Home > Articles > Cisco > CCNP Routing and Switching

  • Print
  • + Share This
This chapter is from the book

Token Ring

After Ethernet, Token Ring is the second most widely used LAN technology, and its second rank is due mostly to its cost factor. Ethernet technology is simply cheaper to implement than is Token Ring. Token Ring is a ring topology created by IBM in the 1970s. The IEEE 802.5 subcommittee—with help from IBM representatives—developed a set of standards that described a token-passing network in a ring topology.

Token-passing networks move a stream of data, called a token, around the network. Any station with a message or data to transmit waits until it receives a free token. It then changes the free token to a busy token and transmits a block of data called a frame. The frame contains the data that needs to be sent to the rest of the network. The token circulates around the ring, passing through as many as three stations at a time until it finds the receiving station.

The receiving station copies the data from the frame, and the frame continues around the ring, making a complete round trip back to the original transmitting station. The transmitting station now knows the frame has been received, and the station then purges the busy token it has been keeping and inserts a new free token on the ring for others to use.

The use of token-passing prevents messages from interfering with one another by guaranteeing that only one station at a time is transmitting. Therefore, collisions cannot occur on the network. Unlike Ethernet, token passing ensures the delivery of the frame.

The Token Ring topology runs at the Physical and Data Link layers of the OSI model, and it is modeled as a star topology using STP wiring. Each station is connected to a central hub called a multistation access unit (MSAU) that houses electromechanical relays to make the physical star into a logical ring. The logical ring is where each station receives signals from its nearest active upstream neighbor (NAUN) and repeats these signals to its downstream neighbors.

Token Ring networks use a priority system that permits certain user- designated, high-priority stations to use the network more frequently. Priority levels are configured by the network administrator. A Token Ring network has two fields inside the frame of the token, as shown in Figure 3.5, that control priority: the priority field and the reservation field. When a priority token is transmitted, it can be seized by only those stations with a priority that is equal to or higher than the priority value contained in that token. The station then seizes the token and changes it to an information frame, and only stations with a priority value higher than that of the transmitting station can reserve the token for the next pass around the network. When the next token is generated, it includes the higher priority of the reserving station. Stations that raise a token's priority level must reinstate the previous priority after the transmission is complete.

The original IBM Token Ring product ran at speeds of 4Mbps. In 1989, IBM released a faster version of Token Ring, which ran at 16Mbps. Over time, a high-speed Token Ring (HSTR) was released that operated at 100Mbps and led to 1Gbps Token Ring. The speed has maintained with the evolving technology and makes Token Ring topology a serious contender against Ethernet.

Frame Format of Token Ring

Token Ring is similar to FDDI frames, in that they both support token formats, as well as data. Figure 3.5 illustrates the frame format of both the token being passed and a frame sent from a node on the ring during a Token Ring network communication.

Here is a brief explanation of each field in a Token Ring frame as shown in Figure 3.5.

  • Start Delimiter—Alerts each station of a token and uses a unique coding for the frame.

  • Access-Control Byte—Contains a series of bits that circulate throughout the ring and are used by the active monitor to ensure delivery: a Priority bit indicates the priority of the frame or token; a Reservation bit indicates the priority required for the next token to gain access to the ring; a Token bit differentiates a token from a data or command frame; and a Monitor bit determines whether a frame is circling the ring endlessly. Active monitor employs a mechanism for detecting and compensating for network fault.

  • Frame Control—Indicates the frame type and contains the Frame type bit, the Reserved bit, and the Control bits.

  • Destination Address—Indicates the address of the receiver.

  • Source Address—Identifies the address of the sender.

  • Data—Indicates the actual data being sent from the upper layers.

  • Frame Control Sequence—Ensures that all the frames are delivered without damage.

  • End Delimiter—Defines the end of the token or frame and contains bits to indicate if a frame is damaged.

  • Frame Status—Terminates the frame and ensures that the frame has been copied to the destination address.

Figure 3.5Figure 3.5 The Token Ring Frame formats.

Active Monitor

Token Ring networks employ a mechanism for detecting and compensating for network faults. Any station on a Token Ring network can be selected to be the active monitor. This active monitor station acts as a centralized source of timing information for the Token Ring stations and makes sure that there isn't more than one token on the ring at any given time. Also, when a sending device fails, its frame may continue to circle the ring. This can prevent other stations from transmitting their frames, which may lock up the network. The active monitor can detect such frames, remove them from the ring, and generate a new token. The active monitor also has several standby monitors that act as backups in case the active monitor goes offline.

  • + Share This
  • 🔖 Save To Your Account

Pearson IT Certification Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Pearson IT Certification 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 Pearson IT Certification 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 Adobe Press. 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.pearsonitcertification.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