Scroatdog
10-18-2005, 02:35 PM
Just wanted to vent a bit. I've been studying for DAYS!!! Test covers LANS, WANS, modems, history of the INternet, subnetting, etc etc etc.
We are allowed to bring one 8 1/2 by 11 sheet of paper (front and back) for notes. And he doesn't care if they're typed. BTW, this is for a Master's degree in Information Technology.
I thought it would be fun to cut & paste my cheast sheet for all to see!!
ENJOY! :confused:
Identify the essential features of networks
Sessions – dialogue between 2 system users. A connection between 2 nodes that enables them to communicate
Network – two+ computers connected by a communication medium, together w/ all communication hw & sw components.
Node – network junction or connection point. PC in a LAN is a node. Terminals connected to mainframes also nodes
Link – a line, channel , circuit, or transmission path over which data is transmitted
Path - the route between any two nodes in a network; set of links, lines, channels, or circuits
Circuit – either the medium connecting 2 communicating devices or a path between sender & receiver that may include 1 or more intermediary nodes. Virtual circuit msgs sent over the same path once established
Packetizing – dividing a msg into fixed-length packets prior to transmitting, contains seq of data & control info
Routing – how the path from sending node to receiving mode is determined.; process for selecting a circuit path for a message
Store & Forward – network system that enables the temp storage of a message for transmission to its destination at a later time. Desirable 4 large networks including the Internet. Info stored in intermediate nodes. Used for time-staged delivery(time zones), valuable when paths to destination are blocked
Topology – Physical layout of a network, the way the nodes are attached to the communication medium
Architecture – more comprehensive term & refers to the way in which media, hw, and sw integrate to form a network.
Complexity – Simple – midrange computer & handful of PC’s, located in same room. More elaborate – several LANS, each of which connected by with a mainframe or midrange computer.
Understand significant events in the history of data communications
When it began – 1837 – Samuel Morse invents mores code; 1876 – telephone invented by Bell; 1969 – Arpanet comes online; 1896 – wireless tech invented; 1969 –ARPANET, 1975 – PC’s introduced (Altaire8800); 1984 ATT Divestiture; 1990 – internet introduced; 1996 Telecommunications Reform Act of 1996 introduced
Main areas of improvement – transistor invented to replace vacuum tubes (1947); faster delivery & less error
E-Commerce Framework – guiding principles: Private sector should lead, Govt’s should avoid undue restrictions on electronic commerce, where gov’t involvement is needed, aim should be to support & enfrorce a predictable, minimalist, consistent, and simple legal envir’t for commerce, electronic commerce over the internet should be facilitated on a global basis
E Commerce key issues – customs & taxation, universal commercial code for e-commerce, privacy, telecom infrastructure & IT, tech standards, electronic payment sys, intellectual property protection, security, content
Data Communication Frameworks
OSI Model – International Standards Organization (ISO) identified & stratified the functions that every network must fulfill. This model makes it easier to develop interfaces among these diverse networking technologies. The OSI Reference Model (Open Systems Interconnection) describes and defines a network architecture. A seven layer set of functions for xmitting data from one use to another. Seven layers are Application Layer, Presentation Layer, Session Layer, Transport Layer, Network Layer, Data Link Layer, Physical Layer. Created in the 70’s by 10 people. Considered all functions of communications. 4U 3L (more layers, more overhead but better security)
TCP/IP – Transmission Control Protocol/Internet Protocol –a set of layered protocols developed by DoD for Internet work files transfers, e-mail transfer, remote logons, and terminal services. Defacto communication protocol of the internet & global standard for communications. TCP/IP layers are: Application, Transport(host-to-host), Internet, Network Access, and Physcial. Protocols at each layer of the model can operate independently from those found at the other layers, which means protocol for a given layer can be modified without having to change the protocols in the other layers.
