2 Overview Network Access Layer Transport Layer Protocols Protocol Data UnitProtocol ArchitectureTCP/IP StackLayered Approach and its AdvantagesRouter
3 Network Access LayerQ:- What is the major function of the network access layer?
4 OSI Model Application Layer 7 Presentation Layer 6 Session Layer 5 TransportLayer 4NetworkLayer 3Data linkLayer 2PhysicalLayer 17 layers OSI model
5 Physical Layer Functions Establishment and termination of a connection to a communication mediumProcess for effective use of communication resources (e.g., contention resolution and flow control)Conversion between representation of digital data in the end user’s equipmentThe physical layer is responsible for movements of individual bits from one hop (node) to the next.
6 Data Link Layer Functions Responds to service requests from the network layer and issues requests to the physical layer.Provides functional and procedural means to transfer data between network entities and to detect and correct errors that may occur in the physical layer.Concerned with:FramingPhysical addressing (MAC address)Flow ControlError ControlAccess ControlThe data link layer is responsible for moving frames from one hop (node) to the next.
8 Network Layer Functions Provides for transfer of variable length sequences from source to destination via one or more networksResponds to service requests from the transport layer and issues requests to the data link layerConcerned with:Data PacketLogical addressing (IP address)RoutingThe network layer is responsible for the delivery of individual packets from the source host to the destination host.
10 Transport Layer Functions Provides transparent data transfer between end usersResponds to service requests from the session layer and issues requests to the network layer.Concerned with:Service-point addressingSegmentation and reassemblyConnection control and Flow Control (end-to-end)Error Control的資料傳輸及控制，是OSI模型中的關鍵角色，它可以將一個較大的資料切割成多個適合傳輸的資料，替模型頂端的第五、六、七等三個通訊層提供流量管制及錯誤控制。The transport layer is responsible for the delivery of a message from one process to another.
12 Session Layer Functions Provides mechanism for managing a dialogue between end-user application processesResponds to service requests from the presentation layer and issues requests to the transport layerSupports duplex or half- duplex operations.Concerned with:Dialogue controlSynchronization (Check point)The session layer is responsible for dialog control and synchronization.
13 Presentation Layer Functions Relieves application layer from concern regarding syntactical differences in data representation with end-user systemsResponds to service requests from the application layer and issues requests to the session layerConcerned with:TranslationEncryptionCompression第六層︰展示層（Presentation Layer） 應用層收到的資料後，透過展示層可轉換表達方式，例如將ASCII編碼轉成應用層可以使用的資料，或是處理圖片及其他多媒體檔案，如JPGE圖片檔或MIDI音效檔。 除了轉檔，有時候當資料透過網路傳輸時，需要將內容予以加密或解密，而這個工作就是在展示層中處理。The presentation layer is responsible for translation, compression, and encryption.
14 Application Layer Functions Interfaces directly to and performs common application services for application processesIssues service requests to the Presentation layerSpecific services provided:Network virtual terminalFile transfer, access and managementMail servicesDirectory servicesHTTP, FTP, DHCP…第七層︰應用層（Application Layer） 應用層主要功能是處理應用程式，進而提供使用者網路應用服務。這一層的協定也很多。使用者常見的通訊協定，有DHCP（Dynamic Host Configuration Protocol）、FTP（File Transfer Protocol）、HTTP（HyperText Transfer Protocol）及POP3（Post Office Protocol-Version 3）等，依據不同的網路服務方式，這些協定能定義各自的功能及使用規範等細部規則。The application layer is responsible for providing services to the user.
16 TCP/IP ProtocolThe lower four layers correspond to the layer of the OSI modelThe application layer of the TCP/IP model represents the three topmost layers of the OSI model.The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application.
19 Topics discussed in this section: AddressingFour levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific.Topics discussed in this section:Physical Addresses Logical Addresses Port Addresses Specific Addresses
22 ExampleIn Figure below a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.
23 A 6-byte (12 hexadecimal digits) physical address. ExampleMost local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below:07:01:02:01:2C:4BA 6-byte (12 hexadecimal digits) physical address.
24 ExampleFigure shows a part of an internet with two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection.
25 ExampleFigure below shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.The physical addresses will change from hop to hop, but the logical addresses usually remain the same.
