Lecture 2: Internet Architecture
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1 CS 3700 Networks and Distributed Systems Lecture 2: Internet Architecture Revised 1/6/14
2 Organizing Network Functionality 2
3 Organizing Network Functionality 2 Networks are built from many components! Networking technologies Ethernet, Wifi, Bluetooth, Fiber Optic, Cable Modem, DSL! Network styles Circuit switch, packet switch Wired, Wireless, Optical, Satellite! Applications , Web (HTTP), FTP, BitTorrent, VoIP How do we make all this stuff work together?!
4 Problem Scenario 3
5 Problem Scenario 3 Web Bittorrent Ethernet Bluetooth
6 Problem Scenario 3 Web Bittorrent Ethernet Bluetooth
7 Problem Scenario 3 Web Bittorrent Ethernet Bluetooth
8 Problem Scenario 3 Web Bittorrent Ethernet Bluetooth
9 Problem Scenario 3 Web Bittorrent Ethernet Bluetooth Cellular
10 Problem Scenario 3 Web Bittorrent Ethernet Bluetooth Cellular
11 Problem Scenario 3 Web Bittorrent VoIP Ethernet Bluetooth Cellular
12 Problem Scenario 3 Web Bittorrent VoIP Ethernet Bluetooth Cellular
13 Problem Scenario 3 Web Bittorrent VoIP This is a nightmare scenario Huge amounts of work to add new apps or media Limits growth and adoption Ethernet Bluetooth Cellular
14 More Problems 4 Bittorrent Bittorrent Ethernet
15 More Problems 4 Bittorrent Bittorrent Application endpoints may not be on the same media Ethernet
16 Solution: Use Indirection 5 Web Bittorrent Magical Network Abstraction Layer Ethernet Bluetooth
17 Solution: Use Indirection 5 Web Bittorrent API Magical Network Abstraction Layer Ethernet Bluetooth
18 Solution: Use Indirection 5 Web Bittorrent Magical Network Abstraction Layer API API API Ethernet Bluetooth
19 Solution: Use Indirection 5 Web Bittorrent Magical Network Abstraction Layer Ethernet Bluetooth
20 Solution: Use Indirection 5 Web Bittorrent VoIP Magical Network Abstraction Layer Ethernet Bluetooth
21 Solution: Use Indirection 5 Web Bittorrent VoIP Magical Network Abstraction Layer Ethernet Bluetooth Cellular
22 Solution: Use Indirection 5 Web Bittorrent VoIP Magical Network Abstraction Layer O(1) work to add new apps, media Few limits on new technology Ethernet Bluetooth Cellular
23 Layered Network Stack 6 Applications Layer N Modularity! Does not specify an implementation! Instead, tells us how to organize functionality Layer 2 Layer 1 Physical Media
24 Layered Network Stack 6 Applications Layer N Layer 2 Layer 1 Physical 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
25 Layered Network Stack 6 Applications Layer N Layer 2 Layer 1 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 Physical Media
26 Layered Network Stack 6 Applications Layer N Layer 2 Layer 1 Physical 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
27 Key Questions 7 How do we divide functionality into layers?! Routing! Congestion control! Error checking! Security! Fairness! And many more
28 Key Questions 7 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? Switch Router Switch
29 Key Questions 7 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? Switch Router Switch
30 Key Questions 7 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? Switch Router Switch
31 8 Outline Layering The OSI Model Communicating The End-to-End Argument
32 The ISO OSI Model 9 OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
33 The ISO OSI Model 9 OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical All devices implement the first three layers Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
34 The ISO OSI Model 9 OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical Layers communicate peer-to-peer Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
35 The ISO OSI Model 9 OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
36 The ISO OSI Model 9 OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
37 The ISO OSI Model 9 OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical Layers communicate peer-to-peer Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
38 The ISO OSI Model 9 OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
39 The ISO OSI Model 9 OSI: Open Systems Interconnect Model Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
40 Layer Features 10 Application Presentation Session Transport Network Data Link Physical Service! What does this layer do? Interface! How do you access this layer? Protocol! How is this layer implemented?
