Home > Articles > Networking

Foundations of Modern Networking: Background and Motivation of Software-Defined Networks (SDN)

This chapter from Foundations of Modern Networking: SDN, NFV, QoE, IoT, and Cloud begins the discussion of software-defined networks (SDNs) by providing some background and motivation for the SDN approach.
This chapter is from the book
  • The requirements for a future all-digital-data distributed network which provides common user service for a wide range of users having different requirements is considered. The use of a standard format message block permits building relatively simple switching mechanisms using an adaptive store-and-forward routing policy to handle all forms of digital data including “real-time” voice. This network rapidly responds to changes in network status.
  • —On Distributed Communications: Introduction to Distributed Communications Networks, Rand Report RM-3420-PR, Paul Baran, August 1964

This chapter begins the discussion of software-defined networks (SDNs) by providing some background and motivation for the SDN approach.

3.1 Evolving Network Requirements

A number of trends are driving network providers and users to reevaluate traditional approaches to network architecture. These trends can be grouped under the categories of demand, supply, and traffic patterns.

Demand Is Increasing

As was described in Chapter 2, “Requirements and Technology,” a number of trends are increasing the load on enterprise networks, the Internet, and other internets. Of particular note are the following:

  • Cloud computing: There has been a dramatic shift by enterprises to both public and private cloud services.
  • Big data: The processing of huge data sets requires massive parallel processing on thousands of servers, all of which require a degree of interconnection to each other. Therefore, there is a large and constantly growing demand for network capacity within the data canter.
  • Mobile traffic: Employees are increasingly accessing enterprise network resources via mobile personal devices, such as smartphones, tablets, and notebooks. These devices support sophisticated apps that can consume and generate image and video traffic, placing new burdens on the enterprise network.
  • The Internet of Things (IoT): Most “things” in the IoT generate modest traffic, although there are exceptions, such as surveillance video cameras. But the sheer number of such devices for some enterprises results in a significant load on the enterprise network.

Supply Is Increasing

As the demand on networks is rising, so is the capacity of network technologies to absorb rising loads. In terms of transmission technology, Chapter 1, “Elements of Modern Networking,” established that the key enterprise wired and wireless network technologies, Ethernet and Wi-Fi respectively, are well into the gigabits per second (Gbps) range. Similarly, 4G and 5G cellular networks provide greater capacity for mobile devices from remote employees who access the enterprise network via cellular networks rather than Wi-Fi.

The increase in the capacity of the network transmission technologies has been matched by an increase in the performance of network devices, such as LAN switches, routers, firewalls, intrusion detection system/intrusion prevention systems (IDS/IPS), and network monitoring and management systems. Year by year, these devices have larger, faster memories, enabling greater buffer capacity and faster buffer access, as well as faster processor speeds.

Traffic Patterns Are More Complex

If it were simply a matter of supply and demand, it would appear that today’s networks should be able to cope with today’s data traffic. But as traffic patterns have changed and become more complex, traditional enterprise network architectures are increasingly ill suited to the demand.

Until recently, and still common today, the typical enterprise network architecture consisted of a local or campus-wide tree structure of Ethernet switches with routers connecting large Ethernet LANs and connecting to the Internet and WAN facilities. This architecture is well suited to the client/server computing model that was at one time dominant in the enterprise environment. With this model, interaction, and therefore traffic, was mostly between one client and one server. In such an environment, networks could be laid out and configured with relatively static client and server locations and relatively predictable traffic volumes between clients and servers.

A number of developments have resulted in far more dynamic and complex traffic patterns within the enterprise data center, local and regional enterprise networks, and carrier networks. These include the following:

  • Client/server applications typically access multiple databases and servers that must communicate with each other, generating “horizontal” traffic between servers as well as “vertical” traffic between servers and clients.
  • Network convergence of voice, data, and video traffic creates unpredictable traffic patterns, often of large multimedia data transfers.
  • Unified communications (UC) strategies involve heavy use of applications that trigger access to multiple servers.
  • The heavy use of mobile devices, including personal bring your own device (BYOD) policies, results in user access to corporate content and applications from any device anywhere any time. As illustrated previously in Figure 2.6 in Chapter 2, this mobile traffic is becoming an increasingly significant fraction of enterprise network traffic.
  • The widespread use of public clouds has shifted a significant amount of what previously had been local traffic onto WANs for many enterprises, resulting in increased and often very unpredictable loads on enterprise routers.
  • The now-common practice of application and database server virtualization has significantly increased the number of hosts requiring high-volume network access and results in every-changing physical location of server resources.

