CptS 455 Intro to Computer Networks

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CptS 455Intro to Computer Networks

• Instructor Dick Lang
• ELS 130P, [phone]
• Texts Computer Networks, Tanenbaum (4th)
• Unix Network Programming, Stevens.
• Office hours Mon-Thurs, 900AM to noon
• Teaching Assistant None

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Course Outline

• Introduction
• Reference Models, OSI, TCP/IP
• Physical Layer
• Data Link Layer
• Medium Access Sublayer
• Network Layer
• Transport Layer
• Application Layer
• Socket Programming

Protocol Stack
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What to expect

• Broad exposure to computer networking concepts.
• Coverage of OSI-like protocol stacks.
• running example TCP/IP
• Significant exposure to UNIX network programming.
• Berkeley Sockets
• Some concepts of network operations.
• e.g. routing, error detection, ...

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What not to expect

• End-user training.
• e.g. How to use FTP, NetWare, WWW,
• Trade school stuff.
• e.g. How to get Novel NetWare certified, how to
  setup a Cisco router
• Detailed discussion of non-TCP/IP protocols.
• e.g. OSI, Appletalk, ...
• Massively Parallel Processing
• e.g. large numbers of interconnected, identical
  processors programmed to solve problems in
  parallel

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Grading

• Homework Assignments (25)
• About seven or so
• Written
• Socket Programming Project (20)
• Client/Server or P2P, UDP, TCP sockets
• Midterm (20)
• Final Exam (30)
• Discretionary (5)

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Introduction

• We live in the Information Age.
• Old model One large centralized computer.
• Current model Many separate but interconnected
  computers.
• Computer Network Interconnected collection of
  autonomous computers.

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Uses of computer networks

• Resource Sharing
• Mainframes are (were?) expensive
• Redundancy among resources
• Client/Server model
• Server contains resource (e.g. file system)
• Client requests resource
• Communication medium
• Access to remote information
• email, videoconferencing, WWW, Usenet,
• Entertainment (e.g. Quake)

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Classifying Networks by Transmission Technology

• Broadcast networks (small, usually localized)
• Single communication channel shared by all
  machines.
• Multicasting
• Point-to-point networks (large geographically)
• Many individual connections between pairs of
  machines.
• Routing packet switching

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Classifying Networks by Scale

• Local Area Networks (LAN)
• Restricted in size
• Broadcast transmission (10-100 Mbps)
• static divvy up time, round-robin allocation
• dynamic centralized/decentralized arbitration
• Topologies
• bus (e.g. Ethernet bus, 10 Mbps to 1Gbps)
• ring (e.g. IBM Token Ring, 4-16 Mbps)

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Large Geographic Networks

• Metropolitan Area Network (MAN)
• big LAN, no packet switching.
• Standard Distributed Queue Dual Bus (DQDB)
• 2 unidirectional buses
• Wide Area Network (WAN)
• Hosts on a LAN are connected to a subnet.
• Most WAN subnets are point-to-point.
• packet-switched, use routers

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Host
Router
Transmission Line
Subnet
LAN
WAN
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Wireless Networks

• Portable Office
• Notebook computers, PDAs, ...
• e.g. UPS Trucks, Military, ...
• Wireless LANS
• slow (1-2 Mbps), high error-rate
• Digital Cellular

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Internetworks

• Communication between different (perhaps
  incompatible) networks.
• Gateways handle the translation.
• internet Collection of interconnected networks.
• e.g. LANs connected to a WAN
• Internet the worldwide internet.

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Network Software

• Original network design focused on hardware.
• Network software is now highly structured.
• Protocol Hierarchies
• Networks are organized as a series of layers.
• Each layer offers services to the layer above.
• Hides implementation detail from higher layers.
• Layer n on one machine converses with layer n on
  another machine.

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Layers, protocols, and interfaces
Host 1
Host 2
Layer 4 protocol
Layer 4
Layer 4
Layer 3/4 interface
Layer 3 protocol
Layer 3
Layer 3
Layer 2/3 interface
Layer 2 protocol
Layer 2
Layer 2
Layer 1/2 interface
Layer 1 protocol
Layer 1
Layer 1
Physical medium
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Network layer terms

• Protocol rules and conventions of communication.
• May be implemented in hardware or software
• Peers entities comprising the corresponding
  layers on different hosts.
• Peers communicate using the protocol.
• Interface defines which primitive operations and
  services the lower layer offers the upper one.

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Network Architecture

• Network Architecture layers protocols
• Does not contain...
• Details of the implementation
• Specification of the interfaces
• Protocol Stack List of protocols used for each
  layer.
• Lower layers can change without affecting higher
  layer.

Hidden inside
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Reading

• Read 1.1 - 1.4 in Tanenbaum.

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Socket Programming Project

• Stevens text describes the details
• In the recent past we have
• Individually developed a server-less chat
  program (for Unix)
• Using UDP (User Datagram Protocol) in a P2P app.
• Each implementation to be interoperable with the
  others, obeying a common protocol spec
• Do you have interests or ideas for our project?