I85PREP
⌘ K
Nokia QoS study materials
Nokia QoS study resources

Nokia QoS practice questions

One question at a time. Build your Nokia QoS understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1QoS fundamentals and Nokia QoS architecture

In the Nokia QoS architecture, which plane is responsible for carrying user traffic and applying the forwarding treatment that QoS policies dictate?

  1. The signalling plane
  2. The control plane
  3. The forwarding plane Correct answer.
  4. The management plane

Explanation

QoS in Nokia systems is enforced where packets are actually handled, which is the forwarding plane. The control plane sets up state and the management plane configures policy, but the per-packet scheduling, marking, and dropping happen in forwarding. This separation is why policy defined centrally still takes effect at the data path.

Question 2QoS fundamentals and Nokia QoS architecture

What is the primary purpose of classifying packets at the ingress of a Nokia QoS-enabled node?

  1. To compress headers to reduce bandwidth usage
  2. To encrypt payloads before they leave the node
  3. To assign each packet to a forwarding class and drop precedence Correct answer.
  4. To synchronize clocks across the network

Explanation

Classification maps incoming traffic to a forwarding class and drop precedence so that the scheduler knows how to treat it. Encryption, compression, and clock synchronization are separate functions unrelated to QoS classification. Without classification, per-hop treatment cannot be differentiated.

Question 3QoS fundamentals and Nokia QoS architecture

A Nokia forwarding class (FC) primarily determines which treatment for a packet?

  1. Its IP address assignment method
  2. Its routing protocol preference
  3. Its queue and scheduling behaviour relative to other traffic Correct answer.
  4. Its MAC learning behaviour

Explanation

A forwarding class groups traffic with the same per-hop behaviour, so it selects the queue and the scheduler treatment. It does not influence addressing, MAC learning, or routing preference. Drop precedence within the class then refines how aggressively packets are discarded under congestion.

Question 4QoS fundamentals and Nokia QoS architecture

Within a single forwarding class in Nokia QoS, what does the drop precedence value control?

  1. The TTL decrement applied to the packet
  2. The VLAN tag applied to the frame
  3. The likelihood that a packet is discarded when the queue is congested Correct answer.
  4. The physical port the packet exits on

Explanation

Drop precedence distinguishes flows of the same class so that, under congestion, higher-precedence packets are dropped first. It does not affect port selection, VLAN tagging, or TTL handling. This lets a provider protect in-profile traffic while discarding out-of-profile traffic of the same class.

Question 5QoS fundamentals and Nokia QoS architecture

Which statement best describes the role of a policer in Nokia QoS?

  1. It meters a traffic stream and marks or drops packets that exceed the committed rate Correct answer.
  2. It reorders packets to prioritize latency-sensitive flows
  3. It fragments large packets to fit the MTU
  4. It buffers excess traffic indefinitely until congestion clears

Explanation

A policer meters traffic against a committed rate and takes action, typically marking down or dropping, on packets that exceed it. It does not buffer traffic, reorder packets, or perform fragmentation. Policing differs from shaping in that it does not delay excess traffic.

Question 6QoS fundamentals and Nokia QoS architecture

How does shaping differ from policing in a Nokia QoS deployment?

  1. Shaping buffers excess traffic and releases it later, while policing acts immediately Correct answer.
  2. Shaping only applies to multicast, while policing applies to unicast
  3. Shaping changes the DSCP value, while policing changes the VLAN
  4. Shaping drops all excess traffic immediately, while policing buffers it

Explanation

Shaping smooths traffic by delaying excess packets in a buffer and releasing them at the configured rate. Policing instead takes immediate action, such as dropping or marking down, on traffic above the rate. The choice affects delay and loss characteristics seen by the application.

Question 7QoS fundamentals and Nokia QoS architecture

In a Nokia HQoS (hierarchical QoS) scheduler, what is the benefit of arranging queues into nested scheduler levels?

  1. It removes the need for classification at ingress
  2. It allows bandwidth to be shared fairly among groups before being distributed within each group Correct answer.
  3. It eliminates the need for drop precedence
  4. It guarantees zero latency for all traffic

Explanation

Hierarchical scheduling lets a parent scheduler allocate bandwidth among child groups, and each child then distributes its share among its own queues. This enforces fairness at multiple levels, such as per-subscriber then per-service. It does not remove classification or drop precedence, nor can it guarantee zero latency.

