COMP 421 /CMPET 401

1. COMP 421 /CMPET 401 COMMUNICATIONS and NETWORKING CLASS 2

2. OSI Reference Model • Developed by the International Standards Organization (ISO) to facilitate the international standardization of communications protocols • For U.S.: ANSI (American National Standard Institute) - www.ansi.org • OSI is ISO's Basic Reference Model for Open Systems Interconnect (hence: ISO/OSI) • The Reference Model itself is not a Network Architecture (does not specify any protocols or services)

3. The ISO/OSI Reference Model • The model describes computer communications protocols in a general sense to facilitate discussion • No assumptions are made regarding: • Programming language bindings • Operating system bindings • Applications programming interfaces • Development of the model started in the mid-1970’s • Biggest Problems • Very long time to complete the model and protocol standards • Very hard to understand the detailed standards • Difficult (expensive) to get the standards documents

4. OSI MODEL

5. OSI MODEL The seven layers divided into two important subnets: 1. Communications Subnet – This is comprised of the lower 3 layers 2. Host Process – This is comprised of the upper three layer The network layer is middle layer and the first end to end layer. It acts as buffer between the two subsets.

6. ISO/OSI Reference Model - Why 7 Layers • One layer for each level of abstraction • Each layer performs (ideally) a limited, well defined function • Functions for each layer are selected with International Standardization as a goal • Layer boundaries are chosen to minimize information crossing the interface • Want to keep the model manageable (5 would have been nice) but not have to jumble together distinct functions

7. Application Application Presentation Presentation Session Session Transport Transport Network Network Data Link Data Link Physical Physical OSI Model App Process X App Process Y Application Data AH Application Data PH Data Unit SH Data Unit TH Data Unit NH Data Unit F A C Data Unit FCS F BITS Physical Transmission Medium Communication Path

8. OSI Layer 1 Layer 1 is the Physical Layer. It handles bit transmission between one node and the next. The functions of this layer include interfacing with the transmission media, encoding the data signal, defining the range of the voltage or current magnitudes, defining the connector sizes, shape, and anything generally associated with the physical transmission of a bit stream.

9. OSI Layer 1 - Physical layer • Primary function is transmitting raw bits over a physical communications channel • Primary design issues include: mechanical, electrical, functional, procedural characteristics • what voltage represents a “1” versus a “0” • How many pins in and the shell shape the connector. • Defines functions between the system and transmission medium • Specifies sequence of events by which bits streams are exchanged across the physical medium • By “raw bits” we mean there is no interpretation of the bits - stream of bits in and bits out

10. OSI Layer 2 - Data Link layer • Primary function is to make Layer 1 into what appears to be a channel free of undetected errors • Deals with data in chunks (typically 100s-1000s of bytes) generally called Frames • This layer must create/recognize frame boundaries • remember - Physical layer does not care • often requires special bit patterns to signal boundaries • may have to deal with possibility of pattern appearing in data

11. OSI Layer 2 In other words it maintains the reliable communications link between adjacent nodes. The DLL inserts addresses in the data frame and provides error control for the data.

12. OSI Layer 2 - Data Link layer • Among the key issues dealt with are: • Error handling (e.g. corrupted frame) • Flow control • Providing various qualities of service • For Broadcast networks, a key issue is controlling access to the channel: • Use a sub-layer called the Media Access Control (MAC) sub-layer

13. OSI Layer 3 - Network layer • Primary function is to control the operation of the layers below • Among the key issues dealt with are: • Routing packets from source to destination through the network (or multiple networks) using static or dynamic routing algorithms • Controlling congestion in the network • Accounting functions (for billing) • Translating between protocols across heterogeneous networks • Concerned with Addressing

14. OSI Layer 3 This layer establishes the path for the traveling data packet

15. OSI Layer 4 - Transport layer • First end-to-end layer • Uses the network to (most often) provide higher layers with a connection oriented, reliable, error free channel that delivers messages (or byte stream) in order • Layer 4 of the OSI Model coordinates communications between systems. • May also perform flow control • Often performs multiplexing of multiple transport connections over one or more network connections • Generally requires Address (or naming)

16. OSI Layer 4 This layer provides reliable delivery of host messages originating at layer 7 the same way as the DLL assures reliable delivery of frames between adjacent nodes. This is the layer responsible for Segmenting long messages in smaller units (packets) and then Reassembling them at the other end.

