Nokia 4A0-220 Nokia GMPLS-Controlled Optical Networks Exam Practice Test

Constrained Shortest Path First (CSPF) is an extension of the shortest path first (SPF) algorithm that is used to find the best path for a Label Switched Path (LSP) in a GMPLS network. CSPF takes into account additional constraints such as bandwidth, latency, priority, or node or link inclusion or exclusion. CSPF works by pruning those links that do not meet the specified constraints and then applying the SPF algorithm to the remaining links. This way, CSPF can find a path that satisfies both the shortest distance and the constraints. References : Constrained Shortest Path First - Wikipedia, Constrained Shortest Path First (CSPF) - Metaswitch

GMPLS is a protocol suite that extends the MPLS signaling and routing capabilities to control different types of switching technologies, such as optical, TDM, and packet switching1. GMPLS has several key features, such as self-discovery, fast protection, and restoration. Self-discovery allows GMPLS nodes to automatically discover their neighbors and exchange information about their capabilities and resources2. Fast protection enables GMPLS nodes to quickly switch to backup paths in case of a failure, without relying on the control plane3. Restoration allows GMPLS nodes to dynamically establish new paths in the network after a failure, using the control plane3. Resource optimization is not a key feature of GMPLS, but rather a potential benefit of using GMPLS to efficiently utilize the network resources and avoid over-provisioning. References:

• 1: Nokia GMPLS-controlled Optical Networks Course | Nokia
• 2: GMPLS - Nokia
• 3: Traffic survivability through Protection and Restoration Combined (PRC) - YouTube
• [4]: GMPLS: Architecture and Applications - Google Books

The Soft Shutting Down state in the NFM-T is an administrative maintenance state where services stay up but no new traffic can be routed over the TE-link. This state is used to prepare a TE-link for maintenance or decommissioning without affecting the existing services. The NFM-T sets the TE-link to Soft Shutting Down state by sending a Notify message with the Administrative State Change flag to the head-end node of the TE-link. The head-end node then stops accepting new LSP requests over the TE-link and sends a PathErr message with the Administrative State Change flag to all the tail-end nodes of the LSPs in the TE-link. The tail-end nodes then stop sending new traffic over the LSPs and send a ResvErr message with the Administrative State Change flag to all the intermediate nodes of the LSPs. The intermediate nodes then update their routing tables and stop forwarding new traffic over the LSPs. The existing traffic, however, continues to flow over the LSPs until they are manually deleted or rerouted by the NFM-T. References : Nokia GMPLS-controlled Optical Networks Course | Nokia, Nokia Advanced Optical Network Management with NFM-T Course | Nokia

Test Mode is a feature of the Link Management Protocol (LMP) that allows testing the connectivity and functionality of a link or a TE-link. Test Mode can be initiated by either end of a link or a TE-link by sending a Test Message with a Test ID and a Test Pattern. The Test Message is sent over the control channel of the link or the TE-link and contains information such as the source and destination IP addresses, the link ID, and the test parameters. The receiving node then verifies the Test Message and sends back a TestStatusAck message with the same Test ID and Test Pattern. The TestStatusAck message indicates whether the test was successful or not, and if not, what was the reason for failure. Test Mode can be used to check if a link or a TE-link is operational, if it has any errors or faults, or if it supports certain features or capabilities. References : Nokia GMPLS-controlled Optical Networks Course | Nokia, RFC 4204 - Link Management Protocol (LMP)

The Feasibility File is a file that contains a set of target values for various optical impairment parameters, such as OSNR, CD, PMD, and PDL, that are used to determine whether a given LSP can be routed through the GMRE network. The Feasibility File is generated by the Network Planning Application (NPA) based on the network design and the service requirements. The Feasibility File is then loaded into the GMRE nodes and used by the GMPLS routing engine to perform feasibility checks for LSP requests. The Feasibility File ensures that the LSPs are routed in accordance with the network plan and the optical performance criteria12. References:

• 1: Nokia GMPLS-controlled Optical Networks Course | Nokia
• 2: GMPLS - Nokia

Tunnel Property Heritage is a feature of GMRE that allows the propagation of certain properties from higher order (HO) LSPs to lower order (LO) LSPs in a multi-layer network. These properties include cost, SRLG, and color. Cost is a metric that reflects the preference of using a certain link or path for routing. SRLG is a set of links that share a common risk of failure. Color is an attribute that can be used to group or filter LSPs based on service classes or customer profiles. By propagating these properties from HO to LO LSPs, GMRE can ensure that the end-to-end LSPs are consistent and optimal across different layers34. References:

• 3: Nokia GMPLS-controlled Optical Networks Course | Nokia
• 4: GMPLS - Nokia

The GMRE functionality is guaranteed in Nokia equipment by controller redundancy. The controller is the hardware component that runs the GMPLS software and controls the switching fabric of the node. Each node has two controllers, one active and one standby, that synchronize their states and databases. If the active controller fails, the standby controller takes over and ensures the continuity of the GMRE functionality. References : Nokia GMPLS-controlled Optical Networks Course | Nokia, 1830 Photonic Service Switch (PSS) | Nokia

RSVP-TE Notify message is a message type defined in the RSVP-TE protocol, which is an extension of the RSVP protocol for MPLS traffic engineering. RSVP-TE Notify message is used to inform non-adjacent nodes of LSP events, such as setup, modification, or teardown. This allows the nodes to update their local state information and perform actions based on the notification. For example, a Notify message can be used to trigger a fast reroute mechanism in case of a link or node failure12. References:

• 1: RFC 3473 - Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Extensions
• 2: RFC 3471 - Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description

The Shutting Down state is a transient state that occurs when a TE-link is set to maintenance mode in the NFM-T. In this state, the TE-link is not available for routing new LSPs, but the existing LSPs (SNCs) that use the TE-link are not immediately terminated. Instead, they are soft-rerouted, which means that they are gracefully switched to alternative paths without disrupting the traffic. The Shutting Down state lasts until all the SNCs on the TE-link are successfully soft-rerouted or forcefully terminated. After that, the TE-link transitions to the Administrative Maintenance state, where no traffic can be routed over the TE-link12. References:

• 1: Nokia GMPLS-controlled Optical Networks Course | Nokia
• 2: Nokia Network Functions Manager for Transport User Guide | Nokia

Preemption is a mechanism that allows a higher priority LSP to tear down an existing lower priority LSP in order to obtain the required resources for its establishment. Preemption can occur when there is not enough bandwidth or other resources available on a link or node to accommodate a new LSP request. In this case, the node can select one or more lower priority LSPs that are using the resources and send them a PathErr message with a Preempt error code. This causes the lower priority LSPs to beterminated and release their resources. The node can then allocate the resources to the higher priority LSP and send a Resv message to confirm its reservation34. References:

• 3: RFC 4829: Label Switched Path (LSP) Preemption Policies for MPLS Traffic Engineering4
• 4: MPLS Applications User Guide | Juniper Networks5

A Shared Risk Link Group (SRLG) is a set of links sharing a common resource, which affects all links in the set if the common resource fails5. These links share the same risk of failure and are therefore considered to belong to the same SRLG. For example, links sharing a common fiber are said to be in the same SRLG because a fault with the fiber might cause all links in the group to fail. SRLGs are used in MPLS and GMPLS networks to provide traffic engineering and protection/restoration mechanisms. When computing the secondary path for an LSP, it is preferable to find a path such that the secondary and primary paths do not have any links in common in case the SRLGs for the primary and secondary paths are disjoint6. This ensures that a single point of failure on a particular link does not bring down both the primary and secondary paths in the LSP. References:

• 5: Shared risk resource group - Wikipedia
• 6: Shared Risk Link Groups for MPLS | Junos OS | Juniper Networks

The 3R resource is a type of optical regeneration resource that can be used to extend the reach of optical signals in a GMPLS-controlled optical network. The 3R resource performs three functions: reshaping, retiming, and reamplifying the optical signal. The 3R resource can be added to the Network Planning Application (NPA) in the Nokia Network Functions Manager for Transport (NFM-T) through the Constraint Wizard. The Constraint Wizard is a tool that allows the user to define various constraints and parameters for the network design, such as optical impairments, wavelength availability, protection schemes, and regeneration resources. The user can select the 3R resource from the list of available resources and specify its location, capacity, and cost. The NPA then uses this information to perform feasibility checks and path computation for the LSP requests12. References:

• 1: Nokia GMPLS-controlled Optical Networks Course | Nokia
• 2: Nokia Network Functions Manager for Transport User Guide | Nokia