Question 8QoS fundamentals and Nokia QoS architecture

Which field does a Nokia node commonly inspect to perform DiffServ classification when traffic is already marked by an upstream device?

  1. The DSCP value in the IP header Correct answer.
  2. The Ethernet preamble
  3. The ARP opcode
  4. The TCP window size

Explanation

DiffServ relies on the DSCP field in the IP header to convey per-hop behaviour, so a node trusts and maps DSCP to internal forwarding classes. The preamble, TCP window, and ARP opcode carry no QoS marking. Trust boundaries determine whether such markings are accepted or re-marked.

Question 9QoS fundamentals and Nokia QoS architecture

What does a trust boundary define in a Nokia QoS design?

  1. The maximum number of VLANs allowed on a port
  2. The boundary between IPv4 and IPv6 domains
  3. The physical location of the route reflector
  4. The point where the network stops trusting incoming QoS markings and enforces its own policy Correct answer.

Explanation

A trust boundary marks where customer or peer markings are no longer trusted, so the network classifies and re-marks traffic according to its own policy. It is a policy concept, not a physical or addressing concept. Placing it correctly prevents users from gaining priority by setting arbitrary DSCP values.

Question 10QoS fundamentals and Nokia QoS architecture

A customer sends voice traffic marked EF (DSCP 46) but the service level agreement only covers best-effort treatment. What should the provider edge do at the trust boundary?

  1. Re-mark the traffic to the class the SLA actually purchased Correct answer.
  2. Drop all voice packets to enforce the contract
  3. Encrypt the DSCP field so it cannot be read
  4. Honour EF unconditionally because the customer marked it

Explanation

At the trust boundary the provider enforces its own policy, so traffic is re-marked to the class the customer is entitled to rather than accepting the customer's marking. Honouring arbitrary markings would let customers obtain unearned priority. Dropping all voice traffic or encrypting the DSCP field are not valid policy actions.

Question 11QoS fundamentals and Nokia QoS architecture

Which scheduling discipline gives strict priority to one queue over all others in a Nokia QoS configuration?

  1. Weighted fair queuing
  2. Random early detection
  3. Strict priority scheduling Correct answer.
  4. Deficit round robin

Explanation

Strict priority scheduling always serves the highest-priority queue first, starving lower queues when it is continuously backlogged. Weighted fair queuing and deficit round robin share bandwidth by weight instead of absolute precedence. Random early detection is a drop mechanism, not a scheduler.

Question 12QoS fundamentals and Nokia QoS architecture

What is the main risk of assigning strict priority to a large volume of traffic in a Nokia QoS deployment?

  1. The MTU is reduced on the interface
  2. Lower-priority queues may be starved of bandwidth Correct answer.
  3. The DSCP field is automatically cleared
  4. The classification tables are bypassed

Explanation

Strict priority always serves the top queue first, so if that traffic is heavy, lower queues receive little or no service. This is why strict priority is normally reserved for small, latency-sensitive flows such as voice. It does not clear DSCP, bypass classification, or change the MTU.

Question 13QoS fundamentals and Nokia QoS architecture

Which mechanism is used in Nokia QoS to begin dropping packets before a queue is completely full, reducing tail-drop synchronization?

  1. Strict priority scheduling
  2. Weighted random early detection Correct answer.
  3. Class-based marking
  4. Traffic shaping

Explanation

Weighted random early detection drops packets probabilistically as the average queue length grows, signalling congestion to TCP senders before the buffer overflows. This reduces global synchronization caused by tail drop. Scheduling, shaping, and marking do not perform early probabilistic dropping.

Question 14QoS fundamentals and Nokia QoS architecture

In WRED, how do the minimum and maximum thresholds relate to drop behaviour?

  1. Drops are disabled above the maximum threshold
  2. Drops begin probabilistically between the thresholds and reach full drop at the maximum Correct answer.
  3. The thresholds control the scheduling weight rather than dropping
  4. Drops occur only below the minimum threshold

Explanation

Below the minimum threshold no packets are dropped; between minimum and maximum the drop probability rises with queue occupancy; at or above the maximum all arriving packets are dropped. This gradual response avoids sudden buffer overflow. The thresholds govern dropping, not scheduling weight.

Question 15QoS fundamentals and Nokia QoS architecture

What is the effect of a marking function in Nokia QoS?

  1. It delays packets to smooth the output rate
  2. It reorders packets by priority
  3. It discards packets above the committed rate
  4. It sets or rewrites QoS fields so downstream nodes apply the intended treatment Correct answer.

