Nokia 4A0-116 Q&A: Which is NOT advantage of using PCE for computation of TE-constrained LSP paths?

Question

Which of the following is NOT an advantage of using a PCE for the computation of TE-constrained LSP paths, as compared to using CSPF locally on the PE router?

A. The ability to create cross-area TE-constrained LSP paths
B. The ability to create LSP paths with bandwidth reservation
C. The ability to create LSPs with primary and secondary paths
D. The ability to ensure that some LSP paths are disjoint

Answer

D. The ability to ensure that some LSP paths are disjoint

Explanation 1

The Path Computation Element (PCE) is a network component that can be used to compute paths for Traffic Engineering (TE)-constrained Label Switched Paths (LSPs) in a Multiprotocol Label Switching (MPLS) network. The PCE can be used to compute paths for LSPs that satisfy specific constraints such as bandwidth, latency, and disjointness.

The advantages of using a PCE for the computation of TE-constrained LSP paths over using Constraint-based Shortest Path First (CSPF) locally on the Provider Edge (PE) router include:

The ability to create cross-area TE-constrained LSP paths
The ability to create LSP paths with bandwidth reservation
The ability to create LSPs with primary and secondary paths

Therefore, the correct answer is D. The ability to ensure that some LSP paths are disjoint.

Explanation 2

The correct answer is B. The ability to create LSP paths with bandwidth reservation.

PCE is a centralized path computation engine that can be used to compute TE-constrained LSP paths. CSPF is a distributed path computation algorithm that is used by PE routers to compute LSP paths.

PCE has several advantages over CSPF, including:

The ability to create cross-area TE-constrained LSP paths.
The ability to create LSPs with primary and secondary paths.
The ability to ensure that some LSP paths are disjoint.

However, PCE cannot create LSP paths with bandwidth reservation. This is because PCE does not have access to the link state database. The link state database is maintained by the PE routers, and it contains information about the available bandwidth on each link.

If you need to create LSP paths with bandwidth reservation, you must use CSPF. CSPF can use the link state database to compute LSP paths that have the desired amount of bandwidth reserved.

In summary, the following are the advantages of using a PCE for the computation of TE-constrained LSP paths, as compared to using CSPF locally on the PE router:

The ability to create cross-area TE-constrained LSP paths.
The ability to create LSPs with primary and secondary paths.
The ability to ensure that some LSP paths are disjoint.

The following is the disadvantage of using a PCE for the computation of TE-constrained LSP paths:

Cannot create LSP paths with bandwidth reservation.

Explanation 3

A PCE (Path Computation Element) is a network entity that can compute optimal paths for traffic engineering (TE) purposes, based on various constraints and optimization criteria. A PCE can be used to compute TE-constrained LSP (Label Switched Path) paths for segment routing (SR) networks, where each segment represents a portion of the end-to-end path.

One of the advantages of using a PCE for the computation of TE-constrained LSP paths, as compared to using CSPF (Constrained Shortest Path First) locally on the PE (Provider Edge) router, is the ability to create cross-area TE-constrained LSP paths. A PE router using CSPF can only compute paths within its own area, while a PCE can have a global view of the network topology and compute paths across multiple areas.

Another advantage of using a PCE for the computation of TE-constrained LSP paths, as compared to using CSPF locally on the PE router, is the ability to create LSPs with primary and secondary paths. A PE router using CSPF can only compute one path for each LSP, while a PCE can compute multiple paths for each LSP and provide backup or alternative paths in case of failures or congestion.

A third advantage of using a PCE for the computation of TE-constrained LSP paths, as compared to using CSPF locally on the PE router, is the ability to ensure that some LSP paths are disjoint. A PE router using CSPF can only compute shortest paths based on link metrics, while a PCE can compute diverse paths based on various criteria, such as node or link disjointness, shared risk link group (SRLG) disjointness, or latency minimization.

