1
BITS 2513
INTERNET TECHNOLOGY
LECTURE 2: UNDERSTANDING
NETWORKS
2
TOPICS
• Basic Terminologies
• Network Components
• Operating Systems on the Network
• Network Model
• OSI
• TCP/IP
• Addressing on a Network
• MAC address,
• IP Address,
• Port Number
BASIC TERMINOLOGIES
Key Terms
• Broadcast
• Send a message that will be received by everyone on
the network
• Unicast
• Send a message to one specific recipient
• Multicast
• Send a message to a group of recipient
• Synchronization
• Coordinate the delivery of messages.
• E.g., agree to start, stop, or coordinate who transmits
Video : Unicast Multicast
Broadcast
Key Terms (2)
• Control data vs. message data
• Control data relates to the messaging protocol
• synchronization, acknowledgements, flow control, priority, etc.
• Message data is the actual data that you want to convey to the
receiver
• Acknowledgement (also known as positive ack.)
• A control message sent from the receiver to the sender to indicate that
a message has been received successfully
• Negative Acknowledgement
• A form of error notification
• A control message sent from the receiver or some network element to
the sender to indicate that a message has NOT been delivered
successfully
Key Terms (3)
• Congestion
• the inability of a network element to receive or transmit
messages at the desired rate, leading to a buildup or
possibly a loss of messages and a deterioration in the
quality of service
• Flow control
• Modifying the rate at which messages are sent to avoid
congestion
• This may includes control messages, such as "slow
down”
• Relay
• Repeater: regenerate the message to extend the
network farther
Key Terms (4)
• Message encoding
• The techniques used to represent a message.
• With digital techniques, this refers to the binary symbols
used to represent the message and how those binary
symbols are transmitted.
• Best-effort message delivery
• An attempt to deliver messages reliably. If a message
does not make it to the destination, try again: retransmit
10
NETWORK
COMPONENTS
11
Network Components
• Hardware:
• Software:
• Network Interface Card
• Operating Systems
• Servers (DNS, DHCP)
• Applications
• Workstations
• Middleware
• Software that
• Device (Hub, MAU,
facilitates exchange of data betw
een two application
Concentrator, Switch,
programs within the same
Router)
environment, or across
different hardware and network e
• Connectors (RJ-45, BNC)
nvironments
• Cable (UTP, coax, fiber)
• UPS (Uninterruptable Power
Supply)
Switch
Hub
NIC
MAU
router
UPS
BNC male
Fiber optic
RJ-45 and
UTP
Functions
• Network Adapter - Usually an expansion card called NIC
(Network Interface Card)
• Hub / Switch – connect segment of a LAN
• Router – connect at least two networks (LAN/WAN)
• MAU – connect PC in ring topology
14
OPERATING SYSTEMS
ON THE NETWORK
15
Operating System
• Communications between computers require network
OS(es) and network protocols.
• Functions of OS in a computer:
• manage applications, hardware, and connection to the
network.
• enabling the computers on the local area network
(LAN) to share their resources
• Protocols specify network functionality.
• Using the same set of network protocols, different
devices can communicate.
• The selected network protocol must be supported by
every operating system on the network.
• Example : HTTP and FTP
16
How resources are shared:
◦ peer-to-peer model: several computers using different
operating systems in a small business or home can be
connected to form a small LAN.
◦ client/server model, a.k.a. domain model, a server is
used to control which resources on the LAN are shared,
and who can access these resources.
17
Client OSes
• Microsoft Windows: Windows XP, Windows 7, Windows 8
• Linux : Thinstation, Ubuntu, RH Linux.
• Macintosh : Mac OS X
• Novell Netware : Novell Client
• Smart Phone : Android, Symbian, iOS,
• Others :
• TinyOS (sensor),
• Femto OS (embedded device)
18
Network OSes
• can be installed on a server and used to
manage network resources, including user
accounts, printers, and file sharing across the
LAN.
◦ user account: a collection of all of the information
that pertains to a user on a computer
◦ authentication, validation, or logging on:
The process of entering a correct user ID and
password to gain access to a computer
19
Network Operating Systems
• Some criteria to consider when selecting a NOS
are as follows:
i.
ii.
iii.
iv.
v.
vi.
vii.
Reliability – stably perform in any condition
Performance – serve the clients in a seamless way
Adaptability – adapt request of different platform
Affordability – ability to pay the cost
Security – ability to eliminate and repel threats
Scalability – cont. function well when size expand
Ease of use and ease of installation
20
THE OSI MODEL
&
TCP/IP MODEL
Why we need network model?
