CS455 Introduction to Computer Networks

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CS455 Introduction to Computer Networks
WSU Vancouver

• Dr. Wenzhan Song
• Assistant Professor, Computer Science

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Course roadmap

• Introduction
• Application Layer WWW, FTP, email, DNS,
  multimedia
• Transport Layer reliable end-end data transfer
  principles, UDP, TCP
• Network Layer IP addressing, routing and other
  issues
• Data Link Layer framing, error control, flow
  control
• Medium Access Control (MAC) Layer
  multiple-access, channel allocation
• Physical Layer wired, wireless, satellite
• Other Topics network security, social issues,
  hot topics, research directions

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Roadmap Network Layer

• Network layer design issues
• overview of service models
• Virtual circuits and datagram networks
• IP Internet Protocol
• datagram format, IPv4 addressing
• NAT, IPv6
• ICMP, ARP, DHCP
• Routing algorithms
• distance vector
• link state
• Routing Protocol in Internet
• RIP
• OSPF
• BGP
• Other issues in network layer

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Other issues in network layer

• Congestion control (in network)
• QoS
• Internetworking

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Congestion

• When too much traffic is offered, congestion sets
  in and performance degrades sharply.

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General Principles of Congestion Control

• Monitor the system .
• detect when and where congestion occurs.
• Pass information to where action can be taken.
• Adjust system operation to correct the problem.

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Congestion Prevention Policies

• Policies that affect congestion.

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Congestion Control in Virtual-Circuit Subnets

• (a) A congested subnet.
• (b) A redrawn subnet, eliminates congestion and a
  virtual circuit from A to B.

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Hop-by-Hop Choke Packets

• (a) A choke packet that affects only the source.
• (b) A choke packet that affects each hop it
  passes through.

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Quality of Service

• Requirements
• Techniques for Achieving Good Quality of Service
• Integrated Services
• Differentiated Services
• Label Switching and MPLS

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Requirements

• How stringent the quality-of-service requirements
  are.

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Techniques to achieve good QoS

• Overprovisioning
• used in telephone network, providing enough
  router capacity, buffer space and bandwidth
• Traffic shaping
• Smooth out the traffic on the server side, rather
  than on client side
• Proportional routing
• Split traffic over multiple paths
• Buffering
• Leaky bucket algorithm
• The token bucket algorithm
• Resource reservation
• Admission control
• Packet scheduling

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Buffering

• Smoothing the output stream by buffering packets.

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The Leaky Bucket Algorithm

• (a) A leaky bucket with water.
• (b) a leaky bucket with packets.

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The Token Bucket Algorithm

• Token Bucket provide different traffic shaping
  than leaky bucket
• Allow burst traffic
• May throw tokens, but not packets

5-34

• (a) Before. (b) After.

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Traffic shape
(a) Input to a leaky bucket. (b) Output from a
leaky bucket. Output from a token bucket with
capacities of (c) 250 KB, (d) 500 KB, (e) 750 KB
(f) Output from a 500KB token bucket feeding a
10-MB/sec leaky bucket.
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Admission Control
5-34

• An example of flow specification.

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Packet Scheduling
Byte-by-byte round robin

• (a) A router with five packets queued for line O.
• (b) Finishing times for the five packets.

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Label Switching and MPLS

• Transmitting a TCP segment using IP, MPLS, and
  PPP.

• MPLS MultiProtocol Label Switching
• MPLS vs. VC network
• Similarity based on label switching, differ
  than routing
• Difference no pre-connection setup, it is
  on-demand VC creation

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Switch and Router

• (a) Two Ethernets connected by a switch.
• (b) Two Ethernets connected by routers.

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Tunneling

• Tunneling a packet from Paris to London.

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Tunneling (2)

• Tunneling a car from France to England.

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Reading Assignment

• Chapter 5