Exam 1 Study Guide Lesson 1: Introduction, History, and Internet Architecture - What are advantages and disadvantages of a layered architecture? - The functionality in a network architecture is implemented by dividing the architectural model into layers. Each layer offers different services. - An example of a network layer is an airline system (ticket, baggage, gates, plan takeoff, airplane routing) - Advantages: - Scalability - Modularity - Flexibility - Disadvantages: - Some layers functionality depend on the information from other layers - One layer may duplicate lower layer functionality - Overhead - What are the differences and similarities of the OSI model and five-layer Internet model? - The Internet Architecture model has 5 layers. - The application, presentation, and session are combined into a single layer known as the application layer. - What are sockets? - Sockets are the interface between the application and the transport layer - Describe each layer of the OSI model. - Application (Message) - - Presentation - Presentation layer plays the intermediate role of formatting the information it receives from the layer below and delivering it to the application layer - Functionality: - Formatting a video stream - Translating integers from big endian to little endian - Session - Session layer is responsible for the mechanism that manages the different transport streams that belong to the same session between end-user application processes. - It ties audio and video stream together for example - Transport (Segment)- Transport layer is responsible for end-to-end communication between end hosts - Network (Datagram) - The network layer is responsible for moving datagrams from one Internet host to another - A source Internet host sends the segment along with the destination address, from the transport layer to the network layer - Data Link (Frame) - The data link layer is responsible to move the frames from one node to the next - Physical - The physical layer facilitates the interaction with the actual hardware. - It is responsible to transfer bits within a frame between two nodes that are connected through a physical link. - Provide examples of popular protocols at each layer of the five-layer Internet model. - Application (Message) - HTTP - SMTP - FTP - DNS - Transport (Segment) - TCP - UDP - Network (Datagram) - IP - Data Link (Frame) - Ethernet - PPP - WiFi - Physical - Twisted pair copper wire - Coaxial cable - Single mode fiber - What is encapsulation, and how is it used in a layered model? - Encapsulation is when data (a header) is appended to the packet through each layer to signify its on the correct path to the destination host.- What is the end-to-end (e2e) principle? - The e2e principle suggests that application level functions cannot be built into the lower levels of the system at the core of the network. - To summarize: - The network core should be simple - The end systems should carry the intelligence - What are the examples of a violation of e2e principle? - Violations of the e2e principle are when it is not possible to implement a functionality entirely at the ends hosts, such as NAT (Network Address Translation), firewalls, and traffic filters. - NAT takes care of the communication between the hosts on the private network and the hosts on the public network - NAT violates the e2e because the hosts that are behind NAT boxes are not globally addressable, or routable. - What is the EvoArch model? - The Evolutionary Architecture model is an hourglass shaped model of the Internet where the outer bands are more frequently modified or replaced. The further in you go, the harder it is for that layer to be altered or modified. - It considers an abstract model of the Internets protocol stack that has the following components: - Layers - Nodes - Edges - Node incoming edges - Node substrates - Node outgoing edges - Layer generality - Node evolutionary value - Node competitors - Node death rate - Node basic birth process - Explain a round in the EvoArch model. - EvoArch is a discrete-time model that is executed over rounds. - At each round: - Introduce new nodes and place them randomly at layers - Examine all layers from top to bottom - Stop the execution of the model when the network reaches a given number of nodes - What are the ramifications of the hourglass shape of the internet?- Many technologies that were not originally designed for the internet have been modified so that they have versions that can communicate over the Internet. - It has been difficult and slow process to transition to IPv6 - Repeaters, hubs, bridges, routers operate on which layers? - Repeats and Hubs: Layer 1 (Physical) - Bridges and Layer2-switches: Layer 2 (Data link) - Routers and Layer3 switches: Layer 3 (Network) - What is a bridge, and how does it “learn”? - A bridge is a device with multiple inputs and outputs. It transfers frames from an input to one or more outputs. (It populates and maintains a forwarding table) - It learns when the bridge receives any frame that is a “learning opportunity” to know which hosts are reachable through which ports. - What is a distributed algorithm? - A distributed algorithm is an algorithm designed to run on computer hardware constructed from interconnected processors. - Explain the Spanning Tree Algorithm. - Every node has an ID. The node with the smallest ID is selected as the root - At each node, it excludes the link if not on the shortest path to the root - Tiebreakers go to the node with the smallest ID - Messages are passed with a message (origin, claimed root, distance) - Each node adds 1 to the distance received in the message and checks to see if the message claimed root is the claimed root. - What is the purpose of the Spanning Tree Algorithm? - The spanning tree algorithm avoids looping packets forever. The goal is to have the bridges select which links (ports) to use for forwarding eliminating loops. It also prevents broadcast storms. Lesson 2: Transport and application layers - What does the transport layer provide? - The transport layer provides an end-to-end connection between two applications that are running on different hosts - What is a packet for the transport layer called? - Segment for a TCP connection- What are the two main protocols within the transport layer? - TCP and UDP - What is multiplexing, and why is it necessary? - Multiplexing is the ability for a host to run multiple applications to use the network