Internet Connectivity Principles

Transcription

1 Internet Connectivity Principles 1 4 Internet Connectivity Principles LEARNING OBJECTIVES To obtain an understanding of Internet connectivity principles, a reader student will learn the followings in this Chapter: Get insight into Internet connectivity, Internet based communication and Communication Protocols, IP, IPv6, RPL, 6LoWPAN, TCP/IP suite, TCP and UDP. [Sections 4.1 and 4.2] (LO 4.1) Get insight of IP addressing and MAC addressing methods, DNS and DHCP [Sections 4.3 and 4.4] (LO 4.2) Get insight into Application Layer Protocols: HTTP, HTTPS, FTP, Telnet and Other Ports [Section 4.5] (LO 4.3) RECALL FROM PREVIOUS CHAPTERS Section 1.1 described the proposed conceptual framework, reference model and reference architecture suggested by internationally acclaimed companies, namely IBM, CISO and Oracle for the IoT/M2M. A reference equation learnt was Gather + Enrich + Stream + Manage + Acquire + organize and Analyse = Internet of Things, The equation means that for an IoT/M2M Application or Service following are the steps: 1. gather the data from the devices (things, Objects, Sensors, Controllers, and devices) in a personal area network or WPAN, 2. enrich that data according to appropriate methods and protocols, 3. send a data stack that in streams over the Internet using Internet protocols, then 4. manage, acquire, organise and analyse that data for the IoT Applications, Services and Business Processes. A lesson learnt from Section 2.1 is that three standard organisations (IETF, ITU-T and ETSI) have proposed the layered model, and reference model and high level architecture. A model shows the layers, stages and steps during interchange of data between two domains, the devices and network, and application and service domains. Another lesson learnt from Section 2.2 is that methods for gathering data and networking the connected devices use the procedures as per the protocols. Network protocols examples are NFC, ZigBee IP, or Bluetooth LE or other wireless or wired technologies. A reader learnt the methods of enriching the data using Gateway functions. (Section 2.3) Gateway at the adaptation layer performs the functions of data management, device management, data Steps Gather + Enrich + Stream + Manage + Acquire + organize and Analyse = Internet of Things network IETF, ITU-T and ETSI Standard models and architecture Gateway functions

2 2 Internet of Things: Internet and Cloud Connected Devices with Intelligence privacy, security, enrichment and consolidation and device management.. A communication Gateway connects the application and service domain using the access and core networks. Lesson learnt from Section 3.1 is that a constrained environment exists for communication between the application and service domain and IoT/M2M device domain. The device data routes over a low power lossy (ROLL) network. The CoAP and LWM2M are the protocols for the ROLL network. A communication mode when using these protocols is Client/Server communication mode, also called request/response mode. RESTful methods and software architecture style are used for the client/server communication. IoT/M2M device Constrained environment and ROLL network Another lesson learnt from Section 3.2 is that IoT/M2M devices Objects and Applications use the Request/Response, Publish/Subscribe, Subscribe/Notify, Push or Pull, Polling, Message Queues, Instant Messaging, presence notification, chat and instant messaging methods for transfer of messages, resources, representations, objects and states. The APIs for messaging can use the CoAP- SMS, CoAP-MQ, MQTT or XMPP protocols. Reader leant use of the (i) HTTP request response model, (ii) SOAP for exchange of objects between the Applications, and (iii) web sockets. The websockets enable bi-directional communication in place of communication over a single TCP connection per instance of data stream transfer and instant messaging and chatting. HTTP, SOAP and WebSockets INTRODUCTION Internet is a huge network with set of communication methods for the 1. connected devices sending the data. Data frames from the devices communicate over the network. The packets communicate through a set of router at the Internet. The Applications, Services and Business Processes manage, acquire, organise and analyse the data of the IoT. 2. the devices do the controlling and monitoring functions using the messages, data frames and commands sent through the Internet by the Applications, Services and Business Processes. Following are key terms and their meanings which are required for understanding the Internet connectivity principles for communication between connected devices network and IoTs Applications/Services/Business processes: 1. Header at a layer consists of Header fields. Fields are a set of parameters encoded in a header of two or more words. Parameters and their encoding are as per the protocol used at that layer. Header field means bits in a header word placed at appropriate bit place between bit 0 and bit 31. Each word has 32-bits. Each header word can have one or more fields. Header is put as per the actions required. The actions are according to the header fields specified for a protocol. 2. IP header means header fields consists of parameters and their encodings which are as per the IP protocol. IP is internet layer protocols at the source or destination. 3. TCP header means header fields consists of parameters and their encoding which are as per the TCP protocol. TCP is transport layer protocol at the source or destination.. 4. TCP Stream is a sequence of bytes or words of data stack from source end transport layer to destination end transport layer. 5. Packet is a fixed maximum size set of bytes which communicates from one router to another till that reaches at physical and data link layer at the receiver end. Internet Always remember the meanings of the basic terminology of Internet connectivity principles

