Core Network Concepts

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Core Network Concepts

• Sri Sharma
• Oakland University
• Winter 2004

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What is a Network?

• A network is a system of hardware, software and
  transmission components that collectively allow
  two application programs on two different
  stations connected to the network to communicate
  well.
• Major Network Types
• The Global Internet
• Internal Corporate Networks
• The Worldwide Telephone System

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Elements of Network

• Applications
• Stations/DTEs
• Frames
• Switches
• Access Links
• Trunk Links

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Elements of a Network Applications
Application
Application
Frame
Networks connect applications on different
stations
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Elements of a Network Stations /DTEs
Frame
Server Station
Client Station
Stations are computers and other devices such as
cellphones and PDAs
Server Station/ /DTEs
Mobile Client Station/ /DTEs
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Elements of a Network Frames
Frame
Server Station
Client Station
Stations communicate by sending messages
called Frames
Server Station
Mobile Client Station
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Elements of a Network Switches
Switch
Frame
Switch
Switch
Switch
Frames may pass through multiple switches Each
switch reads the frame And passes it on
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Elements of a Network Access Links
Access links connect stations to the first
switch Usually copper wire Increasingly, radio
links
Access Link
Access Link
Access Link
Access Link
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Elements of a Network Trunk Links
Trunk Link
Trunk Link
Trunk Link
Trunk links connect switches Higher
capacity than access links Often optical fiber
Trunk Link
Trunk Link
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Client/Server Architecture
Usually, Two Types of Stations Clients and Servers
Server
Client PC
Service
Network
Clients Receive Services
Servers Provide Services
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Clients and Servers (Stations/DTEs)

• Clients mostly Wintel
• Servers
• Standard PC Microprocessor (moderate speed and
  cost)
• Workstation Server
• Custom-Built Microprocessor (fast and expensive)
• Mainframe Server
• Fastest Servers, Ultra-Reliable, Specialized
  Operating System
• NOS (Network Operating System)
• Microsoft Windows Server
• Novell Network
• LINUX (Version of UNIX), UNIX Operating System -
  Highly reliable
• Scalability and Reliability highly important

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Packets and Frames

• Messages in Single Networks are Called Frames
• Messages in Internets are Called Packets

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Packets and Frames

• Packet goes from source host to destination host
  across multiple networks

Destination Host
Source Host
Same Packet
Packet
Same Packet
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Packets and Frames (cont.)

• Within a single network, the packet is carried in
  the data field of that networks frame, probably
  across multiple switches

Packet
Frame
Network 1
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Packets and Frames (cont.)

• The first router removes packet from first
  networks frame, sends back out in a frame with
  the second networks frame format

Same Packet
Frame
Network 1
Second Router
First Router
Frame With Network 2s Frame Format
Network 2
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Switches

• Switch receives a frame and sends it back out
• Packet Switching
• Break message into smaller packets (also known as
  frames)
• Packet Switching Reduces Trunk Line Costs

Trunk Link
Packet from A to B
Packet from C to D
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Switches
Switch receives a frame, sends it back out
1
2
3
4
5
6
Switch
Switch Sends Signal out a Single Port
Station A Transmits to Station C
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Packet Switching
1. Break message into Smaller packets (also known
as frames)
Original Message
Packet Switch A
B
C
Computer X
Packet
Switching Decision
Computer Y
F
E
D
2. Route packets individually Packet switches
along the way Make decisions about the packet
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Packet Switching (cont.)
Packet
Trailer
Header
Data Field
Other Header Field
Address Field
Message Structure
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Quality of Service (QOS)

• Quantitative measures of service quality
• Speed (bits per second)
• Delay (Latency) (milliseconds)
• Congestion
• Reliability
• Availability
• Percent of time available to users for
  transmission and reception
• Want 24x7x365 availability
• Telephone network Five 9s (99.999)
• Error Rate
• Percent of lost or damaged messages or bits

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Quality of Service (QoS) (cont.)

