ITI 510

1
ITI 510 Computer NetworksMeeting 1

• Rutgers University Internet Institute
• Instructor Chris Uriarte

2
Welcome

• ITI-510 Computer Networks
• Section 14
• Instructor Chris Uriarte (chris_at_cju.com)
• Six Meetings, 18 Hours total

3
About The Course

• For Who?
• Anyone who has an interest in, or wants to
  explore, computer networks.
• Pre-requisites
• Basic knowledge of computers. User-level UNIX
  and/or PC administration experience can help, but
  is not required.
• Use of Internet technologies like web and email.

4
What We Explore

• The concepts and theories behind computer
  networking.
• Network architectures
• Network protocols and packet-level analysis
• How network protocols and applications are used
  in the real world
• Introduction to network hardware components
• Basic concepts in network troubleshooting and
  support
• Trends in computer networks today

5
Specific Topics

• OSI Model, network layers, Internet Protocol,
  Transmission Control Protocol, Link Layer
  Protocols, the Internet.
• ARP, RAPR, ICMP, IP Routing, CIDR, networking
  utilities, Routing algorithms and Protocols like
  RIPv1/2, OSPF, BGP, etc.
• TCP, UDP, TCP/IP and packet delivery
• Application layers DNS, FTP, HTTP, NNTP, SMTP,
  SNMP
• Multicast technologies and tools, MBONE
• Security, MAC Protocols, Advanced topics
• Operating system specifics, Microsoft NetBIOS
• Overview of networking hardware

6
How we learn

• Lectures
• Slides
• Internet Resources
• Book TCP/IP, Signature Edition by Sidnie Feit
  (1999, McGraw Hill)
• Websites
• Class notes and slides http//www.cju.com/classe
  s/ITI510-02
• Hands on exercises
• By asking lots of questions.

7
Instructor

• Christopher Uriarte
• Email chris_at_cju.com
• Office 732-847-6249
• Call or email anytime

8
Agenda Meeting 1

• Introduction to networks
• Network devices high level overview
• LAN vs. WAN
• OSI
• Packet Overview
• IP The Internet Protocol
• A few small Exercises

9
What is a computer network?

• Formal Definition Computer Network
• A series of points or nodes interconnected by
  communication paths. Networks can interconnect
  with other networks and contain subnetworks.
• Simple Definition Computer Network
• Connecting computers and/or devices in such a way
  that they can interact with each other.

10
Characterizing Networks

• Sometimes characterized by Topology
• i.e. bus, star or ring network
• by Spatial Distance
• Wide Area Network, Local Area Network
• by Type of Data Transmission or what it carries
• IP Network, Voice Network, Data Network
• by Type of Physical Link
• Fiber Optic Network, Ethernet Network,

11
Network Topology

• In the context of communication networks, a
  topology pictorially describes the configuration
  or arrangement of a network, including its nodes
  and connecting lines.
• Three general network topologies
• Bus
• Star
• Ring

12
Bus Networks

• A bus network is a network topology in which all
  devices are directly attached to a line and all
  signals pass through each of the devices. Each
  device has a unique identity and can recognize
  those signals intended for it.
• Single String of network wire
• Antiquated technologies such as 10Base2 are
  considered a bus network.

13
Examples of Bus Networks

• A single wire or a group of small wires is used
  to create one data path that all traffic flows
  through.
• 2 simple examples

14
Bus Networks Advantages and Disadvantages

• Disadvantages
• If one single point in the network is severed,
  hosts may experience connectivity loss
• Possible bandwidth constraints

15
Ring Networks

• Each device is attached along the same signal
  path to two other devices, forming a path in the
  shape of a ring.
• Each device in the ring has a unique address.
• Information usually flows in one direction and
  there is usually a controlling device that
  intercepts and manages the flow to and from the
  ring.
• Popular ring network technologies are Token Ring
  and FDDI

16
Examples of Ring Networks

• Simple Example of a Ring Network

17
Ring Networks Advantages and Disadvantages

• Advantages
• If a single point of the physical cable is
  detached, traffic can begin to flow in an the
  opposite direction no loss of connectivity.
• Disadvantages
• Possible bandwidth constraints one single pipe
  for all traffic
• In most cases, every computer sees every bit of
  traffic across the ring

18
Star Topology

• Each device has a unique path to a central point
  that distributes data
• Each device hangs off of a piece of hardware,
  such as a hub or a switch
• Very popular today Traditional 10BaseT,
  100BaseT Ethernet networks use this topology.

