Transcript Core network components - Charles Sturt University

ITC242 – Introduction to
Data Communications
TCP/IP and OSI
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“Study algorithm for this unit”
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Make up the background knowledge for this unit.
The subsequent chapter is related logically to the previous chapters.------- This means that you must
make up them if you miss one or more.
You cannot fully understand the contents being covered by only attending the class !
The content I am lecturing in the classes is harder than that of the text
Different learning outcomes, depending on the degree for which you are studying
The exam is relatively easier than…..
Before coming to my classes
(1) Read the corresponding chapter(s) to be covered
(2) Read my PowerPoint slides published on the course website
(3) Write down the questions you have
If you have not done the above, then ……
During my classes
Concentrate on listening and thinking rather than talking !
Concentrate on understanding rather than writing ! ( make notes)
After my classes
Read the text and the slides again !
If you still have questions, then
go to my office
If you still have questions, then
read the reference book(s)
If you still have questions, then
consider withdrawing from this unit
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Last Week
Topic 3 – Distributed Data Processing
• Describe the differences between centralised
and distributed data processing
• Describe different types of distributed data
processing for applications and distributed
databases
• Describe the implications for data comms of
distributed data processing
• Understand the motivation towards client server
architectures
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Last Week
Topic 4 – The Internet
• Discuss the history of the Internet and
explain it’s explosive growth
• Describe the overall Internet architecture
including key components
• Explain the components and operation of
the Domain Name System
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Topic 5 – TCP/IP and OSI
Learning objectives
• Describe the definition of a protocol;
• Discuss the need and benefits of using
protocol architectures;
• Describe the TCP/IP protocol architecture
• Describe the OSI reference model.
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What’s a protocol?
human protocols:
• “what’s the time?”
• “I have a question”
• introductions
… specific msgs sent
… specific actions
taken when msgs
received, or other
events
network protocols:
• machines rather than
humans
• all communication
activity in Internet
governed by protocols
protocols define format,
order of msgs sent and
received among network
entities, and actions
taken on msg
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transmission, receipt
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
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Protocol Architecture –
Modular Approach
• Breaks complex tasks into subtasks
• Each module handles specific subset of
tasks
• Communication occurs
– between different modules on the same
system
– between similar modules on different systems
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Advantages of Modularity
• Easier application development
• Network can change without all programs
being modified
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Organization of air travel
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
airplane routing
• a series of steps
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Layering of airline functionality
ticket (purchase)
ticket (complain)
ticket
baggage (check)
baggage (claim
baggage
gates (load)
gates (unload)
gate
runway (takeoff)
runway (land)
takeoff/landing
airplane routing
airplane routing
airplane routing
departure
airport
airplane routing
airplane routing
intermediate air-traffic
control centers
arrival
airport
Layers: each layer implements a service
– via its own internal-layer actions
– relying on services provided by layer below
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Three-Layer Model
• Distributed data communications involves three
primary components:
– Networks
– Computers
– Applications
• Three corresponding layers
– Network access layer
– Transport layer
– Application layer
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Network Access Layer
• Concerned with exchange of data between
computer and network
• Includes addressing, routing, prioritizing,
etc
• Different networks require different
software at this layer
• Example: X.25 standard for network
access procedures on packet-switching
networks
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Transport Layer
• Concerned with reliable transfer of
information between applications
• Independent of the nature of the
application
• Includes aspects like flow control and error
checking
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Application Layer
• Logic needed to support various
applications
• Each type of application (file transfer,
remote access) requires different software
on this layer
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Addressing
• Each computer on a network requires a
unique address on that network
• Each application requires a unique
address within the computer to allow
support for multiple applications (service
access points, or SAP)
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Data Transmission
• Application layer creates data block
• Transport layer appends header to create PDU
(protocol data unit)
– Destination SAP, Sequence #, Error-Detection Code
• Network layer appends another header
– Destination computer, facilities (e.g. “priority”)
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Simplified Architecture
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Protocol Architecture Operation
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Standardised Protocol
Architectures
• Vendors like standards because they make their
products more marketable
• Customers like standards because they enable
products from different vendors to interoperate
• Two protocol standards are well-known:
– TCP/IP: widely implemented
– OSI: less used, but widely known and still useful for
modeling/conceptualizing
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TCP/IP
• Transmission Control
Protocol/Internet
Protocol
• Developed by DARPA
• No official protocol
model
• Identified by 5 Layers
– Application
– Host-to-Host
(transport)
– Internet (Network)
– Network Access (link)
– Physical
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source
message
segment
M
Ht
M
datagram Hn Ht
M
frame Hl Hn Ht
M
Encapsulation
application
transport
network
link
physical
link
physical
switch
destination
M
Ht
M
Hn Ht
Hl Hn Ht
M
M
application
transport
network
link
physical
Hn Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
M
router
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TCP/IP Physical Layer
• Physical interface between a DTE (e.g.
