Chi So
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Network – a set of devices, software, and
cables that enables the exchange of
information between them
Host Device – anything a person uses to
access the network
Network Device – hubs, repeaters, bridges,
switches, routes, and firewalls
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Point-to-Point – involves two hosts or
devices that are directly connected to each
other and to nothing else.
 i.e. Serial Communication (not always)
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Star – one host or device has multiple
connections to other hosts. Sometimes called
hub-and-spoke.
 Anything that sends traffic through the hub or
central device
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Ring – when one device is connected to the
next one sequentially. The last device is
connected to the first.
 Not always a true circle
 Data moves in a logical circle
 i.e. FDDI and Token Ring
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Bus – a single coaxial cable where hosts are
attached at intervals.
 i.e. cable internet
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Mesh – multiple point-to-point connections
that connect each location to the others
 Full Mesh – all devices are interconnected
 Partial Mesh – some devices are interconnected
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Ethernet is the most common LAN (Local
Area Network) technology
IEEE 802.3
Developed by Digital Equipment Corp., Intel,
and Xerox. Published in 1980
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Segment – A coaxial cable that joins all the
hosts together
Collision – when two hosts try to use the
connection at the same time
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Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) – method for Ethernet
to detect collusions.
 Listen to the line
▪ If clear, start transmission
▪ If used, wait until clear
 If collision occurs
▪ send jam signal
▪ Stop transmission
▪ Wait a random time before sending again (all hosts)
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Collision domain – a group of devices that
are affected by one another’s collusions
 The more hosts in a domain, the more frequent
the collision
 Bridges and switches help resolve this issue
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Half Duplex – Send or receive
Full Duplex – Send and Receive
 8 wires needed. 4 is possible
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Wide Area Network (WAN)
 Interconnect two or more LANs
 Usually this service is bought from another
company
 4 types of WAN technologies
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Dedicated Lease Line
Circuit-Switched Connections
Packet-Switched Connections
Cell-Switched Connections
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Dedicated Leased Line
 A connection that is installed and provisioned for the
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exclusive use of the customer
No other customer can affect the line
Very expensive
A lot of control (QoS, other traffic management)
Usually point to point
Protocols used
▪ Point-to-Point Protocol (PPP)
▪ High-Level Data-Link Control Protcol (HDLC)
▪ Serial Line Internet Protocol (SLIP)
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Circuit-Switched Connections
 Uses the phone company as a service provider
▪ Analog dial-up or digital ISDN connections
▪ Protocols used
▪ PPP
▪ HDLC
▪ SLIP
▪ Really slow, 19.2Kbit to 128Kbit
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Packet-Switched Connections
 Connect to the providers network
 Traffic is affected by others
 Usual technologies are
▪ Frame Relay
▪ X.25 (possible)
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Cell-Switched Connections
 Similar to packet switched
 Difference is the unit size of the data is fixed (cell)
▪ In packet switched networks, data units are called
(frames)
 Dealing with traffic loads are typically easier and
efficient
 Examples
▪ Asynchronous Transfer Mode (ATM)
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IEEE 802.11
 Advantage: Great to eliminate cables and
freedom of movement
 Disadvantage: range (?), reliability, security
 Moderate WAN distances
▪ Line of sight
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Metropolitan Area Network (MAN)
 Found in urban business centers
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Storage Area Network (SAN)
 Access an external storage array as a hard drive
 Expensive
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Content Networks
 Making access to the information faster
 Logging and controlling access to certain kinds of
materials
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Open Systems Interconnection (OSI) model
 Used to standardized networking processes
 No rules imposed onto the manufacturers or
protocol developers
 Only guidelines
 7 Layers
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7 - Application
6 - Presentation
5 - Session
4 - Transport
3 - Network
2 - Data Link
1 - Physical
Any application or utility that store, send or retrieve data
across a network
 Sometimes called the user interface layer
 Examples
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Hypertext Transfer Protocol (HTTP)
File Transfer Protocol (FTP)
Simple Mail Transfer Protocol (SMTP)
Post Office Protocol v3 (POP3)
Network Time Protocol (NTP)
Simple Network Management Protocol (SNMP)
Domain Name Systems (DNS)
Dynamic Host Configuration Protocol (DHCP)
Secure Shell (SSH)
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Responsible for formatting data so that the
application layer (layer 7) can recognize and
work with it.
Examples
 .doc
 .jpg
 .txt
 .avi
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Deals with initiating and terminating network
connections
Provides instructions to
 Connect
 Authenticate (optional)
 Disconnect
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Movement of data is handled by lower layers
Examples
 Login for Telnet, SSH, SQL sessions, RPC
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One of the most important layers
Deals with how two hosts are going to send
data. Two methods:
 Connection-oriented (TCP)
▪ Reliable
 Connectionless (UDP)
▪ Unreliable
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Deals with logical address (usually IP address)
 Other possibilities
▪ IPX
▪ AppleTalk
▪ SNA
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Addresses are assigned in software
IP hosts can communicate if they are on the
same network
 If different networks, need a router to communicate
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Finding a way to communicate between two
networks is call path determination
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With the data unit from Layer 4, the data
segment is now called a packet ( or
datagram)
Header has the following info:
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Since using logical addressing
 Hierarchical
▪ Organized into a formal or ranked order
▪ Easy to build a big system
▪ Build smaller systems, and put them together
▪ Example:
▪ Mailing address
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Protocols:
 Internet Protocol (IP)
 IPX (Novell Netware)
 Internet Connection Management Protocol
(ICMP)
 OSPF, IGRP, EIGRP, RIP, ISIS (Routing Protocols)
 Address Resolution Protocol (ARP), Reverse ARP
(RARP)
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Takes the Layer 3 packet and preparing a
frame for the packet to be transmitted
Examples:
 Ethernet
 Frame Relay
 Point-to-Point (PPP)
 High-Level Data Link Control Protocol (HDLC)
 Cisco Discovery Protocol (CDP)
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Not hierarchical
 Flat addressing
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Address are done with Media Access Control
(MAC)
MAC addresses are assigned in hardware
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Transmit the data onto a wire, optical fiber, or
wireless
All signaling is digital
Electricity On = 1
Electricity Off = 0
Typically RJ-45