What is the primary function of DiffServ in QoS?

Network Security and Management

What is the function of DiffServ?

  1. It automatically identifies traffic.
  2. It guarantees end-to-end bandwidth for traffic.
  3. It categorizes traffic. Source Reference Answer
  4. It provides reserve bandwidth by using RSVP.

Community Votes

C
100%

100% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

The exam tests the distinction between DiffServ's class-based classification model and IntServ's per-flow reservation model using RSVP.

DiffServ (Differentiated Services) functions by categorizing network traffic into different service classes to apply specific Quality of Service (QoS) treatments, rather than guaranteeing bandwidth or automatically identifying flows.

Candidates often select Option B or D because they confuse DiffServ with Integrated Services (IntServ), which uses RSVP to reserve end-to-end bandwidth for specific flows.

Community Discussion (3 comments)

G0y0 👍 1 Selected: C
There are trick with the words. For example in A, what is "to identify trafic" or in C. what is "to categorize traffic?". sot in some times and contexts, both concepts could be similar. However, when we talk about something do any task automatically, there must be an algorithm to do that task continuously. In this sense, DiffServ is not an algorithm that deploy a task, rather it is a model. In this sense, I discard A, and I choose C.
b3532e4 👍 1
The function of DiffServ is discussed in your PDF file on page 317. It operates by categorizing traffic into different classes that require specific Quality of Service (QoS) treatment, which is why the correct answer is: C. It categorizes traffic. Here is the relevant excerpt from the document: "DiffServ model: This model operates on classes that require special QoS treatment. QoS components used in the DiffServ model include classification, marking, congestion management, congestion avoidance, policing and shaping, and link efficiency"
Maleck 👍 2 Selected: C
Answer is C. IntServ provides reserve bandwidth by using RSVP not DiffServ

Comments & Corrections

No comments yet — spotted an error or have a note? Share it below.

Log in to comment, report an error, or add a note about this question.

Submitted for moderation before publishing. Keep it helpful and respectful.

Expert Analysis

Why the Answer Is Correct

DiffServ operates on a coarse-grained approach where traffic is classified and marked at the network edge with Differentiated Services Code Points (DSCP). This categorization allows intermediate routers to apply Per-Hop Behaviors (PHB) based on the traffic class, such as priority queuing or dropping policies. Therefore, its core function is accurately described as categorizing traffic.

Why the Other Options Are Wrong

Option A is incorrect because DiffServ does not inherently contain algorithms to automatically identify traffic; it relies on external classifiers or manual marking before packets enter the DiffServ domain. Options B and D describe the Integrated Services (IntServ) model, which uses Resource Reservation Protocol (RSVP) to establish explicit reservations for individual flows, providing strict bandwidth guarantees that DiffServ cannot offer.

Community Comment Notes

Comment [1] correctly clarifies that RSVP is associated with IntServ, not DiffServ. Comment [2] highlights the semantic trap between 'identifying' and 'categorizing,' noting that DiffServ is a model for handling categories rather than an algorithm for discovery. Comment [3] reinforces that DiffServ works on classes requiring special QoS treatment, aligning with the definition of traffic categorization.

Official Reference

https://www.cisco.com/c/en/us/support/docs/ip/differentiated-services-diffserv/27508-5.html

Exam Strategy

When answering QoS questions, always distinguish between 'reservation' (IntServ/RSVP) and 'classification/priority' (DiffServ). If the question mentions RSVP or guaranteed bandwidth, think IntServ; if it mentions DSCP, PHB, or classes, think DiffServ.

Related Analysis

All calls that involve external parties must be based on a f

A-Grade

A company wants to block all users from forwarding calls to

S-Grade

If a trust boundary is placed on a Cisco IP phone, what occu

S-Grade

← Back to 350-801 Study Guide