3 Internet Connectivity Principles 3 technology provisions for packetising the received data stack at Internet layer (IP layer) for transmission to next lower layer and depacketising (unpacking) at the layer for sending to next upper layer the new data stack. 6. IP Packet is a data stack. The packet includes IP header. The IP packet communicates from a source IP address through the routers to the destination IP address. 7. Network Interface is a system software component or hardware for facilitating communication between two protocol layers or computers or nodes in a network. The interface software-component provides standard functions, for example, connection establishment or closing or message passing. Network interface examples are port (software or hardware component) or network interface device or socket. The interface can be addressed by a unique port number or socket name or node id. 8. Port is an interface to the network using a protocol that sends a data stack at the output to the lower layer. The port receives data stack at the input at the receiver end. Each port at Application layer uses distinct protocol. A port is assigned number according to protocol used for transmission and reception. 9. Socket is a software interface to the network that sends a data stack at the output using a port protocol to the lower layer and using an IP address to the network for another socket at receiver end. The port receives data stack at the input at the receiver end Application layer the data stack at receiver IP address. Each socket at each end has an IP address for the Internet layer and port number for the Application layer. Application data can be considered to flow between the sockets at sender and receiver. 10. Host is a device or node that connects to a network of computers. Host provides the information, resources, services, and Applications to the other nodes on the network. A network layer assigns a host address to each host. 11. IP host is one that uses the Internet Protocol Suite. An IP host has one or more IP addresses for the network interfaces. 12. Subnet is a sub-network which is logical and visible subdivision of an IP network. Subdivision enables addressing of a set of networked computers in the subnet using a common and identical IP address most-significant bit-group. IP address then consists of two groups msb-group and lsb-group, total 32-bits. [msb means maximum significant bit in a set of bits. msbs means maximum significant bits in a set of bits. lsb means least significant bit in a set of bits. lsbs means least significant bits in a set of bits.] 13. Routing prefix: Thirty two bits IP address can be divided into a msb-group consisting of 8 or 16 or 24 bits and remaining lsb-group bits. The division results in the logical division of an IP address into two fields a network address or routing prefix field and the rest field or host identifier. The rest field is an identifier for a specific host or network interface. 14. Host Identifier: The rest field may also have two sub-fields, one for subnet id and other for the host identifier when a network subdivides into subnets and subnet has number of hosts. 15. Data flow graph (DFG) means a representation using arrows from one stage to another, whereas a circle represents a stage and arrow represent direction of flow of data. Inputs at

4 Network 4 Internet of Things: Internet and Cloud Connected Devices with Intelligence each stage compute (process) and cause the outputs from the stage. Inputs at beginning of a circle continue to flow to next circle till the outputs generate at the end stage. Data can be said to flow from beginning to end, after processing at the each stage in-between. 16. Acrylic Data Flow Graph (ADFG) means a DFG where only one set of inputs generate only one set of outputs for the given input set in the DFG model. All inputs are instantaneously available in APDFG, (no delay between various inputs) at each stage. Examples of non-acrylic data input are as follows: (i) an event input (ii) a status flag setting in a device and (iii) input as per output condition of the previous process. Following Sections describe the Internet connectivity principles for the connected devices. The details of the protocols, their usages and implementation are not given here. Reader can refer to standard book of Computer network or Internet and Web Technology for the details. 4.1 INTERNET CONNECTIVITY Figure 4.1 shows a source-end network-layer connected through a set of IP routers to the destination. The figure shows that a communication framework uses an IP address and communicates with the IoT/M2M IoT Apps and Services layer using TCP/IP suite of Application protocols to a destination IP address.. Smart Sensor Application Framework IoT Comm. Framework Sensor Application Framework IoT Comm. Framework Source End IP Address Gateway Data Consolidation Framework IoT Comm. Framework Set of IP routers Set of IP routers Set of IP routers IoT Application Layer TCP/IP Appl. Protocols Transport Layer TCP/IP Network Layer Destination End IP Address Data Link Layer Physical cum data-link layer LO 4.1 Source end network layer connection through set of IP routers up to the destination Source End IP Address Set of IP routers Fig. 4.1 Source end network layer connected through set of IP routers for data packets from an IP address and communicating with IoT/M2M IoT Apps and Services layer using TCP/IP suite of Application protocols

5 Internet Connectivity Principles 5 Internet connectivity is through a set of routers in a huge network of routers which carry data packets as per IP protocol from a source end to another and vice versa. A source sends data packets in IETF standardised formats to destination. Each packet flows towards destination through set of routers. 4.2 INTERNET BASED COMMUNICATION LO 4.1 When data transmits from a layer i to next layer j the actions are performed as follows: 1. each layer perform actions as per the protocol used for communication by that layer, 2. each layer sends the data stack received from the previous upper layer plus sends a new header along with that stack, and thus creates a new stack after performing the actions specified at that layer, 3. layer j will next specify the new parameters as per the protocol and creates new stack for next lower layer 4. the process continues until data communicate over the network. Remember that Application layer is highest in OSI model and Physical layer the lowest. (Fig. 2.1) Thus, data transmits from a layer i to next layer j, when data transmits from Application layer to Physical layer. When data receives from a layer j to next layer i, from IoT device physical layer to the IoT Application, the actions are performed as follows: 1. each layer perform actions as per the header field bits which are received according to the protocol to be used for decoding the fields for the required actions at that layer 2. each layer receives the data stack received from the previous lower layer and after the required actions, subtracts the header words, and thus creates a new stack specified for the next higher layer, 3. the process continues until data receives at the port at the highest Application layer. Upper layers use the header words alone. Lower layer, such as, data-link layer protocol, such as Ethernet provisions for the trailing bits also, in addition to the header words. Trailing bits usages can as error-control bits and end-of-the frame indicating bits. [Note: Ethernet frame communicates between data link layers of two computers on a LAN (local area network). Ethernet frame is of 1518 B. It consists of 32 trailing bits. These bits are called Frame Sequence Check bits or CRC (Cyclic Redundancy Check) bits. CRC bits append during transmission. Receiving end recalculates the CRC from the received data bits. If both match then frame in the sequence is accepted, else the error is reported.] The layers, 7, 4, 3 and 2 of the OSI model are specified in the TCP/IP suite of protocols for Internet communication. Figure 4.2 shows the communication between source and destination. Internet based communication use Application layer L7, and Internet, transport and link layers, L4, L3 and L2. [Note: Ethernet frame communicates between data link layers of two computers on a LAN (local area network). Ethernet frame is of 1518 B. It consists of 32 trailing bits. These bits are called Frame Sequence Check bits or CRC (Cyclic Redundancy Check) bits. CRC bits append during Communication using layers between the Source Application layer and destination Application layer

