01.a. Networks - 01 Basics

8/12/2019 01.a. Networks - 01 Basics

1/36

2012 by Elbit Systems | Elbit Systems Proprietary

Module 01Operating Systems and

Networks

Networks, OSI Model and TCP/IP

Topics

Computer Networks

OSI Model (7-Layers)

TCP/IP UDP


2/36

LAN Standards

Standards are required so that different manufacturers cancreate equipment that will interoperate without specialconfiguration.

Standards groups include:

ISO. International Organization for Standardizationestablishes standards for networking operation.

ANSI.American National Standards Institute is the USrepresentative to ISO.

EIA/TIA. Electronics Industries Alliance/TelecommunicationsIndustry Association is an industry based standards group.

IEEE. Institute of Electrical and Electronics Engineers is aninternational professional organization that setscommunications standards. IEEE Project 802 sets standardsfor cabling and data transmission on local area networks.

Physical Connectivity

Network Interface Card (NIC).Also known as Network

Card or Ethernet Adapter. Transmits and receives signals

to the LAN. Computers can not communicate on LAN

without this device.

Each Network Card has a Media Access Control(MAC)address. This is also known as thephysical addressor

Ethernet address.

MAC address is a unique 12 digit hexadecimal number

that is hard coded into each network interface. The first

half of a MAC address is the manufacturers ID. The

second half a serial number.

-F3-1C-D4Serial number00-04-ACManufacturer ID


3/36

Cable and Wireless

Physical cabling is also known asbounded media.

Transmissions are bound to the physical media.

To communicate, hosts mustbe physically

connected to that media.

Physical cabling is usually located in a buildings

plenum.

Wireless network is known asunbounded media.

Transmissions are not bound to a physical

cable.

To communicate, hosts do not needto be

physically connected.

Coaxial Cable

Coaxial cable is often used in older LANs.

Known asRG58,Thinnet, and10Base2.

Maximum bandwidth of 10 Mbps.

Maximum segment length of 185 meters (605

feet).

Maximum of 30 hosts per segment.


4/36

Coaxial Cable

Hosts on an RG58 network require a network card with

an RG58 adapter.

To add the host to the network, the cable section must

have an RG58connector on both ends with aT piece

fitted between them.

Both ends of the segment should be terminated using a a

piece ofequipment known as aterminator.

A terminator stops signals on the network echoing back

when they reach the end

of thesegment.

Twisted Pair Cable

The most common cabling technology in use

today.

Consists of four pairsof copper wires twisted

around each other. Twists are used because they

reduce interference.

Maximum length:

100 meters (328 feet).

Maximum bandwidth:

1000 Mbps.


5/36

Twisted Pair Cable

Connect to networking devices such as networkinterface cards and switches usingRJ45

connectors.

One end must connect to a host, the other to a

networking device such as a switch. You can only

connect two computers together if you use a

crossover cable, which uses different wiring.

Fiber Optic Cable

Fiber optic cable has better data security than twisted pair

or RG58. You cant intercept the signals without breaking

the cable.

Fiber optic cable is immune to electromagnetic

interference, something that can cause problems for

twisted pair or RG58.

The disadvantages of fiber optic cable is that it is very

expensiveand that it is not very flexible. Bend it too far

and it will break the core, rendering the cable useless.

Fiber optic cable is mostly use as a backboneto connect

LANs together, rather than connecting hosts together

on a LAN.


6/36

Wireless

Wireless networks donot requirephysical

infrastructure like

cables.

Wireless networks have

short range.

Wireless networks have

limited bandwidth.

Transmissions can be

intercepted easilyby a

person outside building

with a wireless access

device.

LAN Topologies

Physical topologyis the actual location and

arrangement of physical connections between

devices on the network.

Logical topologyis the path that a givendatagram travels between two devices. Often

there is more than one way to get from one host

to another.


7/36

Bus Topology

All network devices

connected to acommon cable in

logical linear fashion.

Transmissions are sent

along the length of the

bus segment.

