Intro to Computer Communications
TCP/IP Model
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Application
- Message
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Transport
- Segment
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Network
- Datagram
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Link
- Frame
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Physical
OSI Model takes the Application layer and splits it to 3 different “layers”:
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Application
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Presentation
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Session
8 Bits = 1 Byte
IPv4:
* 32 bit address = 4 bytes
* 8 bits.8 bits.8 bits.8 bits In binary
* Each section can get values from 0-255 = 256 total values
* Network Address = set all host bits to 0
* Broadcast address = set all host bits to 1
* number of available host addresses - need to subtract 2 from # of available addresses (cause of net address and broadcast address)
Packet transmission delay: L (bits) / R (bits/sec)
Propagation delay:
* d(length of physical link)/s (prop speed)
* Often times use speed of light 3*10^8 for fiber
* For copper use 2 * 10^8
* Still quite fast but will never get to speed of light
ARP:
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Send a request via MAC to broadcast and ask for someone’s IP
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MAC broadcast is all bits set to 1, which in HEX will result in an address with lot of F’s
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It is a layer 2-ish protocol
TTL:
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time to live - 1 byte - so can be from 0 to 255
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Measured in hops not seconds or any other time unit
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Start with X for TTL, Every router we pass, TTL = TTL-1
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Once we get to 0, packet gets dropped and often we get an ICMP response telling us that happened
TCP:
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NO BROADCAST EXISTS HERE
- As we need a destination port and 3 way handshake with someone
TCP Socket:
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Needs all 4 of these: SRC IP, SRC PORT, DEST IP, DEST PORT
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Socket is two-way like a pipe with opening on both sides (src - dest)
Broadcast packet never gets past the router (gets dropped), otherwise many more computers than anticipated will get these packets
Switch - Internal to a network
Forwarding table - Where to send packet to
Router:
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Sits between your network and the internet (more or less)
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Converts your internal IP to a public one via Network Address Translation
ICMP:
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Wrapped in an IP packet
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If it is an error report, you will get IP header - ICMP header - IP header
- 2nd ip header is a minimum of first 8 bytes of the packet that caused the error
- Can and may be more bytes of previous packet
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Layer 3ish protocol
Helpful Links
https://gaia.cs.umass.edu/kurose_ross/interactive/ (practice quizzes)
https://www2.ic.uff.br/~michael/kr1999/1-introduction/1_06-delay.htm