Advanced Network Chapter I: Which is very best lecture note

Advanced Network lecture note
for computer science and Engineering students

1. Advanced Computer Networks (CSE 5319) Chapter I Introduction 1

2. Contents Overview of reference models: OSI and TCP/IP Protocols in LAN, MAN and WAN 2

3. Overview of reference models: OSI and TCP/IP An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. An open system is a set of protocols that allows any two different systems to communicate regardless of their underlying architecture. The OSI model is not a protocol; it is a model for understanding and designing a network architecture that is flexible, robust, and interoperable. The OSI model is a layered framework for the design of network systems that allows communication between all types of computer systems. It consists of seven separate but related layers, each of which defines a part of the process of moving information across a network. Understanding the fundamentals of the OSI model provides a solid basis for exploring data communications. 3

4. Protocol and standards Communication between two people or two devices needs to follow some protocol. A protocol is a set of rules that governs communication. A protocol defines what is communicated, how it is communicated, and when it is communicated. The key elements of a protocol are syntax, semantics, and timing. Standards are essential in creating and maintaining an open and competitive market for equipment manufacturers and also in guaranteeing national and international interoperability of data and telecommunications technology and processes. They provide guidelines to manufacturers, vendors, government agencies, and other service providers to ensure the kind of interconnectivity necessary in today’s marketplace and in international communications. Data communication standards fall into two categories: de facto (meaning “by fact” or “by convention”) and de jure (meaning “ by law” or “by regulation”). De facto: standards that have not been approved by an organized body but have been adopted as standards. De jure: standards are those that have been legislated by an officially recognized body. 4

5. Overview of reference models cont….. 5

6. Overview of reference models cont… Organization of the Layers The seven layers can be thought of as belonging to three subgroups. Layers 1, 2, and 3:- are the network support layers; they deal with the physical aspects of moving data from one device to another (such as electrical specifications, physical connections, physical addressing, and transport timing and reliability). Layers 5, 6, and 7:- can be thought of as the user support layers; they allow interoperability among unrelated software systems. Layer 4:- links the two subgroups and ensures that what the lower layers have transmitted is in a form that the upper layers can use. Encapsulation The data part of a packet at level N is carrying the whole packet (data and overhead) from level N + 1. The concept is called encapsulation because level N is not aware what part of the encapsulated packet is data and what part is the header or trailer. For level N, the whole packet coming from level N + 1 is treated as one integral unit. 6

7. Overview of reference models cont….. TCP/IP Protocol Suite It was developed prior to the OSI model. Therefore, the layers in the TCP/IP protocol suite do not match exactly with those in the OSI model. The original TCP/IP protocol suite was defined as four software layers built upon the hardware. Today, however, TCP/IP is thought of as a five-layer model with the layers named similarly to the ones in the OSI model. 7

8. Overview of reference models cont….. Comparison between OSI and TCP/IP Protocol Suite Two layers are missing from the TCP/IP protocol suite. The application layer in the suite is usually considered to be the combination of three layers in the OSI model. Two reasons were mentioned for this decision. First, TCP/IP has more than one transport-layer protocol (connection oriented and connectionless). Second, the application layer is not only one piece of software. If some of the functionalities mentioned in the session and presentation are needed for a particular application, it can be included in the development of that piece of software. TCP/IP is a hierarchical protocol made up of interactive modules, each of which provides a specific functionality, but the modules are not necessarily interdependent. Whereas the OSI model specifies which functions belong to each of its layers, the layers of the TCP/IP protocol suite contain relatively independent protocols that can be mixed and matched, depending on the needs of the system. 8

9. Overview of reference models cont….. Types of Addressing in TCP/IP Four types of addresses are used by systems using the TCP/IP protocol: The physical address (MAC address) used to point to point data transmission (connection) in data link layer, The internetwork address (IP address) used to end to end communication in network layer, The port address an address used in transport layer for the purpose of process to process communication, and Application specific address an address used in application (mostly written in human understandable format). The physical address, also known as the link address, is the address of a node as defined by its LAN or WAN. 9