6 6 Internet of Things: Internet and Cloud Connected Devices with Intelligence transmission. Receiving end recalculates the CRC from the received data bits. If both match then frame in the sequence is accepted, else the error is reported.] UDP Datagram Port for data from or to Application Layer L7 L4 Header L7 Header L7 Data Segment Data Stack from L7 or to L7 Data for TCP Stream PDU = 2 32 B for Applications and Services L3 Header Data Stack from L4 or to L4 PDU = 2 16 B L3 IP packet for the Network L2Header Data Stack from L3 L2Trailing Bits PDU = 1518 B Data Stack from L2 (Link Layer) or to L2 Physical Layer L1 Layer Fig. 4.2 TCI/IP suite four layers model generating data stack for the network, and for physical layer during Internet communication A data segment (maximum 2 32 B per segment) from L7 layer generates a TCP stream at the transport layer using TCP. The stream packetizes at the Internet layer. Alternatively, a datagram (maximum 2 16 B) from L7 layer generates a UDP datagram at the transport layer. Transport layer uses TCP and UDP. Internet layer uses the IP protocol (IPv4 or IPv6 or RPL). Packet routing is as follows: Each router has information about the path to the destination. When a number of paths are available then number of packets of same source simultaneously follows different paths from a router. Destination end transport layer reassembles the packet according to their sequences in source transport layer data streams. Then, the reassembled data segment transfers to IoT Application layer at the destination end. Data-link layer uses a protocol, for example, Ethernet, MAC, PPP, ARP, RARP, NDP and others. [Ethernet is protocol for logical link layer on a local area network (LAN). MAC stands for Media Access Control. PPP stands for Point to Point Protocol. ARP stands for address resolution protocol. RARP stands for reverse address resolution protocol. Resolution means using network data stack to find the MAC address. Reverse means MAC address used for finding IP address. NDP stands for Network Discovery Protocol.] Subsections next describe the features in Ipv4, IPv6 and RPL.

7 4.2.1 IP Protocols Internet Connectivity Principles 7 Internet layer receives and forwards data to next layer using IP version 4 (IPv4) or IP version 6 protocol IPv4 Let n = total number of header words. Figure 4.3 shows Data stack received or transmitted at or to network layer, and IP packet consists of IP header field 160 bits and extended header up to n words. The extension is done when required plus data stack of from or for the transport layer. IPv4 Protocol headers and data stack len [IP Packet length words] Fragment Offset 15 8 Service Type and Precedence Flags 7 4 Service Type and Precedence 3 0 IP version First Byte Sequence Number in the stream Check sum Type of Protocol TTL(Time to Live) Source IP address Destination IP address Header Packet Length len = v/32 words q 160 Extended Option header words and fields plus the words as padding before the data Header q = (32 n 1), [n v q is number of words = 5 words for Data stack of V = [(v q)/32] words header plus options plus padding words for rxtension. Maximum v = (2 14 Data Packet (stack) from or to Transport layer (Maximum Size 2 14 words = 2 16 B n) 32 1 Fig. 4.3 Data stack received or transmitted at or to network layer, and IP packet consists of IP header field 160 bits and extended header up to bit q (extended when required) plus data stack of from or for the transport layer Internet layer protocol is IP when a packet transmits. The transmission is unacknowledged data flow IP packet segment consists of the data which the internet layer receives on transfer from transport layer to the receiver end when using the IP protocol. Protocol data unit, PDU IP = 1 packet and 1 packet has maximum 2 16 B. PDU IP is the maximum data unit which can transmit or receive at the layer when using IP packets. Figure 4.3 shows IP data stack which includes the IP header fields. The figure shows start and end bit numbers in each word and data. The figure shows the data stack received or transmitted at or to Internet layer. IP Packet consists of IP header fields 160 bits and extended header consists of (n 5) words when required plus data stack of len words from or for the transport layer The features of IP protocol are as follows:

