UNIT 3 - EXPLAINING THE NEED OF COMPUTER NETWORK

NETWORK FUNCTIONS

1. UNIT 3: EXPLAINING THE NEED OF COMPUTER NETWORK

2. OUTLINE Network Functions The OSI 802 networking models Drivers How network send data Protocols

3. 3 Networking Models There are many issues to be worked out when attempting to establish digital communication. Just like programming, we decompose a difficult task into smaller (yet easier) tasks 2 dominate networking models are used to decompose the problem networking: OSI: Open Systems Interconnection (OSI) networking suite IEEE 802: family of standards

4. 4 OSI and IEEE 802 Tomsho , Tittel, Johnson (2007) The IEEE defined a set of LAN standards to ensure network interface and cabling compatibility Project 802 (inception on February ( 2 ) of 19 80 ) Concentrates on standards that describe a network’s physical elements NICs, cables, connectors, signaling technologies, media access control OSI model was not standardized until 1983–1984 IEEE 802 standards predate the model Both were developed in collaboration and are compatible with one another

5. OSI Reference Model OSI Reference Model - internationally standardised network architecture. OSI = Open Systems Interconnection : deals with open systems , i.e. systems open for communications with other systems. Specified in ISO 7498. Model has 7 layers.

6. 6 OSI Reference Model OSI model divides the problem into 7 different levels of complexity – called layers. Each layer ‘n’ is only concerned with how to communicate to its neighbor layers, ‘n+1’ and ‘n-1’. Layer ‘n’ could care less about layers ‘n+2’ and ‘n-2’.

7. 7 Structure of the OSI Reference Model Tomsho , Tittel, Johnson (2007)

8. 8 OSI Layers OSI defines the interface between layers. Each layer ‘n’ provides services to layer ‘n+1’. Communicating devices must have compatible protocol stacks. Layer ‘n’ in device ‘A’ has a virtual connection to layer ‘n’ in device ‘B’.

9. The interaction between layers in the OSI model

10. Level at which applications access network services. Represents services that directly support software applications for file transfers, database access, and electronic mail etc. Layer 7: Application Layer

11. Related to representation of transmitted data Translates different data representations from the Application layer into uniform standard format Providing services for secure efficient data transmission e.g. data encryption, and data compression. Layer 6: Presentation Layer

12. Allows two applications on different computers to establish, use, and end a session. e.g. file transfer, remote login Establishes dialog control Regulates which side transmits, plus when and how long it transmits. Performs token management and synchronization . Layer 5: Session Layer

13. Manages transmission packets Repackages long messages when necessary into small packets for transmission Reassembles packets in correct order to get the original message. Handles error recognition and recovery. Transport layer at receiving acknowledges packet delivery. Resends missing packets Layer 4: Transport Layer

14. Manages addressing/routing of data within the subnet Addresses messages and translates logical addresses and names into physical addresses. Determines the route from the source to the destination computer Manages traffic problems, such as switching, routing, and controlling the congestion of data packets. Routing can be: Based on static tables determined at start of each session Individually determined for each packet, reflecting the current network load. Layer 3: Network Layer

15. Packages raw bits from the Physical layer into frames (logical, structured packets for data). Provides reliable transmission of frames It waits for an acknowledgment from the receiving computer. Retransmits frames for which acknowledgement not received Layer 2: Data Link Layer

16. Transmits bits from one computer to another Regulates the transmission of a stream of bits over a physical medium. Defines how the cable is attached to the network adapter and what transmission technique is used to send data over the cable. Deals with issues like The definition of 0 and 1, e.g. how many volts represents a 1, and how long a bit lasts? Whether the channel is simplex or duplex? How many pins a connector has, and what the function of each pin is? Layer 1: Physical Layer

17. 17 Summary of the OSI Layers Tomsho, Tittel, Johnson (2007)

18. Fall 2010 CEG 4188 1- 18 Protocols A protocol is a set of rules that govern all aspects of communication between two or more partners, called peers These rules are human-made; not like chemistry or physics! The purpose of a protocol is to provide a specific communication service. What aspects must be defined for assuring compatibility between the communicating partners ? (see next slides) Who makes protocols? Standardization committees Designers of a new distributed application

