Overview of TCP/IP
 System Administrators and network
administrators
 Why networking - communication
 Why TCP/IP

Provides interoperable communications between all types
of hardware and all kinds of operating systems.
 What is TCP/IP
 An entire suite of data communication protocols,
 Transmission Control Protocol (TCP) and the Internet
Protocol (IP) are two of those protocols in the suite
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TCP/IP and Internet
 1969 ARPAnet
 Experimental packet-switching network
 Study robust, reliable, vendor-independent data
communication
 Very successful
 1975 ARPAnet became operation network
 Development continuing
 TCP/IP was developed
 1983 TCP/IP protocols were adopted as Military
Standards


TCP/IP was implemented in Berkeley Unix.
ARPAnet was divided into MILNET and ARPAnet
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TCP/IP and Internet
 1985 NSFNet
Connected to the then existing Internet (
MILNET plus ARPAnet)
 Linked together the five NSF super computer
centers
 Wanted to extend the network to every
scientist

 1987 new NSFNet backbone
 Faster
 Three-tiered topology: backbone, regional
networks, and local networks.
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TCP/IP and Internet
 1990 ARPAnet passed out of existence
 1995 NSFnet ceased its role as a primary
Internet backbone network
 Today Internet is build by commercial
providers.

Infrastructure is being created by
• National network provider, caller tier-one providers
• Regional network provider
Local access and user services is provided by
Internet Service Providers (ISPs)
 Network Access Points (NAPS): major
interconnection points

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Internet structure: network of networks
 roughly hierarchical
 at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity,
Sprint, AT&T), national/international coverage
 treat each other as equals
Tier-1
providers
interconnect
(peer)
privately
Tier 1 ISP
Tier 1 ISP
NAP
Tier-1 providers
also interconnect
at public network
access points
(NAPs)
Tier 1 ISP
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Tier-1 ISP: e.g., Sprint
Sprint US backbone network
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Tier-1 ISP: e.g., UUNET
UUNET Backbone Connectivity
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Internet structure: network of networks
 “Tier-2” ISPs: smaller (often regional) ISPs
 Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier-2 ISP pays
tier-1 ISP for
connectivity to
rest of Internet
 tier-2 ISP is
customer of
tier-1 provider
Tier-2 ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
NAP
Tier 1 ISP
Tier-2 ISPs
also peer
privately with
each other,
interconnect
at NAP
Tier-2 ISP
Tier-2 ISP
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Tier-2 ISP: e.g., Abilene (Internet2)
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Internet structure: network of networks
 “Tier-3” ISPs and local ISPs
 last hop (“access”) network (closest to end systems)
local
ISP
Local and tier3 ISPs are
customers of
higher tier
ISPs
connecting
them to rest
of Internet
Tier 3
local
local
ISP
Tier-2 ISP
ISP
ISP
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP
local
NAP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
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Internet structure: network of networks
 a packet passes through many networks!
local
ISP
Tier 3
local
local
ISP
Tier-2 ISP
ISP
ISP
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP
local
NAP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
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TCP/IP and the Internet
 Internet has evolved
 From a simple backbone network
 Through a three-tiered hierarchical structure
 To a huge network of interconnected, distributed
network hubs.
 Doubling in size every year since 1983
 est. 50 million host, 100 million+ users
 One thing remained constant:
 Internet is build on the TCP/IP protocol.
 The growth of the Internet spurred interest in
TCP/IP – it is popular.



Other network applications, email, html, http,
Mosaic,instant messaging, games
Local area networking even not connected to Internet.
Enterprise networks intranets.
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TCP/IP Features
 TCP/IP met the need at the right time.
 Open protocol standards
 Free
 Developed independently from any specific
computer hardware or operating system
 Independence from specific physical
network hardware.
Ethernet
 DSL connection
 Dial-up line
 Optical network
Virtually any other kind of transmission medium.

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TCP/IP Features
 Common addressing scheme – allow uniquely
address any device in the entire network.
 Standardized high-level protocols for
consistent, widely available user services.
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Protocol Standards
 What is protocol?
 Formal rules of behavior.
 Internet Standards are developed by Internet
Engineering Task Force (IETE) in open, public
meetings.
 Requests for Comments (RFCs)



Standards (STD)
Best current practices (BCP)
Informational (FYI)
 Official Internet standard is rigorous
 Proposed Standard
 Draft Standard
• At least two interoperable implementations

Internet Standard
• Extensive testing
• Significant benefit to the internet community.
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Protocol Standards
 Two categories
 Technical
Specification – defines a
protocol
 Applicability Statement – defines when
the protocol is to be used.
• Required
• Recommended
• Elective
 More than 3000 RFCs.
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Internet protocol stack
 application: supporting network
applications

