ELC 537 Communication Networks

Transcription

1 Modern Academy for Engineering and Technology Electronics Engineering and Communication Technology Dpt. ELC 537 Communication Networks Prepared by: Dr. Nelly Muhammad Hussein

2 Sections & Objectives Principles of Networking Explain components and types of computer networks. Networking Standards Explain the purpose and characteristics of networking standards. Physical Components of a Network Explain the purpose of physical components of a network. Basic Networking Concepts and Technologies Configure network connectivity between PCs.

3 Principles of Networking

4 Principles of Networking Computer Networks Computer Network Devices and Components Host Devices any device that sends and receives information on the network (computer, printer, etc.) Intermediary Devices exist in between host devices Media component over which the message travels from source to destination Can you name each device or component shown here?

5 Principles of Networking Types of Networks Major types of networks include: Local Area Networks (LANs) Wireless Local Area Networks (WLANs) Personal Area Networks (PANs) Metropolitan Area Networks (MANs) Wide Area Networks (WANs) Peer-to-Peer Networks No dedicated servers Each computer decides which resources to share No central administration or security Client-Server Networks Server with software installed for client access Resources controlled by centralized administrator

6 Networking Standards

7 Networking Standards Reference Models Organizations, such as leee, IETF, and ISO, develop open standards for networks so that any client running any operating system can access network resources. The OSI model and the TCP/IP model are both reference models used to describe the data communication process. As application data is passed down through the layers, protocol information is added at each level. This is known as the encapsulation process.

8 Networking Standards Wired and Wireless Standards When Ethernet operates in half-duplex, the IEEE standard specifies that a network implement the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access control method. The standard also specifies cable types for Ethernet including: 10Base-T 100Base-TX 1000Base-T 10GBase-T The IEEE standard specifies that wireless LANs use Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). WLAN standards include a, b, g, n, and ac When configuring an WLAN, use the strongest encryption available. Since 2006, the strongest encryption has been WPA2.

9 Physical Components of a Network

10 Physical Components of a Network Network Devices Modems convert a computer s digital data into a format that can be transmitted on the ISP s network. Switches microsegment LANs by sending data only to the computer that needs it. Wireless access points (APs) connect wireless devices. Routers use IP addresses to forward traffic to other networks. In a home or small office, a route often includes a switch, a firewall, and an AP.

11 Physical Components of a Network Cables and Connectors Coaxial and twisted-pair cables use electrical signals over copper to transmit data. Fiber-optic cables use light signals to transmit data. These cables differ in bandwidth, size, and cost. There are several types of coaxial cable: 10Base5 (thicknet), 10Base2 (thinnet), RG-59 (cable TV), RG-6 (better than RG-59) Twisted-pair cables are terminated with an RJ-45 connector. Twisted-pair comes in two types: Unshielded Twisted-Pair (UTP) Shielded Twisted-Pair (STP) Fiber-optic cables are broadly classified into two types: Single-mode fiber (SMF) - Uses lasers to send a single ray of light that can travel hundreds of kilometers. Multimode fiber (MMF) - Uses LEDs to send multiple light signals that can travel up to 550 meters.

12 Physical Components of a Network Cables and Connectors Twisted-pair is the most popular type of cabling used in LANs today. There are two different twisted-pair wiring schemes: called T568A and T568B. Each wiring scheme defines the pinout, or order of wire connections, on the end of the cable. Two types of cables can be created: a straight-through cable and a crossover cable. A straight-through cable is the most common cable type. The wiring scheme is the same on both sides. A crossover cable uses both wiring schemes. T568A on one end of the cable and T568B on the other end of the same cable.

