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CS4470 Computer Networking Protocols
6/16/2018 CS Computer Networking Protocols 1. Introduction Huiping Guo Department of Computer Science California State University, Los Angeles
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Outline Introduction to networks Network categories
The Internet and the challenges Protocols and layering 1. Introduction
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Motivation for Networks
6/16/2018 Motivation for Networks Remote Access Sharing of Resources Hardware, software Information Dissemination Newsgroups, ftp sites, web sites Communication , chat and instant messaging, video conferencing 1. Introduction
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Network basics Network Network criteria
A set of devices (nodes) connected by communication links A node can be a computer, printer, or any other device capable of sending/receiving data generated by other nodes on the network Network criteria A network must be able to meet a certain number of criteria Performance Reliability security 1. Introduction
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Network attributes Type of connection
A network is two or more devices connected through links A link is a pathway that transfers data from one device to another Two possible connections point-to-point Broadcast 1. Introduction
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Point-to-point and broadcast
A point-to-point connection provides a dedicated link between two devices The entire capacity of the link is reserved for transmission Broadcast a single link is shared by all the nodes on the network, either spatially or temporally Messages sent by any nodes are received by all the others 1. Introduction
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Network attributes Physical topology Categories of topology
Refers to the way in which a network is laid out physically Two or more devices connect to a link Two or more links form a topology Categories of topology Mesh topology Star topology Bus topology Rings topology 1. Introduction
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Outline Introduction to networks Network categories
The Internet and the challenges Protocols and layering Network performance 1. Introduction
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Categories of Networks
6/16/2018 Categories of Networks Scale Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) The way to transmit data Circuit switching network Packet switching network 1. Introduction
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Local Area Network (LAN)
What are LANs? Privately owned networks within a single building or campus LANs are designed to share resources Characteristics: Restricted in size A few kilometers The worst case transmission time is bounded Transmission technology: broadcast Topologies Bus, tree, ring, star 1. Introduction
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Wide Area Network (WAN)
A WAN is a computer network that covers a broad area Switching elements 1. Introduction
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Metropolitan Area Network
A MAN is a network with a size between a LAN and a WAN It normally covers the area inside a town or a city It’s designed for customers who need a high speed connectivity Example Telephone company network that can provide a high spped DSL line to the customer Cable TV network 1. Introduction
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Circuit Switching network
Source first establishes a connection (circuit) to the destination. Source sends the data over the circuit. then the connection is torn down. Example: telephone network End-end resources reserved for “call” dedicated resources: no sharing guaranteed performance 1. Introduction
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Packet Switching Networks
Source sends information as self-contained packets that have an address. Source may have to break up single message in multiple packets Each packet travels independently to the destination host. Routers and switches use the address in the packet to determine how to forward the packets each packet uses full link bandwidth Packets sent by different users share network resources Efficient: resources used on demand 1. Introduction
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Packet Switching Networks
Store and forward Node receives complete packet before forwarding Packets are self contained units Can use alternate paths – reordering Store and forward delay Resource contention: congestion: packets queue Queue delay Example: the Internet 1. Introduction
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Outline Introduction to networks Network categories
The Internet and the challenges Protocols and layering 1. Introduction
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Internet A collection of interconnected networks Internet
6/16/2018 Internet A collection of interconnected networks A network of networks Host(or nodes): network endpoints (computer, PDA, cell phone, …) Router: node that connects networks Internet What if want to communicate between hosts on different Ethernets? Internet as interoperability layer 1. Introduction
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Challenges Scale: 100,000,000s of hosts Heterogeneity
Diversity of network technologies Fast links, slow links, satellite links, cellular links, carrier pigeons Address formats Performance – bandwidth/latency Packet size Loss rate/pattern/handling Routing How to translate between various network technologies? 1. Introduction
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Need naming and routing
How To Find Nodes? Internet Computer 1 Computer 2 Need naming and routing 1. Introduction
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What’s the IP address for www.calstatela.edu?
Naming What’s the IP address for It is Computer 1 Local DNS Server Translates human readable names to logical endpoints 1. Introduction
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Routers send packet towards destination
Routing Routers send packet towards destination H R H R H R R R R H R H: Hosts R: Routers R H 1. Introduction
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Meeting Application Demands
Reliability Corruption Lost packets Flow and congestion control Fragmentation In-order delivery Etc… 1. Introduction
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What if the Data gets Corrupted?
