Protocols and Protocol SuitReview - Lecture 14

Protocols and Protocol SuitReviewLecture 14OverviewNetwork Access LayerTransport LayerProtocolsProtocol Data UnitProtocol ArchitectureTCP/IP StackLayered Approach and its AdvantagesRouter2What is a Protocol ?Q:- What is a protocol?3Communication ProtocolsDefinitionProtocol is a set of rules that govern all aspect of data communication between computers on a network. These rules include guidelines that regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling, and speed of data transfer. A protocol defines what, how, when it communicated.The key elements of a protocol are syntax, semantics and timing. Protocols are to computers what language is to humans. Since this article is in English, to understand it you must be able to read English. Similarly, for two devices on a network to successfully communicate, they must both understand the same protocols.4Key Elements of protocolSyntaxThe structure or format of the data.Eg. A simple protocol; 5ii) Semantics - Refers to the meaning of each section of bits. - how is a particular pattern to be interpreted, and what action is to be taken based on that interpretation. Eg. Does an address identify the route to be taken or the final of the message?Elements of protocol6iii) TimingRefers to two characteristics:When data to be sentHow fast it can be sentEg. If a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload the receiver and data will be largely lost.Elements of protocol7Characteristics of protocolDirect / indirectcommunication between two entities maybe direct or indirect. i) point-to-point link - connection provides a dedicated link between two devices - the entities in these systems may communicate directly that is data and control information pass directly between entities with no intervening active agent.8ii) multipoint link - connection more than two devices can share a single link - The entities must be concerned with the issue of access control and making the protocol more complex.Characteristics of protocol9Common protocol usedProtocolAcronymRemarksPoint To PointPPPUsed to manage network communication over a modemTransfer/Transmission Control ProtocolTCP / IPBackbone protocol. The most widely used protocol.Internetwork package exchangeIPXStandard protocol for Novell NOSNetBIOS extended user interfaceNetBEUIMicrosoft protocol that doesn’t support routing to other network. Running only Windows-based clients. File transfer ProtocolFTPused to send and received file from a remote hostSimple mail Transfer protocolSMTPUsed to send Email over a networkHyper text transfer protocolHTTPUsed for Internet to send document that encoded in HTMLApple TalkApple TalkProtocol suite to network Macintosh computer and a peer-to-peer network protocolOSI ModelOSI LayersA way of illustrating how information functions travels through network of its 7 layers.10What is a Protocol ?Q:- What is a protocol?11Ans:- A protocol is the set of rules or conventions governing the way in which two entities cooperate to exchange data.Protocols are a set of rules and conventions. By enforcing that communicating parties adhere to a common protocol, communication is made possible. Protocol Architecture The “Common Language”12PDUWhat is a protocol data unit (PDU)?13Protocol Data Units (PDU)At each layer, protocols are used to communicateControl information is added to user data at each layer (PDU = Control + Data)Transport layer may fragment user dataEach fragment has a transport header addedDestination SAP (port)Sequence numberError detection codeThis gives a transport protocol data unit14Protocol Data UnitsNetwork PDU Adds network header, network address for destination computer and Facilities requests15PDUWhat is a protocol data unit (PDU)?16Ans:- A PDU is the combination of data from the next higher communications layer and control information.17Protocol ArchitectureQ:- What is a protocol architecture?18Need For Protocol ArchitectureThere are lots of network applicationsBuilding each application from scratch is very time-consuming and challengingWhat commands should be supported?How to respond to each command?How to identify the two peer applications?Each computer may run multiple applications!How to identify the two computers?How to convert the data into bit stream?How to convert the bit stream into signals?How to detect and handle data loss and data error?The network is not perfect!Etc.19Need For Protocol ArchitectureData exchange can involve complex procedures, cf. file transfer exampleBetter if task broken into subtasksImplemented separately in layers in stackeach layer provides functions needed to perform communication for layers aboveusing functions provided by layers belowPeer layers communicate with a protocol20Key Elements of a ProtocolSyntax – data block formatSemantics - control info. & error handlingTiming - speed matching & sequencing21(Cont.)Most of the network apps share some common modules22Application AModule AModule TModule IModule NModule PApplication BModule BModule TModule IModule NModule PApplication CModule CModule TModule IModule NModule PCommon modules(Cont.)A complex task is broken into subtasks: modular designEach subtask is implemented separately as a layer, arranged in a vertical stackEach layer performs a related subset of the functions required to communicate with another system. It relies on the next lower layer to perform more primitive functions and to conceal the details of those functions. It provides services to the next higher layer.Layers should be defined so that changes in one layer do not require changes in other layers.So, instead of using a single complex protocol, it’s more flexible to implement a stack of protocols!Reduce the design and development workload significantly!23Vertical Stack24Application AModule AModule TModule IModule NModule PApplication BModule BModule CApplication CModule Wcan be replaced by other modulesApplication developersOperating SystemHardwareExampleE.g., A can only speak Chinese, B can only speak Spanish, how can A communicate with B?A finds a translator C, who can speak Chinese and EnglishB finds a translator D, who can speak Spanish and EnglishTwo layers:Higher layer: A and BLower layer: C and D25A Two-layer example26messages in Chinesemessages in Englishmessages in SpanishHow to communicate?ACBDHigher LayerLower LayerLower layer provides services to the next higher layer.Protocol ArchitectureTasks of communications are broken up into modulesEach module (or layer) can have its own protocolIn very general terms, communications can be said to involve three components: applications, computers, and networks.For example, file transfer could use three modules (or layers)File transfer applicationCommunications service moduleNetwork access moduleThe stack of protocols is called “Protocol Stack”Or Protocol Architecture27TCP/IP Protocol ArchitectureDeveloped by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)Used by the global InternetIt consists of a large collection of protocols that have been issued as Internet standard by the Internet Architecture Board (IAB).Check TCP/IP protocol architecture organizes the communication task into five relatively independent layers:Layer 5: Application layerLayer 4: Transport layer, or Host to host (TCP belongs to this layer)Layer 3: Internet layer, or Network layer (IP belongs to this layer)Layer 2: Network access layer, or Link layerLayer 1: Physical layerRemark: Each layer can have lots of different protocols!28ExampleWorld Wide WebReplies on the HTTP protocol29Web browserHTTPTCPIPIEEE 802.11IEEE 802.11gWeb serverHTTPTCPIPIEEE 802.3IEEE 802.3 1000BASE-SXLayer 1Layer 2Layer 3Layer 4Layer 5Standardized Protocol ArchitecturesRequired for devices to communicateVendors have more marketable productsCustomers can insist on standards based equipmentTwo standards:OSI Reference modelNever lived up to early promisesTCP/IP protocol suiteMost widely used30Protocol ArchitectureQ:- What is a protocol architecture?31Ans:- The software structure that implements the communications function. Typically, the protocol architecture consists of a layered set of protocols, with one or more protocols at each layer.32TCP/IPQ:- What is TCP/IP?33OSI layersTCP/IP layersApplicationPresentationSessionFTP,Telnet,SMTP DNSApplication TransportTCPUDP Network Data link PhysicalLower level vendor implementationsIPOSPFIGMPDHCPICMP34Postal SystemTo: Mr. Jacky ChanNo. 123, XX Road,XXX, USA35Inside Postal SystemLocal Post Office (Kowloon Tong)Central Post Office (Hong Kong)Local Post Office (Tseung Kwan O)Central Post Office (Beijing)Central Post Office (New York)The delivery of your package depends on the postal address.TCP/IP Protocol ArchitectureDeveloped by US Defense Advanced Research Project Agency (DARPA) ARPANET packet switched network reuiredNow popular all over the world used by the global InternetProtocol suite comprises a large collection of standardized protocols36TCP/IPAns:- Transmission Control Protocol/Internet Protocol (TCP/IP) are two protocols originally designed to provide low level support for internetworking. The term is also used generically to refer to a more comprehensive collection of protocols developed by the U.S. Department of Defense and the Internet community.37Q:- What is TCP/IP?38LayersQ:- What are some advantages to layering as seen in the TCP/IP architecture?39TCP/IP Layers40Because TCP/IP was developed earlier than the OSI 7-layer mode, it does not have 7 layers but only 4 layersOSI 7-layerTCP/IP Protocol SuiteFTP, SMTP, Telnet, HTTP,TCP, UDPIP, ARP, ICMPNetwork InterfaceBenefit of layeringThe most challenging problem: how to provide a reliable data transfer service on top of an unreliable data network?This problem is so important that today’s Operating Systems all provide such reliable service.The burden of network application developers has been reduced significantly!Hence the application developers can simply focus on the application layer issues.We can easily develop thousands of network applications.41Q:- What are some advantages to layering as seen in the TCP/IP architecture?Ans:- Layering decomposes the overall communications problem into a number of more manageable subproblems42TCP/IP LayersOSI 7-layerTCP/IP Protocol SuiteFTP, SMTP, Telnet, HTTP,TCP, UDPIP, ARP, ICMPNetwork Interface43RouterQ:- What is a router?Router FunctionsLinking WANs and LANsInterconnecting communication linesPath determination and packet switchingApplication of security rules (ACLs)Protocol conversion (encapsulation)E.g. HDLC, PPP etc.44RoutersInternetworking among dissimilar subnetworks is achieved by using routers to interconnect the subnetworks. Essential functions that the router must perform include the following:Provide a link between networks.Provide for the routing and delivery of data between processes on end systems attached to different networks.Provide these functions in such a way as not to require modifications of the networking architecture of any of the attached subnetworks.45RoutersAddressing schemes: The networks may use different schemes for assigning addresses to devices. For example, an IEEE 802 LAN uses 48-bit binary addresses for each attached device; an ATM network typically uses 15-digit decimal addresses (encoded as 4 bits per digit for a 60-bit address). Some form of global network addressing must be provided, as well as a directory service.Maximum packet sizes: Packets from one network may have to be broken into smaller pieces to be transmitted on another network, a process known as segmentation or fragmentation. For example, Ethernet imposes a maximum packet size of 1500 bytes; a maximum packet size of 1000 bytes is common on X.25 packet-switching networks. A packet that is transmitted on an Ethernet system and picked up by a router for retransmission on an X.25 network may have to be fragmented into two smaller ones.46Router47TCP/IP (Sender)Preparing the data. The application protocol prepares a block of data for transmission. For example, an email message (SMTP), a file (FTP), or a block of user input (TELNET)Using a common syntax. If necessary, the data are converted to a form expected by the destination. This may include a different character code, the use of encryption, and/or compression.Segmenting the data. TCP may break the data block into a number of segments, keeping track of their sequence. Each TCP segment includes a header containing a sequence number and a frame check sequence to detect errors.Duplicating segments. A copy is made of each TCP segment, in case the loss or damage of a segment necessitates retransmission. When an acknowledgment is received from the other TCP entity, a segment is erased.48Operation of TCP/IP(Action at Router)Arriving at router. The incoming signal is received over the transmission medium and interpreted as a cell of bits.Processing the cell. The ATM layer removes the cell header and processes it. The header error control is used for error detection. The connection number identifies the source.Routing the packet. IP examines the IP header and makes a routing decision. It determines which outgoing link is to be used and then passes the datagram back to the link layer for transmission on that linkForming LLC PDU. An LLC header is added to each IP datagram to form an LLC PDU. The header contains sequence number and address information.Framing. A MAC header and trailer is added to each LLC PDU, forming a MAC frame. The header contains address information and the trailer contains a frame check sequence.Transmission. Each frame is transmitted over the medium as a sequence of bits.49Router ComponentsHardware components of a router:Network interfacesInterconnection networkProcessor with a memory and CPUPC router: interconnection network is the (PCI) bus and interface cards are NICsAll forwarding and routing is done on central processorCommercial routers:Interconnection network and interface cards are sophisticatedProcessor is only responsible for control functions (route processor) Almost all forwarding is done on interface cards50Functional Components51ControlDatapath:per-packet processingRouting and ForwardingRouting functions include:route calculationmaintenance of the routing tableexecution of routing protocolsOn commercial routers handled by a single general purpose processor, called route processorIP forwarding is per-packet processingOn high-end commercial routers, IP forwarding is distributedMost work is done