CS356 10/5/2006 Handout #13 C. Edmondson-Yurkanan EXAM 1 Preparation (v2) EXAM 1: Tues 10/10 12:30p.m.- 1:45p.m. in our classroom READING: Chapter 1, Chapter 2 thru 2.4 (except 1.3.2, 1.4.2, 2.2.6), Chapter 8.1, 8.3, Read 8.2 pages: 658-661, 664-666. 668 plus the reading on: Problem 20 pg 66-67, and see figure 1.21 plus your class notes --- covering the additional material, such as exploring delay plus the handouts through #13(***handout 8: motivation & application) plus the detailed agendas of lectures 1-9 (see schedule.html) plus the Study Guide for Chapters 1 and 2's topics. TEST FORMAT: Closed book, bring pencil & calculator if desired. OK to bring 1/2 of ONE side of a 3x5 card of notes handwritten, (I.e. ONE side of 3 x 2.5) no xeroxing, no diagrams, just words. EMPHASIS: * Most of the exam will be definitions, explanations, problems similar to hmwks 1&2, and analyzing the characteristics of an application layer protocol. Very little will of the exam will be T/F or multiple choice. * Definitions of key terms * Draw time space diagrams demonstrating the total delay for packet switching. VERY IMPORTANT: Remember, when discussing "switching", an arrow represents 1 bit of data travelling....See Handout #4. Whereas when discussing an appli- cation layer, the arrow represents one complete request or reply message. * Calculate a specific delay amount (be careful to note how the starting event and the end event is described.) See Handout #4 * Comparisons of similar concepts * Check out the topics covered in Ch1, Ch2, & Ch8 review questions & problems. * Problems similar to what we explored in class. CHAPTER 1: Study Guide for Chapter 1 Ch1.1 What is the internet? TERMINOLOGY, components, definition of a protocol Ch1.2 Network Edge TERMS and each of the services that when put together comprise a "connection-oriented set of services", "connectionless set of services" Ch1.3 Network Core TERMS, circuit and packet switching. TERMS, how circuit and packet switching works, pros/cons, what are the historical roots of packet switching and why did they choose not to use circuit switching. Message segmentation. Draw or interpret Time-space diagrams. Role of a queue, store & forward, bursty vs. synchronous data. Sharing a link between multiple senders and receivers (aka multiplexing on a link): 3 solutions * FDM (commonly found in circuit switching) * TDM (commonly found in circuit switching), and * statistical multiplexing (commonly used in packet switching) Ch1.4 Network Access and Physical Media TERMS, access, but focus on features of HFC("cable modem") and DSL... (multiplexing?, upstream, downstream, sharing the line?), impact of your neighbor? how do we share our Internet access with our phones/TVs Ch1.5 ISPs and Internet Backbones TERMs. Relationships between the tiers. When you do a traceroute, can you identify how many ISPs does the packet travel thru? Ch1.6 Delay TERMs, 4 delay types, causes of each delay, formulas if available, Causes of loss, Traceroute - how it works, interpret it. Queuing Delay and Loss, what does "traffic intensity" mean, and what happens if the traffic intensity INCREASES? what if it approaches 1? Ch1.7 Layers A layer at HostA interacts with it's logical peer i.e. the same layer at the other entity(ies), i.e. these two or more parties actually are implementing a protocol at this layer. Layering using the OSI 7 layer model: Name/number and purpose of each layer, and name example protocols for layers 7,4,3, 2. Each layer "i" is a black box to the neighboring layers "i+1", "i-1", except for the service that a layer i provides to upper layer i+1. How layer i interacts with the layer below - by sending it's PDU to the layer i-1, and layer i-1 then ENCAPSULATES the received payload with its "layer I-1" header)... iterating down through the layers. When the protocol's peer receives the PDU, it processes the header, removes it, and sends the payload to i+1 CHAPTER 2 Ch2.1 Principles of appl. layer protocols: what services might applications require of the next layer down? TERMS: user agent, process, port #, well-known-port#, application layer protocol, application, Chapter 2.2-2.4: Basic features that could be found in any application layer protocol, be able to define/discuss/analyze these features & identify if/how that applies to http 1.0, http1.1, smtp, pop, imap, ftp (nntp is NOT part of the exam) Example questions from Handout 11 (i.e. Application Layer Protocol Design) * What is the "data object" that this protocol is "transferring"? How is it formatted and is data-typing supported? How does each application specify the two names: of the specific server, and the object. * minimizing delay: persistent connection; non-persistent connection; pipelining in a connection; concurrent connections; Be able to count RTTs * Is control sent in-band or out of band? * Is there state at the server during one session with the client? Does it survive sessions? What constitutes one "session"? (later on we will talk about "soft state vs hard state") * What transfer methods are needed? push data, pull data (transfer metadata) * How does the protocol "peer" know when it receives the end of a variable length header? how does the receiver know when the variable length data has all arrived? * Does the application layer protocol exchange msgs to setup the session and terminate the session? * What features are unique in http 1.1, http 1.0, ftp,smtp, pop3, imap ----------------------------------------------------------------------------- CHAPTER 8 * Key security terms, focus on authentication protocols, and how they use the cryptographic tools. Session key, nonce, replay, who authenticates whom (a challenge-response protocol is the term for authentication using a nonce). ----------------------------------------------------------------------------- A few sample questions: 1 Assume the link layer provides a reliable delivery service and the transport layer also provides a reliable delivery service. Assume all reliable protocols send an ack for each "message" received. If Host A and Host B are connected with Router R1, then when Host A sends a transport segment to B, how many acks are generated at the link layer, and how many acks are generated at the transport layer. 2 Alice@xyz.com (logged on to HostA) is sending email to Bob@mail.utexas.edu (who is currently logged on to HostB) How many (mail-specific) TCP connections will it take from when Alice clicks on "send" to when Bob is reading the email.