• provides a guideline how network devices should
be manufactured, how OS communicate on a
network
• compatibility between various manufacturer
• Variety –
• OS: Apple OS X, Windows, Linux, Unix, Sun.
• Hardware: Cisco, 3Com, Huawei
22
Understanding the OSI Model
o In an effort to identify and standardize all the levels of
communication needed in networking, ISO developed
a networking model called the Open Systems
Interconnection (OSI) reference model.
o OSI model was created as a framework and reference
model to explain how different networking technologies
work together and interact.
30
Encapsulation/De-encapsulation
• The process of moving data between
layers of the OSI Model
• Encapsulation:
• Data > segment > packet > frame > bits
• De-encapsulation:
• Bits > frame > packet > segment > data
Encapsulation
• At any layer
• The higher level protocol headers are just treated like
data
• Lower level protocol headers can be ignored
Video : OSI Model
Explained
TCP/IP vs OSI Model
• The
Transmission
Control
Protocol/Internet
Protocol (TCP/IP) suite was created by the U.S.
Department of Defense (DoD) to ensure that
communications could survive any conditions and that
data integrity wouldn’t be compromised under malicious
attacks.
• The Open Systems Interconnection Basic Reference
Model (OSI Model) is an abstract description for network
protocol design, developed as an effort to standardize
networking.
36
TCP/IP Protocols at Each Layer
(Continued)
37
TCP/IP Protocols at Each Layer
(Continued)
38
TCP/IP Protocols at Each Layer
• TCP/IP covers the first five layers of the OSI model, and
is included in an operating system as a group of utilities
called the TCP/IP stack.
• Figure 5-41 shows the four major groupings of the OSI
model as applied to TCP/IP networks.
39
TCP/IP Protocols at Each Layer
(Continued)
40
Protocols at the Application,
Presentation, and Session Layers
• The first three layers of the OSI model are handled by
the protocol specific to the application using it and are
best treated as a single group rather than unique layers.
• The language or protocol each of these applications
uses is listed at the Application, Presentation, and
Session layers.
41
Protocols at the Transport Layer
• A TCP/IP network has two protocols that work at the
Transport layer; one protocol guarantees delivery and
the other does not.
• With TCP/IP, the protocol that guarantees delivery is
TCP and the protocol that does not is UDP (User
Datagram Protocol).
• TCP
is used for client and server requests and
responses.
• UDP ??
42
Protocols at the Transport Layer
(Continued)
• Because TCP establishes a connection, it is called a
connection-oriented protocol.
• UDP is a protocol that sends data without caring about
whether the data is received.
• It does not establish a connection first; thus, it is called a
connectionless protocol.
43
Protocols at the Network Layer
• TCP and UDP communicate with the Network layer,
which is sometimes called the Internet layer.
• Some of the other supporting protocols include
• ARP (Address Resolution Protocol), responsible for
locating a host on a LAN;
• RARP (Reverse
Address Resolution Protocol),
responsible for discovering the Internet address of a host
on a LAN; and
• ICMP (Internet Control Message Protocol), responsible
for communicating problems with transmission to devices
that need to know about these problems.
44
Protocols at the Data Link and
Physical Layers
• PPP (Point-to-Point Protocol) is used over telephone
lines, and allows a computer to connect to a network
using a modem.
• PPP is the most popular protocol for managing network
transmission from one modem to another.
Discussion
• Work in a group of five (5) students.
• Use your creativity and understanding to represent the
sequence of the Web browser communication over
TCP/IP model into a diagram. (refer to slide page 45-51)
The OSI Model Applied to a TCP/IP
Network
 The Web browser wants to make a request to a Web server,
and processes the request using an API (Application
Program Interface) call to the OS.
 The API process packages the data using HTTP format,
which includes an HTTP header, and addresses it to an IP
address and
port 80, which is
the default port
for a Web server.
46
Fig 5-33 An application asks the OS to do something using an API call
The OSI Model Applied to a TCP/IP
Network (Continued)
• HTTP delivers the package to TCP, giving the destination
IP address and port.
47
The OSI Model Applied to a TCP/IP
Network (Continued)
• TCP hands the data off to IP, which resides in the network
layer and is also managed by the OS.
48
The OSI Model Applied to a TCP/IP
Network (Continued)
 The data with its header information is a long stream of
bytes. IP breaks it into individual packets. IP adds its
own IP header that contains its own IP address (source)
and the server’s IP address (destination).
IP passes the packets
off to the hardware
(NIC).