41 Physical Layer 11 Application Presentation Session Transport Network Data Link Physical Service! Move information between two systems connected by a physical link Interface! Specifies how to send one bit Protocol! Encoding scheme for one bit! Voltage levels! Timing of signals Examples: coaxial cable, fiber optics, radio frequency transmitters
42 Data Link Layer 12 Application Presentation Session Transport Network Data Link Physical Service! Data framing: boundaries between packets! Media access control (MAC)! Per-hop reliability and flow-control Interface! Send one packet between two hosts connected to the same media Protocol! Physical addressing (e.g. MAC address) Examples: Ethernet, Wifi, DOCSIS
43 Network Layer 13 Application Presentation Session Transport Network Data Link Physical Service! Deliver packets across the network! Handle fragmentation/reassembly! Packet scheduling! Buffer management Interface! Send one packet to a specific destination Protocol! Define globally unique addresses! Maintain routing tables Example: Internet Protocol (IP), IPv6
44 Transport Layer 14 Application Presentation Session Transport Network Data Link Physical Service! Multiplexing/demultiplexing! Congestion control! Reliable, in-order delivery Interface! Send message to a destination Protocol! Port numbers! Reliability/error correction! Flow-control information Examples: UDP, TCP
45 Session Layer 15 Application Presentation Session Transport Network Data Link Physical Service! Access management! Synchronization Interface! It depends Protocol! Token management! Insert checkpoints Examples: none
46 Presentation Layer 16 Application Presentation Session Transport Network Data Link Physical Service! Convert data between different representations! E.g. big endian to little endian! E.g. Ascii to Unicode Interface! It depends Protocol! Define data formats! Apply transformation rules Examples: none
47 Application Layer 17 Application Presentation Session Transport Network Data Link Physical Service! Whatever you want :) Interface! Whatever you want :D Protocol! Whatever you want ;) Examples: turn on your smartphone and look at the list of apps
48 Encapsulation 18 How does data move through the layers? Data Application Presentation Session Transport Network Data Link Physical
49 Encapsulation 18 How does data move through the layers? Data Application Presentation Session Transport Network Data Link Physical
50 Encapsulation 18 How does data move through the layers? Application Data Presentation Session Transport Network Data Link Physical
51 Encapsulation 18 How does data move through the layers? Application Data Presentation Session Transport Network Data Link Physical
52 Encapsulation 18 How does data move through the layers? Application Data Presentation Session Transport Network Data Link Physical
53 Encapsulation 18 How does data move through the layers? Application Data Presentation Session Transport Network Data Link Physical
54 Encapsulation 18 How does data move through the layers? Application Data Presentation Session Transport Network Data Link Physical
55 Encapsulation 18 How does data move through the layers? Application Presentation Session Transport Network Data Link Physical
56 Encapsulation 18 How does data move through the layers? Application Presentation Session Transport Network Data Link Physical Data
57 Encapsulation 18 How does data move through the layers? Application Presentation Session Transport Network Data Link Physical Data
58 Encapsulation 18 How does data move through the layers? Application Presentation Session Transport Network Data Link Physical Data
59 Encapsulation 18 How does data move through the layers? Application Presentation Session Transport Network Data Link Physical Data
60 Encapsulation 18 How does data move through the layers? Application Presentation Session Transport Network Data Link Physical Data
61 Encapsulation 18 How does data move through the layers? Application Presentation Session Transport Network Data Link Physical Data
62 Encapsulation 18 How does data move through the layers? Application Presentation Session Transport Network Data Link Physical Data
63 Real Life Analogy 19
64 Real Life Analogy 19 Label contains routing info
65 Real Life Analogy 19 Postal Service
66 Real Life Analogy 19 Un-packing Postal Service
67 Real Life Analogy 19 Doesn t know how the Postal network works Doesn t know contents of letter Postal Service
68 Network Stack in Practice 20 Host 1 Switch Host 2 Application Presentation Session Transport Network Data Link Physical Network Data Link Physical Application Presentation Session Transport Network Data Link Physical
69 Network Stack in Practice 20 Host 1 Switch Host 2 Application Transport Network Data Link Physical Network Data Link Physical Application Transport Network Data Link Physical
70 Network Stack in Practice 20 Host 1 Switch Host 2 Application Transport Network Data Link Network Data Link Application Transport Network Data Link
71 Network Stack in Practice 20 Host 1 Switch Host 2 FTP Client TCP IP Ethernet IP Ethernet FTP Server TCP IP Ethernet
72 Network Stack in Practice 20 Host 1 Switch Host 2 FTP Client TCP IP Ethernet IP Ethernet FTP Server TCP IP Ethernet
73 Network Stack in Practice 20 Host 1 Switch Host 2 Video Client Video Server UDP UDP IP IP IP Ethernet Ethernet Ethernet
74 Network Stack in Practice 20 Host 1 Switch Host 2 Video Client Video Server UDP UDP IP IP IP n n n
75 Encapsulation, Revisited 21 Web Server TCP IP Ethernet
76 Encapsulation, Revisited 21 Web Page Web Server TCP IP Ethernet
77 Encapsulation, Revisited 21 HTTP Header Web Page Web Server TCP IP Ethernet
78 Encapsulation, Revisited 21 HTTP Header Web Page Web Server TCP Header HTTP Header Web Page TCP IP Ethernet
79 Encapsulation, Revisited 21 HTTP Header Web Page Web Server TCP Header HTTP Header TCP Segment Web Page TCP IP Ethernet
80 Encapsulation, Revisited 21 HTTP Header Web Page Web Server TCP Header HTTP Header TCP Segment Web Page TCP IP Header TCP Header HTTP Header Web Page IP Ethernet
81 Encapsulation, Revisited 21 HTTP Header Web Page Web Server TCP Header HTTP Header Web Page TCP TCP Segment IP Header TCP Header HTTP Header Web Page IP IP Datagram Ethernet
82 Encapsulation, Revisited 21 HTTP Header Web Page Web Server TCP Header HTTP Header Web Page TCP TCP Segment IP Header TCP Header HTTP Header Web Page IP IP Datagram Ethernet Header IP Header TCP Header HTTP Header Web Page Ethernet Trailer Ethernet
83 Encapsulation, Revisited 21 HTTP Header Web Page Web Server TCP Header HTTP Header Web Page TCP TCP Segment IP Header TCP Header HTTP Header Web Page IP IP Datagram Ethernet Header IP Header TCP Header HTTP Header Web Page Ethernet Trailer Ethernet Ethernet Frame
84 The Hourglass 22 HTTP, FTP, RTP, IMAP, Jabber, TCP, UDP, ICMP IPv4 Ethernet, x, DOCSIS, Fiber, Coax, Twisted Pair, Radio,
85 The Hourglass 22 HTTP, FTP, RTP, IMAP, Jabber, TCP, UDP, ICMP IPv4 Ethernet, x, DOCSIS, Fiber, Coax, Twisted Pair, Radio,
86 The Hourglass 22 HTTP, FTP, RTP, IMAP, Jabber, TCP, UDP, ICMP IPv4 Ethernet, x, DOCSIS, Fiber, Coax, Twisted Pair, Radio,
87 The Hourglass 22 HTTP, FTP, RTP, IMAP, Jabber, TCP, UDP, ICMP IPv4 Ethernet, x, DOCSIS, Fiber, Coax, Twisted Pair, Radio,
88 The Hourglass 22 HTTP, FTP, RTP, IMAP, Jabber, TCP, UDP, ICMP IPv4 Ethernet, x, DOCSIS, Fiber, Coax, Twisted Pair, Radio,
89 The Hourglass 22 HTTP, FTP, RTP, IMAP, Jabber, TCP, UDP, ICMP IPv4 Think about the difficulty of deploying IPv6 Ethernet, x, DOCSIS, Fiber, Coax, Twisted Pair, Radio,
90 The Hourglass 22 HTTP, FTP, RTP, IMAP, Jabber, One Internet layer means all networks TCP, UDP, ICMP interoperate All applications function on all networks IPv4 Room for development above and below IP But, changing IP is insanely hard Ethernet, x, DOCSIS, Fiber, Coax, Twisted Pair, Radio,
91 Orthogonal Planes 23 Control plane: How Internet paths are established Application Presentation Session Transport IP Data Link Physical
92 Orthogonal Planes 23 Control plane: How Internet paths are established Application Presentation Session Transport IP Data Link Physical BGP RIP OSPF Control Plane
93 Orthogonal Planes 23 Application Control plane: How Internet paths are established Presentation Well cover this later Session Transport IP Data Link Physical BGP RIP OSPF Control Plane
94 Orthogonal Planes 24 Data plane: How data is forwarded over Internet paths Host 1 Switch(es) Host 2 Application Transport Network Data Link Network Data Link Application Transport Network Data Link
95 Orthogonal Planes 24 Data plane: How data is forwarded over Internet paths Host 1 Switch(es) Host 2 Transport Application Network Data Link Network Data Link Application Transport Network Data Link
96 Orthogonal Planes 24 Data plane: How data is forwarded over Internet paths Host 1 Switch(es) Host 2 Transport Application Network Data Link
