Transcript ITI 510 – Computer Networks Meeting 1

ITI-510
Computer
Networks
ITI 510 – Computer Networks
Meeting 1
Rutgers University Internet Institute
Instructor: Chris Uriarte
Welcome…
ITI-510
Computer
Networks
ITI-510 Computer Networks
Section 14
Instructor: Chris Uriarte ([email protected])
Six Meetings, 18 Hours total
About The Course…
• For Who?
ITI-510
Computer
Networks
– 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.
What We Explore…
ITI-510
Computer
Networks
• 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
Specific Topics…
ITI-510
Computer
Networks
• 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
How we learn…
ITI-510
Computer
Networks
•
•
•
•
Lectures
Slides
Internet Resources
Book: TCP/IP, Signature Edition by Sidnie
Feit (1999, McGraw Hill)
• Websites:
Class notes and slides:
http://www.cju.com/classes/ITI510-02
• Hands on exercises
• By asking lots of questions….
Instructor
• Christopher Uriarte
ITI-510
Computer
Networks
– Email: [email protected]
– Office: 732-847-6249
• Call or email anytime
Agenda: Meeting 1
ITI-510
Computer
Networks
•
•
•
•
•
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Introduction to networks
Network devices – high level overview
LAN vs. WAN
OSI
Packet Overview
IP – The Internet Protocol
• A few small Exercises
What is a computer network?
• Formal Definition: Computer Network
ITI-510
Computer
Networks
– 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.
Characterizing Networks
• Sometimes characterized by Topology
ITI-510
Computer
Networks
– 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,
Network Topology
ITI-510
Computer
Networks
• 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
Bus Networks
ITI-510
Computer
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.
Examples of Bus Networks
ITI-510
Computer
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:
Bus Networks: Advantages and
Disadvantages
• Disadvantages:
ITI-510
Computer
Networks
– If one single point in the network is severed,
hosts may experience connectivity loss
– Possible bandwidth constraints
Ring Networks
ITI-510
Computer
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
Examples of Ring Networks
• Simple Example of a Ring Network:
ITI-510
Computer
Networks
Ring Networks: Advantages and
Disadvantages
• Advantages:
ITI-510
Computer
Networks
– 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
Star Topology
ITI-510
Computer
Networks
• 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.
Example of Star Networks
ITI-510
Computer
Networks
Advantages of Star Networks
ITI-510
Computer
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.
Where Networks are Going…
• 10 Years ago: The 80/20 Rule
ITI-510
Computer
Networks
– 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.
LAN vs. WAN
ITI-510
Computer
Networks
• 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.
The OSI Model
ITI-510
Computer
Networks
• 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.
The OSI 7 Layer Model
ITI-510
Computer
Networks
• 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
Depiction of the 7 Layer Model
ITI-510
Computer
Networks
• Layer 7 (Application) is a “high layer”
• Layer 1 (Physical is a low layer)
APPLICATION
PRESENTATION
SESSION
TRANSPORT
NETWORK
Netscape, Outlook, FTP
Programs, Internet Explorer
HTTP, POP, SMTP
Application ports 25 (SMTP),
23 (Telnet) etc.
TCP, UDP
IP
DATALINK
SLIP, PPP, Ethernet
PHYSICAL
Cables, ASDL, POTS, CAT5,
FDDI, etc.
TCP/IP 5 Layer Model
ITI-510
Computer
Networks
• TCP/IP, a very popular protocol used in
LANs, WANs and the Internet, usually
groups the 7-layer model’s Application,
Presentation and Session layers into one
“Application” layer, resulting in a 5 layer
model.
APPLICATION
TRANSPORT
NETWORK
Web Services, Email
Services, News Services,
etc.
TCP, UDP
IP
DATALINK
SLIP, PPP, Ethernet
PHYSICAL
Cables, ASDL, POTS, CAT5,
FDDI, etc.
Description of the 5 Main OSI
Layers (5 Layer Model)
ITI-510
Computer
Networks
• 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 errorchecking 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)
OSI Layers, con’t.
ITI-510
Computer
Networks
• 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. It’s usually responsible for translating
electrical impulses into 1s and 0s.
Sending and Receiving Data
ITI-510
Computer
Networks
• 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 it’s received by the application
layer.
Typical Flow From Layer to
Layer: Sending Data Move from Top to Bottom
ITI-510
Computer
Networks
APPLICATION
TRANSPORT
NETWORK
DATALINK
PHYSICAL
Email Sent
You use MS Outlook to send an
email to your friend,
[email protected]. The Email
“packets” are sent to the Transport
Layer
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 ISP’s modem?)
The physical layer creates the
necessary electrical impulses and
trasmits the data over the physical
medium.
Typical Flow from Layer to Layer:
Receiving Data
Move from Bottom to Top
ITI-510
Computer
Networks
APPLICATION
TRANSPORT
Your email server receives the full
email from the Transport layer and
you use a client program (Outlook,
Eudora) to read it.
The transport ensures that all the
pieces of the email have arrived.
When it has, it’s passed to the
application layer.
NETWORK
The Network layer verifies where the
email originated from (e.g. What IP
address?)
DATALINK
The DLL converts 1s and 0s
received from the physical layer
and passes them onto the network
layer
PHYSICAL
The physical layer decodes the
electrical impulses it receives into 1s
and 0s
Email Arrives
OSI Example Diagram
ITI-510
Computer
Networks
OSI Points
ITI-510
Computer
Networks
• 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)
Introduction to the Internet
ITI-510
Computer
Networks
• 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.
IP – The Internet Protocol
ITI-510
Computer
Networks
• 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
IP Networks
ITI-510
Computer
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.
IP Networks - Example
ITI-510
Computer
Networks
SPRINT
Rutgers
Network
Network
128.6.*.* IP
Block
24.*.*.* IP
Block
Rutgers obtains
connectivity to the
Internet from
UUNET, their
Internet Service
Provider
UUNET
Network
63.*.*.* IP
Block
UUNET peers with
Sprint, which gives
UUNET access to
Sprint-connected
networks and Sprint
access to UUNET
networks.
= Router
IP Addresses: The Numbers
Behind the Name
ITI-510
Computer
Networks
• 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.
Class Exercise: Introduction to
Binary Numbers…
ITI-510
Computer
Networks
• 1’s and 0’s = on and off
• Question: What is:
1
+1
------???