The document provides an overview of wireless networks and wireless communication technologies. It discusses the key elements of a wireless network including wireless hosts, base stations, wireless links, infrastructure and ad hoc modes. It also covers wireless link characteristics such as signal attenuation, interference and multipath propagation. Finally, it introduces common wireless network standards and protocols including IEEE 802.11 wireless LANs, wireless network characteristics such as the hidden terminal problem, and wireless multiple access protocols.
IPv6 addresses are 128-bit addresses used to identify nodes in an IPv6 network. They are conventionally written in hexadecimal colon notation, divided into eight sections of four hexadecimal digits each. IPv6 addresses have a hierarchical structure, with the type prefix in the first bits indicating the address category such as unicast, multicast, anycast, reserved, or local. Unicast addresses are used to identify a single interface, multicast for groups of interfaces, and anycast to select the nearest available node in a group.
A wireless local area network (WLAN) uses radio frequency technology to transmit and receive data over the air, providing mobility and flexibility as an extension or alternative to wired networks. Key advantages of WLANs include productivity, convenience, lower installation costs and mobility. However, WLANs also have disadvantages such as higher costs for wireless network cards and access points, susceptibility to environmental interference, and lower bandwidth capacity compared to wired networks. Common applications of WLANs include use in corporate, education, medical and temporary settings.
This document discusses different types of routing protocols. It describes static routing protocols where routes are manually configured by an administrator. It then covers dynamic routing protocols which automatically update routing tables. The main dynamic routing protocols covered are RIP, RIPv2, IGRP, and EIGRP. RIP is a distance vector protocol that exchanges full routing tables every 30 seconds. RIPv2, IGRP, and EIGRP are also discussed with their key characteristics.
The document discusses various IEEE 802 standards for networking technologies including Ethernet, wireless LAN (802.11), and their variants and evolutions over time. It provides details on Ethernet standards and implementations such as 802.3, 10BASE5, 10BASE2, 10BASE-T, 10BASE-F, Fast Ethernet, and Gigabit Ethernet. It also summarizes key aspects of wireless networking standards such as 802.11 components, frame format, and physical layer specifications including FHSS, DSSS, OFDM, and associated data rates and frequencies.
There are several types of IP addresses including public, private, static, and dynamic addresses. Public IP addresses are associated with an entire network while private IP addresses uniquely identify devices within a home network. Static IP addresses never change while dynamic IP addresses are temporary and change each time a device connects.
IP addresses are also classified based on version (IPv4 or IPv6), address space (A, B, C, D, E classes), and function (unicast, multicast, broadcast, anycast). Key differences between classes include the number of bits used for network vs. host identification and the total number of possible networks. Specific rules govern how network and host IDs are assigned to ensure unique identification of devices.
Wireless local area networks (WLANs) allow for mobility by using radio frequency or infrared communications instead of cables to connect devices to a network. Common WLAN standards include 802.11a, 802.11b, 802.11g, and 802.11n. WLANs use technologies like direct sequence spread spectrum, frequency hopping spread spectrum, and orthogonal frequency-division multiplexing. The 802.11 architecture defines the physical layer, data link layer including logical link control and media access control, and network topologies like peer-to-peer, access point based, and point-to-multipoint.
IPv6 addresses are 128-bit addresses used to identify nodes in an IPv6 network. They are conventionally written in hexadecimal colon notation, divided into eight sections of four hexadecimal digits each. IPv6 addresses have a hierarchical structure, with the type prefix in the first bits indicating the address category such as unicast, multicast, anycast, reserved, or local. Unicast addresses are used to identify a single interface, multicast for groups of interfaces, and anycast to select the nearest available node in a group.
A wireless local area network (WLAN) uses radio frequency technology to transmit and receive data over the air, providing mobility and flexibility as an extension or alternative to wired networks. Key advantages of WLANs include productivity, convenience, lower installation costs and mobility. However, WLANs also have disadvantages such as higher costs for wireless network cards and access points, susceptibility to environmental interference, and lower bandwidth capacity compared to wired networks. Common applications of WLANs include use in corporate, education, medical and temporary settings.
This document discusses different types of routing protocols. It describes static routing protocols where routes are manually configured by an administrator. It then covers dynamic routing protocols which automatically update routing tables. The main dynamic routing protocols covered are RIP, RIPv2, IGRP, and EIGRP. RIP is a distance vector protocol that exchanges full routing tables every 30 seconds. RIPv2, IGRP, and EIGRP are also discussed with their key characteristics.
The document discusses various IEEE 802 standards for networking technologies including Ethernet, wireless LAN (802.11), and their variants and evolutions over time. It provides details on Ethernet standards and implementations such as 802.3, 10BASE5, 10BASE2, 10BASE-T, 10BASE-F, Fast Ethernet, and Gigabit Ethernet. It also summarizes key aspects of wireless networking standards such as 802.11 components, frame format, and physical layer specifications including FHSS, DSSS, OFDM, and associated data rates and frequencies.
There are several types of IP addresses including public, private, static, and dynamic addresses. Public IP addresses are associated with an entire network while private IP addresses uniquely identify devices within a home network. Static IP addresses never change while dynamic IP addresses are temporary and change each time a device connects.
IP addresses are also classified based on version (IPv4 or IPv6), address space (A, B, C, D, E classes), and function (unicast, multicast, broadcast, anycast). Key differences between classes include the number of bits used for network vs. host identification and the total number of possible networks. Specific rules govern how network and host IDs are assigned to ensure unique identification of devices.
Wireless local area networks (WLANs) allow for mobility by using radio frequency or infrared communications instead of cables to connect devices to a network. Common WLAN standards include 802.11a, 802.11b, 802.11g, and 802.11n. WLANs use technologies like direct sequence spread spectrum, frequency hopping spread spectrum, and orthogonal frequency-division multiplexing. The 802.11 architecture defines the physical layer, data link layer including logical link control and media access control, and network topologies like peer-to-peer, access point based, and point-to-multipoint.
networking and their Routing protocols with commands along with diagram ,(rip, IGRP and OSPF and BGP ) and knowledge about Network devices like Router and Switch. network define and definitions of Lan, router and all the routing protocols and their features.
1. An introduction of LAN.
2. An introduction of VLAN.
3. Properties of VLAN.
4. Types of VLAN.
5. VLAN Identification Method
6. VLAN Trunking Protocol.
7. Inter-VLAN routing.
This document discusses various networking devices used to connect electronic devices and share resources in a computer network. It describes network interface cards (NICs) that provide the physical interface between a computer and cabling. It also covers repeaters that regenerate signals to extend distances, modems that modulate and demodulate signals for internet connections, hubs and switches that connect multiple devices either by broadcasting or selectively forwarding, bridges that segment networks while filtering traffic, and routers that intelligently connect different network types and choose optimal paths between them. The document provides details on the function and layer (physical, data link, network) of operation for each type of networking device.
Circuit switching is a method of establishing a dedicated communication path or circuit between two endpoints in a network before transmission begins. It requires reserving bandwidth throughout the network for the duration of the connection. A circuit-switched network establishes a physical path and dedicates resources to a single connection. It operates in three phases: circuit establishment, data transfer, and circuit disconnection. The public telephone network is an example of a circuit-switched network.
The document summarizes 6LoWPAN, an open IoT networking protocol specified by the IETF. 6LoWPAN allows IPv6 to be used over low-power wireless personal area networks (LoWPANs) by defining an adaptation layer that compresses IPv6 and UDP headers to accommodate the small packet sizes supported by IEEE 802.15.4 networks. It describes how 6LoWPAN uses header compression techniques like IPHC and NHC to reduce header overhead and enable IPv6 connectivity for constrained IoT devices. The document also provides an overview of the Linux-wpan project, which implements 6LoWPAN and IEEE 802.15.4 support in the Linux kernel.
This document provides an overview of Fiber Distributed Data Interface (FDDI), including its timeline, specifications, features, frame format, and applications. FDDI is a standard for transmitting data at up to 200 Mbps using optical fiber cables in a dual ring topology. It supports up to 1000 nodes within a range of 200 km. FDDI specifications include media access control, physical layer protocol, physical layer medium, and station management. Its benefits include high bandwidth and ability to connect over large distances with low noise interference.
This document provides an overview of key concepts in network layer delivery, forwarding, and routing. It discusses delivery and forwarding of packets, including direct vs indirect delivery and next-hop vs route forwarding methods. It also summarizes several unicast routing protocols, including distance vector protocols like RIP and link state protocols like OSPF. Finally, it discusses path vector routing and Border Gateway Protocol (BGP) for interdomain routing.
