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jim zasta

on 26 March 2013

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Transcript of Computer_Networks

Computer Networks A network topology is the generic Arrangement of cables that connect devices together.
The most common are star, ring, bus, tree and hybrid.
Each topology has trade offs and it is up to the administrator to make educated decisions. Network Topology The tree topology breaks the network into different branches.
The benefit is if a single node fails message can still travel through the network.
If a message reaches the endpoint controller without a node taking it then the controller will absorb it. Tree All sites are connected to a single communication line.
Only one can send messages at a time.
Therefore a control mechanism has to be utilized.
Some bus networks have to travel through all the nodes to get a message across while other networks have direct access capability. Bus Ring topology is connected in a closed loop.
Hosts are connected to each other and
Two networks combined with a bridge or gateway.
Each packet is transmitted from node to node in one direction.
Different variations of the Ring topology.
Every node must be connected to properly function unless designed differently Ring Must pass through a central controller.
Star topology enables easy routing because the central controller knows the routes to each node.
Needs to be reliable and able to handle all traffic, even when busy. Star There are four main basic concepts
Cost in money
Communication cost
User’s Environment
The key to choosing the best design is to understand the available technology, as well as the customer’s business requirements and budget. Making a Decision Network Topologies The hybrid technology is an attempt to take any of the four topologies and combine them.
Through combining them you can take the best strong points from certain topologies. Hybrid The Institute of Electrical and Electronics Engineers (IEEE) has specified several standards for wireless networking, each with different ranges. Comparing IEEE LAN
a configuration found within a single office building, warehouse, campus, or similar computing environment data rate that varies from 100 megabits per second to more than 40 gigabits per second

a configuration spanning an area larger than a LAN, ranging from several blocks of buildings to an entire city but not exceeding a circumference of 100 kilometers high-speed network often configured as a logical ring
Types of Networks Although the addresses allow routers to send data from one network to another, they can’t be used to get from one point in a network to another point in the same network
must be done through address resolution, which allows a router to map the original address to a hardware address and store the mapping in a table to be used for future transmissions
A variety of message formats are defined by routing protocols:
These messages are used to allow the protocol to perform its functions, such as:
finding new nodes on a network
testing to determine whether they’re working
reporting error conditions
exchanging routing information
establishing connections
and transmitting data. A router is an internetworking device, primarily software driven, which directs traffic between two different types of LANs or two network segments with different protocol addresses
Routing allows data to get from one point on a network to another
Routers are used extensively for connecting sites to each other and to the Internet
Functions of a router include:
securing the information that is generated in predefined areas
choosing the fastest route from one point to another
providing redundant network connections so that a problem in one area will not degrade network operations in other areas
Most routing protocols are based on an addressing format that uses a network and a node number to identify each node Routing Strategies Domain Name Service (DNS):
a general-purpose distributed data query service whose principal function is the resolution of Internet addresses
Ex: Internet address: someone@icarus.lis.pitt.edu
someone is the logical user
icarus is the host for the user called someone
lis is the net machine for icarus
pitt is the cluster for lis, and
edu is the network for the University of Pittsburgh Names, addresses, and routes are required because sites aren’t directly connected to each other except over point-to-point links
addressing protocols are closely related to the network topology and geographic location of each site
Local name:
refers to the name by which a unit is known within its own system
Global name:
the name by which a unit is known outside its own system Addressing Conventions Transport Protocol Standards Network??? A Computer Network process is a collection of loosely coupled processors interconnected by
communication links using cables, wireless technology, or a combination of both.

First Network ARPANET

Resources include both hardware (such as a CPU, memory, printers, USB ports, and disk drives) and software

Communication Medium- VOIP, Email, Etc


Destination and sequence number of the packet are added to the information uniquely identifying the message to which the packet belongs

Each packet handled independently and a route is selected
Example: Shipping Label

2 advantages
diminish congestion
more reliability Selecting a Path Packet Switching Circuit Switching Routing Information Protocol (RIP)
Path is selected based on the number of intermediate nodes, or hops, between the source and the destination.
Small hops: recommended
Open Shortest Path First (OSPF)
Path is selected only after the state of a network has been determined
Dijkstra’s algorithm: shortest-path tree to get around the failed link. Most Common Routing Protocols Addressing
Network and a node number to identify each node.
Although the addresses allow routers to send data from one network to another, they can’t be used to get from one point in a network to another point in the same network
Address Resolution
Allows a router to map the original address to a hardware address and store the mapping in a table to be used for future transmissions. Routing Protocols Router: A -> B
Directs traffic between 2 different types of LAN

Routing Protocols : addressing, address resolution, message format, and error reporting Network Layer No destination and packet sequence number because a complete path from sender to receiver is established before transmission starts. All the packets that belong to the message use the same route.