13 Basic Networking Concepts and Technologies

14 Basic Networking Concepts and Technologies Networked Equipment Addressing The MAC address is hard coded onto the network interface card (NIC) by the manufacturer. The MAC address is 48 bits represented in hexadecimal The Internet Protocol (IP) address is assigned by network administrators based on the location within the network. Two versions of Internet Protocol (IP) Addressing: IPv4: 32-bit represented in dotted-decimal IPv6: 128-bit represented in hexadecimal

15 Basic Networking Concepts and Technologies Networked Equipment Addressing Host devices need both addresses to communicate on the network. MAC addresses do not change when devices move from one network to another. IP addresses change because they are based on where the device is in the network.

16 Basic Networking Concepts and Technologies Networked Equipment Addressing An IPv4 address is composed of two parts. The first part identifies the network. The second part identifies a host on that network. Computers and routers use the subnet mask to calculate the network portion of the destination IPv4 address. A one bit in the subnet mask means that bit is part of the network portion. So the first 24 bits of the address are network bits. The last 8 bits are host bits.

17 Basic Networking Concepts and Technologies Networked Equipment Addressing Two rules help reduce the number of digits needed to represent an IPv6 address. Rule 1 - Omit Leading 0s Rule 2 Omit All 0 Segments

18 Basic Networking Concepts and Technologies Transport Layer Protocols The two protocols that operate at the transport layer are Transport Control Protocol (TCP) and User Datagram Protocol (UDP) TCP is considered reliable, because it ensures that all of the data arrives at the destination. UDP does not provide for any reliability.

19 Basic Networking Concepts and Technologies Transport Layer Protocols TCP and UDP use a source and destination port number to keep track of application conversations. The destination port number is associated with the destination application on the remote device. The source port number is dynamically generated by the sending device.

20 What is a Protocol? Allows entities (i.e. application programs) from different systems to communicate Shared conventions for communicating information are called protocols Includes syntax, semantics, and timing

21 Why Use Protocol Architecture? Data communications requires complex procedures Sender identifies data path/receiver Systems negotiate preparedness Applications negotiate preparedness Translation of file formats For all tasks to occur, high level of cooperation is required

22 Modular Approach Breaks complex tasks into subtasks Each module handles specific subset of tasks Communication occurs between different modules on the same system between similar modules on different systems

23 Advantages of Modularity Easier application development Network can change without all programs being modified

24 Three-Layer Model Distributed data communications involves three primary components: Networks Computers Applications Three corresponding layers Network access layer Transport layer Application layer

25 Network Access Layer Concerned with exchange of data between computer and network Includes addressing, routing, prioritizing, etc Different networks require different software at this layer Example: X.25 standard for network access procedures on packetswitching networks

26 Transport Layer Concerned with reliable transfer of information between applications Independent of the nature of the application Includes aspects like flow control and error checking

27 Application Layer Logic needed to support various applications Each type of application (file transfer, remote access) requires different software on this layer

28 Addressing Each computer on a network requires a unique address on that network Each application requires a unique address within the computer to allow support for multiple applications (service access points, or SAP)

29 Data Transmission Application layer creates data block Transport layer appends header to create PDU (protocol data unit) Destination SAP, Sequence #, Error-Detection Code Network layer appends another header Destination computer, facilities (e.g. priority )

30 Simplified Architecture

31 Protocol Architecture Operation

32 Standardized Protocol Architectures Vendors like standards because they make their products more marketable Customers like standards because they enable products from different vendors to interoperate Two protocol standards are well-known: TCP/IP: widely implemented OSI: less used, but widely known and still useful for modeling/conceptualizing

33 TCP/IP Transmission Control Protocol/Internet Protocol Developed by DARPA No official protocol standard Identifies 5 Layers Application Host-to-Host (transport) Internet Network Access Physical

34 TCP/IP Physical Layer Physical interface between a DTE (e.g. computer or terminal) and a transmission medium Specifies: Characteristics of medium Nature of signals Data rate

35 TCP/IP Network Access Exchange of data between systems on a shared network Utilizes address of host and destination Can also prioritize transmission Software at this layer depends on network (e.g. X.25 vs. Ethernet) Segregation means that no other software needs to be concerned about net specifics

36 TCP/IP Internet Layer An Internet is an interconnection of two or more networks Internet layer handles tasks similar to network access layer, but between networks rather than between nodes on a network Uses IP for addressing and routing across networks Implemented in workstations and routers

37 TCP/IP Transport Layer Also called host-to-host layer Reliable exchange of data between applications Uses TCP protocols for transmission

38 TCP/IP Application Layer Logic needed to support variety of applications Separate module supports each type of application (e.g. file transfer)

39 TCP & UDP Most TCP/IP applications use TCP for transport layer TCP provides a connection (logical association) between two entities to regulate flow check errors UDP (User Datagram Protocol) does not maintain a connection, and therefore does not guarantee delivery, preserve sequences, or protect against duplication

40 IP and IPv6 IP provides for 32-bit source and destination addresses IPv6 (1996 standard) provides for 128-bit addresses Migraqtion to IPv6 will be a very slow process

41 TCP/IP Applications SMTP (Simple Mail Transfer Protocol) Basic facility, transferring messages among hosts FTP (File Transfer Protocol) Sends files from one system to another on user command Telnet Remote login capability, allowing a user to emulate a terminal on the remote system

42 Internetworking Interconnected networks, usually implies TCP/IP Can appear to users as a single large network The global Internet is the largest example, but intranets and extranets are also examples

43 Routers Equipment used to interconnect independent networks Several essential functions Provide a link between networks Provide routing and delivery of data between processes on systems from different networks Provide the above functions without requiring modification of the attached networks

44 Router Issues Addressing schemes Maximum packet size Interfaces Reliability

45 TCP Segment (TCP PDU) Source port (16 bits) Destination port (16 bits) Sequence number (32 bits) Acknowledgment number (32 bits) Data Offset (4 bits) Reserved (6 bits) Window (16 bits) Checksum (16 bits) Urgent Pointer (16 bits) Options (variable) Flags (6 bits) : URG, ACK, PSH, RST, SYN, FIN

46 IPv4 Header Version (4 bits) Internet 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 (variable) Padding (variable)

47 Why Study OSI? Still an excellent model for conceptualizing and understanding protocol architectures Key points: Modular Hierarchical Boundaries between layers=interfaces

48 OSI Open Systems Interconnection Developed by ISO Contains seven layers (see page 358) Application Presentation Session Transport Network Data Link Physical

49 OSI Lower Layers Physical Data Link Network

50 OSI Physical Layer Responsible for transmission of bits Always implemented through hardware Encompasses mechanical, electrical, and functional interfaces e.g. RS-232

51 OSI Data Link Layer Responsible for error-free, reliable transmission of data Flow control, error correction e.g. HDLC

52 OSI Network Layer Responsible for routing of messages through network Concerned with type of switching used (circuit v. packet) Handles routing between networks, as well as through packetswitching networks

53 OSI Upper Layers Transport Session Presentation Application

54 OSI Transport Layer Isolates messages from lower and upper layers Breaks down message size Monitors quality of communications channel Selects most efficient communication service necessary for a given transmission

55 OSI Session Layer Establishes logical connections between systems Manages log-ons, password exchange, log-offs Terminates connection at end of session

56 OSI Presentation Layer Provides format and code conversion services Examples File conversion from ASCII to EBDIC Invoking character sequences to generate bold, italics, etc on a printer

57 OSI Application Layer Provides access to network for end-user User s capabilities are determined by what items are available on this layer

58 TCP/IP - OSI Comparison

59 Switched Communications Networks Long distance transmission between stations (called end devices ) is typically done over a network of switching nodes. Switching nodes do not concern with content of data. Their purpose is to provide a switching facility that will move the data from node to node until they reach their destination (the end device). A collection of nodes and connections forms a communications network. In a switched communications network, data entering the network from a station are routed to the destination by being switched from node to node. 59

60 Simple Switching Network 60

61 Switching Nodes Nodes may connect to other nodes, or to some stations. Network is usually partially connected However, some redundant connections are desirable for reliability Two different switching technologies Circuit switching Packet switching 61

