CHAPTER 3 : OSI MODEL

1 CHAPTER 3 : OSI MODEL OSI Layer TCP/IP Protocol Suite 7/26/200 09 CHAPTER 3 : THE OSI MODEL Established in 1947, the ISO is a multinational body dedicated to worldwide agreement on international standard d ISO standard which covers all aspects of network communications Open Systems Interconnection (OSI) model Open System a model that allows any two different systems to communicate regardless of their underlying architecture OSI is not a protocol Model for understanding and designing a network architecture that is flexible, robust, and interoperable 2 Idawaty Ahmad 1

3.1 THE MODEL OSI a layered framework for design of network systems that allows for communication across all types of computer system 7 layer architecture Intermediate nodes involve only the first three layers Peer-to-Peer Process? Layer n, use the services provided by layer n-1 and provides services for layer n+1 The process on each machine thatt communicate at a given layer are called peer-to-peer process Use protocol 3 3.1 THE MODEL At sending machine: headers added to the message at L6,5,4,3,2 Trailer is added at only L2 At receiving machine The message is unwrapped layer by layer, received process and removing the data meant for it.(reverse of sending machine) Interfaces between layers control the passing of the data and network information down/up through the layers of sending/receiving machine 4 Idawaty Ahmad 2

3.1 THE MODEL The 7L can grouped into three subgroup L1,2,3 the network support layer deal with the physical aspects of moving data from one device to another L5,6,7 the user support layer allow interoperability among unrelated software systems L4 ensures end-to-end reliable data transmission After pass through L1 of sending machine, the data unit is changed into electromagnetic signal and transportedt along a physical link 5 OSI Model 6 Idawaty Ahmad 3

MODEL RUJUKAN OSI Application Presentation Session Transport Network Data Link Physical Aplikasi Web, SMTP, FTP,Telnet,IRC,News dll Data compression,encryption, character representation Komunikasi yang selamat: Secure Socket Layer (SSL) Connection/less, multiplex,flow dan error control Penghantaran paket ke destinasi Topologi Rangkaian,Pengalamatan, Error, flow control Network card FDDI,ATM, Ethernet, Token Ring, Dialup,wireless 7 OSI Layers 8 Idawaty Ahmad 4

An Exchange Using the OSI Model 9 KONSEP HEADER DALAM MODEL OSI Pelayan Pelanggan Application Presentation Session Transport Network Data Link Physical data data segment packet data frame data TCP header TCP header TCP header IP header IP header Ethernet header Application Presentation Session Transport Network Data Link Physical Network card Idawaty Ahmad 5

3.2 FUNCTION OF EACH LAYER Physical layer (L1) Coordinates the function required to transmit abitstream over a physical medium Deal with the mechanical/electrical spec of the interface and transmission medium Defines the procedures and functions that physical devices and interfaces have to perform for transmission to occur Concerned with: Physical characteristics of interfaces and media Representation of bits Bits must be encoded into signals electrical or optic Data rate the number of bits sent each second Synchronization of bits Line configuration connection of devices to the medium 11 3.2 FUNCTION OF EACH LAYER Concerned with: Physical topology How devices are connected to form a network Transmission mode Direction of signal transmission between two devices 12 Idawaty Ahmad 6

Note: The physical layer is responsible for transmitting individual bits from one node to the next. 13 Physical Layer 14 Idawaty Ahmad 7

3.2 FUNCTION OF EACH LAYER Data Link Layer (L2): Responsible for node-to-node delivery Makes appear error free to the network layer Responsibilities include: Framing divides the stream data to manageable data units frame Physical addressing adds a header to the frame to define the physical address of (destination address) sender( source address) and receiver Flow control to prevent overwhelming at the receiver Error control provides reliability to detect and retransmit damaged or lost frames, also prevent duplication of frames - trailer Access control require a protocol to determine which device has control over the link at any given time > same link with two or more devices connected. Note: The data link layer is responsible for transmitting frames from one node to the next. 15 16 Idawaty Ahmad 8

Data Link Layer 17 Example 1 In the next figure, a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection 18 Idawaty Ahmad 9

Data Link Layer Example 19 3.2 FUNCTION OF EACH LAYER Network Layer (L3): Responsible for the source-to-destination delivery of a packet possibly across multiple networks (links) If two systems are attached to different networks, we need the network layer protocol to accomplish source-todestination delivery Specific responsibility: Logical addressing to distinguish the source and destination systems when a packet passes the network boundary also known network address Routing internetwork/large network route the packet to the final destination 20 Idawaty Ahmad 10

Note: The network layer is responsible for the delivery of packets from the original source to the final destination. 21 Network Layer 22 Idawaty Ahmad 11

Example 2 Network Layer Example In the next figure, we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic. 23 Network Layer Example 24 Idawaty Ahmad 12

3.2 TRANSPORT LAYER Transport Layer (L4): Review of a network layer responsibility: Responsible for source-to-destination (end-to-end) delivery of the entire message Individual packet treats each packet independently transport layer Ensures the whole (entire) message arrives intact and in order Oversee both error control and flow control at source-todestination level To added security, transport layer create a connection between the two end ports Connection - Single logical path between the source and destination 25 3.2 TRANSPORT LAYER Creating connection involves 3 steps: Connection establishment Data transfer Connection release Has more control over sequencing, flow, error correction and detection 26 Idawaty Ahmad 13

3.2 TRANSPORT LAYER Specific responsibilities: Service-point addressing Computers often run several programs at the same time From a specific process(running program) on one computer to a specific process (running program) on the other TL header must include a service-point address or port address Segmentation and reassembly Segment add a sequence number into message segment Connection control Can be either connectionless connection oriented (independent packet) or Flow control End-to-end flow control ( across multiple networks) Error control End-to-end error control ( across multiple networks) 27 Note: The transport layer is responsible for delivery of a message from one process to another. 28 Idawaty Ahmad 14

Figure : Reliable process-to-process delivery of a message 29 Transport Layer 30 Idawaty Ahmad 15

Example 3 Figure shows an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet. 31 Transport Layer Example 32 Idawaty Ahmad 16

Transport Layer Example 33 3.2 SESSION LAYER Session Layer (L5) The network dialog controller Establishes, maintains, and synchronizes the interaction between communicating systems Responsibilities: Dialog control allows two systems to enter into a dialog communication between two process half-duplex or fullduplex Synchronization allows a process to add checkpoints (synchronization points) into a stream of data E.g.: sending a file.. 34 Idawaty Ahmad 17

Session Layer 35 3.2 PRESENTATION LAYER Presentation Layer (L6) Concerned with the syntax and semantics of the information exchanged between two systems. Responsibilities: Translation The process (running programs) in two systems are usually exchanging information Different computers use different encoding systems Responsible for interoperability between different encoding methods Sender machine change the information from its sender- dependent format into a common format Receiver machine change the common format into its receiver-dependent format 36 Idawaty Ahmad 18

3.2 PRESENTATION LAYER Encryption Encryption - transform the original information to another form and sends it over the network Decryption - reverse process at the receiver side assure privacy - to carry a sensitive data/information Compression Reducesthenumberofbitstobetransmitted multimedia data transmission such as text, audio and video 37 Presentation Layer 38 Idawaty Ahmad 19

3.2 APPLICATION LAYER Application Layer (L7) Enables user, whether human or software to access the network Provides user interfaces and support for services such as email, remote file access, shared database mgmt and transfer etc No trailer or header are added here Specific services Network virtual terminal File transfer, access, and management (FTAM) access/manage/control files in a remote computer Mail services - X.400 store and forward email Directory services X.500 provides distributed database sources 39 Application Layer 40 Idawaty Ahmad 20

Note: The application layer is responsible for providing services to the user. 41 Summary of Layer Functions (OSI model) 42 Idawaty Ahmad 21

3.3 TCP/IP PROTOCOL SUITE Developed prior to the OSI model 5 layers also known Internet t model The three topmost layers in the OSI model are represented in TCP/IP by a single layer application layer TCP/IP is a hierarchical protocol the upper-level protocol is supported by one or more lower-level protocols E.g.:@TL TCP,UDP;@NL-IP 43 Summary of Layer Functions (TCP/IP) 44 Idawaty Ahmad 22

PROTOKOL SUIT TCP/IP TCP: Transmission Control Protocol IP: Internet t Protocol Menggunakan dan mendefinasi hanya 4 paras 1974 Dua tujuan utama senibina TCP/IP adalah: Untuk membentuk sambungan antara rangkaian yang berbeza pada sambungan rangkaian dan juga pada OS yang berbeza Untuk menyembunyikan segala details tentang sambungan, jenis rangkaian daripada paras aplikasi. 45 TCP/IP Application Transport Network HTTP, SMTP, FTP,Telnet, POP3,IMAP, ping dll TCP, UDP, SNMP IP, UDP Link ATM,FDDI,Ethernet,PPP dan jenis Rangkaian yang lain 46 Idawaty Ahmad 23

REVISION Q&AS What is peer-to-peer process? What is the difference between a servicepoint-address, a logical address, and a physical address? What is the purpose of translation by the presentation layer? Idawaty Ahmad : Semester 1 : 2009/2010 47 PEER-TO-PEER PROCESS The process on each machine that communicate at a given layer. 48 Idawaty Ahmad 24

