Lecture 2 Computer Networks Models Network Models 1-1
Agenda Introduction to the Internet Reference Models for Computer Networks The OSI Model The TCP/IP Model Network Models 1-2
Announcements Bonus - Research Work Research point selection - due date: 18/2/2018 Progress report Due date: 8/4/2018 Network Models 1-3
The Internet Definition: network of interconnected networks History The Internet evolved from the ARPANET in 1969 in four locations ARPA applied the same packet-switching technology to tactical radio communication and to satellite communication ARPA developed methods and protocols for internetworking (Transmission Control Protocol TCP in 1974) Now, The number of connections to the Internet continues to grow exponentially (billions users, hosts, devices IoT) Network Models 1-4
The Internet Key elements that comprise the Internet Network Models 1-5
Key Elements of the Internet The purpose of the Internet, of course, is to interconnect end systems, called hosts (PCs, workstations, servers, mainframes) Hosts are connected to a network (LAN, WAN) Networks are connected by routers Each router attaches to two or more networks Some hosts, such as mainframes or servers, connect directly to a router rather than through a network Network Models 1-6
An Abstract Look to the Traditional Internet Operation Based on the concept: intelligent end systems and dummy core and offer best effort QoS Operation example A host may send data to another host anywhere on the Internet The source host breaks the data to be sent into a sequence of packets (IP packets) Each packet includes a unique numeric address of the destination host (IP address) Based on this destination address, each packet travels through a series of routers and networks from source to destination Network Models 1-7
Simplified View of Portion of Internet Network Models 1-8
Hierarchical Organization of the Internet Internet Service Provider (ISP): A company that provides other companies or individuals with access to, or presence on, the Internet Network Models 1-9
Network Models A network is a combination of hardware and software sending data from one location to another The hardware consists of the physical equipment that carries signals The software consists of instruction sets that make the required services possible The fundamental job of executing a service with a computer is done by computer hardware At the highest level, a software can direct the execution process such as the details of how this is done by the actual hardware Network Models 1-10
Network Models Illustrative Example Sending an e-mail from one point in the world to another The main tasks are broken into many tasks performed by a separate software package Each software package uses the services of another software package Employing suitable protocol (SMTP) Establishing end-to-end connection (TCP) Adding final destination address (IP) Encrypting data, adding physical address, accessing medium of next hop destination (MAC) At the lowest layer, a signal, or a set of signals, is sent from the source computer to the destination computer Network Models 1-11 (physical layer)
Layered Tasks Network Models 1-12
The Open Systems Interconnection (OSI) Model Introduced in 1970s by the International Standards Organization (ISO) An open system is a set of protocols that allows any two different systems to communicate regardless of their underlying architecture OSI Model Goals facilitating communication between different systems without requiring changes to the logic of the underlying hardware and software understanding and designing a network architecture that is flexible, robust, and interoperable Network Models 1-13
The OSI Layers Network Models 1-14
The Interaction between Layers in the OSI Model Network Models 1-15
TCP/IP Protocol Architecture In general terms, data communications in computer networks can be said to involve three agents: applications, computers, and networks Applications are executed among computers connected to networks Data to be exchanged are transferred by the network from one computer to another Based on previous concepts, the communication task into five relatively independent layers Physical layer Network access layer (Data link layer) Internet layer Host-to-host, or transport layer Application layer Network Models 1-16
TCP/IP Concepts Network Models 1-17
TCP/IP Model The physical layer covers the physical interface between a data transmission device (e.g., computer) and a transmission medium or network The network access or data link layer concerns with the exchange of data between devices attached to the same network (i.e., next neighboring device). The specific software used at this layer depends on the type of network to be used (e.g., circuit switching, packet switching) The Internet layer (Internet protocol (IP) layer) Concerns with routing data between devices attached to different networks. The IP protocol at this layer provides the routing function across multiple networks. Intermediate devices such as routers implements the IP The host-to-host layer, or transport layer Concerns with exchanging data reliably and assures that all of the data arrive at the destination application and that the data arrive in the same order in which they were sent The application layer contains the logic needed to support the various user applications Network Models 1-18
A Comparison of the OSI and TCP/IP Protocol Architectures Network Models 1-19
Addressing in TCP/IP Model Four levels of addresses are used in an internet employing the TCP/IP protocols Physical Addresses: the address of a node as defined by its LAN or WAN. It is included in the frame used by the data link layer. For example, Ethernet uses a 6-byte (48-bit) physical address (MAC address) Logical Addresses: necessary for universal communications that are independent of underlying physical networks. A logical address in the Interne is currently a IPv4 (32-bit) address or IPv6 (128 bits) address that can uniquely define a host connected to the Internet. Used by the network layer. Network Models 1-20
Addressing in TCP/IP Model Port Addresses The IP address and the physical address are necessary for a quantity of data to travel from a source to the destination host arrival at the destination host is not the final objective of data communications on the Internet computers are devices that can run multiple processes at the same time The end objective of Internet communication is a process communicating with another process There is a need to a method to label the different processes such as transferring files and sending emails A port address in TCP/IP is 16 bits in length. Used by the transport layer Network Models 1-21
Addressing in TCP/IP Model Specific Addresses Some applications have user-friendly addresses that are designed for that specific address Examples include the e-mail address and the Universal Resource Locator (URL) These addresses, however, get changed to the corresponding port and logical addresses by the sending computer Used by the application layer Network Models 1-22
Addressing in TCP/IP Model The physical addresses change from hop to hop, but the logical and port addresses usually remain the same Network Models 1-23
Lecture-related Questions List the main key elements of the Internet and describe briefly each one What are some of the factors that determine whether a communication system is a LAN or WAN? Network Models 1-24
Lecture Summary Covered material Introduction to the Internet Reference Models for Computer Networks The OSI Model The TCP/IP Model Material to be covered next lecture Introduction to the physical layer and media Network Models 1-25