Adding hosts to the network requires breaking

the network.

Failure of onehost can cause failureof network.

Star Topology

Connection from

each device to a

central location,

usually a switch.

Most commonly

used physical

topology.

Failure of one

cable does not

bring down

network.


8/36

Ring Topology

Network isconnected in

an endless

loop.

No termination

required.

Uncommon

topology today,

more common

in 1980s.

CSMA/CD

Stands for Carrier Sense Multiple Access with

Collision Detection.

Each device listens to media for transmissions.

When media is clear, initiates transmission and

listens for collision.

If collision occurs, device waits for random

amount of time before attempting transmission

again.

Commonly used on physical networks.

Wait for network

silenceWait for network

silence

00110100010100010010001110010011010001010001001000111001

Begin Transmission Begin Transmission

COLLISION!

Wait random amount

of time

Wait random

amount

of time

0011010001010001001000111001

Begin Transmission


9/36

CSMA/CA

Stands for Carrier Sense Multiple Access with

Collision Avoidance.

Each device listens to media for transmissions.

When media is clear, device sends an intent to

transmit signal. As this signal is small, chances

of collision are minimized.

Used often in wireless networking.

Wait for network silence Wait for network silence

Signal Intent to Transmit

1010111011101110111011101101

ISO OSI networks

International Organization forStandardization (ISO)

Open Systems Interconnection (OSI)

1979 - 7 layer reference model defined

1982ISO begins deliberations onspecific protocols for each layer

1990U.S. mandates all gov.purchased computers must be GOSIPcompliant

1995GOSIP requirement rescinded


10/36


11/36

Layer 1 - Physical

Defines the physical, electrical/opticalspecifications for each network device

Pin layout

Voltages

Optical levels

Modulation scheme

Examples:

Ethernet, SONET, FDDI, IEEE 802.11

Layer 2Data Link Layer

Functions and procedures to

transmit/receive bits over the physical

media.

Media specific addressing

Physical media error

detection/recovery

Bridge, Hub, Switch equipment

Examples:

Ethernet CSMA/CD, HDLC, SDLC


12/36


13/36

Layer 5Session Layer

Control sessions between computers Establish, maintain, terminate

connections

Duplex operation (full or half)

Checkpointing and restart procedures

Layer 6Presentation Layer

Transforms data to/from a common

format

Encoding

Compression Encryption

Examples:

MIME, XML


14/36

Layer 7Application Layer

Program used to interact with computerand data

Specific application for each task

GUI or command line interface

Examples:

SSH, SCP, HTTP, email

OSI Quick Summary

OSI reference model defines modular

stack that allows multi-vendor

interoperations.

Input/output details specified

Internal details left up to individual

vendors

Usually implemented by a series of

function calls


15/36

TCP/P Internet

Direct descendant of ARPAnet

Provides Global packet switched network

services

Standard protocol shipped by most

vendors

Still under active development

IPv6

TCP modifications

TCP/IP Architecture

Copper, Fiber, Radio

Ethernet, Sonet, ATM

IP

TCP, UDP

Network

Based

Applications

L1

L2

L3

L4


16/36

TCP/IP Architecture

Copper, Fiber, Radio

Ethernet, Sonet, ATM

IP

TCP, UDP

Network

Based

Applications

L1

L2

L3

L4

TCP/IP Quick Summary

Grew out of ARPA funded research

program

Free wide spread deployment in BSD 4.2OS

TCP/IP protocols form the Internet


17/36

Architecture Comparison

Physical

Data Link

Network

Transport

Session

Presentation

Application

L1

L2

L3

L4

L5

L6

L7

Copper, Fiber,

Radio

Ethernet,

Sonet, ATM

IP

TCP, UDP

Network

Based

Applications

IP Protocol

IP is a connectionless datagram deliveryservice

Unreliable Delivery

No concept of order

No concept of loss

No concept of late

TTL field to Kill Off packets

Each packet treated separately

Operates over numerous data-link andphysical networks


18/36

IP Header Field

Fixed size header field (20 Bytes),Variable length options

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|Version| IHL | DSCP |ECN| Total Length |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Identification |Flags| Fragment Offset |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Time to Live | Protocol | Header Checksum |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Source Address |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Destination Address |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Options | Padding |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP Address

32 bit unsigned number

Network portion used for global routing

Host portion used to identify specific

host

Usually expressed in dot quad format

192.168.1.1 specifics specific host

192.168.1.0/24 specifies subnet of

hosts


19/36

What is a Network Address?

