Software Networks Flashcards
What is a network function?
Basic element within a network infrastructure with well-defined external interfaces (input/output) and well-defined functional behavior (state, transfer function).
Each interface exposed by the Network Function has to be standardized in order to allow interoperability without
vendor lock-in.
What is SDN?
Software-Defined Networking (SDN) is an approach to networking that uses software-based controllers or application programming interfaces (APIs) to communicate with underlying hardware infrastructure and direct traffic on a network.
SDN as network architecture:
- control and data plane decoupling
- forwarding decision are flow based not destination based
- control logic is in a centralised place
- network is programmable through software application on top of the controller
What is the motivation to use SDN?
Complex old IP network world:
− configuring each network device individually by using low-level or vendor specific commands
− no auto reconfiguration or dynamic fault/load adoption is present
− configuration is rather static
− vertically integrated networks (control and data plane in one device)
Missing flexibility for:
− fast evolution of new network functionalities or protocols
− programming networks
− reconfiguration due to dynamic changes in the network
What are the three layers of SDN?
- application layer
- control layer
- infrastructure layer
What are the advantages of SDN?
- Decoupling Hardware and Software
- Simplify policy enforcement and network reconfiguration
- logically centralized controller as single point of presences
- separation of concerns is the consequence
Describe each of the SDN applications
- Traffic Engineering: load balancing, reducing power consumption
- Measurement & Monitoring
- Security and Dependability: policy enforcement, dos detection, anomaly detection
- Mobility and Wireless: managing the limited spectrum, allocating radio resources, implementing handover mechanisms, managing interference, performing efficient load-balancing between cells
- Data Center Networking: network virtualization, resource allocation
- Service Function Chaining: send packets through a sequence of NFs
- SD-WAN: Apply SDN concepts to WAN, use overlay networks over internet to create WAN
What is cloud computing?
a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g. networks, servers, storage, applications and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.
What are the cloud computing service models?
- software as a service (SaaS)
- platform as a service (PaaS)
- infrastructure as a service (IaaS)
What are the benefits of cloud computing?
- cloud elasticity
- traffic fluctuation
- flexibility in network management operations
- optimizing resource utilization
What is elasticity?
The possibility to increase or decrease available resources on demand.
It is one of the most important properties of cloud infrastructures
- reducing costs - pay only for what is used
- improving QoS without overprovisioning
What are the scalability approaches?
- Vertically:
- increase the capacity by adding new resources to an existing node
→ BUT: it has a physical limitation due to the available hardware in a single location - Horizontally:
- increase the capacity by increasing the number of nodes (in most of the case clone of a basic node)
- NOTE: horizontally infinite resources available
Name the differences between stateful and stateless
- Stateful applications:
- the client is tied to a specific instance for the duration of the all session - Stateless applications:
- the state of a session is stored in the client (fat client) and attached in each request or stored / retrieved by the application from an external database
NOTE: stateless applications usually scale better!
What is virtualization. Explain server virtualization
- Virt.: abstraction of physical hardware for creating multiple virtual instances
- Server Virt: process of dividing a physical server into multiple unique and isolated virtual servers
What are the benefits of virtualization?
- efficient resource utilization (through server consolidation)
- energy-efficient environments (migrate VMs and turn off unused servers)
- intelligent memory management
- avoiding over-dimensioning of deploying physical servers
- less hardware is required
What is Network Function Virtualization (NFV)?
The virtualisation of network equipment functions, which typically run on dedicated appliances, to now run on industry-standard servers with the aim of lowering costs, improving efficiency and increasing agility, via hypervisor technologies
What is the NFV architecture approach?
- Decoupling sw from hw for reliability, availability and performance.
- Flexible network functions deployment with dynamic operation (VNFs placement and scaling).
- This approach provides interoperability with infrastructure and with legacy.
What is the NFV architecture approach?
- Decoupling sw from hw for reliability, availability and performance.
- Flexible network functions deployment with dynamic operation (VNFs placement and scaling).
- This approach provides interoperability with infrastructure and with legacy.
