Comp 390 Midterm Highlight-->UNDERLINED

Packet-switching: store-and-forward

-takes L/R seconds to transmit (push out) L-bit packet into link at R bps -store and forward: entire packet must arrive at router before it can be transmitted on next link -one-hop numerical example: --L = 7.5 Mbits --R = 1.5 Mbps --one-hop transmission delay = 5 sec -*end-end delay* = 2L/R (***assuming zero propagation delay***)

Define Digital modulation?

The processing of converting between bits and signals

What is the difference between ASK, FSK, PSK(also known as BPSK,QPSK)?

*ASK(Amplitude Shift Keying)* - two different voltage levels are used to represent 0 and 1 *FSK(Frequency Shift Keying)* -two (or more) different frequencies are used. *PSK(Phase Shift Keying)* -carrier wave is systematically shifted. -If we shift at 0 or 180 degrees, it is called BPSK (Binary PSK) -If we shift at 45, 135, 225, or 315 degrees at uniformly spaced intervals, it is called QPSK (Quadrature Phase Shift Keying)

Compare the OSI model and TCP/IP model

*Both models* -Both models are based on the concept of independent protocols. -The functionality of layers is roughly similar. -Remember that we are comparing the reference models, not the corresponding protocol stacks. -Three concepts are central to the OSI model: Services, Interfaces and Protocols. -There was no problem with the protocols fitting the model because it fits perfectly. -However, the model did not fit any other protocol stacks

What is the difference between circuit switching and packet switching?

*Circuit Switching* -Finding a physical "copper" path all the way from your phone to the phone you are calling (may include fiber, satellite, microwave links). -Requires setting up an end-to-end path before any data can be sent (can take 10 seconds or more on long distance calls). -For many computer applications (e.g. point of sale credit verification), long setup times are undesirable. -Advantages: Dedicated channel, only delay is 6ms/1000km propagation time *Packet Switching* -Alternative strategy requiring no physical path to be allocated -When sender has a block of data to be sent it is stored in the first switching office, and then forwarded later, one hop at a time -Each block is received in its entirety, inspected for errors then retransmitted (known as store-andforward network). -This is message switching where there is no limit on block size, which means routers must have disks to buffer long blocks. -This also means that a large block may tie up a router-to-router line for many minutes. -Alternative: Place a tight upper limit on block size, allowing packets to be buffered in router main memory -No user can monopolize a line for more than a few tens of msec. -Well-suited to handling interactive traffic.

What is bandwidth?

-A range of frequencies we call bandwidth. -This may be the range of frequencies we can transmit, or the range of frequencies we wish to transmit. -We can speak of the bandwidth of music, or voice, for example. -Bandwidth limits transmission speed of square waves, and thus data rate. -As these two are directly related, you will see bandwidth used to indicate both the range of frequencies and data transmission rates later on. -This now leads us into the text, and Fourier analysis. -By representing the value of voltage or current as a single valued function of time, f(t), we can model the behavior of the signal and analyze it mathematically

What is multiplexing?

-Channels are commonly shared by multiple signals. -It is much more convenient to use a single wire to carry several signals.

Difference Between Computer networks vs Distributed systems?

*Computer network* -User must explicitly log on to one machine. -User must explicitly submit jobs remotely, move files around, and generally handle network management personally *Distributed System* -A collection of independent computers appears to its users as a single coherent system. -Operating system will select the best processor, find and transport files and put results in appropriate place. -the software gives a high degree of cohesiveness and transparency. -Usually a single paradigm called middleware (a layer of software on top of the OS) presents to the users. -Nothing is done explicitly by the user. -A distributed system is a special case of a network. -Distinction lies with the software rather than with the hardware (notably the operating system)

Describe the difference between connection oriented and connection-less services?

*Connection Oriented Service* -Like the telephone system. -User must establish a connection first, uses it, and then terminates the connection. -A negotiation about parameters may take place during connection setup. *Connectionless Service* -Like the postal system. -Each message has destination address and is routed independently -Messages can arrive out of order. -Different quality services may be offered (for example, reliable versus fast).

List and Describe the different network standardization?

*Defacto* -standards that have just happened without a formal plan (e.g. IBM PC, UNIX). *Dejure* -legal standards adopted by some authorized standardization body. These may be by treaty among national governments, or voluntary non-treaty organizations. *ITU-T* - Subgroup concerned with telephone and data communication systems is known as ITU-T (Telecommunications Standardization Sector), formerly called CCITT (Comite Consultatif De Telegraphie Et Telephonique) -ITU-T makes technical recommendations that often become international standards (e.g. RS-232, X.25, V.90 56-kps modem standard, H.264 for video compression, X.509 public key certificates). *ITU-R* - Radiocommunications Sector, coordinating the use by competing interest groups of radio frequencies worldwide. *ITU-D* -: the Development Sector - promotes the development of information and communication technologies to narrow the gaps between countries. *ISO* -Voluntary, non-treaty, founded in 1946. -Members are national standards organizations in 89 countries. -Issues standards on many subjects (e.g. nuts & bolts, telephone pole coatings). -Technical committees deal with specific subjects. -100,000 "volunteers" worldwide. -ISO and ITU-T often cooperate. -It is a member of ITU-T. *ANSI* -American representative in ISO. -Members are manufacturers or common carriers (companies providing communication services and other interested parties). *IEEE* -World's largest professional association. -Develops standards (e.g. 802 LAN). -Publishes journals.

What is the difference between FDM, TDM(vs STDM), CDM,CDMA, and WDM?

*FDM(Frequency Division Multiplexing)* -FDM divides the spectrum into frequency bands. -Each user has exclusive possession of some band to send signals -Filters limit the usable bandwidth to 3,100 Hz though 4,000Hz is allocated per channel. -It is possible to divide the spectrum efficiently without using guard bands. -In OFDM (Orthogonal FDM), the channel bandwidth is divided into many subcarriers that independently send data as seen in Figure 2-26. -The frequency response of each subcarrier is designed so that it is zero at the center of the adjacent subcarriers. *TDM(Time Division Multiplexing)* -The user take turns (in a round-robin fashion) -Each will periodically get the entire bandwidth for a little burst of time. -Small intervals of guard time may be added for timing variations -Confusion: STDM (Statistical TDM) indicates that the individual streams contribute to the multiplexed stream not on a fixed schedule. --Instead, based on the statistics of their demand. --STDM is packet switching by another name. *CDM(Code Division Multiplexing)* -CDM is a form of spread spectrum (a narrow band signal is sent over a wider frequency band) --Thus it is more tolerant of interference. *CDMA(CDM Access)* -It allows multiple signals from different users to share the same frequency band. -CDMA is comparable to each pair talking at once, but with each pair in a different "language". -CDMA, each bit time is subdivided into m short intervals called chips. Typically, there are 64 or 128 chips per bit, but we will use 8 chips/bit for simplicity. -Each station is assigned a unique m-bit code called a chip sequence. -To transmit a 1 bit, a station sends its chip sequence. -To transmit a 0 bit, it sends the one's complement of its chip sequence. -No other patterns are permitted -All chip sequences are pairwise orthogonal, by which we mean that the normalized inner product of any two distinct chip sequences, S and T (written as S•T), is 0. -S•C = ( A + B' + C) • C = A•C + B'•C + C•C = 0 + 0 + 1 = 1 -(0 is based on the orthogonal property of the chip sequences) -In principle, the receiver can listen to all senders in parallel. In practice, the receiver should know which sender is transmitting *WDM(Wavelength Division Multiplexing)* -It is used for fiber optic channels. -It is a variation of FDM -The only difference with electrical FDM is that an optical system using a diffraction grating is completely passive, and thus highly reliable. -Currently, the energy on a single fiber is typically a few gigahertz because of the limitations of the electrical to optical conversion -However, the potential bandwidth of a single fiber band is about 25,000 GHz. -One of potential applications would be FTTH. (Fiber to the Home) -All optical amplifiers are available and can regenerate the entire signal once every 1000 km without opt-electrical conversions.

What is shannon's theorem?

*Formula* Maximum bits/sec= H log₂ (1 + S/N) Where: H=Bandwidth S/N=Signal to noise ratio *Note* Signal to noise ratio is given in decibels(DB) -A S/N ratio of 10 is 10 dB; S/N of 100 is 20 dB, S/N of 1000 is 30 dB, etc

List and Describe the TCP/IP Reference Model

*Internet Layer* -Its job is to permit hosts to inject packets into a network and have them travel independently to the destination. -Packets may arrive in a different order than they were sent. -It is the job of higher layers to re-arrange them, if in-order delivery is needed. -The analogy is with the mail system. -The layer defines an official packet format and protocol called IP. -Packet routing and congestion avoidance are the two major issues here. -It is very similar to the OSI network layer. *Transport Layer* -It is designed to allow peer entities to carry on a conversation. -It is similar to the OSI Transport Layer. -There are two protocols defined: TCP and UDP. --1) TCP is a reliable connection-oriented protocol that allows a byte stream (no message boundary) originating on one machine to be delivered without error on any other machine. -At the source, it fragments the incoming byte stream into discrete messages and passes each one to the internet layer. -At the destination, it reassembles the received messages into the output stream. -TCP also handles flow control. --2) UDP (User Datagram Protocol) is an unreliable, connectionless protocol. -It is widely used for one-shot, client-server type request-reply in which prompt delivery is more important than accurate delivery. *Application Layer* -The TCP/IP does not have session or presentation layers because of little use to most applications. -It contains all high-level protocols such as TELNET, FTP, SMTP, DNS, HTTP, etc. *Host to Network Layer* -Below the internet layer is a great void. -The TCP/IP does not say much about what happens here. -This protocol is not defined in TCP/IP model.

List and describe the different computer networks?

*Local Area network(LAN)* -LANs are usually privately owned within a single building or campus up to a few kms in size. -LANs often use a transmission technology of a single cable to which all machines are attached. -Point-to-point links (star) through a switch are the most common topology in LANs. -Typical speeds are 100 Mbps (fast Ethernet), 1 Gbps (GbE), or even 100Gbps (100GbE), 400Gbps (400GbE) approved in Dec. 2017. -A switch has multiple ports. -A switch can be connected to another switch. -Sometimes, we divide a large physical network into smaller logical networks (Virtual networks). -Has static and Dynamic broadcast subnets. *Personal Area Network(PAN)* -PANs let devices communicate over the range of a person. --Eg. Bluetooth - connect devices without wires. -Bluetooth networks use the master-slave paradigm. The master tells the slaves what addresses to use, when they can broadcast, how long they can transmit, what frequencies they can use, etc... *Metropolitan area network(MAN)* -A MAN is basically a bigger version of a LAN. --Examples are cable TV networks and WiMAX (IEEE802.16). *Wide area network(WAN)* -A WAN spans a large geographical area, often a country or continent. -In a WAN, subnet (communication subnet) usually consists of two components: --Transmission lines (aka circuits or trunks). --Switching elements (intermediate systems or routers) -Please don't get confused with "subnet" used in networking addressing. -When a network is sent from one router to another via one or more intermediate routers, the packet is received at each intermediate router in its entirety, stored there until the required output line is free, and then forwarded. -A subnet using this principle is called a store-and-forward or packet-switched subnet. -The sending host first cuts the message to be sent into packets, each one bearing its number in the sequence. -How router A makes a routing decision is called the routing algorithm. *Internetworks* -A collection of interconnected network is called an internetwork or just internet (not Internet). -Subnets, networks and internetworks are often confused. Subnet makes the most sense in the context of WAN where it refers to the collection of routers and communication lines owned by the network operator. -The combination of a subnet and its hosts forms a network. -In the case of a simple bus LAN, the cable and the hosts form the network and there is no subnet. -An internetwork is formed when distinct networks are connected together.

Contrast the OSI and TCP/IP models

*OSI* -In the Second Edition of the textbook (1989), most experts thought that the OSI and its protocols were going to take over the world and push everything else out of their way. -It can be summarized into four lessons: 1) Bad timing (See Figure 1-23) - Apocalypse of the two elephants. 2) Bad technology 3) Bad implementations 4) Bad politics *TCP/IP* 1) The model does not clearly distinguish the concepts of services, interfaces and protocols. 2) The model is not at all general and is poorly suited to describe any other protocol stack. 3) The host-to-network layer is not really a layer at all in the normal sense. 4) The model does not distinguish the physical and data link layers. 5) TCP and IP protocols were carefully thought out, but some TCP/IP protocols were ad hoc and not well thought out and they are hard to get rid of completely.

List and Describe the OSI model?

*Physical Layer* -Concerned with transmitting raw bits over a communication channel. -Issues are primarily technical, e.g. --Voltage levels. --How long a bit lasts. --Establishing and letting go a connection. --Pin configuration on connectors. --"The domain of the electrical engineer" *Data Link Layer* -Takes a "raw" transmission facility and transforms it into a line that appears free of transmission errors to the network layer. -Does this by having sender break the input data into data frames (typically a few hundred bytes), transmit frames sequentially, and process acknowledgement -Frames sent back by receiver. -Must create and recognize frame boundaries. -Must deal with noise bursts, duplication due to lost acknowledgements, etc. -Must deal with differing transmit and receive speeds. -Must handle two-way traffic on one line *Network Layer* -Concerned with controlling the operation of the subnet. -Determines packet routing (static tables, dynamic methods). -Congestion control. --Accounting. --Protocol differences between heterogeneous networks must be handled. --In broadcasting networks, routing is simple, so network layer may be thin or nonexistent *Transport Layer* - Basic function is to accept data from session layer, split it into smaller units if needed, pass these to the network layer, and ensure that all pieces have arrived correctly at the other end. -Must be done efficiently. -Must isolate the session layer from inevitable changes in hardware technology. -Usually creates a distinct network connection for each transport connection required by the session layer. -However, multiple connections may be created for high throughput or multiplexing to reduce cost. -A true source-to-destination or end-to-end layer. -Program on source machine has conversation with destination machine, using message headers and control messages. -Handles the complexities of multiprogrammed hosts. (Who gets which message?) -Establishes and deletes connections (naming mechanism required). -Regulates flow of information between hosts. (Between router's handled by data link layer.) *Session Layer* -Allows users on different machines to establish sessions between them. -Provides enhanced services like logins to remote time-shared systems, file transfers, etc. -Manages dialog control (may be full or half duplex). -Provides token management when both sides must not attempt the same operation at the same time. -May provide synchronization; i.e. inserting checkpoints into data stream so that a crash in the middle of a long file transfer does not require retransfer of the entire file *Presentation Layer* -Performs certain functions requested sufficiently often enough to warrant finding a general solution for them. -E.g. encoding data in a standard manner (ASCII/EBCDIC, two's complement/one's complement, etc.). -Can define standard coding for transmission. -Data compression. -Cryptography. *Application Layer* -Contains a variety of commonly needed protocols. -Must handle incompatible terminal types. -One way is to define an abstract network virtual terminal that editors and other programs can be written to deal with. -For each real terminal type, software must be written to map functions of the network virtual terminal onto real terminal. -File transfers between different systems are handled at this level. -Also electronic mail, remote job entry, directory lookup, etc.

Describe the difference between point to point and broadcast systems?

*Point to Point* - the network contains numerous cables or leased telephone lines, each connecting a pair of routers. -Two routers not sharing a line may communicate indirectly, via other routers. -Each intermediate router then forwards the message when the required line is free (known as store and forward or packet-switched subnet). -The message is often called a packet in the context of a subnet. -Interconnection topology is an important design issue in point-to-point subnet design. -Local networks usually have a symmetric topology, whereas wide area networks typically have irregular topologies. *Broadcast Systems* -have a single communication channel shared by all machines on the network. -Packets are received by all others. -An address field within the packet specifies the intended user. -When receiving a packet, a machine checks this address. -If the packet is for some other machine, it is ignored. -Broadcast systems usually also allow a packet to be sent to all machines with a special code in the address field. The mode of operation is called broadcasting. -Transmission to a subset of the machines is known as multicasting. -A common multicasting scheme is: -Reserve all addresses with the high order bit set to 1 for multicasting. -Remaining (n - 1) address bits form a bit map corresponding to (n - 1) groups. *Possible Broadcast* 1. Bus: at any instant one machine is the master and is allowed to transmit. Arbitration mechanism is required to resolve conflicts. 2. Satellite or Ground Radio: each router has an antenna for sending and receiving. All routers hear the satellite's output (and in some cases hear other routers' transmissions also). 3. Ring: each bit propagates around on its own, not waiting for the rest of the packet to which it belongs. Again, arbitration is required to handle conflicts.

Difference between protocol hierarchies, network architecture, protocol stack?

*Protocol Hierarchies* -Most networks are organized as a series of layers or levels, each one built on its predecessor. -This reduces design complexity. -Each layer offers certain services to higher layers, hiding details of how the services are implemented. See Figure 1-13. -Entities comprising the corresponding layers on different machines are called peer processes. -Peer processes communicate using the protocol. -Actually, data is not transferred directly from layer n on one machine to layer n on another. -Instead, each layer passes data and control information to the layer immediately below it, until the lowest layer is reached. -Below layer 1 is the physical medium through which actual communication occurs *Network Architecture* -The interface between each pair of adjacent layers defines which primitive operations and services the lower layer offers to the upper one. -The set of layers and protocols is called the network architecture. *Protocol Stack* -A list of protocols used by a certain system, one protocol per layer, is called a protocol stack -This specification must be precise enough to allow implementers to write a program or to build hardware so that it will correctly obey the appropriate protocol. -Essential notion here is the relation between virtual and actual communication, and the difference between protocols and interface

What is the difference between QAM-16 and QAM-64?

*QAM-16* -16 combinations in all, 4 bits per baud. *QAM-64* -64 combinations in all, 6 bits per baud

What is throughput? List and Describe the different types?

*Throughput* -throughput: rate (bits/time unit) at which bits transferred between sender/receiver *Instantaneous* -instantaneous: rate at given point in time *average* -average: rate over longer period of time *bottleneck link* -link on end-end path that constrains end-end throughput

My Question: What are the four sources of packet delay? Winter 2016 Midterm Question *Explain the sources of delays for a packet switched networks. For each source, explain what factors determine the value of the delay*.

*dproc: nodal processing* -check bit errors -determine output link -typically < msec *dqueue: queueing delay* -time waiting at output link for transmission -depends on congestion level of router *dtrans: transmission delay* -L: packet length (bits) -R: link bandwidth (bps) -dtrans = L/R *dprop: propagation delay* -d: length of physical link -s: propagation speed in medium(~2x108 m/sec) -d d prop = d/s

Define and Describe the Network Core Functions

*routing* -routing: determines source destination route taken by packets --routing algorithms *Forwarding* -forwarding: move packets from router's input to appropriate router output

What is a bandwidth limited signals?

-Consider transmitting the ASCII b character in an 8 bit byte (01100010) -Frequency is measured in cycles per second, also known as Hertz. o Abbreviations are cps and Hz. -In some cases this attenuation is a property of the transmission medium. -In other cases a filter is used to limit the amount of bandwidth for each customer. -Now we can look at our signal 01100010 and see how it would look if the bandwidth was so low that only the lowest frequencies were transmitted. - Bandwidth means a range of frequencies. -Time T required to transmit the character depends on the encoding method and signaling speed (number of times per second that the signal changes its value).

What is passband signal?

-For wireless channels, it is not practical to use very low frequency signals since the size of the antenna becomes large. -Fundamentally, we can take a baseband signal (from 0 to B Hz) and shift it to a passband (S to S+B Hz) without changing the capacity. -At the receiver, we can shift down to baseband for detecting signals.

What is the Nyquist Theorem?

-H. Nyquist (1924) derived an equation expressing the maximum data rate for a finite bandwidth noiseless channel. -He proved that a signal run through a low pass filter of bandwidth H can be completely reconstructed by making only 2H samples per second. -The range of frequencies humans can hear is roughly 20 Hz to 20 kHz. --This varies considerably among people - these are the rough limits -For a signal with V discrete levels, Nyquist's theorem states: *Formula* Maximum data rate= 2H log ₂ V (bits/second)

Describe the client server model?

-If we look at the client-server model in detail, we see that two processes (i.e., running programs) are involved, one on the client machine and one on the server machine. -Communication takes the form of the client process sending a message over the network to the server process -The client process then waits for a reply message. When the server process gets the request, it performs the requested work or looks up the requested data and sends back a reply. These messages are shown in Fig. 1-2.

What is queuing delay?

-R: link bandwidth (bps) -L: packet length(bits/packet) -a: average packet arrival rate(packet/s) -Traffic Intensity = La/R -La/R ~ 0: avg. queueing delay small -La/R -> 1: avg. queueing delay large -La/R > 1: more "work" arriving than can be serviced, average delay infinite!

List some of the design issues for layers?

-Reliability is the design issue of making a network that operates correctly even though it is made up of a collection of components that are themselves unreliable. -Each layer must have a mechanism for making and breaking connections. -Some form of addressing is also required. -Data transfer rules vary: --Simplex communication: data can travel in only one direction. --Half duplex: data can travel in either direction, but not at the same time. --Full duplex: data can travel in both directions at the same time. -Protocol must determine how many logical channels the connection corresponds to. -Many provide two: one normal, one urgent. -Error detecting or correcting codes must be agreed on -When it is inconvenient or expensive to setup a separate connection for each pair of communicating processes, multiplexing and de-multiplexing can be used. -When there are multiple paths between source and destination, a route must be chosen. This topic is called routing.

What are service Primitives?

-Service is formally specified by a set of primitives (operations) available to a user process to access the service. -Primitives tell the service to perform some action or report on an action taken by a peer entity. -Primitives can have parameters: --Machine to connect to. --Type of service desired. --Maximum message size, etc.

What is symbol rate (also known as baud rate)?

-The rate at which the signal changes is called the symbol rate, also called baud rate

What is line codes?

-To meet better engineering consideration, more complex schemes called line codes exist. -For fiber, the presence of light might represent a 1 and the absence a 0 -With NRZ, the signal may cycle between + and - -When the bit rate is B b/s, we need at least B/2 Hz WHY? -Given Nyquist's theorem: -Max Data Rate = 2 M log₂ V bits/sec --B b/s = 2 M log₂ 2 = 2 M --M, the bandwidth = B / 2 Hz -One strategy is to use more than two signaling levels (larger V values)

What is clock recovery?

-With NRZ, a long run of either 1's or 0's leaves the signal unchanged. -After a while, it is difficult to tell the bits apart. -Five Solutions: Solution 1: very accurate clocking - but expensive. Solution 2: send a separate clock signal to the receiver. It is no big deal for computer buses like PCIe but costly for data comm. Solution 3 (clever): mix clock signal with data signal by XORing them together. (See Fig. 2-20d.) --It is called Manchaster encoding and used in Ethernet. --Disadvantage: it requires twice as much bandwidth! Why? Solution 4: Code the data to ensure that there are enough transitions in the signal. --Coding a 1 as a transition and a 0 as no transition, or vice versa. --This is called NRZI (Invert) (See Fig. 2-20c.) --Used in USB. --No problem for long runs of 1's --Long runs of 0's => problem! --To fix the problem, we can break up runs of 0's by mapping to a slightly longer patterns (with 1's) --A well-known code is called 4B/5B. See Figure 2-21. (Ethernet 100Mbps uses it while USB 3.0 uses 8B/10B) --This scheme adds a 25% overhead, better than 100% in Manchaster encoding. Solution 5: Make the data look random, known as scrambling. --A scrambler works by XORing the data with a pseudorandom sequence before transmitting. --The receiver then XORs the incoming bits with the same pseudorandom sequence. --Advantage: It adds no bandwidth or time overhead. --However, it doesn't guarantee there will be no long runs since we may get unlucky (or lucky) occasionally

What is passband transmission?

-occupies a band of frequencies around the frequency of a carrier signal. -Schemes that regulate the amplitude, phase or frequency of a carrier signal to convey bits. -It is common for wireless and optical channels

What is Baseband Transmission?

-occupies frequencies from zero to a max. -It is common for wires -The most straightforward way is to use a + voltage for a 1 and a - voltage for a 0. -This is called NRZ (Non-Return to Zero).

What is packet loss?

-queue (aka buffer)preceding link in buffer has finite capacity -packet arriving to full queue dropped (aka lost) -lost packet may be re-transmitted by previous node,by source end system, or not at all

What is a constellation diagram?

-shows legal amplitude and phase combination of each symbol and the diagram

What is bit rate?

Bit Rate = Symbol Rate * (# of bits/symbol) bits/sec

What is Fourier Analysis *KNOW FORMULA*

Fourier proved that any reasonably behaved periodic function, g(t), with period T can be constructed by summing a (possibly infinite) number of sines and cosines. Such a decomposition is called a Fourier series. -From the Fourier series, the function can be reconstructed if the period T and the amplitudes a and b are known. -A data signal with a finite duration can be handled by imagining that it repeats the pattern over and over. -The a and b amplitudes can be computed for any given g(t) by the following formulae *Formula* g(t)=½ c + ∑ aη sin(2*π*η*ƒ*t) +∑bη cos(2*π*η*ƒ*t) Where: ∑ is from for n = 1 to infinity ƒ=1/T is the fundamental frequency and aη and bη are the sine and cosine amplitudes of the nth harmonics

What are the metric units

KB- 10 ^ 3 MB- 10 ^ 6 GB- 10 ^ 9 TB- 10 ^ 12 PB- 10 ^ 15 EB- 10 ^ 18 ZB- 10 ^ 21

Queuing delay,packet loss

queuing and loss: -If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: --packets will queue, wait to be transmitted on link --packets can be dropped (lost) if memory (buffer) fills up