Differentiated Services (DiffServ)

Summary

This lecture covers the concept of differentiated services (DiffServ) in networking, focusing on how traffic is classified and handled differently to ensure quality of service (QoS). The script explains the role of router behaviors, such as expedited forwarding and assured forwarding, which prioritize certain packets over others for minimal delay and loss. It also discusses the use of bits in packet headers to mark premium traffic and outlines the importance of resource management in real-time applications. The lecture emphasizes the need for new service models that support both real-time and traditional applications in networking.

Takeaways

• 😀 Differentiated Services (DiffServ) allocate network resources based on traffic classes instead of individual flows, simplifying routing and improving efficiency.
• 😀 A packet can identify itself as a premium packet by setting a specific bit in the header, signaling its need for priority treatment by routers.
• 😀 If the packet's special bit is set, it indicates premium service; if not, it indicates best-effort delivery.
• 😀 The service provider sets the premium bit when delivering premium services, often based on customer requests and payment for such services.
• 😀 Routers apply different behaviors when they detect a premium bit, using standardized methods defined by the Internet Engineering Task Force (IETF).
• 😀 The router behavior for premium packets includes **Expedited Forwarding**, which prioritizes these packets with minimal delay and loss.
• 😀 Routers use **Weighted Fair Queuing (WFQ)** to manage packets, giving expedited forwarding packets strict priority over others.
• 😀 Another router behavior is **Assured Forwarding**, which employs mechanisms like **Random Early Detection (RED)** to handle packets under congestion.
• 😀 The Type of Service field in the packet header has been redefined to accommodate multiple behaviors, with 6 bits for Differentiated Services Code Point (DSCP) and 2 bits for Explicit Congestion Notification (ECN).
• 😀 The lecture highlights the importance of quality of service (QoS) models, especially for real-time applications that require guaranteed performance beyond traditional best-effort delivery models.
• 😀 The course concludes by discussing the two main approaches for managing traffic: **Integrated Services (IntServ)** and **Differentiated Services (DiffServ)**, both aiming to meet the needs of real-time applications.

Q & A

What is the main focus of differentiated services in the script?

The main focus is on managing network traffic by categorizing it into classes instead of dealing with individual flows, thereby simplifying router operations and improving quality of service.

How does differentiated services differ from traditional end-to-end best-effort delivery?

Differentiated services allocate resources to specific classes of traffic, ensuring that real-time applications receive priority over traditional best-effort traffic, whereas traditional best-effort delivery treats all traffic equally without prioritization.

What is the role of the premium bit in packet headers in differentiated services?

The premium bit in the packet header identifies packets as 'premium,' signaling that they should be treated with higher priority by routers. If the bit is set, the packet is treated as premium; if not, it is treated as best-effort delivery.

Who sets the premium bit in a packet, and under what conditions?

The premium bit is typically set by the service provider, which identifies packets as part of a premium service. The bit is set based on the customer's service agreement and the traffic type.

What happens when a router encounters a packet with the premium bit set?

When a router encounters a packet with the premium bit set, it applies specific behaviors defined by the Internet Engineering Task Force (IETF) to handle it with higher priority, ensuring minimal delay and packet loss.

What are the two key router behaviors defined by IETF in the differentiated services model?

The two key router behaviors defined by IETF are 'expedited forwarding' and 'assured forwarding.' Both aim to ensure priority treatment of certain traffic based on the markings in the packet header.

What is expedited forwarding, and how is it implemented?

Expedited forwarding is a behavior where packets marked for expedited treatment are forwarded by routers with minimal delay and loss. This is achieved by giving these packets strict priority over others using weighted fair queuing.

How does weighted fair queuing work in the context of expedited forwarding?

Weighted fair queuing works by assigning different priority levels to packets. Packets marked for expedited forwarding are given the highest priority, while other packets are processed based on their assigned priority level.

What is assured forwarding, and how does it relate to Random Early Detection (RED)?

Assured forwarding is a behavior that ensures packets are forwarded with a certain level of assurance, even during congestion. It makes use of mechanisms like Random Early Detection (RED) to manage congestion and prioritize traffic based on its markings.

What changes were made to the Type of Service (ToS) field to accommodate differentiated services?

The Type of Service field in the IP header was redefined by allocating six bits for Differentiated Services Code Points (DSCP) and two bits for explicit congestion notification (ECN), allowing more granular control over packet prioritization.