19. Fall 2010 CEG 4188 1- 19 Relevant Standards Bodies ISO (www.iso.org) An agency of the United Nations. Collaborates standards development for information technology. ITU (www.itu.int) UN treaty agency that sets telecommunications standards. ITU-T (Telecommunications section) ANSI (www.ansi.org) American National Standards Institute: the US national standards body. Coordinates and accredits standards development across the US. IEEE (www.ieee.org) US based international professional organization. Among other things, develops standards. IETF / IRTF Internet Engineering Task Force (www.ietf.org) Internet Research Task Force (www.irtf.org) EIA (www.eia.org) Electronic Industries Alliance E.g.; standards for wiring and interconnection

20. 20 Protocol Data Units (PDU) Each layer operates on a set of data called the PDU. The PDU in layer ‘n’ is not the same as the PDU in layer ‘n+1’ (PDU ‘n’) = (Header ‘n’) + (PDU ‘n+1’) The process of adding a header is called encapsulation. Similar to putting a letter in an envelope (the envelope is like a header – it wraps the data).

21. 21 Layers and PDUs

22. TCP/IP PROTOCOL SUITE The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network , internet , transport , and application . However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical , data link , network , transport , and application .

23. TCP/IP Protocol Architecture No official model but a working one. Has 5 layers (OSI has 7 layers) Was the result of research conducted on ARPANET, funded by DARPA (USA). Initially developed as a US military research effort funded by the Department of Defense It has dominated. It is the “heart” of Internet. 2. 23

24. TCP/IP Protocol Architecture Application Layer Host -to-Host or Transport Layer Internet Layer Network Access Layer Physical Layer Contains the logic needed to support user applications (ftp, telnet, http etc.) Each application requires different module. Covers the physical interface between device (computer and transmission medium or network - medium, signals, data rates..) Concerned with the exchange of data between end system and network (destination address, priority etc.) Depends on net. type Provides routing functions across multiple networks. It is implemented in end-systems and routers Concerned with the reliability of transmission/reception (error control, sequencing, flow control)

25. Some TCP/IP Protocols

26. TCP/IP and OSI model

27. ADDRESSING Four levels of addresses are used in an internet employing the TCP/IP protocols: physical , logical , port , and specific . Physical Addresses Logical Addresses Port Addresses Specific Addresses

28. Addresses in TCP/IP

29. Relationship of layers and addresses in TCP/IP

30. In Figure above a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver. Example

31. Physical addresses

32. Most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below: Example 07:01:02:01:2C:4B A 6-byte (12 hexadecimal digits) physical address.

33. The figure below shows a part of an internet with two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection. Example

34. IP addresses

35. 2. 35 The figure below shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination. Example

36. Port addresses

37. 2. 37 The physical addresses will change from hop to hop, but the logical addresses usually remain the same. Note

38. 2. 38 Example A port address is a 16-bit address represented by one decimal number as shown. 753 A 16-bit port address represented as one single number.

39. TCP/IP and OSI Models 39

40. 40 IEEE 802 Standards Wikipedia (n.d.) Defines many types of protocols and services. Maps to the Layers 1 and 2 in the OSI Reference Model. Divides Layer 2 (Link Layer) into two sub-layers: Logical Link Control (LLC) Media Access Control (MAC)

41. 41 IEEE 802 Extensions to the OSI Reference Model Tomsho , Tittel, Johnson (2007)

42. 42 IEEE 802 Specifications Tomsho , Tittel, Johnson (2007)

43. 43 IEEE 802 Specifications (continued) Tomsho , Tittel, Johnson (2007)

44. Tasks involved in sending a letter

45. What happens when… So what happens in the milliseconds after you enter a website address and a webpage is loaded onto your screen? How does information get from your computer to its destination and back?

46. Data Flow Your Computer What is www.yourcompany.com’s IP Address? DHCP Server Web Address IP Address Google.com 74.125.224.72 Yourcompany.com 172.22.30.47 ...... …… www.yourcompany.com = 172.22.30.47

47. Data Flow Most people nowadays have routers or hubs that allow multiple computers (or devices) to share the same connection to your Internet Service Provider (ISP), in your case it’s Cox Communications. Routers are used to convert electrical pulse signals from your copper cable line into a signal your computer’s wireless card can read (radio waves). They are also used to forward information to a specific device connected to your network, via an IP address. When you first turn your computer on, it will send out a request to have an IP address for your home network. This is not a unique address world-wide, but it is unique to your home network. After you type a website address and hit enter, your computer sends that information to the DHCP (Dynamic Host Control Protocol) Server, which has a list of the web address conversion from text to IP addresses. IP addresses are more easily readable by computers than strings of words in a web address. We, as humans, use names and words for the URL because it’s easier for us to remember them.

48. Home ISP Data Flow The Internet yourcompany Server yourcompany ISP

49. Data Flow Once your computer locates the IP address of the website, it will send a request to view your company.com’s website to Cox. Cox will then connect you to the Internet, which is represented by a cloud because we do not know precisely how everything is connected or how your information is routed once you go beyond your ISP. After the request has gone through “the cloud”, it will be connected to your company’s ISP, and finally it will reach your company’s server.

50. Home ISP Data Flow The Internet yourcompany Server yourcompany ISP

51. Data Flow Once your request is accepted by your company’s server, it will forward the requested information back to your computer. This process may not follow the exact route that it initially took to return the data to your computer. (continued on next slide)

52. Data Flow Your Computer What is www.yourcompany.com’s IP Address? DHCP Server www.yourcompany.com = 172.22.30.47 Web Address IP Address Google.com 74.125.224.72 Yourcompany.com 172.22.30.47 ...... ……

53. And now, your webpage has loaded onto your home computer screen.

54. The OSI Model The OSI (Operation Systems Interconnection) Model is used to show how data travels through one device to another through the network.

55. Types of Addresses IP address Ethernet Address Example MAC address: 38:4B:2E:A0:9F

56. IP addresses IP addresses are assigned either manually or automatically. Manual addressing: Is when a website is registered with the IANA (Internet Assigned Numbers Authority), the website is manually given a static IP address. This means that the IP address will not change until the owner chooses to change it or take down the website. Automatic addressing: There is a protocol called DHCP (Dynamic Host Configuration Protocol), where the network gives the users an IP address. When you turn on your computer, it will send a request to the network asking for an IP address. The network will give it an IP address and tell it the length of time it can have that address (DHCP Lease). The DHCP Lease is to allow for multiple users to come on and off the network by recycling the IP addresses. Remember: DHCP-assigned IP addresses are unique to your network but not unique around the world.

57. Ethernet Address Ethernet Address is another way of saying the physical address or MAC (Media Access Control) address. MAC addresses are totally unique to each device, world-wide for computers, tablets, smartphones, etc. Each manufacturer is given a range of MAC addresses to assign to each NIC (network interface card). MAC addresses are composed of a hexadecimal set of numbers, meaning that the characters included will range from 0-9 and A-F.

58. Device Functions Router Switch Vs. Home Work

59. Routers Routers are used to convert electrical pulse signals from your copper cable line into a signal your computer’s wireless card can read (radio waves). They are also used to forward information to a specific device connected to your network, via an IP address. Say that you have two computers working on different projects on the internet at the same time. You don’t want the other person’s research webpage to appear on your computer and your information on theirs, you want to have your information given directly to you. So having a specific IP address allows the router to know who to send the information to. When you first turn your computer on, it will send out a request to your network for an IP address. The network will respond with an IP address and a DHCP Lease (discussed on slide 11). In addition to asking for an IP address, your computer will also give the router it’s MAC address as the unique identifier of the “person” who has this particular IP address.

60. Switches Switches work relatively the same. For large networks, like LSU, there is one main router for multiple switches per network. You can still relate this to a smaller scale. For example, a switch (like your router at home) allows for many devices to connect to a network. A routing switch allows for many switches—each containing multiple users—to connect to the network.

61. Network Drivers Network interface driver similar to mounted block devices A Special block devices registers its disk and methods with kernel and Transmit and Receive block on request Socket Read/Write system call Network driver receive Asyn packet from Outside world Ask to push incoming packet towards kernel

62. Network Drivers… Many administrative works Setting up address, modify transmission param, maintaining traffic, error statistics Network subsystem completely protocol independent Software (IP) and Hardware (Eth, Ring)

63. Network Interface Driver: Snull It simulates conversations with real remote hosts in order to demonstrate the task of writing network drivers