Name some of the benefits of NFV
- Performance
- Co-existence and portability
- Automation
- Scalability
- Interoperability among different solutions
Describe the high level framework and the architecture of ETSI NFV
- Virtualized Network Functions: software implementation of a network function which is capable to run over NFVI
- NFV Infrastructure: is the ‘datacenter’, diversity of physical resources and how these can be virtualized
- NFV Management and Orchestration: orchestration of physical/software resources that support the infrastructure virtualization, and the management of VNFs
Which are the deployment models for VNFc?
1: 1 - One VNFC per VNF
1: n - multiple VNFC per VNF
Please compare stateless and stateful VNFs
Stateless:
− The state of a session is stored in the client (fat client) and attached in each request or stored / retrieved by the VNFC from an external database
Stateful:
− The client is tied to a specific VNFC for the duration of the session
What is elasticity? Which are the elasticity options?
Vertical:
− Increase the capacity adding new resources to an existing node
− But it has a physical limitation due to the available hardware in a single location
Horizontal:
− Increase the capacity increasing the number of nodes (in most of the case clone of a basic node)
Describe the load balancing models in the NFV environment
Internal Load Balancer: The VNF contains a VNFC which acts as load balancer and distribute internally the requests to the other VNFCs
External Load Balancer: An additional VNF that acts as the LB and distributes the requests over the set of VNFs
What are the challenges of dynamic scaling?
- statefulness: Statefulness makes dynamic scaling challenging because it requires load balancing techniques to maintain affinity between source and destination
- low packet processing latencies: Such load balancing techniques have also to be fast to avoid any noticeable disruption to applications.
Please describe the auto-scaling pipeline
- Detecting the need to scale
- monitoring VNFs and generating alarms in case predefined conditions are met
- relevant monitoring information
- threshold-crossing function - Determining the scaling action
- check if actions are feasible or not
- actions based on received alarms - Execute the scaling action from the NFVO (NFV Orchestrator)
What is Fault Management? How does fault management function in an NFV environment?
Mitigate hardware failures providing virtualization-based high-availability mechanisms, for instance, virtual resources migration
In this way the VNF becomes independent of the NFVI faults
Fault Management includes several processes:
- Fault detection
- Fault localization
- Fault reporting
Please describe the MANO domain of ETSI NFV
ETSI = European Telecommunications Standards Institute MANO = Management and Orchestration
- Orchestrator of Network Service: Network Service lifecycle management, Instantiation of VNFs
- VNFs Manager: lifecycle management of VNF instances
- Virtualized Infrastructure Manager (VIM): keeping an inventory of the allocation of virtual resources to physical resources
Please describe the VNF life-cycle management
- prepare virtual resources required
- install the SW of the VNFs
- Configure the VNF SW
Run and control with FCAPS model:
Fault Management, Configuration, Accounting, Performance, Security
Why do 5G systems need an orchestrator?
The orchestrator is the main decision point in the interaction between services and infrastructure.
- allocates and maintains resources
- performs lifecycle management
What is needed to migrate an NF to a virtualized environment?
- decouple the host function from the VNF
- create a new container interface between host and VNF
- divide the interface between NF in virtualized and infrastructure interfaces
Please describe the reliability levels in a virtualized environment
- Service Continuity
- Topological Transparency
- Regression and Preemption
- Distributed Resiliency
Describe web-services
- Web Services are based on the Client-Server paradigm (Request-Response model)
- Main functions: Front-end (interaction with client, example authentication), Worker, Database
- Additional NF: Identity providers, queues, caches, content delivery networks (CDN)
- Benefits: Simple architecture, easy to deploy and manage, scalability, separation of concerns
- Issues: service can become monolithic, front-end may become very large, state of front-end and worker may not be separated.
Describe micro-services
- Micro services aim at keeping VNF components rather small in terms of functionalities offered.
- Include load balancing mechanisms for supporting high scalability
- Decoupling between VNF components to facilitate upgrade procedures
- Redirect the client request with an API Gateway to the correct microservice.
- Benefits: Agility, fault isolation, scalability, data isolation
- Issues: Complexity, dev and testing, network congestion and latency, data integrity.
Please describe the NFVI domain of ETSI NFV
NFVI is the infrastructure comprising of heterogeneous hardware resources on which the hypervisor creates an abstraction towards the NFV domain