8 8 Internet of Things: Internet and Cloud Connected Devices with Intelligence 1. IP header consists of five words. The header can be extended by using option words and padding words. Data stack to network layer has maximum V = (n + len) words where V <= (2 14 n). 2. Header first, second and third word fields are as shown in the figure. 3. Header fourth and fifth words are source IP address and destination IP address. 4. IP protocol transport is half duplex unacknowledged data flow from internet layer at one end (End 1) to internet layer of other end (End 2). 5. Each IP layer data stack is called IP packet, the packet is not guaranteed to reach the destination when transport layer protocol is UDP and guaranteed to reach the destination when transport layer protocol is TCP. 6. One packet communicates in one direction at an instance IPv6 IPv6 (Internet Protocol Version 6) is a protocol with following features: 1. provisioning a larger addressing space 2. permitting the hierarchical address allocation, thus route aggregation across the Internet, and thus limit the expansion of routing tables. 3. provisions additional optimization for the delivery of services using routers, subnets and interfaces, 4. manages device mobility, security, and configuration aspects 5. expanded and simple use of multicast addressing 6. provisions jumbo grams (big size datagram) 7. extensibility of options While an IPv4 address is of size 32-bit, the IPv6 addresses have a size of 128 bits. Therefore, IPv6 has a vastly enlarged address space compared to IPv4. The IPv6 address provides a numerical label. It identifies a network interface of a node or other network nodes and subnets participating in IPv6 Internet. A device is called node when it communicates on a network RPL [IPv6 Routing Protocol for Low Power Lossy Networks (LLNs)] IoT/M2M low power lossy environment uses RPL protocol. Internet layer IPv6 receives and transmits from/to adaptation layer (Fig. 2.1) layer when using IEEE WPAN devices (Fig. 2.5). LLN means a constrained nodes network, which has low data transfer rate, relative to IP low packet delivery rate, unstable links. IETF ROLL RPL is non-storing mode. Data flow model is DODAG (Destination Oriented Directed Acrylic Graph). Directed acrylic graph is a data flow model between the nodes. Destination orientation means either upwards directed (for transport) or downward directed (for device layer end node) in a tree like structure of the DODAGs. The data flow directs downwards in an RPL instance from root at transport layer to child nodes and from child node to leaf node at physical layer device node. The data flow directs upwards in an IPv6 Protocol features of large addressing space and route aggregation IPv6 Routing in low power lossy networks

9 Internet Connectivity Principles 9 RPL instance from a leaf or child node to other child node and then to the root. DODAGs are no share nodes (disjoint). The features of RPL are as follows: 1. is a routing protocol for the LLNs, 2. RPL control messages are DAO (Destination Advertisement Object), DIO (DODAG Information Object) and DIO (DAG Information Object), 3. transfers data at an RPL instance data point to point (one device nodes to one receiver node) as well as point to multipoint (one to many device nodes) or multipoint to point (many device nodes to one receiver node), 4. sends or receives multiple DODAGs at each instance, 5. sends data from DODAGs to DODAG root or the DODAG leaves to supports low data transfer rate compared to IP low packet delivery rate, 6. supports unstable links, 7. has optimisation objective for an RPL instance, 8. supports coexistence of different optimisation objectives using multiple RPL instances, 9. supports nodes inform parents of their presence and reach ability to descendants using DIOs, 10. supports soliciting (seeking) information of a DODAG using DIS, and 11. supports destination inform nodes for discovery of an RPL instance, know about configuration parameters and select DODAG parents using DIOs, LoWPAN Internet layer IPv6 receives and transmits from/to adaptation layer (Fig. 4.1) layer when using IEEE WPAN devices. The data stack uses 6LoWPAN protocol at adaptation layer before data stack transmits to IPv6 Internet layer. 6LoWPAN (IPv6 Over Low Power Wireless Personal Area Networks) is an adaptation layer protocol for the IEEE network devices. The devices are the nodes having low speed and low power. They are the Wireless Personal Area Network (WPAN) nodes. Figure 4.4(a) shows Physical layer IEEE network devices. Figure 4.4(b) shows data link sublayer and adaptation layer r 6LoWPAN protocol. 6LoWPAN protocol at adaptation layer before a data stack transmits to IPv6 Internet layer

10 10 Internet of Things: Internet and Cloud Connected Devices with Intelligence 10s of Bytes of Device App data Device 1 Device 2.. IEEE Device Node Frame 127 B IPv6 Header 40 B UDP Header8 B IEEE Device Security21 B Fragmentation 94 B 127 B IPv6 Link Layer MTU 1280 B [Bytes for and from network and transport layers] Device ( i1) Device i Max. 33 Bytes App data at single data transfer MAC Header 25 B App Data 33B Physical/Data Link Layer Reassembly Adaptation Layer 6LoWPAN Protocol (a) (b) F4 (a) Physical layer IEEE network devices (b) Adaptation layer 6LoWPAN protocol 127 B fragmented frames reassembly into IPv6 e maximum 1280 B or fragmentation of IPv6 MTU 1280B into 127 B frames for transfer to a device. The figure shows that IPv6 over IEEE standard network nodes uses the headers, security and Application data as follows: IPv6 header = 40B; UDP header = 8 B; device node MAC (Media Access Control) = 25 B; AES-128 security = 21 B; Total device node frame size = 127 B. Therefore, 33 Octet are left for the Application data from the device. [MAC is data communication protocol sublayer at the data-link layer. Refer Section for understanding AES. ] IPv6 MTU (maximum transmission unit) at link layer = 1280 B. Therefore, link layer frame fragmentation is needed in order to communicate frame of 127 B over IEEE nodes (device). The frame MTU is 1280 B for transmission to network layer. Fragments from frames from the device of 127 B each reassemble into IPv6 frame. Also, IPv6 MTU at data link layer 1280 B fragments into frame of 127 B each for single transfer to a device node. 6LoWPAN features are as follows: 1. specifies the IETF recommended methods for reassembly of fragments, and IPv6 and UDP (or ICMP) headers compression (6LoWPAN-hc adaptation layer), neighbour discovery (6LoWPAN-nd adaptation layer) and 2. supports mesh routing [ICMP stands for Internet Control Message Protocol. Routers or other devices on the network send error messages or relay the query messages.] 6LoWPAN can be implemented using Berkley IP implementation with operating system TinyOS or 3BSD or other implementations for IoT nodes from Sensinode or Hitachi or others. IPv6 network layer has two options RH4 routing header and hop to hop header RPL option.

