程序代写代做代考 DHCP Chapter 1. Introduction to Data Communications
Chapter 1. Introduction to Data Communications
Networks, Security, and Privacy
158.235
A/Prof Julian Jang-Jaccard
Massey University
(Today covers chapter 1 in the textbook)
Housekeeping
• Textbook
– J. FitzGerald and A. Dennis, “Business Data Communications &
Networking”, 12th edition. Wiley, 2012.
• Delivery
– One Lecture (2-hour) per week, wk1 – wk12 (12 weeks)
– One lab (1-hour) per week, wk2 – 11 (10 weeks)
Housekeeping
• Assessments
– Internal Assessments (40%)
• May have 2-3 assignments throughout the semester
– Final exam (60%)
• Software
– Wireshark (www.wireshark.org) :
• network traffic capture & analysis
– Packet tracer (https://www.netacad.com/about-networking-
academy/packet-tracer/)
• Network simulation
http://www.wireshark.org/
https://www.netacad.com/about-networking-academy/packet-tracer/
https://www.netacad.com/about-networking-academy/packet-tracer/
https://www.netacad.com/about-networking-academy/packet-tracer/
https://www.netacad.com/about-networking-academy/packet-tracer/
https://www.netacad.com/about-networking-academy/packet-tracer/
https://www.netacad.com/about-networking-academy/packet-tracer/
https://www.netacad.com/about-networking-academy/packet-tracer/
Introduction
Our goal:
get “feel” and
terminology
more depth,
detail later in
course
approach:
use Internet as
example
overview:
Network components
types of network
protocol layers
ISO 7 layer
Internet 5 layer
what’s a protocol?
network standards
Components of a Network
circuit (pathway)
network devices
Network Types (based on Scale)
mobile network
global ISP
regional ISP
home
network
institutional
network
Network Types (based on Scale)
• Local Area Networks (LAN) – room, building
– a group of PCs that share a circuit (~100Mbps)
• Backbone Networks (BN) – less than few kms
– a high speed backbone linking together organizational LANs
at various locations. (~100-1000 Mbps)
• Metropolitan Area Networks (MAN) – (more than
a few kms)
– connects LANs and BNs across different locations
– Often uses leased lines or other services used to transmit
data (expensive, high transfer rate; ISP alternative)
• Wide Area Networks (WANs) – (far greater than
10 kms)
– Same as MAN except wider scale
Network: nuts and bolts
• millions of connected
computing devices:
– hosts = end systems
– running network apps
communication links
fiber, copper, radio,
satellite
transmission rate:
bandwidth
Network devices: forward
packets (chunks of data)
routers and switches
wired
links
wireless
links
router
mobile network
global ISP
regional ISP
home
network
institutional
network
smartphone
PC
server
wireless
laptop
Network: nuts and bolts
• Internet: “network of
networks”
– Interconnected ISPs
• protocols control sending,
receiving of msgs
– e.g., TCP, IP, HTTP, Skype,
802.11
• Internet standards
– RFC: Request for comments
– IETF: Internet Engineering Task
Force
mobile network
global ISP
regional ISP
home
network
institutional
network
What is a protocol?
human protocols:
• “what’s the time?”
• “I have a question”
• introductions
… specific msgs sent
… specific actions
taken when msgs
received, or other
events
network protocols:
• machines rather than
humans
• all communication
activity in Internet
governed by protocols
protocols define format, order
of msgs sent and received
among network entities,
and actions taken on msg
transmission, receipt
What is a protocol?
a human protocol and a computer network
protocol:
Hi
Hi
Got the
time?
2:00
TCP connection
response
Get http://www.awl.com/kurose-ross
time
TCP connection
request
Network Protocols
• Used by network model layers
• Sets of standardized rules to define how
to communicate at each layer and how to
interface with adjacent layers
receiver sender
Layer N
Layer N-1
Layer N+1
Layer N
Layer N-1
Layer N+1
Protocol “layers”
Networks are complex,
with many “pieces”:
– hosts
– Routers/switches
– links of various
media
– protocols
– applications
– hardware, software
Question:
is there any hope of
organizing structure
of network?