computer or terminal) and a transmission
medium
• Specifies:
– Characteristics of medium
– Nature of signals
– Data rate
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TCP/IP Network Access (link)
• Exchange of data between systems on a
shared network
• Utilizes address of host and destination
• Can also prioritize transmission
• Software at this layer depends on network
(e.g. X.25 vs. Ethernet)
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TCP/IP Internet Layer
• An Internet is an interconnection of two or more
networks
• Internet layer handles tasks similar to network
access layer, but between networks rather than
between nodes on a network
• Uses IP for addressing and routing across
networks
• Implemented in workstations and routers
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TCP/IP Transport Layer
• Also called host-to-host layer
• Reliable exchange of data between
applications
• Uses TCP protocols for transmission
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TCP/IP Application Layer
• Logic needed to support variety of
applications
• Separate module supports each type of
application (e.g. file transfer)
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TCP & UDP
• Most TCP/IP applications use TCP for transport
layer
• TCP provides a connection (logical association)
between two entities to regulate flow check
errors
• UDP (User Datagram Protocol) does not
maintain a connection, and therefore does not
guarantee delivery, preserve sequences, or
protect against duplication
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TCP service
• Reliable, in-order byte-stream data
transfer
– loss: acknowledgements and retransmissions
• Flow control:
– sender won’t overwhelm receiver
• Congestion control:
– senders “slow down sending rate” when
network congested
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UDP
Goal: data transfer
between end systems
– same as TCP
• UDP - User Datagram
Protocol :
– connectionless
– unreliable data
transfer
– no flow control
– no congestion
control
App’s using TCP:
• HTTP (Web), FTP
(file transfer), Telnet
(remote login),
SMTP (email)
App’s using UDP:
• streaming media,
teleconferencing,
DNS, Internet
telephony
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IP and IPv6
• IP provides for 32-bit source and
destination addresses
• IPv6 (1996 standard) provides for 128-bit
addresses
• Migration to IPv6 will be a very slow
process
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TCP/IP Applications
• SMTP (Simple Mail Transfer Protocol)
– Basic e-mail facility, transferring messages among
hosts
• FTP (File Transfer Protocol)
– Sends files from one system to another on user
command
• Telnet
– Remote login capability, allowing a user to emulate a
terminal on the remote system
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Internetworking
• Interconnected networks, usually implies
TCP/IP
• Can appear to users as a single large
network
• The global Internet is the largest example,
but intranets and extranets are also
examples
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Origins of the OSI reference model
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The early development of LANs, MANs, and WANs was chaotic in many ways. The
early 1980s saw tremendous increases in the number and sizes of networks.
As companies realized that they could save money and gain productivity by using
networking technology, they added networks and expanded existing networks as
rapidly as new network technologies and products were introduced.
By the middle of the 1980s, companies began to experience difficulties from all the
expansions they had made. It became more difficult for networks using different
specifications and implementations to communicate with each other.
To address the problem of networks being incompatible and unable to communicate
with each other, the International Organization for Standardization (ISO) researched
different network schemes.