11 Internet Connectivity Principles TCP/IP Suite TCP/IP Suite means a set of protocols with layers for the Internet. Application layers protocol examples are HTTPS, HTTP, MQTT, XMPP, SOAP, FTP, TFTP, Telnet, PoP3, SMTP, SSL/TLS and others for TCP stream communication and are DNS, TFTP, Bootpc, Bootps, SNMP, DHCP, CoAP, LWM2M and others for the datagram communication using UDP. Application layer security protocols are TLS and DTLS. TCP/IP suite of protocols for the Internet A transport layer protocol example is TCP for the acknowledged data flow using connection oriented protocol. A transport layer protocol is UDP for datagram for the unacknowledged data flow using connectionless protocol. Transport layer also uses RSVP, DCCP and other protocols. Internet layer protocol is IPv4/IPv6/RPL/ICMP/ICMPv6/IPSec or other. Data-link layer protocol is PPP/ARP/RARP/NDP, MAC or other. A MAC protocol is Ethernet or DSL or ISDN or other. Figure 4.5 shows the protocol layers and representative protocols at each layer. Application Layer protocols (DNS, TFTP, Bootpc, Bootps, SNMP, DHCP, CoAP, LWM2M Application Layer protocols (HTTPS, HTTP, MQTT, XMPP, SOAP, FTP, TFTP, Telnet, PoP3, SMTP) Network Management ND, RPL DTLS Datagram (PDU = 2 16 B) Transport UDP Datagram TLS Segment PDU = 2 32 B Transport Layer TCP Acknowledged data flow stream Packet PDU = 2 16 B Internet Layer IPv4/ IPv6 PDU = 1 Frame Adaptation 6LoWPAN, CoAP, LWM2M ARP/RARP Data Link Layer WiFi/Ethernet Fig. 4.5 IoT TCP/IP Suite of Protocols for Internet TCP/UDP Transport layer for the Data Stack from or to Applicatin layer port Following subsections describe the TCP/UDP Transport layer protocols. Transport layer receives or transmits the Data Stack from or to a port at the Application layer. Following subsections describe TCP and UDP protocols.

12 12 Internet of Things: Internet and Cloud Connected Devices with Intelligence TCP Transport layer protocol is TCP when acknowledged data flow when a segment transmits. TCP protocol segment consists of the data which the transport layer receives on transfer from Application layer to the receiver end when using the TCP protocol. Protocol data unit, PDU TCP = 1 Segment and 1 segment maximum value = 2 32 B. PDU TCP is the maximum data unit which can transmit or receive at the layer when using TCP stream.(tcp stream means transmitted or received data from or to the layer in a sequence during one cycle of transmission and acknowledgement of data stack.) Figure 4.6 shows TCP data stack which includes the TCP header fields. The figure shows start and end bit numbers in each word and data. The figure shows the data stack received or transmitted at or to transport layer stream consisting of TCP header field 160 bits and extended header words up to q th bit when required plus data stack of len words from or for the Application layer TCP protocol for the acknowledged data flow and almost confirmed delivery Destination Port number 15 0 Source Port number First Byte Sequence Number in the stream Next expected sequence number in the Acknowledgement w [TCP Byte stream size, len + n) words] urgent [Data End Pointer (Location of data stack last word )] Flags (6-bit), Reserved (6 bit) plus data Offset (4-bit) Check sum q 160 Option header words and fields plus the words as padding before the data Header Extended Header Header q = (32 n 1), [n is number of words = words for header plus options plus padding words v Data of len words v = (n + len) 32 1 q Data stack from or to Application layer Fig. 4.6 Data stack received or transmitted at or to transport layer stream consisting of TCP header field 160 bits (5 words) and extended-header words (= n 5), extension is when required, plus data stack of len words from or for the Application layer The features of TCP protocol are as follows: 1. TCP header consists of five words. The header can be extended by using option words and padding words. Data stack to next layer or data packet to router has maximum V = (n + len) words where V <= (2 14 n).