19
Example of Star Networks

20
Advantages of Star Networks

• A single cable break will usually only disrupt
  service for a single host within a local network
  segment.
• Newer technologies allow you to dedicated and
  guarantee high bandwidth rates for each
  individual host or network hanging off of a
  central switch.
• The ability to eliminate packet broadcasts
  every computers does not have to see every packet
  on the network.

21
Where Networks are Going

• 10 Years ago The 80/20 Rule
• 80 of all traffic stays on the LOCAL network and
  only 20 of traffic is sent off to other networks
  or to the network backbone
• Typically describes the workgroup model of
  computing access devices on your local network
  like file servers, printers, other workstations.
• Today The 20/80 Rule
• 20 or all traffic stays on the LOCAL network and
  80 of traffic is sent to other networks or the
  network backbone.
• Cause by the Increased use of WAN technologies
  and distributed computing models.

22
LAN vs. WAN

• Local Area Networks (LANs) a group of computers
  and associated devices that share a common
  communications line and typically share the
  resources of a single processor or server within
  a small geographic area like an office building.
  Usually privately-owned.
• Wide Area Networks (WANs) a geographically
  dispersed network. It may be privately owned or
  rented, but the term usually connotes the
  inclusion of public (shared user) networks like
  the Internet or the PSTN (Public Switched
  Telephone Network)
• We may use different network technologies,
  protocols, hardware, etc. to connect devices
  within a WAN than we use when connecting devices
  in a LAN.

23
The OSI Model

• OSI (Open Systems Interconnection) is a standard
  description or "reference model" for how messages
  should be transmitted between any two points in a
  telecommunication network.
• Its purpose is to guide product implementers so
  that their products will consistently work with
  other products.
• Developed by representatives of major computer
  and telecommunication companies in 1983 now a
  standard way of examining computer network
  technologies.

24
The OSI 7 Layer Model

• The general OSI model contains 7 layers (layers
  1-7 respectively)
• Physical
• Data Link
• Network
• Transport
• Session
• Presentation
• Application
• Each layer has a specific function

25
Depiction of the 7 Layer Model

• Layer 7 (Application) is a high layer
• Layer 1 (Physical is a low layer)

Netscape, Outlook, FTP Programs, Internet Explorer
APPLICATION PRESENTATION SESSION TRANSPORT NETWORK
DATALINK PHYSICAL
HTTP, POP, SMTP
Application ports 25 (SMTP), 23 (Telnet) etc.
TCP, UDP
IP
SLIP, PPP, Ethernet
Cables, ASDL, POTS, CAT5, FDDI, etc.
26
TCP/IP 5 Layer Model

• TCP/IP, a very popular protocol used in LANs,
  WANs and the Internet, usually groups the 7-layer
  models Application, Presentation and Session
  layers into one Application layer, resulting in
  a 5 layer model.

APPLICATION TRANSPORT NETWORK DATALINK PHYSICAL
Web Services, Email Services, News Services, etc.
TCP, UDP
IP
SLIP, PPP, Ethernet
Cables, ASDL, POTS, CAT5, FDDI, etc.
27
Description of the 5 Main OSI Layers (5 Layer
Model)

• Layer 5 The application layer...This is the
  layer at which communication partners are
  identified, quality of service is identified,
  user authentication and privacy are considered,
  and any constraints on data syntax are
  identified. (e.g. Funcationality provided by web
  browsers, mail reader programs and their
  associated protocols like HTTP and SMTP)
• Layer 4 The transport layer...This layer manages
  the end-to-end control and error-checking of
  network traffic. It checks to see if all packets
  have arrived and ensures complete data transfer
  between parties. (e.g. TCP and UDP protcols)

28
OSI Layers, cont.

• Layer 3 The network layer...This layer handles
  the routing of outgoing data (making sure that a
  packet is sent to the right place) and also
  handles incoming data. (e.g. IP)
• Layer 2 The data-link layer... This layer
  defines the rules for sending and receiving data
  across the physical connection between two
  systems. (e.g. Ethernet, PPP, SLIP)
• Layer 1 The physical layer... This layer governs
  hardware connections and byte preparation for
  transmissions. It is the only layer that involves
  a physical transfer of information between
  network nodes. Its usually responsible for
  translating electrical impulses into 1s and 0s.

