Network Architecture. TOC Architecture

Transcription

1 Network Architecture Introduction Layering Example Internet Layers First Look Layering Step by Step Downside of Layering Interconnecting Networks The Internet TOC Architecture

2 Introduction Issues: Inter-operability Extensibility Applications & Technologies Scalability Internet Solution: Layered Architecture End-to-End Principle Hierachical Addressing & Naming TOC Architecture Introduction

3 Layer: Example Please fax letter to Prof. B, Urgent Prof. A Here is my review of paper 554. I believe its main result is wrong. Here is a counterexample. Prof. B Here is a letter from Prof. A SECRETARY John COVER To: Prof. B Fr: Prof. A Urgent Here is my review of paper 554. I believe its main result is wrong. Here is a counterexample. SECRETARY Mary FAX SYSTEM TOC Architecture Layer Example

4 Layer: Example Prof. A Prof. B Please fax letter to Prof. B, Urgent INTERFACE Here is my review of paper 554. I believe its main result is wrong. Here is a counterexample. Here is a letter from Prof. A FUNCTIONS SECRETARY John SERVICE - SECY COVER To: Prof. B Fr: Prof. A Urgent HEADER Here is my review of paper 554. I believe its main result is wrong. Here is a counterexample. SECRETARY Mary SERVICE - FAX FAX SYSTEM TOC Architecture Layer Example

5 Layer: Example Prof. A SECRETARY John Here is my review of paper 554. I believe its main result is wrong. Here is a counterexample. COVER To: Prof. B Fr: Prof. A Urgent Here is my review of paper 554. I believe its main result is wrong. Here is a counterexample. Prof. B SECRETARY Mary Secretaries implement functions that transform a simple service into a more complex one (E.g., add MULTIPLEXING) They follow rules of communication: PROTOCOL They use the header as control information Note: Encapsulation (adding header) and Decapsulation (removing header) FAX SYSTEM TOC Architecture Layer Example

6 Internet Layers - Intro Browsing Services Names Examples Specifications Encapsulation Functions TOC Architecture Internet Layers: Intro

7 Browsing Name IP Address Connect; Get; Close Supervise Connection Forward Packets Across Many Links Transmit Packets on Each Link Transmit Bits on Each Medium DSN Servers End hosts 5 End hosts 4 Routers 3 Link/LAN 2 Transceivers H R R H TOC Architecture Internet Layers: Intro Browsing

8 Services 5 4 Application Connection Packets: End to End Packets Bits Signals TOC Architecture Internet Layers: Intro Services

9 Names 5 4 Application Connection Packets: End to End Application Transport Packets Bits Signals Network Link TOC Architecture Internet Layers: Intro Names

10 Examples Application 5 Connection Application DNS; HTTP; TFTP; RTP 4 Packets: End to End Transport TCP; UDP; 3 Packets Network IP; ATM; 2 Bits Link Ethernet; ADSL; 1 Signals Fiber-1Gbps; Cat5-100Mbps; Wireless; SONET TOC Architecture Internet Layers: Intro Examples

11 Specifications N + 1 N N - 1 Interfaces: Formats, Functions: Service Provided Typically: State Machine TOC Architecture Internet Layers: Intro Specification

12 Encapsulation N + 1 Data Unit that N Delivers N N - 1 H Header: Control Info of N Examples of H: Addresses Error Control Codes Framing Delimiters TOC Architecture Internet Layers: Intro Encapsulation

13 Functions APP TRAN NET LINK PHY Set Up Connections; Presentation; Multiplexing; Flow Control; Congestion Control Global Addressing; Routing; Forwarding Framing; Error Coding; Local Addressing; Switching Modulation; Demodulation TOC Architecture Internet Layers: Intro Functions

14 Layers Step By Step Data Link Network Transport Application DNS TOC Architecture Layers Step By Step

15 In the beginning were two computers TOC Architecture Layers Step By Step

16 Example: Manchester Encoding Medium Virtual Bit Pipe Synchronous unreliable bit pipe RS232-C Interface Modem Modem RS232-C Interface Interface wires Medium Interface wires TOC Architecture Layers Step By Step

17 Data Link Control Layer! " # $ %& ' & # ( Data Link Protocol Data Link Control Interface Asynchronous reliable bit pipe FH Data Synchronous unreliable bit pipe Bit Stream Data Link Control Interface )* +%, " ) Link %' # ( TOC Architecture Layers Step By Step Link

18 Data Link Control Layer What about a broadcast system? Example: Satellite, ethernet, Individual transmissions can interfere and destroy many frames A multiaccess protocol is required to try and avoid these collisions or the link will be too unreliable Example: TDM, CSMA Makes the bit-pipe provided by the physical layer look intermittent to the DLC Protocol must interface with and DLC layers By convention the Multiaccess Control Layer (MAC) is considered a sub-layer of the DLC TOC Architecture Layers Step By Step Link

19 Data Link Control Layer What about a broadcast system? DLC Need Addresses Burned into NICs DLC MAC DLC MAC Interface Interface Multiaccess Medium MAC Interface TOC Architecture Layers Step By Step Link

20 Network Layer: Routing C D A B E " -#. / Routing information must be contained in a message unless it is part of a circuit Network addressing and protocol required to accomplish delivery over multiple hops TOC Architecture Layers Step By Step Network