13 Internet Connectivity Principles Header first word fields are as follows: upper 16 bits are for the source port number and lower 16 bits are for destination port number. Second and third words are shown in the figure. 3. Header fourth word upper 16 bits, lower 16 bits and Header fourth word upper 16 bits, lower 16 bits are as shown in the figure. 4. TCP protocol transport is a full duplex acknowledged data flow from transport layer at one end (End 1) to transport layer of other end (End 2). 5. Each TCP layer data stack reaches destination almost each time. This is because retransmission takes from the next of last acknowledged sequence number to another sequence number. [Difference in numbers is called window size between two numbers.] 6. One TCP connection communicates in one direction at an instance. 7. Acknowledged flow means that the request as well as response messages communicate in unicast mode. End 2 sends acknowledgement message and the header field of that conveys expected sequence number from transmitter by the receiver End TCP is connection oriented. Connection first establishes using a connection establishment procedure adopted when first time transmitting a TCP data stack. Connection closes using a connection closing procedure adopted when last sequence completes transmission of TCP segment stack] Example 4.1 How is acknowledged data flow used in TCP? How the actions do almost ensure that the segment data of Application layer transmits all bytes and they reassemble successfully at the receiver? How does the TCP ensure high QoS? Solution: This action enables because of the following: 1. Each byte is assigned a sequence number in each segment put forward for transmission by the Application layer. One segment consists of maximum bytes transferrable at an instance from transport layer when using TCP protocol. The sequence numbers are assigned from 0 to maximum (2 32 1). 2. Sequence number of first Byte of TCP stream is placed in a header field. The sequence number header field enables reassembly of all packets of data at the receiver end transport layer. When field bits = 0s, it means no more data left in the segment for transmission of TCP stream. Reassembly need arises out because data packets from network layer may reach at receiver at variable delays. 3. Receiver acknowledges the sequence number of last byte successfully received. The actions is as follows Acknowledgement header field at the receiver consists of next sequence number (means received last byte sequence number plus one). It conveys expected sequence number from the transmitter in next cycle. This enables transmitter to discover from the acknowledged packet. Transmitter discovers how many Bytes from first sequence number of stream sent to the receiver acknowledged thus far and prepares for next cycle of transmission. Same header field consists of last byte sequence number in the segment which is being transmitted at that instance to the network layer. Since network can transmit just one packet (2 16 B

14 14 Internet of Things: Internet and Cloud Connected Devices with Intelligence maximum), the difference in first and the last does not exceed 2 16 in a given TCP stream to next layer. The difference is called window size w in the stream. The w adjusts continuously as per network congestion state. The protocol uses TCP/IP connectivity for the basic network. TCP protocol, unlike UDP, almost guarantees the successful transmission, even though some message may reach duplicate or triplicate. (Message means data words at data stack from or to Application layer.) Why does a message can reach twice? TCP protocol specifies that if within a specified period, there is no acknowledgement of last sent sequence number for the messages or the acknowledged sequence number is less than the last sequence number, then the unacknowledged sequences retransmit. Retransmission is from the next expected sequence number by the receiver. A number of efforts are made till successful acknowledgement of last sequence number receives. This almost ensures successful transmission of all messages. Now assume in the meanwhile during retransmission(s), the messages not reached earlier, also reach. It means messages reached duplicate. The receiver will discard the duplicate messages, as it knows the sequences numbers of each messages received UDP When transport layer transmits an unacknowledged data flow, limited to a datagram, then transport layer protocol is UDP. Datagram means data that is just one message which does not correlate with next message or preceding message during end to end transmission. UDP is also a protocol for the constrained environment and ROLL environment. (Section 3.1) UDP (Universal Datagram Protocol) is transport layer protocol for sending datagram. Data stack of an Application layer protocol ( for example, DNS, TFTP, Bootpc, Bootps, SNMP, DHCP) or an Application support layer protocol (for example, CoAP or LWM2M) is added header fields of 2 words (1 word = 32 bit). Figure 4.7 shows the UDP data stack format for network layer during transmission or to Application layer during reception. The figure shows UDP header fields. The figure also shows pseudo header of 2 words (64 bits) for source and destination IP addresses, which next layer can use. UDP protocol for the unacknowledged data flow when an Application datagram transmits on the Internet

15 Internet Connectivity Principles Source IP address Destination IP address Destination Port number Length (4 m + 8) B 15 0 Source Port number Check Sum p 64 m words p= (m + 8) 32 1 Pseudo Header Header Data stack from or to Application layer Fig. 4.7 Transport Layer UDP Header fields with data stack from the Application layer and Pseudo header of 2 words (64 bits) for source and destination IP addresses The features of UDP protocol are as follows: 1. UDP header consists of two words. Data stack to network layer has maximum m words where m <= (2 14 2). Header first word fields are as follows: upper 16 bits are for the source port number and lower 16 bits are for destination port number. Header second word upper 16 bits are length, and lower 16 bits are checksum. 2. UDP protocol transport is a half duplex unacknowledged data flow from transport layer at one end (End 1) to transport layer of other end (End 2). 3. Each UDP layer data stack may or may not reach destination due unacknowledged flow. 4. One UDP connection communicates in one direction at an instance between two ends. 5. Half duplex means that at a given instance only one direction End 1 to End 2 or End 2 to End 1. Unacknowledged flow means that the request as well as response messages communicate in broadcast mode. End 2 does not send acknowledgement message. 6. UDP is connectionless. It thus permits multicasting, means to multiple destinations. [Connection less means no connection establishment procedure adopted when first time transmitting a UDP data stack and no connection closure procedure adopted.]