Convert the following to binary using 8 bitpositions:

00000010

00010000

00001111

10000000

11111111

11111110

01100011

00000000Cannot be done with 8 bits!

2

16

15

128

255

254

99

0300

What is a Network Address? (cont)

Rules for IP addresses:

32 bits

4 sections called octets

Dotted decimal format

Divided into a network portion and a host

portion

IP addresses range from 0 to 255

(128+64+32+16+8+4+2+1=255)

Network addresses may look like this to us . . .

128.32.15.22

. . . but they look like this to a computer:

10000000.0010000.00001111.00010110


20/36


128 64 32 16 8 4 2 1

I 0 0 0 0 0 0 0

128 64 32 16 8 4 2 10 0 0 I 0 I I 0

128 64 32 16 8 4 2 1

0 0 1 0 0 0 0 0

128 64 32 16 8 4 2 1

0 0 0 0 I I I I

128

32

15

22

128 + 0 = 128

32 + 0 = 32

8 + 4 + 2 + 1 = 15

16 + 4 + 2 = 22

Given the address of 128.32.15.22 . . . . .

This is why 128.32.15.22 = 10000000.00100000.00001111.00010110

Counting IP addresses

120.19.0.12

130.15.16.17

10.0.0.0

15.255.255.0

11.254.254.255

Note: Binary counting ALWAYS starts

with a 0, not a 1. Also, counting like

this does NOT apply to subnet masks

120.19.0.13

130.15.16.18

10.0.0.1

15.255.255.1

11.254.255.0

120.19.0.11

130.15.16.16

9.255.255.255

15.255.254.255

11.254.254.254


21/36

Network addresses are grouped into classes.

Class Network Range Binary Representation

Class A 0-127 00000000 - 01111111

Class B 128-191 10000000 - 10111111

Class C 192-224 11000000 - 11011111

1 byte 1 byte 1 byte 1 byte

(8 bits) (8 bits) (8 bits) (8 bits)

Class A Network Host Host Host

Class B Network Network Host Host

Class C Network Network Network Host

What class of address is 128.32.15.22?



Network addresses consist of two parts

Network address

Host or node address

Similar to an address for your home/business

Networks are like this; we have a few big cities

with lots of homes and lots of small cities with

few homes.

128.32.15.22Network Address Host Address

12050 Main StreetAnytown, MI 48300

Regional Address

Street Address


22/36


Within each class there are are two ranges of IP addresstypes (RFC 1918)

Public range

Allowed on the internetaddresses must be

registered

Private range

Not allowed on the internetunregisteredfor

private use only

Class Private IP Addresses (RFC 1918)

A 10.0.0.0 to 10.255.255.255

B 172.16.0.0 to 172.31.255.255

C 192.168.0.0 to 192.168.255.255

IP Version 4

209.46.18.19511010001.00101110.00010010.11000011

In common use today on the Internet and LANs. Packet

Header varies in size

Uses 32-bit address as shown above in blue or 2^32

When represented in decimal form, an IP address has four

numbers, one for each byte. This notation is dotted quad and

takes the form shown above in red. The decimal value of each

quad is between 0 and 255.

Certain address spaces are reserved for private and multicast

networks. These addresses can not be used on the Internet,

but can be used on LANs.

Private IP address spaceis most commonly used on LANs.

Private address space includes the following ranges.

