1. 1 Internet Protocols Chapter 18

2. 2 Protocol Functions Small set of functions that form basis of all protocols Not all protocols have all functions  Reduce duplication of effort  May have same type of function in protocols at different levels Encapsulation Fragmentation and reassembly Connection control Ordered delivery Flow control Error control Addressing Multiplexing Transmission services

3. Lecture Plan Protocols Functions Principles of Internetworking Connectionless Internetworking Internet protocols  IP Services  Internet protocol  IP Addresses  ICMP IPv6  IP next generation  IPv6 structure  IPv6 Header, Addresses, fragment header, routing header Multicasting

4. Protocol Functions Small set of functions that form basis of all protocols Not all protocols have all functions  Reduce duplication of effort  May have same type of function in protocols at different levels Encapsulation Fragmentation and reassembly Connection control Ordered delivery Flow control Error control Addressing Multiplexing Transmission services

5. Encapsulation Data usually transferred in blocks  Protocol data units (PDUs)  Each PDU contains data and control information  Some PDUs only control information (no data) Three categories of control Address  Of sender and/or receiver Error-detecting code  E.g. frame check sequence Protocol control  Additional information to implement protocol functions Addition of control information to data is referred to as encapsulation Data accepted or generated by entity and encapsulated into PDU  Containing data plus control information  e.g. TFTP, HDLC, frame relay, ATM, AAL5 (Figure 11.15), LLC, IEEE 802.3, IEEE 802.11

6. Fragmentation and Reassembly (Segmentation – OSI) Protocol is concerned with exchanging data between two entities Characterized as sequence of PDUs of some bounded size  Application level, logical unit of data transfer as a message Lower-level protocols may need to break data up into smaller bounded size. This process is called Fragmentation. Communications network may only accept blocks of up to a certain size  ATM 53 octets  Ethernet 1526 octets More efficient error control with a smaller PDU size  Smaller retransmission when a PDU suffers an error Fairer  Prevent station monopolizing medium Smaller buffers

7. Disadvantages of Fragmentation Make PDUs as large as possible because  PDU contains some control information Smaller block, greater the percentage overhead  PDU arrival generates interrupt Smaller blocks, result in more interrupts  More time is spent, processing smaller, more numerous PDUs All of these factors must be taken into account by the protocol designer in determining minimum and maximum PDU size.

8. Reassembly The counterpart of fragmentation is reassembly Segmented data must be reassembled into messages appropriate to the application level If PDUs arrive out of order, the task is complicated

9. PDU’s and Fragmentation (Copied from chapter 2 fig 2.4)

10. Connection Control Connectionless data transfer  Each PDU treated independently of all prior PDU’s  E.g. datagram Connection-oriented data transfer  E.g. virtual circuit  Connection-oriented preferred (even required) for lengthy exchange of data  Logical association, or connection, established between entities Three phases occur  Connection establishment  Data transfer  Connection termination

11. Phases of Connection Oriented Transfer

12. Connection Establishment Entities agree to exchange data Typically, one station issues connection request Central authority may or may not be involved Receiving entity accepts or rejects (simple) May include negotiation concerning  Syntax, semantics, and timing Both entities must use same protocol Must be agreed  E.g. protocol may specify max PDU size 8000 octets; one station may wish to restrict to 1000 octets

13. Data Transfer and Termination Both data and control information exchanged  e.g. flow control, error control Data flow and acknowledgements may be in one or both directions One side may send termination request Or central authority might forcibly terminate a connection

14. Sequencing Many connection-oriented protocols use sequencing  e.g. HDLC, IEEE 802.11 PDUs numbered sequentially Each side keeps track of outgoing and incoming numbers Sequencing supports three main functions  Ordered delivery  Flow control  Error control Not found in all connection-oriented protocols  E.g.frame relay and ATM All connection-oriented protocols include some way of identifying connection  Unique connection identifier  Combination of source and destination addresses