Important Internet Advisory Groups
W3C – Wold Wide Web Consortium, int’l, founded 1994 to develop common standards for the World Wide Web hosted by MIT
ICANN – Internet Corporation for Assigned Names and Number, nonprofit int’l association (1998), managed Internet addresses, domain names, and huge # of parameters with Internet protocols (port #’s, router protocols)
IETF – Internet Engineering Steering Group, since 1986, volunteer org whose working groups are dedicated to identifying problems & providing tech solutions to the Internet.
IAB – Internet Architecture Board, volunteer org that provides architectural guidance to and adjudicates conflicts for the IETF.
Key TCP/IP Protocols
TCP – (Transmission Control Protocol) is the key communications protocol at the transport or host-to-host layer of the TCP/IP stack. Responsible for ensuring that all the data packets transmitted by the sending host arrive at the destination host, & that data is exchanged reliably across hosts located in different networks.
IP – network-layer protocol used on the Internet and many private networks. IP is used to route messages across interconnected networks. Different versions include IPv4 & IP6
FTP – a protocol found at the application layer of the TCP/IP protocol stack that allows files to be transferred from one node to another over the network.
TELNET – program that allows a user to connect to a host in another network. Local computer & remote computer. Allows a user to log on to a remote computer & use it in the same way as if they were directly connected to it.
WAP – Wireless Application Protocol – enables Internet-ready cell phones, pagers, PDA’s and other wireless comm. devices to receive and display Web pages on their small screens
SMTP – simple mail transfer protocol – protocol within TCP/IP suite; application layer protocol used to implement mail services; standard e-mail protocol for the Internet
SNMP – Simple Network Management Protocol – uses TCP/IP to send status messages from network devices to the workstation console to oversee the network; assist in monitoring network performance
HTTP – hypertext transport protocol – communication protocol in TCP/IP networks that enables users to fetch web pages from web servers via hyperlinks
IPv6 – new version or expansion of Internet which provides significant improvements over IPv4, like the expansion of the Internet address space from 32 bits to 128 bits. This will allow 3 x 1038 addresses.
Types of transmission
Parallel – when bits that make up the byte are transmitted simultaneously over multiple lines dedicated 2 data (limited by distance)
Serial – When the bits that make up the byte are transmitted in sequence, one at a time, over the same wire
Asynch – oldest & most common data link protocol. Each character transmitted individually with its own error detection scheme, usually a parity bit, sender & receiver are not synchronized w/ each other.
Synchronous – transmission of data in which both stations are synchronized. Codes sent to receiving station to establish the sync, then data is transmitted in continuous streams. Modems that support have internal clock
UART – Universal asynchronous receiver/transmitter, UART accepts characters via parallel transmission from the terminal or computer and places them on the circuit serially. At the heart of asynch transmission.
Handshaking – signals transmitted back & forth over comm network that establishes a valid connection between two stations. Sending & receiving stations must aggress on # of bits to be used for a character
Simplex – data flows in one direction; radio & tv
Half Duplex – data travels in both directions, one at a time; CB radio
Full Duplex – data transmitted both directions simultaneously; radio wave transmission, coax cable
Analog – transmission of data over phone line; data is represented by a continuously varying electrical signal; data are represented in analog form by varying the amplitude, frequency, or phase of a wave
Interfaces & Interface Standards
DCE – Data communications equipment; includes modems, media, and media support facilities, also called data circuit terminating equipment
DTE – data terminating equipment, a computer or terminal that is the source or destination of signals on a network.
