Transcript CSCI3421_Ch1x

Chapter 1
Computer Networks and the Internet
Tami Meredith
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Hosts (a.k.a. End Systems): Various end user
devices, e.g., computer, cell phone, ipad
Communications Links: Connectors such as
copper wire, fibre optics, coaxial cable
Packet Switches: Routers or Link-Layer
Switches (for network access points)
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Transmission Rate: number of bits / second that
are communicated
Packets: discrete "segments" of data along with
transmission control data (e.g., packet header)
ISP: Internet Service Provider – Internet access
provider
RFC: Request For Comments – IETF (Internet
Engineering Task Force) standards for protocols
and network design
API: Application Programming Interface – Set of
procedures to link (interface) to some other system
(i.e., the Internet)
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A protocol defines the format and order of
messages exchanged between two or more
communicating entities as wall as the actions
taken on the transmission and/or receipt of a
message or other event
A system of (digital) message formats and the
rules for exchanging those messages between
(2) communicating entities
The syntax, semantics, and synchronisation of
communication
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Termination points for a network
May or may not interact with a human (e.g.,
may activate hardware)
Traditionally, some kind of computer
Two categories of hosts: Clients and Servers
Now more varied: Cell phones, video game
consoles, televisions, picture frames,
appliances, cameras, GPS devices, biomedical
sensors
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DSL: Digital Subscriber Line – Telco provided
frequency based communication to a DSLAM
(Digital Subscribe Line Access Multiplexer)
Cable: Cable TV provided HFC (Hybrid Fibre
and Coaxial) communication to a CMTS (Cable
Modem Termination System)
FTTH (Fibre to the Home) – Fibre optic
connection based on either active or passive
optical networks (type of router – powered vs.
unpowered)
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Local
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Ethernet
WiFi (Wireless Access – IEEE 802.11)
Wide Area
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3G (Cellular 3rd Generation)
LTE – Cellular Long Term Evolution
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Twisted Pair Copper – Shielded or Unshielded
Coaxial – concentric copper wires
Fibre Optic
Radio
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Terrestrial: Short, Medium, Long distance
Satellite: Geostationary or LEO (Low Earth Orbit)
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Ignore the content of the data
Break into small uniform pieces
Send pieces separately and then reassemble data at the
other end
Pieces may get lost, go different routes, get garbled,
possibly duplicated
Store and Forward: Receive a packet in its entirety
before forwarding it to the next destination
Queuing Delay: Time spent after reception while
sitting in switches output queue before forwarding
Packet Loss: Discarded packets when buffers full
Forwarding Table: Map that determines which output
link to use for specific address ranges
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Circuit Switching: Connection Oriented
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FDM – Frequency Division Multiplexing
TDM – Time Division Multiplexing
Packet Switching: Connectionless
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More efficient, faster
Becoming most prevalent
More difficult to ensure specific QoS (Quality of
Service)
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A "network of networks"
Network Structure 5
Access ISPs, e.g., Eastlink
2. Regional ISPs, e.g., Rogers
3. Tier 1 ISPs, e.g., AT&T, Sprint
4. IXPs, Internet Exchange Points – 3rd Party ISP
connectors
5. Content Providers – e.g., Google, Amazon
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Processing Delay: Forming packet, adding header,
putting into output queue
 Queuing Delay: Sitting in the output queue
 Transmission Delay: Putting the packet onto the
access medium
 Propagation Delay: Time to get to the destination
 End-to-End Delay: (Latency, Ping Time), sum of all
delays from source to destination
Run traceroute and ping to explore delay
Other delay can occur (e.g., SMTP congestion control)
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Size of Transmission / Time to Receive
Measured in bits/second
Also known as the data transfer rate
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Instantaneous: Current rate at which data is being
received
Average throughput: Overall (averaged) rate at
which data is being received
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Graph-based model for the network topology
Typically a layered model within the hardware
(i.e., end systems, routers)
Service oriented: Each layer provides specific
services
Layers spread across applications, O/S,
hardware
Layers are ideally independent, but this tends
to lead to redundancy
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Application: HTTP, SMTP, FTP
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Presentation – encryption, compression
Session – data delimitation and synchronisation
Transport: TCP, UDP
Network: IP
Link: Ethernet, WiFi, DOCSIS
Physical: Hardware dependent
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Application: message to another application
Transport: segments of the message
Network: datagrams (packets) of the segment
Link: frames of the packet
Physical: bits of the frame
At each layer, we have two fields:
A. Header: administrative information
B. Payload: the data
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Botnet – Network of cooperating (hijacked) hosts
Viruses – require user interaction
Worms – require no interaction
Trojans – look like something else (IP Spoofing)
DoS ( Denial of Service)
Vulnerability Attack
 Bandwidth Flooding
 Connection Flooding
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Packet Sniffing – reading data not addressed to
you
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1961-1972: Independent research on packet
switching
1967: ARPAnet plan produced
1969: UCLA, SRI (Stanford), UCSB, U.of Utah
linked with packet switches
TCP/IP developed in the 70s and used to link
multiple independent networks
Addition of new application layers over time:
HTTP/HTML, Facebook
Services now include processing (i.e., Google’s
Appengine) and storage (i.e., AWS cloud).