15. Ordered Delivery PDUs may arrive out of order  Different paths through network PDU order must be maintained in connection- oriented protocols Number PDUs sequentially Easy to reorder received PDUs basis of sequence no Problem with finite sequence number field  Numbers repeat modulo maximum number e.g. selective-repeat ARQ

16. Flow Control Performed by receiving entity to limit amount or rate of data is sent by a transmitting entity Stop-and-wait  Each PDU must be acknowledged before next sent Credit provided to the transmitter  Amount of data that can be sent without acknowledgment  E.g. HDLC sliding-window Must be implemented in several protocols  Network traffic control  Buffer space  Application overflow E.g. Application could be hung up waiting for disk access

17. Error Control Guard against loss or damage of data and control information Error detection and retransmission  Sender inserts error-detecting code in PDU Function of other bits in PDU  Receiver checks code on incoming PDU  If error, discard  If transmitter doesn’t get acknowledgment in reasonable time, sender retransmits the PDU Error-correction code Enables receiver to detect and possibly correct errors Error control is performed at various layers of protocol  Between station and network  Inside network

18. TCP/IP Concepts

19. Addressing Level Level in communication architecture at which entity is named Unique address for each end system  e.g. workstation or server And each intermediate system  (e.g., router) Network-level address  IP address or internet address  OSI - network service access point (NSAP)  Used to route PDU through network At destination data must routed to some process  Each process assigned an identifier  TCP/IP port  Service access point (SAP) in OSI

20. Connection Identifiers Connection identifiers comes into play when we consider connection-oriented data transfer rather than connection less Connection identifier used by both entities for future transmissions and has several advantages: Reduced overhead  Generally shorter than global identifiers Routing  Fixed route may be defined  Connection identifier identifies route to intermediate systems Multiplexing  Entity may wish more than one connection simultaneously  PDUs must be identified by connection identifier Use of state information  Once connection established, end systems can maintain state information about connection  Flow and error control using sequence numbers

21. Addressing Mode Usually address refers to single system or port  Individual or unicast address Address can refer to more than one entity or port  Multiple simultaneous recipients for data  Broadcast for all entities within domain  Multicast for specific subset of entities

22. Multiplexing Multiple connections into single system  E.g. frame relay, can have multiple data link connections terminating in single end system  Connections multiplexed over single physical interface Can also be accomplished via port names  Also permit multiple simultaneous connections  E.g. multiple TCP connections to given system Each connection on different pair of ports

23. Transmission Services A Protocol may provide additional services to entities E.g.: Priority  Connection basis  On message basis E.g. terminate-connection request Quality of service  E.g. certain classes of data may require a minimum throughput or maximum delay threshold Security  Security mechanisms, restricting access These services depend on underlying transmission system and lower-level entities

24. Internetworking Terms (1) Communications Network  Facility that provides data transfer service An internet  Collection of communications networks interconnected by bridges and/or routers The Internet - note upper case I  The global collection of thousands of individual machines and networks Intranet  Corporate internet operating within the organization  Uses Internet (TCP/IP and http)technology to deliver documents and resources

25. Internetworking Terms (2) End System (ES)  Device attached to one of the networks of an internet  Supports end-user applications or services Intermediate System (IS)  Device used to connect two networks  Permits communication between end systems attached to different networks

26. Internetworking Terms (3) Bridge/ Switch  IS used to connect two LANs using similar LAN protocols  Address filter passing on packets to the required network only  OSI layer 2 (Data Link) Router  Connects two (possibly dissimilar) networks  Uses internet protocol present in each router and end system  OSI Layer 3 (Network)

27. Requirements of Internetworking The overall requirements for an internetworking facility are as follows: Provide a link between networks  At Minimum physical and link control connection is needed Provide for the routing and delivery of data between processes on different networks Provide an accounting services that keeps track of the use of the various networks and routers and maintain status information Provide services independent of the network architectures

28. Network Architecture Features Internetworking facility must accommodate a number of differences among the networks including the following:  Different addressing schemes  Different packet size  Different Network access mechanism  Different timeouts  Error recovery  Status reporting  Routing techniques  User access control  Connection based or connectionless

