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Computer Communication and Networking Abdul Wahab Yaqoob B.E(Telecom)MUET,CCNA,CCNP,MCSA,CCDA Department of Information Technology Campus Dadu ,University of Sindh [email protected] Unit #01 Lecture#03 Protocols and Layered Models Computer Communication and Networking Title of Subject : Computer Communication and Networking Effective : 2K13 Batch Marks : 100(theory) + 50 (Practical) Credit Hours : 2+1 This Class will meet at: 9:00-11:00 AM on Thursday Recommended Books ” Data Communications & Networking”, by Behroz Forouzan ” Data and Computer Communications”, by William Stallings ” Computer Networks, 4th Edition”, by Andrew S Tanenbaum Department of Information Technology Sindh U, Campus Dadu 2 Computer Communication and Networking Protocol in Network Communication A protocol is a set of predetermined rules A set of instruction, manners b/w communication devices Implemented in software that is loaded on each host and network device Network protocols are used to allow devices to communicate successfully Protocols agree on structure of message (specific to PDU’s) Protocols agree on the process of sharing, error handling, and termination procedures – all functions necessary for communication Require layer dependent encapsulations Department of Information Technology Sindh U, Campus Dadu 3 Computer Communication and Networking Function of Protocol in Network Communication Example includes DHCP TFTP FTP SMTP POP IP TCP UDP Department of Information Technology Sindh U, Campus Dadu 4 Computer Communication and Networking Why OSI Model Provides a layered structure model The model was developed by the International Organization for Standardization (ISO) in 1984. The OSI model divides the tasks into seven smaller, more manageable task groups Benefits of using a layered model Assists in protocol design Fosters competition (different vendors can work together) Changes in one layer do not affect other layers Provides a common language Department of Information Technology Sindh U, Campus Dadu 5 Computer Communication and Networking Layers with OSI Model DATA segments Packets Frames bits Department of Information Technology Sindh U, Campus Dadu 6 Computer Communication and Networking PDU : Layer Specification Data. PDUs are SPECIFIC to each layer! Department of Information Technology Sindh U, Campus Dadu 7 Computer Communication and Networking Layers with TCP/IP Model TCP/IP Model – created in early 1970s – Department of Information Technology Sindh U, Campus Dadu 8 Computer Communication and Networking Comparing TCP/IP and OSI Model Know these layers and how they compare between the two models Department of Information Technology Sindh U, Campus Dadu 9 Computer Communication and Networking APPLICATION LAYER Department of Information Technology Sindh U, Campus Dadu 10 Computer Communication and Networking Applications Layer – allows user to interface with the network! Provides the interface between the applications on either end of the network Department of Information Technology Sindh U, Campus Dadu 11 Computer Communication and Networking Application Layer Protocols • DNS – Matches domain names with IP addresses • HTTP – Used to transfer data between clients/servers using a web browser • SMTP & POP3 – used to send email messages from clients to servers over the internet • FTP – allows the download/upload of files between a client/server • Telnet – allows users to login to a host from a remote location and take control as if they were sitting at the machine (virtual connection) • DHCP – assigns IP addresses, subnet masks, default gateways, DNS servers, etcs. To users as they login the network Department of Information Technology Sindh U, Campus Dadu 12 Computer Communication and Networking DHCP Dynamic Host Configuration Protocol • enables devices to obtain IP addresses, subnet masks, gateways, DNS server information, etc. from a DHCP server. • An IP address that is not being used is assigned from a range of available addresses • Not permanently assigned – only leased for a specific period of time (usually 8 hours – 8 days) • If the host logs off or the power is lost, the IP address they were using is returned to the pool to be re-assigned to another host when needed. • This is how you are able to use Wi-Fi at various places in the world! • Don’t use DHCP for devices such as servers, printers, routers, switches, etc. These should be statically assigned. Department of Information Technology Sindh U, Campus Dadu 13 Computer Communication and Networking FTP • • • Commonly used application layer protocol Allows for the transfer of files between clients/servers. Requires 2 connections to the server 1) Commands – uses TCP port 21 2) Actual data – uses TCP port 20 Department of Information Technology Sindh U, Campus Dadu 14 Computer Communication and Networking DNS Services DNS Servers resolve names to IP addresses. It would be difficult to remember the IP address of every website we like to