10. Protocols in LAN, MAN and WAN Local Area Network (LAN) A LAN can be used as an isolated network to connect computers in an organization for the sole purpose of sharing resources, most LANs today are also linked to a wide area network (WAN) or the Internet. The LAN market has seen several technologies such as Ethernet, token ring, token bus, Fiber Distributed Data Interface (FDDI), and Asynchronous Transfer Mode (ATM) LAN. Some of these technologies survived for a while, but Ethernet is by far the dominant technology. Ethernet has gone through a four-generation evolution during the last few decades, the main concept has remained the same. Ethernet has changed to meet the market needs and to make use of the new technologies. The IEEE has subdivided the data link layer into two sublayers: logical link control (LLC) and media access control ( MAC ) . IEEE has also created several physical layer standards for different LAN protocols. 10

11. Ethernet STANDARD ETHERNET (10MbPS) FAST ETHERNET (100 MbPS ) GIGABIT ETHERNET (1GbPS) 10-GIGABIT ETHERNET Features Connectionless and unreliable Addressing (physical address): each hosts uses a unique 48 bits mac address. Frame length: minimum 64 Bytes and maximum 1518 Bytes including frame header information Auto-negotiation Topology Half/Full duplex features 11

12. Ethernet MAC (CSMA/CD) Packet? Sense Carrier Discard Packet Send Detect Collision Jam channel b=CalcBackoff(); wait(b); attempts++; No Yes attempts < 16 attempts == 16 Carrier Sense Multiple Access/Collision Detection 12

13. Ethernet’s CSMA/CD (more) Jam Signal: make sure all other transmitters are aware of collision; 48 bits; Exponential Backoff : If deterministic delay after collision, collision will occur again in lockstep If random delay with fixed mean Few senders  needless waiting Too many senders  too many collisions Goal : adapt retransmission attempts to estimated current load heavy load: random wait will be longer 13

14. Ethernet cont…. Preamble: this field contains 7 bytes (56 bits) of alternating 0s and 1s that alert the receiving system to the coming frame and enable it to synchronize its clock if it’s out of synchronization. Start frame delimiter ( SFD ): this field (1 byte: 10101011) signals the beginning of the frame. The SFD warns the station or stations that this is the last chance for synchronization. The last 2 bits are (11)2 and alert the receiver that the next field is the destination address. Type. This field defines the upper-layer protocol. 14

15. Switched Ethernet Shared Ethernet: fixed amount of bandwidth Shared by all devices on a segment All nodes on segment belong to same collision domain Switched Ethernet: enables multiple nodes to simultaneously transmit and receive data over different logical network segments Increases effective bandwidth of network segment 15

16. Ethernet NIC The Network Interface card allows computers to communicate with each other through the network Each NIC has a 48-bit unique hexadecimal address called the MAC address A computer or device on a network can be reached by its MAC address through the NIC card An example of a MAC address: A1B2C3D4E5F6 The first 6 hex digits in the MAC address is the OUI (organizationally unique identifier), assigned by the IEEE to each manufacturer (e.g. Cisco, Intel etc ). The rest of the MAC address can be assigned in any way by the manufacturer to the individual networking devices that it manufactures 16

17. Token Ring Network Originally developed by IBM in 1970’s Still IBM’s primary LAN technology In cases of heavy traffic, the token ring network has higher throughput than Ethernet due to the deterministic (non-random) nature of the medium access Is used in applications in which delay when sending data must be predictable Is a robust network i.e. it is fault tolerant through fault management mechanisms Can support data rates of around 16 Mbps Typically uses twisted pair 17

18. IEEE 802.5 and Token Ring Proposed in 1969 and initially referred to as a Newhall ring. Token ring :: a number of stations connected by transmission links in a ring topology. Information flows in one direction along the ring from source to destination and back to source. Medium access control is provided by a small frame, the token , that circulates around the ring when all stations are idle. Only the station possessing the token is allowed to transmit at any given time. 18

19. Token Ring Operation When a station wishes to transmit, it must wait for token to pass by and seize the token. One approach: change one bit in token which transforms it into a “start-of-frame sequence” and appends frame for transmission. Second approach: station claims token by removing it from the ring. Frame circles the ring and is removed by the transmitting station. Each station interrogates passing frame, if destined for station, it copies the frame into local buffer. {Normally, there is a one bit delay as the frame passes through a station.} 19

20. Wireless-LAN (Wi-Fi) Wireless communication is one of the fastest-growing technologies. The demand for connecting devices without the use of cables is increasing everywhere. In a wireless LAN, the medium is air, the signal is generally broadcast. When hosts in a wireless LAN communicate with each other, they are sharing the same medium (multiple access). A wireless isolated LAN, called an ad hoc network in wireless LAN terminology, is a set of hosts that communicate freely with each other. There are several characteristics of wireless LANs that either do not apply to wired LANs or the existence of which is negligible and can be ignored. These are: Attenuation Interference Multipath propagation Error 20

21. Wi-Fi Cont…. Carrier sense multiple access with collision avoidance ( CSMA /CA) was invented for wireless networks. Collisions are avoided through the use of CSMA /CA’s three strategies: the interframe space, the contention window, and acknowledgments. 21

22. Wi-Fi cont….. Interframe Space (IFS): every host sent a carrier signal to detect the line is free or not before transmitting a data. When the host detects an idle channel is found, the station does not send immediately. Instead, it waits for a period of time called IFS . Even though the channel may appear idle when it is sensed, a distant station may have already started transmitting. The contention window is an amount of time divided into slots. A station that is ready to send chooses a random number of slots as its wait time. Acknowledgment. With all these precautions, there still may be a collision resulting in destroyed data. In addition, the data may be corrupted during the transmission. The positive acknowledgment and the time-out timer can help guarantee that the receiver has received the frame. 22

23. Wireless Networks: 802.11 Notable standards: 802.11b, 802.11a, 802.11g Share many characteristics e.g., Half-duplex signaling Access Method: MAC services append 48-bit physical addresses to frames to identify source and destination Use Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to access shared medium Minimizes potential for collisions ACK packets used to verify every transmission 23

24. Wireless Networks: 802.11 (continued) Access Method (continued): Request to Send/Clear to Send (RTS/CTS) protocol enables source node to issue RTS signal to an access point Request exclusive opportunity to transmit Association: Communication between station and access point enabling station to connect to network Scanning: station surveys surroundings for access point(s) Active scanning: station transmits a probe on all available channels within frequency range Passive scanning: station listens on all channels within frequency range for beacon frame issued from an access point Contains info required to associate node with access point [e.g., Service Set Identifier (SSID)] WLANs can have multiple access points Reassociation : station changes access points 24

25. Wireless Networks: 802.11 (continued) Frames: For each function, 802.11 specifies frame type at MAC sublayer Management frames involved in association and re-association Duration/Connection ID: indicates the time (in microseconds) the channel will be allocated for successful transmission of a MAC frame. Control frames related to medium access and data delivery (management, control and data) Addresses ( Receiver Address (RA), Transmitter Address (TA), Basic Service Set Identifier (BSSID), Destination Address (DA) and Source Address (SA) ) Basic 802.11 MAC frame format 25

26. Characteristics of wireless LANs Advantages Very flexible within reception area Ad-hoc networks do not need planning No wiring difficulties (e.g. historic buildings, firewalls) More robust against disasters like, e.g., earthquakes, fire Disadvantages low bandwidth compared to wired networks many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE 802.11) many national restrictions for wireless, long time to establish global solutions 26

27. Design Goals of wireless LANs global, seamless operation low power for battery use no special permissions or licenses needed to use the LAN robust transmission technology easy to use for everyone, simple management protection of investment in wired networks security, privacy, and safety (low radiation) transparency concerning applications and higher layer protocols, but also location awareness if necessary 27

28. Categories of Wireless Networks Base Station :: all communication through an access point {note hub topology}. Other nodes can be fixed or mobile. Infrastructure Wireless :: base station network is connected to the wired Internet. Ad hoc Wireless :: wireless nodes communicate directly with one another. MANETs (Mobile Ad Hoc Networks) :: ad hoc nodes are mobile. Wireless LANs Wireless WANs 28