Explanation

Marking writes QoS fields such as DSCP or priority bits so that downstream devices can classify the traffic consistently. Delaying packets is shaping, discarding above a rate is policing, and reordering is not a QoS function. Marking is often combined with metering to reflect in-profile versus out-of-profile traffic.

Question 16QoS fundamentals and Nokia QoS architecture

A two-rate three-colour marker in a Nokia QoS configuration classifies traffic into which three colours?

  1. Blue, orange, and purple
  2. High, medium, and low
  3. Green, yellow, and red Correct answer.
  4. Gold, silver, and bronze

Explanation

Two-rate three-colour marking uses green for traffic within the committed rate, yellow for traffic between committed and peak rates, and red for traffic above the peak rate. The colours map to drop precedences so that red is discarded first. The other colour sets are not standard in this context.

Question 17QoS fundamentals and Nokia QoS architecture

Why is the committed information rate (CIR) important when configuring a policer in Nokia QoS?

  1. It defines the physical line rate of the port
  2. It determines the DSCP value of the traffic
  3. It sets the maximum queue depth
  4. It defines the rate up to which traffic is treated as conforming Correct answer.

Explanation

The CIR is the rate that traffic is allowed to send while still being considered conforming, typically marked green. Traffic above the CIR but within the peak information rate may be marked yellow. The CIR does not set queue depth, DSCP values, or the physical line rate.

Question 18QoS fundamentals and Nokia QoS architecture

Which statement correctly describes the relationship between a service queue and a forwarding class in Nokia QoS?

  1. Each queue can carry only one drop precedence
  2. Each forwarding class maps to a physical port
  3. Forwarding classes exist only on the control plane
  4. Each forwarding class maps to a queue, and drop precedence selects the sub-queue or threshold within it Correct answer.

Explanation

Forwarding classes select the queue that determines scheduling treatment, while drop precedence selects the sub-queue or WRED threshold within that queue. A queue is not tied to a physical port, and it can carry multiple drop precedences. Forwarding classes are a forwarding-plane concept.

Question 19QoS fundamentals and Nokia QoS architecture

What does the peak information rate (PIR) represent in a two-rate policer?

  1. The minimum rate guaranteed during congestion
  2. The rate at which packets are reordered
  3. The upper rate above which traffic is marked as non-conforming Correct answer.
  4. The rate at which the queue is flushed

Explanation

The PIR is the upper bound of the metered rate; traffic above it is marked red and is most likely to be dropped. Traffic between the CIR and PIR is typically marked yellow. The PIR is not a guaranteed minimum and does not govern reordering or queue flushing.

Question 20QoS fundamentals and Nokia QoS architecture

In a Nokia QoS design, why is it important to align the DSCP marking with the internal forwarding class mapping?

  1. So that the routing table converges faster
  2. So that MAC addresses are learned correctly
  3. So that the MTU is uniform across the network
  4. So that traffic retains consistent treatment as it crosses nodes with different internal mappings Correct answer.

Explanation

Different nodes may map DSCP to forwarding classes differently, so consistent marking ensures uniform per-hop behaviour end to end. This alignment is about QoS treatment, not routing convergence, MTU uniformity, or MAC learning. Without it, traffic can change class unexpectedly at a node boundary.

Question 21QoS fundamentals and Nokia QoS architecture

Which queue parameter determines how much traffic a Nokia scheduler can hold before it must drop or apply congestion avoidance?

  1. The drop precedence value
  2. The queue buffer size Correct answer.
  3. The forwarding class identifier
  4. The queue weight

Explanation

The buffer size defines how much traffic a queue can hold, after which packets are dropped or WRED begins discarding. The weight influences scheduling share, the forwarding class identifies the treatment group, and drop precedence refines discard behaviour. Buffer size is the capacity parameter.

Question 22QoS fundamentals and Nokia QoS architecture

A network operator wants to guarantee that management traffic remains reachable during severe congestion. Which Nokia QoS approach best supports this?

  1. Rely on WRED to drop management traffic last
  2. Disable classification for management traffic
  3. Place management traffic in the best-effort class with no reservation
  4. Place management traffic in a dedicated high-priority class with reserved bandwidth Correct answer.

Explanation

A dedicated high-priority class with reserved bandwidth ensures management traffic is served even when other classes are congested. Leaving it in best-effort or relying on WRED offers no guarantee. Disabling classification would remove the ability to protect it at all.