Traditional Network Architectures are Inadequate

Even with the greater capacity of transmission schemes and the greater performance of network devices, traditional network architectures are increasingly inadequate in the face of the growing complexity, variability, and high volume of the imposed load. In addition, as quality of service (QoS) and quality of experience (QoE) requirements imposed on the network are expanded as a result of the variety of applications, the traffic load must be handled in an increasingly sophisticated and agile fashion.

The traditional internetworking approach is based on the TCP/IP protocol architecture. Three noteworthy characteristics of this approach are as follows:

  • Two-level end system addressing

  • Routing based on destination
  • Distributed, autonomous control

Let’s look at each of these characteristics in turn.

The traditional architecture relies heavily on the network interface identity. At the physical layer of the TCP/IP model, devices attached to networks are identified by hardware-based identifiers, such as Ethernet MAC addresses. At the internetworking level, including both the Internet and private internets, the architecture is a network of networks. Each attached device has a physical layer identifier recognized within its immediate network and a logical network identifier, its IP address, which provides global visibility.

The design of TCP/IP uses this addressing scheme to support the networking of autonomous networks, with distributed control. This architecture provides a high level of resilience and scales well in terms of adding new networks. Using IP and distributed routing protocols, routes can be discovered and used throughout an internet. Using transport-level protocols such as TCP, distributed and decentralized algorithms can be implemented to respond to congestion.

Traditionally, routing was based on each packet’s destination address. In this datagram approach, successive packets between a source and destination may follow different routes through the internet, as routers constantly seek to find the minimum-delay path for each individual packet. More recently, to satisfy QoS requirements, packets are often treated in terms of flows of packets. Packets associated with a given flow have defined QoS characteristics, which affect the routing for the entire flow.

However, this distributed, autonomous approach developed when networks were predominantly static and end systems predominantly of fixed location. Based on these characteristics, the Open Networking Foundation (ONF) cites four general limitations of traditional network architectures [ONF12]:

  • Static, complex architecture: To respond for demands such as differing levels of QoS, high and fluctuating traffic volumes, and security requirements, networking technology has grown more complex and difficult to manage. This has resulted in a number of independently defined protocols each of which addresses a portion of networking requirements. An example of the difficulty this presents is when devices are added or moved. The network management staff must use device-level management tools to make changes to configuration parameters in multiple switches, routers, firewalls, web authentication portals, and so on. The updates include changes to access control lists (ACLs), virtual LAN settings, QoS settings in numerous devices, and other protocol-related adjustments. Another example is the adjustment of QoS parameters to meet changing user requirements and traffic patterns. Manual procedures must be used to configure each vendor’s equipment on a per-application and even per-session basis.
  • Inconsistent policies: To implement a network-wide security policy, staff may have to make configuration changes to thousands of devices and mechanisms. In a large network, when a new virtual machine is activated, it can take hours or even days to reconfigure ACLs across the entire network.
  • Inability to scale: Demands on networks are growing rapidly, both in volume and variety. Adding more switches and transmission capacity, involving multiple vendor equipment, is difficult because of the complex, static nature of the network. One strategy enterprises have used is to oversubscribe network links based on predicted traffic patterns. But with the increased use of virtualization and the increasing variety of multimedia applications, traffic patterns are unpredictable.
  • Vendor dependence: Given the nature of today’s traffic demands on networks, enterprises and carriers need to deploy new capabilities and services rapidly in response to changing business needs and user demands. A lack of open interfaces for network functions leaves the enterprises limited by the relatively slow product cycles of vendor equipment.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020