School of Computing Science

1

• School of Computing Science
• Simon Fraser University
• CMPT 880 Internet Architectures and Protocols
• Instructor Dr. Mohamed Hefeeda

2
Course Objectives

• Understand
• principles of designing and operating computer
  networks
• structure and protocols of the Internet
• services that can/cannot be offered by the
  Internet
• Know how to
• analytically analyze performance of a
  system/protocol
• implement network protocols and applications
• And, more importantly,
• Have fun!

3
Course Info

• Most of the course will be lectures given by the
  instructor
• Last three weeks, each student presents at most
  one chapter/paper
• Course web page
• http//nsl.cs.surrey.sfu.ca/teaching/06/880/
• Or access it from my web page
• http//www.cs.sfu.ca/mhefeeda

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Course Info Textbooks and References

• All are on reserve in SFU Surrey Library
• Kurose and Rose, Computer Networking  A top-down
  Approach Featuring the Internet, 2005
• Background materials
• Ch 7 Multimedia Networking and QoS
• Hassan and Jain, High Performance TCP/IP
  Networking, 2004 
• Several chapters on analyzing TCP/IP in different
  environments
• Stallings, High-speed Networks and Internets
  Performance and Quality of Service, 2002
• Three chapters on (basics of) probability and
  queuing
• Papers will be posted on the course web page

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Course Info Grading

• Homework 20
• 3 4 problem sets
• Projects 30
• 3 projects later two of them are group projects
• Class participation 15
• Ask and answer questions
• Present one chapter/paper
• Final exam 35
• Comprehensive

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Course Info Schedule

• Schedule is posted on the course web page
• Let us quickly review it

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• Review of Basic Networking Concepts

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Review of Basic Networking Concepts

• Internet structure
• Protocol layering and encapsulation
• Internet services and socket programming
• Network Layer
• Network types Circuit switching, Packet
  switching
• Addressing, Forwarding, Routing
• Transport layer
• Reliability and congestion control
• TCP, UDP
• Link Layer
• Multiple Access Protocols
• Ethernet

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The Internet

• Millions of hosts (end systems)
• Inter-connected, running network apps
• Diverse communication links
• fiber, copper, radio, satellite
• Routers
• forward packets
• Internet network of networks
• loosely hierarchical
• Public, versus private intranet

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Cool Internet appliances
Web-enabled toaster weather forecaster
IP picture frame http//www.ceiva.com/
Worlds smallest web server http//www-ccs.cs.umas
s.edu/shri/iPic.html
Internet phones
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Internet structure network of networks

• roughly hierarchical
• at center tier-1 ISPs (e.g., MCI, Sprint,
  ATT, Cable and Wireless), national/international
  coverage
• treat each other as equals

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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Tier-1 ISP e.g., Sprint
Sprint US backbone network
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Internet structure Tier-2 ISPs

• 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 Tier-3 ISPs

• 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 packet journey

• a packet passes through many networks!

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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A snapshot of the Internet in 1999 showing major
ISPs
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Review of Basic Networking Concepts

• Internet structure
• Protocol layering and encapsulation
• Internet services and socket programming
• Network Layer
• Network types Circuit switching, Packet
  switching
• Addressing, Forwarding, Routing
• Transport layer
• Reliability and congestion control
• TCP, UDP
• Link Layer
• Multiple Access Protocols
• Ethernet

18
Protocol Layers

• Networks are complex!
• many pieces
• hosts
• routers
• links of various media
• applications
• protocols
• hardware, software

• Question
• Is there any hope of organizing structure of
  network?
• Or at least our discussion of networks?

19
Layering of Airline Functionality

• Layers each layer implements a service
• via its own internal-layer actions
• relying on services provided by layer below

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Why layering?

• Dealing with complex systems
• explicit structure allows identification,
  relationship of complex systems pieces
• 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
• What is the downside of layering?

21
Internet protocol stack

• application supporting network applications
• FTP, SMTP, HTTP
• transport host-host 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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Encapsulation
datagram
frame
23
Review of Basic Networking Concepts

• Internet structure
• Protocol layering and encapsulation
• Internet services and socket programming
• Network Layer
• Network types Circuit switching, Packet
  switching
• Addressing, Forwarding, Routing
• Transport layer
• Reliability and congestion control
• TCP, UDP
• Link Layer
• Multiple Access Protocols
• Ethernet

24
Internet Services

• View the Internet as a communication
  infrastructure that provides services to apps
• Web, email, games, e-commerce, file sharing,
• Two communication services
• Connectionless unreliable
• Connection-oriented reliable

25
Internet Services

• Connectionless
• No connection set up, simply send
• Faster, less overhead
• No reliability, flow control, or congestion
  control
• UDP User Datagram Protocol

• Connection-oriented
• Prepare for data transfer ahead of time
• establish connection ? set up state in the two
  communicating hosts
• Usually comes with reliability, flow and
  congestion control
• TCP Transmission Control Protocol

How can we access these services?
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Network (Socket) Programming

• Process sends/receives messages to/from its
  socket
• Socket analogous to door
• sending process shoves message out door
• sending process relies on transport
  infrastructure on other side of door which brings
  message to socket at receiving process

controlled by app developer
Internet
controlled by OS

• Socket is the interface (API) between application
  and transport layer

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Addressing Processes

• We use ports
• Process is identified by
• IP address,
• Transport protocol, and
• Port number
• Example port numbers
• HTTP server 80 (TCP)
• Mail server 25 (TCP)

• For a process to receive messages, it must have
  an identifier
• A host has a unique32-bit IP address
• Q does the IP address of the host on which the
  process runs suffice for identifying the process?
• A No, many processes can be running on same host
  ?

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Socket Programming

• Socket API
• introduced in BSD 4.1 UNIX, 1981
• explicitly created, used, released by apps
• client/server paradigm
• provides two services
• reliable, byte stream-oriented
• unreliable datagram

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Socket Programming using TCP

• TCP service reliable transfer of bytes from one
  process to another
• virtual pipe between sender and receiver

controlled by application developer
controlled by application developer
controlled by operating system
controlled by operating system
internet
host or server
host or server
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Socket Programming using TCP
Server (running on hostid)
Client
read reply from clientSocket
close connectionSocket
close clientSocket
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Socket Programming using TCP

• Server process must first be running, and
• creates a socket (door) that welcomes clients
  contact, then wait
• Client contacts server by creating local TCP
  socket using IP address, port number of server
  process
• When client creates socket
• client TCP establishes connection to server TCP
• When contacted by client
• server TCP creates new socket for server process
  to communicate with client
• allows server to talk with multiple clients
• source port numbers and IPs used to distinguish
  clients

32
Socket programming using UDP

• UDP Service unreliable transfer of groups of
  bytes (datagrams) between client and server
• no connection between client and server
• no handshaking
• sender explicitly attaches IP address and port of
  destination to each packet
• server must extract IP address, port of sender
  from received packet
• transmitted data may be received out of order, or
  lost

33
Socket Programming using UDP
Server (running on hostid)
Client
34
Review of Basic Networking Concepts

• Internet structure
• Protocol layering and encapsulation
• Internet services and socket programming
• Network Layer
• Network types Circuit switching, Packet
  switching
• Addressing, Forwarding, Routing
• Transport layer
• Reliability and congestion control
• TCP, UDP
• Link Layer
• Multiple Access Protocols
• Ethernet

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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

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Network Core Circuit Switching

• Network resources (e.g., bandwidth) divided into
  pieces using
• Frequency division multiplexing (FDM)
• Time division multiplexing (TDM)
• Pieces allocated to calls (connections)
• ? guaranteed performance
• Resource piece idle if not used by owning call
• no sharing
• Connection setup is required
• Examples
• (Traditional) Telephone network

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Circuit Switching Dedicated Circuits
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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
• store and forward packets move one hop at a time
• Node receives complete packet before forwarding

• resource contention
• aggregate resource demand can exceed amount
  available
• congestion packets queue, wait for link use

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Packet Switching Statistical Multiplexing
10 Mb/s Ethernet
C
A
statistical multiplexing
1.5 Mb/s
B
queue of packets waiting for output link

• Sequence of A B packets does not have fixed
  pattern, shared on demand ? statistical
  multiplexing
• In contrast, in TDM each host gets same slot in
  revolving TDM frame

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Packet Switching Efficiency

• Packet switching allows more users to use network!

• 1 Mb/s link
• each user
• 100 kb/s when active
• active 10 of time
• circuit-switching
• 10 users
• packet switching
• with 35 users, probability gt 10 active less than
  0 .0004

Q how did we get value 0.0004?
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Packet Switching

• Advantages
• no call setup ? simpler
• resource sharing (statistical multiplexing) ?
• better resource utilization
• more users or faster transfer (a single user can
  use entire bw)
• Well suited for bursty traffic (typical)
• Disadvantages
• Congestion may occur ?
• packet delay and loss
• need protocols to control congestion and ensure
  reliable data transfer

42
Packet Switching Two Classes

• Datagram network
• Example The Internet
• Virtual-circuit network
• Examples ATM (Asynchronous Transfer Mode), frame
  relay, X.25

43
Packet-switched Datagram Networks

• no call setup at network layer
• routers no state about end-to-end connections
• no network-level concept of connection
• packets forwarded using destination host address
• packets between same source-dest pair may take
  different paths

44
Packet-switched VC Networks

• Source-to-dest path behaves much like telephone
  circuit
• ? performance-wise
• connection setup, teardown for each call before
  data can flow
• each packet carries VC identifier (not
  destination address)
• every router on source-dest path maintains state
  for each passing connection
• link, router resources (bandwidth, buffers) may
  be allocated to VC
• Examples
• ATM (Asynchronous Transfer Mode), frame relay,
  X.25

45
VC Networks Connection Setup

• Signaling protocols are used to
• setup, maintain, and teardown VCs
• Note not used in the current Internet

6. Receive data
5. Data flow begins
4. Call connected
3. Accept call
1. Initiate call
2. incoming call
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VC Networks VC Implementation

