1 Network Core and Network Edge By Muhammad Hanif To BS IT 4 th Semester

Now back to work ☺ r Ninety-nine percent of the failures come from people who have the habit of making excuses. –George Washington 2

Network Core and Edge r Network Devices and Components r Internet overview r what’s a protocol? r network edge, core, access network r performance: loss, delay r layering and service models r backbones, NAPs, ISPs 3

A Simple Network 4

Network Devices and Components r Four major components 1. End Points PCs, Servers, Printers, Smart Phones, etc 2. Interconnections NIC cards, Media, Connectors 3. Switches Connects endpoints to the Local Area Network (LAN) 4. Router Connect multiple LANs to form Internetworks Chooses best path between LAN and Wider Area Networks (WAN) 5

6 What’s the Internet: “nuts and bolts” view r millions of connected computing devices: hosts, end-systems m pc’s workstations, servers m PDA’s, phones, running network apps r communication links m fiber, copper, radio, satellite r routers: forward packets (chunks) of data thru network local ISP company network regional ISP router workstation server mobile

7 What’s the Internet: “nuts and bolts” view r protocols: control sending, receiving of msgs m e.g., TCP, IP, HTTP, FTP, PPP r Internet: “network of networks” m loosely hierarchical m public Internet versus private intranet r Internet standards m RFC: Request for comments m IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile

8 What’s the Internet: a service view r communication infrastructure enables distributed applications: m WWW, , games, e- commerce, database, m more? r communication services provided: m connectionless m connection-oriented

9 What’s a network protocol? … specific msgs sent … specific actions taken when msgs received, or other events r all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

10 What’s a protocol? a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection req. TCP connection reply. Get time

11 A closer look at network structure: r network edge: applications and hosts r network core: m routers m network of networks r access networks m residential m institutional m mobile r physical media m wire (digital / analog) m wireless (radio / cellular)

12 The network edge: r end systems (hosts): m run application programs m e.g., WWW, m at “edge of network” r client/server model m client host requests, receives service from server m e.g., WWW client (browser)/ server; client/server r peer-peer model: m host interaction symmetric m e.g.: teleconferencing

13 Network edge: connection-oriented service Goal: data transfer between end sys. r handshaking: setup (prepare for) data transfer ahead of time m set up “state” in two communicating hosts r TCP - Transmission Control Protocol m Internet’s de-facto connection-oriented service TCP service [RFC 793] r reliable, in-order byte- stream data transfer m dealing with loss: acknowledgements and retransmissions r flow control: m sender won’t overcome receiver r congestion control: m senders “slow down sending rate” when network congestion detected

14 Network edge: connectionless service Goal: data transfer between end systems m same as before! r UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service m unreliable data transfer m no flow control m no congestion control App’s using TCP: r HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP ( ) App’s using UDP: r streaming media, teleconferencing, Internet telephony

15 The Network Core r mesh of interconnected routers r the fundamental question: how is data transferred through net? m circuit switching: dedicated circuit per call: telephone net m packet-switching: data sent thru net in discrete “chunks”

16 Network Core: Circuit Switching End-end resources reserved for “call” r link bandwidth, switch capacity r dedicated resources: no sharing r circuit-like (guaranteed) performance r call setup required

17 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” r pieces allocated to calls r resource piece idle if not used by owning call (no sharing) r dividing link bandwidth into “pieces” m frequency division m time division m code division

18 Network Core: Packet Switching each end-end data stream divided into packets r user A, B packets share network resources r each packet uses full link bandwidth r resources used as needed, resource contention: r aggregate resource demand can exceed amount available r congestion: packets queue, wait for link use r store and forward: packets move one hop at a time m transmit over link m wait turn at next link Bandwidth division into “pieces” Dedicated allocation Resource reservation

19 Network Core: Packet Switching A B C 10 Mbs Ethernet 1.5 Mbs 45 Mbs D E statistical multiplexing queue of packets waiting for output link

20 Packet-switched networks: routing r Goal: move packets among routers from source to destination m we’ll study several path selection algorithms r datagram network: m destination address determines next hop m routes may change during session

21 Access networks and physical media Q: How to connect end systems to edge router? r residential access nets r institutional access networks (school, company) r mobile access networks Keep in mind: r bandwidth (bits per second) of access network? r shared (e.g. cable, ethernet) or dedicated (e.g., DSL)?

22 Residential access: point to point access r Dialup via modem m up to 56Kbps direct access to router (conceptually) r DSL: digital subscriber line m up to 1 Mbps home-to-router m up to 8 Mbps router-to-home

23 Institutional access: local area networks r company/univ local area network (LAN) connects end system to edge router r Ethernet: m shared or dedicated cable connects end system and router m 10 Mbs, 100Mbps, Gigabit Ethernet

24 Wireless access networks r shared wireless access network connects end system to router r wireless LANs: m radio spectrum replaces wire m e.g., Wavelan 10 Mbps r wider-area wireless access m wireless access to ISP router via cellular network base station mobile hosts router

25 Delay in packet-switched networks packets experience delay on end-to-end path r four sources of delay at each hop r nodal processing: m check bit errors m determine output link r queueing m time waiting at output link for transmission m depends on congestion level of router A B propagation transmission nodal processing queueing

26 Delay in packet-switched networks Transmission delay: r R=link bandwidth (bps) r L=packet length (bits) r time to send bits into link = L/R Propagation delay: r d = length of physical link r s = propagation speed in medium (~2x10 8 m/sec) r propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantitites!

27 Protocol “Layers” Networks are complex! r many “pieces”: m hosts m routers m links of various media m applications m protocols m hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?

28 Why layering? Dealing with complex systems: r explicit structure allows identification, relationship of complex system’s pieces m layered reference model for discussion r layering considered harmful?

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30 Internet protocol stack r application: supporting network applications m ftp, smtp, http r transport: host-host data transfer m tcp, udp (reliable delivery, rate regulation) r network: routing of datagrams from source to destination m ip, routing protocols r link: data transfer between neighboring network elements m ppp, ethernet, wireless, multiple access protocols r physical: bits “on the wire” application transport network link physical

31 Protocol layering and data Each layer takes data from above r adds header information to create new data unit r passes new data unit to layer below application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

32 Internet structure: network of networks r roughly hierarchical r national/international backbone providers (NBPs) m interconnect (peer) with each other privately, or at public Network Access Point (NAPs) r regional ISPs m connect into NBPs r local ISP, company m connect into regional ISPs NBP A NBP B NAP regional ISP local ISP local ISP

33 Intro: Summary Covered a “ton” of material! r Internet overview r what’s a protocol? r network edge, core, access network r performance: loss, delay r layering and service models r backbones, NAPs, ISPs You now hopefully have: r context, overview, “feel” of networking r more depth, detail later in course