29. The 802.11 Wi-Fi Protocol Summary Protocol Frequency Signal Year Max. Data Rate Legacy 802.11 2.4 GHz FHSS / DSSS 1997 2 Mbps 802.11a 5 GHz OFDM 1999 54 Mbps 802.11b 2.4 GHz HR-DSSS 1999 11 Mbps 802.11g 2.4 GHz OFDM 2003 54 Mbps 802.11n 5 GHz OFDM-MIMO 2010 600 Mbps 802.11ac 5 GHz 256 QAM 2014 1.3 G bps 29

30. FDDI (Fiber Distributed Data Interface) FDDI is a standard developed by the American National Standards Institute (ANSI) for transmitting data on optical fibers Supports transmission rates of up to 200 Mbps Uses a dual ring First ring used to carry data at 100 Mbps Second ring used for primary backup in case first ring fails If no backup is needed, second ring can also carry data, increasing the data rate up to 200 Mbps Supports up to 1000 nodes Has a range of up to 200 km 30

31. Fiber Distributed Data Interface (FDDI) FDDI uses a ring topology of multimode or single mode optical fiber transmission links operating at 100 Mbps to span up to 200 kms and permits up to 500 stations. Employs dual counter-rotating rings. 16 and 48-bit addresses are allowed. In FDDI, token is absorbed by station and released as soon as it completes the frame transmission {release after transmission}. 31

32. FDDI Data Encoding Instead each ring interface has its own local clock . Outgoing data is transmitted using this clock. Data is encoded using a 4B/5B encoder. For each four bits of data transmitted, a corresponding 5-bit codeword is generated by the encoder. There is a maximum of two consecutive zero bits in each symbol. The symbols are then shifted out through a NRZI encoder which produces a signal transition whenever a 1 bit is being transmitted and no transition when a 0 bit is transmitted  guarantees a signal transition at least every two bits. Local clock is 125MHz. This yields 100 Mbps (80% due to 4B/5B). data is received using a clock that is frequency and phase locked to the transitions in the incoming bit stream. 32

33. Differences between 802.5 and FDDI Token Ring Shielded twisted pair 4, 16 Mbps No reliability specified Differential Manchester Centralized clock Priority and Reservation bits New token after receive FDDI Optical Fiber 100 Mbps Reliability specified (dual ring) 4B/5B encoding Distributed clocking Timed Token Rotation Time New token after transmit 33

34. WiMAX The Worldwide Interoperability for Microwave Access (WiMAX): provides the “last mile” broadband wireless access. WiMAX provides two types of services to subscribers: fixed and mobile. 34

35. CELLULAR TELEPHONY Cellular telephony is designed to provide communications between two mobile stations ( MSs ), or between mobile station and stationary unit. A service provider must be able to locate and track a caller, assign a channel to the call, and transfer the channel from base station to base station as the caller moves out of range. Operation: Frequency-Reuse Principle Transmitting Receiving Handoff Roaming Variations First generation (1G) Second generation (2G) Third generation (3G) Fourth generation (4G), and Fifth generation (5G) 35

36. WAN Protocol For transmission of data beyond a local area, communication is typically achieved by transmitting data from source to destination through a network of intermediate switching devices. The switching nodes are not concerned with the content of the data; rather, their purpose is to provide a switching (forwarding/routing) facility that will move the data from node to node until they reach their destination. Two different technologies are used in wide area switched networks: circuit switching and packet switching. These two technologies differ in the way the nodes switch information from one link to another on the way from source to destination. 36

37. Asynchronous Transfer Mode (ATM) Asynchronous transfer mode is a switching and multiplexing technology that employs small, fixed-length packets called cells . A fixed-size packet makes switching and multiplexing efficient and a small cell size was chosen to support delay-intolerant interactive voice service. ATM is a connection-oriented packet-switching technology that was designed to provide the performance of a circuit-switching network and the flexibility and efficiency of a packet-switching network. ATM was intended to provide a unified networking standard for both circuit-switched and packet-switched traffic, and to support data, voice, and video with appropriate QoS mechanisms. ATM is used by ISP to implement wide area networks. Many DSL implementations use ATM over the basic DSL hardware for multiplexing and switching. 37