16 16 Internet of Things: Internet and Cloud Connected Devices with Intelligence LET S RECONFIRM OUR UNDERSTANDING OF FOLLOWINGS Internet layer forwards data to next layer using IP protocol. Internet connectivity is through a set of routers in a huge network of routers. Routers carry data packets as per IP protocol from a source end to a destination, and vice versa. Four layers for Internet communication are Application, Transport, Internet and Data Link layers. Internet communication layers use the TCP/IP suite of protocols. Application, Transport and Internet layers add the header words in the data stack for transmission to next layer as new data stack. Data link layer add the header words as well as the trailing bits at the end before transmitting using physical layer. Transport layer uses TCP or UDP. The Internet layer uses IP version 4 (IPv4) or IP version 6 or RPL. Application layer communicates a data segment or a datagram. It depends on which protocol (or port) the layer uses. Application layer communicates a data segment (maximum 2 32 B per segment) from L7 layer and generates a TCP stream at the transport layer using TCP. The stream packetizes (maximum 2 16 B per packet) at the Internet layer. Alternatively, Application layer communicates a datagram (maximum 2 16 B) at L7 layer for sending a UDP datagram from the transport layer. Internet layer uses an IP protocol for packet or message forwarding. IP protocol is IPv4 or IPv6 or RPL or other. Internet layer in IPv6 receives and transmits from/to adaptation layer when using IEEE WPAN devices. The data stack uses 6LoWPAN protocol at adaptation layer before data stack transmits to IPv6 Internet layer. UDP header has fields for source and destination port numbers. TCP header has fields for sequence number of the data segment from where the data stack communicates and for window size which specifies number of transmitting bytes. IP packet header has fields for IP version and source and destination IP addresses. Self-Assessment Exercise linked to LO 4.1 Q4.1.1 Why does a header add when data stack transmits from higher layer to lower layer? Why does a header subtract when data stack transmits from lower layer to higher layer? Q4.1.2 How do four layers generate data stack for the network and physical layers during Internet communication? Show diagrammatically Q4.1.3 Compare the features in IPv4 and IPv6. Q4.1.4 How do packets route over the Internet using a set of four routers between source and destination? Show diagrammatically. Q4.1.5 What are the features of RPL? Q4.1.6 List the features of 6LoWPAN. Q4.1.7 Make a table for the Application layer and corresponding protocol used at transport for the an Application/Service/Business Process in TCP/IP suite of protocols. Q4.1.8 List the header fields in a UDP header and their functions.

17 Internet Connectivity Principles 17 Q4.1.9 List the functions of the header fields in IP header when packets transmit between source and destination. Q List the functions of the header fields in TCP header at transmitting end. How the fields used when sending acknowledgement from receiver end? 4.3 IP ADDRESSING OF THE IoTS LO 4.2 An IP header consists of source and destination addresses, called IP addresses. Internet generally uses IPv4 addresses. IoT/M2M use IPv6 addresses. Following subsections describe the addressing schemes IP Address IP version 4 address consists of 32 bits. However, it can be considered as four decimal numbers separated by dots, for example, for 32 bits Each decimal number is decimal value of an Octet (=8 bits). IP addresses can be between to , total 2 32 addresses due to 32-bit address. Three separate fields with a decimal number each for each set of 8 bits are easier to use. Consider an address: McGraw-Hill Education, 2Pennsylvania Plaza, New York City, USA. Three fields separate by comma and a new line each. A mail routes to the destination using the address. First mail routes to USA, then to New York City, then to Pennsylvania Plaza and then the destination. Similar are the actions, when packets route to destination IP address from a source IP address. Each device or node that communicates on the Internet must have an IP address. Number of nodes or devices can be very large. Recapitulate Fig A communication framework may communicate with number of sensors. Each sensor or device is assigned the addresses used internally. The framework communicates with Internet with one IP address externally to the Applications. One solution of large number of nodes is dividing the network into Internet address and subnet address. For example, 2 Pennsylvania Plaza, New York City, USA may be globally visible address. Internally, mail to be directed to which individual at McGraw-Hill Education is decided by internal distribution network, invisible to outside world. Alternatively, New York City, USA may be globally visible address. Internally, mail to be directed to which individual at McGraw-Hill Education, 2 Pennsylvania Plaza is decided by internal distribution network, invisible to outside world. Internet address is visible to outside world that means to the routers on the Internet. Subnet address is for use within the group internally and is invisible to outside world. A subnet is a subnetwork consisting of number of hosts or nodes or devices or machines. 32-bit IP address Analogy with postal network addressing method

18 18 Internet of Things: Internet and Cloud Connected Devices with Intelligence A subnet mask and network 32-bit IP address after ANDing operation gives individual subnet address. Logical AND operation with complement of subnet mask with the IP address gives the host identifier on the subnet. Example 4.3 later will clarify the procedure. IP address is visible on the Internet. Number of servers, such as web server, mail server and FTP server are invisible and these have same IP address globally and separate addresses internally on a subnet of server or nodes or devices. An IP address serves the purpose of uniquely identifying an individual network interface of a host. The interface locates on the network using that address. The address enables routing of IP packets between the hosts. IP addresses are present in fields of the packet header for routing. Header indicates both source and destination of the packet. A subnet with number of nodes (devices) using common IP address (es) Static A static IP address is the one assigned by Internet service provider. The service provider may provide individual just one address. When a company has number of hosts, a service provider may provide a class C network address consisting of a group of 254 (=28 2) IP addresses. Following example gives the classifications A, B, C and D and how the allocations of static addresses made to a group of hosts: Example 4.2 How does the IP addresses allot to a group of hosts on the Internet? What do class A, B, C and D network mean when using the subnets? Give analogy with postal network for communication to McGraw-Hill Education, 2Pennsylvania Plaza, New York City, USA. Solution: A group of hosts on the Internet allotted IP addresses as follows: Class A network group address means address n.x.x.x, where x is between 0 to 255 and n is between 1 and 126 for the addresses between and 126.x.x.x. This is because the IP address 32-bit has msb bit 31 =0. A static IP address for number of hosts Class A, B, C and D networks and Analogy with postal network addressing method Three x.x.x specifies a network group of hosts, just as USA specifies a large group of addresses in USA. [Minus 2 is because all 0s and all 1s in.x.x.x not allotted in subnet.] Class B network group address means address n.m.x.x, where x is between 0 to 255 and n.m is between to for the addresses between and x.x. This is because the IP address 32-bit has two msb bits = 10. Two x.x specifies a network group of (2 16 2) hosts, just as New York City, USA specifies a group of addresses in New York City, USA. [Minus 2 is because all 0s and all 1s in.x.x not allotted in subnet.] Class C network group address means address n.m.k.x, where x is between 0 to 255 and n.m.k is between and for the addresses between and x. This is because the IP address 32-bit has three msb bits = 110.

