Computer Networks

1. Computer Networks This PPT is Dedicated to my inner controller AMMA BHAGAVAN– ONENESS Founders. Developed by, EDITED BY, S.V.G.REDDY,B.Keerthi Reddy, Associate professor, student of M.tech(SE). Dept.of CSE, GIT, GITAM UNIVERSITY.

2. OSI MODEL • A model defines the stages or tasks of a protocol as it prepares to send data • OSI - OPEN SYSTEM INTERCONNECTION • Open meaning standards available to all. • The model is divided into seven distinct layers • Each subsequent layer should perform a well-defined function and the layer boundaries are designed to minimize the information flow across the interfaces.

3. OSI model

4. OSI MODEL LAYERS • Application Layer • Provides a user interface (examples: HTTP, SMTP) • Includes file, print, database, app. Services • Presentation Layer • Presents the data (example: JPEG) • Includes encoding techniques,encryption, compression and translation services • Session Layer • This provides a session between source & destination and decides the mode of communication(simplex, half duplex & full duplex) • Transport Layer • Provides reliable delivery with alignment of packets • Performs error detection • Includes end to end connection

5. OSI MODEL LAYERS • Network Layer • Provides logical addressing and identifies the network • Generates the Route to the destination • Data Link Layer • Combines packets into bytes then into frames • Performs error detection (not correction) • Provides Media access addressing (point-to-point) and identifies the client system • Media Access Control and Data Link Control • Physical Layer • physical movement of bits between devices.

6. Tcp/Ip model

7. TCP/IP MODEL • TCP (Transmission Control Protocol) is the main transport protocol utilized in IP networks. The TCP protocol exists on the Transport Layer of the OSI Model. • The TCP protocol is a connection-oriented protocol which provides end-to-end reliability. • Internet protocol is the set of techniques used by many hosts for transmitting data over the Internet. • The TCP/IP model is a description framework for computer network protocols and it is evolved from ARPANET which was the world's first wide area network and a predecessor of the Internet. • This model sometimes called internet model .

8. There are four layers in this model. • Application layer: Defines how TCP/IP application protocols and how host programs interface with transport layer services to use the network. protocols regarding this layer are FTP,HTTP,SMTP,TELNET,SNMP. • Transport layer: Provides communication session management between host computers. Defines the level of service and status of the connection used when transporting data. Protocols involved in this layer are TCP,UDP. • Internet layer: Packages data into IP datagram's, which contain source and destination address information that is used to forward the datagram's between hosts and across networks. Performs routing of IP datagram's. Internet layer is also having some protocols ARP, RARP, IGMP, ICMP. • Physical layer: The physical movement of bits from source to destination.

9. Multiple Access Protocols • If multiple nodes tries to access the single channel for data transmission, CHANNEL

10. ALOHA • Here every node is allowed to transmit its data packets in the same channel • Then, when one node is transmitting data, then if some other node also transmits then it leads to COLLISIONS • In this ALOHA, lot of chances to have more collisions • collision probability increases: • frame sent at t0 collides with other frames sent in [t0-1,t0+1]

11. PURE ALOHA EFFICIENCY P(success by given node) = P(node transmits) . P(no other node transmits in [t0-1,t0] . P(no other node transmits in [t0,t0+1] = p . (1-p)N-1 . (1-p)N-1 = p . (1-p)2(N-1) … choosing optimum p and then letting n ->  Efficiency = 1/(2e) = .18

12. SLOTTED ALOHA • Here every node is given an equal amount of time slot. • when its turn comes, the node will transmit its data packets in that time slot . • Here less chances to have collisions.

13. SLOTTED ALOHA EFFICIENCY • Efficiency is the long-run fraction of successful slots when there are many nodes, each with many frames to send • Suppose N nodes with many frames to send, each transmits in slot with probability p • prob that node 1 has success in a slot = p(1-p)N-1 • prob that any node has a success = Np(1-p)N-1

14. CARRIER SENSE MULTIPLE ACCESS(CSMA) • Here the node listens to the channel before transmission • If channel is idle: transmit entire frame • If channel is busy, defer transmission • Human analogy: don’t interrupt

15. CSMA/CD (COLLISION DETECTION) • If two nodes simultaneously sense the channel and if the channel is idle and both will attempt to transmit, which leads to collisions. • if any two or more nodes senses the channel and gets the Idle status, then this protocol will take care by Blocking the nodes and minimise collisions.

