Dependable Distributed Systems

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Dependable Distributed Systems Communication Basics I Slide set in light of one by Professor Paul Francis, Cornell University

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Overview of Lecture Introduction to the system layer Classic perspective of system layer OSI stack Classic view no more (never was?) precise End-to-end contention Internet segments (has, switches, joins, and so on.) Protocol layering essentials IP, UDP, TCP, advantages and disadvantages, SCTP Ethereal - decent convention observing and troubleshooting instrument

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Who perceives this? int sockfd; struct sockaddr_in addr; addr.sin_family = AF_INET; addr.sin_addr.s_addr = inet_addr(SERV_HOST_ADDR); addr.sin_port = htons(SERV_TCP_PORT); sockfd = attachment (AF_INET, SOCK_STREAM, 0); associate (sockfd, (struct sockaddr *) &addr, sizeof(serv_addr)); do_stuff(stdin, sockfd);

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Start with host name (perhaps) Classic perspective of system API foo.bar.com

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Start with host name Get an IP address Classic perspective of system API foo.bar.com gethostbyname() 10.5.4.3

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Start with host name Get an IP address Make an attachment (convention, address) Classic perspective of system API foo.bar.com gethostbyname() 10.5.4.3 socket();connect();… sock_id

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Start with host name Get an IP address Make an attachment (convention, address) Send byte stream (TCP) or parcels (UDP) Classic perspective of system API foo.bar.com gethostbyname() 10.5.4.3 socket();connect();… sock_id … 1,2,3,4,5,6,7,8,9 . . . TCP sock UDP sock Network Eventually touch base all together May or may not arrive

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Classic approach "broken" from various perspectives IP address diverse relying upon who requests it Address might be changed in the system IP address may not be reachable (despite the fact that goal is up and joined) Or might be reachable by you however not another host IP address may change in no time flat or hours Packets may not originate from who you think (organize stores)

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Classic OSI stack

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Classic OSI stack Forget it!

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PPP IP Application Ethernet IPsec L2TP PPPoE UDP TCP PPP IP Example Microsoft VPN stack

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Example Microsoft VPN stack Application TCP IP PPP L2TP UDP IPsec IP PPP PPPoE The connection layer Ethernet

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Example Microsoft VPN stack Application TCP IP PPP L2TP UDP IPsec IP A sensible connection layer PPP PPPoE The connection layer Ethernet

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Example Microsoft VPN stack Application TCP IP PPP L2TP UDP IPsec A passage IP A legitimate connection layer PPP PPPoE The connection layer Ethernet

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Example Microsoft VPN stack Application TCP IP PPP L2TP A security layer UDP IPsec A passage IP An intelligent connection layer PPP PPPoE The connection layer Ethernet

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Example Microsoft VPN stack Application TCP IP A system reflection that Microsoft finds advantageous PPP L2TP A security layer UDP IPsec A passage IP A coherent connection layer PPP PPPoE The connection layer Ethernet

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Example Microsoft VPN stack The real end-to-end system and transport layers Application TCP IP A system deliberation that Microsoft finds helpful PPP L2TP A security layer UDP IPsec A passage IP A consistent connection layer PPP PPPoE The connection layer Ethernet

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Example Microsoft VPN stack Application TCP TCP: Transport Control Protocol IP: Internet Protocol PPP: Point-to-Point Protocol L2TP: Layer 2 Tunneling Protocol UDP: User Datagram Protocol IPsec: Secure IP PPPoE: PPP over Ethernet IP PPP L2TP UDP IPsec IP PPP PPPoE Ethernet

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That the web is a develop innovation Kludges on kludges What would we be able to gain from this? Application TCP IP PPP L2TP UDP IPsec IP PPP PPPoE Ethernet

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That the web is a develop innovation Kludges on kludges Having the greatest organization isn't adequate for Bill What would we be able to gain from this? Application TCP IP PPP L2TP UDP IPsec IP PPP PPPoE Ethernet

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That the web is a develop innovation Kludges on kludges That having the greatest organization isn't sufficient for Bill That the end-to-end contention really works! What would we be able to gain from this? Application TCP IP PPP L2TP UDP IPsec IP PPP PPPoE Ethernet

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What about the end-to-end contention? More or less: If you need something done well, you gotta do it without anyone else's help "End-To-End Arguments In System Design", Saltzer, Reed, Clark, ACM Transactions on Computer Systems, 1984

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End-to-end contention is generally about unwavering quality Early 80's: industry expected that the system ought to do everything Guaranteed conveyance, sequencing, copy concealment If the system does it, the end framework doesn't need to X.25, for instance