19 Internet Connectivity Principles 19 One.x specifies a smaller group of (2 8 2) hosts, just as 2 Pennsylvania Plaza, New York City, USA specifies a group of addresses at 2 Pennsylvania Plaza, New York City, USA and one of them is McGraw-Hill education. [Minus 2 is because all 0s and all 1s in.x.x not allotted in subnet.] Class D addresses are for multicasting and are from and are less than Address 0.x.x.x is a reserved address. Address 127.x.x.x is also a reserved address. Following example gives the method of finding the subnet address and host on the subnet using the IP address and subnet mask of a subnet in case of classifications A, B, C and D for the allocations of static addresses to a group of hosts: Example 4.3 A subnet and its hosts communicate with the Internet using a subnet mask. How does an IP address and subnet mask find the subnet address and host on the subnet? What is the procedure for evaluation of subnet address and host address? Solution: IP address consists of two parts. Upper bits (msbs) are for the network address. Lower bits (lsbs) are for subnet address and individual host. Upper bits in a subnet mask allots for each node to address that node with the address of group of hosts on a subnet. Subnet mask bits depend on class of the network group address. Mask bits are as follows: Class A network group address node has a subnet mask and the mask consists of all eight msbs = and remaining twenty four bits are set as per the subnet and host address. Subnet id is invisible to outside world of Internet. These 24 bits identify the host on a subnet. Class A group subnet masks are for hosts. Class B network group address node has a subnet mask and the mask consists of all sixteen msbs = 1s and remaining sixteen bits are set as per the subnet id and host address at the subnet invisible to outside world of Internet. Last 16 bits identify subnet and the host on that subnet. Class B group subnet masks are for hosts. Class C network group address node has a subnet mask and the mask consists of all twenty four msbs = 1s and remaining eight bits are set as per the subnet id and host address on the subnet. Subnet id is invisible to outside world of Internet. Last 8 bits identify a subnet id and the host on that subnet. Class C group subnet masks are for subnet plus host address bits. Following is the procedure for evaluation of Subnet address and host address: Suppose 14 hosts function as subnets on a network. Assume that a Class C network group address when network communication is with 14 subnets. Each subnet thus identifies by 4 higher bits after the network address 24 bits. Therefore, subnet mask will 24 msbs as 1s plus 4 higher bits among 8 remaining bits in the subnet mask will be 1s. Subnet masks for an individual subnets will be ( ), ( ), to ( ). ANDing of 32-bit IP group address and 32-bit subnet mask gives the internal subnet address. Higher 4 bits identify the individual subnet among the 14 subnets functioning as host. Subnet Class A, B, C and D networks and Analogy with postal network addressing method

20 20 Internet of Things: Internet and Cloud Connected Devices with Intelligence address is network address bits plus 4 subnet identifier bits and plus 4 bits 0000 in the example ion above paragraph. ANDing of complement of 32-bit subnet mask with 32-bit IP group address gives the host identifier in the external IP address for the Internet. [If 30 hosts function as subnets, then subnet mask will 24 msbs as 1s plus 5 higher bits among 8 remaining bits in the subnet mask will be 1s. This is because 30 equals Then last 3 bits of subnet mask will be 000.] A new scheme, called Classless Inter-Domain Routing (CIDR) is used now-a-days. For example, Class C /4 which means four IP addresses Class C allotted for Internet routing by 4 public domain servers. System administrator at a company allots which server allotted which of the 4 IP addresses, for the same domain name Dynamic Once a device connects to Internet, it needs to be allotted individual IP address. When the device connects to a router, router and device use the DHCP (Dynamic Host Control Protocol) which assigns an IP address at an instance to the device. This address is called dynamic IP address. When device disconnects or switches off or the router boots again, then dynamic IP address looses, a new allocation takes place on device reconnecting. A dynamic IP address for a node connecting to Internet DNS Consider an IP address, ( ). It is difficult to remember or use. Domain name for the address is rajkamal.org. An access to web-server hosted at the domain is made using the website name, An access to mail-server hosted at the domain is made using the mail server name, Another example is domain name, mheducation.com/. The.com,.org,.in and.us are called Top Level Domain (TLD). A TLD can further subdivide, for example,.co.in or.gov.in. or.gov.uk. A Registrar provides the domain name at certain cost per year. DNS server at the Registrar has a control panel (cpanel). DNS can be configured using cpanel. Domain Names System (DNS) is an Application which provides the IP address for the corresponding service from the named domain service DHCP When a sensor, actuator or IoT device or node needs to connect to Internet, a server, called DHCP server provides a dynamic IP address, subnet mask, and ARP and RARP caches. The server (subnet) has its own IP address to provide connectivity to the Internet. Dynamic host configuration protocol (DHCP) is a protocol to dynamically provide new IP addresses and set subnet masks for the connected node so that it can use the subnet server and subnet router at the communication framework. DHCP client and DHCP server for dynamic addresses allocation