16. COLLISION FREE PROTOCOLS Bit-Map Method: • In this method, there will be N time slots. If node0 has a frame to send, it sets the bit ‘1’ during the first slot and transmit the frame in first slot. No other node is allowed to transmit during this slot. • This is done for all the nodes. In general node j may declare the fact that it has a frame to send by inserting ‘1’ into slot j. • The basic problem with this protocol is its inefficiency during low load. If a node has to transmit and no other node needs to do so, even then it has to wait for the bitmap to finish.

17. Bit-Map Method

18. Binary Countdown • In this protocol, a node which wants to signal that it has a frame to send does so by writing its address into the header as a binary number. • The arbitration is such that as soon as a node sees that a higher bit position that is 0 in its address has been overwritten with a 1, it gives up. • The final result is the address of the node which is allowed to send. After the node has transmitted the whole process is repeated all over again. • Given below is an example situation. Nodes Addresses A 0010 , B 0101 , C 1010 , D 1001 ---- Node C 1010 having higher priority gets to transmit. • The problem with this protocol is that the nodes with higher address always wins. Hence this creates a priority which is highly unfair and hence undesirable

19. Binary Countdown

20. LAN Local area network - A group of computers that share a common connection and are usually in a small area or even in the same building. For example an office or home network. They are usually connected by Ethernet cables and have high speed connections. If it was a wireless setup it would be called a WLAN, which would have a lower connection speed

21. LAN

22. MAN Metropolitan area network - This is a larger network that connects computer users in a particular  geographic area or region. For example a large university may have a network so large that it may be classified as a MAN. The MAN network usually exist to provide connectivity to local ISPs, cable TV, or large corporations. It is far larger than a LAN and smaller than a WAN. Also large cities like London and Sydney, Australia have metropolitan area networks.    

23. MAN

24. WAN Wide area network - This is the largest network and can interconnect networks throughout the world and is not restricted to a geographical location. The Internet is an example of a worldwide public WAN. Most WANs exist to connect LANs that are not in the same geographical area.

25. WAN

26. ETHERNET Dominant wired LAN technology • cheap $20 for 100Mbs! • first widely used LAN technology • Simpler, cheaper than token LANs and ATM • Kept up with speed race: 10 Mbps – 10 Gbps Ethernet sketch

27. Bus Topology: Shared All nodes connected to a wire Star Topology: All nodes connected to a central repeater ETHERNET TOPOLOGIES

28. Network Topologies

29. ETHERNET CONNECTIVITY 10Base5 – ThickNet < 500m Controller Vampire Tap Bus Topology Transceiver

30. ETHERNET CONNECTIVITY 10Base2 – ThinNet < 200m Controller Transceiver BNC T-Junction Bus Topology

31. ETHERNET CONNECTIVITY 10BaseT < 100m Controller Star Topology

32. ETHERNET FRAME STRUCTURE Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame Preamble: • 7 bytes with pattern 10101010 followed by one byte with pattern 10101011 • Used to synchronize receiver, sender clock rates (Manchester encoding)

33. ETHERNET FRAME STRUCTURE • Addresses: 6 bytes • if adapter receives frame with matching destination address, or with broadcast address (eg ARP packet), it passes data in frame to net-layer protocol • otherwise, adapter discards frame • Type: multiple network layer protocols may be in use at the same time on the same machine, when ethernet frame arrives, kernel has to know it . • CRC: checked at receiver, if error is detected, the frame is simply dropped

34. ETHERNET SPECIFICATIONS • Coaxial Cable • Up to 500m • Taps • > 2.5m apart • Transceiver • Idle detection • Sends/Receives signal • Repeater • Joins multiple Ethernet segments • < 5 repeaters between any two hosts • < 1024 hosts

35. ETHERNET MAC ALGORITHM • Sender/Transmitter • If line is idle (carrier sensed) • Send immediately • Send maximum of 1500B data (1527B total) • Wait 9.6 s before sending again • If line is busy (no carrier sense) • Wait until line becomes idle • Send immediately • If collision detected • Stop sending and jam signal • Try again later

36. Node A starts transmission at time 0 Node B starts transmission at time T ETHERNET MAC ALGORITHM Node A Node B At time almost T, node A’s message has almost arrived  How can we ensure that A knows about the collision?

37. 1 0 0 0 0 1 0 1 1 1 1 MANCHESTER ENCODING • This is a return to zero (RTZ) signal. • Each bit period is divided into two equal intervals. • Binary “1” -> High Voltage level in the first half and Low Voltage level in the second half. • Binary “0” -> Just opposite of the above.

38. 1 0 0 0 0 1 0 1 1 1 1 DIFFERENTIAL MANCHESTER ENCODING • In each bit interval there is a transition of the level in the middle. • If the bit value is “0” then there is a presence of a transition at the start of interval. • If the bit value is “1”, then there is absence of a transition at the start of interval. • One of the properties of this signal is that is self clocking.

39. SWITCHED ETHERNET A simple example of switched Ethernet.

40. Switched Ethernet • An Ethernet LAN that uses switches to connect individual hosts or segments. This type of network is sometimes called a desktop switched Ethernet. • In the case of individual hosts, the switch replaces the repeater and effectively gives the device full 10 Mbps bandwidth (or 100 Mbps for Fast Ethernet) to the rest of the network. • In the case of segments, the hub is replaced with a switching hub. • Switched Ethernets are becoming very popular because they are an effective and convenient way to extend the bandwidth of existing Ethernets.

41. FAST ETHERNET (100BASE-T) How to achieve 100 Mbps capacity? Media Independent Interface provides three choices. LLC Data Link Layer MAC Convergence Sublayer Physical Layer MII Media Independent Interface Media Dependent Sublayer

42. FAST ETHERNET [IEEE 802.3U] Fast ethernet uses fiber distributed data interface(FDDI) FDDI CHARACTERISTICS: • 100 Mbps data rate • Distances of up to 200 km • Up to 1000 hosts attached • Based on fiber optic cabling

43. GIGABIT ETHERNET (1000 BASE X) • Provides speeds of 1000 Mbps (i.e., one billion bits per second capacity)for half-duplex and full-duplex operation. • Uses Ethernet frame format and MAC technology • CSMA/CD access method with support for one repeater per collision domain. • Backward compatible with 10 BASE-T and 100 BASE-T. • Uses 802.3 full-duplex Ethernet technology. • Uses 802.3x flow control. • All Gigabit Ethernet configurations are point-to-point!

44. GIGABIT ETHERNET TECHNOLOGY Gigabit Ethernet cabling. 1000 BASE SX fiber - short wavelength 1000 BASE LX fiber - long wavelength 1000 BASE CX copper - shielded twisted pair 1000 BASE T copper - unshielded twisted pair

45. GIGABIT ETHERNET (1000 BASE-T) LLC Data Link Layer MAC GMII Gigabit Media Independent Interface Physical Layer Media Dependent Interface Medium

46. GIGABIT ETHERNET (a) A two-station Ethernet. (b) A multistation Ethernet.

47. WIRELESS LAN • A wireless LAN (or WLAN, for wireless local area network, sometimes referred to as LAWN, for local area wireless network) is one in which a mobile user can connect to a local area network (LAN) through a wireless(radio) connection. • The IEEE 802.11 group of standards specify the technologies for wireless LANs. 802.11 standards use the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing and include an encryption method

48. WIRELESS LANS • The 802.11 Protocol Stack • The 802.11 Physical Layer • The 802.11 MAC Sub layer Protocol • The 802.11 Frame Structure • Services

49. THE 802.11 PROTOCOL STACK Part of the 802.11 protocol stack.

50. Wireless LAN uses different parts of the spectrum. They are • Infrared - speed upto 1 mbps - signal which is used in TV remote control. • FHSS(frequency hopping spread spectrum) & DSSS(direct sequence spread spectrum) - speed upto 1-2 mbps – signal which is used in cordless telephones which does not require licensing. • OFDM(orthogonal frequency division multiplexing) - speed upto 54 mbps. • HRDSSS(high rate DSSS) - speed upto 11 mbps • OFDM(orthogonal frequency division multiplexing) - another version of OFDM – speed upto 54 mbps at a different frequency band.