Introduction 1-1 Chapter 1: Computer networks and the Internet 1.1 What is the Internet? 1.2 Network edge  end systems, access networks, links 1.3 Network core  circuit switching, packet switching, network structure 1.4 Network performance evaluation  Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History

Introduction 1-2 What’s the Internet: “nuts and bolts” view  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  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data)

Introduction 1-3 Packet switching versus circuit switching  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 7) Is packet switching a “slam dunk winner?” Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

Introduction 1-4 Internet structure: network of networks  “Tier-2” ISPs: smaller (often regional) ISPs  Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier 1 ISP 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.

Introduction 1-5 Internet structure: network of networks  “Tier-3” ISPs and local ISPs  last hop (“access”) network (closest to end systems) Tier 1 ISP 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 1-6 Internet structure: network of networks  a packet passes through many networks! Tier 1 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP

Introduction 1-7 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 A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers

Introduction 1-8 Delay in packet-switched networks 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 (~2x10 8 m/sec)  propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!

Introduction 1-9 Nodal delay  d proc = processing delay  typically a few microsecs or less  d queue = queuing delay  depends on congestion  d trans = transmission delay  = L/R, significant for low-speed links  d prop = propagation delay  a few microsecs to hundreds of msecs

Introduction 1-10 Queueing delay (revisited)  R=link bandwidth (bps)  L=packet length (bits)  a=average packet arrival rate traffic intensity = La/R  La/R ~ 0: average queueing delay small  La/R -> 1: delays become large  La/R > 1: more “work” arriving than can be serviced, average delay infinite!

Introduction 1-11 Packet loss  queue (aka buffer) preceding link in buffer has finite capacity  packet arriving to full queue dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not at all A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area)

Introduction 1-12 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 server, with file of F bits to send to client link capacity R s bits/sec link capacity R c bits/sec pipe that can carry fluid at rate R s bits/sec) pipe that can carry fluid at rate R c bits/sec) server sends bits (fluid) into pipe

Introduction 1-13 Throughput (more)  R s < R c What is average end-end throughput? R s bits/sec R c bits/sec  R s > R c What is average end-end throughput? R s bits/sec R c bits/sec link on end-end path that constrains end-end throughput bottleneck link

Introduction 1-14 Why layering? Dealing with complex systems:  explicit structure allows identification, relationship of complex system’s pieces  layered reference model for discussion  modularization eases maintenance, updating of system  change of implementation of layer’s service transparent to rest of system  e.g., change in gate procedure doesn’t affect rest of system  layering considered harmful?

Introduction 1-15 Internet protocol stack  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

Introduction 1-16 ISO/OSI reference model  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  needed? application presentation session transport network link physical

application transport network link physical application transport network link physical Source Destination

Introduction 1-18 source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch Encapsulation message M HtHt M HnHn frame

5: DataLink Layer5-19 A day in the life: scenario Comcast network /13 Google’s network / web server DNS server school network /24 browser web page

5: DataLink Layer5-20 A day in the life… connecting to the Internet  connecting laptop needs to get its own IP address, addr of first-hop router, addr of DNS server: use DHCP router (runs DHCP) DHCP UDP IP Eth Phy DHCP UDP IP Eth Phy DHCP r DHCP request encapsulated in UDP, encapsulated in IP, encapsulated in Ethernet r Ethernet frame broadcast (dest: FFFFFFFFFFFF ) on LAN, received at router running DHCP server r Ethernet demux’ed to IP demux’ed, UDP demux’ed to DHCP

5: DataLink Layer5-21 A day in the life… connecting to the Internet  DHCP server formulates DHCP ACK containing client’s IP address, IP address of first-hop router for client, name & IP address of DNS server router (runs DHCP) DHCP UDP IP Eth Phy DHCP UDP IP Eth Phy DHCP r encapsulation at DHCP server, frame forwarded (switch learning) through LAN, demultiplexing at client Client now has IP address, knows name & addr of DNS server, IP address of its first-hop router r DHCP client receives DHCP ACK reply

5: DataLink Layer5-22 A day in the life… ARP (before DNS, before HTTP)  before sending HTTP request, need IP address of DNS DNS UDP IP Eth Phy DNS r DNS query created, encapsulated in UDP, encapsulated in IP, encasulated in Eth. In order to send frame to router, need MAC address of router interface: ARP r ARP query broadcast, received by router, which replies with ARP reply giving MAC address of router interface r client now knows MAC address of first hop router, so can now send frame containing DNS query ARP query Eth Phy ARP ARP reply

5: DataLink Layer5-23 A day in the life… using DNS DNS UDP IP Eth Phy DNS r IP datagram containing DNS query forwarded via LAN switch from client to 1 st hop router r IP datagram forwarded from campus network into comcast network, routed (tables created by RIP, OSPF, IS-IS and/or BGP routing protocols) to DNS server r demux’ed to DNS server r DNS server replies to client with IP address of Comcast network /13 DNS server DNS UDP IP Eth Phy DNS