28 Internet Protocol (IP) Provides connection-less, best-effort service for delivery of packets through the inter-networkBest-effort: No error checking or tracking done for the sequence of packets (datagrams) being transmittedUpper layer should take care of sequencingDatagrams transmitted independently and may take different routes to reach same destinationFragmentation and reassembly supported to handle data links with different maximum – transmission unit (MTU) sizes
29 Internet Control Message Protocol (ICMP) Companion protocol to IPProvides mechanisms for error reporting and query to a host or a routerQuery message used to probe the status of a host or a routerError reporting messages used by the host and the routers to report errors
30 Internet Group Management Protocol (IGMP) Used to maintain multicast group membership within a domainSimilar to ICMP, IGMP query and reply messages are used by routers to maintain multicast group membershipPeriodic IGMP query messages are used to find new multicast members within the domainA member sends a IGMP join message to the router, which takes care of joining the multicast tree
31 Dynamic Host Configuration Protocol (DHCP) Used to assign IP addresses dynamically in a domainExtension to Bootstrap Protocol (BOOTP)Node Requests an IP address from DHCP serverHelps in saving IP address space by using same IP address to occasionally connecting hosts
32 Internet Routing Protocols Routing Information Protocol (RIP)An intra-domain distance vector routing protocolUses the Bellman-Ford algorithm to calculate routing tableDistance information about all the nodes is conveyed to the neighbors.Open Shortest Path First (OSPF)Based on shortest path algorithm, sometimes also known as Dijkstra algorithmHosts are partitioned into autonomous systems (AS)AS is further partitioned into OSPF areas that helps boarder routers to identify every single node in the areaLink-state advertisements sent to all routers within the same hierarchical area
33 Internet Routing Protocols Border Gateway Protocol (BGP)Intra-autonomous systems communicate with each other using path vector routing protocolEach entry in the routing table contains the destination network, the next router, and the path to reach the destination
35 Abstract model of a wireless network in the form of a graph A routing table maintained at each node, indicating the best known distance and next hop to get thereCalculate w(u,v), is the cost associated with edge uvCalculate d(u), the distance of node u from a root nodeFor each uv, find minimum d(u,v)Repeat n-1 times for n-nodesTCP6Root2431-1Abstract model of a wireless network in the form of a graphApplication LayerTop three layers (session, presentation, and application) merged into application layerRouting using Bellman-Ford Algorithm
36 TCP (ctd) Abstract model of a wireless 6 4 123-146RootAbstract model of a wirelessnetwork in the form of a graphTo Node1234Pass 0*Pass 1Pass 2Pass 3Pass 4To Node1234Pass 0Pass 1Pass 27Pass 3Pass 488Successive calculation of distance D(u) from node 0Predecessor from node 0 to other network nodes
37 TCP over WirelessThe wireless domain is not only plagued by the mobility problem, but also by high error rates and low BWTraditional TCP: provides a connected-oriented, reliable, and byte stream serviceTCP functions: flow-control (controlled by sliding window), congestion-control (congestion window), data segmentation, retransmission, and recoverySlow Start: resets the congestion window (CW) size to one and let threshold to half of the current CW sizeDouble the CW on every successful transmission until the CW reach threshold and after that increases the CW by one for each successful transmission
38 Solutions for Wireless Environment Networking layering provides good abstraction in the network designWireless networks are interference limited, and the information delivery capability is closely dependent on current channel qualityAdoption in physical and link layer broadcast could lead to efficient resource usageProtocol changes need to be made in MSs and mobile access points to ensure compatibility with existing TCP applications
39 End-to-End Solutions TCP-SACK WTCP Protocol Freeze-TCP Protocol Selective Acknowledgement and Selective Retransmission.Sender can retransmit missing data due to random errors/mobilityWTCP ProtocolSeparate flows for wired (Sender to AP) and wireless (AP to MS) segments of TCP connectionsLocal retransmission for mobile link breakageAP sends ACK to sender after timestamp modification to avoid change in round trip estimatesFreeze-TCP ProtocolMobile detects impending handoffAdvertises Zero Window size, to force the sender into Zero Window Probe mode
40 End-to-End Solutions (Cont’d) Explicit Band State Notification (EBSN)Local Retransmission from BS (AP) to shield wireless link errorsEBSN message from BS to Source during local recoverySource Resets its timeout value after EBSNFast Retransmission ApproachTries to reduce the effect of MS handoffMS after handoff sends certain number of duplicate ACKsAvoids coarse time-outs at the sender, accelerates retransmission
41 Link Layer Protocols Snoop Protocol Transport layer aware Snoop Agent at BSAgent monitors all TCP segments destined to MS, caches it in bufferAlso monitors ACKs from MSLoss detected by duplicate ACKs from MS or local time-outLocal Retransmission of missing segment if cachedSuppresses the duplicate ACKs