29
Sending and Receiving Data

• Layers only interact with other layers directly
  above and below them.
• When data is sent, it originates at the
  application layer and moves down the OSI layers
  until it is transmitted to another host.
• When data arrives, it originates at the physical
  layer and moves up the OSI model until its
  received by the application layer.

30
Typical Flow From Layer to Layer Sending Data
Move from Top to Bottom
You use MS Outlook to send an email to your
friend, friend_at_hotmail.com. The Email packets
are sent to the Transport Layer

APPLICATION TRANSPORT NETWORK DATALINK PHYSICA
L
The transport layer takes the email and packages
it in a format that ensures it will be completely
delivered.
The Network layer makes sure the email knows how
to get to the hotmail.com server
The DLL converts the information from the layers
above into 1s and 0s that can be understood by a
peer on the other end of the phone line or
network connection (e.g. your ISPs modem?)
The physical layer creates the necessary
electrical impulses and trasmits the data over
the physical medium.
Email Sent
31
Typical Flow from Layer to Layer Receiving Data
Move from Bottom to Top
Your email server receives the full email from
the Transport layer and you use a client program
(Outlook, Eudora) to read it.

APPLICATION TRANSPORT NETWORK DATALINK PHYSICA
L
The transport ensures that all the pieces of the
email have arrived. When it has, its passed to
the application layer.
The Network layer verifies where the email
originated from (e.g. What IP address?)
The DLL converts 1s and 0s received from the
physical layer and passes them onto the network
layer
The physical layer decodes the electrical
impulses it receives into 1s and 0s
Email Arrives
32
OSI Example Diagram
33
OSI Points

• The OSI model allows hardware and software
  manufacturers to keep a limited scope when
  developing and manufacturing
• A vendor only has to create a product that can
  function within its specific layer and interact
  with only the layers directly above and below
• For example, a manufacturer of network cards need
  only know how to operate within the Physical
  layer and how to pass data to the Data Link layer
  the network card does not need to know anything
  about the network, transport or application
  layers.
• Example 2 If you are writing a web browser
  (Application layer), you only need to know how to
  interact with the Transport layer (usually
  referred to as the TCP Stack within an operating
  system)

34
Introduction to the Internet

• The Internet is a global network that is
  comprised of smaller networks owned by commercial
  entities, educational institutions, government
  agencies, etc.
• No one owns the Internet.
• Traffic is carried through the Internet using a
  hardware (physical layer) and communication links
  (data link layer).
• Host-to-host communication is accomplished using
  TCP/IP or UDP/IP the combination of the TCP or
  UDP transmission layer protocols and the IP
  (Internet Protocol) network-layer protocol.

35
IP The Internet Protocol

• In an IP network, individual hosts are
  distinguished by a unique address, known as an
  IP address
• An IP address is comprised of four Octals (8-bit
  numbers), separated by a decimal point, e.g.
• 126.14.34.18
• Each decimal number (126, 14, 34, 18, etc.) has a
  BINARY equivalent that is used many network
  equations.
• 128.14.34.18 10000000.00001110. 00100010.
  00010010

36
IP Networks

• Internet service providers (ISPs) are assigned
  blocks of IP addresses, which they are free to
  use on their Internal networks.
• ISPs form peering agreements with other service
  providers so they have a pathway other other
  provider's networks.
• ISP networks are connected through hardware
  devices knows as routers, which are responsible
  for directing traffic to and from other networks.

37
IP Networks - Example

SPRINT Network 24... IP Block
Rutgers Network 128.6.. IP Block


Rutgers obtains connectivity to the Internet from
UUNET, their Internet Service Provider
UUNET peers with Sprint, which gives UUNET access
to Sprint-connected networks and Sprint access to
UUNET networks.


UUNET Network 63... IP Block
Router

38
IP Addresses The Numbers Behind the Name

• The common internet hostnames we use everyday
  (www.yahoo.com, iti.rutgers.edu, etc.) all have
  corresponding IP addresses behind them.
• Routers move packets and messages from network to
  network based on IP address not based on
  hostname.

39
Class Exercise Introduction to Binary Numbers

• 1s and 0s on and off
• Question What is
• 1
• 1
• -------
• ???