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The system doesn't generally work right Applications needed to verify whether the system truly did its employment… … and repair the issue if the system didn't carry out its occupation End-to-end understanding: If the application needs to do it in any case, why do it in the system by any means? Keep the system basic

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So when ought to the system accomplish more? When you get execution picks up Link-level retransmissions over a lossy connection are quicker than E2E retransmissions Also When the system doesn't believe the end client Corporation or military encode a connection on the grounds that the end client won't not do it Some things just isn't possible toward the end Routing calculations Billing User verification

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God, Motherhood, Apple Pie, and the E2E Principle E2E took after with religious intensity in IETF Often connected to tending to, which has nothing to do with the first E2E contention Reaction to NAT was to settle the system (IPv6), effectively dishearten "altering" the host Laudable objective, yet in a path inverse of E2E "soul" Sometimes execution hurt in respect to E2E Compression of Voice over IP (RTP, Real Time Protocol) Mobile IP Brief Rant

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R Network segments Point to point interface : interface with two hubs (switch or host) Router : Forwards IP parcels Host : Source and sink of IP bundles H Broadcast connect : interface with different hubs H

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Network parts Network: Collection of hosts, connections, and switches Site : Stub arrange, ordinarily in one area and under control of one organization Firewall/NAT : Box between the website and ISP that gives separating, security, and Network Address Translation ISP : Internet Service Provider. Travel organize that gives IP availability to destinations Backbone ISP : Transit arrange for territorial ISPs and expansive locales Inter-trade (peering point) : Broadcast interface where various ISPs associate and trade directing data (peering) Hosting focus : Stub arrange that backings bunches of hosts (web administrations), ordinarily with rapid associations with numerous spine ISPs. Respective peering : Direct association between two spine ISPs

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Internet topology IXs started things out IXs have a tendency to be execution bottlenecks Hosting focuses and two-sided peering are a reaction to poor IXs Hosting Center Hosting Center Backbone ISP Backbone ISP Backbone ISP IX Site ISP S Sites S

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Protocol layering Communications stack comprises of an arrangement of administrations , each giving a support of the layer above, and utilizing administrations of the layer beneath Each administration has a programming API , simply like any product module Each administration needs to pass on data at least one companions over the system This data is contained in a header The headers are transmitted in an indistinguishable request from the layered administrations

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HTTP Router Link1 Link2 Link1 TCP IP Protocol layering case Browser prepare Web server handle Physical Link 1 Physical Link 2

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Router Protocol layering case Browser needs to ask for a page. Calls HTTP with the web address (URL). HTTP's occupation is to pass on the URL to the web server. HTTP takes in the IP address of the web server, includes its header, and calls TCP. Program handle Web server prepare HTTP H TCP IP Link1 Link2 Link1 Physical Link 1 Physical Link 2

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Router Protocol layering case TCP's occupation is to work with server to ensure bytes arrive dependably and all together. TCP includes its header and calls IP. (Prior to that, TCP builds up an association with its companion.) Browser prepare Web server handle HTTP TCP H T IP Link1 Link2 Link1 Physical Link 1 Physical Link 2

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Router Protocol layering illustration IP's occupation is to get the bundle directed to the companion through at least zero switches. IP decides the following jump from the goal IP address. IP includes its header and calls the connection layer (i.e. Ethernet) with the following bounce address. Program prepare Web server handle HTTP TCP IP H T I Link1 Link2 Link1 Physical Link 1 Physical Link 2

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Router Protocol layering case The connection's employment is to get the bundle to the following physical box (here a switch). It includes its header and sends the subsequent parcel over the "wire". Program handle Web server prepare HTTP TCP IP Link1 Link2 Link1 Physical Link 1 Physical Link 2 H T I L1

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Router Protocol layering illustration The switch's connection layer gets the parcel, strips the connection header, and hands the outcome to the IP sending process. Program handle Web server prepare HTTP TCP IP H T I Link1 Link2 Link1 Physical Link 1 Physical Link 2

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Router Protocol layering illustration The switch's IP sending process takes a gander at the goal IP address, figures out what the following bounce is, and hands the bundle to the proper connection layer with the fitting next jump interface address. Program prepare Web server handle HTTP TCP IP H T I Link1 Link2 Link1 Physical Link 1 Physical Link 2

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Router Protocol layering illustration The bundle goes over the connection to the web server, after which every layer procedures and strips its relating header. Program prepare Web server handle HTTP H TCP H T IP H T I Link1 Link2 Link1 Physical Link 1 Physical Link 2 H T I L2

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