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TCP/IP Essentials
A Lab-Based Approach
Chapter 0
TCP/IP Overview
Shivendra Panwar, Shiwen Mao
Jeong-dong Ryoo, and Yihan Li
The Internet
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A global information system consisting of millions of
computer networks around the world.
History
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Late 1960s, ARPA sponsors the development of a packetswitching network, called the ARPANET.
1974, The TCP/IP protocols and model are proposed by Cerf
and Kahn.
1983, ARPANET adopts TCP/IP. At this time, the ARPANET has
200 routers.
1984, NSF funds a TCP/IP based backbone network. This
backbone grows into the NSFNET, which becomes the
successor of the ARPANET.
1995, NSF stops funding the NSFNET. The Internet is
completely commercial.
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Internet Standards Control
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Internet Society (ISOC): a professional membership organization
that comments on policies, practices, and oversees others dealing
with network policy issues.
Internet Architecture Board (IAB): responsible for defining overall
architecture of the Internet with guidance and broad direction to the
IETF.
Internet Engineering Task Force (IETF): responsible for protocol
engineering and development.
Internet Research Task Force (IRTF): responsible for focused,
long-term research.
Internet Corporation for Assigned Names and Numbers
(ICANN): in charge of defining all “unique parameters” in the
Internet, including domain names and IP addresses.
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Internet Standardization Process
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A typical (but not only) way of standardization is:
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Internet Drafts
RFC (Request for Comments)
Proposed Standard
Draft Standard (requires 2 working implementation)
Internet Standard (declared by IAB)
David Clark, MIT, 1992: "We reject: kings, presidents,
and voting. We believe in: rough consensus and
running code.”
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A Hierarchical Communication
Architecture
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Networking can be quite complex and requires a high
degree of cooperation between the involved parties.
Cooperation is achieved by forcing parties to adhere to a
set of rules and conventions (protocols).
The complexity of the communication task is reduced by
using multiple protocol layers:
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Each protocol is implemented independently.
Each protocol is responsible for a specific subtask.
Protocols are grouped in a hierarchy.
A structured set of protocols is called a communications
architecture or protocol suite.
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TCP/IP Protocols
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Internet Protocol
Suite
A combination of
different protocols
Organized into four
layers
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Functions of the Layers
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Data Link Layer
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Network Layer
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Service: Moves packets inside the network.
Functions: Routing, addressing, switching, congestion control.
Transport Layer
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Service: Reliable transfer of frames over a link.
Functions: Synchronization, error control, flow control.
Service: Controls delivery of data between hosts.
Functions: Connection establishment/termination, error control,
flow control.
Application Layer
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Service: Handles details of application programs.
Functions: Everything is application specific.
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Protocols in Different Layers
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Internetworking Devices
Computers are connected by
internetworking devices.
 Classified according to their functionality
and layers
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 Hub
 Bridge
 Switch
 Router
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Hosts Communicating over a Hub
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Hosts Communicating over a bridge
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Hosts Communicating over a router
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Encapsulation
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The application data is sent down
Each layer adds a header to the data (PDU)
from its higher layer.
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Multiplexing and Demultiplexing
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Different higher layer
protocols can use the
service by the same
lower layer protocol.
The same higher
layer protocol can use
the service by
different lower layer
protocols.
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Naming and Addressing
Uniquely identify processes in different
computers for communications.
 Port number
 Domain name
 IP address
 MAC address
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Domain Name
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Identify a host
User friendly
Hierarchically organized
Domain Name System (DNS): resolves a
domain name to the corresponding IP address.
 DNS
servers and the domain name database
 Name caching
 DNS query and reply
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The Domain Name Space
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Port Number
Address for the application layer user
process.
 Port Number field in TCP or UDP header.
 Well-known port numbers
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1
to 255: Internet wide services
 256 to 1023: preserved for Unix specific
services
 1024 and up: ephemeral port numbers
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IP Address
Each host interface in the Internet has a
unique IP address.
 IPv4, 32 bits, dotted-decimal notation
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IPv6, 128-bit address
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Five Classes of IP Addresses
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Subnetting
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Three levels of an IP address:
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Network ID
Subnet ID
Host ID
Subnet mask: separates subnet ID and host ID
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Ethernet Frame Format
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Source Ethernet (MAC) Address
Destination Ethernet Address
Frame Type: used to identify the payload
CRC: used for error control
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IP Header Format
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Size: 20 bytes if without options.
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UDP Header Format
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Checksum: computed using the UDP header,
UDP data and a pseudo-header as below.
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TCP Header Format
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An Example:
How TCP/IP Protocols Work Together
Bob, a user, wants to book an air ticket
from an online booking website.
 Bob knows the domain name
www.expedia.com
 The remote computer with the domain
name is a web server.
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An Example – the Application
The web server provides the web service.
 Bob uses a web browser, which is a web
client, to request and receive web service.
 The HyperText Transfer Protocol (HTTP) is
used by the web server and browser.
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An Example – DNS
Bob starts Netscape in his computer, and
types http://www.exedia.com/index.html.
 The domain name needs to be translated
to an IP address.
 A DNS query is sent to a DNS server.
 A DNS reply will return to the client with
the IP address.
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An Example – TCP Connection
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The client establishes a TCP connection to the web
server.
A port number is carried in all packets in this process.
Application data (an HTTP request message for the
index.html file) is sent over the TCP connection,
encapsulated in a TCP segment.
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An Example – IP Layer
The TCP segment is sent down to the IP
layer and encapsulated in an IP datagram.
 Routers will forward the IP datagram hop
by hop to the web server by checking their
routing tables.
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An Example – MAC Layer
Bob’s host sends the IP datagram and the
next-hop router’s IP address down to the
MAC layer.
 The IP datagram is encapsulated in an
Ethernet frame.
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An Example – ARP
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The Ethernet frame needs to be sent to the
interface of the next-hop router.
Only Ethernet MAC address can be recognized.
ARP request/reply is used to resolve the MAC
address.
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An Example – on the Other End
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The web server receives the Ethernet frame.
The packet is delivered to the upper layers.
When the application layer receives the HTTP
request message, it sends an HTTP response
message to the client.
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