38. ATM cont….. ATM Logical Connections Virtual channel connections (VCCs) is analogous to a virtual circuit; it is the basic unit of switching in an ATM network. A VCC is set up between two end users through the network, and a variable-rate, full-duplex flow of fixed-size cells is exchanged over the connection. VCCs are also used for user–network exchange (control signaling) and network–network exchange (network management and routing). A virtual path connection (VPC) is a bundle of VCCs that have the same endpoints. Thus, all of the cells flowing over all of the VCCs in a single VPC are switched together. 38

39. ATM cont…. Advantages of using a virtual paths: Simplified network architecture Increased network performance and reliability Reduced processing and short connection setup time Enhanced network services Virtual Path/Virtual Channel Characteristics ITU-T recommend the following as characteristics: Quality of service ( QoS ) Switched and semipermanent virtual channel connections Cell sequence integrity Traffic parameter negotiation and usage monitoring Virtual channel identifier restriction within a VPC (unique for Virtual Path) 39

40. SONET / (SDH) These are a standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from LEDs. SDH/SONET are placed at the bottom of the protocol stack in the physical layer, along with the very fiber upon which it transmits its signal. The fundamental principle of the SDH protocol is time-division multiplexing (TDM). TDM ensures that there is a constant stream of data travelling through the network and taking advantage of the fiber bandwidth available. Lower bit-rate streams of information are combined, or multiplexed, up into higher bit-rate streams at the native bit rate of the SDH system. The fundamental SDH frame is known as STM1 (synchronous transport module); its SONET is OC3 (optical container). Each provides a bit rate of 155 Mbps with a total frame size of around 20 kbps. 40

41. SONET/SDH cont…. Each frame is physically transmitted through the fiber row by row, each row from left to right. An STM1 frame is formed by nine rows and 270 columns of bytes of information. The first nine columns is SOH, which provides a comprehensive range of facilities such as error monitoring, network management, and automatic switching between fiber links should one be unavailable. The remainder of the frame is termed a VC. This contains the data – except for the first column, which is the POH, whose function it is to monitor the quality of the link and indicate the type of data payload it is carrying. 41

42. Point to Point Protocol (PPP) It is a layer 2 communications protocol between two routers directly without any host or any other networking in between. It can provide connection authentication, transmission encryption, and compression. PPP is commonly used as a data link layer protocol for connection over synchronous and asynchronous circuits. The only requirement for PPP is that the circuit provided be duplex. PPP is used over many types of physical networks including serial cable, phone line, trunk line, cellular telephone, specialized radio links, and fiber optic links such as SONET. ISPs have used PPP for customer access to the Internet, since IP packets cannot be transmitted over a modem line on their own, without some data link protocol. Two derivatives of PPP, Point-to-Point Protocol over Ethernet ( PPPoE ) and Point-to-Point Protocol over ATM ( PPPoA ), are used most commonly by ISPs to establish a digital subscriber line (DSL) Internet service connection with customers. 42

43. PPP cont…. PPP is a layered protocol that has three components: An encapsulation component that is used to transmit datagrams over the specified physical layer. A Link Control Protocol (LCP) to establish, configure, and test the link as well as negotiate settings, options and the use of features. One or more Network Control Protocols (NCP) used to negotiate optional configuration parameters and facilities for the network layer. There is one NCP for each higher-layer protocol supported by PPP. PPP detects looped links using a feature involving magic numbers. When the node sends PPP LCP messages, these messages may include a magic number. If a line is looped, the node receives an LCP message with its own magic number, instead of getting a message with the peer's magic number. PPP may include the following LCP options; Authentication, Compression , Error detection, and Multipath PPP. 43

44. SATELLITE NETWORKS A satellite network is a combination of nodes, some of which are satellites, that provides communication from one point on the Earth to another. Satellite networks are like cellular networks in that they divide the planet into cells. Satellites can provide transmission capability to and from any location on Earth. This advantage makes high-quality communication available to undeveloped parts of the world without requiring a huge investment in ground-based infrastructure. Issues related to the operation of satellites: Orbits Footprint : it is the satellite signal coverage area. Frequency Bands for Satellite Communication (1.5 GHz-30GHz) : for uplink and downlink communication satellites uses different frequencies. 44