The ability to create LSP paths with bandwidth reservation is not an advantage of using a PCE for the computation of TE-constrained LSP paths, as compared to using CSPF locally on the PE router. Both CSPF and PCE can take into account bandwidth constraints when computing TE-constrained LSP paths, and both can reserve bandwidth along the computed path by signaling protocols such as RSVP-TE or SR-PCEP.

Explanation 4

The answer is A. The ability to create cross-area TE-constrained LSP paths.

PCE is a centralized path computation engine that can be used to compute TE-constrained LSP paths. CSPF is a distributed path computation algorithm that is run on each PE router.

One advantage of using PCE is that it can be used to create cross-area TE-constrained LSP paths. CSPF can only be used to create LSP paths within a single area.

Another advantage of using PCE is that it can be used to create LSP paths with bandwidth reservation. CSPF can only be used to create LSP paths without bandwidth reservation.

PCE can also be used to create LSPs with primary and secondary paths. CSPF cannot do this.

Finally, PCE can be used to ensure that some LSP paths are disjoint. CSPF cannot do this.

Therefore, the only advantage of using CSPF that is not also an advantage of using PCE is the ability to create cross-area TE-constrained LSP paths.

Here is a table that summarizes the advantages and disadvantages of using PCE and CSPF:

Feature	PCE	CSPF
Ability to create cross-area TE-constrained LSP paths	Yes	No
Ability to create LSP paths with bandwidth reservation	Yes	No
Ability to create LSPs with primary and secondary paths	Yes	No
Ability to ensure that some LSP paths are disjoint	Yes	No
Centralized path computation	Yes	No
Scalability	Good	Poor
Complexity	High	Low

Overall, PCE is a more powerful and flexible path computation algorithm than CSPF. However, PCE is also more complex and less scalable.

Explanation 5

The correct answer is B. The ability to create LSP paths with bandwidth reservation.

To explain, a PCE is a network entity that can compute optimal paths for traffic engineering (TE) constrained label switched paths (LSPs) based on the network topology and resource availability. A PCE can provide several advantages over using constrained shortest path first (CSPF) locally on the PE router, such as:

The ability to create cross-area TE-constrained LSP paths: A PCE can have a global view of the network topology across multiple areas or domains, and can compute end-to-end paths that span multiple areas or domains.
The ability to ensure that some LSP paths are disjoint: A PCE can compute diverse or backup paths for LSPs that avoid common links, nodes, or shared risk link groups (SRLGs) with the primary paths.
The ability to create LSPs with primary and secondary paths: A PCE can compute and provision both primary and secondary paths for LSPs, and can also support make-before-break (MBB) operations to switch between the paths without traffic disruption.

However, a PCE cannot create LSP paths with bandwidth reservation by itself. Bandwidth reservation is a function of the label distribution protocol (LDP), resource reservation protocol (RSVP), or segment routing (SR) protocols that are used to establish and maintain the LSPs in the data plane. A PCE can only compute the paths based on the bandwidth constraints and availability, but it cannot reserve the bandwidth for the LSPs.

Explanation 6

The answer is A. The ability to create cross-area TE-constrained LSP paths.

PCE is a centralized path computation engine that can be used to compute TE-constrained LSP paths across an entire network. This can be useful for creating paths that avoid congested areas or that meet specific QoS requirements. However, PCE cannot create cross-area TE-constrained LSP paths. This is because PCE is a layer-2 protocol, and layer-2 protocols do not have any concept of areas.

CSPF, on the other hand, is a distributed path computation algorithm that can be used to create cross-area TE-constrained LSP paths. This is because CSPF is a layer-3 protocol, and layer-3 protocols do have a concept of areas.

