CS671 Advanced Computer Networking

1. CS671 Advanced Computer Networking Chen Qian Fall 2014 Introduction CQ (2014)

2. What you can learn • Basic knowledge of conventional Internet • Protocols layers • Introduction of current hot topics in networking • Wireless and mobile networks • Data center networking • Software defined networking • Future Internet • Research skills in system and network area • Presentation skills

3. Wireless networks Introduction C. Q. (8/13)

4. Cloud Computing Introduction C. Q. (8/13)

5. Data centers Introduction C. Q. (8/13)

6. Data centers Introduction C. Q. (8/13)

7. Data center networks Introduction C. Q. (8/13)

8. Future Internet • Content-based network? (YouTube, Netflix, etc.) • Most devices are mobile? (smartphones, laptops, touch pads, etc.) Introduction C. Q. (8/13)

9. Lecture 1: Introduction 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers

10. millions of connected computing devices: hosts = end systems running network apps: Web browser, YouTube, Skype, etc. PC server wireless laptop cellular handheld access points wired links router What’s the Internet: “nuts and bolts” view • communication links • fiber, copper, radio, satellite • transmission rate = bandwidth • routers: forward packets (chunks of data)

11. Internet: “network of networks” loosely hierarchical public Internet versus private intranet protocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, DNS, Ethernet Mobile network Global ISP Home network Regional ISP Institutional network What’s the Internet: “nuts and bolts” view

12. communication services provided to apps: reliable data delivery from source to destination File transfer, email, E-bank. “best effort” (unreliable) data delivery Multimedia (cell phone, video streaming, VoIP) What’s the Internet: a service view

13. human protocols: “Homework assignment” Turn in “I have a question” Explain … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols What’s a protocol? protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

14. a human protocol and a computer network protocol: TCP connection response Get http://www.cs.uky.edu/~qian Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection request Hi

15. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers

16. network edge:applications and hosts A closer look at network structure: • access networks, physical media:wired, wireless communication links • network core: • interconnected routers • network of networks

17. end systems (hosts): run application programs e.g. Web, email at “edge of network” peer-peer client/server The network edge: • client/server model • client host requests, receives service from always-on server • e.g. Web browser/server; email client/server • peer-peer model: • minimal (or no) use of dedicated servers • e.g. Skype, BitTorrent

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

19. Ethernet Internet access 100 Mbps Institutional router To Institution’sISP Ethernet switch 100 Mbps 1 Gbps 100 Mbps server • Typically used in companies, universities, etc • 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet • Today, end systems typically connect into Ethernet switch

20. shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps wider-area wireless access provided by telco operators ~1 Mbps over cellular system (3G) WiMAX promises 10’s Mbps over wide area Wireless access networks router base station mobile hosts

21. Typical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access point Home networks wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet

22. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers

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

24. Sequence of A & B packets does not have fixed pattern bandwidth shared on demand queueing delay, packet loss D E Packet Switching 100 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B queue of packets waiting for output link

25. store and forward: entire packet must arrive at router before it can be transmitted on next link A file/message larger than maximum packet size is transmitted as multiple packets store-and-forward L R R R

26. each end-end data stream divided into packets packets of different users share network resources each packet uses full link bandwidth resources used as needed Network Core: Packet Switching resource contention: • aggregate resource demand can exceed amount available • congestion: packets queue, wait for link use

27. Smaller end-to-end delay from pipelining Less data loss from transmission errors Packet Switching versus Message Switching Advantages of packet switching Disadvantages of packet switching • More header bits • Additional work to do segmentationand reassembly

28. 1 Mb/s link each user: 100 kb/s when “active” active 10% of time (a “bursty” user) circuit-switching: 10 users packet switching: with 35 users, probability > 10 active at same time is less than .0004 Packet switching allows more users to use network! Packet switching versus circuit switching N users 1 Mbps link Q: how did we get value 0.0004?

29. great for bursty data resource sharing simpler, no call setup excessive congestion: packet delay and loss protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps solution may impact network neutrality Is packet switching a “slam dunk winner?” Packet switching versus circuit switching

30. roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage treat each other as equals Tier-1 providers interconnect (peer) privately Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

31. POP: point-of-presence to/from backbone peering … …. … … … to/from customers Tier-1 ISP: e.g., Sprint

32. “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISPs also peer privately with each other. Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet • tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

33. “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

34. a packet passes through many networks! Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

35. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers

36. packets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers How do loss and delay occur? A B

37. 1. nodal processing: check bit errors determine output link transmission A propagation B nodal processing queueing Four sources of packet delay • 2. queueing • time waiting at output link for transmission • depends on congestion level of router

38. 3. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R 4. Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/s transmission A propagation B nodal processing queueing Delay in packet-switched networks

39. Nodal delay (from when last bit of packet arrives at this node to when last bit arrives at next node) dnodal = dproc + dqueue + dtrans + dprop End-to-end delay over Nidentical nodes/links from client c to server s (from when last bit of packet leaves client to when last bit arrives at server) dc-s = dprop + Ndnodal Round trip time (RTT) RTT = dc-s + ds-c + tserver where tserver is server processing time End-to-End Delay

40. Relative importance of bandwidth and “distance” for a small message (e.g. 1 byte), distance(1 ms vs. 100 ms propagation time) is moreimportant than bandwidth (1 Mbps vs. 100 Mbps) for a large message (e.g., 25 Mbyte),bandwidth is more important than distance Delay x Bandwidth product Example:for 100 ms end to end delay and 45 Mbps bandwidth,there can be up to 560 Kbyte of data in flight Implications of end-to-end delay

41. pipe that can carry fluid at rate Rsbits/sec pipe that can carry fluid at rate Rcbits/sec Throughput • throughput: rate (bits/time unit) at which bits transferred between sender/receiver • instantaneous: rate at given point in time • average: rate over longer period of time link capacity Rcbits/sec link capacity Rsbits/sec server, with file of F bits to send to client server sends bits (fluid) into pipe

42. Rs > RcWhat is average end-end throughput? Rsbits/sec Rcbits/sec Rcbits/sec bottleneck link link on end-end path that constrains end-end throughput Throughput (more) • Rs < RcWhat is average end-end throughput? Rsbits/sec

43. Throughput: Internet scenario • per-connection end-end throughput: min(Rc,Rs,R/10) • in practice: Rc or Rs is often bottleneck • Or the server is the bottleneck Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link Rbits/sec

44. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers

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

46. Use abstraction to hide complexity Each layer provides a service via its own internal actions as well as relying on service provided by layer below is a network of processes Can have alternative abstractions at each layer (resulting in protocol graph rather than protocol stack) Layered architecture

47. involves two or more peers two interfaces defined service interface: operations a local user can perform on a protocol entity and get results peer-peer interface: form and meaning of messages exchanged by protocol entities (also called peers) to provide protocol service term “protocol” generally used to refer to peer-peer spec High-level entity Protocol entity Each protocol Host 1 Host 2 High-level entity Service interface Protocol entity Peer-to-peer interface

48. application: supporting network applications FTP, SMTP, HTTP transport: process-process data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network link physical Internet protocol stack

49. presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application application presentation session transport network link physical ISO/OSI reference model

50. E.g.: transport accept data from application add addressing, reliability check info to form a message send message to peer via a delivery service wait for peer’s reply (ack) network link physical application transport network link physical application transport network link physical application transport network link physical application transport network link physical Logical communication between peers data transport ack data data transport