17. OSI Layer 5 - Session layer • Manages dialog control (e.g. may manage who’s turn it is to talk in a high-level half-duplex protocol) • Manages synchronization of transactions which may need to be able to roll back in case of a crash • Sort of an unwanted layer, this layer is usually very thin and little more than a pass through for most protocols • Key services provided include: • Dialogue discipline • Grouping - data mark as belonging to a special group • Recovery – checkpoint mechanism

18. OSI Layer 5 In other words it establishes and terminates process to process communications Sessions between hosts.

19. OSI Layer 6 - Presentation layer • Rather than being concerned with moving information, the Presentation layer is concerned with the interpretation of information representation • Ensures that the syntax and meaning is the same for each participant in a communication • Provides for standard representation and may provide capabilities for conversion of data

20. OSI Layer 6 Simply put this layer establishes the syntax in which data is exchanged between the two hosts. It provides a data manipulation function rather than a communication function (data compression and data encryption are examples of this layers activities)

21. OSI Layer 7 - Application layer • The layer where end-user applications live • This is the highest level of abstraction and the level which is of primary importance (for most users) • All the rest of the layers exist to support these applications • Layering exists so we can move these around to different machines, and so they can communicate across any platforms - Open Systems Interconnect

22. OSI Layer 7

23. OSI Examples

24. Review - Functions of the OSI Layers • Layer 1 (physical): Transmission of bits • Layer 2 (data link): Transmission of frames on one given link • Layer 3 (network): Routing of packets through the network • Layer 4 (transport): End-to-end delivery of messages

25. Review - Functions of the OSI Layers • Layer 5 (session): Setup and management of end-to-end conversation, synchronization • Layer 6 (presentation): Formatting, encryption, and compression of data • Layer 7 (application): user applications

26. Introduction to TCP/IP

27. What is TCP/IP • Transmission Control Protocol/Internet Protocol • TCP/IP refers to an entire suite of networking protocols, developed for use on the Internet • TCP and IP are certainly two of the most important

28. TCP/IP Protocol Suite • Advanced Research Project Agency (ARPA) of DoD sponsored the development of ARPANET in 1970s. • TCP/IP has been adopted as the ARPANET protocol suite • TCP/IP became popular by the inclusion of this protocol in BSD Unix system (a version of Unix developed by University of California @ Berkley)

29. TCP/IP (cont.) • Transport Layer-TCP (Transmission Control Protocol) • Provides fully reliable, connection-oriented service • Byte-stream transmission • Network Layer- IP (Internet Protocol) • IP provides datagram service (used in packet switching) • It is connectionless unreliable service • IP handles routing

30. TCP/IP Characteristics • TCP/IP provides the services necessary to interconnect computers and to interconnect networks, creating the Internet • Independence from underlying network topology, physical network hardware, and OS • Unique IP Address • Universal connectivity throughout the network • Standardize high-level protocols

31. TCP/IP Protocol Architecture Model Application Application TCP TCP IP IP Network Access Network Access Network Physical Physical Trans- Mission System Source Transmitter Receiver Destination Source System Destination System

32. A Comparison Application User Space Application Presentation Session Software Transport Transport Network IP Operating System Network Access Firmware Data Link Hardware Physical Physical

33. user processor user processor TCP UDP IP hardware interface TCP/IP Network Structure UDP: User Datagram Protocol ICMP: Internet Control Message Protocol IP: Internet Protocol ARP: Address Resolution Protocol RARP: Reverse ARP OSI Layer 5-7 OSI Layer 4 OSI Layer 3 ARP RARP ICMP OSI Layer 1-2

34. user proc.A user proc.B user proc.C user proc.D user proc.E user proc.F user proc.G UDP TCP PEX SPP IP IDP Ethernet interface Ethernet interface Ethernet interface Ethernet interface Port Number XNS protocol suite TCP/IP protocol suite Ethernet cable 1 Ethernet cable 2

35. Applications 1 2 3 4 ( ) ( ) ( ) ( ) Transport Network access Port Assignments • Servers are known by ports number • FTP 20, TELNET 23, SMTP 25, HTTP 80 • Port numbers are generally allocated by • 0 --not used • 1-255 --Reserved ports for well-known services • 256-1023 --Other reserved ports • 1024-65535 --user-defined server ports • Unix stores general used ports in /etc/services directory