Problem: Data Corruption GET index.html GET windex.html Internet Solution: Add a checksum X 0,9 9 6,7,8 21 4,5 7 1,2,3 6 1. Introduction
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What if Network is Overloaded?
Problem: Network Overload Solution: Buffering and Congestion Control Short bursts: buffer What if buffer overflows? Packets dropped Sender adjusts rate until load = resources “congestion control” 1. Introduction
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What if the Data gets Lost?
Problem: Lost Data GET index.html Internet Solution: Timeout and Retransmit GET index.html GET index.html Internet GET index.html 1. Introduction
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What if the Data Doesn’t Fit?
Problem: Packet size On Ethernet, max IP packet is 1.5kbytes Typical web page is 10kbytes Solution: Fragment data across packets ml x.ht inde GET GET index.html 1. Introduction
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What if the Data is Out of Order?
Problem: Out of Order ml inde x.ht GET GET x.htindeml Solution: Add Sequence Numbers ml 4 inde 2 x.ht 3 GET 1 GET index.html 1. Introduction
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Outline Introduction to networks Network categories
The Internet and the challenges Protocols and layering 1. Introduction
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Protocols and layering
What is layering Modular approach to network functionality Example Application Application-to-application channels Host-to-host connectivity Link hardware 1. Introduction
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Why layering? Networks are complex!
We need a way to organize the structure of network functionalities and to reduce the design complexities Benefits of layering Interoperability Reuse Hiding underlying details 1. Introduction
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Many many Network Components
6/16/2018 Many many Network Components Application Application Router Software (many protocols) Operating System Operating System Links Computer Network Interface Protocol Software Router Hardware Computer Bridge HW/SW 1. Introduction
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Protocols and layering
6/16/2018 Protocols and layering What is a Protocol Module in layered structure Set of rules governing communication between network elements (applications, hosts, routers) Protocols define: Interface to higher layers (API) Interface to peer Format and order of messages Actions taken on receipt of a message 1. Introduction
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A human protocol and a computer network protocol
Hi TCP connection request Hi TCP connection response Got the time? Get 2:00 <file> time 1. Introduction
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Protocol interfaces Each protocol offers an interface to its users, and expects one from the layers on which it builds Syntax and semantics Data formats Interface characteristics, e.g. IP service model Protocols build upon each other Add value E.g., a reliable protocol running on top of IP Reuse E.g., OS provides TCP, so apps don’t have to rewrite 1. Introduction
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TCP/IP Model: the Internet model
6/16/2018 TCP/IP Model: the Internet model Each layer relies on services from layer below Each layer exports services to layer above Interface between layers defines interaction Hides implementation details Layers can change without disturbing other layers Application Transport Network Data link Physical 1 2 3 4 5 1. Introduction
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TCP/IP Model: the Internet model
application: supporting network applications FTP, SMTP, HTTP transport: host-host data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” 1. Introduction
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TCP/IP protocols suite
6/16/2018 TCP/IP protocols suite FTP HTTP NV TFTP Applications UDP TCP TCP UDP Waist IP Data Link NET1 NET2 … NETn Physical The Hourglass Model The waist facilitates interoperability 1. Introduction
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Protocols for Interoperability
Many implementations of many technologies: Hosts running FreeBSD, Linux, Windows, MacOS, People using Mozilla, Explorer, Opera, … Routers made by cisco, juniper, … Hardware made by IBM, Dell, Apple, … And they change all the time. But they can all talk together because they use the same protocol(s) Application level protocols: HTTP, SMTP, POP, IMAP, etc. Hardware protocols (ethernet, etc) 1. Introduction
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Protocols for Abstraction & Reuse
Multiple choices of protocol at many layers Physical: copper, fiber, air, carrier pigeon Link: ethernet, token ring, SONET, FDDI Transport: TCP, UDP, SCTP But we don’t want to have to write “a web (HTTP) browser for TCP networks running IP over Ethernet on Copper” and another for the fiber version… Reuse! Abstraction! Protocols provide a standard interface to write to Layers hide the details of the protocols below 1. Introduction
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TCP/IP protocols suite
6/16/2018 TCP/IP protocols suite A B HTTP message HTTP HTTP TCP segment TCP TCP router router IP packet IP packet IP packet IP IP IP IP Ethernet interface Ethernet interface SONET interface SONET interface Ethernet interface Ethernet interface 1. Introduction
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Layer Encapsulation User A User B Get index.html Connection ID
6/16/2018 Layer Encapsulation User A User B Get index.html Connection ID Source/Destination Link Address 1. Introduction
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