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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