How does the Internet Look Like?

Transcription

1 Computer s EEE 448 Lecture #2 Dept of Electrical and Electronics Engineering Çukurova University Organizing Functionality s are built from many components ing technologies, Wifi, Bluetooth, Fiber Optic, Cable Modem, DSL styles Circuit switch, packet switch Wired, Wireless, Optical, Satellite s , Web, FTP, Bittorrent, Skype How do we make all this stuff work together?! 2 Problem Scenario More Problems Web Bittorrent Vo Bittorrent Bittorrent This is a nightmare scenario Huge amounts of work to add new apps or media Limits growth and adoption endpoints may not be on the same media Bluetooth Cellular How does the Internet Look Like? Key Questions How do we divide functionality into layers? Routing Congestion control Error checking Security Fairness And many more How do we distribute functionality across devices? Example: who is responsible for security? 5 Switch Router Switch 6 1

2 22/03/2016 Common Services Many applications may share common functionalities Can you think of examples? These functionalities need to be integrated on each application Layering Abstraction Layer: A set of functionalities encapsulated in an object that can be used by other network components Example: The network layer implements the end-to-end (E2E) packet delivery Why layering? Think complexity and common services Layers consist of protocols Or be abstracted in common services 7 8 What are Protocols? Layering An agreement between parties on how communication should take place Module in layered structure s define: Interface to higher layers (API) Interface to peer (syntax & semantics) Actions taken on receipt of a messages Format and order of messages Error handling, termination, ordering of requests, etc. Example: Buying airline ticket Friendly greeting Muttered reply Destination? Istanbul Thank you 9 Example: -to-application channels Host-to-host connectivity Link hardware 10 Layered Stack Layering Characteristics s Layer N Layer 2 Layer 1 Media Modularity Does not specify an implementation Instead, tells us how to organize functionality Encapsulation Interfaces define cross-layer interaction Layers only rely on those below them Flexibility Reuse of code across the network Module implementations may change Unfortunately, there are tradeoffs Interfaces hide information As we will see, may hurt performance 11 Each layer relies on services from layer below and exports services to layer above defines interaction with peer on other hosts Hides implementation - layers can change without disturbing other layers (black box) 12 2

3 A simple layering example RRP: Request/reply protocol MSP: Message streaming protocol HHP: Host-to-host protocol Looking into layers a bit closer Protocols in each layer have Service interface with upper layer/lower layer Peer-to-peer interface with host on same layer The ISO OSI Model ISO: International Organization for Standardization OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Layers All devices communicate Layers implement the peer-to-peer communicate peer-to-peer first three layers 15 The Layers Features Why do you need this layer? What does this layer do? How do you access this layer? How is this layer implemented? 16 Layer Deals with the transmission of 0s and 1s over the physical media Translation of bits into signals Move information between two systems connected by a physical link Specifies how to send one bit Encoding scheme for one bit Voltage levels Timing of signals Examples: coaxial cable, fiber optics, radio frequency transmitters 17 Layer Manages the flow of data over the physical media Responsible for error-free transmission over the physical media Data framing: boundaries between packets Media access control (MAC) Per-hop reliability and flow-control Send one packet between two hosts connected to the same media addressing (e.g. MAC address) Examples:, Wifi, DOCSIS 18 3

4 Layer Addressing and routing the packets Example application at the router If the packet size is large, splits into small packets Deliver packets across the network Handle fragmentation/reassembly Packet scheduling Buffer management Send one packet to a specific destination Define globally unique addresses Maintain routing tables Example: Internet Protocol (), v6 19 Layer Repackage proper and efficient delivery of packages Error free, In sequence, Without duplication Multiplexing/demultiplexing Congestion control Reliable, in-order delivery Send message to a destination Port numbers Reliability/error correction Flow-control information Examples:, 20 Layer Oversee a communication session Establish, Maintain, Terminate Access management Synchronization It depends-nfs ( File System) Token management Insert checkpoints 21 Examples: none Layer Formats data for exchange between points of communication Ex: Between nodes in a network Convert data between different representations E.g. big endian to little endian E.g. ASCII to Unicode It depends(pict,tiff,jpeg,midi,mpeg) Define data formats Apply transformation rules Examples: none 22 Layer User application to network service interface Whatever you want :) Whatever you want :D Whatever you want HTTP, SMTP, Examples: turn on your smartphone and look at the list of apps 23 Encapsulation How does data move through the layers? Data Data 24 4

5 Encapsulation Example The process of embedding a or trailer Real Life Analogy Doesn t know how the Postal network works Label contains Un-packing routing info Doesn t know contents of letter 25 Postal Service 26 Stack in Practice Encapsulation, Revisited Host 1 Switch Host 2 Video FTP Client Data n Link Data n Link FTP Video Server Data n Link 27 HTTP HTTP Segment HTTP Datagram HTTP Frame Web Page Web Page Web Page Web Page Trailer Web Server 28 The Hourglass Orthogonal Planes HTTP, FTP, RTP, IMAP, Jabber, One Internet layer means all networks,, ICMP interoperate Think about the All applications function v4 on all networks difficulty of Room for development above and deploying below v6 But, changing, x, is insanely DOCSIS, hard Fiber, Coax, Twisted Pair, Radio, 29 Data Plane Well cover this later BGP R OSPF Control Plane 30 5