visit, but we can remember names. THANK YOU DNS SERVER! Department of Information Technology Sindh U, Campus Dadu 15 Computer Communication and Networking PRESENTATION LAYER Department of Information Technology Sindh U, Campus Dadu 16 Computer Communication and Networking Presentation Layer • Present the data to the Network in common format for Communication • Includes Alpha Numerical Code set ASCII, Compression, file format, Encoding and Decoding Department of Information Technology Sindh U, Campus Dadu 17 Computer Communication and Networking SESSION LAYER Department of Information Technology Sindh U, Campus Dadu 18 Computer Communication and Networking Session Layer • Establish, Terminate and Maintain sessions(Log in, Log out) Authentication, Permission Department of Information Technology Sindh U, Campus Dadu 19 Computer Communication and Networking TRANSPORT LAYER Department of Information Technology Sindh U, Campus Dadu 20 Computer Communication and Networking Transport Layer Role and Services Department of Information Technology Sindh U, Campus Dadu 21 Computer Communication and Networking • Purpose: Track individual communication between applications on source/destination hosts Segment data and manage each piece of data – prepares it to be sent across the network (network layer). Encapsulation is required on each piece of data including information that will allow that data to be tracked. WITHOUT SEGMENTATION, only ONE application would be able to receive data. Re-assemble segments back into streams of application data at the receiving host. Prepares it to be passed back to the application layer. Identify the different applications using port numbers. Each software process that needs to access the network is assigned a port # that is unique in that host. Indicates which application that piece of data is associated with. Department of Information Technology Sindh U, Campus Dadu 22 Computer Communication and Networking Transport Layer Role and Services Department of Information Technology Sindh U, Campus Dadu 23 Computer Communication and Networking Controlling conversations • Segmentation and reassembly – Transport layer divides application data into blocks of data that are the appropriate size. At the destination, the transport layer reassembles the data before sending it up to the application or service. • Conversation multiplexing – Many applications or services might be running on each host. Each is assigned a port # so that the Transport layer can determine which application or service is associated with that data. • TCP at the transport layer also provide (see next slide for details) Connection-oriented conversations Reliable/accurate delivery Ordered data reconstruction Flow control Department of Information Technology Sindh U, Campus Dadu 24 Computer Communication and Networking Controlling Conversations (cont’d) • Establish a session – connection-oriented (TCP) or connectionless (UDP) • Reliable delivery – ensures that all pieces reach their destination by having the source device retransmit any data that is lost • Same order delivery – numbering and sequencing segments ensures the transport layer segments are reassembled in the proper order • Flow control – hosts have limited resources (memory, bandwidth, etc.) If these get over-taxed, transport layer can request the flow of data be slowed. Why do this? Prevent the receiver from being overwhelmed with data! Department of Information Technology Sindh U, Campus Dadu 25 Computer Communication and Networking Reliable communication Department of Information Technology Sindh U, Campus Dadu 26 Computer Communication and Networking TCP vs. UDP - characteristics UDP – Connectionless Advantage – low overhead data delivery pieces – datagrams ‘Best Effort’ delivery Used by application that don’t require reliable delivery Minimal delays TCP – connection-oriented More overhead Same order delivery Reliability flow-control Department of Information Technology Sindh U, Campus Dadu 27 Computer Communication and Networking HEADERS OF TCP AND UDP Web browsers E-mail File transfers DNS VoIP Video streaming Department of Information Technology Sindh U, Campus Dadu 28 Computer Communication and Networking 3-way Handshake • Steps to establish a connection 1) The sender sends an initial SEQ value (set by TCP) to begin communication! 