29. Architectural Approaches A key characteristic of an internet architecture is whether the mode of the operation is Connection oriented Connectionless

30. Connection Oriented Assume that each network is connection oriented IS connect two or more networks  IS appear as ES to each network  Logical connection set up between ESs Concatenation of logical connections across networks  Individual network virtual circuits joined by IS May require enhancement of local network services  IEEE 802, FDDI these networks have a datagram style of transmission, therefore network service must be enhanced

31. Connection Oriented IS Functions A connection-oriented IS performs the following key functions: Relaying  Data units arriving from one network via the network layer protocol are relayed (retransmitted) on another network. Traffic is over logical connections that are spliced together at the ISs Routing  When an end-to-end logical connections and the sequence of logical connections, is to be setup, each IS in the sequence must make a routing decision that determine the next hop in the sequence Connection oriented not often used  (using IP is dominant)

32. Connectionless Operation Corresponds to datagram mechanism in packet switched network Each NPDU treated separately, and routed from source DTE to destination DTE through a series of routers and networks. All DTEs and all routers share a common network-layer protocol known generically as the internet protocol Internet Protocol  One such internet protocol developed for ARPANET  RFC 791 (Get it and study it) Below the IP a lower layer protocol needed to access particular network

33. Connectionless Internetworking IP provides a connectionless, or datagram, service between end systems. There are a number of advantages to this approach: Advantages  Flexibility  Robust  No unnecessary overhead Unreliable  Not guaranteed delivery  Not guaranteed order of delivery Packets can take different routes  Reliability is responsibility of next layer up (e.g. TCP)

34. IP Operation

35. 35 Internet Protocol - IP All Internet transport protocols use the Internet Protocol (IP) to carry data from source host to destination host.

36. 36 IP Features IP is a connectionless or datagram internetwork service, providing no end-to-end delivery guarantees. IP datagrams may arrive at the destination host damaged, duplicated, out of order, or not at all.

37. 37 IP Features The layers above IP are responsible for reliable delivery service when it is required. The IP protocol includes provision for addressing, type-of-service specification, fragmentation and re-assembly, and security. The datagram or connectionless nature of IP is a fundamental and characteristic feature of the Internet architecture.

38. 38 Connectionless IP Internetworking Advantages  Flexibility  Robust  No unnecessary overhead Unreliable  Not guaranteed delivery  Not guaranteed order of delivery Packets can take different routes  Reliability is responsibility of next layer up (e.g. TCP)

39. 39 IP Operation

40. 40 Router-based Networking

41. 41 Internetworking Protocols

42. 42 IP provides several services: Addressing. IP headers contain 32-bit addresses which identify the sending and receiving hosts. These addresses are used by intermediate routers to select a path through the network for the packet. Fragmentation. IP packets may be split, or fragmented, into smaller packets. This permits a large packet to travel across a network which can only handle smaller packets. IP fragments and reassembles packets transparently. Packet timeouts. Each IP packet contains a Time To Live (TTL) field, which is decremented every time a router handles the packet. If TTL reaches zero, the packet is discarded, preventing packets from running in circles forever and flooding a network. Type of Service. IP supports traffic prioritization by allowing packets to be labeled with an abstract type of service. Options. IP provides several optional features, allowing a packet's sender to set requirements on the path it takes through the network (source routing), trace the route a packet takes (record route), and label packets with security features.

43. 43 Internet Protocol Packet Header

44. 44 VERS - Version The version of the IP protocol. The current version is 4. 5 is experimental and 6 is IPng (see IP: The Next Generation (IPng)). The version of the IP protocol

45. 45 LEN - Length The length of the IP header counted in 32-bit quantities. This does not include the data field. The length of the IP header

46. 46 Type of Service The type of service is an indication of the quality of service requested for this IP datagram. quality of service??

