Chapter 1: Introduction Our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example Overview: what’s the Internet what’s a protocol? network edge network core access net, physical media Internet/ISP structure performance: loss, delay protocol layers, service models network modeling Introduction

What’s the Internet: “nuts and bolts” view millions of connected computing devices: hosts = end systems 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 Introduction

ISPs –Internet service providers e.g.Dial-up, Broadband,High speed LANs,wireless protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP Internet: “network of networks” router workstation server mobile local ISP regional ISP company network Introduction

What’s the Internet: a service view communication infrastructure enables distributed applications: Web, email, games, e-commerce, file sharing communication services provided to apps: Connectionless unreliable connection-oriented reliable Introduction

What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions … 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 protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction

What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 <file> time Introduction

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 Introduction

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

The network edge: end systems (hosts): client/server model run application programs e.g. Web, email at “edge of network” 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, Introduction

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 reliable, in-order byte-stream data transfer loss: acknowledgements and retransmissions flow control: sender won’t overcome receiver congestion control: senders “slow down sending rate” when network congested Introduction

Network edge: connectionless service Goal: data transfer between end systems same as before! UDP - User Datagram Protocol connectionless unreliable data transfer no flow control no congestion control App’s using TCP: HTTP (Web), FTP (file transfer), SMTP (email) App’s using UDP: streaming media, teleconferencing, Introduction

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 Introduction

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” Introduction 1-13 13

Circuit Switching In circuit switched networks the resources needed along a path to provide for communication between the end systems are reserved for the duration of communication session In packet switched networks these resources are not reserved A sessions messages use the resources on demand & as a consequence may have to wait (that is , queue) for access to communication link

Telephone networks are examples of the circuit switched networks When one person wants to send information to another over a telephone network Before the sender can send information the network must establish a connection between sender & receiver this connection is called circuit

When networks established circuit it is also reserves a constant transmission rate in the networks links for duration of the connection Since bandwidth has been reserved for this sender to receiver connection The sender can transfer data to receiver at the guaranteed constant rate

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 Introduction

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 Introduction

Circuit Switching: FDM and TDM 4 users Example: FDM frequency time TDM 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 Introduction

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: Node receives complete packet before forwarding Introduction

Packet Switching: Statistical Multiplexing 100 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B queue of packets waiting for output link D E Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing. Introduction

Packet-switching: store-and-forward Store and forward transmission means that switch must receive entire packet before it can began to transmit first bit of the packet onto the link Each packet switch has multiple links attached to it For each attached link the packet switch has an output buffer also called an output queue which stores packets that router is about to send into link Introduction

If the arriving packets needs to be transmitted across a link but finds the link busy with the transmission of another packet then arriving packet must wait in the output buffer The amount of buffer space is finite an arriving packets may find that buffer is completely filled with other packets waiting for transmission In this case packet loss will occur either the arriving packet or one of the already queued packets will dropped Introduction 1-23 23

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 Introduction

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? Introduction

Access networks and physical media Access networks classified into three categories: Residential Access: connecting home end system into network Company Access: connecting end systems in a business or educational institution into network Wireless Access: connecting end systems (i.e. mobile networks) into end system Introduction 1-26 26

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” Residential access refers to connecting a home end system( typically a PCs) to an router One form of residential access is the dial-up-modem Introduction

2.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, Introduction

3.Wireless access networks shared wireless access network connects end system to router via base station “access point” wireless LANs: 54 Mbps wider-area wireless access 3G base station mobile hosts router Introduction

Physical Media Twisted Pair (TP) two insulated copper wires Category : traditional phone wires, 10 Mbps Ethernet Category : 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 Introduction

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 low error rate: resistant to electromagnetic noise Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable broadband: multiple channels on cable Introduction

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 Delay & loss in packet-switched networks 1.6Protocol layers, service models 1.7 History Introduction

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 Delay & loss in packet-switched networks 1.6 Protocol layers, service models Introduction

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

Four sources of packet delay 1. nodal processing: check bit errors determine output link time it takes to process packet in network node (swith,router,hub) 2. queueing time waiting at output link for transmission depends on congestion level of router A B propagation transmission nodal processing queueing Introduction

Delay in packet-switched networks 3. Transmission delay: R=link bandwidth (bps) i.e.Tranmission Rate 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 propagation delay = d/s A B propagation transmission nodal processing queueing Introduction

Protocol “Layers” Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Introduction

Internet protocol stack application: where network applications & their application layer protocols reside FTP, SMTP, HTTP (supporting network applications) transport: transport application layer message between client & server TCP, UDP network: routing of datagrams from source to destination (moving network layer packets known as datagrams from one host to another) IP application transport network link physical Introduction

link: The internet’s network layer routes a datagram through a series of packet switches (called router in the internet) between the source & destination data transfer between neighboring network elements (to move packets from one node (host or packet switch) to the next node in the route, the network layer relies on the services of the link layer) (In link layer packets are known as frames) Ex: PPP (ponit to point), Ethernet physical: While the job of the link layer is to move entire frames from one network element to an adjacent network element The job of the physical layer is to move the individual bits within the frame from one node to the next node bits “on the wire”

Encapsulation source destination application transport network link message M application transport network link physical segment Ht M Ht datagram Ht Hn M Hn frame Ht Hn Hl M link physical switch destination network link physical Ht Hn M Ht Hn Hl M M application transport network link physical Ht Hn M Ht M Ht Hn M router Ht Hn Hl M Introduction

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 Introduction