Interface between DCE & DTE divided into 4 sections: mechanical (kind of connectors to be used), electrical (allowable line voltages), functional (which signals re to be carried by each pin in connector), procedural (define how signals are exchanged and delineate the envt necessary to transmit & receive data
Subnetting enables network managers to extend the network portion of IPv4 addresses by taking away a portion of the host/node portion of the IP address, The portion that is taken away is used as a subnet identifier A subnet mask is a binary bit pattern that is stored in hosts, nodes, and routers;
Subnet mask is matched up with an incoming packet’s destination IP address to determine whether to accept or reject the packet; Every TCP/IP network host/node or router stores a subnet mask along with its IP address; The subnet mask specifies which bits in an IP address should be treated as an extended network address (network + subnet) and which bits represent the host/node portion of the address, Default subnet masks exists for class A, B, and C networks
Error Detection Approaches
Parity check – AKA vertical redundancy check; for each character xmitted, parity bit. Most commonly used for asynch xmsn
LRC – longitudinal redundancy check – block check character appended to a block of xmitted characters, usually combined with VRC (parity check), but neither is sufficient to detect al errors
Checksums – used to check for errors in blocks of data by adding decimal values of each characters in a block of data
CRC – detects bit errors better than VRC, LRC; uses a polynomial function to generate the block check characters. Very efficient
Sequence checks, check digits, hash totals, byte counts, character echo
Error Correction Approaches
ARQ – automatic repeat request – most widely used; receiver requests retransmission if error occurs
Discrete ARQ – stop & wait ARQ; sender xmits a packet & waits for + ACK or – NAK before transmitting another character or packet. If NAK received, retransmits original packet; least efficient because of time
Continuous ARQ – go-back/sliding window ARQ; appends sequence numbers to packets, allows sender to keep sending packets up to a fixed number. If error, NAK is sent with the packet sequence # and all other packets following the error packet
Selective ARQ – also sliding window protocol more efficient than discrete; allow for re-transmitting only the error packet; more efficient than continuous & has highest throughput
Forward Error-Correction Codes – receiver not only detects errors but also corrects some of them because it has the code; most common is hamming code & trellis coded modulation (TCM)
Port – Once IP address are received by destination host/node & begin processing up the TCP/IP protocol stack, they must be directed to the appropriate applicaton; TCP & UDP use port numbers, which are included in every TCP or UDP header. Port number identifies the application layer protocol that generated that data in packet
Socket – consists of a combination of a TCP port number and an IP address. Sockets are used in TCP/IP networks to direct data to appropriate applications on hosts.
Ok, I'm off to the library to continue studying! 4 1/2 hours to go ! :fact:
We are allowed to bring one 8 1/2 by 11 sheet of paper (front and back) for notes. And he doesn't care if they're typed. BTW, this is for a Master's degree in Information Technology.
I thought it would be fun to cut & paste my cheast sheet for all to see!!
ENJOY! :confused:
Identify the essential features of networks
Sessions – dialogue between 2 system users. A connection between 2 nodes that enables them to communicate
Network – two+ computers connected by a communication medium, together w/ all communication hw & sw components.
Node – network junction or connection point. PC in a LAN is a node. Terminals connected to mainframes also nodes
Link – a line, channel , circuit, or transmission path over which data is transmitted
Path - the route between any two nodes in a network; set of links, lines, channels, or circuits
Circuit – either the medium connecting 2 communicating devices or a path between sender & receiver that may include 1 or more intermediary nodes. Virtual circuit msgs sent over the same path once established
Packetizing – dividing a msg into fixed-length packets prior to transmitting, contains seq of data & control info
Routing – how the path from sending node to receiving mode is determined.; process for selecting a circuit path for a message
Store & Forward – network system that enables the temp storage of a message for transmission to its destination at a later time. Desirable 4 large networks including the Internet. Info stored in intermediate nodes. Used for time-staged delivery(time zones), valuable when paths to destination are blocked
Topology – Physical layout of a network, the way the nodes are attached to the communication medium
Architecture – more comprehensive term & refers to the way in which media, hw, and sw integrate to form a network.
Complexity – Simple – midrange computer & handful of PC’s, located in same room. More elaborate – several LANS, each of which connected by with a mainframe or midrange computer.