47. 47 Type of Service - Precedence Is a measure of the nature and priority of this datagram:  000 Routine  001 Priority  010 Immediate  011 Flash  100 Flash override  101 Critical  110 Internetwork control  111 Network control

48. 48 TOS - Type Of Service Specifies the type of service value: 1000 Minimize delay 0100 Maximize throughput 0010 Maximize reliability 0001 Minimize monetary cost 0000 Normal service A detailed description of the type of service can be found in the RFC 1349

49. 49 MBZ - Must Be Zero Reserved for future use ("must be zero" unless participating in an Internet protocol experiment which makes use of this bit)

50. 50 Total Length Total length of the IP datagram in bytes Maximum size is 64k because there are 16 bits for it That means a single IP datagram cannot be bigger than 65536 bytes including the header

51. 51 Fragmentation Related Information The next 32 bits contain information related to fragmentation This information can be used to reassemble a fragmented IP datagram Fragmentation means that on its way a single IP datagram was broken into smaller IP datagrams because the intervening network was unable to carry the original datagram because it was too big

52. 52 Why Fragment? When an IP datagram travels from one host to another, it can cross different physical networks. Physical networks have a maximum frame size, called the Maximum Transmission Unit (MTU), which limits the length of a datagram that can be placed in one physical frame. Therefore, a scheme has been put in place to fragment long IP datagrams into smaller ones, and to reassemble them at the destination host. IP requires that each link has an MTU of at least 68 bytes, so if any network provides a lower value than this, fragmentation and re-assembly must be implemented in the network interface layer in a way that is transparent to IP.

53. 53 Why Fragment?

54. 54 Fragmentation Procedure An unfragmented datagram has all-zero fragmentation information. That is, the more fragments flag bit is zero and the fragment offset is zero. When fragmentation is to be done, the following steps are performed:

55. 55 Fragmentation Procedure The DF flag bit is checked to see if fragmentation is allowed. If the bit is set, the datagram will be discarded and an error will be returned to the originator using ICMP. Based on the MTU value, the data field is split into two or more parts. All newly created data portions must have a length which is a multiple of 8 bytes, with the exception of the last data portion.

56. 56 Fragmentation Procedure Each of these fragmented datagrams is now forwarded as a normal IP datagram. IP handles each fragment independently, that is, the fragments may traverse different routers to the intended destination, and they may be subject to further fragmentation if they pass through networks that have smaller MTUs.

57. 57 Reassembley Procedure At the destination host, the data has to be reassembled into one datagram. The identification field of the datagram was set by the sending host to a unique number (for the source host, within the limits imposed by the use of a 16-bit number). As fragmentation doesn't alter this field, incoming fragments at the receiving side can be identified, if this ID field is used together with the Source and Destination IP addresses in the datagram. The Protocol field is also to be checked for this identification.

58. 58 Reassembley Procedure - 2 In order to reassemble the fragments, the receiving host allocates a buffer in storage as soon as the first fragment arrives. A timer routine is then started. When the timer timeouts and not all of the fragments have been received, the datagram is discarded. The initial value of this timer is called the IP datagram time-to-live (TTL) value. It is implementation dependent, and some implementations allow it to b configured; for example AIX Version 3.2 provides an ipfragttl option with a default value of 60 seconds.

59. 59 Re-assembly Procedure - 3 When subsequent fragments of the datagram arrive, before the timer expires, the data is simply copied into the buffer storage, at the location indicated by the fragment offset field. As soon as all fragments have arrived, the complete original unfragmented datagram is restored, and processing continues, just as for unfragmented datagrams.

60. 60 Fragmentation Fields Identification - A unique number assigned by the sender to aid in reassembling a fragmented datagram. Fragments of a datagram will have the same identification number. Fragment Offset - Used with fragmented datagrams, to aid in reassembly of the full datagram. The value is the number of 64-bit pieces (header bytes are not counted) that are contained in earlier fragments. In the first (or only) fragment, this value is always zero.

61. 61 Flags Where: 0 Reserved, must be zero DF Don't Fragment:  0 means allow fragmentation  1 means do not allow fragmentation MF More Fragments: 0 means that this is the last fragment of this datagram, 1 means that this is not the last fragment.

