Exam Study Guide - Chapter 2
Exam Study Guide - Chapter 2 IST 233 - M001
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This 5 page Study Guide was uploaded by Frankie Prijatel on Tuesday October 6, 2015. The Study Guide belongs to IST 233 - M001 at Syracuse University taught by D. Molta in Fall 2015. Since its upload, it has received 218 views. For similar materials see Introduction to Computer Networking in Information technology at Syracuse University.
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Date Created: 10/06/15
Chapter 2 Review Monday September 28 2015 Terms a 848 PM protocol layered communication model message ordering and syntax TCP 3way handshake reliable and unreliable protocols Ethernet frame header trailer data field payload ports port numbers and sockets encodingdecoding ASCII code codec vertical and horizontal communications Review Questions You will need to be able to do basic conversion both ways between 8bit binary and decimal numbers without using a calculator Explain the role that standards play in networking What are the most important bene ts associated with standards What is the relationship between messages packets and frames How do standards related to interoperability Explain what is meant by the statement that interoperability is best described in shades of a b grey V Network standards are rules of operation that govern the exchange of messages between two hardware or software processes this includes message semantics syntax message order reliability and connection orientation Standards are important because they allow products from different vendors to interoperate work together across different technologies and operating systems It is described as shades of quotgreyquot because the translation from OS to OS and technology platform to platform is never quite seamless Summarize the 3 network standards characteristics message ordering message semantics and message syntax V V V Message Ordering proper message sequencing ex TCP 3way handshake Message Semantics the meaning of field contents addresses data encoding flags etc Message Syntax how a message is organized more rigid version of English grammar where every field has a precise location Explain the concept of message ordering using HTI39P and the TCP 3way handshake as examples V HTTP Message Ordering the client who always initiates the cycle sends a request and the server sends a response the server cannot transmit unless the client has sent it an HTTP request message TCP 3way handshake message ordering via TCP segments 1st HOST A client initiates the communication by transmitting a TCP SYN segment to HOST B indicating that HOST Awishes to communicate 2nd HOST B sends back a TCP SYNACK segmentSYN it wants to initiate communication ACK acknowledgement of HOST A39s SYN message 3rd HOST A sends back a pure TCP ACK segment acknowledging HOST B39s SYNACK e What are the two key elements found in every network packet What is the third element found in some packets What is a packet eld How many bits are there in a eld What s the difference between a frame and a packet V The two elements found in every network packet are the source and V destination IP address and the third element found in some packets is a TCP segment The data field is the heart of the message and contains the actual content being delivered by the message Frames carry packets in their data fields called packet elds Field lengths can be measured in bits and 8 bits equal an octet otherwise known as a byte There are 32 bits in a field A packet is encapsulated within a frame f What is the fundamental difference between a reliable and an unreliable network protocol Brie y explain why TCP is referred to as a highoverhead connectionoriented reliable transport protocol Why would anyone choose to use an unreliable protocol ls Ethernet reliable or unreliable What about Wi Fi F The difference between reliable and unreliable network protocols is that TCP or Wifi reliable protocols correct errors whereas unreliable protocols such as HTTP and Ethernet are known as quotbest effort protocolsquot which check for errors but merely discard them rather than correcting them TCP is reliable which means it incurs a lot of overhead due to error correction capabilities It is also referred to as quotconnectionorientedquot because it uses connections 39 so that it can apply sequence numbers to segments allowing it to fragment long application messages and deliver the segments with an indication of their order 39 So that it can provide reliable data to the application layer program above it Someone might choose an unreliable protocol because although it doesn39t correct errors it is still relatively reliable and doesn39t incur as much overhead as reliable protocols g With respect to packetswitching networks what is a layered standards architecture Provide an example of a speci c technology or standard that operates at each of the ve layers of the network model V 1 5 Layered Standards Architecture 5 Interoperability of application programs Transmission 4 across an internet xes problems and does 39agmentation and reassembly Transport Transmission 3 Internet CICFOSS an internet packet organization and raw packet delivery Transmission 2 Data Link across a single switched or wireless network Transmission 1 across a single network Physical Application Govern how 2 apps work with each other even if they39re from different vendors Govern aspects of endto end communication between 2 end hosts that aren39t handled by the intern et layer also allow hosts to work together even if the 2 computers are from different vendors or have different internal designs Govern the transmission of packets across an intern et typically by sending them thru several routers along the route also govern packet syntax and reliability Govern the transmission of frames across a single switched network typically by sending them thru several switches along the data link also govern frame syntax and reliability Govern transmission between adjacent devices connected by a physical trans miss io 11 medium 39 Layer 3 and 4 standards developed by IETF 39 Layers 1 and 2 standards developed by IEEE h Explain how ASCII encoding is used to transmit letters and numbers on a digital network Explain how encoding works for network voice and video services V Encoding is the process of converting messages into bits via the application layer programs transport and lower layer messages are already in bits whereas application layer messages can consist of text images numbers video etc Applications use the ASCII code to convert text data to binary whose individual symbols are each 7 bits long Additionally video and audio messages can be encoded When we speak into a microphone your voice rises and falls at different frequencies sending different pressure waves into the mouthpiece The mic converts these crests and troughs into electric signals called analog signals which are analogous to the voice signal39s rising and falling Using an electrical circuit called a codec the analog signal is then converted to binary Codecs converts between both encoding and decoding converting digital signals into analog signals creating its own sound i How can a protocol analyzer packet sniffer like Wireshark be used to analyze network problems V Wireshark can be used to analyze network problems by recording the incoming and outgoing packets on a particular network and analyzing where errors are occurring or if there39s a connection problem j What is http and how does it differ from https Why do these protocols use TCP as a transport protocol How do web applications use port numbers V HTTP is the hypertext protocol but is less secure than HTTPS These protocols use TCP as a transport protocol because it39s reliable k What is the difference between vertical communication within a host and horizontal communication between hosts V On any given device in a network different software and hardware routines and devices may be functioning on any or all of these layers simultaneously Since in general all of these are supposed to be working together to implement networking functions there is a need for layers to communicate verticaly between the layers within a particular host Vertical Communication therefore deals with communication between protocol layers within the same machine Horizontal Communication occurs between specific software or hardware elements running at the same layer on different machines within a network 1 Explain how a receiving host determines whether or not an error has occurred during the transmission of a speci c packet V The host uses a header checksum to calculate the signature for error detection V Each host transmitting an Ethernet frame uses a polynomial math equation called a cyclic redundancy check CRC to calculate a quotsignaturequot of the bits in the header and data field Receiving hosts perform the same calculation on the received header and data field BUT All it does is trashes the packet doesn39t send a message back bc that would require more fields which creates more overhead TCP protocol corrects the error and detects that the packet was discarded because of an error TCP Segment ampt0 Bn31 Source Port Number 16 bits Destination Port Number 6 bits Sequence Number 32 bits Acknowledgment Number 32 bits 33 Reserved Flag Fields Window Size 4 bits 6 bits 6 bus 16 bits TCP Checksum 16 bits Urgent Pointer 16 bits Options if any 39 Padding Data Field Fixes the error with the sequence number Used to perform error correction and to insure proper ordering of application data and acknowledgement number V Unreliable programs perform error detection but not error correction If a packet is not received correctly TCP will drop that packet and retransmit the packet again until it receives ack
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