Differentiated Services (DiffServ) and Traffic Classification

Differentiated Services (DiffServ) is defined as a class of service(COS) model that is used to describe and control the IP network traffic by class. The main aim of differentiated services is to give priority to the specific traffic that needs an uninterrupted flow of data. In Differentiated services, the traffic is divided into multiple classes and each class is treated and prioritized differently. This technique of classification used by differentiated services is useful when there are limited or less number of resources. Differentiated services work at the Network layer of the Open Systems Interconnection(OSI) Model. An example of Differentiated services is voice traffic.

As compared to the quality of service (QoS) approach Differentiated services provide with more scalable and flexible way of controlling the traffic. In the Differentiated Services model, each packet is given one of the 64 possible forwarding behaviors also known as per-hop behavior (PHBs).PHB is used to define the packet forwarding procedure of each node that is determined by the DiffServ code point.

What is Meant By DiffServ Code Point (DSCP)?

The 8-bit ToS field consists of two fields namely IP header and PHB for the required flow of packets. This IP header consists of a bit field that is known as a Differentiated Services Code Point(DSCP). The value of DSCP can range from 0 to 63. The DSCP field is used to mark the packet. The marked packet is treated differently as compared to other packets. IP precedence value and ToS field are also used to mark the traffic packet in order to get the PHB in the network.

Working of Differentiated Services

DiffServ Domain is used to identify the scope of the DiffServ protocol. The domain consists of two nodes. They are:

• Edge Routers
• Core Routers

1. Edge Routers: Edge routers are located at the borders of the domain. The functions performed by edge routers are:

• To horizontally map the DiffServ and QoS protocol that is inside the incoming domain.
• To assign the same DSCP values to the traffic flows that have same QoS requirements.
• To assign the DSCP value to all of the packets according to the QoS information stated by the incoming network.

2. Core Routers: Core routers are present inside the domain. The functions performed by core routers are:

• To forward the packets that have different policies according to their DSCP values.
• To make sure that DSCP values are treated similarly inside the domain.

The traffic classes are grouped into three types by DiffServ protocol. They are as follows:

1. Expedited Forwarding(EF): Expedited Forwarding(EF) identifies the traffic with specific QoS requirements like telephony.

2. Assured Forwarding (AF): Assured Forwarding (AF) consists of traffic classes such as AF1, AF2 , AF3 and AF4.

3. Best Effort (BE): Best Effort (BE) does not assure about QoS.

Advantages of Differentiated Services (DiffServ)

• There is no need for Differentiated services to maintain the soft state and refresh each reserved node periodically to recover from errors.

• Differentiated services are more scalable as the allocation of resources takes place in the granularity of class.

• Differentiated services can simplify network operations.

• Differentiated services are used where there is a need to provide prioritized service mechanisms.

Disadvantages of Differentiated Services (DiffServ)

• Differentiated services do not provide guaranteed performance.

• Differentiated services work more effectively only when the high-priority traffic is less.

Traffic Classification

Traffic classification in computer networks is defined as a process of identifying and classifying the data packets that traverse over the network. This network classification is used for various tasks such as QoS management, policy enforcement, managing the utilization of resources, enforcing security policies, improving the overall performance of the network and prioritizing incoming and outgoing traffic. Traffic classification is used in networking devices such as routers, switches, intrusion detection systems(IDS), and firewalls.

Traffic classification mainly groups the same and related traffic into a single category that is majorly required for data fusion for network management and security. For the network management operators and administrators classification of network traffic helps to provide high quality of service (QoS) for network users.

Traffic Classification Methods

Traffic classification can be achieved through various methods such as:

1. Port based classification

Port-based classification is defined as a type of traffic classification method where port numbers from the transport layer are used to identify the application concerning traffic. This type of classification method is supported by many networking devices and consumes fewer resources. Port-based classification method has a limitation in that it can be used only for services and applications that have fixed port numbers. For example, HTTP (Hyper Text Transfer Protocol) makes use of port 80.

2. Deep Packet Inspection (DPI)

Deep Packet Inspection(DPI) is defined as a technique of traffic classification where all the contents of packets are inspected and analyzed in real-time. The deep packet inspection method analyses the packet data at the application layer. This method checks for actual payload along with the data that is transmitted. The deep packet inspection method provides more accurate results but has a drawback in that it is more resource-intensive. The packets in the DPI method are evaluated based on the rules that are stated by network administrators.

3. Signature-Based Classification

Signature-based classification method makes use of predefined patterns and signatures for identifying the protocols that are used over the internet. Whenever any incoming traffic passes through the classification system, the new patterns or data is compared with the patterns and signatures already stored in the database. This type of method is mainly used for well-known applications and services.

FAQs on Differentiated Services (DiffServ) and Traffic Classification

Q.1: What is meant by Terms of Service(ToS)?

Answer:

Terms of Service(ToS) is defined as a type of document that describes about the responsibiliies of service provider and the user obligations that must be followed in order to continue the service. The users get terminated from the service if they don’t follow the rules that are described in Terms of Service.

Q.2: What are the three different types of network traffic and state the transmission protocol used for each?

Answer:

The three categories of network traffic are voice traffic, video traffic and data traffic. Where UDP is used for voice and video traffic because both are real time and sensitive traffic. TCP is used for data traffic as it is insensitive traffic and the retransmission mechanism of TCP can guarantee the transmission.

Q.3: What is meant by per-hop behavior in the differentiated services model?

Answer:

In Differentiated services model, each packet is given with one of the 64 possible forwarding behaviours also known as per-hop behaviour(PHBs). PHB is used to define the packet forwarding procedure of each node that is determined by DiffServ code point.