62 Circuit Switching Circuit switching: There is a dedicated communication path between two stations (end-to-end) The path is a connected sequence of links between network nodes. On each physical link, a logical channel is dedicated to the connection. Communication via circuit switching has three phases: Circuit establishment (link by link) Routing & resource allocation (FDM or TDM) Data transfer Circuit disconnect Deallocate the dedicated resources The switches must know how to find the route to the destination and how to allocate bandwidth (channel) to establish a connection. 62

63 Circuit Switching Properties Inefficiency Channel capacity is dedicated for the whole duration of a connection If no data, capacity is wasted Delay Long initial delay: circuit establishment takes time Low data delay: after the circuit establishment, information is transmitted at a fixed data rate with no delay other than the propagation delay. The delay at each node is negligible. Developed for voice traffic (public telephone network) but can also applied to data traffic. For voice connections, the resulting circuit will enjoy a high percentage of utilization because most of the time one party or the other is talking. But how about data connections? 63

64 Public Circuit Switched Network Subscribers: the devices that attach to the network. Subscriber loop: the link between the subscriber and the network. Exchanges: the switching centers in the network. End office: the switching center that directly supports subscribers. Trunks: the branches between exchanges. They carry multiple voice-frequency circuits using either FDM or synchronous TDM. 64

65 Packet Switching Principles Problem of circuit switching designed for voice service Resources dedicated to a particular call For data transmission, much of the time the connection is idle (say, web browsing) Data rate is fixed Both ends must operate at the same rate during the entire period of connection Packet switching is designed to address these problems. 65

66 Basic Operation Data are transmitted in short packets Typically at the order of 1000 bytes Longer messages are split into series of packets Each packet contains a portion of user data plus some control info Control info contains at least Routing (addressing) info, so as to be routed to the intended destination Recall the content of an IP header! store and forward On each switching node, packets are received, stored briefly (buffered) and passed on to the next node. 66

67 Use of Packets 67

68 Advantages of Packet Switching Line efficiency Single node-to-node link can be dynamically shared by many packets over time Packets are queued up and transmitted as fast as possible Data rate conversion Each station connects to the local node at its own speed In circuit-switching, a connection could be blocked if there lacks free resources. On a packet-switching network, even with heavy traffic, packets are still accepted, by delivery delay increases. Priorities can be used On each node, packets with higher priority can be forwarded first. They will experience less delay than lower-priority packets. 68

69 Packet Switching Technique A station breaks long message into packets Packets are sent out to the network sequentially, one at a time How will the network handle this stream of packets as it attempts to route them through the network and deliver them to the intended destination? Two approaches Datagram approach Virtual circuit approach 69

70 Datagram Each packet is treated independently, with no reference to packets that have gone before. Each node chooses the next node on a packet s path. Packets can take any possible route. Packets may arrive at the receiver out of order. Packets may go missing. It is up to the receiver to re-order packets and recover from missing packets. Example: Internet 70

71 Datagram 71

72 Virtual Circuit In virtual circuit, a preplanned route is established before any packets are sent, then all packets follow the same route. Each packet contains a virtual circuit identifier instead of destination address, and each node on the preestablished route knows where to forward such packets. The node need not make a routing decision for each packet. Example: X.25, Frame Relay, ATM 72

73 Virtual Circuit A route between stations is set up prior to data transfer. All the data packets then follow the same route. But there is no dedicated resources reserved for the virtual circuit! Packets need to be stored-and-forwarded. 73

74 Virtual Circuits v Datagram Virtual circuits Network can provide sequencing (packets arrive at the same order) and error control (retransmission between two nodes). Packets are forwarded more quickly Based on the virtual circuit identifier No routing decisions to make Less reliable If a node fails, all virtual circuits that pass through that node fail. Datagram No call setup phase Good for bursty data, such as Web applications More flexible If a node fails, packets may find an alternate route Routing can be used to avoid congested parts of the network 74

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