Understand significant events in the history of data communications
When it began – 1837 – Samuel Morse invents mores code; 1876 – telephone invented by Bell; 1969 – Arpanet comes online; 1896 – wireless tech invented; 1969 –ARPANET, 1975 – PC’s introduced (Altaire8800); 1984 ATT Divestiture; 1990 – internet introduced; 1996 Telecommunications Reform Act of 1996 introduced
Main areas of improvement – transistor invented to replace vacuum tubes (1947); faster delivery & less error
E-Commerce Framework – guiding principles: Private sector should lead, Govt’s should avoid undue restrictions on electronic commerce, where gov’t involvement is needed, aim should be to support & enfrorce a predictable, minimalist, consistent, and simple legal envir’t for commerce, electronic commerce over the internet should be facilitated on a global basis
E Commerce key issues – customs & taxation, universal commercial code for e-commerce, privacy, telecom infrastructure & IT, tech standards, electronic payment sys, intellectual property protection, security, content
Data Communication Frameworks
OSI Model – International Standards Organization (ISO) identified & stratified the functions that every network must fulfill. This model makes it easier to develop interfaces among these diverse networking technologies. The OSI Reference Model (Open Systems Interconnection) describes and defines a network architecture. A seven layer set of functions for xmitting data from one use to another. Seven layers are Application Layer, Presentation Layer, Session Layer, Transport Layer, Network Layer, Data Link Layer, Physical Layer. Created in the 70’s by 10 people. Considered all functions of communications. 4U 3L (more layers, more overhead but better security)
TCP/IP – Transmission Control Protocol/Internet Protocol –a set of layered protocols developed by DoD for Internet work files transfers, e-mail transfer, remote logons, and terminal services. Defacto communication protocol of the internet & global standard for communications. TCP/IP layers are: Application, Transport(host-to-host), Internet, Network Access, and Physcial. Protocols at each layer of the model can operate independently from those found at the other layers, which means protocol for a given layer can be modified without having to change the protocols in the other layers.
Important Internet Advisory Groups
W3C – Wold Wide Web Consortium, int’l, founded 1994 to develop common standards for the World Wide Web hosted by MIT
ICANN – Internet Corporation for Assigned Names and Number, nonprofit int’l association (1998), managed Internet addresses, domain names, and huge # of parameters with Internet protocols (port #’s, router protocols)
IETF – Internet Engineering Steering Group, since 1986, volunteer org whose working groups are dedicated to identifying problems & providing tech solutions to the Internet.
IAB – Internet Architecture Board, volunteer org that provides architectural guidance to and adjudicates conflicts for the IETF.
Key TCP/IP Protocols
TCP – (Transmission Control Protocol) is the key communications protocol at the transport or host-to-host layer of the TCP/IP stack. Responsible for ensuring that all the data packets transmitted by the sending host arrive at the destination host, & that data is exchanged reliably across hosts located in different networks.
IP – network-layer protocol used on the Internet and many private networks. IP is used to route messages across interconnected networks. Different versions include IPv4 & IP6
FTP – a protocol found at the application layer of the TCP/IP protocol stack that allows files to be transferred from one node to another over the network.
TELNET – program that allows a user to connect to a host in another network. Local computer & remote computer. Allows a user to log on to a remote computer & use it in the same way as if they were directly connected to it.
WAP – Wireless Application Protocol – enables Internet-ready cell phones, pagers, PDA’s and other wireless comm. devices to receive and display Web pages on their small screens
SMTP – simple mail transfer protocol – protocol within TCP/IP suite; application layer protocol used to implement mail services; standard e-mail protocol for the Internet
SNMP – Simple Network Management Protocol – uses TCP/IP to send status messages from network devices to the workstation console to oversee the network; assist in monitoring network performance
HTTP – hypertext transport protocol – communication protocol in TCP/IP networks that enables users to fetch web pages from web servers via hyperlinks
IPv6 – new version or expansion of Internet which provides significant improvements over IPv4, like the expansion of the Internet address space from 32 bits to 128 bits. This will allow 3 x 1038 addresses.