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As a result of this research, the ISO created a model that would help vendors create
networks that would be compatible with, and operate with, other networks.
the OSI reference model describes how data travels from application programs (for
example, spreadsheets), through a network medium, to an application program
located in another computer, even if the sender and receiver are connected using
different network media.
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OSI
• Open Systems
Interconnection
• Developed by ISO
• Contains seven layers
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OSI Lower Layers
• Physical
• Data Link
• Network
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OSI Physical Layer
• Responsible for transmission of bits--binary transmission
• Always implemented through hardware
• This layer outlines the functional, procedural, electrical,
and mechanical specifications for controlling physical
links. The specifications relate to the activation,
maintenance, and deactivation of physical links. It also
controls the transmitting of data onto physical media.
• e.g. RS-232
• A “hub” operates at this layer
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OSI Data Link Layer
• The data-link layer arranges bits from the physical layer into logical
chunks of data, known as frames. A frame is a contiguous series of
data with a common function. Framing enables the network to
organize bits into a logical data format and send them to the correct
computer.
• This layer controls how data is formatted and how transmission on
the network is controlled
• Responsible for error-free, reliable transmission of data
• Flow control, error correction
• Controls access to the medium
• e.g. HDLC, ethernet
• A “switch” operates at this layer
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OSI Network Layer
• Responsible for routing of messages through network
• ensures data delivery by providing connectivity and path
selection between two host systems.
• selects the most appropriate path for sending data, and
routes data packets
• Concerned with type of switching used (circuit v. packet)
• Handles routing between networks, as well as through
packet-switching networks
• provides logical LAN-to-LAN communications by
supporting the routing of data between different networks
• IP protocol and IP addressing at this layer
• A “router” operates at this layer
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OSI Upper Layers
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•
•
•
Transport
Session
Presentation
Application
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OSI Transport Layer
• Aids point-to-point communications
• Isolates messages from lower and upper layers
• Provides reliability in the transportation of data between
hosts and ensures complete data transfer. The transport
layer uses error detection and recovery information flow
control to establish, maintain, and terminate all virtual
circuits.
• Breaks down message size
• Monitors quality of communications channel
• Selects most efficient communication service necessary
for a given transmission
• TCP/UDP operate at this layer
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OSI Session Layer
• Establishes logical connections between
hosts:connection establishment, data
transfer, and connection release
• Manages log-ons, password exchange,
log-offs
• Terminates connection at end of session
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OSI Presentation Layer
• manages data representation
• transforms data into a mutually agreed format
that each application can understand
• Provides format and code conversion services
• Examples
– File conversion from ASCII to EBDIC(Extended
Binary-Coded Decimal Interchange Code )
– Encryption and compression
– Invoking character sequences to generate bold,
italics, etc on a printer
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OSI Application Layer
• Provides access to network for end-user
• User’s capabilities are determined by what
items are available on this layer
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Layering: The OSI Model
layer-to-layer communication
Application
Application
Presentation
Presentation
Session
Session
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6
5
4
3
2
1
7
6
Peer-layer communication
Transport
Router
Router
Transport
Network
Network
Network
Network
Link
Link
Link
Link
Physical
Physical
Physical
Physical
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4
3
2
1
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TCP/IP - OSI Comparison
Application
Presentation
FTP
ASCII/Binary
Session
TCP
Transport
IP
Network
Ethernet
Link
Transport
Network
Link
Physical
Application
The 7-layer OSI Model
The 4-layer Internet model
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Example: FTP over the Internet
Using TCP/IP and Ethernet
1
2
3
4
App
“A” Stanford
“B” (MIT)
OS
Ethernet
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App
19
18
17
OS
Ethernet
5
R1 6
7 8
9 R2
10
R4
14
R5
15
11 16
R3 12
13
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In the sending host
1. Application-Programming Interface (API)
– Application requests TCP connection with
“B”
2. Transmission Control Protocol (TCP)
– Creates TCP “Connection setup” packet
– TCP requests IP packet to be sent to “B”
TCP Packet
TCP
Data
TCP
Header
Type = Connection Setup
Empty
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In the sending host (2)
3. Internet Protocol (IP)
– Creates IP packet with correct
addresses.
