Outline
CS4254
Computer Network Architecture and
Programming
•OSI Layering Architecture
•TCP/IP Layers
Dr. Ayman A. Abdel-Hamid
Computer Science Department
Virginia Tech
OSI and TCP/IP Layers
OSI and TCP/IP Layers
© Dr. Ayman Abdel-Hamid, CS4254 Spring 2006
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Multiple Layers of Network Protocols
OSI and TCP/IP Layers
© Dr. Ayman Abdel-Hamid, CS4254 Spring 2006
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Multiple Layers of Network Protocols
Client and Server on same Ethernet
Client and server on different LANs connected through a WAN
User process
Protocol stack
within kernel
Differentiate
¾Hub
¾L2 switch
¾L3 switch
¾Router
Ethernet
OSI and TCP/IP Layers
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OSI and TCP/IP Layers
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OSI Layers
Layers in OSI Model and Internet Protocol Suite
OSI: Open Systems Interconnection model for computer communications
ISO: International Organization for Standardization
User process, application details
kernel, communication details
OSI and TCP/IP Layers
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OSI and TCP/IP Layers
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Physical Layer 1/2
Physical Layer 2/2
•Functions
¾Transmission of a raw bit stream
¾Forms the physical interface between devices
•Issues
¾Which modulation technique (bits to pulse (analog signal))?
¾Which Line Coding technique (bits to digital signal?)
¾How long will a bit last? (bit interval vs bit rate)
¾Bit- serial or parallel transmission?
¾Half- or Full- duplex transmission?
¾How many pins does the network connector have?
¾How is a connection set up or torn down?
OSI and TCP/IP Layers
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Line Coding Example: Manchester Encoding
OSI and TCP/IP Layers
Data Link Layer 1/2
© Dr. Ayman Abdel-Hamid, CS4254 Spring 2006
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Data Link Layer 2/2
•Functions
¾Provides reliable transfer of information between two
adjacent nodes (physical link is a raw transmission facility)
¾Creates frames (manageable data units) from bits and vice
versa
¾Physical addressing (identify frame sender and/or receiver)
¾Provides frame- level error control (normally through a
trailer added at end of frame)
¾Provides flow control
¾Access Control (through a MAC sub layer)
•In summary, the data link layer provides the network layer with
what appears to be an error- free link for packets
OSI and TCP/IP Layers
© Dr. Ayman Abdel-Hamid, CS4254 Spring 2006
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OSI and TCP/IP Layers
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Network Layer 2/2
Network Layer 1/2
•Functions
¾Source-to-destination delivery of packets across multiple
networks
¾Logical addressing
¾Responsible for routing decisions
9Dynamic routing
9Fixed routing
•Performs congestion control
¾In the Internet model, the network layer does not perform
congestion control
¾Congestion control at the network layer is a current area of
research
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OSI and TCP/IP Layers
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Transport Layer
Session Layer
•Functions
¾Process-to-process delivery of entire message
¾Port addressing
¾Connection control
¾Provides reliable end-to-end communication
¾Perform end-to-end flow control
¾Perform packet retransmission when packets are lost by the
network
¾In the Internet model, the transport layer also offers
congestion control.
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•Functions
¾Network dialog controller
9Establish, maintain, and synchronize interaction
between communicating entities
¾May perform synchronization between several
communicating applications
¾Groups several user- level connections into a single
“session”
OSI and TCP/IP Layers
Presentation Layer
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Application Layer
•Functions
¾Concerned with syntax and semantics of information
exchanged between 2 systems
¾Performs specific functions that are requested regularly by
applications
9Encryption
9Compression
9Translation
‰ASCII to Unicode, Unicode to ASCII
‰LSB- first representations to MSB- first
representations
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•Functions
¾Application layer protocols are application-dependent
¾Implements communication between two applications of
the same type
¾Examples
9FTP
9HTTP
9SMTP (email)
OSI and TCP/IP Layers
OSI Layering Problems
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Internet Design Principles
•Seven layers not widely accepted
•Scale
¾Protocols should work in networks of all sizes and distances
•Standardized before implemented
•Incremental deployment
•Top three layers fuzzy
¾New protocols need to be deployed gradually
•Internet or TCP/ IP layering widespread
•Heterogeneity
¾Different technologies, autonomous organizations
•End-to-end argument [End-to-end Arguments in System Design]
¾Networking functions should be delegated to the edges; application
knows best
¾“A function can only be completely and correctly implemented with
the knowledge and help of the applications standing at the
communication end points”
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