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Administrative Things

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Presentation on theme: "Administrative Things"— Presentation transcript:

1 Administrative Things
Office hours: TuTh 3:30pm to 4:30pm ??? Room change: not easy . . . Permission number: pick it up after class Mailing list: to be done (check class homepage) Suggestions from the survey Give one lecture on socket programming Two projects will be programmed using C Lecture notes will be posted on the web SPEAK LOUDER ! ! ! More than 90% are very interested in networking Lecture-2

2 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-2

3 The soul of the Internet
A network protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event. Lecture-2

4 What’s a protocol? a human protocol and a computer network protocol:
Hi TCP connection req Hi TCP connection response Got the time? Get 2:00 <file> time Lecture-2

5 What’s the Internet: “nuts and bolts” view
millions of connected computing devices: hosts, end-systems PCs workstations, servers PDAs phones, toasters running network apps communication links fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile Lecture-2

6 What’s the Internet: “nuts and bolts” view
router workstation protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP Internet: “network of networks” loosely hierarchical server mobile local ISP regional ISP company network Lecture-2

7 What’s the Internet: a service view
communication infrastructure enables distributed applications: Web, , games, e-commerce, database., voting, file (MP3) sharing communication services provided to apps: connectionless connection-oriented Lecture-2

8 A closer look at network structure:
network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links Lecture-2

9 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-2

10 The network edge: end systems (hosts): client/server model
run application programs e.g. Web, at “edge of network” client/server model client host requests, receives service from always-on server e.g. Web browser/server; client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Gnutella, KaZaA Lecture-2

11 Network edge: connection-oriented service
Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol set up “state” in two communicating hosts TCP - Transmission Control Protocol Internet’s connection-oriented service TCP service [RFC 793] reliable, in-order byte-stream data transfer loss: acknowledgements and retransmissions flow control: sender won’t overwhelm receiver congestion control: senders “slow down sending rate” when network congested Lecture-2

12 Network edge: connectionless service
Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service unreliable data transfer no flow control no congestion control App’s using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP ( ) App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony Lecture-2

13 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-2

14 The Network Core 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” Lecture-2

15 Network Core: Circuit Switching
End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Lecture-2

16 Network Core: Circuit Switching
network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” frequency division time division Lecture-2

17 Circuit Switching: FDMA and TDMA
4 users Example: FDMA frequency time TDMA frequency time Two simple multiple access control techniques. Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling. As we will see, used in AMPS, GSM, IS-54/136 Lecture-2

18 Network Core: Packet Switching
each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed resource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use store and forward: packets move one hop at a time transmit over link wait turn at next link Bandwidth division into “pieces” Dedicated allocation Resource reservation Lecture-2

19 Packet Switching: Statistical Multiplexing
10 Mbs Ethernet C A statistical multiplexing 1.5 Mbs B queue of packets waiting for output link D E Sequence of A & B packets does not have fixed pattern  statistical multiplexing. In TDM each host gets same slot in revolving TDM frame. Lecture-2

20 Packet switching versus circuit switching
Packet switching allows more users to use network! 1 Mbps link each user: 100 kbps when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active less than .0004 N users 1 Mbps link Lecture-2

21 Packet switching versus circuit switching
Is packet switching an “absolute winner?” 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 still an unsolved problem (chapter 6) Lecture-2

22 Packet-switching: store-and-forward
L R R R Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps Entire packet must arrive at router before it can be transmitted on next link: store and forward delay = 3L/R Example: L = 7.5 Mbits R = 1.5 Mbps delay = 15 sec Lecture-2

23 Packet Switching: Message Segmenting
Now break up the message into 5000 packets Each packet 1,500 bits 1 msec to transmit packet on one link pipelining: each link works in parallel Delay reduced from 15 sec to sec Lecture-2

24 Packet-switched networks: forwarding
Goal: move packets through routers from source to destination we’ll study several path selection (i.e. routing)algorithms (chapter 4) datagram network: destination address in packet determines next hop routes may change during session analogy: driving, asking directions virtual circuit network: each packet carries tag (virtual circuit ID), tag determines next hop fixed path determined at call setup time, remains fixed thru call routers maintain per-call state Lecture-2

25 Network Taxonomy Telecommunication networks Circuit-switched networks
FDM TDM Packet-switched networks Networks with VCs Datagram Datagram network is not either connection-oriented or connectionless. Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps. Lecture-2

26 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-2

27 Access networks and physical media
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? Lecture-2

28 Residential access: point to point access
Dialup via modem up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on” ADSL: asymmetric digital subscriber line up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone Lecture-2

29 Residential access: cable modems
HFC: hybrid fiber coax asymmetric: up to 10Mbps upstream, 1 Mbps downstream network of cable and fiber attaches homes to ISP router shared access to router among home issues: congestion, dimensioning deployment: available via cable companies, e.g., MediaOne Lecture-2

30 Company access: local area networks
company/univ local area network (LAN) connects end system to edge router Ethernet: shared or dedicated link connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet deployment: institutions, home LANs happening now LANs: chapter 5 Lecture-2

31 Wireless access networks
shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b (WiFi): 11 Mbps wider-area wireless access provided by telco operator 3G ~ 384 kbps Will it happen?? WAP/GPRS in Europe base station mobile hosts router Lecture-2

32 Home networks Typical home network components: ADSL or cable modem
router/firewall/NAT Ethernet wireless access point wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet (switched) Lecture-2

33 Physical Media Twisted Pair (TP) two insulated copper wires
Category 3: traditional phone wires, 10 Mbps Ethernet Category 5 TP: 100Mbps Ethernet Bit: propagates between transmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Lecture-2

34 Physical Media: coax, fiber
Fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 5 Gbps) low error rate: repeaters spaced far apart ; immune to electromagnetic noise Coaxial cable: two concentric copper conductors baseband: single channel on cable legacy Ethernet broadband: multiple channel on cable HFC Lecture-2

35 Physical media: radio Radio link types:
terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., WaveLAN) 2Mbps, 11Mbps wide-area (e.g., cellular) e.g. 3G: hundreds of kbps satellite up to 50Mbps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low altitude satellite signal carried in electromagnetic spectrum no physical “wire” propagation environment effects: reflection obstruction by objects interference Lecture-2

36 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-2

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