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COMMUNICATION NETWORKS

COMMUNICATION NETWORKS. Mr. DEEPAK P. Associate Professor ECE Department SNGCE. UNIT 3 Inter Networking. Inter network. DEEPAK.P. 3. Inter network. Internetworking is the practice of connecting a computer network with other networks through the use of gateways.

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COMMUNICATION NETWORKS

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  1. COMMUNICATION NETWORKS Mr. DEEPAK P. Associate Professor ECE Department SNGCE DEEPAK.P

  2. UNIT 3 Inter Networking DEEPAK.P

  3. Inter network DEEPAK.P 3

  4. Inter network Internetworking is the practice of connecting a computer network with other networks through the use of gateways. Internetworking is a combination of the words inter ("between") and networking; The most common example of internetworking is the Internet Inter networking can be classified in to two Connection oriented or concatenated of virtual circuit subnets Connectionless or Datagram DEEPAK.P 4

  5. Connection Oriented Virtual circuit DEEPAK.P 5

  6. Virtual Circuit A virtual network link is a link that does not consist of a physical (wired or wireless) connection between two computing devices but is implemented using methods of network virtualization. DEEPAK.P 6

  7. Concatenated of Virtual Circuit A X.25 ATM Routers Subnet 3 SNA M M Subnet 1 B Host Subnet 2 Multi protocol router (Gateway) SNA-System Network Architecture DEEPAK.P 7

  8. Virtual Circuit Establishment Subnet shows that the destination is remote destination and builds a virtual circuit to the router nearest to the destination. It then constructs a virtual circuit from that router to an external gateway (multi protocol router). This gateway notes down the existence of this virtual circuit in its table and builds another virtual circuit to a router which is in the next subnet. This process continues until the destination host has been reached. DEEPAK.P 8

  9. Virtual Circuit Establishment 5.After building the virtual circuit, data packets begin to flow along the path Advantage Buffer can be reserved in advance Shorter header can be used Sequencing can be guaranteed Drawbacks There is no alternate path to avoid congestion Router failure creates big problems DEEPAK.P 9

  10. Connection less DEEPAK.P 10

  11. Datagram Internetworking A Datagram packets Routers Subnet 3 Path 1 M M Subnet 1 Datagram packets B M M Host Subnet 2 Multi protocol router (Gateway) Path 2 DEEPAK.P 11

  12. Datagram Internetworking The packets that are forwarded across the Internet are known as IP datagrams An IP datagram consists of a header and a payload The header contains information that allows Internet routers to forward the datagram from the source host to the destination host DEEPAK.P 12

  13. Datagram Internetworking Header contains all information needed to deliver datagrams to destination computer Destination address Source address Identifier Other delivery information Router examines header of each datagram and forwards datagram along path to destination DEEPAK.P 13

  14. Advantage& Disadvantage Datagram Advantage Higher Bandwidth Deal with congestion in a better way It is robust in Router failure Drawbacks No guarantee of packets Addressing is difficult Longer header is needed DEEPAK.P 14

  15. Datagram forwarding in IP DEEPAK.P 15

  16. Delivery of an IP datagram Internetwork is a collection of LANs or point-to-point links or switched networks that are connected by routers. DEEPAK.P 16

  17. IP forwarding Using Datagram The IP forwarding algorithm, commonly known as IP routing. It is a specific implementation of routing for IP networks and gives a more directed approach in forwarding datagram's over a network. In order to achieve a successful transfer of data the algorithm uses a routing tableto select a next-hop router as the next destination for a datagram. The IP address that is selected is known as the next-hop address. DEEPAK.P 17

  18. Datagram forwarding in IP An IP network is a logical entity with a network number We represent an IP network as a “cloud” DEEPAK.P 18

  19. Networks and IP addressing IP address: Network part + Host part Network: Any host can physically be reached by any other host without intervening router All hosts in the same network have the same network number DEEPAK.P 19

  20. Forwarding Datagrams Header contains all information needed to deliver datagrams to destination computer Destination address – Source address – Identifier – Other delivery information Router examines header of each datagram and forwards datagram along path to destination DEEPAK.P 20

  21. Routing tables Each router and each host keeps a routing table which tells the router how to process an outgoing packet Main columns: 1. Destination address: where is the IP datagram going to? 2. Next hop: how to send the IP datagram? 3. Interface: what is the output port? DEEPAK.P 21

  22. IP Frame format Header Beginning of Data Payload DEEPAK.P 22

  23. IP Header Protocol Version(4 bits) : This is the first field in the protocol header. This field occupies 4 bits. This signifies the current IP protocol version being used. Most common version of IP protocol being used is version 4 while version 6 is out in market and fast gaining popularity. DEEPAK.P 23

  24. IP Header Header Length(4 bits) : This field provides the length of the IP header. The length of the header is represented in 32 bit words. Since this field is of 4 bits so the maximum header length allowed is 60 bytes. DEEPAK.P 24

  25. IP Header Type of service(8 bits) : The first three bits of this field are known as priority bits and are ignored as of today. The next 4 bits represent type of service and the last bit is left unused. The 4 bits that represent TOS are : minimize delay, maximize throughput, maximize reliability and minimize monetary cost. DEEPAK.P 25

  26. IP Header Total length(16 bits): This represents the total IP datagram length in bytes. Since the header length (described above) gives the length of header and this field gives total length so the length of data and its starting point can easily be calculated using these two fields. Since this is a 16 bit field and it represents length of IP datagram so the maximum size of IP datagram can be 65535 bytes. DEEPAK.P 26