• Service Level Agreements (SLAs)
• Quantitative guarantees for various service
  parameters
• Example Better than 99 availability and a
  packet loss error rate of less 0.5 measured over
  each day latency not exceeding 45 ms 99 of the
  time.
• Network provider pays performance penalties if
  guarantees are not met

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Types of Networks

• Geographic scope
• Local Area Network (LAN)
• Wide Area Network (WAN)
• Metropolitan Area Network (MAN)
• Personal Area Network (PAN)
• Storage Area Network (SAN)
• Communities served
• The Internet
• Intranet
• Extranet

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LAN

• Limited geographical distance home, office,
  building, campus, industrial part
• Customer premises operation
• User firm chooses technology
• User firm needs to manage on ongoing basis
• Low cost per bit transmitted
• Companies can afford high speed
• 100 Mbps to the desktop is typical

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WAN
WAN

• To link sites
• Long distances
• Requires the use of carriers to provide service
• Limited and complex choices but carrier manages
• High cost per bit transmitted
• Companies cannot afford high speeds
• Usually low speed (56 kbps to a few megabits per
  second)

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LAN-WAN Network

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Internet

• An internet is a group of networks linked
  together with routers in a way that allows an
  application program on any station on any network
  in the internet to be able to communicate with an
  application program on another station on any
  other network.

Router
Network 1
Network 2
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An Internet
Multiple Networks Connected by Routers Path of a
Packet is its Route
Single Network
Routers
Packet
Route
Single Network
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An Internet (cont.)
Single Networks Have Switches Switches Connect
Station-to-Router or Router-to-Router
Network Y
Network X
Switches
Routers
Network Z
Switches
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The Internet
The global Internet has thousands of networks
Network
Webserver Software
Browser
Packet
Packet
Router
Route
Router
Router
Packet
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The Internet (cont.)
Network
Webserver Software
Browser
Packet
Packet
Router
Route
Router
Router
Packet
Webserver (Host) IP Address141.210.6.40 Host
namewww.oakland.edu
User PC (Host) IP Address141.210.150.21
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Internet Configuration
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Hosts

• All computers connected to the Internet are hosts
• Server hosts (webservers, FTP servers, etc.)
• Also client PCs at home, at school, and at work
• Also PDAs and Internet-enabled cellphones
• The Internet treats all hosts of all sizes as
  equals
• Only application software distinguishes between
  them (browsers for client PCs, webserver
  applications for server hosts, etc.)

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Host Addresses and Host Names

• Host IP Address
• Official address of host on the Internet
• Every host must have an IP address, including
  client PCs and PDAs
• 32 bits long
• Often expressed in dotted Decimal Notation for
  human reading (e.g., 141.210.6.40)
• Hosts and routers work with 32-bit binary form

1000110111010010 (32 bits) (Used by Hosts and
Routers)
Segment (6)
IP Address 141.210.6.40
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Host Addresses and Host Names

• Host Name
• Several labels separated by dots
  (www.sba.oakland.edu)
• Like nickname easy to remember
• Not the official address of the host

Host Name www.sba.oakland.edu
Label (sba)
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Host Addresses and Host Names

• Domain Name System (DNS)
• You cannot send messages to a host if you only
  know its host name
• Computer must know its official address (IP
  Address)
• DNS provides a way of finding a hosts IP address
  if only its host name is known

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Domain Name System (DNS) Host
DNS Request Message The targets host name is
www.sba.oakland.edu
Originating Hosts DNS Resolver
DNS Host
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Domain Name System (DNS) Host
DNS Table
Host Name www.sba.oakland.edu
IP Address 141.210.150.78
DNS Response Message The targets IP address is
141.210.150.178
Originating Host
DNS Host
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Internet Service Providers (ISPs) and Internet
Backbone Carriers
Webserver
User PC
Internet Backbone (Multiple Carriers)
Router
ISP
ISP
Internet Service Provider
Internet Service Provider
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The Internet, Intranets, and Extranets

• The Internet
• Goal is universal community include everyone
• Intranets
• Community is a single (possibly multi-site)
  organization
• Use Internet transmission standards and
  applications
• Controlled communication with the outside world
  via firewalls
• Extranets
• Community is a group of sellers and purchasers
• Only some hosts within each company are included

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Security

• Attacks roughly doubling each year
• Attacks becoming more damaging when they occur
  (1 billion USD per major virus outbreak)
• Companies and nations now face the prospect of
  far more destructive cyberwar and cyberterrorism

41
Firewalls
Deny an Attack Packet
Attack Packet
1. Deny
Attacker
Intranet Server
Internet
Internet Firewall
Attack Packet
Public Webserver
Intranet Client
Intranet Client
Log
Corporate Network
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Firewalls (cont.)
Pass a Legitimate Packet
Attacker
2. Pass
Intranet Server
Internet
Legitimate Packet
Internet Firewall
Public Webserver
Intranet Client
Intranet Client
Log
Corporate Network
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Firewalls (cont.)
Permit a Legitimate Outgoing Packet
Attacker
Intranet Server
Internet
Legitimate Packet
Internet Firewall
3. Pass
Public Webserver
Intranet Client
Intranet Client
Log
Corporate Network