This document provides an overview of computer networks, including different topologies for high-speed switching fabrics, common transmission mediums like twisted pair, fiber optics, radio, and Ethernet coax. It also reviews concepts like logarithms, channel capacity, the Hartley-Shannon law, and the seven layers of the OSI model from the physical layer to the application layer. Key networking technologies and protocols are defined at each layer of the OSI model.

1. NETWORKS
• Covering
– High speed switching fabrics
– Twisted pair
– Mediums
– Fiber optics
– Radio
– Ethernet Coax

2. NETWORKS
– Logarithms
– Channel capacity
– Hartley-Shannon Law
– Review of the Layers
– Things you need to get started on a LAN

3. High Speed Switching
Fabrics
• Aside from the Bus topologies,
there are many others, with higher
throughput, like
• ring
• Transputer Topology
• Torus Topology
• Cray T3D

4. The Transputer
Topology
4 way connectivity

5. The Torus Topology
4 way connectivity

6. Torus Topology
5 way connectivity

7. Cray T3D, Torus
Topology
6 way connectivity

8. Diagram of a typical packet radio setup
TNC
Mac
ASYNC SYNC Modem Radio
Serial Serial
CPU
Memory
We left out the redundant curcuitry in the
gray box to make poor mans packet

9. Twisted Pair
• Typically a balanced digital line
• 2 conductor insulated wire
• Twisting the wire minimizes the
electromagnetic interference
• A primary medium for voice traffic
• used as serial cable to hookup
networks

10. Twisted Pair
• The repeat coil (transformer) or
Op-Amp can be used
S+I
S
+ S+I-(-S+I)=2S
-
-S
-S+I
I

11. Twisted Pair
• In telephone modem terms this is
known as a DAA (Data Access
Arrangement).

12. Mediums
• UTP (unshielded twisted pair)
– typical voice line
– Generally good for star LAN short haul 10
Mbps
• STP (shielded twisted pair)
– level 5 data grade (100 Mbps)
• RS-422
– balanced serial data communications
• RS-232
– unbalanced serial data communications

13. Mediums
• Coax
– CATV (community antenna TV)
– telephone long line via FDM carries 10,000
voices
– LAN-WAN
– cable TV

14. Mediums
• Fiber Optics
– use total internal reflection
– This occurs in a transparent medium
whose index of refraction is higher that
surrounding medium
– optic fiber is a wave guide in the
10 raised 14 to 10 raised 15 hz range

15. Fiber Optics
• multimode
– different rays have different path lengths,
loss occurs
• multimode-graded index
– variable core index, focuses rays more
efficiently that multimode
• single mode
– only the axial ray passes, most efficient.

16. Fiber Optics
• LED (light emmiting diode)
– inexpensive
• ILD (injection laser diode )
– more expensive (more efficient and higher
bandwidth that LED).
• Detectors
– Photo Diodes

17. Fiber Optics
• light propagates best at 850, 1300
and 1500 nm
• 640 nm = wavelength of HE-NE
red = .64 micro meters
• ultra pure fused silica is best,
plastic is cheapest and worst

18. Fiber Optics
– bandwidth - 2 Gbps (typical)
– smaller size and weight than copper
– lower attenuation than coax
– electromagnetically isolated
– greater repeater spacing, 5 Gbs over 111
km w/o repeater
– phasing out cable. core, one or more strands
cladding, one for each fiber
Jacket

19. Radio
• Microwave
– line-of-sight
– parabolic dish
d = 7.14 kh = distance to horizon
d in meters
h = height of antenna in meters
k = adjustment factor, microwaves bend with the curature of the earth

20. Ethernet Coax
• For Ethernet coax
– ASIC’s which give a digital interface to a
bus topology LAN
– For example, the Crystal Semiconductor
Corporation CS83C92 is a Coaxial
Transceiver Interface on a chip

21. Ethernet Coax
CS83C92
TX-
GND TX+
TXO CD-
CDS CD+
RXI RX-
RX+
Shi el d

22. Ethernet Coax
• CS83C92
– Balanced serial inputs
– Uses Manchester codes
– All operations with IEEE 802.3 of the
10Base5 (Ethernet) and 10Base2
(Cheapernet) standard

23. Ethernet Coax
• CS83C92 have
– equalizers
– amplifiers
– idle detectors, receiver squelch circuits
– collision testers
– oscillators
– differential line drivers
– (with other stuff too!!!)
• A manchester code convert chip
is also needed

24. Logarithms
• Log Review
if x = a y then y = log a x
so
if x = 210 then 10 = log 2 x

25. Logarithms
• For example
find log 2 4096
4096 = 2 y
ln 4096 = y ln 2
ln 4096
= y = 12
ln 2

26. Logarithms
so
ln x
log 2 x =
ln 2
if base = B then
ln x log10 x
log B x = =
ln B log10 B

27. Logarithms
• Laws of Logarithms
log a (xy) = log a x + log a y
log a (x / y) = log a x − log a y
log a x n = n log a x