• A VC consists of
• Path from source to destination
• VC numbers, one number for each link along path
• Entries in forwarding tables in routers along
  path
• Packet belonging to VC carries same VC number
• VC number must be changed on each link
• New VC number comes from forwarding table

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VC Networks Forwarding table
Forwarding table in northwest router
Each routers maintains connection state
information!
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ATM vs. Internet QoS
Guarantees ?
Network Architecture Internet ATM ATM ATM ATM
Service Model best effort CBR VBR ABR UBR
Congestion feedback no (inferred via
loss) no congestion no congestion yes no
Bandwidth none constant rate guaranteed rate gua
ranteed minimum none
Loss no yes yes no no
Order no yes yes yes yes
Timing no yes yes no no
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Network Taxonomy
50
Review of Basic Networking Concepts

• Internet structure
• Protocol layering and encapsulation
• Internet services and socket programming
• Network Layer
• Network types Circuit switching, Packet
  switching
• Addressing, Forwarding, Routing
• Transport layer
• Reliability and congestion control
• TCP, UDP
• Link Layer
• Multiple Access Protocols
• Ethernet

51
Network Layer

• Network layer protocols in every host and router
• Network layers goal
• transport data from sending host to receiving
  host
• We focus on datagram networks (Internet)

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Network Layer in the Internet

• Host, router network layer functions

Transport layer TCP, UDP
Network layer
Link layer
physical layer
53
Routing vs. Forwarding

• Routing
• determine route taken by packets from source to
  destination
• Routing algorithms, e.g., RIP, OSPF, BGP
• Forwarding
• move packets from routers input to appropriate
  output
• use forwarding table populated by routing
  algorithm
• E.g., IP forwarding function

54
IP Datagram Format
IP protocol version number
32 bits
total datagram length (bytes)
header length (bytes)
head. len
type of service
ver
length
for fragmentation/ reassembly
fragment offset
Provides some QoS
flgs
16-bit identifier
max number remaining hops (decremented at each
router)
time to live
upper layer
Internet checksum
32 bit source IP address
32 bit destination IP address
upper layer protocol to deliver payload to
E.g. timestamp, record route taken, specify list
of routers to visit.
Options (if any)
data (variable length, typically a TCP or UDP
segment)

• how much overhead with TCP?
• 20 bytes of TCP
• 20 bytes of IP
• 40 bytes app layer overhead

IP ver 4.0
55
IP Addressing Introduction

• IP address
• 32-bit identifier for each host, router network
  interface
• Represented in Dotted-decimal notation

11011111 00000001 00000001 00000001
223.1.1.1
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IP Addressing

• Network interface
• connection between host/router and physical link
• routers typically have multiple interfaces
• host typically has one interface
• Unique IP addresses associated with each interface

223.1.1.1
How do we assign IPs?
223.1.1.4
223.1.2.9
223.1.1.3
Divide network into subnets, each has a common ID
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Subnets

• Subnet is
• a group of devices that can reach each other
  without intervening router
• identified by high order bits of IP addresses

11011111 00000001 00000001 00000001
Host ID
Subnet ID
223.1.1.0/24
/24 bits in subnet portion of address, subnet
mask
58
Subnets

• How many subnets?
• 6 subnets
• Recipe
• detach each interface from its host or router,
  creating isolated networks
• Each isolated network is a subnet

59
IP Addressing CIDR

• CIDR Classless InterDomain Routing
• subnet portion of address of arbitrary length
• address format a.b.c.d/x, where x is bits in
  subnet portion of address
• Old Classful Addressing
• Subnet length had to be /8 (class A), /16 (class
  B), /24 (class C)
• Why CIDR?
• Finer control over address allocation ? reduce
  waste of addresses
• Ex company with 2000 machines would have to get
  class B, wasting 63,000 addresses

60
IP Addresses How to Get One?

• Q How does host get IP address?
• hard-coded by system admin in a file
• WIN control-panel-gtnetwork-gtconfiguration-gttcp/ip
  -gtproperties
• UNIX /etc/rc.config
• DHCP Dynamic Host Configuration Protocol
  dynamically get address from as server
• plug-and-play

61
IP Addresses How to Get One?

• Q How does network get subnet part of IP addr?
• A gets allocated portion of its provider ISPs
  address space

ISP's block 11001000 00010111 00010000
00000000 200.23.16.0/20 Organization 0
11001000 00010111 00010000 00000000
200.23.16.0/23 Organization 1 11001000
00010111 00010010 00000000 200.23.18.0/23
Organization 2 11001000 00010111 00010100
00000000 200.23.20.0/23 ...
..
. . Organization 7
11001000 00010111 00011110 00000000
200.23.30.0/23
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Hierarchical Addressing Route Aggregation
Hierarchical addressing allows efficient
advertisement of routing information
Organization 0
Organization 1
Send me anything with addresses beginning
200.23.16.0/20
Organization 2
Fly-By-Night-ISP
Internet
Organization 7
Send me anything with addresses beginning
199.31.0.0/16
ISPs-R-Us
63
IP Addressing the last word...

• Q How does an ISP get block of addresses?
• A ICANN Internet Corporation for Assigned Names
  and Numbers
• allocates addresses
• manages DNS
• assigns domain names, resolves disputes