Unit 1: Physical Layer PDF

Unit 1: Physical Layer Taxonomy Computer Network Taxonomy: Transmission technology and Scale 1. Transmission technology: broadcast links & point-to-point links Point-to-point links connect individual pairs of m/c. Often multiple routes, of different lengths, are possible, so finding g...

Unit 1: Physical Layer Taxonomy Computer Network Taxonomy: Transmission technology and Scale 1. Transmission technology: broadcast links & point-to-point links Point-to-point links connect individual pairs of m/c. Often multiple routes, of different lengths, are possible, so finding good ones is important in p-t-p networks. P-t-p transmission with exactly one sender and exactly one receiver is called as unicasting. In contrast, on a broadcast network, the commn ch is shared by all the m/c on the n/w; pkts sent by any m/c are received by all the others. Address field.  A wireless network is a common example of a broadcast link. Some broadcast systems also support transmission to a subset of m/c, which is known as multicasting. 2. Scale: Distance is important as a classification metric bcoz different technologies are used as different scales. TYPES OF NETWORK PAN (Personal Area Network) : ex: Bluetooth, RFID LAN (Local Area Network): ex: bldg, home, office etc. Access point, wireless router or base station. Wireless LAN (IEEE 802.11 known as WiFi) speed 11-100Mbps The topology of many wired LANs is build from p- t-p links (Ethernet IEEE 802.3)  MAN (Metropolitan Area Network): covers city; ex: Cable WiMAX (IEEE 802.16) High speed wireless internet access. WAN (Wide Area Network): Country/continent; A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. PAN WAN WAN Infrastructure and Ad- Hoc Mode Network Architectures The Client-Server network model focuses on information sharing whereas, the Peer-to-Peer network model focuses on connectivity to the remote computers. The main difference between the Client-Server and Peer-to-Peer network model is that in Client- Server model, the data management is centralised whereas, in Peer-to-Peer each user has its own data and applications Client-Server The Client-Server network model is widely used network model. Here, Server is a powerful system that stores the data or information in it. On the other hands, the Client is the machine which let the users access the data on the remote server. The system administrator manages the data on the server. The client machines and the server are connected through a network. It allows the clients to access data even if the client machine and server are far apart from each other. In Client-Server model, the client process on the client machine sends the request to the server process on the server machine. When the server receives the client request, it lookouts for the requested data and send it back with the reply. As all the services are provided by a centralized server, there may be chances of server getting bottlenecked, slowing down the efficiency of the system. Peer-to-Peer Unlike Client-Server, the Peer-to-Peer model does not distinguish between client and server instead each node can either be a client or a server depending on the whether the node is requesting or providing the services. Each node is considered as a peer. To become a part of peer-to-peer, a node must initially join the network. After joining it must start to provide services to and must request the services from other nodes in the peer-to-peer system. There are two ways to know which node provides which services; they are as follow: When a node enters the peer-to-peer system, it must register the services it will be providing, into a centralized lookup service on the network. When a node desires for any specific service it must contact centralized lookup services to check out which node will provide the desired services. Rest of the communication is done by the desiring node and the service providing node. A node desiring for the specific services must broadcast the request for services to all other nodes in the peer-to-peer system. The node providing the requested service will respond to the node making the request. Peer-to-Peer network has the advantage over client-server that the server is not bottlenecked as the services are provided by the several nodes distributed in a peer-to-peer system.  BASIS FOR CLIENT-SERVER PEER-TO-PEER COMAPAISON Basic There is a specific Clients and server server and specific are not clients connected to distinguished; each the server. node act as client and server. Service The client request Each node can for service and request for services server respond with and can also provide the service. the services. Focus Sharing the Connectivity. information. Data The data is stored in Each peer has its a centralized server. own data. Server When several clients As the services are request for the provided by several services servers distributed simultaneously, a in the peer-to-peer server can get system, a server in bottlenecked. not bottlenecked. Expense The client-server are Peer-to-peer are less Standardized Protocol 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, still useful for modeling / conceptualizing The OSI Reference Model Principles for the seven layers Layers created for different abstractions Each layer performs well-defined function Function of layer chosen with definition of international standard protocols in mind Minimize information flow across interfaces between boundaries Number of layers optimum ISO is the organization; OSI is the model.  Physical Layer Bit (0 or 1) Bi-direction Connection (estb, tear down) Connectors Voltage Pin assignments e.g. RS-232 Data Link Layer Access to media Provides reliable transfer of data across media. Flow control. Framing Addressing Error control e.g. HDLC Network Layer Controlling Subnet Routing Addresses Resolution Congestion Control Mgt. Determines Quality of Service Concerned with type of switching used Example: X.25 standard for network access procedures on packet-switching networks Transport Layer End-to-end connection reliability Establishes, maintains, and terminates virtual circuits. / multiple network connections Error Control Flow Control Congestion Control Fragmentation and reassembly Session Layer Establishes, manages and terminates sessions between applications Manages log-ons, password exchange, log-offs Sessions offer various services, including dialog control, token management and synchronization. Presentation Layer Data representation Format of data Ensure data is readable by receiving system Negotiates data transfer syntax for application layer Examples File conversion from ASCII to EBDIC Application Layer Provides network services to application processes ( E- mail, file transfer, terminal emulation ) Summary of OSI Layers A private internet  Communication at the physical layer Legend Source Destination A R1 R3 R4 B Physical Physical layer layer Link 1 Link 3 Link 5 Link 6 011... 