The Link Layer's Service

Options for Link Layer Service
(Reliable)

Options for Link Layer Service
(Error control)

Distringuish: Service Versus Implementation

Basic Link Layer Functions - Framing

Basic Link Layer Functions - Error Control

Basic Link Layer Functions - Connection Setup

Basic Link Layer Functions - Flow Control

Framing

Framing by Character Counting

Basic Technique: Put Control Data into a Header

Framing by Flag Bytes/Byte stuffing

Framing by Flag Bit Patterns / Bit Stuffing

Framing by Coding Violations

Error Control
(basic aspects)

Error Control
(Detect, but do not correct)

Error Control
(Correct, but do not detect)

Error Detection

Error Detection
(Bild)

Error Control - Redundancy
(1)

Error Control - Redundancy
(2)

How Do Illegal Messages Help With Detecting Bit Errors?

How Do Illegal Messages Help With Detecting Bit Errors?
(Hope)

How Do Illegal Messages Help With Detecting Bit Errors?
(realizing hope)

Altering Frames by Changing Bits

Simple Redundancy Examples: Parity (1)
(Odd parity)

Simple Redundancy Examples: Parity (1)
(even parity)

Simple Redundancy Examples: Parity (1)
(Example)
- Original message without redundancy: 01101011001
- Odd parity: ??
- Even parity: ??

Simple Redundancy Examples: Parity (2)
- Send 1 0 1 1 0 0 0 in even parity

Simple Redundancy Examples: Parity (2)
- Send 1 0 1 1 0 1 0 in even parity

Simple Redundancy Examples: Parity (2)
(even parity expectations)

Simple Redundancy Examples: Parity (3)
(Parity bit problems + how to solve them)

Simple Redundancy Examples: Parity (3)
(Parity bit probolems - Example)

Simple Redundancy Examples: Checksum (1)
(Checksums)

Simple Redundancy Examples: Checksum (1)
(Checksum example)

Simple Redundancy Examples: Checksum (2)

Distance Between Frames

Hamming Distance of a Set of Frames

Hamming Distance and Error Detection/Correction

Hamming Distance and Detection/Correction

Hamming Distance and Detection/Correction

Generalization - Required Hamming Distances
(detect)

Generalization - Required Hamming Distances
(correct)

Frame Sets - Code Booke, Codes
(terminology aspect - code book / code)

Frame Sets - Code Books, Codes
(teminology aspect - R)

Frame Sets - Code Books, Codes
(terminology aspect -

Frame Sets - Code Books, Code

How to Construct Error Correcting Codes

How to Construct Error Correcting Codes
(simple example)

How to Construct Error Detecting Codes - CRC

How to Construct Error Detecting Codes - CRC
(CRC)

How to Construct Error Detecting Codes - CRC
(basic operation bassed on polynomial arithmetic)

Modulo 2 Arithmetic

Modulo 2 Division

Modulo 2 Division
(Number example)
**

Modulo 2 Division With Remainder
(Number example)
**

Polynomials Over Modulo 2 Arithmetic

Bit Strings and Polynomial Modulo 2
(Idea)

Bit Strings and Polynomial Modulo 2

Use Polynomials to Compute Redundancy Bits - CRC
(1)

Use Polynomials to Compute Redundancy Bis - CRC
(2)

CRC Transmission and Reception
(What happens in the channel after transmitting T(x)? - No errors)

CRC Transmission and Reception
(What happens in the channel after transmitting T(x)? - Bit errors)

CRC Transmission and Reception
(At the receiver)

CRC - Overview

Choice of G(x) Determines CRC Properties
(When is remainder of E(x) / G(x) != 0?)

Choice of G(x) Determines CRC Properties
(Odd number of errors)

Commonly Used CRC Generator Polynomials

How to Handle Detected Errors?

How to Handle Detected Errors?
(Forward)

How to Handle Detected Errors?
(Backward)

How to Handle Detected Errors
(ARQ)

A Simple, Simplex, Acknowledgement-Based Protocol

Acknowledgment-Based Protocol, Second Trial
(Cure one Problem)

Acknowledgment-Based Protocol, Second Trial
(first solution attempt)

Acknowledgement-Based Protocol, Second Trial - Does Second Version Work Correctly?

Acknowledgement-Based Protocol, Second Trial - Does Second Version Work Correctly?
(Does it ensure that all packets arrive, in correct order?)

Acknowledgement-Based Protocol, Second Trial - Does Second Version Work Correctly?
(What if an acknowledgment is lost?)