42 Split TCP ApproachIndirect TCP: splits the TCP connection into two distinct connections, one is MS and BS and another is BS and corresponding node (CN)The AP acts as a proxy for MSThe AP acknowledges CN for the data sent to MS and buffers this data until it is successfully transmitted to MSHandoff may take a longer time as all the data acknowledged by AP and not transmitted to MS must be buffered at the new AP
43 Indirect TCPWireless linkWired DomainMSAPCN(Acts as proxy)
44 Split TCP Approach (Cont’d) M-TCP ProtocolSplit the connection into wired component and wireless componentBS relays ACKs for sender only after receiving ACKs from MSIn case of frequent disconnections, receiver can signal sender to enter in persist mode by advertising Zero Window size
45 Impact of MobilityHandoffs occur in wireless domains when an MN moves into a new BS’s domainThe result of the packet loss during handoff is slow startThe solution involves artificially forcing the sender to go into fast retransmission mode immediately, by sending DUP ACK after the handoff, instead of go into slow startUsing multicast: the MN is required to define a group of BSs that it is likely to visit in the near futureReduce the handoff latency: Only one BS is in contact with the MN and the others buffer the packets addressed to the multicast address
46 Internet Protocol Version 6 (IPv6) Designed to address the unforeseen growth of the internet and the limited address space provided by IPv4Features of IPv6:Enhanced Address Space: 128 bits long, can solve the problem created by limited IPv4 address space (32 bits)Resource Allocation: By using “Flow Label”, a sender can request special packet handlingModified Address Format: Options and Base Header are separated which speeds up the routing processSupport for Security: Encryption and Authentication options are supported in option header
47 IPv4 Header Format Version(4 bits) Header length (4 bits) Type of service (8 bits)Total length (16 bits)Identification (16 bits)Flags(3 bits)Fragment offset(13 bits)Time to live(8 bits)Protocol (8 bits)Header checksum (16 bits)Source address (32 bits)Destination address (32 bits)Options and padding (if any)
48 IPv6 Header Format Version Traffic Class Flow Label Payload Length Address SpaceResource AllocationModified Header FormatSupport for SecurityVersionTraffic ClassFlow LabelPayload LengthNext HeaderHop LimitSource AddressDestination AddressData
49 Format of IPv6 Name Bits Function Version 4 IPv6 version number Traffic Class8Internet traffic priority delivery valueFlow Label20Used for specifying special router handling from source to destination(s) for a sequence of packetsPayload Length16, unsignedSpecifies the length of the data in the packet. When set to zero, the option is a hop-by-hop Jumbo payloadNext HeaderSpecifies the next encapsulated protocol. The values are compatible with those specified for the IPv4 protocol fieldHop Limit8, unsignedFor each router that forwards the packet, the hop limit is decremented by 1. When the hop limit field reaches zero, the packet is discarded. This replaces the TTL field in the IPv4 header that was originally intended to be used as a time based hop limitSource Address128The IPv6 address of the sending nodeDestination AddressThe IPv6 address of the destination node
50 Differences between IPv4 and IPv6 Expanded Addressing CapabilitiesSimplified Header FormatImproved Support for Options and ExtensionsFlow Labeling CapabilitiesSupport for Authentication and Encryption
51 Network Transition from IPv4 to IPv6 Dual IP-Stack:IPv4-hosts and IPv4-routers have an IPv6-stack, this ensures full compatibility to not yet updated systemsIPv6-in-IPv4 Encapsulation (Tunneling):Encapsulate IPv6 datagram in IPv4 datagram and tunnel it to next router/host
53 Network Access LayerThe Internet Protocol Suite (commonly known as TCP/IP) is the set of communications protocols used for the Internet and other similar networks.Transmission Control Protocol (TCP) and the Internet Protocol (IP)The Internet Protocol Suite may be viewed as a set of layers. Each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the upper layer protocols based on using services from some lower layers.The TCP/IP model consists of four layers. This layer architecture is often compared with the seven-layer OSI Reference Model. From lowest to highest, these arethe Network Access Layer,the Internet Layer,the Transport Layer,and the Application LayerThe TCP/IP Network Access Layer canencompass the functions of two lower layersof theOSI reference Model:Data Link, and Physical.
54 Network Access LayerQ:- What is the major function of the network access layer?Ans: The network access layer is concerned with the exchange of data between a computer and the network to which it is attached.
56 Transport Layer RecapQ:- What tasks are performed by the transport layer?Isolates messages from lower and upper layersBreaks down message sizeMonitors quality of communications channelSelects most efficient communication service necessary for a given transmission
57 Transport LayerConcerned with reliable transfer of information between applicationsIndependent of the nature of the applicationIncludes aspects like flow control and error checking
58 Transport Layer RecapQ:- What tasks are performed by the transport layer?Ans:- The transport layer is concerned with data reliability and correct sequencing.
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