Here is a table that summarizes the advantages of using PCE for the computation of TE-constrained LSP paths, as compared to using CSPF locally on the PE router:

Advantage	PCE	CSPF
Ability to create LSP paths with bandwidth reservation	Yes	No
Ability to create LSPs with primary and secondary paths	Yes	No
Ability to ensure that some LSP paths are disjoint	Yes	No
Ability to create cross-area TE-constrained LSP paths	No	Yes

Explanation 7

The Path Computation Element (PCE) is a network component that can compute paths for Traffic Engineering (TE) Label Switched Paths (LSPs). The PCE can be used to compute TE-constrained LSP paths instead of using Constraint-based Shortest Path First (CSPF) locally on the Provider Edge (PE) router. The advantages of using a PCE for the computation of TE-constrained LSP paths include:

The ability to create cross-area TE-constrained LSP paths.
The ability to create LSP paths with bandwidth reservation.
The ability to create LSPs with primary and secondary paths.

Therefore, the answer is D. The ability to ensure that some LSP paths are disjoint. This is because using a PCE does not guarantee that some LSP paths are disjoint.

Explanation 8

The Nokia Segment Routing exam certifies that a candidate has the skills and knowledge to implement and manage segment routing solutions using Nokia products. Exam questions are based on official Nokia training materials, the Nokia documentation site and the Nokia developer site.

Therefore, the correct answer to your question is B. The ability to create LSP paths with bandwidth reservation.

This answer is based on the following reasoning:

Option A is not correct because one of the advantages of using a PCE for the computation of TE-constrained LSP paths is the ability to create cross-area TE-constrained LSP paths. A PCE can have a global view of the network topology and can compute optimal paths across multiple areas or domains.
Option B is correct because creating LSP paths with bandwidth reservation is not an advantage of using a PCE for the computation of TE-constrained LSP paths, as compared to using CSPF locally on the PE router. Both PCE and CSPF can compute LSP paths with bandwidth reservation, as they use similar algorithms and constraints.
Option C is not correct because another advantage of using a PCE for the computation of TE-constrained LSP paths is the ability to create LSPs with primary and secondary paths. A PCE can compute multiple diverse paths for a given LSP request and provide backup paths in case of failures.
Option D is not correct because yet another advantage of using a PCE for the computation of TE-constrained LSP paths is the ability to ensure that some LSP paths are disjoint. A PCE can enforce path diversity constraints and avoid common links or nodes between different LSPs.

Explanation 9

The correct answer is C. The ability to create LSPs with primary and secondary paths.

Using a Path Computation Element (PCE) for the computation of Traffic Engineering (TE)-constrained Label Switched Path (LSP) paths offers several advantages compared to using Constraint-based Shortest Path First (CSPF) locally on the Provider Edge (PE) router. Let’s discuss the advantages of using a PCE:

A. The ability to create cross-area TE-constrained LSP paths: A PCE has a global view of the network and can compute LSP paths that span multiple areas or domains. This enables end-to-end TE path computation across a network, providing greater flexibility in traffic engineering.

B. The ability to create LSP paths with bandwidth reservation: A PCE can take into account bandwidth constraints and available resources while computing TE-constrained LSP paths. This allows for efficient utilization of network resources and better QoS provisioning.

D. The ability to ensure that some LSP paths are disjoint: A PCE can compute disjoint or diverse LSP paths, ensuring that they follow different physical paths to provide resiliency and fault tolerance. This helps in avoiding single points of failure and improves network reliability.

However, option C, “The ability to create LSPs with primary and secondary paths,” is not a specific advantage of using a PCE for TE path computation. The concept of primary and secondary paths typically relates to protection mechanisms such as fast reroute or protection tunnels. While a PCE can be involved in computing primary and secondary paths, it is not a unique advantage over using CSPF locally on the PE router.

Therefore, the correct answer is C. The ability to create LSPs with primary and secondary paths.

Reference

Nokia Segment Routing 4A0-116 certification exam practice question and answer (Q&A) dump with detail explanation and reference available free, helpful to pass the Nokia Segment Routing 4A0-116 exam and earn Nokia Segment Routing 4A0-116 certification.