This document provides an overview of basic local area network (LAN) concepts including definitions, hardware, media, and sample implementations. It defines a LAN as a group of computers and devices sharing resources within a small geographic area. Common LAN hardware includes hubs, switches, bridges, and routers which connect devices and segment traffic at different OSI model layers. Wired media include twisted pair, coaxial, and fiber optic cables while common wireless technologies are Wi-Fi and WiMax. Sample configurations show home and business LAN setups connecting devices via these components.
The document compares Layer 2 and Layer 3 switching. Layer 2 switching uses MAC addresses to forward frames within a broadcast domain, while Layer 3 switching uses IP addresses to forward packets, allowing for greater scalability and security. Some benefits of Layer 2 switching include hardware-based bridging and high speeds, while benefits of Layer 3 switching include scalability, security, QoS, and lower latency.
This document provides an overview of subnetting IP networks and addressing schemes. It covers subnetting IPv4 networks, including calculating subnets and hosts for various prefix lengths. It also discusses variable length subnet masking to better utilize address space. Finally, it touches on considerations for structured network design and address planning.
Link-state routing protocols use Dijkstra's algorithm to calculate the shortest path to all destinations based on a link-state database containing the full network topology. Each router runs the same algorithm locally to determine the optimal path. Key aspects include link-state advertisements to share connectivity information, the topological database to store network maps, and shortest path first calculations to derive routes. Common link-state protocols are OSPF and IS-IS. They provide fast convergence and scalability but require more resources than distance-vector protocols.
Mobile Transport Layer protocols aim to address challenges with TCP over mobile networks. Traditional TCP uses congestion control like slow start and fast retransmit/recovery that can reduce performance over mobile. Indirect TCP splits the connection at the access point to avoid wireless errors affecting the wired segment. Snooping TCP buffers packets at the access point and performs local retransmissions on errors. Mobile TCP splits the connection and uses an optimized TCP between the supervisory host and mobile host, choking the sender when the mobile is disconnected to avoid buffering large amounts of undelivered data.
The document discusses IEEE standards for local area networks (LANs) including Ethernet LANs, Token Ring LANs, and wireless LANs. It describes the IEEE 802 standards family, common LAN topologies and cabling, how CSMA/CD and token protocols work, and comparisons of Ethernet and Token Ring technologies. It also outlines wireless LAN specifications including 802.11, 802.11a, 802.11b, and 802.11g.
- OSPF is a link-state routing protocol that was developed in 1991 as an improvement over the distance vector routing protocol RIP. It is based on the Bellman-Ford algorithm.
- OSPF networks can be divided into sub-domains called areas. Areas limit the scope of route information distribution and reduce the number of routes that need to be propagated. All routers within an area must be connected.
- The backbone area, with an ID of 0.0.0.0, acts as a hub that connects all other areas and distributes routing information between them. It must remain continuously connected.
This document provides information about star topology for a computer network. It describes the key aspects of a star topology including that it has a central node or hub that all other nodes connect to. When a device needs to send data to another device, it sends it to the hub which then relays the data to the other connected devices. Main advantages are that a single node failure does not take down the whole network and it is easy to add additional nodes. Main disadvantages include being susceptible to single point of failure if the hub fails and requiring more cable length. The document discusses usages, applications, comparisons to bus topology, and concludes that star topology is best for smaller networks.
ARP works by broadcasting packets to all hosts on a LAN to find the MAC address associated with a given IP address. Each host maintains an ARP table mapping IP addresses to MAC addresses. ARP broadcasts are propagated through bridges and switches but not routers. When host 1.1 needs to send data to 1.3, it first uses ARP to find 1.3's MAC address by broadcasting an ARP request packet containing 1.3's IP address.
An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing.
This document discusses unicasting and multicasting in computer networks. It provides details on:
- The key differences between unicasting (one-to-one communication) and multicasting (one-to-many communication), including how routers handle forwarding for each.
- Common applications that use multicasting like audio/video distribution, file sharing, and conferencing.
- Approaches to multicast routing including source-based trees, group-shared trees, and protocols like PIM, CBT, and MBONE tunneling to connect isolated multicast networks.
- Mechanisms used in multicast routing protocols like RPF, pruning/grafting, and IGMP to discover multicast group members
Black Hole Attack:
A malicious node advertises the wrong paths as good paths to the source node during the pathfinding process.
When the source selects the path including the attacker node, the traffic starts passing through the adversary node and this node starts dropping the packets selectively or in whole.
Black hole region is the entry point to a large number of harmful attacks.
This document discusses different types of computer network switching, including circuit switching, packet switching, and virtual circuit switching. Circuit switching establishes a dedicated connection between nodes for the duration of a call. Packet switching divides messages into packets that are routed independently through a network on a first-come, first-served basis without dedicated connections. Virtual circuit switching combines aspects of circuit switching and packet switching by establishing paths for packets through a three-phase process of setup, data transfer using local addressing, and teardown.
The document discusses computer communication architecture and the OSI and TCP/IP models. It provides details on each layer of the OSI model, including the layer number, name, function, and PDU. It also discusses data encapsulation, analogies to explain how data moves through the OSI layers, and compares the OSI and TCP/IP models. The TCP/IP model has fewer layers and is focused on interoperability rather than standards.
This document provides an overview of digital communication and covers several topics:
- It describes different types of transmission media including guided media like twisted pair cable, coaxial cable, and fiber optic cable. It also covers unguided or wireless media.
- It discusses characteristics of different transmission media and how signals are transmitted through them. This includes concepts like attenuation, distortion, and noise.
- It defines key terms used to measure signal quality like decibels and signal-to-noise ratio.
networking and their Routing protocols with commands along with diagram ,(rip, IGRP and OSPF and BGP ) and knowledge about Network devices like Router and Switch. network define and definitions of Lan, router and all the routing protocols and their features.
1. An introduction of LAN.
2. An introduction of VLAN.
3. Properties of VLAN.
4. Types of VLAN.
5. VLAN Identification Method
6. VLAN Trunking Protocol.
7. Inter-VLAN routing.
This document discusses various networking devices used to connect electronic devices and share resources in a computer network. It describes network interface cards (NICs) that provide the physical interface between a computer and cabling. It also covers repeaters that regenerate signals to extend distances, modems that modulate and demodulate signals for internet connections, hubs and switches that connect multiple devices either by broadcasting or selectively forwarding, bridges that segment networks while filtering traffic, and routers that intelligently connect different network types and choose optimal paths between them. The document provides details on the function and layer (physical, data link, network) of operation for each type of networking device.
Circuit switching is a method of establishing a dedicated communication path or circuit between two endpoints in a network before transmission begins. It requires reserving bandwidth throughout the network for the duration of the connection. A circuit-switched network establishes a physical path and dedicates resources to a single connection. It operates in three phases: circuit establishment, data transfer, and circuit disconnection. The public telephone network is an example of a circuit-switched network.
The document summarizes 6LoWPAN, an open IoT networking protocol specified by the IETF. 6LoWPAN allows IPv6 to be used over low-power wireless personal area networks (LoWPANs) by defining an adaptation layer that compresses IPv6 and UDP headers to accommodate the small packet sizes supported by IEEE 802.15.4 networks. It describes how 6LoWPAN uses header compression techniques like IPHC and NHC to reduce header overhead and enable IPv6 connectivity for constrained IoT devices. The document also provides an overview of the Linux-wpan project, which implements 6LoWPAN and IEEE 802.15.4 support in the Linux kernel.
This document provides an overview of Fiber Distributed Data Interface (FDDI), including its timeline, specifications, features, frame format, and applications. FDDI is a standard for transmitting data at up to 200 Mbps using optical fiber cables in a dual ring topology. It supports up to 1000 nodes within a range of 200 km. FDDI specifications include media access control, physical layer protocol, physical layer medium, and station management. Its benefits include high bandwidth and ability to connect over large distances with low noise interference.
This document provides an overview of key concepts in network layer delivery, forwarding, and routing. It discusses delivery and forwarding of packets, including direct vs indirect delivery and next-hop vs route forwarding methods. It also summarizes several unicast routing protocols, including distance vector protocols like RIP and link state protocols like OSPF. Finally, it discusses path vector routing and Border Gateway Protocol (BGP) for interdomain routing.
This document provides an overview of basic local area network (LAN) concepts including definitions, hardware, media, and sample implementations. It defines a LAN as a group of computers and devices sharing resources within a small geographic area. Common LAN hardware includes hubs, switches, bridges, and routers which connect devices and segment traffic at different OSI model layers. Wired media include twisted pair, coaxial, and fiber optic cables while common wireless technologies are Wi-Fi and WiMax. Sample configurations show home and business LAN setups connecting devices via these components.
The document compares Layer 2 and Layer 3 switching. Layer 2 switching uses MAC addresses to forward frames within a broadcast domain, while Layer 3 switching uses IP addresses to forward packets, allowing for greater scalability and security. Some benefits of Layer 2 switching include hardware-based bridging and high speeds, while benefits of Layer 3 switching include scalability, security, QoS, and lower latency.
This document provides an overview of subnetting IP networks and addressing schemes. It covers subnetting IPv4 networks, including calculating subnets and hosts for various prefix lengths. It also discusses variable length subnet masking to better utilize address space. Finally, it touches on considerations for structured network design and address planning.
Link-state routing protocols use Dijkstra's algorithm to calculate the shortest path to all destinations based on a link-state database containing the full network topology. Each router runs the same algorithm locally to determine the optimal path. Key aspects include link-state advertisements to share connectivity information, the topological database to store network maps, and shortest path first calculations to derive routes. Common link-state protocols are OSPF and IS-IS. They provide fast convergence and scalability but require more resources than distance-vector protocols.
Mobile Transport Layer protocols aim to address challenges with TCP over mobile networks. Traditional TCP uses congestion control like slow start and fast retransmit/recovery that can reduce performance over mobile. Indirect TCP splits the connection at the access point to avoid wireless errors affecting the wired segment. Snooping TCP buffers packets at the access point and performs local retransmissions on errors. Mobile TCP splits the connection and uses an optimized TCP between the supervisory host and mobile host, choking the sender when the mobile is disconnected to avoid buffering large amounts of undelivered data.
The document discusses IEEE standards for local area networks (LANs) including Ethernet LANs, Token Ring LANs, and wireless LANs. It describes the IEEE 802 standards family, common LAN topologies and cabling, how CSMA/CD and token protocols work, and comparisons of Ethernet and Token Ring technologies. It also outlines wireless LAN specifications including 802.11, 802.11a, 802.11b, and 802.11g.
- OSPF is a link-state routing protocol that was developed in 1991 as an improvement over the distance vector routing protocol RIP. It is based on the Bellman-Ford algorithm.
- OSPF networks can be divided into sub-domains called areas. Areas limit the scope of route information distribution and reduce the number of routes that need to be propagated. All routers within an area must be connected.
- The backbone area, with an ID of 0.0.0.0, acts as a hub that connects all other areas and distributes routing information between them. It must remain continuously connected.
This document provides information about star topology for a computer network. It describes the key aspects of a star topology including that it has a central node or hub that all other nodes connect to. When a device needs to send data to another device, it sends it to the hub which then relays the data to the other connected devices. Main advantages are that a single node failure does not take down the whole network and it is easy to add additional nodes. Main disadvantages include being susceptible to single point of failure if the hub fails and requiring more cable length. The document discusses usages, applications, comparisons to bus topology, and concludes that star topology is best for smaller networks.
ARP works by broadcasting packets to all hosts on a LAN to find the MAC address associated with a given IP address. Each host maintains an ARP table mapping IP addresses to MAC addresses. ARP broadcasts are propagated through bridges and switches but not routers. When host 1.1 needs to send data to 1.3, it first uses ARP to find 1.3's MAC address by broadcasting an ARP request packet containing 1.3's IP address.
An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing.
This document discusses unicasting and multicasting in computer networks. It provides details on:
- The key differences between unicasting (one-to-one communication) and multicasting (one-to-many communication), including how routers handle forwarding for each.
- Common applications that use multicasting like audio/video distribution, file sharing, and conferencing.
- Approaches to multicast routing including source-based trees, group-shared trees, and protocols like PIM, CBT, and MBONE tunneling to connect isolated multicast networks.
- Mechanisms used in multicast routing protocols like RPF, pruning/grafting, and IGMP to discover multicast group members
Black Hole Attack:
A malicious node advertises the wrong paths as good paths to the source node during the pathfinding process.
When the source selects the path including the attacker node, the traffic starts passing through the adversary node and this node starts dropping the packets selectively or in whole.
Black hole region is the entry point to a large number of harmful attacks.
This document discusses different types of computer network switching, including circuit switching, packet switching, and virtual circuit switching. Circuit switching establishes a dedicated connection between nodes for the duration of a call. Packet switching divides messages into packets that are routed independently through a network on a first-come, first-served basis without dedicated connections. Virtual circuit switching combines aspects of circuit switching and packet switching by establishing paths for packets through a three-phase process of setup, data transfer using local addressing, and teardown.
The document discusses computer communication architecture and the OSI and TCP/IP models. It provides details on each layer of the OSI model, including the layer number, name, function, and PDU. It also discusses data encapsulation, analogies to explain how data moves through the OSI layers, and compares the OSI and TCP/IP models. The TCP/IP model has fewer layers and is focused on interoperability rather than standards.
This document provides an overview of digital communication and covers several topics:
- It describes different types of transmission media including guided media like twisted pair cable, coaxial cable, and fiber optic cable. It also covers unguided or wireless media.
- It discusses characteristics of different transmission media and how signals are transmitted through them. This includes concepts like attenuation, distortion, and noise.
- It defines key terms used to measure signal quality like decibels and signal-to-noise ratio.
The data link layer provides services to the network layer such as framing data and applying error detection methods like parity checks, checksums and cyclic redundancy checks to frames. Common data link protocols are used at this layer.
The document discusses several networking concepts:
- Classless Inter-Domain Routing (CIDR) allows ISPs to allocate blocks of IP addresses to organizations in a more efficient manner than previous methods.
- Network Address Translation (NAT) allows a local network to use private IP address ranges behind a NAT-enabled router that maps the private addresses to a single public IP address for communication with external networks.
- Subnetting and Variable Length Subnet Masking (VLSM) allow networks to be divided into subnets to better utilize limited IP address blocks and assign addresses based on subnet needs.
- Supernetting combines multiple classful network blocks into larger supernets to more efficiently use address space.
The document describes routing algorithms used in computer networks. It discusses two main types of routing algorithms: link-state algorithms and distance-vector algorithms. Link-state algorithms use a complete map of the entire network topology to calculate the shortest paths between all nodes, while distance-vector algorithms use an iterative process where each router shares routing information with neighbors to determine the shortest paths. The document then provides examples of how Dijkstra's algorithm, a link-state algorithm, and the Bellman-Ford distance-vector algorithm work to calculate the optimal paths through a sample network.
Controlled access protocols allow only one node to send at a time to avoid message collisions. There are three main controlled access methods: reservation, polling, and token passing. Reservation methods divide time into intervals, with reservation frames preceding data frames to reserve slots. Polling methods involve a primary station periodically polling secondary stations for data. Token passing methods use a token frame that circulates between stations, with each station only allowed to transmit when holding the token.
Circuit switching directly connects the sender and receiver through a dedicated physical path. Message switching transmits entire messages from node to node without establishing a dedicated path. Packet switching breaks messages into packets that can take different routes to the destination and are reassembled, allowing for more efficient use of bandwidth but introducing complexity.
The network layer is responsible for routing packets from source to destination using a routing algorithm. The routing algorithm must deal with issues of correctness, stability, fairness, and optimality. The network layer also handles congestion when more packets enter an area than can be processed. When connecting different network technologies, the same problems are present but are worse as packets may travel through many different networks with different formats and technologies.
Packet switching refers to protocols where messages are divided into packets before being transmitted. Each packet is transmitted individually and can take different routes to the destination. Once all packets arrive, they are recompiled into the original message. There are two main approaches: virtual circuits establish a pre-planned route before transmission, while datagrams treat each packet independently without connection setup. Virtual circuits provide sequencing but are less reliable if a node fails, while datagrams are more flexible but packets may arrive out of order.
1. Layer 2 switches break up large collision domains into smaller ones by making each switch port its own collision domain, allowing a more efficient Ethernet LAN network than with hubs.
2. Bridges and switches learn MAC addresses and their associated ports by reading the source MAC address of each received frame and recording the port on which the MAC address was received.
3. The Spanning Tree Protocol provides a loop-free redundant network topology by placing certain switch ports in the blocking state and identifying one switch as the root bridge using BPDUs.
The document discusses the gap between desired behaviors and what electronic devices can actually do. Early computers attempted to assemble raw devices into purpose-built machines for each behavior. A general purpose computer helps bridge this gap by using software to organize basic electronic components and allow for varied applications.
This document discusses multiple access techniques for wireless communications, including FDMA, TDMA, and CDMA. It provides details on how each technique works and its advantages and disadvantages. FDMA divides the frequency band into channels that can be assigned to individual users. TDMA divides each channel into time slots that can be assigned to users. CDMA allows all users to use the whole available bandwidth simultaneously by using unique codes to distinguish users.
This document discusses different methods for allowing one-to-one communication between nodes in large networks, including direct connections, central controllers, and common buses. It focuses on switching networks, which consist of interlinked switches that can create temporary connections between devices. There are three main types of switching networks: circuit switching, packet switching, and message switching. Packet switching breaks messages into small packets that contain user data and control information and are briefly stored at nodes before being passed to the next node.
There are two main switching techniques used in communications networks: circuit switching and packet switching. Circuit switching establishes a dedicated communication path between two stations for the duration of the connection. Packet switching transmits data in small packets that are routed individually through the network on a non-dedicated basis, allowing for more efficient use of bandwidth. The telephone system uses circuit switching while the internet uses packet switching, which is more suitable for data traffic since it allows for variable bandwidth and priority routing.
The presentation given at MSBTE sponsored content updating program on 'PC Maintenance and Troubleshooting' for Diploma Engineering teachers of Maharashtra. Venue: Government Polytechnic, Nashik Date: 17/01/2011 Session-2: Computer Organization and Architecture.
The document discusses the network layer in computer networking. It describes how the network layer is responsible for routing packets from their source to destination. It covers different routing algorithms like distance vector routing and link state routing. It also compares connectionless and connection-oriented services, as well as datagram and virtual circuit subnets. Key aspects of routing algorithms like optimality, stability, and fairness are defined.
There are two types of network links: point-to-point links between two nodes and broadcast links where nodes share a common transmission medium. Broadcast links use multiple access protocols to determine how nodes access the shared medium as only one node can transmit at a time. Common multiple access protocols for broadcast links include Aloha, CSMA, and CSMA/CD which use random access or carrier sensing to regulate transmissions and avoid or detect collisions between nodes transmitting simultaneously. Controlled access protocols like token passing also exist where nodes must obtain a token to transmit on the shared medium.
This document provides an overview of content delivery networks (CDNs) with three key points:
1. CDNs replicate content across multiple mirrored web servers to improve performance and overcome bandwidth limitations by distributing content closer to end-users.
2. A CDN has four main architectural components: original servers, a distribution system, a request routing system, and an account system. The request routing system directs clients to optimal surrogate servers.
3. There are two main pricing models for CDNs - pricing based on aggregate monthly usage billed in tiers (e.g. 50TB/month) and percentile-based pricing which calculates the 95th percentile of monthly bandwidth usage to determine fees.
The document discusses wireless local area networks (WLANs) and personal area networks (PANs). It describes the characteristics and fundamentals of WLANs, including their advantages like flexibility and lower costs, and disadvantages such as lower bandwidth and security issues. It provides details on common wireless standards like IEEE 802.11, Bluetooth, and HomeRF. It also compares infrastructure-based and ad-hoc network topologies and summarizes key aspects of the IEEE 802.11 standard including services, physical layers, and frame formats.
The document discusses wireless networks and IEEE 802.11 standards. It describes the components of wired LANs like repeaters, hubs, bridges, and switches. It then covers wireless networks including wireless LAN standards like 802.11b, 802.11a, and 802.11g. It also discusses wireless network topologies, services, and the medium access control of 802.11 which uses CSMA/CA for distributed coordination function and an alternative point coordination function for centralized access control.
The document discusses various networking devices used to connect and extend local area networks (LANs). It describes repeaters as devices that receive and regenerate signals to allow them to travel longer distances. Hubs are multiport repeaters that connect multiple nodes to a single device. Bridges operate at the data link layer and logically separate network segments. Switches provide dedicated connections and are multiport bridges that separate collision domains for improved performance.
The document discusses various networking devices used to connect and extend local area networks (LANs). It describes repeaters as devices that receive and regenerate signals to allow them to travel longer distances. Hubs are multiport repeaters that connect multiple nodes to a single device. Bridges operate at the data link layer and logically separate network segments. Switches provide dedicated connections and are multiport bridges that separate collision domains for improved performance.
802.11 wireless LAN provides wireless network connectivity using access points that act as bridges between the wireless and wired networks. Access points are connected to the wired network and have antennas to provide wireless connectivity. The range of wireless connectivity depends on structural barriers and the access point antenna's RF gain. To cover larger areas, multiple access points with 20-30% overlap may be installed.
The document discusses 802.11 wireless LAN technologies. It describes how an access point acts as a bridge between the wired and wireless networks, and how wireless connectivity is provided through antennae on the access point. It also discusses the different 802.11 standards including 802.11b, 802.11a, and 802.11g, and how they operate on different frequency bands and support different data rates. Finally, it summarizes the differences between repeaters, hubs, bridges, and switches, and how they operate at different layers of the OSI model.
The document discusses wireless local area networks (WLANs) and the IEEE 802.11 standards. It describes some of the challenges of wireless transmissions and provides an overview of the IEEE 802.11 standards including 802.11, 802.11a, 802.11b, 802.11e, and 802.11g. It also summarizes the IEEE 802.11 network architecture including the physical layer, data link layer, and different network topologies like IBSS, BSS, and ESS.
A local area network (LAN) connects devices within a small geographic area like a home or office building. Devices share network resources through a common communication line or wireless link. Basic LAN hardware includes hubs, switches, bridges, and routers to connect devices and manage traffic. Common wired media are twisted pair, coaxial, and fiber optic cables. Wireless LANs use radio waves to transmit over short distances without cables. Example LAN implementations show how these components connect devices in home and business settings.
CN 5151(15) Module I part 1.3 21072020.pdfADARSHN40
This document provides an overview of computer networks and wireless local area networks (WLANs). It discusses the TCP/IP model and layers, Ethernet protocols, wired and wireless LAN architectures and their differences. Wireless LAN characteristics like attenuation, interference and multipath propagation are described. The document also covers wireless LAN access control using CSMA/CA, the IEEE 802.11 project, services like BSS and ESS. Key components of a WLAN like the MAC sublayer, DCF, PCF, and common LAN connecting devices are summarized.
A local area network (LAN) connects devices within a small geographic area like a home or office building. Devices share network resources through a common communication line or wireless link. Basic LAN hardware includes hubs, switches, bridges, and routers to connect devices and manage traffic. Common wired media are twisted pair, coaxial, and fiber optic cables while wireless uses radio frequencies. An example home LAN uses a wireless router to share an internet connection among devices. A typical business LAN connects multiple floors or buildings with switches, routers, and fiber optic backbone.
The document provides an overview of WiFi networks and various IEEE 802.11 standards. It discusses basic WiFi concepts and deployment issues. It then summarizes several key WiFi versions including 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, and 802.11ad and how each standard improved data rates and functionality compared to previous versions through techniques like channel bonding and MIMO.
802.11 wireless LANs provide network connectivity over wireless media using access points that act as bridges between wireless and wired networks. Access points are connected to the wired network and have antennas to provide wireless connectivity. The range of wireless connectivity depends on structural hindrances and the access point's antenna gain. Multiple access points with overlapping ranges can service larger areas. Common 802.11 standards include 802.11b, 802.11a, and 802.11g.
This document provides information on wireless LAN (WLAN) technology and components. It discusses how an 802.11 wireless network connects desktop and laptop devices to a wired LAN using access points. Access points act as bridges between the wireless and wired networks. The document also covers the MACA protocol for wireless transmission and the different 802.11 wireless standards. It defines the functions of repeaters, hubs, bridges, and switches as components used in both wired and wireless networking.
A local area network (LAN) connects devices within a small geographic area like a home or office building. Devices on a LAN share network resources through a common communication line or wireless link. Basic networking hardware like hubs, switches, bridges and routers help connect devices on a LAN and manage traffic. Wired LANs commonly use twisted pair or fiber optic cable, while wireless LANs transmit over radio frequencies. The document provides examples of home and business LAN configurations using these basic networking concepts and components.
Network devices such as repeaters, hubs, bridges, switches, routers, and gateways are used to extend and segment computer networks. Repeaters regenerate signals to increase network distance while hubs connect multiple cables but do not segment traffic. Bridges and switches segment networks into broadcast domains to reduce collisions. Routers connect different network types, choose optimal paths, and prevent broadcast traffic between segments. Gateways translate between different network protocols.
This document provides an overview of local area networks (LANs) and discusses various LAN topics including common topologies (bus, ring, star), frame transmission methods, the roles of hubs and switches, and how bridges and routers can be used to interconnect multiple LANs. It describes the three main layers (physical, media access control, logical link control) of the IEEE 802 LAN protocol architecture and compares it to the OSI model. Key concepts covered include shared medium access, the functions of bridges and switches, and how layer 2 switches improved upon earlier hub technologies to increase network capacity and performance.
The document summarizes several IEEE 802 standards for local area networks (LANs):
- IEEE 802 defines the LLC and MAC sublayers for LANs. IEEE 802.3 specifies Ethernet LANs using CSMA/CD. IEEE 802.5 specifies Token Ring LANs.
- IEEE 802.3 Ethernet uses CSMA/CD where computers listen for traffic before transmitting and can detect collisions.
- IEEE 802.5 Token Ring LANs use a token passing protocol where a token circulates and only the computer holding the token can transmit.
IEEE 802.11 defines wireless local area networks. It uses CSMA/CA for media access and includes encryption. Wireless networks can operate in ad-hoc mode with no base station or in infrastructure mode with an access point. Infrastructure networks can connect multiple basic service sets to extend the network. Stations can have no, basic, or extended mobility between networks. Physical layer standards include FHSS, DSSS, OFDM, and their variants.
This document discusses wireless local area networks (WLANs). It describes how WLANs use wireless transmission to connect devices within a local area, avoiding the need for wired networking. It covers different types of WLAN configurations including single-cell, multi-cell, infrastructure and ad-hoc networks. It also discusses wireless networking technologies like infrared, spread spectrum and microwave transmission and compares their strengths and weaknesses. Finally, it examines the IEEE 802.11 wireless networking standard and its media access control protocols.
This document discusses various computer arithmetic operations including addition, subtraction, multiplication, and division for signed magnitude and two's complement data representations. It describes the Booth multiplication algorithm, array multipliers for performing multiplication using combinational circuits, and the division algorithm. It also covers detecting divide overflow conditions.
The document provides an introduction to computer security including:
- The basic components of security such as confidentiality, integrity, and availability.
- Common security threats like snooping, modification, and denial of service attacks.
- Issues with security including operational challenges and human factors.
- An overview of security policies, access control models, and security models like Bell-LaPadula and Biba.
Cookies and sessions allow servers to remember information about users across multiple web pages. Cookies are small files stored on a user's computer that identify users and can store data to be accessed on subsequent page requests. Sessions use cookies to identify users and store temporary data on the server side to be accessed across multiple pages in one application, such as usernames or preferences. Both cookies and sessions must be started before any page output to ensure headers are sent before the page body.
This document discusses different aspects of functions in programming including declaring and calling functions, passing arguments to functions, and returning values from functions. It also covers variable scope. Some key points covered are declaring functions with and without arguments, specifying default values, returning single values or arrays from functions, and understanding variable scope and how it relates to the global and $GLOBALS keywords and array.
This document discusses various aspects of working with web forms in PHP, including:
1) Useful server variables for forms like QUERY_STRING and SERVER_NAME.
2) Accessing form parameters submitted to the server.
3) Processing forms with functions, including validating form data with techniques like checking for required fields and valid email addresses.
4) Displaying default values or error messages for form fields.
5) Stripping HTML tags from form inputs and encoding special characters for safe display.
The document provides examples of implementing each of these techniques.
The document discusses various programming concepts related to decision making and repetition in code including understanding true and false values, using if/elseif/else statements, equality and relational operators, logical operators, and using while and for loops to repeat code. Specific topics covered include evaluating booleans, making single and multi-line if statements, comparing different data types, negation, and printing select menus with loops.
This document discusses working with arrays in PHP. It covers array basics like creating and accessing arrays, looping through arrays with foreach and for loops, modifying arrays by adding/removing elements and sorting arrays. It also discusses multidimensional arrays, how to create them and access elements within them.
This document discusses text and numbers in programming. It covers defining and manipulating text strings using single or double quotes. Escape characters can be used inside strings. Text can be validated and formatted using various string functions like trim(), strlen(), strtoupper(), substr(), and str_replace(). Numbers can be integers or floats. Variables hold data and can be operated on with arithmetic and assignment operators like +, -, *, /, %, and .=. Variables can also be incremented, decremented, and placed inside strings.
This document provides an introduction and overview of PHP for beginners. It discusses PHP's use for building websites, how PHP code is run on web servers and accessed through browsers. It then highlights some key advantages of PHP like being free, cross-platform, and widely used. It demonstrates a basic "Hello World" PHP program and shows how to output HTML forms and formatted numbers. Finally, it outlines some basic rules of PHP programs regarding tags, syntax, whitespace, comments, and case sensitivity.
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Data warehousing involves assembling and managing data from various sources to provide an integrated view of enterprise information. A data warehouse contains consolidated, historical data used to support management decision making. It differs from operational databases by containing aggregated, non-volatile data optimized for queries rather than updates. The extract, transform, load (ETL) process migrates data from source systems to the warehouse, transforming it as needed. Process managers oversee loading, maintaining, and querying the warehouse data.
Search engines allow users to search the vast collection of documents on the web. They consist of crawlers that fetch web pages, indexers that analyze page content and links, and interfaces that allow users to enter queries. Crawlers add pages to an index by following links, and indexers create inverted indexes to map words to pages. When a query is searched, results are retrieved from the index and ranked based on relevance. PageRank is a key algorithm that ranks pages higher that receive more links from other highly ranked pages. While it effectively searches the large, diverse and dynamic web, search poses challenges in understanding ambiguous queries over an evolving collection.
Web mining involves applying data mining techniques to discover useful information from web data. There are three types of web mining: web content mining analyzes data within web pages, web structure mining examines the hyperlink structure between pages, and web usage mining involves analyzing server logs to discover patterns in user behavior and interactions with websites. Web mining has applications in website design, web traffic analysis, e-commerce personalization, and security/crime investigation.
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The document discusses cluster analysis, which groups data objects into clusters so that objects within a cluster are similar but dissimilar to objects in other clusters. It describes key characteristics of clustering, including that it is unsupervised learning and the clusters are determined algorithmically rather than by humans. Various clustering algorithms are covered, including partitioning, hierarchical, density-based, and grid-based methods. Applications of clustering discussed include business intelligence, image recognition, web search, outlier detection, and biology. Requirements for effective clustering in data mining are also outlined.
Association analysis is a technique used to uncover relationships between items in transactional data. It involves finding frequent itemsets whose occurrence exceeds a minimum support threshold, and then generating association rules from these itemsets that satisfy minimum confidence. The Apriori algorithm is commonly used for this task, as it leverages the Apriori property to prune the search space - if an itemset is infrequent, its supersets cannot be frequent. It performs multiple database scans to iteratively grow frequent itemsets and extract high confidence rules.
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Introduction to Data Mining and Data WarehousingKamal Acharya
This document provides details about a course on data mining and data warehousing. The course objectives are to understand the foundational principles and techniques of data mining and data warehousing. The course description covers topics like data preprocessing, classification, association analysis, cluster analysis, and data warehouses. The course is divided into 10 units that cover concepts and algorithms for data mining techniques. Practical exercises are included to apply techniques to real-world data problems.
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bryophytes.pptx bsc botany honours second semester
Media Access Layer
1. Medium Access(MAC) Sub-Layer
Multiple access Protocols
Topologies
Overview of IEEE Standard 802 for LANS and MANS
Introduction to Wireless Communication
Introduction to Bridge, Switch and Router
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48.
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50.
51.
52.
53.
54. Elements of a wireless network
network
infrastructure
55. wireless hosts
laptop, smartphone
run applications
may be stationary (non-
mobile) or mobile
wireless does not
always mean mobility
Elements of a wireless network
network
infrastructure
56. base station
typically connected to
wired network
relay - responsible for
sending packets
between wired network
and wireless host(s) in
its “area”
e.g., cell towers,
802.11 access
points
Elements of a wireless network
network
infrastructure
57. wireless link
typically used to
connect mobile(s) to
base station
also used as backbone
link
multiple access
protocol coordinates
link access
various data rates,
transmission distance
Elements of a wireless network
network
infrastructure
58. infrastructure mode
base station connects
mobiles into wired
network
handoff: mobile
changes base station
providing connection
into wired network
Elements of a wireless network
network
infrastructure
59. ad hoc mode
no base stations
nodes can only
transmit to other
nodes within link
coverage
nodes organize
themselves into a
network: route
among themselves
Elements of a wireless network
60. Wireless Link Characteristics
important differences from wired link ….
