Introduction Switches and Access

2 Chapter 1 Introduction Computer Networking: A Top Down Approach Featuring the Internet, 5 rd edition. Jim Kurose, Keith Ross Addison-Wesley, July A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:  If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!)  If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright J.F Kurose and K.W. Ross, All Rights Reserved

3 The Network Core  mesh of interconnected routers  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”

4 Network Core: Circuit Switching End-end resources reserved for “call”  link bandwidth, switch capacity  dedicated resources  circuit-like (guaranteed) performance  call setup required

5 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 lending)  dividing link bandwidth into “pieces” m Frequency Division Multiplexing (FDM) m Time Division Multiplexing (TDM)

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

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

8 Network Core: Packet Switching each end-end data stream divided into packets  Packets from different users 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: packet must be completely received before being forwarded  packet loss: drop a packet from the queue, when too many packets Bandwidth division into “pieces” Dedicated allocation Resource reservation

9 Packet switching versus circuit switching  Great for bursty data m resource sharing m simpler, no call setup  Does not restrict the number of simultaneous users  Takes advantage of “silent periods” of users  Excessive congestion: packet delay and loss m protocols needed for reliable data transfer, congestion control Is packet switching a “slam dunk winner?”

10 Packet-switched networks: forwarding  Goal: move packets through routers from source to destination m we’ll study several path selection (i.e. routing)algorithms (chapter 4)  datagram network (Internet): m destination address in packet determines next hop m routes may change during session m analogies: USPostal mail, asking directions when driving  virtual circuit network (X.25, frame relay, ATM): m each packet carries tag (virtual circuit ID), tag determines next hop m fixed path determined at call setup time, remains fixed thru call m routers maintain per-call state

11 Network Taxonomy Telecommunication networks Circuit-switched networks FDM TDM Packet-switched networks Networks with VCs Datagram Networks TelephonesInternet

Introduction 1-12 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

Introduction 1-13 Residential access: point to point access  Dialup via modem m up to 56Kbps direct access to router (often less) m Can’t surf and phone at same time: can’t be “always on”  ADSL: Asymmetric Digital Subscriber Line m up to 1 Mbps upstream m up to 8 Mbps downstream m FDM:

Introduction 1-14 Residential access: cable modems  HFC: Hybrid Fiber Coax m asymmetric: up to 1Mbps upstream, 10 Mbps downstream  network of cable and fiber attaches homes to ISP router m shared access to router among homes  deployment: available via cable companies.

Introduction 1-15 Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes

Introduction 1-16 Cable Network Architecture: Overview home cable headend cable distribution network (simplified)

Introduction 1-17 Cable Network Architecture: Overview home cable headend cable distribution network server(s)

Introduction 1-18 Cable Network Architecture: Overview home cable headend cable distribution network Channels VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO DATADATA DATADATA CONTROLCONTROL FDM:

Introduction 1-19 Company access: local area networks  company/univ Local Area Network (LAN) connects end system to edge router  Ethernet: m shared or dedicated link connects end system and router m 10 Mbs, 100Mbps, Gigabit Ethernet  deployment: institutions, home LANs happening now  LANs: chapter 5

Introduction 1-20 Wireless access networks  shared wireless access network connects end system to router m via base station aka “access point”  wireless LANs: m b (WiFi): 11 Mbps base station mobile hosts router

Introduction 1-21 Internet structure: network of networks  roughly hierarchical  at center: “tier-1” ISPs (e.g. Sprint, AT&T, UUNet, Level3), national/international coverage m treat each other as equals Tier 1 ISP NAP Tier-1 providers interconnect at public Network Access Points (NAPs)

Introduction 1-22 Tier-1 ISP: e.g., Sprint Sprint US backbone network

Introduction 1-23 Internet structure: network of networks  “Tier-2” ISPs: smaller (often regional) ISPs m Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other, interconnect at NAP

Introduction 1-24 Internet structure: network of networks  “Tier-3” ISPs and local ISPs m last hop (“access”) network (closest to end systems) Tier 1 ISP NAP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet

Introduction 1-25 Internet structure: network of networks  a packet passes through many networks! Tier 1 ISP NAP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP