Lecture Nine - Network Management Flashcards
Quality of Service - Internet Nature
Operates as a “best effort” network, with no guaranteed service quality.
Quality of Services - Challenges
Inelastic applications like video conferencing require low delay.
Flexible applications still need minimum service guarantees.
Quality of Services (QoS) Definition
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.
Performance Metrics for QoS
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.
QoS Issues Addressed
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.
QoS Principles (Principle 1)
Packet Marking: Differentiates between traffic types, allowing routers to prioritize packets accordingly.
Policy Implementation: New policies required for routers to manage marked packets.
QoS Principles (Principle 2)
Isolation: Protects different flows from interfering with each other.
Marking and Policing: Needed at network edges to enforce bandwidth compliance.
Application Misbehaviour
Issue: FTP bursts can congest routers, dropping audio packets.
Solution: Implement policing mechanisms to ensure adherence to bandwidth requirements.
Bandwidth Allocation
Assigns specific bandwidth portions to each flow.
Efficiency Concern: Allocated bandwidth may be underutilized if a flow does not use its full allocation.
QoS Principles (Principle 3)
Efficient Resource Use: Ensures network resources are used effectively, minimizing waste.
Dynamic Allocation: Adjusts resource allocation based on current network demands.
Finite Resources
Network capacity is limited, and traffic beyond link capacity cannot be served.
QoS Principles (Principle 4)
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.
Admission Control
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.
Traffic Shaping
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.
Leaky and Token Buckets
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.
Token Bucket Mechanics
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.
Leaky and Token Buckets - Solution
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)
Packet Scheduling - Router Handling of Packets
Determines how incoming packets are processed.
First-In-First-Out (FIFO):
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.
Random Early Detection (RED)
Approach: Drops packets randomly based on queue size.
Objective: Prevents congestion by proactively managing buffer utilization.
Packet Scheduling - Fair Queueing
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.
Packet Scheduling (Fair Queueing) - Improvement
Size Consideration: Prioritize packets by considering arrival time and size.
Weighted Fair Queueing: Assigns weights to prioritize flows with different service rates.
Integrated Services
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.
Resource reSerVation Protocol (RSVP)
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.
IntServ Architecture Cons
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.
Differentiated Services (DiffServ)
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.
Expedited Forwarding
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.
Assured Forwarding
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.
