Home > Articles > Operating Systems, Server

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

1.3 Network Protocols

This section is a brief introduction to TCP, UDP, IP, and ICMP. First, we briefly examine the two transport protocols, TCP and UDP, and then take a cursory look at IP and ICMP.

Transport Layer Protocols: TCP and UDP

We briefly mentioned the TCP and UDP protocols in the context of the TCP/IP model described earlier in this chapter. We now examine the Transport layer in greater detail.

The Transport layer offers either a high-overhead, guaranteed, connection-oriented transport service such as that offered by TCP, or a low-overhead, connectionless, nonguaranteed service such as the one offered by UDP. See Chapter 7 for more information about the Transport layer protocols and Chapters 5 and 13 for details about the IP protocols (IPv4, IPv6) that route the Transport protocols data.

Transmission Control Protocol (TCP)

TCP provides a connection-oriented, guaranteed, reliable transport service. TCP has significant overhead because every byte of transmitted data is both acknowledged and sequenced by both ends of the connection. The data itself is delivered in one or more segments, which are TCP's basic units of data. In addition, TCP establishes a connection at the Transport layer, which must be formed before transmission of client data may occur over the Transport layer.

Although TCP guarantees data delivery, it must be remembered that TCP is routed over IP and therefore uses the same underlying packet-based routing service as UDP—namely, IP, which is not guaranteed. Both TCP and UDP use IP to route their data, but they impose different levels of reliability and overhead as determined by their own specifications as Transport layer protocols. TCP extensively monitors the quality of data sent and received, whereas UDP has only a simple checksum error checking method, which is often turned off and therefore ignored.

The cost of TCP reliability, as just stated, is significant overhead. The TCP protocol sends a sequenced (numbered) byte stream of segmented data. The sequence numbering of bytes ensures that the destination TCP protocol at the receiving end orders the data stream correctly. Unfragmented IP datagrams that arrive in the wrong order (which have encapsulated TCP segments) are simply passed up the stack to TCP, which ensures that the data is delivered to the application in the correct order. Fragmented IP datagrams, on the other hand, are reassembled by IP itself before being passed to TCP based on fragment offset information stored in the IP header. Some example TCP client applications are telnet, ftp, and sendmail, all of which require a guaranteed delivery service and therefore use TCP rather than UDP.

EXAM NOTES

Key Learning Points

  • TCP is a connection-oriented protocol.

  • The segment is the TCP unit of data.

  • TCP is a Transport layer protocol.

  • TCP is encapsulated and routed by IP.

  • TCP is said to offer a guaranteed, reliable, connection-oriented service that creates significant overhead.

Essentially, if data security must be guaranteed, TCP is a better choice than UDP, although more expensive in terms of both the amount of control data transmitted and the control overhead incurred. Chapter 7 examines the TCP protocol in greater detail.

User Datagram Protocol (UDP)

UDP is a connectionless transport protocol, which means that no connection is established at the Transport layer prior to data being sent between client and server applications.

Some applications—for example, a router propagating routing information every 30 seconds—can afford to lose an occasional data packet. Routing clients that miss the occasional routing table update do not usually suffer adverse effects. The Routing Information Protocol (RIP) uses UDP. DNS queries also use UDP, as speed is more important than reliability for this application. UDP applications tend to send small packets that can be transported in a single UDP datagram. UDP has an optional checksum error check, which introduces minimal overhead and is usually turned off.

To check the UDP checksum variable (udp_do_checksum) under Solaris 8 use ndd:

# ndd –get /dev/udp udp_do_checksum
0

A value of 0 means false; that is, disable the UDP checksum feature. A value of 1, which means true, indicates that the UDP protocol checksum feature is enabled.

To enable the UDP checksum feature, issue the following command:

# ndd –set /dev/udp udp_do_checksum 1

To check the current value of udp_do_checksum:

# ndd –get /dev/udp udp_do_checksum
1

EXAM NOTES

Key Learning Points

  • UDP is a connectionless protocol.

  • UDP is a transport protocol.

  • UDP is encapsulated and routed in IP.

  • UDP is not guaranteed.

  • UDP does minimal error checking.

  • UDP has a simple checksum for error checking.

  • UDP's header is only eight bytes.

Chapter 7 looks at the UDP protocol in greater detail.

Internet Protocol (IPv4)

IPv4 is a connectionless protocol like UDP. Unlike UDP, however, IP is not a transport protocol but instead offers a datagram routing service to the Transport layer (a datagram is the unit of data for the IP layer). The Transport layer protocols, TCP and UDP, use IP to route their client data between application client and server hosts. It is worth stressing, therefore, that IP routes data between hosts, and in effect, between the Transport layers on end-to-end hosts, but not between clients and server processes. The Transport layer protocols, TCP and UDP, transport the data between client and server processes, using IP to form a bridge between hosts. IP as a protocol is responsible for the following:

  • fragmenting of IP datagrams if the Network Interface layer MTU demands it

  • reassembly of IP fragments

  • making the IP datagram routing decision

EXAM NOTES

Key Learning Points

  • IP is a connectionless protocol.

  • IP is an Internet layer protocol.

  • IP is encapsulated in many different datalink technologies such as Ethernet, Token Ring, and Point-to-Point Protocol (PPP).

  • IP is not guaranteed.

Chapter 5 looks in detail at IPv4, and Chapter 13 explores IPv6. Next we look at ICMP, which also functions at the Internet layer (3).

Internet Control Message Protocol (ICMP)

ICMP is considered almost part of the IP protocol, even though it is a separate protocol in its own right. ICMP generates messages, which receive a response either from the IP layer itself or a higher layer protocol such as TCP or UDP. Although ICMP is at the same layer as IP, it is not an alternative to IP; rather, it assists IP with IP error detection and correction.

ICMP data is encapsulated in IP datagram(s), as is TCP and UDP data, but ICMP is not a Transport layer protocol. Error messages such as network unreachable, host unreachable, and port unreachable are examples of ICMP error messages.

See Chapter 5 for further details about ICMP.

EXAM NOTES

Key Learning Points

  • ICMP is a connectionless protocol.

  • ICMP is an Internet layer protocol.

  • ICMP is unusual in that it is encapsulated in IP but is not a transport protocol.

  • ICMP assists IP with error detection and correction.

  • ICMP generates two types of messages: error and query.

  • + 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