COMT 429

The Internet Protocols

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History

1969 First version of a 4 node store and forward network, the ARPAnet

1972 Formal demonstration of ARPAnet with 20 packet switches and 50 hosts

mid-70s UNIX distributed to academic and research sites. DEC PDP-11 systems gain wide acceptance. Initial research on TCP.

1980 DEC VAXs appear and replace PDP-11. Berkley UNIX provided with TCP implementation.

1983 ARPAnet goes to TCP full-time. Sun Computers incorporate TCP/IP.

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Protocol Overview

Ethernet, X.25, HDLC etc.

IP ICMP ARP RARP (Auxiliary Services)

TCP UDP

E-Mail HTTP (WWW) Remote LoginFile Transfer

X.25 PacketLayer

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Network Hierarchy

“Backbone”“Gateway”

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Types of Connections

Connection-Oriented Protocols– Requires Set-Up and Termination– Provides Sequencing, Flow Control,

Error Handling Connection-Less Protocols

– Also referred to as “Datagram” or “Best Effort” Delivery

– Typically does include Error Detection

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Connection Types in TCP/IP

Data Link Layer and Physical Network

Network Layer

Transport Layer TCP: Connection Oriented

UDP: Connection-less

Connection-less

Depends on the network

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The IP Protocol

TCP/IP

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IP HeaderVersion

Timeout Protocol Header Checksum

Source Address

Destination Address

Header Len Class of Service

Total Length

Identification

D M Fragment Position

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UDP Header

Source Port Destination Port

Length Checksum

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TCP Header

Source Port Destination Port

Sequence Number

Acknowledgement Number

Window (flow cntrl)misc Flags

Checksum Urgent

Options

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Addressing

IP Addresses are 32 bits long, originally using one of threeformats:

0NNNNNNN HHHHHHHH HHHHHHHH HHHHHHHH

or

10NNNNNN NNNNNNNN HHHHHHHH HHHHHHHH

or

110NNNNN NNNNNNNN NNNNNNNN HHHHHHHH

N = Network Address Bit

H = Host Address Bit

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Notation

Dotted Decimal:– 192.149.89.61 =

1100 0000 1001 0101 0101 1001 0011 1101 = C0 95 59 3D

– 132.235.75.17 The Network:

– 192.149.89.0 Broadcast on that network:

– 192.149.89.255

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Routing in an Autonomous System

Assign a network class that grants enough host addresses.

The internet routes based on one network number

Do we find a host inside the autonomous system?

OUInternet

132.235.0.0CS (Morton)

RTVC

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Subnetworks

Divide the Host Section Network 132.235.0.0

– Use half of the host id as a subnetwork

–10NNNNNN NNNNNNNN SSSSSSSS HHHHHHHH Network Mask 255.255.255.0 132.235.75.17

– Internet network 132.235.0.0– Internal Network 132.235.75.0– Host 17

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An Example

“Backbone”

Web Server:

www.lerc.nasa.govWeb

Browser

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The Request

User types into the browser:

“http://www.lerc.nasa.gov/index.htm”

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Browser Interpretation

“http://www.lerc.nasa.gov/index.htm” Protocol to use is HTTP (HyperText

Transfer Protocol); the transport protocol is TCP

The requested server is named www.lerc.nasa.gov

The SAP address is 80 The requested file is “index.htm”

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Name Resolution

www.lerc.nasa.gov is not an actual address

Make a call to the “resolver” (or, in most PCs, the “stub resolver”) to get a numeric address.

The answer may come from local storage, or may itself require a network transmission using the Domain Name System (DNS) protocols.

The name space and the address space are unrelated, except that they can be translated into each other.

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HTTP Message

The browser assembles a text message:

First line:– GET index.htm

Optional additional lines:– Browser type– HTTP version number– Transmission option negotiation

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Request to TCP

Browser makes a call to TCP, asking to open a connection to the numeric browser address

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Request to IP

TCP creates a header with the origin and destination SAPs

TCP sets a “flag” (bit) to request a new connection (SYN)

TCP may set other parameters and options

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Locate the Gateway

IP needs to find a way to get the TCP PDU (called a segment) to the destination address.

Since the destination is on a different network, it needs a gateway.

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Locate the Physical Gateway Address

IP knows the global (IP) address of the gateway.

To make a request of the data link layer, it needs the physical (MAC - Media Access Control) address of the gateway.

The ARP protocol is used to broadcast a request for the “owner” of the IP gateway address.

The gateway responds to the broadcast; IP learns the MAC address from the response.

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Dispatch the SYN Packet

IP creates one or more packets (usually one in this case).

The header has the origin and destination IP addresses and other options.

The packet goes to the Ethernet driver, which attaches the MAC (Ethernet origin and destination), and sends the packet to the gateway.

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Routing

The gateway receives the packet, and determines that it is not:– addressed to the gateway itself (at

the IP level)– addressed to any networks the

gateway is attached to The gateway examines its routing

table, and selects a circuit to send the packet out on.

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Receipt

www.lerc.nasa.gov receives the packet.

IP removes its headers after error-checking the header

TCP removes its headers, after error-checking the entire packet.

TCP consults the owner of SAP 80, and determines that the web browser is willing to create the connection.

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Response

TCP creates an empty packet The packet acknowledges the receipt

of the SYN TCP responds to any options that may

have been requested in the SYN

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Request Transmission

The browser is informed that the connection has been created.

The actual text message (the GET…) is now handed to TCP

TCP attaches its header and contacts IP

IP attaches its header and uses the Ethernet driver to send the packet to the gateway

etc.

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Response

The packet is received and checked by IP and TCP; they each remove their headers.

TCP notifies the web server The web server reads the GET request The server creates a header with

responses to the options requested by the browser

The server adds a line to the header indicating the format of the file (MIME)

The header is followed by a blank line and the actual file content.

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Standards Setting

Internet

Operations and Management

Routing

Security Transport

User ServicesGeneral ApplicationsAreas

Working Groups

Area Directors

IETF

ISOC

IABIESG

IANA