Flashcards
Networking
Cards in this deck (40)
- 1ACKAcknowledgmnt
- 2Address ResolutionTo send a message the sender must be able to translate the application layer address (or server name) of the destination into a network layer address and in turn translate that into a data link layer address. Tis process is called address resolution. Tere are many different approaches to address resolution that range from completely decentralized (each computer is responsible for knowing all addresses) to completely centralized (there is one computer that knows all addresses). TCP/IP uses two different approaches one for resolving application layer addresses into IP addresses and a different one for resolving IP addresses into data link layer addresses.
- 3Application Architecturesthe way in which the functions of the application layer sofware are spread among the clients and servers in the network.
- 4Address Resolution Protocol (ARP)that says “Whoever is IP address xxx.xxx.xxx.xxx please send me your data link layer address.” Te sofware in the computer with that IP address then sends an ARP response with its data link layer address. Te sender transmits its message using that data link layer address. Te sending computer also stores the data link layer address in its address table for future use.
- 5Bandwiththe difference between the highest and the lowest frequencies in a band or set of frequencies. Te range of human hearing is between 20 Hz and 14 000 Hz so its bandwidth is 13 880 Hz. Te maximum symbol rate for analog transmission is usually the same as the bandwidth as measured in hertz. If the circuit is very noisy the maximum symbol rate may fall as low as 50% of the bandwidth. If the circuit has very little noise it is possible to transmit at rates up to the bandwidth
- 6Border Gateway Protocol (BGP)a dynamic distance vector exterior routing protocol used on the Internet to exchange routing information between autonomous systems—that is large sections of the Internet. Although BGP is the preferred routing protocol between Internet sections it is seldom used inside companies because it is large complex and ofen hard to administer.
- 7backbone network (BN)A larger central network connecting several LANs other BNs MANs and WANs. BNs typically span from hundreds of feet to several miles and provide very high-speed data transmission commonly 100 to 1 000 Mbps.
- 8BroadbandDSL and cable modem technologies are commonly
- 9Codecit is possible to translate analog voice data into digital form for transmission over digital computer circuits using a device called a codec. Once again there are two codecs one at the sender’s end and one at the receiver’s end. Why bother to translate voice into digital? Te answer is that digital transmission is “better” than analog transmission. Specifcally digital transmission offers fve key benefts over analog transmission:
- 10fve key benefts over analog transmission:Digital transmission produces fewer errors than analog transmission. Because the transmitted data are binary (only two distinct values) it is easier to detect and correct errors. ◾ Digital transmission permits higher maximum transmission rates. Fiber-optic cable for example is designed for digital transmission. Digital transmission is more efcient. It is possible to send more data through a given circuit using digital rather than analog transmission. Digital transmission is more secure because it is easier to encrypt. Finally and most importantly integrating voice video and data on the same circuit is far simpler with digital transmission
- 11Data FlowCircuits can be designed to permit data to flow in one direction or in both directions. Actually there are three ways to transmit: simplex half-duplex and full-duplex Obviously one factor is the application. If data always need to flow only in one direction (e.g. from a remote sensor to a host computer) then simplex is probably the best choice. In most cases however data must flow in both directions. Te initial temptation is to presume that a full-duplex channel is best; however each circuit has only so much capacity to carry data. Creating a full-duplex circuit means that the circuit offers full capacity both ways simultaneously. In some cases it makes more sense to build a set of simplex circuits in the same way a set of one-way streets can increase the speed of trafc. In other cases a half-duplex circuit may work best Physical Layer connected to mainframes ofen transmit data to the host wait for a reply transmit more data and so on in a turn-taking process; usually trafc does not need to flow in both directions simultaneously. Such a trafc pattern is ide
- 12Domain Name Service(DNS)Troughout the Internet a series of computers called name servers provides DNS services. Tese name servers have address databases that store thousands of Internet addresses and their corresponding IP addresses. Tese name servers are in effect the “directory assistance” computers for the Internet. Anytime a computer does not know the IP number for a computer it sends a message to the name server requesting the IP number.
- 13Enhanced Interior Gateway Routing Protocol (EIGRP)a dynamic hybrid interior routing protocol developed by Cisco and is commonly used inside organizations. Hybrid means that it has some features that act like distance vector protocols and some other features that act like link-state protocols. As you might expect EIGRP is an improved version of Interior Gateway Routing Protocol (IGRP). EIGRP records information about a route’s transmission capacity delay reliability and load. EIGRP is unique in that computers orRouting routers store their own routing tables as well as the routing tables for all of their neighbors so they have a more accurate understanding of the network.
- 14Error DetectionIt is possible to develop data transmission methodologies that give very high error-detection performance. Te only way to do error detection is to send extra data with each message. Tese error-detection data are added to each message by the data link layer of the sender on the basis of some mathematical calculations performed on the message (in some cases error-detection methods are built into the hardware itself). Te receiver performs the same mathematical calculations on the message it receives and matches its results against the error-detection data that were transmitted with the message. If the two match the message is assumed to be correct. If they don’t match an error has occurred. In general the larger the amount of error-detection data sent the greater the ability to detect an error. However as the amount of error-detection data is increased the throughput of useful data is reduced because more of the available capacity is used to transmit these error-detection data and less is used to transmit the actual message itself. Terefore the efciency of data thro
- 15Ethernetuses digital transmission over either serial or parallel circuits depending on which version of Ethernet you use. One version of Ethernet that uses serial transmission requires 1/10 000 000 of a second to send one symbol; that is it transmits 10 million symbols (each of 1 bit) per second. Tis gives a data rate of 10 Mbps and if we assume that there are 8 bits in each character this means that about 1.25 million characters can be transmitted per second in the circuit.
- 16extranetsimilar to an intranet in that it too uses the same technologies as the Internet but instead is provided to invited users outside the organization who access it over the Internet. It can provide access to information services inventories and other internal organizational databases that are provided only to customers suppliers or those who have paid for access. Typically users are given passwords to gain access but more sophisticated technologies such as smart cards or special sofware may also be required. Many universities provide extranets for Web-based courses so that only those students enrolled in the course can access course materials and discussions.
- 17intranetsAn intranet is a LAN that uses the same technologies as the Internet (e.g. Web servers Java HTML [Hypertext Markup Language]) but is open to only those inside the organization. For example although some pages on a Web server may be open to the public and accessible by anyone on the Internet some pages may be on an intranet and therefore hidden from those who connect to the Web server from the Internet at large. Sometimes an intranet is provided by a completely separate Web server hidden from the Internet. Te intranet for the Information Systems Department at Indiana University for example provides information on faculty expense budgets class scheduling for future semesters (e.g. room instructor) and discussion forums
- 18Frameall the letters or data in one group of data are transmitted at one time as a block of data.
- 19Simplex transmissionOne- way transmission
- 20Helf-duplex transmissionTwo-way transmission but you can transmist in only one direction at a time
- 21Full-duplexCan transmit in both directions simulaneously with no turnaround time
- 22Multiplexingto break one high-speed physical communication circuit into several lower-speed logical circuits so that many different devices can simultaneously use it but still “think” that they have their own separate circuits (the multiplexer is “transparent”). It is multiplexing without multiplexing the Internet would have collapsed in the 1990s. Multiplexing ofen is done in multiples of 4 (e.g. 8 16). Figure 3-4 shows a four-level multiplexed circuit. Note that two multiplexers are needed for each circuit: one to combine the four original circuits into the one multiplexed circuit and one to separate them back into the four separate circuits. Te primary beneft of multiplexing is to save money by reducing the amount of cable or the number of network circuits that must be installed. For example if we did not use multiplexers in Figure 3-4 we would need to run four separate circuits from the clients to the server. If the clients were located close to the server this would be inexpensive. However if they were located several miles away the extra costs could be substantial.
- 23Geosynchronoussatellite remains stationary over one point on the earth.
- 24Groups of Layers(Applications Layer Internetwork Layer Hardware Layer.) Te layers in the Internet are ofen so closely coupled that decisions in one layer impose certain requirements on other layers. Te data link layer and the physical layer are closely tied together because the data link layer controls the physical layer in terms of when the physical layer can transmit. Because these two layers are so closely tied together decisions about the data link layer ofen drive the decisions about the physical layer. For this reason some people group the physical and data link layers together and call them the hardware layers. Likewise the transport and network layers are so closely coupled that sometimes these layers are called the internetwork layer. See Figure 1-3. When you design a network you ofen think about the network design in terms of three groups of layers: the hardware layers (physical and data link) the internetwork layers (network and transport) and the application layer.
- 25HyperText Transport Protocol(HTTP)(Can't find data in book)
- 26Information bitsbits in a communication protocol those used to convey the user’s meaning.
- 27Transmission Efficiencydefned as the total number of information bits (i.e. bits in the message sent by the user) divided by the total bits in transmission (i.e. information bits plus overhead bits). For example let’s calculate the transmission efciency of asynchronous transmission. Assume we are using 7-bit ASCII. We have 1 bit for parity plus 1 start bit and 1 stop bit. Terefore there are 7 bits of information in each letter but the total bits per letter is 10 (7 + 3). Te efciency of the asynchronous transmission system is 7 bits of information divided by 10 total bits or 70%. In other words with asynchronous transmission only 70% of the data rate is available for the user; 30% is used by the transmission protocol. If we have a communication circuit using a dial-up modem receiving 56 Kbps the user sees an effective data rate (or throughput) of 39.2 Kbps. Tis is very inefcient. We can improve efciency by reducing the number of overhead bits in each message or by increasing the number of information bits. For example if we remove the stop bits from asynchronous transmission efciency
- 28Troughputthe total number of information bits received per second afer taking into account the overhead bits and the need to retransmit frames containing errors. Generally speaking small frames provide better throughput for circuits with more errors whereas larger frames provide better throughput in less-error-prone networks. Fortunately in most real networks the curve shown in Figure 4-12 is very flat on top meaning that there is a range of frame sizes that provide almost optimum performance. Frame sizes vary greatly among different networks but the ideal frame size tends to be between 2 000 and 10 000 bytes.
- 29MANMetropolitan Area Network
- 30WANWide Area Network
- 31Software as a Service (SaaS)an organization outsources the entire application to the cloud provider (see the last column of Figure 2-7) and uses it as any other application that is available via a browser (thin client). SaaS is based on multitenancy. Tis means that rather than having many copies of the same application there is only one application that everybody shares yet everybody can customize it for his or her specifc needs. Imagine a giant ofce building in which all people share the infrastructure (water A/C electricity) but can customize the ofces they are renting. Te customers can customize the app and don’t have to worry about upgrades security or underlying infrastructure because the cloud provider does it all. Te most frequently used SaaS application is email. At Indiana University all student email is outsourced to Google’s Gmail. Customer relationship management (CRM) from Salesforce.com is another very commonly used SaaS.
- 32Platform as a Service(PaaS)What if there is an application you need but no cloud provider offers one you like? You can build your own application and manage your own data on the cloud infrastructure provided by your cloud supplier. Tis model is called Platform as a Service (PaaS). Te developers in your organization decide what programming language to use to develop the application of choice. Te needed hardware and sofware infrastructure called the platform is rented from the cloud provider (see Figure 2-7). In this case the organization manages the application and its own data but uses the database sofware (data access logic) and operating system provided by the cloud provider. PaaS offers a much faster development and deployment of custom applications at a fraction of the cost required for the traditional client-server architecture. PaaS providers include Amazon Elastic Cloud Compute (EC2) Microsof Windows Azure and Google App Engine.
- 33Infrastructure as a Service (IaaS)As you can see in Figure 2-7 with IaaS the cloud provider manages the hardware including servers storage and networking components. Te organization is responsible for all the sofware including operating system (and virtualization sofware) database sofware and its applications and data. IaaS is sometimes referred to also as HaaS or Hardware as a Service because in this cloud model only the hardware is provided; everything else is up to the organization. Tis model allows a decrease in capital expenditures for hardware and maintaining the proper environment (e.g. cooling) and redundancy and backups for data and applications. Providers of IaaS are Amazon Web Services Microsof Windows Azure and Akamai.
- 34Simple Mail Transfer Protocol(SMTP)Is the most commonly used email standard simply becuse it is the email standard used on the internet. Email works similarly tohow the web works but it is a bit more complex. SMTP email is usually implmented as a two-tier thick client-server applications but not always. We first explain how the normal two-tier thick client architecture works and then quickly contrast that with two alternate architectures
- 35Post Office Protocol (POP)Email protocol that must delete the mail message off the server and place a copy onto the clients HDD
- 36Post Office Protocol (POP)Email protocol that must delete the mail message off the server and place a copy onto the clients HDD
- 37Internet Message Access Protocol (IMAP)Email protocol that saves the message onto the mail server
- 38Open Systems Interconnection Reference Model (OSI model)Applications Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer
- 39Negative acknowledgment (NAK)If the message contained an error
- 40endend
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- Flashcards on Networking, created by Momo Momo on 01/10/2018.
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