ECE506/2 #1Spring 2009© 2000-2009, Richard A. Stanley

ECE537 Advanced and High Performance Networks

1: Network Layer Review

Professor Richard A. Stanley, P.E.

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Overview of Tonight’s Class

• Administration

• Is computer security a problem, or just an interesting topic?

• What is different between computer security and network security?

• Computer security objectives and approaches

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Organizational Details

• Prof. Stanley contact information– Office: Atwater-Kent 303, but rarely there– Hours: by appointment, preferably after class– Phone: (508) 269-6482– Email: rstanley@ece.wpi.edu

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Administrivia

• Class will normally meet 4:00 – 8:00 PM every Wednesday here. Please be on time.

• We will hold 10 classes; cancellations will be announced in advance (except weather)

• Breaks as needed

• If class is cancelled for bad weather, you should receive notice. Double-check with ECE Dept. (5231) or with me if in doubt.

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Recall

• We need to set up a way for notification of cancelled/late classes

• Please put the following information on the sheet going around:– Name– Email– Telephone

• Volunteer to be at the top of the list?

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Course Text

• None. 

• Additional material will be in the form of handouts and research reports

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Course Web Page

• http://ece.wpi.edu//courses/ee579sw/ECE537

• Slides will be posted to the page before class, barring any unfortunate problems

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Policies

• Homework is due at the class following the one in which it is assigned. It will be accepted--with a one grade penalty--up to the second class after that in which it is assigned, but not after that, except in truly emergency situations. By definition, emergencies do not occur regularly.

• There is a difference between working in teams and submitting the same work. If work is a team product, it must be clearly labeled as such.

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Elements of the Course• Assignments: There will be weekly assignments,

which will be graded• Presentation: At the end of the course, student

teams will present a report prepared on a cryptography-related subject. The presentation should be well-prepared and should give an overview of a special topic in cryptography (e.g. eCash, wireless security, SSL, biometric authentication systems etc.).

• Examinations: There will be a two written examinations that will cover all topics discussed in class. The questions will range from mild to hard.

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Research Projects

• Teams of 3-5 individuals per project• Research an advanced networking topic• Prepare a report on the research• Present findings

– Note: a presentation is not the report copied into PowerPoint

• Given the nature of this course, we will do mini-reports throughout

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Grading

• Grade components– Course exams (30%)– Homework (10%)– Class participation (10%)– Course projects (50%)

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Course Topics

• Ad hoc networking

• Network extensions by wireless means

• Management challenges in high performance networks

• Colored and colorless networks

• Emerging network technologies

• Your preferences?

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Link Layer: Ethernet

Spring 2009© 2000-2009, Richard A. Stanley

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Internet Architecture

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Fundamental Network Layer Function

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Data Flow Across Layers

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Protocol Layering and Data

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Network Service Model

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Virtual Circuits

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Packet Switching

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Packet Switching vs. Virtual Circuits

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Routing Principles

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1

23

0111

value in arrivingpacket’s header

routing algorithm

local forwarding tableheader value output link

0100010101111001

3221

Interplay between routing and forwarding

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Datagram or VC network: why?

Internet• data exchange among computers

– “elastic” service, no strict timing req.

• “smart” end systems (computers)

– can adapt, perform control, error recovery

– simple inside network, complexity at “edge”

• many link types

– different characteristics

– uniform service difficult

ATM• evolved from telephony

• human conversation:

– strict timing, reliability requirements

– need for guaranteed service

• “dumb” end systems

– telephones

– complexity inside network

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Router Architecture Overview

Two key router functions:

• run routing algorithms/protocol (RIP, OSPF, BGP)• forwarding datagrams from incoming to outgoing link

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Input Port Functions

Decentralized switching: • given datagram dest., lookup output port

using forwarding table in input port memory

• goal: complete input port processing at ‘line speed’

• queuing: if datagrams arrive faster than forwarding rate into switch fabric

Physical layer:bit-level reception

Data link layer:e.g., Ethernetsee chapter 5

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Three types of switching fabrics

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Switching Via MemoryFirst generation routers:• traditional computers with switching under direct control of CPU

•packet copied to system’s memory• speed limited by memory bandwidth (2 bus crossings per datagram)

InputPort

OutputPort

Memory

System Bus

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Switching Via a Bus

• datagram from input port memory

to output port memory via a shared bus

• bus contention: switching speed limited by bus bandwidth

• 1 Gbps bus, Cisco 1900: sufficient speed for access and enterprise routers (not regional or backbone)

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Switching Via An Interconnection Network

• Overcome bus bandwidth limitations• Banyan networks, other interconnection nets initially

developed to connect processors in multiprocessor• Advanced design: fragmenting datagram into fixed

length cells, switch cells through the fabric. • Cisco 12000: switches Gbps through the

interconnection network

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Output Ports

• Buffering required when datagrams arrive from fabric faster than the transmission rate• Scheduling discipline chooses among queued datagrams for transmission

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Output port queueing

• buffering when arrival rate via switch exceeds output line speed• queueing (delay) and loss due to output port buffer overflow!

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Input Port Queuing• Fabric slower than input ports combined -> queueing

may occur at input queues • Head-of-the-Line (HOL) blocking: queued datagram at

front of queue prevents others in queue from moving forward

• queueing delay and loss due to input buffer overflow!

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Routing Algorithms

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A Link-State Routing Algorithm

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Dijkstra’s Algorithm

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Dijkstra’s Algorithm Example

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Dijkstra’s Algorithm Discussion

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Network Routing

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Distance Vector Routing

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Constructing Distance Vector

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DV Algorithm Example

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DV Algorithm Example

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Maintaining the Distance Vector

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Link Cost Changes

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Link Cost Changes (con’t.)

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DV Poisoned Reverse

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Routing Loops

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Distance Vector Example

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Distance Vector to Routing Table

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LS & DV Algorithms Compared

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Internet Network Layer

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IP Addressing

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IP Network & Hierarchical Addressing

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IP Addressing: Original Standard

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IP Addressing: CIDR

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DHCP

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NAT

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IP Packet Format (v4)

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Packet Fragmentation & Reassembly

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Routing on the Internet

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Hierarchical Routing

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Intra-/Inter-AS Routing

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Intra-AS & Inter-AS Routing

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Internet Routing

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RIP: An Intra-AS Routing Protocol

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RIP Example

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RIP Example (2)

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RIP Table Processing

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RIP Table Example

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OSPF: Another Intra-AS Routing Protocol

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Hierarchical OSPF

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Inter-AS Routing in the Internet

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BGP Routing Protocol

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BGP: Controlling Who Routes to You

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BGP: Controlling Who Routes to You

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BGP Routing Table: Whole Internet

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Why Two-Level Intra- and Inter-AS Routing?

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Summary

• Network layer takes care of routing datagrams

• Routing protocols either link status or autonomous system based

• IP a very common network layer protocol, but far from the only one!

• Routing protocols are complex and can be a topic of long study all by themselves

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Homework

• Research IPv6 and prepare a paper or presentation on this protocol (1100 words or so as a guideline). What does it bring that IPv4 does not provide? What does it lack? What is the good, the bad, and the ugly of this protocol?

ECE506/4 #81Spring 2009© 2000-2009, Richard A. Stanley

Disclaimer

Parts of the lecture slides contain original work of James Kurose, Larry Peterson, Keith Ross, Eytan Modiano, Liudvikas Bukys, and Henry Warren, and remain copyrighted materials by the original owner(s). The slides are intended for the sole purpose of instruction of computer networks at Worcester Polytechnic Institute.