2) The receiver responds with an ACK value = to the SEQ value + 1. The ACK should always be the NEXT expected Byte. 3) Sender responds with an ACK value = to SEQ value it received + 1. Department of Information Technology Sindh U, Campus Dadu 29 Computer Communication and Networking 3-way Handshake – Session Termination Department of Information Technology Sindh U, Campus Dadu 30 Computer Communication and Networking Managing TCP Sessions Department of Information Technology Sindh U, Campus Dadu 31 Computer Communication and Networking Managing TCP Sessions If an acknowledgement isn’t sent that data was received, the host will RESEND the data because it has reached a timeout. Department of Information Technology Sindh U, Campus Dadu 32 Computer Communication and Networking Managing TCP Sessions • Window size – the amount of data a source can transmit before an ACK must be received. It enables the management of lost data and flow control. Department of Information Technology Sindh U, Campus Dadu 33 Computer Communication and Networking UDP Protocol • Go over characteristics of UDP – used by DNS, SNMP, DHCP, RIP, TFTP, Online games, streaming video, etc. Department of Information Technology Sindh U, Campus Dadu 34 Computer Communication and Networking UDP Protocol • UDP doesn’t care if datagrams are out of order! Department of Information Technology Sindh U, Campus Dadu 35 Computer Communication and Networking NETWORK LAYER Department of Information Technology Sindh U, Campus Dadu 36 Computer Communication and Networking Network Layer Protocols and Internet Protocol (IP) Provides services to exchange data over the network between end devices. 4 Processes: Addressing Encapsulation Routing De capsulation Department of Information Technology Sindh U, Campus Dadu 37 Computer Communication and Networking Network Layer Protocols and Internet Protocol (IP) Department of Information Technology Sindh U, Campus Dadu 38 Computer Communication and Networking Network Layer Protocols and Internet Protocol (IP) • Connectionless systems (IP, UDP) • Receiving host is NOT contacted before the message is sent Department of Information Technology Sindh U, Campus Dadu 39 Computer Communication and Networking Network Layer Protocols and Internet Protocol (IP) • Source/Destination IP addresses get added at the network layer (layer 3). Department of Information Technology Sindh U, Campus Dadu 40 Computer Communication and Networking Why separate hosts in a network? • Common issues with large networks: performance degradation, security issues, and address management (identifying hosts). Discuss Broadcast domains.. Be able to identify how many there are! Department of Information Technology Sindh U, Campus Dadu 41 Computer Communication and Networking DATALINK LAYER Department of Information Technology Sindh U, Campus Dadu 42 Computer Communication and Networking Data Link Layer – Accessing the Media • 2 basic services – – Allows upper layers to access the media – Controls how data is placed onto the media using media access control and error detection Data link layer terms Frame – PDU for layer 2 Node – device on a network Media – physical means to carry the signals Network – 2 or more nodes connected to a common medium Department of Information Technology Sindh U, Campus Dadu 43 Computer Communication and Networking Data-link layer DIVIDED! • Logical Link Control (LLC) – defines the software process that provide services to the network layer protocols. Places information in the frame that identifies which protocol is being used (IP, IPX, Appletalk, etc.). – closest to the Network Layer • Media Access Control (MAC) – defines the media access processes performed by the hardware. Will be specific to the type of media being used. – closest to the physical layer Department of Information Technology Sindh U, Campus Dadu 44 Computer Communication and Networking Data Link Layer – Accessing the Media • Function – responsible for controlling the transfer of frames across the media. Department of Information Technology Sindh U, Campus Dadu 45 Computer Communication and Networking Media Access Control Techniques • Logical topology – way a network transfers frames from one node to the next. This is what the data link layer ‘sees’ when controlling media access. These are virtual connections • Physical topology – physical arrangement of the nodes and connections. These 2 are not usually the same! Department of Information Technology Sindh U, Campus Dadu 46 Computer Communication and Networking Media Access Control Techniques • Very simple media access control • Data can only travel to/from 1 other place. No need to be complicated! Department of Information Technology Sindh U, Campus Dadu 47 Computer Communication and Networking Traveling frames • As frames traverse the network, the source and destination addresses may change. • Source MAC – gets reset to the next device (routers) as it travels • Destination MAC – gets set to the next device in line (router or pc) • Source IP – NEVER CHANGES • Destination IP – NEVER CHANGES Department of Information Technology Sindh U, Campus Dadu 48 Computer Communication and Networking PHYSICAL LAYER Department of Information Technology Sindh U, Campus Dadu 49 Computer Communication and Networking Physical layer tasks • Takes frame from data link layer • Sees the frame as bits – no structure • Encodes the bits as signals to go on the medium Department of Information Technology Sindh U, Campus Dadu 50 Computer Communication and Networking Physical layer standards define: • Physical and electrical properties of the media • Mechanical properties (materials, dimensions, pinouts) of the connectors and NICs • Bit representation by the signals (encoding) • Definition of control information signals Department of Information Technology Sindh U, Campus Dadu 51 Computer Communication and Networking Throughput and Goodput • Throughput is the actual rate of transfer of bits at a given time • Varies with amount and type of traffic, devices on the route etc. • Always lower than bandwidth • Goodput measures usable data transferred, leaving out overhead. (headers etc.) Department of Information Technology Sindh U, Campus Dadu 52 Computer Communication and Networking Media • Copper cable (twisted pair and coaxial) • Fibre optic cable • Wireless Department of Information Technology Sindh U, Campus Dadu 53 Computer Communication and Networking Coaxial cable • Central conductor • Insulation • Copper braid acting as return path for current and also as shield against interference (noise) • Outer jacket Department of Information Technology Sindh U, Campus Dadu 54 Computer Communication and Networking Connectors for coaxial cable Department of Information Technology Sindh U, Campus Dadu 55 Computer Communication and Networking Coaxial cable • Good for high frequency radio/video signals • Used for antennas/aerials • Used for cable TV and Internet connections, often now combined with fibre optic. • Formerly used in Ethernet LANs – died out as UTP was cheaper and gave higher speeds Department of Information Technology Sindh U, Campus Dadu 56 Computer Communication and Networking Unshielded twisted pair (UTP) cable • 8 wires twisted together into 4 pairs and with an outer jacket. • Wires have colour-coded plastic jackets • Commonly used for Ethernet LANs Department of Information Technology Sindh U, Campus Dadu 57 Computer Communication and Networking Straight through cable • • • • Both ends the same Connect PC to switch or hub Connect router to switch or hub Installed cabling is straight through Department of Information Technology Sindh U, Campus Dadu 58 Computer Communication and Networking Crossover cable • Wire 1 swaps with 3 • Wire 2 swaps with 6 • Connect similar devices to each other • Connect PC direct to router Department of Information Technology Sindh U, Campus Dadu 59 Computer Communication and Networking Rollover cable • Wire order completely reversed • Console connection from PC serial port to router – to configure router • Special cable or RJ45 to D9 adaptor. Department of Information Technology Sindh U, Campus Dadu 60 Computer Communication and Networking UTP cable • EIA/TIA sets standards for cables • Category 5 or higher can be used for 100Mbps Ethernet. Cat 5e can be used for Gigabit Ethernet if well installed. • We have Cat 5e. A new installation now would have Cat 6. • The number of twists per metre is carefully controlled. Department of Information Technology Sindh U, Campus Dadu 61 Computer Communication and Networking Shielded twisted pair (STP) • Wires are shielded against noise • Much more expensive than UTP • Might be used for 10 Gbps Ethernet Department of Information Technology Sindh U, Campus Dadu 62 Computer Communication and Networking Noise • Electrical signals on copper cable are subject to interference (noise) • Electromagnetic (EMI) from device such as fluorescent lights, electric motors • Radio Frequency (RFI) from radio transmissions • Crosstalk from other wires in the same cable or nearly cables Department of Information Technology Sindh U, Campus Dadu 63 Computer Communication and Networking Fibre optic cable • • • • Transmits flashes of light No RFI/EMI noise problem Several fibres in cable Paired for full duplex Department of Information Technology Sindh U, Campus Dadu 64 Computer Communication and Networking Single mode fibre optic • • • • Glass core 8 – 10 micrometres diameter Laser light source produces single ray of light Distances up to 100km Photodiodes to convert light back to electrical signals Department of Information Technology Sindh U, Campus Dadu 65 Computer Communication and Networking Multimode fibre optic • Glass core 50 – 60 micrometres diameter • LED light source produces many rays of light at different angles, travel at different speeds • Distances up to 2km, limited by dispersion • Photodiode receptors • Cheaper than single mode Department of Information Technology Sindh U, Campus Dadu 66 Computer Communication and Networking Fibre optic connectors Straight tip (ST) connector single mode Single mode lucent connector Subscriber connector (SC) multimode Multimode lucent connector Duplex multimode lucent connector (LC) Department of Information Technology Sindh U, Campus Dadu 67 Computer Communication and Networking Which cable for the LAN? UTP copper Fibre optic Max 100 m length 100km or 2km Noise problems No noise problems Within building only Within/between buildings Cheaper More expensive Easier to install Harder to install Department of Information Technology Sindh U, Campus Dadu 68 Computer Communication and Networking Thanks Department of Information Technology Sindh U, Campus Dadu