Transcript 429-07a-TCPIP

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
1983
DEC VAXs appear and replace PDP-11. Berkley
UNIX provided with TCP implementation.
ARPAnet goes to TCP full-time. Sun Computers
incorporate TCP/IP.
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Protocol Overview
E-Mail
HTTP (WWW)
File Transfer
TCP
IP
Remote Login
UDP
ICMP ARP RARP
(Auxiliary Services)
X.25 Packet
Layer
Ethernet, X.25, HDLC etc.
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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
Transport Layer
TCP: Connection Oriented
UDP: Connection-less
Network Layer
Data Link Layer and Physical Network
Connection-less
Depends on the network
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The IP Protocol
TCP/IP
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IP Header
Version
Header Len
Class of Service
Total Length
Identification
D
M
Timeout
Fragment Position
Protocol
Header Checksum
Source Address
Destination Address
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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
misc Flags
Window (flow cntrl)
Checksum
Urgent
Options
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Addressing
IP Addresses are 32 bits long, originally using one of three
formats:
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?

OU
Internet
RTVC
132.235.0.0
CS (Morton)
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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
Web Server:
www.lerc.nasa.gov
Web
Browser
“Backbone”
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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
ISOC
IANA
IESG
IAB
IETF
Area Directors
Areas
Internet
Routing
Operations and Management
General
Security
User Services
Applications
Transport
Working Groups
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