Lecture 1 Internet Overview: roadmap 1.1 What is the Internet? 1.2 Network edge  end systems, access networks, links 1.3 Protocol layers, service models 1.4 Network core  network structure, circuit switching, packet switching 1.5 Delay, loss and throughput in Internet 1-1

Lecture 1 What is the Internet? 1-2 Internetworked networks – Internet ! Image courtesy:

Lecture 1 What is the Internet?  A vast universe of computer networks growing continuously  Not just computers but also other mobile devices like our smart phones, PDAs etc. are also becoming part of it  Difficult to manage without a proper structure…  Designed as a hierarchical structure  A simple example:  Computers combine to form a Local Area Network (LAN) (e.g., our lab)  LANs combine to form an Autonomous System (AS) (e.g., our college or CUNY)  Autonomous Systems combine to form the Internet! 1-3

Lecture 1 What’s the Internet: the “hardware” view 1. Millions of connected computing devices: hosts = end systems  running network apps Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points 2. Communication links  Wired (example: fiber, copper cables)  Wireless (example: radio, satellite) 3. Routers  forward packets (chunks of data) 1-4

Lecture 1 What’s the Internet: “operational” view  Internet: “network of networks”  Requires sending, receiving of messages  Requires mechanisms (protocols) to control sending, receiving of messages  Design of protocols is the key for Internet Home network Institutional network Mobile network Global ISP Regional ISP 1-5

human protocols: … specific questions asked … specific actions taken when questions asked… … constant learning of protocols Lecture 1 What’s a protocol? A protocol is defined as a code of correct conduct. human protocol Hi Got the time? 2:00 time 1-6

Lecture 1 Internet:  computers rather than humans  But the concept of protocol remains same  Code of correct conduct  set of rules which is used by computers to communicate with each other across a network What’s a protocol in the Internet? 1-7  As the Internet grows rapidly so does the necessity of these rules (protocols)…

Connection reply Auhtentication req. Lecture 1 A web browsing protocol example a human protocol and a computer network protocol: Internet protocol example Hi Got the time? 2:00 Connection req. Username, password Get time human protocol 1-8 Time request Slides request

Lecture 1 Thus protocols define format, order of messages sent and received among network entities, actions taken on message transmission and receipt address conflicts among network entities What’s the Internet: an operational view 1-9

Lecture 1 That is a high-level overview of the Internet! Now, A closer look at the Internet structure! 1-10

Lecture 1 We already know the components of Internet:  Hosts (end-users)  e.g. computers  Access networks, physical media: wired, wireless communication links  Interconnected routers 1-11 Let’s look at little more detail of each of these components!

Lecture 1 The network edge: two communication models  End-users (hosts):  run application programs  e.g. Web, client/server peer-peer  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. Skype, BitTorrent 1-12

Lecture 1 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 1-13

Lecture 1 Residential access: point to point access  Dialup via modem  up to 56Kbps direct access to router (conceptually)  ADSL: asymmetric digital subscriber line  up to 1 Mbps home-to-router  up to 8 Mbps router-to-home  ADSL deployment: happening 1-14

Lecture 1 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  deployment: available via cable companies, e.g., MediaOne, CableVision 1-15

Lecture 1 Institutional access: local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet:  shared or dedicated cable connects end system and router  10 Mbps, 100Mbps, Gigabit Ethernet  deployment: institutions, home LANs happening now 1-16

Lecture 1 Wireless access networks  shared wireless access network connects end system to router  wireless LANs:  radio spectrum replaces wire  e.g., b/g (WiFi): 11 or 54 Mbps  wider-area wireless access  WiMAX (10’s Mbps) over wide area base station mobile hosts router 1-17

1-18 Protocol “Layers” Networks are complex!  Millions of components:  hosts  routers  Access networks Question: How to organize such complex structure? Lecture 1  Millions of operations and conflicts among them: 1. What if multiple computers transmit at the same time? 2. What if packets get lost? 3. How to retransmit packets? 4. Retransmission: How many times? 5. What about the other packets? 6. How to find routes in the Internet? 7. What if I am browsing web or I am watching live broadcasting? 8. How to distinguish among computers (addressing)?  Just a few mentioned here…

1-19 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing An analogy: Organization of airline functionality  a series of steps  Layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer above/below  Another example: Postal Service! Lecture 1

1-20 What are the adv. of layering?  Reduce the design complexity  Ease of updating the system  change of implementation of layer’s service transparent to rest of system  e.g., Postal service (overnight flight or overnight ground)  Network is a huge complex system  Why not take help of layering architecture? Lecture 1

1-21 Internet protocol stack application transport network link physical Lecture 1  application  support host/network applications  , FTP, HTTP (HTML)  transport  process-process data transfer  TCP, UDP  network  routing of datagrams from src. to destn.  IP address, routing protocols  link  data transfer between neighboring network elements  Ethernet, PPP  physical  bits “on the wire” (Compare with the Postal System!)

1-22 ISO/OSI reference model (Open Systems Interconnection model)  presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine- specific conventions  session: synchronization, checkpointing, recovery of data exchange  The 5-layer protocol stack is more famous application presentation session transport network link physical Lecture 1