Question 23QoS fundamentals and Nokia QoS architecture

What is the function of a shaper's token bucket in a Nokia QoS implementation?

  1. It authenticates traffic before forwarding
  2. It stores packet payloads for retransmission
  3. It accumulates credits at a configured rate that permit packets to be transmitted Correct answer.
  4. It records the DSCP of each packet

Explanation

A token bucket accumulates credits at the configured shaping rate, and packets may be transmitted only when sufficient tokens are available. This enforces the average rate while permitting limited bursts. Token buckets do not store payloads, record DSCP, or authenticate traffic.

Question 24QoS fundamentals and Nokia QoS architecture

Which statement about the default forwarding class treatment of unclassified traffic in Nokia QoS is most accurate?

  1. Unclassified traffic is always discarded at ingress
  2. Unclassified traffic is typically mapped to a default best-effort class Correct answer.
  3. Unclassified traffic bypasses the scheduler entirely
  4. Unclassified traffic is automatically given strict priority

Explanation

Traffic that matches no classification rule is normally assigned to a default best-effort class so it is still forwarded but without special treatment. It is not automatically discarded, nor given strict priority, and all traffic passes through a scheduler. Explicit default handling keeps behaviour predictable.

Question 25QoS fundamentals and Nokia QoS architecture

How does a Nokia QoS scheduler use queue weights in weighted fair queuing?

  1. Higher weights cause the queue to be served last
  2. Weights determine the physical port speed
  3. Weights set the DSCP value of queued packets
  4. Higher weights receive a proportionally larger share of available bandwidth Correct answer.

Explanation

In weighted fair queuing, each queue's weight determines its relative share of available bandwidth when multiple queues are backlogged. A higher weight means a larger share, not lower priority. Weights do not set DSCP values or change port speed.

Question 26QoS fundamentals and Nokia QoS architecture

In Nokia QoS, which term describes the per-hop behaviour that a packet receives at each node, determined by its forwarding class and drop priority?

  1. Forwarding class group
  2. Per-hop behaviour (PHB) Correct answer.
  3. Scheduler policy
  4. Service queue group

Explanation

The per-hop behaviour is the externally observable treatment a packet receives at each node, and in Nokia QoS it is derived from the internal forwarding class plus the drop probability (colour) assigned during classification. PHB is the DiffServ term that maps onto this internal treatment.

Question 27QoS fundamentals and Nokia QoS architecture

Which statement best describes the role of the drop priority (colour) assigned during classification in a Nokia QoS node?

  1. It decides how aggressively the packet is discarded when its queue congests. Correct answer.
  2. It determines the queue's scheduler weight.
  3. It selects which physical port the packet egresses.
  4. It sets the maximum transmission unit for the flow.

Explanation

Drop priority, often expressed as a colour such as green, yellow, or red, tells the congestion-avoidance mechanism how likely a packet is to be dropped when the queue fills. Higher drop priority (for example red) is discarded earlier than lower drop priority.

Question 28QoS fundamentals and Nokia QoS architecture

What is the primary purpose of a QoS classification policy in a Nokia service router?

  1. To encrypt traffic between provider edge routers.
  2. To redistribute routing protocols between areas.
  3. To assign incoming traffic to forwarding classes and drop priorities based on match criteria. Correct answer.
  4. To count bytes per subscriber for billing.

Explanation

Classification matches fields such as DSCP, IP precedence, or SAP ingress criteria and maps the matching traffic to a forwarding class and drop priority. Those internal assignments then drive queue selection and congestion treatment.

Question 29QoS fundamentals and Nokia QoS architecture

In Nokia QoS, what does a meter (policer) do to traffic that exceeds its configured rate?

  1. It duplicates the excess onto a second path.
  2. It drops or re-marks the excess according to the configured action. Correct answer.
  3. It re-marks the excess to a higher priority.
  4. It buffers the excess until the queue drains.

Explanation

A meter measures the traffic rate against configured CIR/PIR parameters and applies an action to non-conforming traffic, typically dropping it or re-marking it to a lower drop priority. It does not buffer, because buffering is the job of queues and shapers.

Question 30QoS fundamentals and Nokia QoS architecture

An operator wants EF-marked voice to be scheduled ahead of all other traffic in a queue group, while still bounding voice bandwidth so it cannot starve other classes. Which combination achieves this in Nokia QoS?