Acknowledgement-Based Protocol, Second Trial - Does Second Version Work Correctly?
(Summary of Second Version: Send and Wait)
(1)

Acknowledgement-Based Protocol, Second Trial - Does Second Version Work Correctly?
(Summary of Second Version: Send and Wait)
(2)

Acknowledgement-Based Protocol, Second Trial - Does Second Version Work Correctly?
(Summary of Second Version: Send and Wait)
(3)

Overcoming the Problem of Send and Wait
(Problem - Sender)

Overcoming the Problem of Send and Wait
(Problem - Receiver)

Overcoming the Problem of Send and Wait
(Solution)

Acknowledgements & Sequence Numbers - 3rd Version

Assessment of 3rd Version - Altering Bit Protocol
(1)

Assessment of 3rd Version - Altering Bit Protocol
(2)

Alternating Bit Protocol - Efficiency

Improving Efficiency - Have More "Outstanding" Packets
(1)

Improving Efficiency - Have More "Outstanding" Packets
(2)

Improving Efficiency - Have More "Outstanding" Packets
(3)

Improving Efficiency - Have More "Outstanding" Packets
(Bild)

Sliding Windows to Handle Multiple Outstanding Packets

Sliding Windows to Handle Multiple Outstanding Packets
(Sender)

Sliding Windows to Handle Multiple Outstanding Packets
(Receiver)

Sliding Window - Simple Example

Transmission Errors and Receiver Window Size
(Assumption)

Transmission Errors and Receiver Window Size
(Bild)

Go-Back-N
(receiver window size 1)

Go-Back-N
(timeout)

Go-Back-N
(Assessment)

Selective Reject (Selective Repeat)

Duplex Operation and Piggybacking
(so far)

Duplex Operation and Piggybacking
- What happens when the upper service interface should support full-duplex operation?
(One option)

Duplex Operation and Piggybacking
- What happens when the upper service interface should support full-duplex operation?
(better option)

Duplex Operation and Piggybacking
- What happens when the upper service interface should support full-duplex operation?
(best (and usual) option)

Performance: Error-Free Send and Wait (1)

Send and Wait Link Utilization

Performance: Error-Free Send and Wait (2)

Performance: Send-and-Wait ARQ with Errors

The Parameter a

Stop-and-Wait Timing (transmission time = 1; propagation time = a)

Performance of Send and Wait

Performance: Error-Free Sliding Windows ARQ (1)
(what is W)

Performance: Error-Free Sliding Windows ARQ (1)
(Case 1 & 2)

Timing of Sliding-Window Protocol

Performance: Sliding Windows Utilization as Function of a
(y-Achse = Utilization
x-Achse = a)

Performance: Normalized Throughput in Case of Errors

Performance: ARQ Utilization as Function of a

Performance: ARQ Utilization as Function of W

Conclusions - Data Link Layer
(Errors)

Conclusions - Data Link Layer
(Flow Control)

Conclusions - Data Link Layers
(error control scheme)

Conclusions - Data Link Layers
(Connections)

Chapter 10

Security Objectives of IPSec
(IPSec aims to ensure the following security objectives)
(Data origin authentication/connectionless data integrity)
(Replay protection)

Security Objectives of IPSec
(IPSec aims to ensure the following security objectives)
(Confidentiality)

Security Objectives of IPSec
(Security policy)

IPSec: Security Association

IPSec: Security Association
(An SA can be set up between the following peers)

IPSec: Security Association
(There are two conceptual databases associated with SAs)

IPSec: Protocol Modes
(An AS is always of one of the following types)
(Transport mode)

IPSec: Protocol Modes
(An AS is always of one of the following types)
(Tunnel Mode)

IPSec: Protocol Modes
(Transport mode)

IPSec: Protocol Modes
(Tunnel Mode)

IPSec: Nesting of Security Associations

IPSec: Authentication Head (AH)

IPSec: Encapsulating Security Payload (ESP)

IPSec: Establishment of Security Associations

IPSec: Establishment of Security Associations
(SA establishment can be realized:)

IPSec: Establishment of Security Associations
(IPSec defines a standardized method for SA establishment:)
(ISAKMP)

IPSec: Establishment of Security Associations
(IKE)

Internet Firewalls

Firewalls: Terminology
(Firewall)

Firewalls: Terminology
(Packet Filtering)

Firewalls: Terminology
(Bastion Host)

Firewalls: Terminology
(Dual homed host)

Firewalls: Terminology
(Proxy)

Firewalls: Terminology
(Network Address Translation (NAT))

Firewalls: Terminology
(Perimeter Network)

Firewalls: Architectures
(1)

Firewalls: Architectures
(2)

Firewalls: Architectures
(3)

Firewalls: Packet Filtering
(What can be done with packet filtering)

Firewalls: Packet Filtering
(Basic packet filtering enables to control data transfer on)

Firewalls: An Example Packet Filtering Request