1. Department of Computer Science Southern Illinois University Carbondale CS441 – Mobile & Wireless Computing Overview of Computer Networking Protocols and Layering
Thanks to:
Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004
Data and Computer Communications 7th Edition.
William Stallings
Prentice-Hall PTR
Computer Network 4th edition Andrew S. Tanenbaum Prentice-Hall PTR
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2. What’s the Internet: “nuts and bolts” view
Millions of connected computing devices: hosts = end systems
Running network apps
Communication links
fiber, copper, radio, satellite
transmission rate = bandwidth
Routers: forward packets (chunks of data)
Protocols control sending, receiving of msgs
e.g., TCP, IP, HTTP, FTP, PPP
Internet: “network of networks”
loosely hierarchical
public Internet versus private intranet
Internet standards
RFC: Request for comments
IETF: Internet Engineering Task Force
local ISP
company
network
regional ISP
router
workstation
server
mobile
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3. The network edge End systems (hosts) Client/Server model
Run application programs
e.g., web,
at “edge of network”
Client/Server model
Client host requests, receives service from always-on server
e.g., Web browser/server; client/server
Peer-Peer model
Minimal (or no) use of dedicated servers
e.g., Gnutella, KaZaA
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4. What’s the Internet: a service view
Communication infrastructure enables distributed applications
Network edge: applications and hosts
Network core:
routers
network of networks
Physical media: communication links
Applications: Web, , games, e-commerce, file sharing
Communication services provided to apps:
Connectionless unreliable
Connection-oriented reliable
Various protocols are used for communication services
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5. 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 messages sent and received among network entities, and actions taken on message transmission, receipt
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6. What’s a protocol? A human protocol and a computer network protocol:Hi
Got the
time?
2:00
TCP connection
req
response
Get
<file>
time
Q: Other human protocols?
Key Elements of a Protocol:
Syntax
Data formats
Signal levels
Timing
Speed matching
Sequencing
Semantics
Control information
Error handling
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7. Protocol “Layers” Networks are complex! Many “pieces”:
hosts
routers
links of various media
applications
protocols
hardware, software
Consider the following analogy:
Organization of air travel
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
Question:
Is there any hope of organizing structure of network?
Or at least our discussion of networks?
A series of steps
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8. Layering of airline functionality
ticket (purchase)
baggage (check)
gates (load)
runway (takeoff)
airplane routing
departure
airport
arrival
intermediate air-traffic
control centers
ticket (complain)
baggage (claim
gates (unload)
runway (land)
ticket
baggage
gate
takeoff/landing
Layers: Each layer implements a service
via its own internal-layer actions
relying on services provided by layer below
Why Layering?
Dealing with complex systems
Explicit structure allows identification, relationship of complex system’s pieces
Layered reference model for discussion
Modularization eases maintenance, updating of system
Change of implementation of layer’s service transparent to rest of system
e.g., change in gate procedure doesn’t affect rest of system
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9. Standardized Protocol Architectures
Required for devices to communicate
Vendors have more marketable products
Customers can insist on standards based equipment
Two standards:
OSI Reference model
Open Systems Interconnection
Developed by the International Organization for Standardization (ISO)
Seven layers
Never lived up to early promises
TCP/IP protocol suite
Most widely used
De facto standard
Also: IBM Systems Network Architecture (SNA)
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10. OSI - The Model A layer model
Each layer performs a subset of the required communication functions
Each layer relies on the next lower layer to perform more primitive functions
Each layer provides services to the next higher layer
Changes in one layer should not require changes in other layers
Why OSI did not take over the world
Bad timing
Bad technology
Bad implementations
Bad politics
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11. The OSI Environment
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12. OSI as Framework for Standardization
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13. Elements of Standardization
Protocol specification
Operates between the same layer on two systems
May involve different operating system
Protocol specification must be precise
Format of data units
Semantics of all fields
Allowable sequence of PCUs
Service definition
Functional description of what is provided
Addressing between applications
Referenced by SAPs
Services between adjacent layers expressed in terms of primitives and parameters
Primitives specify function to be performed
Parameters pass data and control info
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14. OSI Layers Transport Physical Session Data Link Presentation Network
Exchange of data between end systems
Error free
In sequence
No losses
No duplicates
Quality of service
Session
Control of dialogues between applications
Dialogue discipline
Grouping
Recovery
Presentation
Data formats and coding
Data compression
Encryption
Application
Means for applications to access OSI environment
Physical
Physical interface between devices
Mechanical
Electrical
Functional
Procedural
Data Link
Means of activating, maintaining and deactivating a reliable link
Error detection and control
Higher layers may assume error free transmission
Network
Transport of information
Higher layers do not need to know about underlying technology
Not needed on direct links
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15. Use of a Relay
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16. TCP/IP Protocol Architecture
Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)
Used by the global Internet
No official model but a working one.
Application layer
Host to host or transport layer
Internet layer
Data link layer
Physical layer
Problems:
Service, interface, and protocol not distinguished
Not a general model
No exact separate mention of physical and data link layers
Sometimes called host-to-network layer
Minor protocols deeply entrenched, hard to replace
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17. Layer Descriptions Physical Layer Data Link Layer Internet (IP) Layer
Physical interface between data transmission device (e.g. computer) and transmission medium or network
Characteristics of transmission medium
Signal levels
Data rates
Data Link Layer
Exchange of data between neighboring network nodes
Invoking services like priority
Internet (IP) Layer
Systems may be attached to different networks
Routing functions across multiple networks
Implemented in end systems and routers
Transport Layer (TCP)
Reliable delivery of data
Ordering of delivery
Application Layer
Support for user applications: HTTP, SMTP
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18. OSI vs TCP/IP
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19. Protocols and networks in the TCP/IP model
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20. How is a connection established?
TCP/IP is already part of your computer’s OS
Application layer initiates the process
TCP adds the PORT number (known as SAP in OSI Model) to the packet
For each application there is a different port number (e.g., SMTP= 25)
Makes a connection request to the receiving side
IP adds the IP address of the destination computer
Link or MAC layer determines the destination MAC address and creates a frame by appending that address
Passes it to physical layer for transmission
Physical layer converts it to bits and transmits
The reverse order is followed at the receiver site to receive the packet at the given PORT
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21. PDUs in TCP/IP
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22. Encapsulation source destination application transport network link
message M
application
transport
network
link
physical
segment Ht M
datagram Ht Hn M
frame Ht Hn Hl M
link
physical Ht Hn Hl M Ht Hn Hl M
switch
destination
network
link
physical Ht Hn M Ht Hn M M
application
transport
network
link
physical Ht Hn Hl M Ht Hn Hl M Ht M Ht Hn M
router Ht Hn Hl M
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23. Some Protocols in TCP/IP Suite
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