Lecture Nine - Network Management

Question 1

Quality of Service - Internet Nature

Answer 1

Operates as a “best effort” network, with no guaranteed service quality.

Question 2

Quality of Services - Challenges

Answer 2

Inelastic applications like video conferencing require low delay.
Flexible applications still need minimum service guarantees.

Question 3

Quality of Services (QoS) Definition

Answer 3

Overall Network Performance: As perceived by users.
Performance Guarantees: Provided by the network to users.
Examples of Inelastic Applications: Video calls, VoIP.
Examples of Flexible Applications: Web browsing, email.

Question 4

Performance Metrics for QoS

Answer 4

Error Rates: Frequency of transmission errors.
Bit Rate: Speed of data transmission.
Throughput: Actual data rate achieved.
Transmission Delay: Time taken for data to reach the destination.
Availability: Uptime and accessibility of network services.
Jitter: Variation in packet arrival times.

Question 5

QoS Issues Addressed

Answer 5

Application Requirements: Meeting specific needs of applications.
Traffic Regulation: Controlling data flow to prevent congestion.
Resource Provisioning: Allocating necessary resources for efficient network operation.
Network Health: Maintaining optimal network performance.

Question 6

QoS Principles (Principle 1)

Answer 6

Packet Marking: Differentiates between traffic types, allowing routers to prioritize packets accordingly.
Policy Implementation: New policies required for routers to manage marked packets.

Question 7

QoS Principles (Principle 2)

Answer 7

Isolation: Protects different flows from interfering with each other.
Marking and Policing: Needed at network edges to enforce bandwidth compliance.

Question 8

Application Misbehaviour

Answer 8

Issue: FTP bursts can congest routers, dropping audio packets.
Solution: Implement policing mechanisms to ensure adherence to bandwidth requirements.

Question 9

Bandwidth Allocation

Answer 9

Assigns specific bandwidth portions to each flow.
Efficiency Concern: Allocated bandwidth may be underutilized if a flow does not use its full allocation.

Question 10

QoS Principles (Principle 3)

Answer 10

Efficient Resource Use: Ensures network resources are used effectively, minimizing waste.
Dynamic Allocation: Adjusts resource allocation based on current network demands.

Question 11

Finite Resources

Answer 11

Network capacity is limited, and traffic beyond link capacity cannot be served.

Question 12

QoS Principles (Principle 4)

Answer 12

Call Admission Process: Applications declare their resource needs through a flow description.
Service Admission: Network may refuse service if unable to meet the declared needs.
Objective: Prevent overloading and ensure QoS for existing connections.

Question 13

Admission Control

Answer 13

Function: Regulates incoming traffic to avoid network congestion.
Process:
Flow Description: Transmitter/receiver describes the flow to be generated.
Network Evaluation: Assesses current state to admit or reject the call.
Example: Describes the flow’s required bandwidth, latency, and jitter.

Question 14

Traffic Shaping

Answer 14

Objective: Regulate average rate and burstiness of data flows.
Traffic Characteristics:
Bursty Traffic: Arrives at non-uniform rates due to app switching and compression variability.
Service Level Agreement (SLA): Agreement between network and users on expected traffic patterns.
Mechanisms: Monitor and enforce compliance with SLAs.

Question 15

Leaky and Token Buckets

Answer 15

Purpose: Determine if a flow conforms to agreed average and peak data rates.
Functionality:
Rate Limiting: Long-term flow rates are limited, allowing short bursts within a regulated length.
Burst Management: Smoothes large bursts to prevent congestion.

Question 16

Token Bucket Mechanics

Answer 16

Token Consumption: Sending a packet requires consuming a token.
Max Burst Duration: Calculated based on token bucket capacity, generation rate, and max data output rate.

Question 17

Leaky and Token Buckets - Solution

Answer 17

Let:
B: max token bucket capacity (bytes);
R: token generation rate (bytes/sec);
M: max data output rate (bytes/sec)
Consider a burst of length S (Secs)
Maximum burst duration is calculated using the formula
S = B/(M-R)

Question 18

Packet Scheduling - Router Handling of Packets

Answer 18

Determines how incoming packets are processed.

Question 19

First-In-First-Out (FIFO):

Answer 19

Process: Packets processed sequentially as they arrive.
Tail Drop: New arrivals are rejected if the buffer is full.
Issues: Vulnerable to high-jacking by bursty flows, may cause global TCP synchronization.

Question 20

Random Early Detection (RED)

Answer 20

Approach: Drops packets randomly based on queue size.
Objective: Prevents congestion by proactively managing buffer utilization.

Question 21

Packet Scheduling - Fair Queueing

Answer 21

Separate Queues: Maintains a queue for each flow.
Round Robin Scheduling: Flows are served based on a round robin approach.
Issue: Long packets may receive favorable treatment.

Question 22

Packet Scheduling (Fair Queueing) - Improvement

Answer 22

Size Consideration: Prioritize packets by considering arrival time and size.
Weighted Fair Queueing: Assigns weights to prioritize flows with different service rates.

Question 23

Integrated Services

Answer 23

IETF RFCs Focus: Initially targeted multimedia streaming requirements.
Motivation:
Digital Video Broadcasting (DVB): Dynamic group membership changes as viewers switch channels.
Scalability Challenge: Pre-allocated bandwidth is inefficient and unsustainable.
Solution: Introduce protocols and architectures to support dynamic bandwidth allocation and QoS.

Question 24

Resource reSerVation Protocol (RSVP)

Answer 24

Role: Main component of IntServ architecture for resource provisioning.
Functions:
Bandwidth Allocation: Reserves network resources like bandwidth, memory, and CPU cycles.
Multicast Support: Facilitates many-to-many communications.
Flexibility: Allows receivers to switch channels and manage congestion.
Optimization: Efficiently utilizes bandwidth and eliminates congestion through proactive reservations.

Question 25

IntServ Architecture Cons

Answer 25

Communication Overhead: Establishing each flow requires significant overhead.
Per-Flow State Maintenance: Routers maintain internal states for each flow.
Router Failure Impact: Flow setup must restart if a router crashes.
Complexity: Increases router communication complexity and code footprint.

Question 26

Differentiated Services (DiffServ)

Answer 26

Architecture: Class-based approach defined by network administrators (e.g., ISPs).
Service Classes:
Examples: Web-browsing vs. VoIP; premium vs. regular clients.
Packet Marking: Each packet is marked with its service class for differentiated handling.
Per Hop Behavior: Each router treats packets based on class, without network-wide guarantees.
Advantages:
No Setup Required: No resource reservation or end-to-end negotiation needed.

Question 27

Expedited Forwarding

Answer 27

Universal Class: Standardized class distinguishing high QoS traffic from regular traffic.
Network Support: Provides dedicated resources for expedited forwarding (e.g., priority schedulers).
Note: Does not require additional ICT infrastructure, utilizes existing physical lines.

Question 28

Assured Forwarding

Answer 28

Scheme Overview: Elaborate class-based architecture with multiple service classes.
Structure:
Priority Classes: Four levels, each with dedicated resources.
Discard Classes: Three levels to handle congestion.
Total Service Classes: 12 distinct classes defined.
Packet Handling: Labeled at source, subject to forwarding and policing rules at each hop.