Transcript Network Protocols

Introduction and Review –
Network Protocols
Copyright © Lopamudra Roychoudhuri
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What’s a Protocol?
Human protocols:
Network protocols:
 “What’s the time?”
 Machines rather than
 “I have a question”
humans
 Introductions and good-  All communication
byes
activity in Internet
governed by protocols
… Specific messages sent
… Specific actions taken
when messages
received, or other
events
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What’s a protocol?
A human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
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Network Protocols


A set of agreed-upon rules in which computers exchange
information (rules for communication)
 Define what is communicated; how it is
communicated; when it is communicated
Key elements of a protocol:
 Syntax:
 structure or format of the data
 Semantics:
 Meanings of each section of bits
 Timing/Procedure:
 when data should be sent and how fast it can be
sent.
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Layered Protocol Architecture


Modules arranged in a vertical stack
Each layer in stack:
 Performs related functions (Each layer
implements a service)



Relies on lower layer for more primitive
functions
Provides services to next higher layer
Communicates with corresponding peer
layer of neighboring system using a
protocol
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OSI model
 International Standards Organization
(ISO, est. 1947)
 A multinational body dedicated to worldwide
agreement on international standards
 Open Systems Interconnection (OSI)
model
 An ISO standard that covers all aspects of
network communications
 First introduced in 1977.
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OSI Layers
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Layer 1 - Physical
The physical layer is responsible for the movement of
individual bits from one hop (node) to the next.
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Layer 2 - Data Link
The data link layer is responsible for moving frames from
one hop (node) to the next hop.
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Layer 3 - Network
The network layer is responsible for the delivery of
individual packets from the source host to the destination
host via hops.
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Source-to-destination delivery
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Layer 3-Network cont.



Addressing of network nodes
Sends data to correct address (possibly
across multiple networks)
Examples: IP (Internet Protocol),
Appletalk, Novell IPX
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Layer 4 - Transport
The transport layer is responsible for the delivery of a
whole message (called segment) from one process to
another process.
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Reliable process-to-process
delivery of a message
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Layer 4 – Transport cont.


Controls end-to-end error correction
and flow control
Example: Transmission Control Protocol
(TCP)
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Layer 5 – Session




Sets up and manages logical sessions
between client programs and servers
Synchronization – mechanism for
inserting check points
Dialog control – half-duplex or fullduplex
Example: NetBIOS Extended User
Interface (NETBEUI) (Microsoft)
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Layer 6: Presentation
Provides conversions between different code sets
(e.g., ASCII to EBCDIC or vice versa)
Also provides compression and encryption
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ASCII Code vs. EBCDIC Code
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Layer 7: Application
(directory
Services)
(File transfer,
Access & mgmt)
(msg handling
Services)
Functional application, not brand names
Examples: File Transfer Protocol (FTP), Telnet, Simple
Mail Transfer Protocol (SMTP)
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Summary of OSI Layers
e.g. EBCDIC to ASCII
Synchronization mechanisms and Dialog
control (half-duplex or full-duplex)
Messages
End-to-end Error and Flow
Control
Packets
Frames
Error and Flow Control over a
single link
Bits
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OSI Layers cont.
Source
Destination
Hop
Hop
‘End-to-end’ protocols
‘Hop-to-Hop’ protocols
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Internet Protocol Stack


Developed by Cerf/Kahn in the early
‘70s (earlier to OSI model)
Application:
supporting network
applications
 FTP, SMTP, SSH

Transport:


host-host data transfer
TCP, UDP, SCTP
Network:
routing of datagrams from source
to destination
 IP, routing protocols


