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8/12/2019 01.a. Networks - 01 Basics
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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
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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
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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.
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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.
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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.
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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.
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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What is a Network Address? (cont)
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
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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?
What is a Network Address? (cont)
What is a Network Address? (cont)
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
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What is a Network Address? (cont)
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
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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
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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.
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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.
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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
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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
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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.
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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
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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
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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
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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