Term
| Communication Links & Packet Suites |
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Definition
| End Systems are connected by a network of _______ & _______ |
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Term
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Definition
| _______ takes a packet arriving on one incoming communication links and forwards it |
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Term
| Routers and link layer switches |
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Definition
| Which Types of switches forward packets toward their ultimate destinations? |
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Term
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Definition
| _______ used in access networks |
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Term
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Definition
| _______ used in the network core |
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Term
| Route or Path through the network |
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Definition
| The sequence of communication links and packet switches traversed by a packet from the sending end system to the receiving end system |
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Term
| Internet Service Providers |
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Definition
| End Systems access the Internet through _______ |
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Term
| Application Programming Interface (API) |
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Definition
| _______ specify how a program running on one end system asks the Internet infrastructure to deliver data to a specific destination program running on another end system. |
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Term
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Definition
| A _______ defines the format and the order of messages exchanged between two or more communicating entities as well as the actions taken on the transmission and/or receipt of a message or other event. |
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Term
| Each telephone line carries both data and traditional telephone signals simultaneously, which are encoded at different frequencies |
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Definition
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Term
| There is no difference. Throughout this text, the words “host” and “end system” are used interchangeably. End systems include PCs, workstations, Web servers, mail servers, Internet-connected PDAs, WebTVs, etc. |
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Definition
| What is the difference between a host and an end system? List the types of end systems. Is a Web Server an end System? |
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Term
| Suppose Alice, an ambassador of country A wants to invite Bob, an ambassador of country B, over for dinner. Alice doesn’t simply just call Bob on the phone and say, “come to our dinner table now”. Instead, she calls Bob and suggests a date and time. Bob may respond by saying he’s not available that particular date, but he is available another date. Alice and Bob continue to send “messages” back and forth until they agree on a date and time. Bob then shows up at the embassy on the agreed date, hopefully not more than 15 minutes before or after the agreed time. Diplomatic protocols also allow for either Alice or Bob to politely cancel the engagement if they have reasonable excuses. |
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Definition
| The word protocol is often used to described diplomatic relations. Give an example of a diplomatic protocol. |
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Term
| A networking program usually has two programs, each running on a different host, communicating with each other. The program that initiates the communication is the client. Typically, the client program requests and receives services from the server program. |
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Definition
| What is a client program? What is a server program? Does a server program request and receive services from a client program? |
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Term
| 1. Dial-up modem over telephone line: residential; 2. DSL over telephone line: residential or small office; 3. Cable to HFC: residential; 4. 100 Mbps switched Etherent: company; 5. Wireless LAN: mobile; 6. Cellular mobile access (for example, WAP): mobile |
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Definition
| List six access technologies, Classify each one as residential access, company access or mobile access. |
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Term
| HFC bandwidth is shared among the users. On the downstream channel, all packets emanate from a single source, namely, the head end. Thus, there are no collisions in the downstream channel. |
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Definition
| Is HFC transmission rate dedicated or shared among users? Are collisions possible in a downstream HFC channel? Why or Why not? |
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Term
| Current possibilities include: dial-up; DSL; cable modem; fiber-to-the-home. |
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Definition
| List the available residential access technologies in your city. For each type of access, prove the advertised downstream rate, upstream rate and monthly price. |
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Term
| Ethernet LANs have transmission rates of 10 Mbps, 100 Mbps, 1 Gbps and 10 Gbps. For an X Mbps Ethernet (where X = 10, 100, 1,000 or 10,000), a user can continuously transmit at the rate X Mbps if that user is the only person sending data. If there are more than one active user, then each user cannot continuously transmit at X Mbps. |
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Definition
| What is the transmission rate of Ethernet LANs? For a given transmission rate, can each user on the LAN continuously transmit at that rate? |
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Term
| Ethernet most commonly runs over twisted-pair copper wire and “thin” coaxial cable. It also can run over fibers optic links and thick coaxial cable. |
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Definition
| What are some of the physical media that Ethernet can run over? |
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Term
| Dial up modems: up to 56 Kbps, bandwidth is dedicated; ISDN: up to 128 kbps, bandwidth is dedicated; ADSL: downstream channel is .5-8 Mbps, upstream channel is up to 1 Mbps, bandwidth is dedicated; HFC, downstream channel is 10-30 Mbps and upstream channel is usually less than a few Mbps, bandwidth is shared. FTTH: 2-10Mbps upload; 10-20 Mbps download; bandwidth is not shared. |
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Definition
| Dial-upmodems, HFC DSL and FTTH are all used for residential access. For each of these access technologies, provide a range of transmission rates and comment on whether the transmission rate is shared or dedicated. |
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Term
There are two most popular wireless Internet access technologies today:
a)
Wireless LAN
In a wireless LAN, wireless users transmit/receive packets to/from a base station (wireless access point) within a radius of few tens of meters. The base station is typically connected to the wired Internet and thus serves to connect wireless users to the wired network.
b)
Wide-area wireless access network
In these systems, packets are transmitted over the same wireless infrastructure used for cellular telephony, with the base station thus being managed by a telecommunications provider. This provides wireless access to users within a radius of tens of kilometers of the base station. |
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Definition
| Describe the most popular wireless Internet access technologies today. Compare and contrast them. |
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Term
| A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth. |
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Definition
| What advantage does a circuit-switched network have over a packet-switched network? What advantages does TDM have over FDM in a circuit-switched network? |
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Term
| In a packet switched network, the packets from different sources flowing on a link do not follow any fixed, pre-defined pattern. In TDM circuit switching, each host gets the same slot in a revolving TDM frame. |
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Definition
| Why is it said that packet switching employs statistical multiplexing? Contrast statistical multiplexing with the multiplexing that takes place in TDM? |
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Term
| A tier-1 ISP connects to all other tier-1 ISPs; a tier-2 ISP connects to only a few of the tier-1 ISPs. Also, a tier-2 ISP is a customer of one or more tier-1. |
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Definition
| What is the key distinguishing difference between a tier-1 ISP and a tier-2 ISP? |
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Term
| The delay components are processing delays, transmission delays, propagation delays, and queuing delays. All of these delays are fixed, except for the queuing delays, which are variable. |
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Definition
| Consider sending a packet from a source host to a destination host over a fixed route. List the delay components in the end to end delay. Which of these delays are constant and which are variable? |
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Term
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Definition
| Visit the Transmission Versus Propagation Delay applet at the companion Web Site. Among the rates, propagation delay, and packet sizes available, find a combination for which the sender finishes transmitting before the first bit of the packet reaches the receiver. Find another combination for which the first bit of the packet reaches the receiver before the sender finishes transmitting. |
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Term
| Five generic tasks are error control, flow control, segmentation and reassembly, multiplexing, and connection setup. Yes, these tasks can be duplicated at different layers. For example, error control is often provided at more than one layer. |
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Definition
| List five tasks that a layer can perform. Is it possible that one (or more) of these tasks could be performed by two (or more) layers? |
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Term
| The five layers in the Internet protocol stack are – from top to bottom – the application layer, the transport layer, the network layer, the link layer, and the physical layer. The principal responsibilities are outlined in Section 1.5.1. |
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Definition
| What are the five layers in the internet protocol stack? What are the principal responsibilities of each of these layers? |
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Term
| Application-layer message: data which an application wants to send and passed onto the transport layer; transport-layer segment: generated by the transport layer and encapsulates application-layer message with transport layer header; network-layer datagram: encapsulates transport-layer segment with a network-layer header; link-layer frame: encapsulates network-layer datagram with a link-layer header. |
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Definition
| What is an application layer message? A transport layer segment? A network layer datagram? A link layer frame? |
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Term
| Routers process layers 1 through 3. (This is a little bit of a white lie, as modern routers sometimes act as firewalls or caching components, and process layer four as well.) Link layer switches process layers 1 through 2. Hosts process all five layers. |
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Definition
| Which layers in the Internet protocol stack does a router process? Which layers does a link layer switch process? which layers does a host process? |
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Term
| The Web: HTTP; file transfer: FTP; remote login: Telnet; Network News: NNTP; e-mail: SMTP. |
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Definition
| List five nonproprietary Internet applications and the application layer protocols that they use. |
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Term
| Network architecture refers to the organization of the communication process into layers (e.g., the five-layer Internet architecture). Application architecture, on the other hand, is designed by an application developer and dictates the broad structure of the application (e.g., client-server or P2P) |
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Definition
| What is the difference between network architecture and application architecture? |
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Term
| The process which initiates the communication is the client; the process that waits to be contacted is the server. |
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Definition
| For a communication session between a pair of processes, which process is the client and which is the server? |
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Term
| No. As stated in the text, all communication sessions have a client side and a server side. In a P2P file-sharing application, the peer that is receiving a file is typically the client and the peer that is sending the file is typically the server. |
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Definition
| For a P2P file-sharing application, do you agree with the statement, "There is no notion of client and server sides of a communication session"? Why or why not? |
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Term
| The IP address of the destination host and the port number of the destination socket. |
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Definition
| What information is used by a process running on one host to identify a process running on another host? |
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Term
| You would use UDP. With UDP, the transaction can be completed in one roundtrip time (RTT) - the client sends the transaction request into a UDP socket, and the server sends the reply back to the client's UDP socket. With TCP, a minimum of two RTTs are needed - one to set-up the TCP connection, and another for the client to send the request, and for the server to send back the reply. |
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Definition
| Suppose you wanted to do a transaction from a remote client to a server as fast as possible. Would you use UDP or TCP? Why? |
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Term
a) Reliable data transfer
TCP provides a reliable byte-stream between client and server but UDP does not.