62. 62 Dealing with Failure in Re-assembly Re-assembly may fail if some fragments get lost Need to detect failure Re-assembly time out  Assigned to first fragment to arrive  If timeout expires before all fragments arrive, discard partial data Use packet lifetime (time to live in IP)  If time to live runs out, kill partial data

63. 63 Specifies the time (in seconds) this datagram is allowed to travel. Each router where this datagram passes is supposed to subtract from this field its processing time for this datagram. Actually a router is able to process a datagram in less than 1 second; thus it will subtract one from this field, and the TTL becomes a hop-count metric rather than a time metric. When the value reaches zero, it is assumed that this datagram has been traveling in a closed loop and it is discarded. The initial value should be set by the higher-level protocol which creates the datagram. TTL - Time To Live

64. 64 Protocol- Protocol Number Indicates the higher-level protocol to which IP should deliver the data in this datagram. Some important values are:  0 Reserved  1 Internet Control Message Protocol (ICMP)  2 Internet Group Management Protocol (IGMP)  3 Gateway-to-Gateway Protocol (GGP)  4 IP (IP encapsulation)  5 Stream  6 Transmission Control (TCP)  8 Exterior Gateway Protocol (EGP)  9 Private Interior Routing Protocol  17 User Datagram (UDP)  89 Open Shortest Path First The full list can be found in STD 2 - Assigned Internet Numbers.

65. 65 Header Checksum Is a checksum on the header only. It does not include the data. The checksum is calculated as the 16- bit one's complement of the one's complement sum of all 16-bit words in the header. For the purpose of this calculation, the checksum field is assumed to be zero. If the header checksum does not match the contents, the datagram is discarded because at least one bit in the header is corrupt, and the datagram may even have arrived at the wrong destination.

66. 66 Options Various options regarding this datagram, including how to route it, how to identify it (security labeling), how to trace the places through which it passes, how to time-stamp it for delay measurement, etc. Security Source routing Route recording Timestamping

67. 67 Options Options – Up to 40 bytes of option data added by source host or intermediate routers  1 byte Option id, followed by an optional 1 byte Option length, followed by Option data  Padded to a multiple of 4 bytes  5 options currently defined Security – Security identifier source routing – Complete route specified Record route – Each router appends its address to the list Timestamp – Each router appends address & timestamp stream id (used for voice) for stream line transmission

68. Updated Ipv4 Packet Header 68 DS (8 bits): This field supports the Differentiated Service function ECN (2 bits): The Explicit Congestion Notification field, defined in RFC 3168, enables routers to indicate to end nodes packets that are experiencing congestion, without the necessity of immediately dropping such packets.

69. Type of Service Changed ! Originally defined as the Type of Servicefield, this field is now redefined.New technologies are emerging that require real-time data streaming and therefore will make use of the DSCP field. An example is Voice over IP (VoIP) that is used for interactive data voice exchange. quality of service??

70. DS (8 bits): This field supports the Differentiated Service function Type of Service Changed ! Differentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying, managing network traffic and providing Quality of Service (QoS) guarantees on modern IP networks. DiffServ can, for example, be used to provide low-latency to critical network traffic such as voice or video while providing simple best-effort traffic guarantees to non-critical services such as web traffic or file transfers. DiffServ uses the 6-bit Differentiated Services Code Point (DSCP) field in the header of IP packets for packet classification purposes. DSCP replaces the outdated IP precedence, a 3-bit field in the Type of Service byte of the IP header originally used to classify and prioritize types of traffic.

71. Type of Service Changed ! ECN (2 bits): The Explicit Congestion Notification field, defined in RFC 3168, enables routers to indicate to end nodes packets that are experiencing congestion, without the necessity of immediately dropping such packets. A value of 00 indicates a packet that is not using ECN. A value of 01 or 10 is set by the data sender to indicate that the end-points of the transport protocol are ECN-capable. A value of 11 is set by a router to indicate congestion has been encountered.

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