6 Reality Check The layered abstraction is very nice Does it hold in reality? No. Where to Place Functionality How do we distribute functionality across devices? Example: who is responsible for security?????? Firewalls Analyze application layer s Transparent Proxies Simulate application endpoints within the network NATs Break end-to-end network reachability 31 Switch Switch Router The End-to-End Arguments in System Design Saltzer, Reed, and Clark The Sacred Text of the Internet Endlessly debated by researchers and engineers 32 Basic Observation Example: Reliable File Transfer Some applications have end-to-end requirements Security, reliability, etc. Implementing this stuff inside the network is hard Every step along the way must be fail-proof End hosts Can t depend on the network Can satisfy these requirements without network level support 33 Integrity Check Integrity Check Solution 1: Make the network reliable Integrity Check App has to do a check anyway! Solution 2: App level, end-to-end check, retry on failure 34 Example: Reliable File Transfer Please Retry In-network implementation Doesn t reduce host complexity Does increase network complexity Increased overhead for apps that don t need functionality Full functionality can But, in-network performance may be better be built at App level Solution 1: Make the network reliable Solution 2: App level, end-to-end check, retry on failure 35 Moderate Interpretation Think twice before implementing functionality in the network If hosts can implement functionality correctly, implement it a lower layer only as a performance enhancement But do so only if it does not impose burden on applications that do not require that functionality 36 6

7 The Internet Engineering Task Force Standardization is key to network interoperability The hardware/software of communicating parties are often not built by the same vendor yet they can communicate because they use the same protocol Internet Engineering Task Force Based on working groups that focus on specific issues Request for Comments Document that provides information or defines standard Requests feedback from the community Can be promoted to standard under certain conditions consensus in the committee interoperating implementations The Internet Architecture The Internet Architecture / Model FTP HTTP TFTP Net 1 Net 1 FDDI FTP: File Transfer Protocol HTTP: Hypertext Protocol TFTP: Trivial File Transfer Protocol DNS : Transmission Control Protocol : User Datagram Protocol : Internet Protocol Layer programs using the network Layer (/) Management of end-to-end message transmission, error detection and error correction Layer () Handling of datagrams : routing and congestion Layer Management of cost effective and reliable data delivery, access to physical networks Layer Media 40 Comparison of the two architectures Structure : User Datagram Protocol: ICMP: Internet Control Message Protocol : Internet Protocol ARP: Address Resolution Protocol RARP: Reverse ARP processor processor OSI Layer 5-7 OSI Layer 4 ICMP ARP RARP OSI Layer 3 hardware interface OSI Layer

8 / protocol suite proc.a Port Number interface proc.b cable 2 proc.c proc.d proc.e PEX interface interface proc.f IDP SPP proc.g cable 1 interface XNS protocol suite 44 = User Datagram Protocol Hierarchical Addressing Scheme Connection defines the communication link between two processes 16-bit source port # 16-bit dest. port # protocol = internet 32-bit source addr internet 32-bit dest. addr frame type = 48-bit source addr 48-bit dest. addr frame data data data data trailer 45 The Layer layer defines the mechanical, electrical, and timing interfaces to the network. theoretical analysis of data transmission three kinds of transmission media : guided : copper wire and fiber optics Wireless: terrestrial radio satellite To be transmitted, data must be transformed to electromagnetic signals. 47 layer: The Theoretical Basis The number of the highest harmonic passed through is roughly 3000/(b/8) or 24,000/b Relation between data rate and harmonics : Guided Transmission Media Magnetic Media Bandwidth characteristics is excellent Delay characteristics is poor Twisted Pair A twisted pair consists of two insulated copper wires, typically about 1 mm thick. Twisting is done because two parallel wires constitute a fine antenna. Twisted pair categories: Category 3 UTP (Unshielded Twisted Pair) (a) Category 5 UTP (Unshielded Twisted Pair) (b) They are similar to category 3 pairs, but with more twists per centimeter, which results in less crosstalk and a better-quality signal over longer distances, making them more suitable for highspeed computer communication. 8

9 Coaxial Cable It has better shielding than twisted pairs, so it can span longer distances at higher speeds. Two kinds of coaxial cable 50-ohm cable : is commonly used when it is intended for digital transmission. 75-ohm cable: is commonly used for analog transmission and cable television The bandwidth possible depends on the cable quality, length, and signal-to-noise ratio of the data signal. Fiber Optics An optical transmission system has three key components: Light source: Conventionally, a pulse of light indicates a 1 bit and the absence of light indicates a 0 bit. Transmission medium: is an ultra-thin fiber of glass Detector: generates an electrical pulse when light falls on it. Fiber Optics When a light ray passes from one medium to another, for example, from fused silica to air, the ray is refracted (bent) at the silica/air boundary Fiber types multimode fiber single-mode fiber: diameter is reduced to a few wavelengths of light Fiber Optics Fiber Cables multimode fibers : The core is typically 50 microns in diameter, about the thickness of a human hair single-mode fibers : The core is 8 to 10 microns. Fibers can be connected in three different ways Connectors Mechanical Fusion Two kinds of light sources are typically used to do the signaling LEDs (Light Emitting Diodes) Semiconductor lasers receiving end of an optical fiber consists of a photodiode Fiber Optics A comparison of semiconductor diodes and LEDs as light sources. Comparison of Fiber Optics and Copper Wire Fiber can handle much higher bandwidths than copper, Fiber not being affected by power surges, electromagnetic interference, or power failures, Fiber is thin and lightweight, Security in fiber is high, Fiber is a less familiar technology requiring skills not all engineers have, Fibers can be damaged easily by being bent too much, Optical transmission is inherently unidirectional, two-way communication requires either two fibers or two frequency bands on one fiber, Fiber interfaces cost more than electrical interfaces.. 9

10 Last words Layering is a nice way to organize network functions Unified Internet layer decouples apps, enables innovation E2E argument (attempts) to keep layer simple Think carefully when adding functionality into the network 56 10