DIFFERENT Service point address identifies the application process on the station at L4 Logical address/lna defines the sender and receiver at L3 and is used to deliver message across multiple networks Physical address is the local address of a node, is used by L2 to deliver data from one node to another within the same network 49 THE PHYSICAL LAYER Definition : Specifications for the physical components of the network What Physical Layer Components do: Specifications for: Cabling Interconnection Methods Data Encoding Electrical Properties Examples Ethernet (IEEE 802.3) Token Ring (IEEE 802.5) FDDI (ANSI X3T9.5) IEEE 802.11b (Wireless) 50 Idawaty Ahmad 25

THE PHYSICAL LAYER What Physical Layers Components do: Specifications for the physical components of the network Examples (What Defined) Ethernet (Physical Spec) Token Ring (Physical Spec) FDDI 802.11b (Physical Spec) T Carrier (T1) Where is on my computer NIC card and cabling 51 THE DATA LINK LAYER What Data Link Layer Components do: Media Access Control (MAC) and Logical Link Control (LLC) Addresses network devices (MAC Address) Places data in a Data Frame (packet) Gives the data bits to the NIC card (MAC) Controls the Network Interface Card s (NIC) Access to the Media (MAC) Detects transmission errors (LLC) 52 Idawaty Ahmad 26

THE NETWORK LAYER Definitions: Provides network-wide addressing and mechanism to move packets between multiple networks What Networking Layer Components do: Network Addressing Move of packets between different networks routing Examples Internet Protocol (TCP/IP) IPX (Netware) What defined Network Addressing Move of packets between different networks routing Where is it on my computer: TCP/IP Software 53 THE TRANSPORT LAYER Definitions: Provides end-to-end communication and reliable data delivery Examples Transport Control Protocol (TCP/IP), User Datagram Protocol (UDP) What Transport Layer Components do: Receives data from application and segments it Can provide transmission error detection and correction 54 Idawaty Ahmad 27

THE SESSION LAYER Definitions: Allows application to maintain an ongoing g communication (session) Examples NetBIOS Netware Core Protocol What Session Layer Components do: Manage user sessions Track user sessions Where is it on my computer: Workstation and Server Service Software (Windows) 55,Redirector or Requestor (Netware), Windows Client for Netware (Netware) THE PRESENTATION LAYER Definitions: Provides common data formatting between communicating devices Examples Multipurpose Internet Mail Extensions (MIME) What Presentation Layer Components do: Make sure the receiving station can read the transferred data Where is it on my computer: Workstation or server service Email client 56 Idawaty Ahmad 28

THE APPLICATION LAYER Definitions: Gives end-user applications access to network resources Examples Workstation and Server Service Software (Windows) Windows Client for Netware (Netware) What Application Layer Components do: Gives end-user applications access to network resources Where is it on my computer: Workstation or server service (Session, Presentation and Application) 57 58 Idawaty Ahmad : Semester 1 : 2009/2010 Idawaty Ahmad 29

JENIS ALAMAT DI ANTARA RANGKAIAN Tiga jenis alamat yang digunakan antara rangkaian Alamat Paras Data Link: Alamat yang membezakan tiap-tiap perkakasan dalam rangkaian Dikenali sebagai physical atau hardware address Alamat MAC : Alamat Media Access Control: MAC Lebih kurang sama fungsinya dengan Alamat Paras Data Link Alamat IP: Lanjutan tentang ini dalam kuliah yang lain kemudian 59 ALAMAT MAC Panjangnya 48bits 12 digit dalam bentuk hexadecimal Di pelopori oleh IEEE 6 digit pertama:mengenalpasti vendor atau pembuat perkakasan tersebut (OUI: Organizationally Unique Identifier) 6 digit terakhir : Nombor siri untuk perkakasan tersebut dan ditentukan oleh vendor tersebut: (Intel dsb) Dikenali juga sebagai burned-in-address (BIAs) kerana alamat ini akan terdapat dalam ROM (read only memory) dan di salin kedalam RAM semasa perkakasan (network card) tersebut initialize 60 Idawaty Ahmad 30

ALAMAT PARAS DATA LINK DAN ALAMAT MAC LAN 3 LAN 4 FDDI Trdpt5 Terdapat alamat lmtmac pada Penghala A Penghala A FDDI LAN 2 Token Ring U N I V E R S I T Y Dialup Ethernet LAN 1 61 Hakcipta: Idawaty Ahmad FSKTM UPM Idawaty Ahmad 31