Chapter 1: Computer networks and the Internet

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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

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Whats 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)

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Packet switching versus circuit switching

• Is packet switching a slam dunk 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 7)

Q human analogies of reserved resources
(circuit switching) versus on-demand allocation
(packet-switching)?
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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 1 ISP
Tier 1 ISP
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Internet structure network of networks

• Tier-3 ISPs and local ISPs
• last hop (access) network (closest to end
  systems)

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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Internet structure network of networks

• a packet passes through many networks!

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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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
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Delay in packet-switched networks

• 4. Propagation delay
• d length of physical link
• s propagation speed in medium (2x108 m/sec)
• propagation delay d/s

• 3. Transmission delay
• Rlink bandwidth (bps)
• Lpacket length (bits)
• time to send bits into link L/R

Note s and R are very different quantities!
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Nodal delay

• dproc processing delay
• typically a few microsecs or less
• dqueue queuing delay
• depends on congestion
• dtrans transmission delay
• L/R, significant for low-speed links
• dprop propagation delay
• a few microsecs to hundreds of msecs

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Queueing delay (revisited)

• Rlink bandwidth (bps)
• Lpacket length (bits)
• aaverage packet arrival rate

traffic intensity La/R

• La/R 0 average queueing delay small
• La/R -gt 1 delays become large
• La/R gt 1 more work arriving than can be
  serviced, average delay infinite!

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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

buffer (waiting area)
packet being transmitted
A
B
packet arriving to full buffer is lost
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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

link capacity Rs bits/sec
link capacity Rc bits/sec
server, with file of F bits to send to client
server sends bits (fluid) into pipe
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Throughput (more)

• Rs lt Rc What is average end-end throughput?

Rs bits/sec
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Why layering?

• Dealing with complex systems
• explicit structure allows identification,
  relationship of complex systems pieces
• layered reference model for discussion
• modularization eases maintenance, updating of
  system
• change of implementation of layers service
  transparent to rest of system
• e.g., change in gate procedure doesnt affect
  rest of system
• layering considered harmful?

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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

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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?

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Destination
Source
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Encapsulation
source
message
application transport network link physical
segment
datagram
frame
switch
destination
application transport network link physical
router
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A day in the life scenario
DNS server
Comcast network 68.80.0.0/13
school network 68.80.2.0/24
web page
web server
Googles network 64.233.160.0/19
64.233.169.105
5 DataLink Layer
5-19
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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

• DHCP request encapsulated in UDP, encapsulated in
  IP, encapsulated in 802.1 Ethernet

router (runs DHCP)

• Ethernet frame broadcast (dest FFFFFFFFFFFF) on
  LAN, received at router running DHCP server

• Ethernet demuxed to IP demuxed, UDP demuxed to
  DHCP

5 DataLink Layer
5-20
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A day in the life connecting to the Internet

• DHCP server formulates DHCP ACK containing
  clients IP address, IP address of first-hop
  router for client, name IP address of DNS
  server

• encapsulation at DHCP server, frame forwarded
  (switch learning) through LAN, demultiplexing at
  client

router (runs DHCP)

• DHCP client receives DHCP ACK reply

Client now has IP address, knows name addr of
DNS server, IP address of its first-hop router
5 DataLink Layer
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A day in the life ARP (before DNS, before HTTP)

• before sending HTTP request, need IP address of
  www.google.com DNS

• 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

• ARP query broadcast, received by router, which
  replies with ARP reply giving MAC address of
  router interface

• client now knows MAC address of first hop router,
  so can now send frame containing DNS query

5 DataLink Layer
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A day in the life using DNS
DNS server
Comcast network 68.80.0.0/13

• 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

• IP datagram containing DNS query forwarded via
  LAN switch from client to 1st hop router

• demuxed to DNS server
• DNS server replies to client with IP address of
  www.google.com

5 DataLink Layer
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A day in the life TCP connection carrying HTTP

• to send HTTP request, client first opens TCP
  socket to web server

• TCP SYN segment (step 1 in 3-way handshake)
  inter-domain routed to web server

• web server responds with TCP SYNACK (step 2 in
  3-way handshake)

web server
64.233.169.105

• TCP connection established!

5 DataLink Layer
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A day in the life HTTP request/reply

• web page finally (!!!) displayed

• HTTP request sent into TCP socket

• IP datagram containing HTTP request routed to
  www.google.com

• web server responds with HTTP reply (containing
  web page)

web server

• IP datgram containing HTTP reply routed back to
  client

64.233.169.105
5 DataLink Layer
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Addressing routing to another LAN

• walkthrough send datagram from A to B via R
• assume A knows Bs IP
  address
• two ARP tables in router R, one for each IP
  network (LAN)

5 DataLink Layer
5-26
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• A creates IP datagram with source A, destination
  B
• A uses ARP to get Rs MAC address for
  111.111.111.110
• A creates link-layer frame with R's MAC address
  as dest, frame contains A-to-B IP datagram
• As NIC sends frame
• Rs NIC receives frame
• R removes IP datagram from Ethernet frame, sees
  its destined to B
• R uses ARP to get Bs MAC address
• R creates frame containing A-to-B IP datagram
  sends to B

S.IP 111.111.111.111 D.IP222.222.222.222 S.MAC
1A-23-F9-CD-06-9B D.MAC 49-BD-D2-C7-56-2A
S.IP 111.111.111.111 D.IP222.222.222.222 S.MAC
74-29-9C-E8-FF-55 D.MAC E6-E9-00-17-BB-4B
5 DataLink Layer
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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

2 Application Layer
28
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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

Transport Layer
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Chapter 4 Network Layer

• 4. 1 Introduction
• 4.2 Virtual circuit and datagram networks
• 4.3 Whats 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

Network Layer
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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

5 DataLink Layer
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Chapter 6 Wireless and Mobile Networks

• 6.1 Introduction
• Wireless
• 6.2 Wireless links, characteristics
• CDMA
• 6.3 IEEE 802.11 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

6 Wireless and Mobile Networks
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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

7 Multimedia Networking
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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