Home > Articles > Software Development & Management

Latency and Jitter on Your LAN

  • Print
  • + Share This
Broadband connections to the Internet have boosted the popularity of streaming multimedia and videoconferencing applications. Tailoring your LAN for those new services requires a good understanding of how latency and jitter originate and how they affect LAN performance.

This content is excerpted from Barry and Marcia Press’ book, Networking by Example .

Most of the time, the only LAN performance characteristic that you're going to care about is the data rate, which determines the time it takes to get something done. If you're doing something like talking in a network videoconference or across your LAN, though, you'll also care about how long it takes for individual messages to move across the LAN and about how variable those times are. Those two measurements are called latency and jitter.

Latency and jitter are the important performance measures for videoconferencing because interactive streaming applications depend on an uninterrupted flow of messages to keep the processing on the computers running smoothly. If you delay or drop messages in those applications, it's likely that the software will pause noticeably. Pauses are irritating in video and can make audio unintelligible.

Latency and jitter originate inside your computers, as shown in Figure 1. Each block in the two computers is a processing step that has a minimum time delay. The delay that a specific message encounters in each step is variable and most often depends on what's happening at that instant of time on the LAN infrastructure (even though the cable and hub themselves have a relatively constant transit time).

Figure 1

Sources of network latency and jitter

Each processing step has its own function and own unique reasons for introducing latency and jitter:

  • LAN adapter—The interaction between the LAN adapter and the network infrastructure is the original source of latency and jitter beyond the minimums because the LAN adapter is required to wait until there is no interfering traffic on the cable before it transmits a message. If there's no traffic on the network, the wait will be the minimum possible; if there's very heavy traffic, the wait can be relatively long.

    Because it's possible for two computers to believe that the cable is clear and to start transmitting a message at the same time, collisions can occur, corrupting both messages and requiring both to be retransmitted. The loss of the transmitted messages introduces delay in getting the messages to their destination, increasing latency. LAN adapters in Ethernet networks are required to wait a random time before attempting to retransmit, which increases jitter.

  • LAN adapter device driver—The device driver is responsible for controlling the operation of the LAN adapter, giving it messages to send, accepting received messages, and monitoring the adapter for problems. Drivers from different manufacturers use different techniques to decide whether it's possible to hand off or receive messages, and to find out about problems, differences that cause variations in transit time that add to latency and jitter.

  • Protocol stack—Even with the best efforts of the LAN adapter and the device driver, messages can get lost on networks. When they do, the first line of defense responding to the problem will be the protocol stack implementing TCP/IP, SPX/IPX, or NetBEUI. Messages can be lost without notification, though, so protocol stacks have to wait for a timeout period before declaring the message lost. The timeout periods are very long compared to normal latencies, introducing a lot of delay and one of the major sources of jitter.

  • Application software—How the application software handles lost or delayed messages ultimately determines how stringent the latency and jitter requirements on your network will be. Applications insensitive to latency and jitter typically send enough data in every message that dropped messages might cause a skip in what you perceive, but this won't stall the receiving program. More data has to be transmitted in each message to meet that requirement, though, increasing the traffic on the LAN. More sensitive applications actually wait for the receiver to send back a confirmation that each message has arrived. Those applications generate less traffic but can stall completely when a collision causes a message to be dropped.

Ultimately, the source of abnormal latency and jitter on a LAN is collisions on the cable or in the hub. You can reduce the probability of collisions by increasing the network data rate, which reduces the time each message takes to transit the network and also increases the percentage of free time. For a given traffic load, networks running at 100Mbps will have lower latency and jitter than ones at 10Mbps, which in turn will display lower latency and jitter than 1Mbps networks. If videoconferencing or other streaming multimedia applications are important on your network, you'll want to favor the higher-speed technologies.

Collisions are also the reason why you're unlikely to be able to use more than about 80 percent of the transmission data rate on LAN, and you might get far less. Simulations and traffic analysis show that when there are too many collisions, the computers end up spending all their time retransmitting lost messages, and no useful work gets done.

  • + Share This
  • 🔖 Save To Your Account

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