  1. A strict-priority queue with a configured rate limit. Correct answer.
  2. A weighted queue with the lowest weight in the group.
  3. A best-effort queue with WRED enabled.
  4. A queue with the largest buffer and no rate limit.

Explanation

Strict priority ensures the voice queue is served before other queues, and applying a rate limit to that queue caps how much bandwidth it can consume. Together they give low latency to voice without letting it starve the other classes.

Question 31QoS fundamentals and Nokia QoS architecture

A service provider maps customer traffic into eight forwarding classes but only wants four egress queues on a constrained access port. What is the most appropriate Nokia QoS approach?

  1. Configure eight queues and let the port drop the extra four.
  2. Map multiple forwarding classes onto shared queues using a queue mapping policy. Correct answer.
  3. Disable classification on the access port.
  4. Convert all traffic to a single strict-priority queue.

Explanation

A queue mapping policy lets several forwarding classes share a smaller number of queues, preserving relative treatment while fitting the hardware queue budget. This is the standard way to reconcile more classes than available queues.

Question 32QoS fundamentals and Nokia QoS architecture

What is the effect of configuring a queue as best-effort with high weight in a weighted scheduler group?

  1. It is limited to the committed information rate only.
  2. It receives a larger share of available bandwidth relative to lower-weight queues. Correct answer.
  3. It is exempt from congestion avoidance.
  4. It is always served before any other queue in the group.

Explanation

In a weighted scheduler, the weight determines the relative share of bandwidth each queue receives when the group is congested. A high weight means a larger proportional share, not absolute priority.

Question 33QoS fundamentals and Nokia QoS architecture

Why does Nokia QoS separate ingress classification from egress queueing at the network boundary?

  1. Because egress ports cannot read DSCP values.
  2. Because queueing is only needed on provider core links.
  3. Because ingress ports have more buffer memory than egress ports.
  4. Because classification occurs once near the edge while consistent queueing treatment is applied at every hop. Correct answer.

Explanation

Classifying near the trust boundary lets the network set forwarding classes and drop priorities once, and each subsequent node applies consistent queueing based on those internal markings. This scales better than re-classifying complex fields at every hop.

Question 34QoS fundamentals and Nokia QoS architecture

A customer's traffic arrives unmarked at a Nokia provider edge. Which design choice best protects the provider's QoS treatment from being manipulated by the customer?

  1. Re-mark all customer traffic to a single best-effort class.
  2. Trust the incoming DSCP values and forward them unchanged.
  3. Copy the IP precedence bits into the queue identifier.
  4. Classify and re-mark at the ingress trust boundary according to the service contract. Correct answer.

Explanation

Re-marking at the ingress trust boundary ensures that customer-set markings cannot influence provider treatment beyond what the contract allows. The provider assigns forwarding classes and drop priorities itself.

Question 35QoS fundamentals and Nokia QoS architecture

In Nokia QoS, what is the purpose of a scheduler policy attached to a port or channel?

  1. To define which DSCP values are accepted on ingress.
  2. To define how queues within a group are served and how bandwidth is distributed among them. Correct answer.
  3. To define the maximum number of MAC addresses per port.
  4. To define the routing metric for attached subnets.

Explanation

A scheduler policy specifies the scheduling behaviour for queues, including priority and weighted sharing, so that bandwidth is distributed as intended during contention. It operates on the egress side where queues compete for transmission.

Question 36QoS fundamentals and Nokia QoS architecture

A network carries both delay-sensitive signalling and bulk backup traffic in the same forwarding class. Which refinement most improves the QoS outcome without adding a new forwarding class?

  1. Apply a drop priority differentiation so bulk traffic is dropped first during congestion. Correct answer.
  2. Remove congestion avoidance from the combined queue.
  3. Increase the queue buffer for the combined class.
  4. Convert the combined class to strict priority.

Explanation

Assigning a higher drop priority to bulk traffic lets congestion avoidance discard backup packets before signalling packets within the same queue. This preserves the signalling traffic without requiring an additional forwarding class.

Question 37QoS fundamentals and Nokia QoS architecture

Which outcome indicates that a Nokia QoS design has an incorrectly configured mapping between DSCP and forwarding class?

  1. Bulk traffic marked AF11 is served with a low weight.
  2. Voice marked EF is queued in the same class as best-effort web traffic and experiences the same delay. Correct answer.
  3. Voice marked EF is queued in a low-latency class and meets its delay budget.
  4. Management traffic marked CS6 is protected during congestion.