28. • Intermodulation noise
– results when signals at different
frequencies share the same transmission
medium

29. • the effect is to create harmonic
interface at
f 1 + f 2 and / or f 1 − f 2
f 1 = frequency of signal 1
f 2 = frequency of signal 2

30. • cause
– transmitter, receiver of intervening
transmission system nonlinearity

31. • Crosstalk
– an unwanted coupling between signal
paths. i.e hearing another conversation on
the phone
• Cause
– electrical coupling

32. • Impluse noise
– spikes, irregular pulses
• Cause
– lightning can severely alter data

33. Channel Capacity
• Channel Capacity
– transmission data rate of a channel (bps)
• Bandwidth
– bandwidth of the transmitted signal (Hz)
• Noise
– average noise over the channel
• Error rate
– symbol alteration rate. i.e. 1-> 0

34. Channel Capacity
• if channel is noise free and of
bandwidth W, then maximum rate
of signal transmission is 2W
• This is due to intersymbol
interface

35. Channel Capacity
• Example
w=3100 Hz
C=capacity of the channel
c=2W=6200 bps (for binary transmission)
C = 2Wlog 2 m
m = # of discrete symbols

36. Channel Capacity
• doubling bandwidth doubles the
data rate
if m=8
c = 2(3100 hz)log 2 8 = 18, 600 bps

37. Channel Capacity
• doubling the number of bits per
symbol also doubles the data rate
(assuming an error free channel)
(S/N):-signal to noise ratio
signal power
(S / N)dB = 10log
noise power

38. Hartley-Shannon Law
• Due to information theory
developed by C.E. Shannon (1948)
C:- max channel capacity in bits/second
S
C = w log2 (1 + )
N
w:= channel bandwidth in Hz

39. Hartley-Shannon Law
• Example
W=3,100 Hz for voice grade telco lines
S/N = 30 dB (typically)
Ps
30 dB = 10 log
Pn

40. Hartley-Shannon Law
Ps
3 = log
Pn
Ps
log10 =3
Pn
Ps
10 3 = = 1000
Pn
C = 3100 log 2 (1 + 1000) = 30,898 bps

41. Hartley-Shannon Law
• Represents the theoretical
maximum that can be achieved
• They assume that we have AWGN
on a channel

42. Hartley-Shannon Law
C/W = efficiency of channel utilization
bps/Hz
Let R= bit rate of transmission
1 watt = 1 J / sec
Eb =enengy per bit in a signal

43. Hartley-Shannon Law
S = signal power (watts)
T b = the time required to send a bit
1
R=
Tb
Eb = ST b
Eb
= energy per noise power density per hertz
N0

44. Hartley-Shannon Law
Eb S / R S
= =
N0 N0 kTR
k=boltzman’s constant
by
Eb = ST b
Eb
S= ∴S / R = Eb
Tb
N0 = kTR

45. Hartley-Shannon Law
assuming R=W=bandwidth in Hz
In Decibel Notation:
Eb
= S −10 log R + 228. 6dbW − 10 logT
N0

46. Hartley-Shannon Law
S=signal power
R= transmission rate and -10logk=228.6
So, bit rate error (BER) for digital data
Eb
is a decreasing function of
N0
Eb
For a given N0 , S must increase
if R increases

47. Hartley-Shannon Law
• Example
For binary phase-shift keying
Eb
=8.4 dB is needed for a bit error rate
N0
of 10 −4
let T= k = noise temperature = C,
R=2400 bps & Pe = 10 −4 = BER

48. Hartley-Shannon Law
• Find S
Eb
−S = − −10 log R + 228. 6dbW − 10log T
N0
−S = −8. 4 − 10 log2400 + 228.6dbW −10 log 290
S=-161.8 dbw

49. ADC’s
• typically are related at a
convention rate, the number of
bits (n) and an accuracy (+- flsb)
• for example
– an 8 bit adc may be related to +- 1/2 lsb
• In general an n bit ADC is related
to +- 1/2 lsb

50. ADC’s
• The SNR in (dB) is therefore
S
SNRdB = 10 log10
N
where
S = 2n
1 −n −n −1
N = 2 =2
2
2n+1
SNRdB = 10 log10 2 = (20n +10)log10 2
about SNRdB = 6n + 3

51. Review of the Layers
• Physical Layer (bits)
• The Link Layer (frames)
• The Network Layer (packets)
• The Transport Layer
• Session Layer
• The Presentation Layer
• The Application Layer

52. Physical Layer
• The function is to send & receive
bits (marks & spaces)
• deals with
– Physical connections (duplex or half
duplex)
– Physical service data units (PSDU’s) one
bit in serial xmission, nbits in parallel
xmission

53. Physical Layer
– circuit identification
– bit sequencing
– notification of false conditions
– deriving quality of service parameters
– modulation and demodulation
– signaling speed