36. 16-bit UDP source port # 16-bit UDP dest. port # data protocol = UDP internet 32-bit source addr internet 32-bit dest. addr UDP header data IP header UDP header data frame type = IP Ethernet 48-bit source addr Ethernet 48-bit dest. addr Ethernet header IP header UDP header Ethernet trailer data Ethernet frame Hierarchical Addressing Scheme • Connection defines the communication link between two processes UDP = User Datagram Protocol

37. FDDI TCP/IP Internetworking Router Token Ring Private Nets and Internet

38. LAN and Devices LANs are designed to : • Operate within a limited geographic area • Allow multi-access to high-bandwidth media • Control the network privately under local administration • Provide full-time connectivity to local services • Connect physically adjacent devices Ethernet Switch ATM Switch Bridge Hub Router

39. X.25 or Frame Relay Switch Modem CSU/DSU TA/NT1 Comm. Server ATM Switch Router Multiplexor S stat mux Wide-Area Networks and Devices WANs are designed to : • Operate over geography of telecommunications carriers • Allow access over serial interfaces operating at lower speeds • Control the network subject to regulated public services • Provide full-time and part-time connectivity • Connect devices separated over wide, even global areas

40. TCP/IP Architectural Layers Application Network Applications End-to-end Services Transport Internet Routing Network Network Interface Physical Transmission

41. Layer Hardware Application Transport Internet • Routers, PAD’s, X.25 switches • Bridges, LAN switches, ATM switches and terminal servers • Transceivers, repeaters, hubs, FDDI concentrators, modems, terminal adapters, DSU’s, CSU’s, MUX and NIC’s Network Physical

42. Transceivers • A transceiver connects a network device to the network cable • A transceiver listens to the bus to determine if it is being used by another station • A transceiver determines if the bus is being used by another station • A transceiver alerts the connected device when there is a collision during transmission • A transceiver may have DIP switches for controlling the exchange of SQE or heartbeat signals with the directly connected device.

43. Transceivers Attachment Interface Unit (AUI): The portion of the Ethernet standard that specifies how a cable is to be connected to an Ethernet card. AUI specifies a coaxial cable connected to a transceiver that plugs into a 15-pin socket on the network interface card (NIC).

44. Repeaters • A repeater is used to connect two segments of the same network • A repeater receives a signal from one segment, cleans and boosts the signal and sends it to the other segment • A repeater is responsible for ensuring that a collision is propagated to all attached segments • A repeater may be used to extend the network beyond the limitations of the network’s architecture by increasing segment length • Cannot add an infinite number of repeaters as this would adversely affect collision propagation.

45. Hubs • A hub often attaches at least four nodes and many hubs include connectors for linking to other hubs • A hub provides connectivity by passing incoming signals to connected nodes • Hubs may be cascaded together to allow small workgroups with low-intensity applications to be formed • Hubs typically have LEDs to indicate the status of each port • Hubs may do partitioning to allow isolation of a non-functioning node • Hubs allow connection to different physical media.

46. NIC’s • A NIC is an internetworking device that is a component part of a much larger host • NICs are used to connect the systems to the network • NICs will be different for each type of host system and type of network topology (and for each bus type) • Remote access is achieved through remote access to the host system • When installing a NIC it is important to consider the network topology, cabling and electrical considerations to avoid network disruption.

47. Internet TCP/IP Networking Software • TCP/IP protocol suites define a set of universal communication services • Services can be implemented in a standardized manner in the networking software, normally bundled with OS TCP/IP Comm. Software TCP/IP Comm. Software

48. TCP/IP and Internet • 1957 USSR sputnik, USA established ARPA • 1969 ARPA funded ARPANET • 1971 Network with 15 nodes • 1974 Cerf/Kahn Protocol • 1973 Ethernet (Ph.D Dissertation Bob Metcalfe) • 1982/83 TCP/IP as a core protocol • 1983 4.2 BSD Unix with TCP/IP from UCB (univ. of California @ Berkley)

49. TCP/IP Standards

50. Internet Technical Bodies • ISOC - Internet Society.Professional society to promote the use of Internet for research and scholar communication and collaboration • IAB - Internet Architecture Board.Technical oversight and coordination, falls under ISOC • IETF - Internet Engineering Task force.Current protocols and specifications for standardization. Meets 3 times a year, organized in working groups • IRTF - Internet Research Task force.Research oriented for future.