Explanation

If EF-marked voice lands in the best-effort class, it receives the same queueing treatment as web traffic and loses its latency advantage. Correct mapping should place EF in a low-latency, appropriately protected class.

Question 38QoS fundamentals and Nokia QoS architecture

A service provider observes that a policer configured with a low committed rate is dropping bursts of well-behaved application traffic. Which adjustment is most appropriate?

  1. Lower the committed information rate further.
  2. Increase the committed burst size so short bursts conform. Correct answer.
  3. Remove the policer entirely from the interface.
  4. Change the policer action to re-mark traffic upward.

Explanation

Token-bucket policers allow bursts up to the configured burst size, so a burst size that is too small will drop legitimate short bursts even when the average rate is within contract. Increasing the burst size lets normal application bursts conform.

Question 39QoS fundamentals and Nokia QoS architecture

An operator must ensure that a low-priority class still receives some service during sustained congestion while a higher class is protected. Which Nokia QoS design principle applies?

  1. Use strict priority for all queues so each is served in turn.
  2. Give every queue equal weight and rely on tail drop.
  3. Combine a bounded strict-priority queue for the protected class with weighted service for the remaining classes. Correct answer.
  4. Disable congestion avoidance on the low-priority class.

Explanation

Bounding the strict-priority queue prevents the protected class from consuming all bandwidth, while weighted service guarantees the remaining classes a proportional share. This balances protection with fairness during sustained congestion.

Question 40QoS fundamentals and Nokia QoS architecture

A Nokia QoS deployment must support per-subscriber bandwidth guarantees across many subscribers sharing one uplink. Which architectural feature is most relevant?

  1. Hierarchical QoS with per-subscriber shapers under a shared parent scheduler. Correct answer.
  2. DSCP re-marking at the core nodes.
  3. A single flat policer applied to the uplink.
  4. WRED thresholds on the uplink queue only.

Explanation

Hierarchical QoS places per-subscriber shapers beneath a shared parent scheduler, so each subscriber's guarantee is enforced while the uplink bandwidth is divided fairly. This scales guarantees across many subscribers on one link.

Question 41QoS classification, marking and queuing on Nokia IP routers

On Nokia IP routers, which QoS component decides how a packet is treated after it has been assigned to a forwarding class?

  1. The classifier, which inspects header fields and sets the forwarding class
  2. The queue scheduler, which selects the queue mapped to that forwarding class Correct answer.
  3. The shaper, which delays packets to enforce an aggregate rate
  4. The policer, which compares the flow rate against a committed rate

Explanation

Classification assigns traffic to a forwarding class, but the actual treatment comes from the queue and scheduler configuration mapped to that class. Each forwarding class is bound to one or more queues, and the scheduler decides which queue is served and how much bandwidth it receives. Policing and shaping act on rates, not on selecting the queue for an already classified packet.

Question 42QoS classification, marking and queuing on Nokia IP routers

A Nokia router is configured with a single default forwarding class and no explicit classification rules. What happens to ingress traffic?

  1. Traffic is dropped because no forwarding class matches
  2. Traffic is randomly distributed across all configured queues
  3. Traffic is placed in the default forwarding class and default queue Correct answer.
  4. Traffic is assigned to the highest-priority expedited queue

Explanation

When no classification rule matches, Nokia routers apply the configured default forwarding class, which maps to a default queue. This ensures all traffic receives deterministic treatment even without explicit match criteria. Administrators can change the default class, but absent configuration the built-in default applies.

Question 43QoS classification, marking and queuing on Nokia IP routers

Which field is most commonly used at the edge of a Nokia IP network to classify traffic into forwarding classes based on a pre-marked DSCP value?

  1. The 12-bit VLAN identifier in the Ethernet header
  2. The 8-bit TTL field in the IP header
  3. The 6-bit DSCP field in the IP header Correct answer.
  4. The 32-bit sequence number in the TCP header

Explanation

DSCP occupies the upper six bits of the IP Type of Service or Traffic Class byte and is the standard trust field for DiffServ classification. Edge routers map DSCP values to forwarding classes so that downstream treatment is consistent. VLAN ID, TCP sequence number, and TTL are not QoS marking fields.

Question 44QoS classification, marking and queuing on Nokia IP routers

What is the primary purpose of marking packets with a DSCP value at the ingress edge of a Nokia IP network?

