1 / 19

Upper OSI Layers

Upper OSI Layers. Lecture 10, May 7, 2003 Mr. Greg Vogl Data Communications and Networks Uganda Martyrs University. OSI Layers and Protocols. Functions of Transport Layer. End-to-end reliability (time to live counter) Packet sequencing (numbering, resend)

wray
Download Presentation

Upper OSI Layers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Upper OSI Layers Lecture 10, May 7, 2003 Mr. Greg Vogl Data Communications and Networks Uganda Martyrs University

  2. OSI Layers and Protocols Data Communications and Networks: Lecture 10: Upper OSI Layers

  3. Functions of Transport Layer • End-to-end reliability (time to live counter) • Packet sequencing (numbering, resend) • Message segmentation/assembly (max. size) • Flow control (ack, wait) • Error detection/correction (checksum/CRC) • Addressing (network, node, process) • Security (encryption keys, user/password) Data Communications and Networks: Lecture 10: Upper OSI Layers

  4. Reliability and packet sequencing • Time-to-live counter: no. of hops or secs. • When counter reaches 0, discard packet • Keeps a packet from moving forever • Sequence numbers in transport header • Used to check if packets are missing • Receiver sends ack of received packets • Missing packets are resent • In connectionless sessions, restore packet order Data Communications and Networks: Lecture 10: Upper OSI Layers

  5. Flow and error control • Flow control • Ack is needed after sending some messages • If receiver’s buffer fills, tell sender to wait • Rate control depends on source and destination processing speed • Error control • checksum in header • in addition to error checking in lower layers Data Communications and Networks: Lecture 10: Upper OSI Layers

  6. Transport Control Protocol • Connection-based; full duplex • Set up, manage, close a virtual connection • Messages transferred as stream of bytes • Sequenced delivery • Flow control • Sliding window of acks • Error detection and recovery; reliable • Port-level addressing Data Communications and Networks: Lecture 10: Upper OSI Layers

  7. TCP Segment Data Communications and Networks: Lecture 10: Upper OSI Layers

  8. TCP Ports • Client and server processes communicate • network + host + port = unique process address • Server uses well known port address 0-1023 • FTP-21, Telnet-23, SMTP-25, HTTP-80, etc. • No need to include port number in URL • http://www.w3.org:80 = http://www.w3.org • Client uses any unused port • Handshake sets up source/dest port numbers Data Communications and Networks: Lecture 10: Upper OSI Layers

  9. User Datagram Protocol • Connectionless, no connections like IP • Uses ports much like TCP • Lower overhead, higher speed • No reliability/ack • Used for non-critical messages; good for LANs • MS Messenger Service, BOOTP, DHCP, RIP • Higher levels manage delivery and reliability • e.g. NFS, use of timeout counters Data Communications and Networks: Lecture 10: Upper OSI Layers

  10. UDP Datagram Data Communications and Networks: Lecture 10: Upper OSI Layers

  11. Functions of Session Layer • Establishes sessions between services • Synchronises and performs naming services • Example protocols: • Dynamic Host Configuration Protocol (DHCP) • Bootstrap Protocol (BOOTP) • Domain Name Service (DNS) • Network Basic Input Output System (NetBIOS) • Remote Procedure Call (RPC) Data Communications and Networks: Lecture 10: Upper OSI Layers

  12. Dynamic Host Configuration Protocol • Server assigns IP number to a computer • Client obtains IP number automatically • User can move PC without involving admin • Good for portable users • Can also provide IP of local router, DNS • Microsoft helped define DHCP • Based on BOOTP (for diskless workstations) Data Communications and Networks: Lecture 10: Upper OSI Layers

  13. Domain Name Service • Translates IP numbers  host names • E.g. 207.46.230.229  microsoft.com • Easier to remember names than IP numbers • Uses: both providing and receiving services • Local control, available to all, fast, robust • DNS servers keep a distributed database • Static hosts files would be too big to maintain • Web browsers and mail servers use DNS server Data Communications and Networks: Lecture 10: Upper OSI Layers

  14. Top-Level Domains • .com: commercial/business/for profit • .edu: educational • .gov: US government • .mil: US military • .net: service providers, online organisations • .org: nonprofits, associations, societies • .ug, .us, .ca, etc.: country codes Data Communications and Networks: Lecture 10: Upper OSI Layers

  15. DNS Database Structure • Tree structure with final “.” to indicate root • Top-level domain names have 2-3 letters • First-level name is the organisation name • Second and third levels used by large org’s • home.umu.ac.ug is a subdomain of umu.ac.ug • Each domain name has at least 1 IP number • DNS servers: Win2000 Server, Unix BIND Data Communications and Networks: Lecture 10: Upper OSI Layers

  16. Network Basic Input/Output System • The first Windows networking technology • Designed as API for small peer-peer LANs • Windows now uses NBF and/or NetBT • NetBEUI has become a NetBIOS Frame (NBF) • NetBIOS routed in TCP/IP packets (NetBT) • Uses Windows Internet Name Service • with DNS, resolves NetBIOS resource names Data Communications and Networks: Lecture 10: Upper OSI Layers

  17. Remote Procedure Call • One host’s program executes another’s code • Client requests to execute code on server • A result message is returned to the caller • Used to implement client-server computing • Developed by Sun, several implementations • Developers write communications code for: • authentication, sessions, errors, custom services Data Communications and Networks: Lecture 10: Upper OSI Layers

  18. Functions of Presentation Layer • Network characters  specific platforms • Data compression, encoding, encryption • Network shell • Direct local and network requests appropriately • Local and network resources treated the same • Application development is easier • e.g. Microsoft Redirector • e.g. Sun eXternal Data Representation for RPC Data Communications and Networks: Lecture 10: Upper OSI Layers

  19. Important Application Protocols • File Transfer Protocol (FTP), TFTP, NTP • Telnet; rlogin, rcp, rexec, rsh; ssh • Simple Mail Transfer Protocol • “Simple” Network Management Protocol • (Secure) Hypertext Transfer Protocol • Network File System (Sun remote mount) • X Window System (Unix client-server GUI) Data Communications and Networks: Lecture 10: Upper OSI Layers

More Related