Link:
data transfer between neighboring
network elements
 PPP, Ethernet
Physical:
bits “on the wire”
5-layer
Application
Transport
Network
Link
Physical
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TCP/IP vs. OSI Model
Connection-oriented
Connectionless
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Connectionless vs. Connectionoriented
Connectionless Service
No connection setup necessary before sending data
Data sequencing is not guaranteed
Example – UDP, IP
•Connection-oriented Service
A connection must be established first before data
transmission
Data sequencing is guaranteed
Example - TCP
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Addresses in TCP/IP
•Unique address of
Network Interface Card.
•Also supports for
multicast and broadcast
physical addresses.
•e.g. Ethernet 48 bit
globally unique address
•Numerical Address
assigned to a device
participating in a network
•e.g. 32-bit IP address for
devices in an IP network
•No two computers on
the Internet can have the
same IP address
Address for processes
to communicate with
each other
- e.g. 16-bit TCP/UDP
port addresses
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Relationship of layers and addresses in TCP/IP
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Physical Addresses
Ethernet uses a 6-byte (48 bits, 12 hexadecimal digits) physical
address, like
07:01:02:01:2C:4B
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MAC Addresses

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Every Ethernet interface (NIC) has a 6-byte
physical address, also called MAC address
(Media Access Control) or hardware
address, which is assigned and burned into
hardware when it is manufactured.
MAC address of every Ethernet device is
guaranteed to be globally unique.
Identifies some destination device on the
same LAN. Cannot identify destination device
across any router. It is a local address.
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How do you find your MAC address?
•
•
By running “ipconfig /all” in a command window
Output from ipconfig /all
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Is MAC Address all we need?

The MAC address provides the physical
address for the network interface card, but
provides no information about





its network location
what LAN,
which building, city, or
even the country in which the network resides
IP addressing provides a solution to
worldwide addressing.
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IP addresses
An internet address in IPv4
is a 4 byte global address,
separated by decimals (dotted
decimal notation),
such as 132.24.75.9
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Layer 3 IP Addresses
Carried in Internet Protocol header
Identifies a particular host (computer), which
may be on any subnet or network. It is a
global address.
4 bytes, split into
 IP Network
 IP Host
Stored by operating system. Assigned by:
IANA, ARIN and/or ISP (Network part)
Local network administrator (Host part)
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IP Addressing


Initially ‘classful’
We will discuss Classless (CIDR)
addressing later
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Dotted Decimal Notation
Class A: Large networks
Class B: Medium networks
Classful IP Addresses
Class C: Small networks
Hostid with all 0’s or all 1’s are special.
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00000000. 0 ……0
01111111. 1 ……1
10000000. 0 ……0
10111111. 1 ……1
11000000. 0 ……0
11011111. 1 ……1
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Figure 5.9
Blocks in Class A
Figure 5.10
Blocks in Class B
Figure 5.11
Blocks in Class C
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Figure 5.15
netid
Information extraction in classful addressing
000 ... 0
First address
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How do you find your IP address?
•
•
By running “ipconfig /all” in a command window
Output from ipconfig /all
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Port addresses
A port address is represented
as a 16-bit integer, such as 80
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Layer 4 TCP Ports
 Carried in TCP header
 Identifies a particular user/server process
 2 byte port codes
 Well-Known Port Numbers assigned by
ICANN / IANA and stored in “services” file
Examples:
HTTP = port 80
File Transfer (FTP) = port 21
E-mail (SMTP) = port 25
Remote login (Telnet) = port 23
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Example: Web Browsing
- I’m running Chrome on my Windows machine
- I type http://www.google.com.sa and hit ENTER.
WHAT HAPPENS???
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Web Browsing Stack
My computer is running the following protocols:
•- Application Layer = HTTP (Chrome)
•- Transport Layer = TCP
•- Network Layer = IP
•- Data Link Layer = Ethernet
•- Physical Layer = Ethernet
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Relationship of layers and addresses in TCP/IP
Example: web browser
implementing HTTP
Interface. e.g. WINSOCK on PCs
Implemented in TCP and
UDP software.
HTTP uses TCP.
e.g. TCP port 80
for web server
e.g. 192.168.1.12 (32bit)
Implemented in IP
software
e.g. Ethernet Medium
Access Control (MAC)
implemented in NIC card
(Network Interface Card)
and driver software
e.g. Ethernet address
(48-bit)
e.g. Ethernet PHY layer.
Implemented in NIC card
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