5: DataLink Layer5-24 A day in the life… TCP connection carrying HTTP HTTP TCP IP Eth Phy HTTP r to send HTTP request, client first opens TCP socket to web server r TCP SYN segment (step 1 in 3-way handshake) inter- domain routed to web server r TCP connection established! web server SYN TCP IP Eth Phy SYN SYNACK r web server responds with TCP SYNACK (step 2 in 3- way handshake)

5: DataLink Layer5-25 A day in the life… HTTP request/reply HTTP TCP IP Eth Phy HTTP r HTTP request sent into TCP socket r IP datagram containing HTTP request routed to r IP datgram containing HTTP reply routed back to client web server HTTP TCP IP Eth Phy r web server responds with HTTP reply (containing web page) HTTP r web page finally (!!!) displayed

5: DataLink Layer5-26 Addressing: routing to another LAN R 1A-23-F9-CD-06-9B E6-E BB-4B CC-49-DE-D0-AB-7D A C-E8-FF B2-2F-54-1A-0F B BD-D2-C7-56-2A walkthrough: send datagram from A to B via R assume A knows B’s IP address  two ARP tables in router R, one for each IP network (LAN)

5: DataLink Layer5-27  A creates IP datagram with source A, destination B  A uses ARP to get R’s MAC address for  A creates link-layer frame with R's MAC address as dest, frame contains A-to-B IP datagram  A’s NIC sends frame  R’s NIC receives frame  R removes IP datagram from Ethernet frame, sees its destined to B  R uses ARP to get B’s MAC address  R creates frame containing A-to-B IP datagram sends to B R 1A-23-F9-CD-06-9B E6-E BB-4B CC-49-DE-D0-AB-7D A C-E8-FF B2-2F-54-1A-0F B BD-D2-C7-56-2A S.IP: D.IP: S.MAC: C-E8-FF-55 D.MAC: E6-E BB-4B S.IP: D.IP: S.MAC: 1A-23-F9-CD-06-9B D.MAC: 49-BD-D2-C7-56-2A

2: Application Layer 28 Chapter 2: Application layer  2.1 Principles of network applications  2.2 Web and HTTP  HTTP: protocol design and performance evaluation  2.3 FTP  2.4 Electronic Mail  SMTP, POP3, IMAP  2.5 DNS  2.6 P2P applications  2.7 Socket programming with TCP  2.8 Socket programming with UDP

Transport Layer 3-29 Chapter 3 Transport Layer  3.1 Transport-layer services  3.2 Multiplexing and demultiplexing  3.3 Connectionless transport: UDP  3.4 Principles of reliable data transfer  3.5 Connection-oriented transport: TCP  segment structure  reliable data transfer  flow control  connection management  3.6 Principles of congestion control  3.7 TCP congestion control

Network Layer4-30 Chapter 4: Network Layer  4. 1 Introduction  4.2 Virtual circuit and datagram networks  4.3 What’s inside a router  4.4 IP: Internet Protocol  Datagram format  IPv4 addressing  ICMP  IPv6  4.5 Routing algorithms  Link state  Distance Vector  Hierarchical routing  4.6 Routing in the Internet  RIP  OSPF  BGP  4.7 Broadcast and multicast routing

5: DataLink Layer5-31 Chapter 5: The Data Link Layer  5.1 Introduction and services  5.2 Error detection and correction  5.3Multiple access protocols  Channel Partitioning  Random access CSMA/CD ALOHA, Sloted ALOHA  Taking turns  5.4 Link-layer Addressing  5.5 Ethernet  5.6 Link-layer switches  5.7 PPP  5.8 Link virtualization: MPLS  5.9 A day in the life of a web request

6: Wireless and Mobile Networks 6-32 Chapter 6 Wireless and Mobile Networks 6.1 Introduction Wireless  6.2 Wireless links, characteristics  CDMA  6.3 IEEE wireless LANs (“wi-fi”)  CSMA/CA  6.4 Cellular Internet Access  architecture  standards (e.g., GSM) Mobility  6.5 Principles: addressing and routing to mobile users  6.6 Mobile IP  6.7 Handling mobility in cellular networks  6.8 Mobility and higher- layer protocols 6.9 Summary

7: Multimedia Networking 7-33 Chapter 7 Multimedia Networking 7.1 multimedia networking applications 7.2 streaming stored audio and video 7.3 making the best out of best effort service 7.4 protocols for real- time interactive applications RTP,RTCP,SIP 7.5 providing multiple classes of service 7.6 providing QoS guarantees

Chapter 8 Network Security 8.1 What is network security? 8.2 Principles of cryptography 8.3 Message integrity 8.5 Securing TCP connections: SSL 8.6 Network layer security: IPsec 8.8 Operational security: firewalls and IDS