circuit Switched networks a dedicated channel is established prior to data being sent.
The best example of a circuit switched network is the Plain Old Telephone System (POTS) as used in many businesses and homes.
Once the circuit is established, you and the person on the other end of the telephone effectively have a wire connecting both telephones for the duration of the telephone call.
This course however is primarily concerned with Packet Switched networks.
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Some history of Packet Switched Networks
The US defence forces required a communications network that could withstand any part of the network being obliterated by enemy attack.
The concern was that in the face of thermo-nuclear warfare their communications could be rendered useless if critical parts were bombed by the enemy.
To this end DARPA (Defence Advanced Research Projects Agency) was given the responsibility of creating a network that could withstand such disruption.
Using a circuit switched communication the bomb(s) could destroy the phone line.
Using a packet switched network packets could be routed around the bombed bits!
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Conception of packet switching
In the 1960’s the concept of switching small blocks of data (packet switching) was conceived independently in both the USA and in the UK.
The individuals involved were:
Paul Baran at the RAND corporation in the USA.
Donald Davies at the National Physics Laboratory (NPL) in the UK.
Davies subsequently incorporated packet switching into the NPL network.
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ARPANET (Advanced Research Projects Agency Network)
The ARPANET was an early packet switched network that incorporated both packet switching and TCP/IP protocols.
Both these technologies underpin the Internet.
Funding for the ARPANET came from the US Defence Research Projects Agency.
Implementation required the development of devices that could switch packets between networked machines. DARPA sent out a request for quotation for such switching devices.
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Interface Message Processors (IMPs)
The company contracted to build the network (BBN Technologies) delivered the first IMP to UCLA on 30th August 1969.
An IMP was the first implementation of a device that could perform the duties of today’s Internet ROUTERS.
From this early start the Internet has developed into the ubiquitous packet switched internetwork of networks that underpins so much of our lives today.
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Packet fragmentation and reassembly
The network infrastructure of the Internet can only handle relatively small packets of data (up to 1500 bytes in length).
The basic concept of packet switching relies on the fragmentation and reassembly of packets.
Large messages at the source must be broken up into manageable sized packets for transportation to the destination, each packet free to “find its own way”
At the destination reassembly of packets is therefore required. Any given packet might have been unavoidably delayed!
Damaged packets or network congestion can cause packets to be lost or delivered out of sequence, hence packet switched networks require mechanisms to deal with such events.
We will discuss these issues later in associated sections of ITECH1102.
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Packet switching – where is it used
Packet switching is used on:
Small home networks (WiFi or cable connected)
Larger networks (business/university networks)
On the Internet (from source (your home PC) to remote resources (web servers))
Mobile telephone systems
But how are all these devices interconnected?
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Basic networking hardware
Network interactions involve 2 or more devices. (Example PC and web server (eBay))
To facilitate networking each device needs a Network Interface Card (NIC) that can be uniquely distinguished from other Network interface cards.
Ethernet NIC
WiFi
Bluetooth
Token Ring NIC (old technology)
Fibre channel Interface cards
Others
The NIC transmits and receives (binary) data to and from network media.
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Network hub (Ethernet)
Ethernet Hubs can be used to connect multiple devices to facilitate data exchange.
(4, 8 & 24 port devices were common)
Hub traffic from any port is broadcast to all other ports.
Hubs are seldom used today (switches are preferred). (Hubs can however be useful for monitoring network traffic)
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Network Switch (Ethernet)
Network Switches are smart devices. They learn the ports to which each device is connected.
Incoming traffic is directed to the specific port of the destination device.
Switches find wide usage in today’s networks.
The photo shows three switches and associated cabling of a Fed Uni switchroom.
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Routers
Unlike PC’s and Servers that normally only have one Network card (NIC), Routers have at least two network cards.
Routers are networking devices that allow one network to communicate with at least one other network and hence require multiple NIC’s.
Routes are the devices that provide Internet connectivity.
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Routers connecting two populated networks
Router 1 is connected to Network 1 & Network 3 (two NIC’s)
Note - the path between populated networks is a network itself.
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Reference networks
The following three slides show networks layouts that we will refer to frequently throughout the course to demonstrate various networking technologies.
Reference networks:
Home or small business network
Large campus network (for instance the Federation University network)
The Internet
Many details are missing from these reference networks, such detail will be discussed as we cover associated technologies.
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Home or small business network
Home networks connect:
Personal computers (PC)
Tablets
Printers
Internet
TV’s
Game consoles
Phones
Fridge
Security camera
Etc, etc – the upcoming Internet of Things (IOT)
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Common technologies employed
The most common technology used in domestic environments is WiFi.
Advantages include:
Simple connectivity
Data is encrypted
Low power transmissions
Ethernet connectivity is also popular in homes and small businesses.
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Reference Home or small business network
Home or small Business Network: Such networks typically include:
- Internet Access
- WiFi connectivity
- Ethernet switch
- Printer
- TV
- PC
- Tablets
- Notebook computers
- Mobile Phones
- Game consoles
- other devices
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Campus network (Eg. Fed Uni network)
Class Exercise – Form into groups and discuss extra functionality required on campus type networks.
Possible answers:
Servers, including File Servers, Video streaming servers, email, Learning Management Systems (Moodle), Web Servers, Printers, Faxes, Application servers, Internet firewalls.
The network is likely to be divided into multiple sub-networks at different locations separated by routers. For instance the Fed Uni network connects separate locations (sub-networks) together as one network.
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Reference Campus network
Campus type network
Attributes include:
Multiple sub-networks (Eg. Mt Helen, Gippsland, SMB, Berwick)
Connection to the Internet
User devices like PCs, Printers, phones, scanners, faxes etc. in each subnet
Various server in each subnet, including:
File servers
Database server
Application servers
DHCP, DNS, LDAP servers
Learning Management servers
Video servers
Routers connection the different subnets
(Mt Helen)
(Gippsland)
(Berwick)
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The Internet
One definition from the Internet itself is:
The Internet is “a vast computer network linking smaller computer networks worldwide”
Each individual network on the Internet is identified by a unique network number (or Network ID).
This ID allows traffic to traverse intermediary network so traffic travels between source and destination networks.
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Reference The Internet
The Internet
This diagram only shows a small section of the Internet.
Note – Each separate network has its own Network ID so that data transfers arrive at the right location.
Many of the Internets networks would contain multiple sub-networks as is the case for the campus network above.
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Questions relating to my eBay interaction (Some possible complexities of networking)
How did the eBay server identify the particular Browser tab I had open?
How did my PC know which device on my local network that it should use to send my eBay request?
How is it that I can be assured my payment is not compromised?
What happens if an electrical storm corrupts data to or from the eBay web site?
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Techno babble & confusion.
Networking involves many areas of technology working together to allow computing system to exchange data (reliably??).
Our simple demonstration of an eBay purchase demonstrated that even the cable from your PC to the local switch on your network is underpinned by many complicated technologies.
If we had detailed every part of that transaction, we could have mentioned load sharing servers at eBay, application servers, database server, public/private key encryption with paypal and the bank, reliability and many other technical details.
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Making it simple / Divide and conquer
In an attempt to make any complicated system understandable we often resort to breaking the large problem into understandable parts.
Two such simplifications of networking are the:
OSI Reference Model (of networking)
The Internet Model (also known as the TCP/IP model)
The two models are closely related to one another.
In networking literature both models are used when describing networking concepts, equipment etc. Hence to make sense of such discussions networking (computing) professionals need to have a good understanding of each networking model.
Much of this course and subsequent courses will assume understanding of both networking models.
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Divide and conquer analogy
Trainee doctor developing understanding of the human body:
It is far to hard to understand everything at once so:
Learn how the nervous system works
Learn how the vascular system works
Understand the skeletal system works etc. etc
Finally understand how each system interrelates with each other.
Divide and conquer to understand a large problem.
This is what the Internet and OSI models of networking attempt to do. Break a large problem down into manageable understandable parts.
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What exactly are we trying to model
A PC (sender of for example the eBay request) will break large data transmissions into packets.
Packets are sent to the network for delivery to the destination (to eBay)
The packets arrive at the eBay server and are reassembled into the correct order and then acted upon.
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The Internet Model (TCP/IP protocol suite)
The Internet model gives us a framework with which to understand how networking works from a TCP/IP perspective.
TCP (Transmission Control Protocol) and IP (Internet Protocol) are the two most important networking protocols in use today, they are the protocols that are used on the Internet and hence underpin the majority of all network traffic.
Other Protocol Suites (sets of communications protocols such as Novell’s IPX/SPX, DecNet and others) were common many years ago, however all have fallen into disuse in preference for TCP/IP.
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The Internet Model (TCP/IP)
The Internet Model
Provides services to users programs like: File transfer, email services, web server access etc. Also handles data format like encryption and login
Provides packet reassembly and reliable data transfers. TCP operates at this layer.
Internet layer is also referred to as the network layer. IP operates at this layer.
This layer is concerned with access to the network media. (Ethernet & Token-ring operate at this layer)
The Physical layer is not officially part of the Internet Model. The model assumes the hardware infrastructure. (The official Internet model is only concerned with software layers)
Application (Layer 5)
Transport (Layer 4)
Internet (Network) (Layer 3)
Network Interface (Data Link) (Layer 2)
Physical (Layer 1)
Sending Data
to the network
Receive Data from the network
The Internet model describes how TCP/IP communications works.
In reality it is a combination of hardware (the network interface card) and software that resides on all networked computer systems.
User applications (eg. Firefox, Internet Explorer, Microsoft Word) pass messages to the Application layer software for delivery to a remote network location.
The Application layer software processes the message then passes it to the next layer (Transport layer). The Transport layer adds transport layer information then passes the resulting data unit (called a protocol Data Unit) to the Network layer.
This process continues and results in the message arriving at the correct remote location.
At the remote location the message passes up through the layers of software to arrive at the server software to which it was intended.
We will discuss the details of the interactions at each layer as we progress through the course. For now we need to understand that outbound messages pass down through the TCP/IP layers and result in network traffic. At the destination the received data passes up through the layers to the intended server application.
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The Open Systems Interconnection (OSI) model
The OSI model defines a theoretical networking framework to describe networking in seven layers.
Each of the 7 layers describes a different part of how networking should work.
For instance one layer describes physical characteristics of the network media, another looks at delivery to a local machine, while another describes how to maintain reliable data transfers in electrically (or optically, or radio) noisy environments.
Remember this is a theoretical framework. It just describes how things should work.
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The OSI Model – What happens at each layer ?
The model has 7 layers as named below.
For example if you are having login problems to your Bank which layer may hold the answer?
The Session Layer manages login/logout.
Application services for file transfer, email etc.
How data is represented (eg. Encryption, ASCII etc.).
Establish, manage and terminate connections.
End to end delivery between hosts (also reliability).
Routing technologies, internetworking, addressing.
Local exchange of data.
Physical characteristics, cabling, electrical signals etc.
Application (Layer 7)
Presentation (Layer 6)
Session (Layer 5)
Transport (Layer 4)
Network (Layer 3)
Data Link (Layer 2)
Physical (Layer 1)
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Networking literature that relates to the models
Networking switches are often described as being Layer 2 switching devices. This means that the switch operates at the Data Link layer.
Discussion of the Data Link layer (later) will reveal how such switches work.
Hubs on the other hand work at layer 1. This means a hub acts in many respects like some types of network media (a single shared cable to be more precise). This will become more evident as we work our way through the different layers.
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How the models relate to one another
Internet Model (TCP/IP) OSI Reference model
TCP/IP model application layer is equivalent to 3
Layers of OSI.
<< ------------->>
<< ------------->>
<< ------------->>
<< ------------->>
Layers 1,2,3 & 4 essentially provide the same functionality in both models.
Application (Layer 5)
Transport (Layer 4)
Internet (Network) (Layer 3)
Network Interface (Data Link) (Layer 2)
Physical (Layer 1)
Application (Layer 7)
Presentation (Layer 6)
Session (Layer 5)
Transport (Layer 4)
Network (Layer 3)
Data Link (Layer 2)
Physical (Layer 1)
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How do the models relate to real data transfers
This diagram shows a PC sending a single request (possibly of multiple packets) from Firefox to a remote Web Server.
Each Layer is responsible for its part of the request transmission.
This diagram shows a single network packet being sent from a web browser on the PC to a remote web server.
The packet contains all of the following:
A request from the web browser (Eg. A web page request)
Transport layer information that among other things identifies the remote program (In this case the web server application)
Network Layer information (In this case the address of the web servers host computer)
Data Link information (This identifies the two devices for each hop of the transmission) (As such this changes at each step along the way from source to destination)
For the packet to get to the destination it must travel one step at a time, firstly from the PC to the Local Router, then from the Local Router to the Remote Router and finally from the Remote Router to the destination. Normally there would be more than two routers in such interactions however the same concepts apply.
Reply packet/s from the Web Server back to the PC would undertake a similar journey in the opposite direction.
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Tool Talk - Linux
Linux Lite is based on ubuntu Linux.
Version 3.2 was released in October 2016.
We will be using Linux Lite for some of the operating system and networking tasks throughout the semester.
This week’s lab will look at the Linux Lite GUI interface and some of its GUI applications.
----- Demo of Linux Lite -----
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Next Week
Layer 5 – The Application layer
The role of the Internet Model’s Application Layer.
Client – Server networking.
Peer to Peer networking.
Cloud architectures
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