b) A guarantee that a certain value for throughput will be maintained
Neither
c) A guarantee that data will be delivered within a specified amount of time
Neither
d) Security
Neither |
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Definition
| List the four broad classes of services that a transport protocol can provide. For each of the service classes, indicate if either UDP or TCP (or both) provides such a service. |
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Term
| A protocol uses handshaking if the two communicating entities first exchange control packets before sending data to each other. SMTP uses handshaking at the application layer whereas HTTP does not. |
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Definition
| What is meant by a handshaking protocol? |
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Term
| The applications associated with those protocols require that all application data be received in the correct order and without gaps. TCP provides this service whereas UDP does not. |
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Definition
| Why do HTTP, FTP, Smtp, POP3 run on top of TCP rather than on UDP? |
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Term
| When the user first visits the site, the site returns a cookie number. This cookie number is stored on the user’s host and is managed by the browser. During each subsequent visit (and purchase), the browser sends the cookie number back to the site. Thus the site knows when this user (more precisely, this browser) is visiting the site. |
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Definition
| Consider an e-commerce site that wants to keep a purchase record for each of its customers. Describe how this can be done with cookies. |
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Term
| Web caching can bring the desired content “closer” to the user, perhaps to the same LAN to which the user’s host is connected. Web caching can reduce the delay for all objects, even objects that are not cached, since caching reduces the traffic on links. |
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Definition
| Describe how Web caching can reduce the delay in receiving a requested object. Will Web caching reduce the delay for all objects requested by a user or for only some of the objects? Why? |
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Term
FTP uses two parallel TCP connections, one connection for sending control information (such as a request to transfer a file) and another connection for actually transferring the file. Because the control information is not sent over the
same connection that the file is sent over, FTP sends control information out of band. |
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Definition
| Why is it said that FTP sends control information "Out of Band"? |
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Term
| With download and delete, after a user retrieves its messages from a POP server, the messages are deleted. This poses a problem for the nomadic user, who may want to access the messages from many different machines (office PC, home PC, etc.). In the download and keep configuration, messages are not deleted after the user retrieves the messages. This can also be inconvenient, as each time the user retrieves the stored messages from a new machine, all of non-deleted messages will be transferred to the new machine (including very old messages). |
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Definition
| From a user's perspective, what is the difference between the download and delete mode and the download and keep mode in POP3? |
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Term
| Yes an organization’s mail server and Web server can have the same alias for a host name. The MX record is used to map the mail server’s host name to its IP address. |
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Definition
| Is it possible for an organization's Web server and mail server to have exactly the same alias for a hostname (for example, foo.com)? What would be the type for the RR that contains the hostname of a mail server? |
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Term
| It is not necessary that Bob will also provide chunks to Alice. Alice has to be in the top 4 neighbors of Bob for Bob to send out chunks to her; this might not occur even if Alice is provides chunks to Bob throughout a 30-second interval. |
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Definition
| In BitTorrent, suppose Alice provides chunks to Bob throughout a 30 second interval. Will Bob necessarily return the favor and provide chunks to Alice in this same interval? Why or why not? |
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Term
a) User location
b) NAT traversal |
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Definition
| Skype uses P2P techniques for two important function. What are they? |
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Term
a) File Distribution
b) Instant Messaging
c) Video Streaming
d) Distributed Computing |
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Definition
| List at least four different applications that are naturally suitable for P2P architectures. |
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Term
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Definition
True/False
A user request a Web page that consists of some text and three images. For this page, the client will send one request message and receive four response messages. |
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Term
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Definition
True/False
Two distinct Web pages (for example, www.mit.edu/research.html and www.mit.edu/students.html) can be sent over the same persistent connection. |
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Term
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Definition
True/False
With non persistent connections between browser and origin server, it is possible for a single tcp segment to carry two distinct HTTP request messages. |
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Term
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Definition
True/False
The Date: header in the HTTP response message indicates when the object in the response was last modified. |
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Term
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Definition
True/False
Http response messages never have an empty message body |
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