Midterm Review - Network Layers

Computer 1Computer 2 2

Application Layer (Chapter 2) 3 Application Layer Network Layer Transport Layer Applications (e.g., , web, word processing) The software that enables the user to perform useful work Application architecture The way in which the functions of the application layer software are spread among the clients and servers on the network Functions of Application Layer

2.1 Application Architecture Splitting the work across the client and the server Basic Software Components: Presentation Logic Application Logic Data Access Logic Data 4

2.2 Various Architectures Host-Based Client-Based Client-Server Based Thin Client/Thick Client Multi-Tier Architectures 5

2.3 Sending HTTP Request & Web Transmission 2-Tier network – Client/Server Thin Client HTTP Request, HTTP Response Transmission 2-Tier network – Client Server Thick and Thin Clients SMTP, POP, IMAP 6

Computer 1Computer 2 7

Transport layer (Chapter 5) Responsible for end-to-end delivery of messages Responsible for segmentation and reassembly  Breaking the message into several smaller pieces at the sending end  Reconstructing the original message into a single whole at the receiving end Interacts with Application Layer Transport Layer Application Layer Network Layer 8

Transmission Control Protocol (TCP) Links the application layer to the network layer Performs packetization and reassembly Ensures reliable delivery of packets TCP Header 9 How many bytes does the TCP header add to a message? 24 bytes (if option used) or 20 bytes w/out option

Packetization and Reassembly receiver TCP IP FTP TCP IP FTP sender Application layer sees message as a single block of data TCP packetization Delivers incoming packets as they arrive (e.g., Web pages) or to wait until entire message arrives (e.g., ) TCP reassembly What size packet to use? 10 Done through negotiations

5.2.2 Linking to Application Layer TCP may serve several Application Layer protocols at the same time  Problem  Solution How do we know what number the server uses? What would be the other type of number used and why? TCP HTTP FTPSMTP … Standards Non- Standard Port requiring further configuration (provides greater security

5.2.3 Session Management A session can be thought of as a conversation between two computers. Types of Session Management Connection Oriented What is connection oriented? How does it work? What protocols use connection oriented? Why? Connectionless Routing What protocols use connectionless? Why?

Computer 1Computer 2 13

Network Layer (Chapter 5) Responsible for addressing and routing of messages  Selects best path from computer to computer until the message reaches destination Performs encapsulation on sending end  Adds network layer header to message segments Performs decapsulation on receiving end  Removes the network layer header at receiving end and passes them up to the transport layer Network Layer Transport Layer Data Link Layer 14

IP Packet Formats: IPv4 (24 bytes) vs. IPv6 (40 bytes) 15 IPv4 IPv6

5.1 Types of Addresses Application Layer Address Assignment How do we get the URL’s IP address? How do this work? Address Resolution Network Layer Address Assignment (Subnets) What is sent out to assign IP Address? Data Link Layer Address Assignment What is sent out if MAC Address is unknown? Network Layer Data Link Layer Application Layer Transport Layer

5.2 Routing Process of identifying what path to have a packet take through a network from sender to receiver Routing Tables  Used to make routing decisions  Shows which path to send packets on to reach a given destination  Kept by computers making routing decisions Routers  Special purpose devices used to handle routing decisions on the Internet  Maintain their own routing tables Dest. B C D E F G Next B D B

Network Layers 18 Computer 1Computer 2

Data Link Layer (Chapter 4) Responsible for moving messages from one device to another Controls the way messages are sent on media Organizes physical layer bit streams into coherent messages for the network layer Major functions of a data link layer protocol  Media Access Control  Error Control  Message Delineation Data Link Layer Physical Layer Network Layer 19

4.1 Media Access Control (MAC) Controlling when and what computer transmit  Why used  When to use Two possible approaches  Controlled access  Contention based access 20

4.2 Major Functions of Error Control Error prevention Error detection (how do these work, which is better?) Parity checks (Even and Odd) Cyclic Redundancy Check (CRC) Error correction Retransmission 21

4.3 Automatic Repeat reQuest (ARQ) Process of requesting a data transmission be resent Main ARQ protocols  Stop and Wait ARQ (A half duplex technique)  Continuous ARQ (A full duplex technique)  Flow Control Window 22

4.4 Data Link Protocols Classification  Asynchronous transmission  Synchronous transmission Differ by  Message delineation  Frame length  Frame field structure frame k frame k+1frame k-1 23

Network Layers 24 Computer 1Computer 2

Physical Layer (Chapter 3) Includes network hardware and circuits Types of Circuits  Physical circuits connect devices & include actual wires  Logical circuits refer to the transmission characteristics of the circuit  Physical and logical circuits may be the same or different. For example, in multiplexing, one physical wire may carry several logical circuits. 25 Physical Layer Network Layer Data Link Layer

3.1 Circuits 26 Physical connection (wire) Configuration types (physical layout of the circuit):  Point-to-Point Configuration  Multipoint Configuration

3.1.2 Data Flow (Transmission) 27 How does data flow through the circuit (circuits can be designed to permit data flow) Configuration types:  Simplex  Half-Duplex  Full-Duplex

3.1.3 Multiplexing Breaking up a higher speed circuit into several slower (logical) circuits  Several devices can use it at the same time  Requires two multiplexer: one to combine; one to separate Main advantage: cost  Fewer network circuits needed Categories of multiplexing:  Frequency division multiplexing (FDM)  Time division multiplexing (TDM)  Inverse Multiplexing 28

3.2 Media – Guided Media 29 Physical matter that carries the transmission Types: Guided Media Radiated (Unguided) Media

3.2 Media Summary 30

3.3 Transmission of Data Computers produce binary data (0 or 1) (i.e. discrete, predictable values) Standards needed to ensure both sender and receiver understands this data  Codes  Signals Digital Bipolar, Unipolar Analog Frequency, Amplitude, Phase 31

3.3 Transmission Modes Bits in a message can be sent on:  a single wire one after another (Serial transmission)  multiple wires simultaneously (Parallel transmission) Two Modes of transmission: Serial Mode Parallel Mode 32

Overall Efficiency of Transmissions You want to transmit a 500 byte message. What would be the efficiency in transmitting this message? Overhead: SMTP: TCP: IP: Ethernet: What about an HTTP file of 4000 bytes? bytes 34 bytes 100 bytes (could be variable) EFF = 500/( ) = 73% EFF = [# of data bytes]/ [#data bytes + # of overhead]