10.0.0.0 to 10.255.255.255 Class A172.16.0.0 to 172.31.255.255 Class B

192.168.0.0 to 192.168.255.255 Class C


23/36

IPv6

bits 16 16 16 16 16 16 16 16 = 128

IPv62001:0db8:85a3:08d3:1319:8a2e:0370:7344

In limited use today, is likely to be in common use by the end of

the decade. Being tested on Internet II

Uses a 128-bitaddress, represented as a 32-digit hexadecimal

address. Normally written as eight groups of 4 hex digits as

shown above in red.

Will allow every network device in the world to have a unique

address.

Supported by modern operating systems.

Different IPv6 forms of expression

1080:0000:0000:0000:0000:7435:192.168.100.1

1080:0:0:0:0:7435:192.168.100.1

1080:0:7435:192.168.100.1

1080::7435:192.168.100.1

IP Version 6 The next generation of the IP protocol is IPv6. 2^128

340 undecillion or 340 trillion, trillion, trillion addresses

It uses a fixed packet header size of 40 bytes so thatinformation always appears in the same place.

Goals of IPv6

To provide for transition from IPv4

Simplify the header fields of IP

Provide for authentication and privacy

To expand routing capabilities

To expand addressing capabilities

To expand quality of service capabilities

To improve support for options


24/36

Subnet Mask

255.255.240.0

11111111.11111111.11110000.00000000

Like an IPv4 address, a 32-bit number.

Used with IPv4 addresses to logically segment networks.

A host uses its IP address and the subnet maskto

determine which addresses are on the local networkand

which are on remote networks.

Traffic destined for hosts on the local network is sent

directly to that host.

Traffic destined for remote networks is sent to the router.

Network Address Translation

Where onepublic IP address(one that

is unique to theInternet) is shared by

hosts on theprivate network.

Hosts on the Internet can not initiatecontact with a host on the private

network.

Hosts on the private network can initiate

contact with hosts on the Internet.

Once contact is established, bi-

directional communication is possible.


25/36

Address Assignment

Addresses mustbe unique to the network.

Two hosts on the Internet cannothave

the same IP address.

Two hosts on an organizations private

network cannothave the same IP

address.

Two hosts on different organizations

private networks canhave the same IP

address.

DHCP Address Assignment

Addresses can be assignedmanuallyor

dynamically.

DHCPis commonly used to assign

TCP/IP addresses automatically. Computer boots up and is assigned

TCP/IP configuration via network.

Addresses can be assigned on a first

come, first serve basis from a pool or

reserved on the basis of MAC

address.


26/36

Dynamic Host Configuration Protocol

(DHCP) Bootstrap Protocol (BOOTP)

DHCP assigns addresses from a poll, then removes it frompool

Host sends DHCPDISCOVER message on local IPsubnet to find the DHCP server, using IP broadcastaddress

DHCP server response with DHCPOFFER message

Host sends DHCPREQUEST message to identify theserver to be used

Server response with DHCPACK message with theassigned IP for client

Host sends on port 67 UDP Server sends on port 68 UDP

Address can be reserved for a specific MAC

DHCP Relay Agents can help cross subnets for server

Dynamic Host Configuration Protocol

(DHCP) Bootstrap Protocol (BOOTP)

Parameters a DHCP can automatically set

IP address

Subnet mask

Gateway (router) address DNS address

WINS address

Wins client mode

BOOTP diskless operating systems,

automatically configure host during bootup on a

TCP/IP network


27/36

DNS (Domain Name System)

Used to translate friendly names such as

www.emcp.com into IP Addresses such as

209.46.18.195.

DNS is distributed. No single server hosts all

DNS records.

Records are segmented intozones.A zone is a

common namespace.

DNS servers that host zones near the top of the

DNS hierarchy can refer requests to DNS

servers that host zone towards the bottom of

the DNS hierarchy.

DNS Addresses

DNS addresses, also known as Fully Qualified Domain

Name (FQDN), are a collection of zone information

proceeded by a host name.

Each element is separated by a period.

A DNS address is read from back to front or right to left.

au, edu, and unimelb are all separate zones, hosted on

separate DNS servers. Host name library is part of the

unimelb zone.