97 Orthogonal Planes 24 Data plane: How data is forwarded over Internet paths Host 1 Switch(es) Host 2
98 Reality Check 25 The layered abstraction is very nice
99 Reality Check 25 The layered abstraction is very nice Does it hold in reality?
100 Reality Check 25 The layered abstraction is very nice Does it hold in reality? No.
101 Reality Check 25 The layered abstraction is very nice Does it hold in reality? No. Firewalls Analyze application layer headers
102 Reality Check 25 The layered abstraction is very nice Does it hold in reality? No. Firewalls Analyze application layer headers Transparent Proxies Simulate application endpoints within the network
103 Reality Check 25 The layered abstraction is very nice Does it hold in reality? No. Firewalls Analyze application layer headers Transparent Proxies Simulate application endpoints within the network NATs Break end-to-end network reachability
104 26 Outline Layering The OSI Model Communicating The End-to-End Argument
105 From Layers to Eating Cake 27 IP gives us best-effort datagram forwarding! So simple anyone can do it! Large part of why the Internet has succeeded! but it sure isn t giving us much Layers give us a way to compose functionality! Example: HTTP over TCP for Web browsers with reliable connections but they do not tell us where (in the network) to implement the functionality
106 Where to Place Functionality 28 How do we distribute functionality across devices?! Example: who is responsible for security?????? Switch Router Switch
107 Where to Place Functionality 28 How do we distribute functionality across devices?! Example: who is responsible for security?????? Switch Router Switch The End-to-End Arguments in System Design! Saltzer, Reed, and Clark! The Sacred Text of the Internet! Endlessly debated by researchers and engineers
108 Basic Observation 29 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! Different applications have different needs End hosts! Can t depend on the network! Can satisfy these requirements without network level support
109 Example: Reliable File Transfer 30
110 Example: Reliable File Transfer 30
111 Example: Reliable File Transfer 30 Solution 1: Make the network reliable
112 Example: Reliable File Transfer 30 Integrity Check Integrity Check Integrity Check Solution 1: Make the network reliable
113 Example: Reliable File Transfer 30 Solution 1: Make the network reliable
114 Example: Reliable File Transfer 30 Solution 1: Make the network reliable
115 Example: Reliable File Transfer 30 Solution 1: Make the network reliable
116 Example: Reliable File Transfer 30 Solution 1: Make the network reliable
117 Example: Reliable File Transfer 30 Solution 1: Make the network reliable
118 Example: Reliable File Transfer 30 Solution 1: Make the network reliable App has to do a check anyway!
119 Example: Reliable File Transfer 30 Solution 1: Make the network reliable App has to do a check anyway! Solution 2: App level, end-to-end check, retry on failure
120 Example: Reliable File Transfer 31 Solution 1: Make the network reliable Solution 2: App level, end-to-end check, retry on failure
121 Example: Reliable File Transfer 31 Solution 1: Make the network reliable Solution 2: App level, end-to-end check, retry on failure
122 Example: Reliable File Transfer 31 Please Retry Solution 1: Make the network reliable Solution 2: App level, end-to-end check, retry on failure
123 Example: Reliable File Transfer 31 Solution 1: Make the network reliable Solution 2: App level, end-to-end check, retry on failure
124 Example: Reliable File Transfer 31 Solution 1: Make the network reliable Full functionality can be built at App level Solution 2: App level, end-to-end check, retry on failure
125 Example: Reliable File Transfer 31 In-network implementation Doesn t reduce host complexity Does increase network complexity Increased overhead for apps that don t need functionality But, in-network performance may be better Solution 1: Make the network reliable Solution 2: App level, end-to-end check, retry on failure
126 Conservative Interpretation 32
127 Conservative Interpretation 32 Don t implement a function at the lower levels of the system unless it can be completely implemented at this level (Peterson and Davie) Basically, unless you can completely remove the burden from end hosts, don t bother
128 Radical Interpretation 33 Don t implement anything in the network that can be implemented correctly by the hosts
129 Radical Interpretation 33 Don t implement anything in the network that can be implemented correctly by the hosts Make network layer absolutely minimal Ignore performance issues
130 Moderate Interpretation 34 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 and if it doesn t cost too much $ to implement
131 Reality Check, Again 35 Layering and E2E principals regularly violated Firewalls Transparent Proxies NATs Conflicting interests! Architectural purity! Commercial necessity
132 Takeaways 36 Layering for network functions! Helps manage diversity in computer networks! Not optimal for everything, but simple and flexible Narrow waist ensures interoperability, enables innovation E2E argument (attempts) to keep IP layer simple Think carefully when adding functionality into the network
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