Notes On Chapter Twenty -- Internetworking: Concepts, Architecture, and Protocols

• 20.0 Study Guide
  
  
  • Be able to explain the concept of universal service
  • Understand that the Internet is composed of multiple networks connected by routers, which are something like packet switches.
  • Understand that the Internet creates a virtual network.
  • Know that the TCP/IP family of protocols is a major component of the architecture of the Internet
  
  
• 20.1 Introduction
  
  
  • Inter-networking technology
  • Motivation for inter-networking
  • Hardware Used for inter-networking
  • Architecture of an internet
  • Significance of inter-networking concepts
  
  
• 20.2 The Motivation for Internetworking
  
  
  • There are different kinds of networks for different needs.
  • Therefore different kinds of networks arise
  • Therefore we need inter-networking technology to join diverse networks
  
  
• 20.3 The Concept of Universal Service
  
  
  • It can be difficult or impossible to figure out ways for two computers to communicate when they each belong to a different and incompatible type of network.
  • However, people naturally want universal service - they want service that allows any pair of computers to communicate, any time.
  • Part of the reason why universal service is desirable is because it enables people to be more productive.
  
  
• 20.4 Universal Service in a Heterogeneous World
  
  
  • One cannot join incompatible networks simply by connecting media together. Even if the media used are the same, there will be other incompatibilities such as differing frequencies, voltages, and coding techniques.
  • Nor is it enough to employ bridge technology to connect incompatible networks. Bridges work by forwarding frames, and frame formats (including addresses) vary dramatically from network to network.
  
  
• 20.5 Internetworking
  
  
  • By using a combination of hardware and software, one may form a network of networks of great size - an internetwork or internet
  
  
• 20.6 Physical Network Connection with Routers
  
  
  • The basic unit of hardware used to form an internet is a router.
  • A router has some characteristics in common with a bridge:
    • A router contains a CPU and memory - so like a bridge it is a type of special-purpose computer.
    • A router has connections to two or more networks.
    • The interfaces used in a router to connect to networks are ordinary network interfaces - they are just like the interfaces that all other computers use to connect to that type of network.
    
    
  • Typically a bridge connects two network segments that are the exact same type of network.
  • Unlike a bridge, a router typically connects two or more networks that are NOT the same type of network. For example, a router might connect:
    • an Ethernet to a WAN, or
    • an Ethernet to a WiFi network, or
    • a WiFi network to an IBM Token Ring network.
  • The two networks connected by a router are often depicted by a "cloud" in diagrams. The cloud represents an arbitrary network technology.
  
  
  
  
• 20.7 Internet Architecture
  
  
  • The job of a router is to forward packets. To forward a packet, a router receives a packet on one of its network interfaces and transmits it out over another of its network interfaces.
  • A router has to process information about a packet in its CPU to decide on which interface to use to transmit the packet.
  • The more interfaces a router has, the more incoming packets it may be required to process per unit of time.
  • To keep their workload manageable, routers are usually built with a fairly small number of network interfaces.
    
    
    
    
  • Also, it's good to build an internet with redundant links and routers - so that the network is not likely to be partitioned if just a handful of routers and/or links fail. So that's another reason not to connect too many networks together with a single router.
  • When deciding on router hardware and connection topology, Internet architects must consider:
    • need for reliability
    • need for channel capacity
    • cost constraints
    • expected traffic
    • expected performance characteristics of available router hardware
  
  
• 20.8 Intranets and Internets
  
  
  • An intranet is a private internet.
  • The Internet (proper noun) is the public global internet.
  • Sometimes the distinction between the two concepts is difficult to maintain, since TCP/IP protocols are often used throughout, and because intranets are usually connected to the Internet.
  
  
• 20.9 Achieving Universal Service
  
  
  • The job of an internet is to allow any pair of computers to communicate.
  • Therefore the system of routers has to assure that packets are forwarded all the way from the source to the destination.
  • How can this be done, given that the frame formats and addressing techniques on the various networks are utterly incompatible?
  • It can be done through the use of protocol software on hosts and routers.
  
  
• 20.10 A Virtual Network
  
  
  • Through the use of routers and Internet protocol software the Internet creates a virtual network by overlaying and unifying component physical networks.
  • The Internet provides universal service. In other words communication is possible between any pair of hosts on the Internet.
  • Users and applications can function without knowing anything about how the component networks are joined together, how addressing works, or how routing works.
  
  
  
  
• 20.11 Protocols for Internetworking
  
  
  • The protocol family utilized to construct the Internet is the TCP/IP protocol suite.
  • Joint work on TCP/IP and the Internet architecture has been ongoing since the 1970s.
  
  
• 20.12 Review of TCP/IP Layering
  
  
  • The IP layer is layer 3 in the TCP/IP networking model.
  • IP specifies Internet packet format and mechanisms for forwarding packets.
  • TCP is at layer 4. It deals with the messages and procedures that ensure reliable transfer.
  
  
  
  
• 20.13 Host Computers, Routers, and Protocol Layers
  
  
  • A host computer (also known simply as a host) is a computer that connects to the Internet and runs applications. A host can be large or small - a mainframe computer, a PC, a mobile device, or even an embedded system.
  • The design of the Internet requires that host computers and routers execute TCP/IP protocol software.
  • However, routers, at least mostly, execute IP software.