101 01 1... 10 1 011... 101 011... 101 Note The unit of communication at the physical layer is a bit.  Communication at the data link layer Legend Source Destination D Data H Header A R1 R3 R4 B Data link Data link Physical Physical Link 1 Link 3 Link 5 Link 6 D2 H2 Frame D2 ame Fr H2 D2 H2 D2 H2 Frame Frame Note The unit of communication at the data link layer is a frame.  Communication at the network layer Legend Source Destination D Data H Header A R1 R3 R4 B Network Network Data link Data link Physical Physical D3 H3 Datagram D3 H3 Datagram Note The unit of communication at the network layer is a datagram.  Communication at transport layer A Legend Source Destination D Data H Header B Transport Transport R1 R3 R4 Network Network Data link Data link Physical Physical D4 H4 Segment D4 H4 Segment Note The unit of communication at the transport layer is a segment, user datagram, or a packet, depending on the specific protocol used in this layer. TCP/IP Transmission control Protocol/Internet Protocol Developed by DARPA No official protocol standard Can identify four layers Application Host-to-Host (transport) Internet Network Access  Host to Host Internet Network Access Network Topology Network topology defines the manner in which the nodes are geometrically arranged and connected to one another. Types of topology: Mesh Star Bus Ring Mesh Every node has a dedicated p-t-p link to all the nodes within network. The link shares traffic Between the two nodes only. Mesh has n(n-1)/2 physical channels to link n devices. Advantages Disadvantages Dedicated link Large amount of cable (optimized rate and min and i/o ports traffic) Privacy and security Redundant link increases cost No Single point of failure Difficult in installation Fault identification easy Difficult to re-config Star Consists of no of devices connected by p-t-p links to central hub. If a node wants to send data to another nodes, it sends the data to central hub, which then relays the data to desired node. Advantages Disadvantages Needs one i/o port and link Hub failure, entire n/w fails Easy to install and configure Cost of installation is high Link failure, doesn’t affect n/w Difficult in installationPerformance is based on the hub that is it depends on its capacity Fault identification easy Easy to modify (add new node without disturbing the n/w)  Bus Uses multipoint cabling i.e multiple devices are connected by means of connectors or drop cables. One long cable acts as a backbone to link all the nodes. Advantages Disadvantages to install Easy When a device sends data, its traffic Heavy received by all but -> slow accepted by once using address. Less cables Difficult reconnection and Bus topology requires termination and cannot be troubleshooting No ofleft un-terminated. i/o ports required is less. Difficult to add new node Backbone cable can be extended Needs terminators by using repeater Cost of n/w is low Single point of failure (backbone cable)  Ring Each device is connected by a dedicated p-t-p Connection to its adjacent device. Signal travels in one direction. Advantages Disadvantages Easy to install. Max ring length and no of devices is limited. Link failure is easy If one node fails, n/w fails. Transmitting network is not Adding or deleting the affected by high traffic or by computers disturbs the network adding more nodes, as only the activity. nodes having tokens can transmit data. Design issues for Layers  Reliability Security  Error detection  Confidentiality  Error correction  Authentication  Routing  Integrity  Evolution of network  Protocol layering  Addressing or naming  Internetworking  Scale  Resource allocation  Multiplexing  Flow control  Congestion control  Real-time (QoS) Transmission Mediums Cat- Length Speed Mhz Applicatio n Cat-5 100m 100Mbps 100 Ethernet, Fast Ethernet, Token Ring Cat- 100m 1Gbps 100 Ethernet, 5e(enhanced) Fast Ethernet, Gigabit Ethernet Cat-6 100m 10Gpbs 250 Gigabit Ethernet, 10G Ethernet (55m) Cat- 100m 10Gbps 500 Gigabit 6a(Augmented Ethernet, ) 10G Network Devices Repeater Hub Bridge Switch Router Brouter Wireless Communication Narrow Band Radio Signal o Narrow band of freq, i.e 98.3MHz FM o Requires lots of power o Easy to intercept, jam and interfere Spread Spectrum Radio Signal o Broad BW o Low power consumption o More secure SPREAD SPECTRUM In wireless applications, stations must be able to share the medium without interception by an eavesdropper and without being subject to jamming from a malicious intruder. To achieve these goals, spread spectrum techniques add redundancy; they spread the org spectrum needed for each station. If req. BW for each station is B, spread spectrum expands it to Bss. [Bss>>B]. Spread Spectrum achieves its goals through two principles: The BW allocated to each station needs to be, by far, larger than what is needed. [Redundancy] The expanding of the original BW B to Bss must be done by a process that is independent  After the signal is created by the source, the spreading process uses a spreading code and spreads the BW. The spreading code is a series of numbers that look random, but are actually a pattern. Use of SS -military -Cordless phones -GPS -Wireless LANs Frequency Hopping (FHSS) Uses M diff carrier freq that are modulated by the source signal. At one moment, signal modulates one carrier freq; at the next, another. The BW occupied by a source after spreading is Bfhss >> B. Direct Sequence (DSSS) In DSSS, each data bit is replaced by n bits using spreading code. Each bit is assigned a code of n bits,(chips), where the chip rate is n times that of data bit. In wireless LAN, Bakers sequence is used, where n=11. The pattern used is 10110111000. FHSS FHSS devices will transmit signal by changing or hopping from one freg to another in a random but predictable seq. Channels: Specific hop pattern Dwell time: transmits on a freq for a specific amount of time Hop time: a very small amount of time during a freq change in which the radio is not transmitting. To be 802.11 compliant FHSS wireless LAN devices must operate in the 2.4GHz-2.5GHz Band. DSSS Channel: each ch is a contiguous band of freqs 22 MHz wide -Ch1 operates from 2.401GHz to 2.423GHz -Chs are displayed at their center point 2.412GHz +-11  Old roll numbers 66,71,47,21,52,65,68,67,35,16,18,22,04,64,51,62, 58,50,48,73,56,8,11,9,19,33,36,37,07,14,55,63,75 ,72