Transcript Networks and Stuff

Networks and Stuff
Networks and wiring ‘em
Networks
Connecting things together
 Can be:

– Computers
– Embedded devices
– Telephones
– Radios
– TV’s
– Anything!
Lots of different types
One directional or two directional
 Addressed or non-addressed
 broadcast/hubbed or switched or even

ringed!
Internetworked or not
 None of ‘em or all of ‘em!

Hubs or Switches
Linear: everything wired together in a
straight line.
 Hub: A box repeats the signal from one
computer or thingy to all the others
ones. “Star topology”. Cable TV.
 Switch: A box sends information from
one thingy to only the thingy that needs
to hear. “Switched star topology”.
Telephones.

Layers (Simplified!)
Physical Layer: thing over which
communication takes places. Wires,
radio, and so on.
 Transport Layer: way in which
information is transmitted
 Application Layer: thing we do with
network. Software we run, and so on.
 Pieces of net are called nodes.

Physical Layer

Lots of different ways to move signals
around
– Wires: few wires, lots of wires
– Fibre Optics
– Wireless: radio, space, lots of transmission
methods. Bluetooth, spread spectrum,
OFDM, and more!

Same physical layer can be used for
different types of networks
Transport Layer
Really a group of different layers
 Contains the main protocols: TCP/IP
(internet), ATM, WAP
 Where the information that we’re
moving around is described
 Can operate over many different
physical layers

Application Layer

Higher protocols that are specific to the
applications
– HTTP for web
– SMTP for mail
– Telnet for logins
Software that communicates over the
network
 Can work over different transport layers
and physical layers.

Addressing
Can say where the information comes from,
or, usually, where it’s going, or both.
 Can have lots of wires that send the
address, and more wires that send the data
-- computer bus. SCSI bus, GPIB bus
(science data), printers. FAST!
 Can have address and data sent in sequence
-- telephones, the internet, USB. Slower, but
wiring simpler. LOTS of addresses!

Packets, Frames, Cells, and all
that stuff
Often data is sent in pieces of information,
one “byte” after another.
 The pieces can contain addresses, followed
by information describing what kind of
communication is being used, and then the
data.
 Packets, Frames, and Cells are just different
ways of doing this.
 Ethernet and Internet based on packets.

Ethernet (IEEE 802.3)
Transport (actually, link) layer: very simple
packets with addresses based on 6 bytes of
data (note: Internet v4 has only 4!)
 In raw form, based on “carrier-sense multiple
access with collision detection”, CSMA/CD:
every computer hears every other one, and
waits for a quiet spot to send information.
 Basis for all modern networks.

Ethernet addresses
Byte has 8 “bits”, like digits. Number 0255. 100 = 0110 0100 = #64
(Hexadecimal!). 4 bits = nybble!
 #64 = 6*16 + 4 = 100. (52 = 5*10 + 2)
 0=#0, 1=#1, …. 10 =#A,
11=#B,….15=#F (= 1111 binary). #FF =
255 = 1111 1111
 All ethernet cards have a unique ethernet
address. 48 bits = 6 bytes.

A little more on Binary
Digits are 0 or 1
 Just like decimal has each digit worth
10 times the one to the right, binary
has each digit worth twice the value to
the right.
 So, 157 in decimal =
(1*10*10+5*10+7)
 1011 in binary =(1*8+0*4+1*2+1*1)
= 11 in decimal.

A little more
1101 0011 = “11” followed by “3”
 So, 1101 0011 = #B3 (#B=11)
 #B3 = 11*16 + 3*1 = 179 decimal
 In other words, each “hex” digit is 16
times the one to the left.

Physical Layer
Serial link: 100 = #64 = 0110 0100 = OFF ON
ON OFF OFF ON OFF OFF
 Only for Local Area Network
 Different forms
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– 10B5 or “Thick Ethernet” - 100 nodes per segment,
10Mbps
– 10B2 or “Thin Ethernet” - 30 nodes per segment,
10Mbps
– 10/100/1000 BT, twisted pair, 2 nodes, 10Mbps to
1Gbps
– 10/100/1000 BF, fibre optic
Ethernet Packets
Six bytes destination
 Six bytes source
 2 bytes type or length (for IEEE)
 46-1500 bytes data (“payload”)
 4 bytes checksum
 If checksum is wrong, throw away
packet

Not everything is IP
Windows networking
 Novell
 Apple networking
 A lot of the basic controlling protocols
(ARP, and more)

Not everything is ethernet
GPIB: science and medical
 SCSI: large disk storage
 Firewire and USB: simple networking,
nanosatellites!
 MIL-STD-1553B: jet fighters, the space
station!

Physics!!!
All wiring has noise
 Communication systems need a range
of electrical or radio frequencies to
transmit on: “bandwidth” (Hz, or cycles
per second)
 The bigger a bandwidth you need to
listen to, to communicate, the more
noise you pick up
 further you go, more noise you pick up

More physics

Eventually noise swamps signal
– Maximum length (10BaseT = 100m)
– Maximum data rate

Lower data rates go further
– 1000BaseT doesn’t go very far! T1
(1.5Mbps does)!

Fibre Optic, very low noise, goes far!
2km or more. Also high bandwidth, so
high data rate.
Project Groups

Groups sizes
– 1: 1: (IP number, security, interop)
– 2: 1 group: (WML)
– 3: 2 group: (Bluetooth), (WAP)
– 4: 1 (3/2): 3G network (compat/social?)
– 5: 1: environment and networks, space,
and all that stuff.