What is the Internet?
           Hosts (a.k.a. End Systems): Various end 
            user devices, e.g., computer, cell phone, 
            ipad
           Communications Links: Connectors such 
            as copper wire, fibre optics, coaxial cable
           Packet Switches: Routers or Link-Layer 
            Switches (for network access points)
                                   Terminology
            Transmission Rate: number of bits / second that 
             are communicated
            Packets: discrete "segments" of data along with 
             transmission control data (e.g., packet header)
            ISP: Internet Service Provider – Internet access 
             provider
            RFC: Request For Comments – IETF (Internet 
             Engineering Task Force) standards for protocols 
             and network design
            API: Application Programming Interface – Set of 
             procedures to link (interface) to some other 
             system (i.e., the Internet)
                               Protocol
       1.   A protocol defines the format and order 
            of messages exchanged between two or 
            more communicating entities as wall as 
            the actions taken on the transmission 
            and/or receipt of a message or other 
            event
       2.   A system of (digital) message formats 
            and the rules for exchanging those 
            messages between (2) communicating 
            entities
       3.   The syntax, semantics, and 
            synchronisation of communication
                             End Systems
           Termination points for a network
           May or may not interact with a human 
            (e.g., may activate hardware)
           Traditionally, some kind of computer
           Two categories of hosts: Clients and 
            Servers
           Now more varied: Cell phones, video 
            game consoles, televisions, picture 
            frames, appliances, cameras, GPS 
            devices, biomedical sensors
                       Access Networks
           DSL: Digital Subscriber Line – Telco 
            provided frequency based 
            communication to a DSLAM (Digital 
            Subscribe Line Access Multiplexer)
           Cable: Cable TV provided HFC (Hybrid 
            Fibre and Coaxial) communication to a 
            CMTS (Cable Modem Termination System)
           FTTH (Fibre to the Home) – Fibre optic 
            connection based on either active or 
            passive optical networks (type of router – 
            powered vs. unpowered)