  27. IP Header Identification(16 bits): This field is used for uniquely identifying the IP datagrams. This value is incremented every-time an IP datagram is sent from source to the destination. This field comes in handy while reassembly of fragmented IP data grams. DEEPAK.P 27

  28. IP Header Flags(3 bits): This field comprises of three bits. While the first bit is kept reserved as of now, the next two bits have their own importance. The second bit represents the ‘Don’t Fragment’ bit. The third bit represents the ‘More Fragment’ bit. DEEPAK.P 28

  29. IP Header Fragment offset(13 bits): In case of fragmented IP data grams, this field contains the offset( in terms of 8 bytes units) from the start of IP datagram. So again, this field is used in reassembly of fragmented IP datagrams. DEEPAK.P 29

  30. IP Header Time to live(8 bits) : This value represents number of hops that the IP datagram will go through before being discarded. The value of this field in the beginning is set to be around 32 or 64 (lets say) but at every hop over the network this field is decremented by one. When this field becomes zero, the data gram is discarded. So, we see that this field literally means the effective lifetime for a datagram on network. DEEPAK.P 30

  31. IP Header Protocol(8 bits) : This field represents the transport layer protocol that handed over data to IP layer. This field comes in handy when the data is demultiplex-ed at the destination as in that case IP would need to know which protocol to hand over the data to. DEEPAK.P 31

  32. IP Header Header Checksum(16 bits) : This fields represents a value that is calculated using an algorithm covering all the fields in header (assuming this very field to be zero). This value is calculated and stored in header when IP data gram is sent from source to destination and at the destination side this checksum is again calculated and verified against the checksum present in header. If the value is same then the datagram was not corrupted else its assumed that data gram was received corrupted. So this field is used to check the integrity of an IP datagram. DEEPAK.P 32

  33. IP Header Source and destination IP(32 bits each) : These fields store the source and destination address respectively. Since size of these fields is 32 bits each so an IP address os  maximum length of 32 bits can be used. So we see that this limits the number of IP addresses that can be used. To counter this problem, IP V6 has been introduced which increases this capacity. DEEPAK.P 33

  34. IP Header Options(Variable length) : This field represents a list of options that are active for a particular IP datagram. This is an optional field that could be or could not be present. If any option is present in the header then the first byte is represented as follows : DEEPAK.P 34

  35. IP Header In the description above, the ‘copy flag’ means that copy this option to all the fragments in case this IP datagram gets fragmented. The ‘option class’ represents the following values : 0 -> control, 1-> reserved, 2 -> debugging and measurement, and 3 -> reserved. Some of the options are given below : DEEPAK.P 35

  36. IP Header DEEPAK.P 36

  37. IP Header Data: This field contains the data from the protocol layer that has handed over the data to IP layer. Generally this data field contains the header and data of the transport layer protocols. Please note that each TCP/IP layer protocol attaches its own header at the beginning of the data it receives from other layers in case of source host and in case of destination host each protocol strips its own header and sends the rest of the data to the next layer. DEEPAK.P 37

  38. Routing tables Next hop and interface column can often be summarized as one column Routing tables are set so that datagrams gets closer to the its destination. DEEPAK.P 38

  39. Delivery with routing tables DEEPAK.P 39

  40. Tunneling DEEPAK.P 40

  41. Tunneling It is used when source and destination networks of same type are to be connected through a network of different type. Consider an ethernet network to be connected to another ethetnet through a WAN The task is send on IP packet from host A of Ethernet 1 to the host B of ehernet 2 wia a WAN. In this example, the IP packet do not have to deal with WAN. DEEPAK.P 41

  42. Tunneling The host A&B do not have to deal with WAN The multiprotocol routers M1 and M2 will have to understand about IP and WAN packet. Therefore WAN can be imagined to be equivalent to a big tunnel extending between multiprotocol routers M1 and M2. So this technique is called Tunneling DEEPAK.P 42

  43. Tunneling WAN Tunnel HOST HOST A B M2 M1 Ethernet 1 Ethernet 2 IP IP WAN packet Header Ethenet Frame IP packet is inside the payload field of WAN packet DEEPAK.P 43

  44. Sequence of events in Tunneling Host A construct a packet containing the IP address of host B It then inserts this IP packet in to ethernet frame. This frame is addressed to the multi protocol router M1. Host A then puts this frames on Ethernet. DEEPAK.P 44

  45. Sequence of events in Tunneling When M1 receives this frames, it removes IP packet, inserts it in the IP payload packet of the WAN network layer packet and addresses the WAN packet to M2. The multi protocol router M2 remeoves the IP packet and send it to host B in an ethernet frame. DEEPAK.P 45

  46. ARP DEEPAK.P 46

  47. ARP Address Resolution Protocol (ARP) is a telecommunications protocol used for resolution of network layer addresses into link layer addresses ARP was defined by RFC (radio Frequency Committee) 826 in 1982 If a machine talks to another machine in the same network, it requires its physical or MAC address. ARP is used to convert an IP address to a physical address such as an Ethernet address DEEPAK.P 47

  48. ARP IP address of the destination node is broadcast and the destination node informs the source of its MAC address. Assume broadcast nature of LAN Broadcast IP address of the destination Destination replies it with its MAC address. Source maintains a cache of IP and MAC address bindings DEEPAK.P 48

  49. ARP DEEPAK.P 49

  50. ARP DEEPAK.P 50

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