FTP, SMTP, HTTP
 transport: host-host data transfer
 TCP, UDP
 Internet: defines the datagram and
handles the routing of data.
 IP, routing protocols
 Network Access Layer: Consist of
routines for accessing physical
network.
 PPP, Ethernet
Application
Transport
Internet
Network
Access
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Internet protocol stack
Application Layer
:
Transport Layer Header :
Internet Layer :
Network Access Layer:
Data

Header Data


Header Header Data


Header Header Header Data
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Network Access Layer
 provide the means to deliver data to other device
 Encompass functions of Network, Datalink and
Physical in OSI Reference Model
 Many access protocol – one for each physical
network. New hardware needs new protocol.
Typically show as device drivers and related
programs.
 Functions:
 Encapsulation of IP datagrams to frames
 Mapping IP addresses to physical addresses.
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Internet Layer
 Internet Protocol (IP) is the most important in this layer
 IPv4 and IPv6
 Internet Protocol Functions





Defining the datagram
Defining the Internet addressing scheme
Moving data between Network Access Layer and the Transport
Layer
Routing datagrams to remote hosts
Performing fragmentation and re-assembly of datagrams.
 IP is connectionless protocol
 IP depends on other layers to do error detection
and error recovery – some time called unreliable
protocol
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The Datagram
IP datagram format
Version
IHL
Type of
Service
Total Length
1
Identification
2
3
4
5
6
Time to
Live
Protocol
flags
Fragmentation
offset
Herder Checksum
Source Address
Destination Address
Options
Padding
Data begins here
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Datagrams
 IP delivers by checking destination address
 Host on same network, diver directly
 Otherwise, routing via gateway
 Routing datagrams
 Host -> gateway -> gateway … -> host
 Fragmenting datagrams
 Maxium transmission unit (MTU) for each type of
network
 If the datagram received from one network is longer
than the other network’s MTU, it must be divided into
smaller fragments.
 Header word 2 contains info that identifies which
datagram and info how to re-assemble them
• Identification – what datagram the fragment belongs to
• Offset – what piece of the datagram
• Flag – more fragments bit
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 Passing datagrams to the transport layer
 Done
by using protocol number from word3
 Internet Control Message Protocol (ICMP)
 Part of internet layer
 Uses the IP datagram delivery facility to send
message
 Functions
• Flow control – ICMP Source Quench Message, ask
source to stop sending temporarily
• Detecting unreachable destinations – Destination
Unreachable Message for host and port
• Redirecting routes – ICMP Redirect Message
• Checking remote hosts – ICMP Echo Message
– Ping
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Transport Layer
 Two most important protocal
 Transition Control Protocol (TCP)
• Reliable data delivery

User Datagram Protocol (UDP)
• Low-overhead, connectionless datagram delivery
 UDP
 No techniques in the protocol to verify data
reached the other end
 16-bit sort port and destination port
 Why use UDP?
• Small data
• Query-response model application
• Application provide their own techniques for reliable
data delivery
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Transport Layer
 UDP Message format
0
Source Port
Length
16
Destination Port
31
Checksum
Data begins here
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Transport Layer
 TCP
 Reliable
• Positive Acknowledgment with Retransmission (PAR)

connection-oriented
• Establish a logical end-to-end connection
• Three-way Handshake before data is transmitted
Host A
SYN
Host B
SYN,ACK
ACK,data
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Transport Layer
 TCP

Byte-stream data
• TCP views data as continuous stream of bytes
• Sequence Number and Acknowledgement Number
keep track of the bytes
• Exchanging initial sequence number (ISN) – random
number
• First byte of data has Sequence number ISN+1
• Sequence number identifies the sequential position in
the data stream of the first data byte in the
segment.

Acknowledgment Segment (ACK)
• Positive acknowledgement
• Flow control - window
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Transport Layer
 TCP segment format
0
16
Source Port
31
Destination port
Sequence Number
Acknowledgement number
Offset
Reserved
Flags
Checksum
Window
Urgent Pointer
Options
Padding
Data begins here
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Application Layer
 Included all processes that use the Transport
Layer protocols to deliver data

telnet
• Remote login over network

ftp
• File transfer protocol for transferring files between hosts

SMTP
• Simple Mail Transfer protocol, which delivers electronic
mail

HTTP
• Hypertext transfer protocol, delivers web pages over the
network.

Domain Name System (DNS)
• Map IP addresses to the names assigned to network
devices.
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Application Layer

Network File System (NFS)
• Allows files to be shared by various hosts.

Programming network application: socket API
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Summary
We’ve talked about
 TCP/IP and Internet
 TCP/IP four layers: applications, transport,
Internet and Network Access.
Next, we will look how IP datagram moves
through a network when data is delivered
between hosts.
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