.auCountry Code

.edu.unimelblibrary

Top level

domain

Organization

domain name

Host name


28/36

Local DNS Servers

Almost all LANs have a local DNS server.

Clients on the LAN address all DNS requests to the local

DNS server.

The local DNS server either returns the answer to the

request from its own database, or it will query other DNS

servers to locate the answer.

In the past, DNS information was entered manuallyby

administrators.

Today, many DNS servers can be automatically updated,

so that hosts that have different IP addresses can be easily

contacted via DNS name.

DNS Resolution

DNS client host1.emcp.com queries its preferred DNS server.

The DNS server in turn queries a series of DNS servers,

beginning at the top of the DNS hierarchy until it returns a

result from the server that holds the zone that the target host islocated in.


29/36

CIDR Rules

IP address is ANDed with bit mask toextract network portion

Classless Inter-domain Routing (CIDR)

Specifies length of bit mask

Example 192.168.2.10/23

C0A8020A + FFFFFE00 = C0A80100

Range is 192.168.1.0192.168.2.255

First and last addresses in subnet are

reserved

Network Infrastructure

Switch1

Switch 2 Switch 3

R1

R3

R4

R2

R7

R6R9

R8

R5

Switch 4


30/36

IP Fragmentation

Routers may break packets into smallerchunks (fragmentation)

Destination host is responsible for

reassembling all fragments into original

packet

Performance impact on modern (ASICbased) routers

IP Dont Fragment

Flag in header to indicate that packet

should be discarded instead of

fragmented

Basis for Path MTU Discovery protocol

Find the largest packet that can transit

the entire end-to-end path

Router may return an ICMP error

message when it discards the packet

PMTU black holes can occur


31/36

TCP Protocol

TCP provides connection orientateddelivery service

Reliable Delivery

In-order guarantee

Loss detection and recovery

Flow control

Error detection

Hides network details fromapplications

TCP Header

Fixed size header field (20 Bytes),Variable length options

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Source Port | Destination Port |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Sequence Number |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Acknowledgment Number |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Data | |C|E|U|A|P|R|S|F| |

| Offset|Reserve|W|C|R|C|S|S|Y|I| Window |

| | |R|E|G|K|H|T|N|N| |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Checksum | Urgent Pointer |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Options | Padding |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


32/36


33/36

TCP Reno

Most common version of TCP today

Loss based detection to switch from

Slow Start to Congestion Avoidance flow

control

Transmit and Receive windows to

guarantee reliability

TCP modifications

Most changes to TCPs Congestion Avoidance

growth algorithm

Recognized that linear growth is not efficient

for Fast Long-Distance Paths

Delay Based

Detection

Vegas

Fast

Loss Based

Detection

Reno

High Speed

BIC, Cubic


34/36

UDP Protocol

UDPUser Datagram ProtocolApplication must provide

Reliability

Flow Control

Useful for short messages

DNS

Real Time audio/video

UDP Header

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Source Port | Destination Port |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Length | Checksum |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Data Octets

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


35/36

Real-time Transport Protocol

RTPReal-time Transport Protocol Carries data with real-time properties

Used for Audio and Video streams

Header contains sequence number

and timestamp to provide receiver with

pkt info

RTCPRTP Control Protocol Carries control information about the

stream from receiver back to sender

Unicast vs Multicast

Unicast packets - 1 source & 1 destination

Multicast packets

IP addresses (224.0.0.0239.255.255.255)

Single source, multiple receivers Multiple sources, multiple receivers

Routers and Switches must support multicastto prevent unwanted packets from floodingthe network

Multiple unicast streams can be used to emulatea multicast session


36/36

Multicast Traffic

Source starts sending packets using amulticast IP address

Local router/switch uses controlmessages to advertise traffics availability

Receivers send request-to-joinmessages

New path from receiver to merge pointis created and traffic flow begins

01.a. Networks - 01 Basics

Documents

Transcript of 01.a. Networks - 01 Basics