Types of transmission
Parallel – when bits that make up the byte are transmitted simultaneously over multiple lines dedicated 2 data (limited by distance)
Serial – When the bits that make up the byte are transmitted in sequence, one at a time, over the same wire
Asynch – oldest & most common data link protocol. Each character transmitted individually with its own error detection scheme, usually a parity bit, sender & receiver are not synchronized w/ each other.
Synchronous – transmission of data in which both stations are synchronized. Codes sent to receiving station to establish the sync, then data is transmitted in continuous streams. Modems that support have internal clock
UART – Universal asynchronous receiver/transmitter, UART accepts characters via parallel transmission from the terminal or computer and places them on the circuit serially. At the heart of asynch transmission.
Handshaking – signals transmitted back & forth over comm network that establishes a valid connection between two stations. Sending & receiving stations must aggress on # of bits to be used for a character
Simplex – data flows in one direction; radio & tv
Half Duplex – data travels in both directions, one at a time; CB radio
Full Duplex – data transmitted both directions simultaneously; radio wave transmission, coax cable
Analog – transmission of data over phone line; data is represented by a continuously varying electrical signal; data are represented in analog form by varying the amplitude, frequency, or phase of a wave
Interfaces & Interface Standards
DCE – Data communications equipment; includes modems, media, and media support facilities, also called data circuit terminating equipment
DTE – data terminating equipment, a computer or terminal that is the source or destination of signals on a network.
Interface between DCE & DTE divided into 4 sections: mechanical (kind of connectors to be used), electrical (allowable line voltages), functional (which signals re to be carried by each pin in connector), procedural (define how signals are exchanged and delineate the envt necessary to transmit & receive data
Subnetting enables network managers to extend the network portion of IPv4 addresses by taking away a portion of the host/node portion of the IP address, The portion that is taken away is used as a subnet identifier A subnet mask is a binary bit pattern that is stored in hosts, nodes, and routers;
Subnet mask is matched up with an incoming packet’s destination IP address to determine whether to accept or reject the packet; Every TCP/IP network host/node or router stores a subnet mask along with its IP address; The subnet mask specifies which bits in an IP address should be treated as an extended network address (network + subnet) and which bits represent the host/node portion of the address, Default subnet masks exists for class A, B, and C networks
Error Detection Approaches
Parity check – AKA vertical redundancy check; for each character xmitted, parity bit. Most commonly used for asynch xmsn
LRC – longitudinal redundancy check – block check character appended to a block of xmitted characters, usually combined with VRC (parity check), but neither is sufficient to detect al errors
Checksums – used to check for errors in blocks of data by adding decimal values of each characters in a block of data
CRC – detects bit errors better than VRC, LRC; uses a polynomial function to generate the block check characters. Very efficient
Sequence checks, check digits, hash totals, byte counts, character echo
Error Correction Approaches
ARQ – automatic repeat request – most widely used; receiver requests retransmission if error occurs
Discrete ARQ – stop & wait ARQ; sender xmits a packet & waits for + ACK or – NAK before transmitting another character or packet. If NAK received, retransmits original packet; least efficient because of time
Continuous ARQ – go-back/sliding window ARQ; appends sequence numbers to packets, allows sender to keep sending packets up to a fixed number. If error, NAK is sent with the packet sequence # and all other packets following the error packet
Selective ARQ – also sliding window protocol more efficient than discrete; allow for re-transmitting only the error packet; more efficient than continuous & has highest throughput
Forward Error-Correction Codes – receiver not only detects errors but also corrects some of them because it has the code; most common is hamming code & trellis coded modulation (TCM)
Port – Once IP address are received by destination host/node & begin processing up the TCP/IP protocol stack, they must be directed to the appropriate applicaton; TCP & UDP use port numbers, which are included in every TCP or UDP header. Port number identifies the application layer protocol that generated that data in packet
Socket – consists of a combination of a TCP port number and an IP address. Sockets are used in TCP/IP networks to direct data to appropriate applications on hosts.
Ok, I'm off to the library to continue studying! 4 1/2 hours to go ! :fact: