Computer Science OverviewChap4-Networking and the Internet (2)
JainShing Wu
Networking TopologyThe layout of the
interconnections of the nodes of a computer network
Types◦Bus◦Star◦Token ring◦Mesh
Bus NetworkA set of clients are connected via a shared
communications lineEthernetAdvantage
◦ Easy to setupDisadvantage
◦ Reconfiguration, fault isolation and installation of new devices tends to be difficult
◦ A fault along the shared communication line stops all transmissions in the network
BUS Network
Star NetworkConsists of one central switch,
hub or computer to which all other nodes are connected
Client and Server
Star NetworkAdvantage
◦ Better performance◦ Isolation of devices◦ Benefits from centralization◦ Easy to detect faults and to remove parts◦ No disruptions to the network when connecting or
removing devices◦ Installation and configuration is easy
Disadvantage◦ High dependence of the system on the functioning
of the central hub◦ Failure of the central hub renders the network
inoperable
Star Network
Token RingEach node connects to exactly
two other nodes, forming a ringFiber Distributed Data Interface
(FDDI)
Token Ring
Mesh NetworkEach node captures and
disseminates its own data, but also serve as a relay for other nodes
Mobile ad hoc networks (MANET)
Mesh Network
EthernetComputer networking
technologies for local area networks (LANs)
Ethernet was commercially introduced in 1980 and standardized in 1985 as IEEE 802.3
Several wiring and signaling variants of the OSI physical layer in use with Ethernet
EthernetThe original 10BASE5 Ethernet
used coaxial cable as a shared medium
EthernetHubBridgeSwitchRouter
Ethernet HubA device for connecting multiple
Ethernet devices together and making them act as a single network segment
Multiple input/output (I/O) ports
BridgeNetwork equipment to allow two
or more communication networks, or two or more network segments
SwitchOperate at one or more layers of
the OSI model including data link and network
Operates simultaneously at more than one of these layers
Switch
RouterA device that
◦Forwards data packets between computer networks
◦Creating an overlay internetworkConnected to two or more data
lines from different networks
RouterReads the address information in
the packet to determine its ultimate destination
Using information in its routing table or routing policy, it directs the packet to the next network on its journey
Router
Internet Protocol SuiteA set of communications
protocols used for the Internet and similar networks
OSI seven layersKnown as
◦Transmission Control Protocol (TCP)◦Internet Protocol (IP)
OSI Seven LayersOSI Model
Data Unit Layer Function
Host Layers
Data
7. Application Network process to application
6. Presentation
Data representation, encryption and decryption, convert machine dependent data to machine independent data
5. Session Inter-host communication, managing sessions between applications
Segments 4. Transport End-to-end connections, reliability and flow control
MediaLayers
Packet/Datagram 3. Network Path determination and logical
addressingFrame 2. Data Link Physical addressing
Bit 1. Physical Media, signal and binary transmission
Physical LayerDefines electrical and physical
specifications for devicesDefines the relationship between
a device and a transmission medium◦Copper cable ◦Fiber optical cable◦Includes the layout of pins, Voltages,
line impedance, cable specifications, signal timing, hubs, repeaters, network adapters, host bus adapters
Data Link LayerProvides the functional and
procedural means to transfer data between network entities
Detect possibly errors that may occur in the physical layer
Intended for ◦Unicasts◦Multicasts◦Broadcasts
Network LayerProvides the functional and procedural
means of transferring variable length data sequences from host (source) to host (destination)
Maintains the quality of service (QoS) requested by the transport layer
Performs ◦ Network routing functions◦ Fragmentation and reassembly◦ Report delivery errors
Network LayerDivided into three sub-layers:
◦Subnetwork access –considers protocols that deal with the interface to networks
◦Subnetwork-dependent convergence – when it is necessary to bring the level of a transit network up to the level of networks on either side
◦Subnetwork-independent convergence – handles transfer across multiple networks
Transport LayerProvides transparent transfer of
data between end usersProvides reliable data transfer
services to the upper layersControls the reliability of a given
link through flow control, segmentation/desegmentation, and error control
Session LayerControls the dialogues
(connections) between computers
Establishes, manages and terminates the connections between the local and remote application
Presentation LayerEstablishes context between
application-layer entitiesProvides a mapping between the
application-layer entities that may use different syntax and semantics
Presentation service data units are encapsulated into session protocol data units, and passed down the stack
Application LayerIs the OSI layer closest to the end
userBoth the OSI application layer
and the user interact directly with the software application
Identify communication partners, determine resource availability, and Synchronizing communication
Transmission Control Protocol (TCP)One of the core protocols of the
Internet Protocol SuiteThe protocol used by major
Internet applications Provides reliable, ordered
delivery of a stream of octets from a program on one computer to another program on another computer
Transmission Control Protocol (TCP)The protocol corresponds to the
transport layerProvides a communication
service at an intermediate level between an application program and the Internet Protocol (IP)
Transmission Control Protocol (TCP)Detect the problem
◦ IP packets can be lost, duplicated, or delivered out of order
Requests retransmission of lost dataRearranges out-of-order dataHelps minimize network congestionA reliable stream delivery service that
guarantees all bytes received identical with bytes sent and in the correct order
Internet Protocol (IP)A principal communications
protocol used for relaying datagrams (network packets) across an internetwork
It is the primary protocol that establishes the Internet
Deliver datagrams from the source host to the destination host based on the addresses
Internet Protocol (IP)The primary protocol in the
network layerAddress hosts and route
datagrams (packets)
Internet Protocol (IP)Datagram construction
◦ Each datagram has two components, header and payload
◦ Header Source IP address, Destination IP address,
and other meta-data needed to route and deliver the datagram
◦ Payload the data to be transported
◦ This process of nesting data payloads in a packet with a header is called encapsulation
Internet Protocol (IP)IP address and routing algorithms
◦IP Addressing refers to How end hosts are assigned IP addresses How subnetworks of IP host addresses
are divided and grouped◦Routing algorithms
Routing is performed by all hosts, but most importantly by routers
Routing algorithms decide how to move datagrams among networks
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