Layered Implementation
Applications
OS
Applications
OS
Multi layer
implementation
-Breaking down into
smaller components
-Easier to implement
Single layer
implementation
-Networking with
large components
is complex to
understand and
implement
Applications
OS
Applications
OS
Multi-layer Network Models
• The two most important such network models:
OSI and Internet
• Open Systems Interconnection Model (OSI)
– Created by International Standards Organization (ISO)
as a framework for computer network standards in 1984
– Based on 7 layers
• Internet Model (also called TCP/IP model)
– Created by DARPA originally in early 1970’s
– Developed to solve the problem of internetworking
– Based on 5 layers
– Based on Transmission Control Protocol/ Internet
Protocol (TCP/IP) suite
7-Layer Model of OSI
• Application Layer
– set of utilities used by application programs
• Presentation Layer
– formats data for presentation to the user
– provides data interfaces, data compression and
translation between different data formats
• Session Layer
– initiates, maintains and terminates each logical session
between sender and receiver
“Please Do Not Touch Steve’s Pet Alligators”
Physical DataLink Network Transport Session Presentation Application
7-Layer Model of OSI
• Transport Layer
– deals with end-to-end issues such as segmenting the
message for network transport, and maintaining the
logical connections between sender and receiver
• Network Layer
– responsible for making routing decisions from source to
destination
• Data Link Layer
– Responsible for moving messages from one device to
another reliably
• Physical Layer
– defines how individual bits are formatted to be
transmitted through the network
Internet’s 5-Layer Model
• Application Layer –
– Combines Application, Presentation, session layer of
OSI model
• Transport Layer – Same as transport layer of OSI
model
• Network Layer – Same as OSI model
• Data Link Layer – Same as OSI model
• Physical Layer – Same as OSI model
“Please Do Not Touch Alligators”
Physical DataLink Network Transport Application
LAN, BB, WAN, and Internet
mobile network
global ISP
regional ISP
home
network
institutional
network
Comparison of Network Models
Network models
• Protocol defines the language of transmission
– It specifies the rules, functionality, and
messages for communication at the layer
• Protocol Data Unit (PDU) contains layer-specific
information necessary for a message to be
transmitted through a network
– Each layer adds a PDU
– PDUs act like nested envelopes
– Encapsulation occurs when a higher level PDU
is placed inside of a lower level PDU
Network Models
Layer Purpose Example Protocols /
Standards
PDU
5. Application User’s access to network, software to
perform work
Packet (or Data)
4. Transport TCP, UDP Segment
3. Network Deciding where the message goes
1.Addressing
2.Routing
IP, ICMP Packet
2. Data Link Move a message from one device to the next
1.Controls hardware
2.Formats the message
3.Error checking
Ethernet Frame
1. Physical Transmits the message 100BASE-T, 802.11n
HTTP, SMTP, DNS, FTP,
DHCP, IMAP, POP, SSL
End-to-End Management
1.Link application layer to network
2.Segmenting and tracking
3.Flow control
Sender PDU Receiver
Application
Message
Transport Segment
Network
Packet/
Datagram
Data
Link
Frame
Physical
TCP HTTP Request
Ethernet
IP
TCP
HTTP Request HTTP Request
IP
TCP
IP TCP HTTP Request
Ethernet Ethernet IP TCP HTTP Request IP TCP HTTP Request
TCP HTTP Request
HTTP Request
Points about Network Layer View
• Layers allow simplicity of networking in some
ways
– Easy to develop new software that fits each layer
– Relatively simple to change the software at any level
• Matching layers communicate between different
computers and computer platforms
– Accomplished by standards that we all agree on
– e.g., Physical layer at the sending computer must
match up with the same layer in the receiving computer
• Somewhat inefficient
– Involves many software packages and packets
– Packet overhead (slower transmission, processing time)
– Interoperability achieved at the expense of perfectly
streamlined communication
Network Standards
• Why?
– Provide a “fixed” way for hardware and/or software
systems (different companies) to communicate
– Help promote competition and decrease the price
• Types of Standards
– Formal standards
• Developed by an industry or government standards-
making body
– De-facto standards
• Emerge in the marketplace and widely used
• Lack official backing by a standards-making body
Major Standards Bodies
• ISO (International Organization for
Standardization)
• ITU-T (International Telecommunications Union –
Telecom Group
• ANSI (American National Standards Institute)
• IEEE (Institute of Electrical and Electronic
Engineers)
• IETF (Internet Engineering Task Force)