49
Fig 5-36 IP divides data into packets, which are then released to the network
The OSI Model Applied to a TCP/IP
Network (Continued)
 On the NIC, each
packet is given
information at its
beginning and end
in the form of frame.
A checksum is
calculated using a
technique called
cyclical
redundancy check
(CRC). Then each
frame is sent off to
the Ethernet cable.
 At the destination,
the checksum is
verified and passed
to the IP layer to be
regrouped.
50
The OSI Model Applied to a TCP/IP
Network (Continued)
• IP then passes the reassembled data and header stream
on to the TCP layer who acknowledges the TCP layer on
the client.
51
The OSI Model Applied to a TCP/IP
Network (Continued)
• The HTTP server, listening at port 80, receives the data
and passes it on to the Web server.
52
53
ADDRESSING ON A
NETWORK
Three Types of Addressing
• Physical Address (Data Link)
• IP Address (Network)
• Port Number (Application)
55
MAC (Media Access Control) Addresses
• MAC addresses function at the lowest (Data Link)
networking level.
• permanently encoded in each network card, which is why
the data link layer address is also commonly called the
physical address or the MAC address.
• If a host does not know the MAC address of another host
on a local area network, it uses the operating system to
discover the MAC address.
• MAC-48 addresses in human-friendly form is six groups of
two hexadecimal digits
e.g. 01-23-45-67-89-ab or 01:23:45:67:89:ab
56
IP Addresses
• All the protocols of the TCP/IP suite identify a device on
the Internet or an intranet by its IP address.
• An IP address is 32 bits long, made up of 4 bytes
separated by periods.
• Within
an IP address, each of the four numbers
separated by periods is called an octet.
• The first part of an IP address identifies the network, and
the last part identifies the host.
57
Classes of IP Addresses
• IP addresses that can be used by companies and
individuals are divided into three classes: Class A, Class
B, and Class C, based on the number of possible IP
addresses in each network within each class.
• The group of IP addresses assigned to an organization
are unique to all other IP addresses on the Internet and
are available for use on the Internet.
• The IP addresses available to the Internet are called
public IP addresses.
58
Private IP Addresses
• Private IP addresses are IP addresses that are
assigned by a network administrator for use on
private intranets that are isolated from the Internet.
• The RFC 1918 recommends that the following IP
addresses be used for private networks:
• 10.0.0.0 through 10.255.255.255
• 172.16.0.0 through 172.31.255.255
• 192.168.0.0 through 192. 168. 255.255
• Tips: Public IP address = outside range of
private IP add
59
Dynamically Assigned IP Addresses
• Instead of IP addresses permanently being assigned to
computers (called static IP addresses), an IP address
is assigned for the current session only (called a
dynamic IP address).
• Internet service providers (ISPs) are organizations
through which individuals and businesses connect to
the Internet.
60
Network Address Translation
• If the hosts on a network using private IP addresses
need to access the Internet, a problem arises because
the private IP addresses are not allowed on the Internet.
• The solution is to use NAT (Network
Address
Translation), which uses a single public IP address to
access the Internet on behalf of all hosts on the
network using other IP addresses.
61
Plans for New IP Addresses
• Because of an impending shortage of IP addresses,
as well as some limitations in the current standards for
IP, a new scheme of IP addresses called the IPv6 (IP
version 6) standard is currently being developed and
implemented.
• Current IP addresses using the current IPv4 (IP
version 4) have 32 bits with eight bits in each of four
octets.
63
Plans for New IP Addresses
(Continued)
• With the new system, each address segment can have 32
bits, for a total of 128 bits for the entire address.
• A disadvantage of IPv6 is the fact that so much software
used on the Internet would become outdated because
current software is designed to hold 32-bit IP addresses
and, with the new system, this number would no longer be
sufficient.
64
Ports
• A port is a number used to address software or services
running on a computer.
• Communication endpoint at the machine
• Port number: 16-bit value
• Port number = transport endpoint
• Allows application-application communication
• Identifies a specific data stream
• Some services use well-known port numbers (0 – 1023)
• A host computer might have several services running on
it. To identify the data associated with each process
• The port is written at the end of the IP address, separated
from the IP address
169.49.209.19:80
with
a
colon—like
this:
• IANA:
Internet
Assigned
(www.iana.org)
• Also see the file /etc/services
• ftp: 21/TCP
• ssh: 22/tcp
• smtp: 25/tcp
• http: 80/tcp
• ntp: 123/udp
• Ports for proprietary apps: 1024 – 49151
• Dynamic/private ports: 49152 – 65535
Numbers
Authority