21 Network Layer: Complexity C D A E B Topology discovery Link State monitoring Forwarding Buffer management -. # * # # # TOC Architecture Layers Step By Step Network

22 Network Layer: Routers/Switches C D A R S B E & % 0, 0 % # ( TOC Architecture Layers Step By Step Network

23 Network Layer Network Asynchronous path Asynchronous path Network PH Data PH Data Network Data Link Control Asynchronous reliable bit pipe FH Data Data Link Control Asynchronous reliable bit pipe FH Data Data Link Control Interface Synchronous unreliable bit pipe Link Interface Synchronous unreliable bit pipe Link Interface )* TOC Architecture Layers Step By Step Network

24 Transport Layer APP C D a b c A B x y z E APP 1 -. TOC Architecture Layers Step By Step Transport

25 Transport Layer Transport TH Data Transport Network Asynchronous routed path Asynchronous routed path Network PH Data PH Data Network Data Link Control Asynchronous reliable bit pipe FH Data Data Link Control Asynchronous reliable bit pipe FH Data Data Link Control Interface Synchronous unreliable bit pipe Synchronous unreliable bit pipe Interface Interface Link Link End Node Subnet Node End Node )* TOC Architecture Layers Step By Step Transport

26 Application Layer Application Data Application Transport TH Data Transport Network Asynchronous routed path Asynchronous routed path Network PH Data PH Data Network Data Link Control Asynchronous reliable bit pipe FH Data Data Link Control Asynchronous reliable bit pipe FH Data Data Link Control Interface Synchronous unreliable bit pipe Interface Synchronous unreliable bit pipe Interface Link Link End Node Subnet Node End Node )* +6 7 # TOC Architecture Layers Step By Step Application

27 Network Directory Servers C D X A R S B E 8 # 15" % TOC Architecture Layers Step By Step DNS

28 Encapsulation Application Application Data Transport Transport TH Data Network Asynchronous routed path PH TH Data Network Asynchronous routed path PH TH Data Network Data Link Control Asynchronous reliable bit pipe Asynchronous reliable bit pipe Data Link Control FH PH TH Data FH PH TH Data Data Link Control Interface Synchronous unreliable bit pipe Interface Synchronous unreliable bit pipe Interface Link Link End Node Subnet Node End Node ) 9 TOC Architecture Layers Step By Step Encapsulation

29 The downside of layering Efficiency Suboptimal network behavior TCP and wireless links Redundant Implementation Fragmentation and reassembly Multiple address spaces Confusion in actual networks Layer 2, Layer 4 and Layer 4-7 switches What layer does the function security belong to? Network devices (such as routers) may run application protocols TOC Architecture Downside

30 Inter-Connecting Networks Global Address IP1 E1 IP1 IP4 Data A = E1 E2 PCKT PCKT IP2 E2 R IP3 E3 B - Addresses IP4 E4 E3 E4 PCKT A - Addresses Destination Next Hop IP4 E4 B Router R sees network B as a direct link TOC Architecture Interconnecting

31 The Internet Overview Minimal Router State Layering End-to-End Argument Success Caveats TOC Architecture - Internet

32 Overview Interconnect networks with different Speeds, Reliability, Cost Go across multiple networks Internet Service = Best Effort datagram service: Try hard to deliver each packet Anything more, e.g. voice grade service, would Preclude many networks from joining the internet Require great amounts of co-ordination and compliance monitoring Create an endless clamoring for even other kinds of guarantees such as video grade service TOC Architecture - Internet Overview

33 Case for minimal router state Adding connection state to routers creates problems in the presence of failures How to clean up the bad state? Scaling router state with number of transport connections would be very expensive Adding connection state in only some routers might not be good enough What if many congested routers did not implement state So: The internet provides datagram service. Under this constraint, the internet is designed to support as many different types of applications as possible. TOC Architecture - Internet Minimal State

34 Layering Application TCP UDP IP Network BGP HTTP RTP TFTP TCP UDP IP Ethernet FDDI Token Etc. Almost Any kind of application can write directly on IP Including new transport protocols IP cannot be avoided As long as the routers speak IP, any application that can make do with datagram service can be written and implemented on the end devices. No co-ordination, standards activity etc. is required!! TOC Architecture - Internet Layering

35 End-to-End Argument (Saltzer, Reed and Clark 1984) Implement a network function at the end hosts unless it cannot be implemented correctly in this manner. OR Don t implement a function at the lower levels of the system unless it can be completely implemented at this level (Peterson and Davie) TOC Architecture - Internet E2E Argument

36 Success TOC Architecture - Internet - Success

37 Success 4/1-4/ ,224,733 IP addresses, 2,093,194 IP links, 932,000 destinations, 70% of globally routable network prefixes; 10,999 ASes (84% of ASes), 34,209 peering sessions TOC Architecture - Internet Success

38 Caveats Internet is actually a lot more complicated and messy than today s lecture would suggest The end-to-end argument is being subverted and under attack The internet does a poor job of supporting high performance traffic such as voice and video The phone network is hardly going away We will deal with these issues in much more detail towards the end of the course TOC Architecture Internet - Caveats