54. Physical Layer
– transmission of data and handshaking
signals
– characterization of communication media
– maintains an actual electrical connection
with its peers. Other layers uses virtual
connections

55. The Link Layer
• The Link Layer of data link control
arranges the bits into frames
• Most common protocol is ISO
high-level Data Link Control
Procedures (ISO 3309)

56. The Link Layer
• This layer
– Establishes and releases one or more link
connections
– exchanges data-link service data units
(DLSDUs)-frames
– identifies end-points
– keeps DLSDUs / frames in proper
sequence

57. The Link Layer
– notifies the network layer when errors are
detected
– controls data flow
– selects optional qualityof service
parameters

58. The Network Layer
• Arranges data into packets
– Adds the network information to the
frames to form packets
• SLIP
– Serial Line Internet Protocol is network
layer protocol
– uses the EIA-232 Physical layer
– Internet protocol is a network layer
protocol

59. The Network Layer
– keep track of the network node address
while routing outgoing packets and
recognizing packets that are intended for
the local node

60. The Network Layer
• ARP
– Address Resolution Protocol provides
addresses form required by IP
– User may specify the datagram route
– APR will stay aware of manually generated
routing tables for the datagram routing
function

61. The Network Layer
•in CCITT x.25 protocol the network layer
is called the packet layer.

62. The Network Layer
• The function provided by the
network layer are
– network addressing and identifiers
– network connections and release
– transmission of network service data units
NSDU’s (packets)
– quality of service parameters

63. The Network Layer
– notifies the transport layer of errors
– flow control
– expedited service network
– may provide sequenced delivery

64. The Network Layer
• Two types of network layer
protocols
– connection oriented
– connectionless

65. Connection Protocol
• set up a virtual circuit (VC)
between two end points
• Advantage is that since each
packet does not contain complete
addressing information, the
overhead is lower

66. Connectionless
Protocol
• Uses a datagram (DG) which
contains complete addressing
information in each packet so that
it can use any variable route
through the network

67. Connectionless
Protocol
• The advantage is that packets
may freely choose the best
available routes for the transfer
rather than being stuck on a VC
with variable quality

68. The Transport Layer
• uses transport protocol data units
(TPDU)
• TPDU = packets + transport layer
data
• TCP = transmission control
protocol

69. The Transport Layer
• This layer ensures that
– all data send is received completely
– is sequenced
– transmission of TPDU messages
– multiplexing and demultiplexing to share a
net connection between two or more Xport
connections

70. The Transport Layer
– error detection
– error recovery
– connection establishment
– data xfer
– release of connections

71. The Transport Layer
• CCITT transport protocol in X.224
says there are 5 classes of
transport classes
– 0. simple class
– 1. error recovery
– 2. multiplexing
– 3. error recovery and multiplexing
– 4. error detection and recovery class

72. The Transport Layer
• The amount of work done is
dependent on the protocol (VC or
datagram) used at the network
layer

73. The Transport Layer
• Datagrams may arrive out of
sequence, in a connectionless
net, and buffers may be needed to
resequence
• connection nets allow a leaner
transport layer

74. Session Layer
• Organizes data into SPDU
(session protocol data units)

75. Session Layer
• This layer does
– dialog management
– Data flow control
– mapping address with name (domain name
service)
– graceful or abrupt disconnection
– buffering data until delivery time

76. Session Layer
• has phases of service
– connection establishment
– data xfer
– connection release

77. Presentation Layer
• responsible for the terminal
management
• Performs
– transfer of syntax for character sets, text
strings data display format, graphics file
organization and data types

78. Presentation Layer
– data encoding, decoding and compacting
– interpret character sets ( i.e. ASCII)
– code conversion

79. Application Layer
• The only layer which does not
interface with a higher one
• It does
– log in identification of communication
partners
– password checking and authority to
communicate

80. Application Layer
– determine adequacy of resources
– determine acceptable quality of service
– synchronization of application programs
– selecting the dialog procedures
– agreement on error-recovery responsibility
– procedures for control of data integrity
– identifying data syntax constraints

81. Application Layer
• has 5 groups
– 1. System management protocols
– 2. Application management protocols
– 3. System protocols
– 4. Industry specific protocols
– 5. Enterprise protocols

82. Things you need to get
started on a LAN
• IP ADDRESS
– this a 32 bit number issued by your local IP
coordinator
– it is expressed as 4 numbers separated by
periods
– looks like 44.112.0.200.

83. Things you need to get
started on a LAN
• HOST TABLE
– A file that list all the folks around you that
also have IP addresses
– It must have your IP address and
hostname (call sign) at least

84. Things you need to get
started on a LAN
• HOST TABLE
– you can get this from your coordinator
– It looks like this
44.112.0.1 unix.n3cv1
44.112.0.2 w3vc
44.112.0.3 darth.wa3yoa