– IP requests packet to be sent to router.
TCP Packet
TCP
Data
TCP
Header
Encapsulation
IP
Data
IP Packet
IP
Header
Destination Address: IP “B”
Source Address: IP “A”
Protocol = TCP
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In the sending host (3)
4. Link (“MAC” or Ethernet) Protocol
– Creates MAC frame with Frame Check
Sequence (FCS).
– Wait for Access to the line.
– MAC requests PHY to send each bit of the
frame
.
IP Packet
IP
Data
IP
Header
Destination Address: MAC “R1”
Source Address: MAC “A”
Protocol = IP
Encapsulation
Ethernet
FCS
Ethernet
Data
Ethernet
Header
Ethernet Packet
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In Router R1
5. Link (“MAC” or Ethernet) Protocol
– Accept MAC frame, check address and
Frame Check Sequence (FCS).
– Pass data to IP Protocol.
IP Packet
IP
Data
IP
Header
Decapsulation
Ethernet
FCS
Ethernet
Data
Ethernet
Header
Ethernet Packet
Destination Address: MAC “R1”
Source Address: MAC “A”
Protocol = IP
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In Router R1
6. Internet Protocol (IP)
– Use IP destination address to decide
where to send packet next (“next-hop
routing”).
– Request Link Protocol to transmit packet.
IP
Data
IP
Header
Destination Address: IP “B”
Source Address: IP “A”
Protocol = TCP
IP Packet
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In Router R1
7. Link (“MAC” or Ethernet) Protocol
– Creates MAC frame with Frame Check
Sequence (FCS).
– Wait for Access to the line.
– MAC requests PHY to send each bit of the
IP. Packet
frame
IP
Data
IP
Header
Encapsulation
Ethernet
FCS
Ethernet
Data
Ethernet Packet
Ethernet Destination Address: MAC “R2”
Header Source Address: MAC “R1”
Protocol = IP
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In Router R5
16. Link (“MAC” or Ethernet) Protocol
– Creates MAC frame with Frame Check Sequence
(FCS).
– Wait for Access to the line.
– MAC requests PHY to send each bit of the frame.
IP Packet
IP
Data
IP
Header
Encapsulation
Ethernet
FCS
Ethernet
Data
Ethernet
Header
Ethernet Packet
Destination Address: MAC “B”
Source Address: MAC “R5”
Protocol = IP
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In the receiving host
17. Link (“MAC” or Ethernet) Protocol
– Accept MAC frame, check address and
Frame Check Sequence (FCS).
– Pass data to IP Protocol.
IP Packet
IP
Data
IP
Header
Decapsulation
Ethernet
FCS
Ethernet
Data
Ethernet
Header
Ethernet Packet
Destination Address: MAC “B”
Source Address: MAC “R5”
Protocol = IP
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In the receiving host (2)
18. Internet Protocol (IP)
– Verify IP address.
– Extract/decapsulate TCP packet from IP
packet.
– Pass TCP packet to TCP Protocol.
TCP Packet
TCP
Data
TCP
Header
Decapsulation
IP
Data
IP Packet
IP
Header
Destination Address: IP “B”
Source Address: IP “A”
Protocol = TCP
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In the receiving host (3)
19. Transmission Control Protocol (TCP)
– Accepts TCP “Connection setup” packet
– Establishes connection by sending “Ack”.
20. Application-Programming Interface (API)
– Application receives request for TCP
connection with “A”.
TCP Packet
TCP
Data
TCP
Header
Type = Connection Setup
Empty
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Topic 5 Summary
• Looked at what a protocol is
• Discuss the need for and benefits of using
protocol architectures;
• Describe the TCP/IP protocol architecture
• Describe the OSI reference model.
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