ICOM 5026-090: Computer Networks
Review for Final Exam
By Dr. Yi Qian
Department of Electronic and
Computer Engineering
Fall 2006
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Chapter 1: Introduction to Computer Networks
• What is a computer network?
• What is a distributed system?
• What are the differences between a
distributed system and a computer network?
• The client-server model
• Peer-to-peer model
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Chapter 1: Introduction to Computer Networks
Size of Networks
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Chapter 1: Introduction to Computer Networks
Network Software: Important Concepts
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Protocol
Protocol Hierarchies
Interface
Service
Service Primitive
Relationship of Service and Protocol
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Chapter 1: Introduction to Computer Networks
ISO/OSI Reference Model
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Chapter 1: Introduction to Computer Networks
ISO/OSI Model / 7 Layers
• Physical Layer: provide transmission channel
• Data link Layer: provide reliable communication
(ACK)
• Network Layer: Control the operation of subnet
– Routing, congestion control, quality of service
• Transport Layer: accept upper packets, split if
necessary, pass to network layer, ensure arrive
correctly
• Session Layer: allows users on different machines to
establish sessions between them
• Presentation Layer: is concerned with the syntax
and semantics of the information transmitted
• Application Layer: contains a variety of protocols
that are commonly needed by users
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Chapter 1: Introduction to Computer Networks
TCP/IP Reference Model
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Chapter 1: Introduction to Computer Networks
TCP/IP Layers
• Internet
– Connectionless
– Interface: send, receive
• Transport
– UDP: User datagram protocol
• Connectionless
• Unreliable, connectionless
– TCP: transmission control protocol
• Connection oriented
• Reliable, connection-oriented, with flow control
• Application
– Telnet, FTP, SMTP, DNS, HTTP
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Chapter 1: Introduction to Computer Networks
TCP/IP Reference Model
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Chapter 1: Introduction to Computer Networks
• The similarity and differences between
ISO/OSI and TCP/IP models?
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Chapter 2: The Physical Layer
• Important Concepts
– Bandwidth
• Decibel (dB)
– The dB value is calculated by taking the log of the
ratio of the measured or calculated power (P2) with
respect to a reference power (P1).
• dB=10 x log_10 (P2/P1)
– 0 dBW = 1 watt
– 0 dBm = 1 milliwatt = 0.001 watt
– * For amplitude, we shall use
• dB=20 x log_10 (A2/A1)
• Example: P=V^2/R
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Chapter 2: The Physical Layer
Maximum Data Rate of A Channel
• Nyquist theorem
– A signal passes through a lowpass filter with
bandwidth H
– The output signal can be completely reconstruct by
making 2H samples per second
– Max data rate = 2H log_2 V bits/sec
• V is the number of discrete level of the signal
– Condition: noiseless system
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Chapter 2: The Physical Layer
Maximum Data Rate of A Channel
• In a noisy condition, the signal-to-noise ratio
SNR is defined as
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S/N
S: power of the signal
N: power of the noise
10*log_10 (S/N) is often used
• Shannon capacity
– Max number of bits per sec= H log_2 (1+S/N)
– Example: H=3,000Hz, S/N=30dB
• Max data rate = 30,000 bps
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Chapter 3: The Data Link Layer
• DLL Design Issues
– Services Provided to the Network Layer
– Framing
• To determine the start and end of a frame
– Error Control
• To provide reliable communications
– Flow Control
• To regulate the transmission of sender
– Example: fast sender and slow receiver
• Possible Service
– Unacknowledged connectionless service
– Acknowledged connectionless service
– Acknowledged connection-oriented service
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Chapter 3: The Data Link Layer
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Framing
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Error Detection and Correction
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Error-Correcting Codes
Error-Detecting Codes
Codeword
Hamming Distance & Hamming Code
Parity
Polynomial Code
CRC Algorithm
Elementary Data Link Protocols
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Character count
Flag bytes with byte stuffing
Starting and ending flags with bit stuffing
Physical layer coding violations
An Unrestricted Simplex Protocol
A Simplex Stop-and-Wait Protocol
A Simplex Protocol for a Noisy Channel
Sliding Window Protocols
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A One-Bit Sliding Window Protocol
A Protocol Using Go Back N
A Protocol Using Selective Repeat
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Chapter 4: The Medium Access Control Sublayer
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Static Channel Allocation
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TDM
FDM
Problem
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Might not be efficient if
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Dynamic Channel Allocation
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1. Station Model
2. Single Channel Assumption
3. Collision Assumption
4.(a) Continuous Time
4.(b) Slotted Time
5.(a) Carrier Sense
5.(b) No Carrier Sense
Multiple Access Protocols
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The number of users is large and continuously varying, or
The traffic is bursty
ALOHA
Carrier Sense Multiple Access Protocols
Collision-Free Protocols
Limited-Contention Protocols
Ethernet, Fast Ethernet, Gigabit Ethernet
802.2 Logical Link Control
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Chapter 5: The Network Layer
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Services Provided to the Transport Layer
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Connectionless
Connection-oriented
The Internet
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Traditionally, Internet only provide the connectionless services in the network layer
The next generation Internet may provide connection-oriented services
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Implementation of Connectionless Service
Implementation of Connection-Oriented Service
Comparison of Virtual-Circuit and Datagram Subnets
Routing Algorithms
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Quality-of-service concerns
Efficiency concerns
The Optimality Principle
Shortest Path Routing
Flooding
Distance Vector Routing
Link State Routing
Hierarchical Routing
Broadcast Routing
The Network Layer in the Internet
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The IP Protocol
IP Addresses
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Chapter 6: The Transport Layer
• What is the functionality of transport layer?
• The Internet transport protocol: UDP
• The Internet transport protocol: TCP
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