– decreased signal strength: radio signal attenuates as it
propagates through matter (path loss)
– interference from other sources: standardized wireless
network frequencies (e.g., 2.4 GHz) shared by other
devices (e.g., phone); devices (motors) interfere as
well
– multipath propagation: radio signal reflects off
objects ground, arriving ad destination at slightly
different times
…. make communication across (even a point to point)
wireless link much more “difficult”
61. Wireless Link Characteristics
• SNR: signal-to-noise ratio
– larger SNR – easier to extract signal from noise (a “good
thing”)
• SNR versus BER tradeoffs
– given physical layer: increase power -> increase SNR->decrease
BER
62. Wireless network characteristics
Multiple wireless senders and receivers create additional
problems (beyond multiple access):
A
B
C
Hidden terminal problem
B, A hear each other
B, C hear each other
A, C can not hear each other
means A, C unaware of their
interference at B
A B C
A’s signal
strength
space
C’s signal
strength
Signal attenuation:
B, A hear each other
B, C hear each other
A, C can not hear each other
interfering at B
63. IEEE 802.11 Wireless LAN
802.11b
• 2.4-5 GHz unlicensed spectrum
• up to 11 Mbps
802.11n: multiple antennae
2.4-5 GHz range
up to 200 Mbps
802.11a
– 5-6 GHz range
– up to 54 Mbps
802.11g
– 2.4-5 GHz range
– up to 54 Mbps
all use CSMA/CA for multiple access
all have base-station and ad-hoc network versions
64. 802.11 LAN architecture
wireless host
communicates with base
station
base station = access
point (AP)
Basic Service Set (BSS)
(aka “cell”) in
infrastructure mode
contains:
wireless hosts
access point (AP): base
station
ad hoc mode: hosts only
BSS 1
BSS 2
Internet
hub, switch
or router
65. 802.11: Channels, association
• 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at
different frequencies
– AP admin chooses frequency for AP
– interference possible: channel can be same as that
chosen by neighboring AP!
• host: must associate with an AP
– scans channels, listening for beacon frames containing
AP’s name (SSID) and MAC address
– selects AP to associate with
– may perform authentication
– will typically run DHCP to get IP address in AP’s
subnet
66. 802.11: passive/active scanning
AP 2AP 1
H1
BSS 2BSS 1
1
2
3
1
passive scanning:
(1) beacon frames sent from APs
(2) association Request frame sent:
H1 to selected AP
(3) association Response frame sent
from selected AP to H1
AP 2
AP 1
H1
BSS 2BSS 1
1
22
3
4
active scanning:
(1) Probe Request frame broadcast
from H1
(2) Probe Response frames sent
from APs
(3) Association Request frame sent:
H1 to selected AP
(4) Association Response frame sent
from selected AP to H1
67. IEEE 802.11: multiple access
• avoid collisions: 2+ nodes transmitting at same time
• 802.11: CSMA - sense before transmitting
– don’t collide with ongoing transmission by other node
• 802.11: no collision detection!
– difficult to receive (sense collisions) when transmitting due to weak
received signals (fading)
– can’t sense all collisions in any case: hidden terminal, fading
– goal: avoid collisions: CSMA/C(ollision)A(voidance)
space
A
B
C
A B C
A’s signal
strength
C’s signal
strength
68. IEEE 802.11 MAC Protocol: CSMA/CA
802.11 sender
1 if sense channel idle for DIFS then
transmit entire frame (no CD)
2 if sense channel busy then
start random backoff time
timer counts down while channel idle
transmit when timer expires
if no ACK, increase random backoff interval,
repeat 2
802.11 receiver
- if frame received OK
return ACK after SIFS (ACK needed due to
hidden terminal problem)
sender receiver
DIFS
data
SIFS
ACK
69. An Overview of Repeaters
• Used for extending the physical span of a
network
– An example is the extension of the distance
between a hub and a node
• Span is often limited by design considerations
• 10base5
– The span is limited to 500 meters
71. Operations of a Repeater Within the
ISO OSI Model
• Operates at the lower level of the ISO OSI
model
– Physical layer
Medium
Physical
Layer
Repeater
Medium
Physical
Layer
72. An Overview of a Bridge
• A device used for connecting two LANs
operating under the same protocol
• Currently, the term bridge is loosely being
used to describe different interconnecting
devices
– Used now for connecting LANs operating under
different protocols as well
73. Purpose of a Bridge
• Facilitate the movement of data packet from
one network segment to another
• Not a sophisticated internetworking device
• Bridge does not perform the routing of
information to different segments of a
network
• Connects two network segments and not
multiple network segments
74. Bridge
Bridge : ISO-OSI Layer of Operation
X Medium X Medium
Physical
Layer
Physical
Layer
Data
Link
Layer
Data
Link
Layer
A simple bridge operates at the
second layer of the ISO model.
76. Local and Remote Bridges
• Local bridge
– Connects two different LANs located locally
• Remote bridge
– Connects LAN segments that are geographically
apart
– An example is a device that provide dial-up access
to a LAN
77. Switch Definition and Purpose
• A switch is defined as a device that allows a
LAN to be segmented
– The segments will operate under the same
protocol
78. Difference Between a Switch and a
Bridge
• A switch focuses on segmenting a LAN
• A bridge is concerned with linking two
network segments that operate under
different protocols
79. Purpose of a Switch
• Improve the network performance and
reliability
• Better manage the network in general
84. Switching Technology Operation at the
ISO Layer
• In each of the two cases of switching
technologies no protocol conversion takes
place
• Forwarding and filtering are done at the MAC
layer
85. The Purpose of a Router
• Connect LANs operating under different
protocols
• The LANs connected are better known as sub-
networks instead of network segments
– The term segments is nevertheless used in
practice
86. Router Characteristics
• A router true internetworking device
– Connects different sub-networks together
• Establishes a logical path of communication
between the sub-networks
• Contributes to the modular construction of a
network
– Network itself is better managed
– Network resources are better utilized
87. Internetworking with a Router
IEEE 802.3
Sub-network IEEE 802.5
Sub-network
PC-NFS
Sub-network
Router
88. Difference Between Routers, Switches
and Hubs
• Hubs
– Simply provides the mechanical and electrical
connections between the nodes
• Switches
– Examine the data packet for the destination
address
– Do not alter the data packets
• Routers
– Examine and alter the data packets
– Perform protocol conversion
89. Router Requirements
• Requires more processing power compared to
switches and bridges
• Operations fall within the network layer of the
ISO-OSI communication model
90. Router : Network Layer Interface
X MEDIUM X MEDIUM
PHYSICAL
LAYER
PHYSICAL
LAYER
DATA LINK
LAYER
DATA LINK
LAYER
NETWORK
LAYER
ROUTER
NETWORK
LAYER
92. An Introduction to Gateways
• Gateways are comprehensive internetworking
devices
• They can be computers themselves
93. Gateways in the Past
• Very popular
• They were the only devices that could be used
for internetworking
• Computers of the past were not designed with
network connections in mind
– Interconnection of different computer systems
has to be managed and driven by an advanced
device such as a gateway
94. The Present Scenario
• Computers are now designed with due
consideration given to network connections
• Larger networks could today be configured
using internetworking devices
– Routers, switches, hubs etc.
95. Gateway’s Functional Relationship to
the ISO-OSI Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
96. Link layer: introduction
terminology:
hosts and routers: nodes
communication channels that
connect adjacent nodes along
communication path: links
wired links
wireless links
LANs
layer-2 packet: frame,
encapsulates datagram
data-link layer has responsibility of
transferring datagram from one node
to physically adjacent node over a link
global ISP
97. Link layer: context
datagram transferred by
different link protocols over
different links:
e.g., Ethernet on first link,
frame relay on
intermediate links, 802.11
on last link
each link protocol provides
different services
e.g., may or may not
provide rdt over link
transportation analogy:
trip from Princeton to Lausanne
limo: Princeton to JFK
plane: JFK to Geneva
train: Geneva to Lausanne
tourist = datagram
transport segment =
communication link
transportation mode = link
layer protocol
travel agent = routing
algorithm
98. Link layer services
• framing, link access:
– encapsulate datagram into frame, adding
header, trailer
– channel access if shared medium
– “MAC” addresses used in frame headers to
identify source, dest
• different from IP address!