  1. To reduce the packet size for more efficient transmission
  2. To encrypt the payload for confidentiality
  3. To identify the originating autonomous system
  4. To carry the QoS treatment decision across devices that trust the marking Correct answer.

Explanation

Marking encodes the QoS decision in the packet header so that every downstream device honoring the marking applies consistent per-hop behavior. It avoids re-classifying on every router and keeps treatment uniform end to end. Marking does not provide encryption, compression, or AS identification.

Question 45QoS classification, marking and queuing on Nokia IP routers

Which Nokia router component is responsible for buffering packets that cannot be transmitted immediately because the egress port is congested?

  1. The egress queue Correct answer.
  2. The ARP cache
  3. The control plane processor
  4. The routing table

Explanation

Egress queues hold packets awaiting transmission when the output port is busy, allowing the scheduler to decide service order. Queue depth and scheduling determine delay and loss behavior under congestion. The control plane, routing table, and ARP cache do not buffer user data for transmission.

Question 46QoS classification, marking and queuing on Nokia IP routers

In a Nokia strict-priority scheduling configuration, how is the highest-priority queue served relative to other queues?

  1. It receives an equal share of bandwidth with every other queue
  2. It is served in round-robin order with the other queues
  3. It is served only after all other queues are empty
  4. It is served first whenever it has packets, up to its configured rate limit Correct answer.

Explanation

Strict priority means the scheduler always serves the priority queue before lower queues, as long as it has traffic and stays within any configured rate limit. Without a rate cap, a busy priority queue can starve lower queues. Equal sharing and round-robin describe other scheduling disciplines.

Question 47QoS classification, marking and queuing on Nokia IP routers

What does a two-rate, three-color policer on a Nokia router use to determine whether a packet is green, yellow, or red?

  1. The packet length and the ingress port speed only
  2. The DSCP value alone, without any rate measurement
  3. The committed and peak rates with their associated burst sizes Correct answer.
  4. The egress queue occupancy at the moment of arrival

Explanation

A two-rate three-color policer meters traffic against a committed rate and burst plus a peak rate and burst. Packets within the committed allowance are green, those within the excess allowance are yellow, and the remainder are red. DSCP alone and egress occupancy are not the metering basis for this algorithm.

Question 48QoS classification, marking and queuing on Nokia IP routers

Why is it a common design practice to re-mark or police traffic at the untrusted edge of a Nokia IP network rather than trusting customer markings blindly?

  1. Because policing disables classification on the interface
  2. Because the router cannot read DSCP bits on untrusted interfaces
  3. Because DSCP bits are encrypted in transit and must be decrypted
  4. Because subscribers may set arbitrary DSCP values that would otherwise receive undeserved treatment Correct answer.

Explanation

If the edge trusts markings from untrusted sources, a subscriber can mark all traffic as high priority and gain preferential treatment. Policing or re-marking at ingress enforces the service level the customer actually purchased. DSCP bits are not encrypted, and routers can read them on any interface.

Question 49QoS classification, marking and queuing on Nokia IP routers

A Nokia router maps several DSCP values to the same forwarding class. What is the effect on scheduling treatment for those packets?

  1. Packets are dropped because of the mapping conflict
  2. All packets in that forwarding class share the queue treatment of that class Correct answer.
  3. Only the lowest DSCP value is honored
  4. Each DSCP value receives a distinct queue automatically

Explanation

Forwarding classes aggregate traffic for treatment; multiple DSCP values can map to one class, and all such packets receive the same queue and scheduler behavior. Differentiation between those DSCP values is lost unless they map to different classes. The router does not create queues per DSCP value automatically.

Question 50QoS classification, marking and queuing on Nokia IP routers

An engineer wants guaranteed low latency for voice while preventing voice from starving data during congestion. Which combination on a Nokia router best achieves this?

  1. Tail-drop for voice and weighted random early detection for data
  2. Strict priority for voice with a configured rate limit, plus fair scheduling for other classes Correct answer.
  3. Round-robin for all classes with equal weights
  4. Pure strict priority for voice with no rate limit, plus best-effort for data

Explanation

Strict priority gives voice the lowest latency, and a rate limit caps how much bandwidth voice can consume so it cannot starve other classes. The remaining classes are then served by a fair or weighted scheduler. Unlimited strict priority risks starvation, and equal round-robin cannot guarantee low latency.