on the interface cards52Basic Architectural ComponentsPer-packet processingRoutingDecisionForwardingDecisionForwardingDecisionRoutingTableRoutingTableRoutingTableSwitch FabricOutputScheduling53Router ComponentsOn a PC router: interconnection network is the (PCI) bus Interface cards are NICs (e.g., Ethernet cards)All forwarding and routing is done on central processorOn Commercial routers:Interconnection network and interface cards can be sophisticatedCentral processor is the route processor (only responsible for control functions)54Router55Q:- What is a router?Router OperationsLayer 3 deviceAccepts PDUs on incoming networkExamines PDU dataMakes decision(s) for next stage of PDU journeyMay modify PDU contents (not payload)Passes PDU on to outgoing networkRouter56Q:- What is a router?Ans:-A router is a device that operates at the Network layer of the OSI model to connect dissimilar networks.SummaryNetwork Layer FunctionalityTask performed @ Transport Layer Protocol and Protocol StackProtocol Data UnitProtocol ArchitectureTCP/IP StackLayering Advantages in TCP/IPRouter Architecture and Functionality5758QuestionQ:- A broadcast network is one in which a transmission from any one attached station is received by all other attached stations over a shared medium. Examples are a bustopology local area network, such as Ethernet, and a wireless radio network. Discuss the need or lack of need for a network layer (OSI layer 3) in a broadcast network.59Routing in Case of BroadcastA case could be made either way. First, look at the functions performed at the network layer to deal with the communications network (hiding the details from the upper layers). The network layer is responsible for routing data through the network, but with a broadcast network, routing is not needed. Other functions, such as sequencing, flow control, error control between end systems, can be accomplished at layer 2, because the link layer will be a protocol directly between the two end systems, with no intervening switches. So it would seem that a network layer is not needed. Second, consider the network layer from the point of view of the upper layer using it. The upper layer sees itself attached to an access point into a network supporting communication with multiple devices. The layer for assuring that data sent across a network is delivered to one of a number of other end systems is the network layer. This argues for inclusion of a network layer. In fact, the OSI layer 2 is split into two sublayers. The lower sublayer is concerned with medium access control (MAC), assuring that only one end system at a time transmits; the MAC sublayer is also responsible for addressing other end systems across the LAN. The upper sublayer is called Logical Link Control (LLC). LLC performs traditional link control functions. With the MAC/LLC combination, no network layer is needed (but an internet layer may be needed).6061Question:Q:- A TCP segment consisting of 1500 bits of data and 160 bits of header is sent to the IP layer, which appends another 160 bits of header. This is then transmitted through two networks, each of which uses a 24-bit packet header. The destination network has a maximum packet size of 800 bits. How many bits, including headers, are delivered to the network layer protocol at the destination?Sol:- Data plus transport header plus internet header equals 1820 bits. This data is delivered in a sequence of packets, each of which contains 24 bits of network header and up to 776 bits of higher-layer headers and/or data. Three network packets are needed. Total bits delivered = 1820 + (3 x 24) = 1892 bits.6263UDP RequirementQ:- Why is UDP needed? Why can't a user program directly access IP?Ans:- UDP provides the source and destination port addresses and a checksum that covers the data field. These functions would not normally be performed by protocols above the transport layer. Thus UDP provides a useful, though limited, service.6465IP, TCP and UDP Error ChecksumQ:- IP, TCP, and UDP all discard a packet that arrives with a checksum error and do not attempt to notify the source. Why?Ans:- In the case of IP and UDP, these are unreliable protocols that do not guarantee delivery, so they do not notify the source. TCP does guarantee delivery. However, the technique that is used is a timeout. If the source does not receive an acknowledgment to data within a given period of time, the source retransmits.6667TCP UDP Header LengthQ:- Why does the TCP header have a header length field while the UDP header does not?Ans:- UDP has a fixed-sized header. The header in TCP is of variable length.68SummaryNetwork Layer FunctionalityTask performed @ Transport Layer Protocol and Protocol StackProtocol Data UnitProtocol ArchitectureTCP/IP StackLayering Advantages in TCP/IPRouter Architecture and Functionality69