• reliable delivery between adjacent nodes
– seldom used on low bit-error link (fiber, some
twisted pair)
– wireless links: high error rates
99. flow control:
pacing between adjacent sending and receiving nodes
error detection:
errors caused by signal attenuation, noise.
receiver detects presence of errors:
• signals sender for retransmission or drops frame
error correction:
receiver identifies and corrects bit error(s) without resorting to
retransmission
half-duplex and full-duplex
with half duplex, nodes at both ends of link can transmit, but not
at same time
Link layer services (more)
100. Where is the link layer implemented?
• in each and every host
• link layer implemented in
“adaptor” (aka network
interface card NIC) or on a
chip
– Ethernet card, 802.11
card; Ethernet chipset
– implements link, physical
layer
• attaches into host’s system
buses
• combination of hardware,
software, firmware
controller
physical
transmission
cpu memory
host
bus
(e.g., PCI)
network adapter
card
application
transport
network
link
link
physical
101. Adaptors communicating
sending side:
encapsulates datagram
in frame
adds error checking bits,
rdt, flow control, etc.
receiving side
looks for errors, rdt, flow
control, etc
extracts datagram,
passes to upper layer at
receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
102. Error detection
EDC= Error Detection and Correction bits (redundancy)
D = Data protected by error checking, may include header fields
• Error detection not 100% reliable!
• protocol may miss some errors, but rarely
• larger EDC field yields better detection and correction
otherwise
103. Parity checking
single bit parity:
detect single bit
errors
two-dimensional bit parity:
detect and correct single bit errors
0 0
104. Internet checksum (review)
sender:
• treat segment contents
as sequence of 16-bit
integers
• checksum: addition (1’s
complement sum) of
segment contents
• sender puts checksum
value into UDP checksum
field
receiver:
compute checksum of
received segment
check if computed
checksum equals checksum
field value:
NO - error detected
YES - no error detected.
But maybe errors
nonetheless?
goal: detect “errors” (e.g., flipped bits) in transmitted
packet (note: used at transport layer only)
105. Cyclic redundancy check
more powerful error-detection coding
view data bits, D, as a binary number
choose r+1 bit pattern (generator), G
goal: choose r CRC bits, R, such that
<D,R> exactly divisible by G (modulo 2)
receiver knows G, divides <D,R> by G. If non-zero remainder:
error detected!
can detect all burst errors less than r+1 bits
widely used in practice (Ethernet, 802.11 WiFi, ATM)
106. CRC example
want:
D.2r XOR R = nG
equivalently:
D.2r = nG XOR R
equivalently:
if we divide D.2r by
G, want remainder
R to satisfy:
R = remainder[ ]
D.2r
G
107. Multiple access links, protocols
two types of “links”:
• point-to-point
– PPP for dial-up access
– point-to-point link between Ethernet switch, host
• broadcast (shared wire or medium)
– old-fashioned Ethernet
– upstream HFC
– 802.11 wireless LAN
shared wire (e.g.,
cabled Ethernet)
shared RF
(e.g., 802.11 WiFi)
shared RF
(satellite)
humans at a
cocktail party
(shared air, acoustical)
108. Multiple access protocols
single shared broadcast channel
two or more simultaneous transmissions by nodes:
interference
collision if node receives two or more signals at the
same time
multiple access protocol
distributed algorithm that determines how nodes share
channel, i.e., determine when node can transmit
communication about channel sharing must use channel itself!
no out-of-band channel for coordination
109. An ideal multiple access protocol
given: broadcast channel of rate R bps
desiderata:
1. when one node wants to transmit, it can send at
rate R.
2. when M nodes want to transmit, each can send at
average rate R/M
3. fully decentralized:
• no special node to coordinate transmissions
• no synchronization of clocks, slots
4. simple
110. MAC protocols: taxonomy
three broad classes:
• channel partitioning
– divide channel into smaller “pieces” (time slots, frequency, code)
– allocate piece to node for exclusive use
• random access
– channel not divided, allow collisions
– “recover” from collisions
• “taking turns”
– nodes take turns, but nodes with more to send can take longer
turns
111. Channel partitioning MAC protocols: TDMA
TDMA: time division multiple access
access to channel in "rounds"
each station gets fixed length slot (length =
pkt trans time) in each round
unused slots go idle
example: 6-station LAN, 1,3,4 have pkt,
slots 2,5,6 idle
1 3 4 1 3 4
6-slot
frame
6-slot
frame
112. FDMA: frequency division multiple access
channel spectrum divided into frequency bands
each station assigned fixed frequency band
unused transmission time in frequency bands go idle
example: 6-station LAN, 1,3,4 have pkt, frequency bands 2,5,6
idle
frequencybands
FDM cable
Channel partitioning MAC protocols: FDMA
113. Random access protocols
• when node has packet to send
– transmit at full channel data rate R.
– no a priori coordination among nodes
• two or more transmitting nodes ➜
“collision”,
• random access MAC protocol specifies:
– how to detect collisions
– how to recover from collisions (e.g., via
delayed retransmissions)
• examples of random access MAC protocols:
– slotted ALOHA
– ALOHA
– CSMA, CSMA/CD, CSMA/CA
114. Slotted ALOHA
assumptions:
all frames same size
time divided into equal size
slots (time to transmit 1
frame)
nodes start to transmit only
slot beginning
nodes are synchronized
if 2 or more nodes transmit
in slot, all nodes detect
collision
operation:
when node obtains fresh
frame, transmits in next slot
if no collision: node can
send new frame in next
slot
if collision: node
retransmits frame in each
subsequent slot with prob.
p until success
115. Pros:
single active node can
continuously transmit at
full rate of channel
highly decentralized: only
slots in nodes need to be
in sync
simple
Cons:
collisions, wasting slots
idle slots
nodes may be able to
detect collision in less
than time to transmit
packet
clock synchronization
Slotted ALOHA
1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
116. suppose: N nodes with
many frames to send,
each transmits in slot with
probability p
prob that given node has
success in a slot = p(1-p)N-
1
prob that any node has a
success = Np(1-p)N-1
max efficiency: find p*
that maximizes
Np(1-p)N-1
for many nodes, take limit
of Np*(1-p*)N-1 as N goes
to infinity, gives:
max efficiency = 1/e = .37
efficiency: long-run
fraction of successful
slots
(many nodes, all with
many frames to send)
at best: channel
used for useful
transmissions
37%
of time!
!
Slotted ALOHA: efficiency
117. Pure (unslotted) ALOHA
unslotted Aloha: simpler, no synchronization
when frame first arrives
transmit immediately
collision probability increases:
frame sent at t0 collides with other frames sent in
[t0-1,t0+1]
118. Pure ALOHA efficiency
P(success by given node) = P(node transmits) .
P(no other node transmits in [t0-1,t0] .
P(no other node transmits in [t0-1,t0]
= p . (1-p)N-1 . (1-p)N-1
= p . (1-p)2(N-1)
… choosing optimum p and then letting n
= 1/(2e) = .18
even worse than slotted Aloha!
119. CSMA (carrier sense multiple access)
CSMA: listen before transmit:
if channel sensed idle: transmit entire frame
• if channel sensed busy, defer transmission
• human analogy: don’t interrupt others!
120. CSMA collisions
• collisions can still occur:
propagation delay
means two nodes may
not hear each other’s
transmission
• collision: entire packet
transmission time
wasted
– distance & propagation
delay play role in in
determining collision
probability
spatial layout of nodes
121. CSMA/CD (collision detection)
CSMA/CD: carrier sensing, deferral as in CSMA
collisions detected within short time
colliding transmissions aborted, reducing channel
wastage
collision detection:
easy in wired LANs: measure signal strengths,
compare transmitted, received signals
difficult in wireless LANs: received signal strength
overwhelmed by local transmission strength
human analogy: the polite conversationalist
123. Ethernet CSMA/CD algorithm
1. NIC receives datagram
from network layer,
creates frame
2. If NIC senses channel idle,
starts frame transmission.
If NIC senses channel
busy, waits until channel
idle, then transmits.
3. If NIC transmits entire
frame without detecting
another transmission, NIC
is done with frame !
4. If NIC detects another
transmission while
transmitting, aborts and
sends jam signal
5. After aborting, NIC enters
binary (exponential)
backoff:
– after mth collision, NIC
chooses K at random
from {0,1,2, …, 2m-1}.
NIC waits K·512 bit
times, returns to Step 2
– longer backoff interval
124. CSMA/CD efficiency
Tprop = max prop delay between 2 nodes in LAN
ttrans = time to transmit max-size frame
efficiency goes to 1
as tprop goes to 0
as ttrans goes to infinity
better performance than ALOHA: and simple, cheap,
decentralized!
transprop /tt
efficiency
51
1
125. “Taking turns” MAC protocols
channel partitioning MAC protocols:
– share channel efficiently and fairly at high load
– inefficient at low load: delay in channel access,
1/N bandwidth allocated even if only 1 active
node!
random access MAC protocols
– efficient at low load: single node can fully utilize
channel
– high load: collision overhead
“taking turns” protocols
126. polling:
• master node “invites”
slave nodes to transmit
in turn
• typically used with
“dumb” slave devices
• concerns:
– polling overhead
– latency
– single point of
failure (master)
master
slaves
poll
data
data
“Taking turns” MAC protocols
127. token passing:
control token passed
from one node to next
sequentially.
token message
concerns:
token overhead
latency
single point of failure
(token)
T
data
(nothing
to send)
T
“Taking turns” MAC protocols
128. MAC addresses and ARP
• 32-bit IP address:
– network-layer address for interface
– used for layer 3 (network layer) forwarding
• MAC (or LAN or physical or Ethernet) address:
– function: used ‘locally” to get frame from one
interface to another physically-connected interface
(same network, in IP-addressing sense)
– 48 bit MAC address (for most LANs) burned in NIC
ROM, also sometimes software settable
– e.g.: 1A-2F-BB-76-09-AD
hexadecimal (base 16) notation
(each “number” represents 4 bits)
129. LAN addresses and ARP
each adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
(wired or
wireless)
130. LAN addresses (more)
MAC address allocation administered by IEEE
manufacturer buys portion of MAC address
space (to assure uniqueness)
analogy:
MAC address: like Social Security Number
IP address: like postal address
MAC flat address ➜ portability
can move LAN card from one LAN to another
IP hierarchical address not portable
131. ARP: address resolution protocol
ARP table: each IP node (host,
router) on LAN has table
IP/MAC address
mappings for some
LAN nodes:
< IP address; MAC address; TTL>
TTL (Time To Live):
time after which
address mapping will
be forgotten
(typically 20 min)
Question: how to determine
interface’s MAC address,
knowing its IP address?
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
137.196.7.23
137.196.7.78
137.196.7.14
137.196.7.88
132. ARP protocol: same LAN
• A wants to send datagram
to B
– B’s MAC address not in A’s
ARP table.
• A broadcasts ARP query
packet, containing B's IP
address
– dest MAC address = FF-FF-
FF-FF-FF-FF
– all nodes on LAN receive
ARP query
• B receives ARP packet,
replies to A with its (B's)
MAC address
– frame sent to A’s MAC
• A caches (saves) IP-to-
MAC address pair in its
ARP table until
information becomes old
(times out)
– soft state: information that
times out (goes away)
unless refreshed
• ARP is “plug-and-play”:
– nodes create their ARP
tables without intervention
from net administrator
133. walkthrough: send datagram from A to B via R
– focus on addressing – at IP (datagram) and MAC layer
(frame)
– assume A knows B’s IP address
– assume A knows IP address of first hop router, R
(how?)
– assume A knows R’s MAC address (how?)
Addressing: routing to another LAN
R
1A-23-F9-CD-06-9B
222.222.222.220
111.111.111.110
E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111.111.111.112
111.111.111.111
74-29-9C-E8-FF-55
A
222.222.222.222
49-BD-D2-C7-56-2A
222.222.222.221
88-B2-2F-54-1A-0F
B
139. Ethernet
“dominant” wired LAN technology:
• cheap $20 for NIC
• first widely used LAN technology
• simpler, cheaper than token LANs and ATM
• kept up with speed race: 10 Mbps – 10 Gbps
Metcalfe’s Ethernet sketch
140. Ethernet: physical topology
• bus: popular through mid 90s
– all nodes in same collision domain (can collide with
each other)
• star: prevails today
– active switch in center
– each “spoke” runs a (separate) Ethernet protocol
(nodes do not collide with each other)
switch
bus: coaxial cable
star
141. Ethernet frame structure
sending adapter encapsulates IP datagram (or
other network layer protocol packet) in
Ethernet frame
preamble:
7 bytes with pattern 10101010 followed by
one byte with pattern 10101011
used to synchronize receiver, sender clock
dest.
address
source
address
data
(payload) CRCpreamble
type
142. Ethernet frame structure (more)
addresses: 6 byte source, destination MAC
addresses
if adapter receives frame with matching
destination address, or with broadcast address
(e.g. ARP packet), it passes data in frame to
network layer protocol
otherwise, adapter discards frame
type: indicates higher layer protocol (mostly IP
but others possible, e.g., Novell IPX, AppleTalk)
CRC: cyclic redundancy check at receiver
error detected: frame is dropped
dest.
address
source
address
data
(payload) CRCpreamble
type
143. Ethernet: unreliable, connectionless
• connectionless: no handshaking between
sending and receiving NICs
• unreliable: receiving NIC doesnt send acks or
nacks to sending NIC
– data in dropped frames recovered only if initial
sender uses higher layer rdt (e.g., TCP), otherwise
dropped data lost
144. Switch: multiple simultaneous transmissions
• hosts have dedicated, direct
connection to switch
• switches buffer packets
• Ethernet protocol used on each
incoming link, but no collisions;
full duplex
– each link is its own
collision domain
• switching: A-to-A’ and B-to-B’
can transmit simultaneously,
without collisions switch with six interfaces
(1,2,3,4,5,6)
A
A’
B
B’ C
C’
1 2
345
6
145. Switch forwarding table
Q: how does switch know
A’ reachable via interface 4,
B’ reachable via interface
5?
switch with six interfaces
(1,2,3,4,5,6)
A
A’
B
B’ C
C’
1 2
345
6 A: each switch has a
switch table, each entry:
(MAC address of host,
interface to reach host, time
stamp)
looks like a routing table!
Q: how are entries created,
maintained in switch table?
something like a routing
protocol?
146. A
A’
B
B’ C
C’
1 2
345
6
Switch: self-learning
• switch learns which hosts
can be reached through
which interfaces
– when frame
received, switch
“learns” location of
sender: incoming
LAN segment
– records
sender/location pair
in switch table
A A’
Source: A
Dest: A’
MAC addr interface TTL
Switch table
(initially empty)
A 1 60
147. A
A’
B
B’ C
C’
1 2
345
6
Self-learning, forwarding: example
A A’
Source: A
Dest: A’
MAC addr interface TTL
switch table
(initially empty)
A 1 60
A A’A A’A A’A A’A A’
• frame destination, A’,
locaton unknown:flood
A’ A
destination A location
known:
A’ 4 60
selectively
send
on just one link
148. Interconnecting switches
switches can be connected together
Q: sending from A to G - how does S1 know to
forward frame destined to F via S4 and S3?
A: self learning! (works exactly the same as in
single-switch case!)
A
B
S1
C D
E
F
S2
S4
S3
H
I
G
149. Self-learning multi-switch example
Suppose C sends frame to I, I responds to C
Q: show switch tables and packet forwarding in S1,
S2, S3, S4
A
B
S1
C D
E
F
S2
S4
S3
H
I
G
150. Switches vs. routers
both are store-and-forward:
routers: network-layer
devices (examine network-
layer headers)
switches: link-layer devices
(examine link-layer
headers)
both have forwarding tables:
routers: compute tables
using routing algorithms, IP
addresses
switches: learn forwarding
table using flooding,
learning, MAC addresses
application
transport
network
link
physical
network
link
physical
link
physical
switch
datagram
application
transport
network
link
physical
frame
frame
frame
datagram
151. VLANs: motivation
consider:
CS user moves office to EE,
but wants connect to CS
switch?
single broadcast domain:
all layer-2 broadcast
traffic (ARP, DHCP,
unknown location of
destination MAC
address) must cross
entire LAN
security/privacy,
Computer
Science Electrical
Engineering
Computer
Engineering
152. VLANs
port-based VLAN: switch ports
grouped (by switch management
software) so that single physical
switch ……
switch(es) supporting
VLAN capabilities can
be configured to
define multiple virtual
LANS over single
physical LAN
infrastructure.
Virtual Local
Area Network
1
8
9
16102
7
…
Electrical Engineering
(VLAN ports 1-8)
Computer Science
(VLAN ports 9-15)
15
…
Electrical Engineering
(VLAN ports 1-8)
…
1
82
7 9
1610
15
…
Computer Science
(VLAN ports 9-16)
… operates as multiple virtual
switches
153. Port-based VLAN
1
8
9
16102
7
…
Electrical Engineering
(VLAN ports 1-8)
Computer Science
(VLAN ports 9-15)
15
…
traffic isolation: frames
to/from ports 1-8 can only
reach ports 1-8
can also define VLAN based on
MAC addresses of endpoints,
rather than switch port
dynamic membership:
ports can be dynamically
assigned among VLANs
router
forwarding between VLANS:
done via routing (just as with
separate switches)
in practice vendors sell combined
switches plus routers