Advantage: Routing decision made only once

Disadvantage: If a node fails, all virtual circuits using that node become unavailable and congestion is more difficult to resolve. Virtual Circuit Packet Switching Circuit Switching Connection Models Cont.. Message Format
messages are to perform its functions, such as establishing connections, transmitting data, etc.
Error Reporting
errors such as unable to reach a destination because of a malfunctioning node or network.
report the error. 1980s Fast Pace growth
integrate dissimilar network devices
Number of devices
Created a single universally adopted network architecture. OSI International Organization for Standardization (IOS) Open Systems Interconnection reference Model Once all services were identified, similar functions were collected together into seven logical clusters known as layers. The Layers Layer 6—The Presentation Layer
Data manipulation functions
Formatting, Compression and Encryption.
Data conversion, syntax conversion, and protocol conversion
Gateways connecting networks with different protocols

Layer 7—The Application Layer
Application programs, terminals, and computers access the network.
Provides the interface to users
Formats user data before passing to lower layers
File transfer and e-mail are two common application protocols and functions.

Once the OSI model is assembled, it allows nodes to communicate with each other.
Each layer provides a completely different array of functions to the network, but all
the layers work in unison to ensure that the network provides reliable transparent service
to the users. Layer 4 —The Transport Layer
Known as the host-to-host or end-to-end layer
Maintains reliable data transmission between end users.
Uses message headers and control messages.
Handles user addressing and ensures that all the packets of data have been received and that none have been lost.
Regulates the flow of information
Fast host can’t overrun a slower terminal or an overloaded host.
Layer protocol
Transmission Control Protocol (TCP).

Layer 5—The Session Layer
Provides a user-oriented connection
Responsible for creating and maintaining a logical connection between two points.
Known as the “data flow control” layer
Establishes the connection between two applications or processes
Enforces the regulations for carrying on the session
Controls the flow of data
Resets the connection if it fails Layer 1 – The Physical Layer
The bottom of the model
Mechanical electrical
Only Layer concerned with hardware

Layer 2 – The Data Link Layer
Programmable device: front-end processors, network node, or micro computer
Bridges Two Homogenous networks together.
Establishes and controls the physical path of communications
Creates Frames that contain data combined with control and error detection
Data Link Protocols
High-Level Data Link Control (HDLC)
Synchronous Data Link Control (SDLC).

Layer 3 – The Network Layer
Responsible for addressing and routing
Allows a node and its network to be identified
Uses algorithms to handle address resolution
routing tables
track of all possible routes
Determines amount of circuits between two packet switching nodes.
Tracks failed circuit and the transmission volume present in the active circuits. TCP/IP Transmission Control Protocol/Internet Protocol Whats the difference? The significance that TCP/IP places on internetworking and providing connectionless services, and its management of certain functions, such as accounting for use of resources.. 3 Main components
Processes- execute on the host
Hosts- two major tasks:
Manages the transfer of information to the host in which the process resides
Ensures it gets to the correct process within the host
Network- routing data between hosts Layers Network Access Layer
Equivalent to the physical, data link, and part of the network layers of the OSI model.
Protocols provide access to a communication network.
Functions are flow control, error control, security, and priority implementation.

Internet LayerEquivalent part of the network layer of the OSI model
Performs routing functions.
Implemented within gateways and hosts.

Host-Host LayerEquivalent to transport and session layers of the OSI model.Supports mechanisms to transfer data between two processes on different host computers.
Services include error checking, flow control, and manipulate connection control signals.

Process/Application Layer
Equivalent to the presentation and application layers of the OSI model
Includes protocols for computer-to-computer resource sharing
and terminal-to-computer remote access
Standards- File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), and Telnet Is better for short and intermittent traffic

One the easier techniques to implement

Bad performance under heavy load

Contention Technique Allows each node on the network to use the communication medium

Round robin is an efficient technique when there are many nodes transmitting over long periods of time. Round Robin Round Robin


Contention Access Control Techniques Token Bus
In networks, a special electronic message is called a "TOKEN"

Token Passing Suited for lengthy and continuous traffic.

This technique is good for a configuration with several terminals connected to a host computer through a single I/O port. Reservation Technique Packet Switching Shared by many transmissions

Used by high-volume networks

Transmits in batches

High line efficiency Dedicated to a single transmission

Preferred for voice communications

Transmits in real time

Reduced line efficiency Circuit Switching WAN
configuration that interconnects communication facilities in different parts of the world, or that’s operated as part of a public utility The first WAN, ARPANET, was developed in 1969 by the Advanced Research Projects Agency (ARPA)Generally slower than LANs

local area network that uses wireless technology to connect computers or workstations located within the range of the network
each computer in the network can act as a client or server for the other computers in the network, allowing shared access to various resources such as files, peripherals, and sensors without the need for a central server. The model assigns one of two roles to the computers in a network: Client or server. A server is a computer system that selectively shares its resources; a client is a computer or computer program that initiates contact with a server in order to make use of a resource. Any Questions???
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