Transcript Week_2._Building_blocks

Layered Communication
Building Blocks: Hardware
Layers in LAN
Multi-layer Network Models
The process of transferring a message
between sender and receiver is more easily
implemented by breaking it down into
simpler components.
Instead of a single layer, a group of layers
are used, dividing up the tasks required for
network communications.
The best known network model is the OSI
models.
The OSI Networking Reference Model
OSI= Open Systems Interconnect. Created by the
International Standards Organization (ISO) in 1984
as a network standards framework.
The model’s seven layers from high to low are:







7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical
Application Layers
The application layers are the user’s
connection to the network and include the
application software and other software used
to connect the application to the network:



7. Application: provides a set of utilities
used by application programs.
6. Presentation: formats data for
presentation to the user, provides data
interfaces, data compression and translation
between different data formats.
5. Session: responsible for initiating,
maintaining and terminating each logical
session between sender and receiver.
Internetwork Layers
The internetwork layers connect
applications to the network and as well as
determine the best route for sending
messages between sender and receiver.


4. Transport: deals with end-to-end issues
such as segmenting the message for network
transport, and maintaining the logical
connections between sender and receiver.
3. Network: responsible for making routing
decisions.
Hardware Layers
The hardware layers move messages from
one computer or device to another.


2. Data Link: deals with message
delineation, error control and network
medium access control.
1. Physical: defines how individual bits are
formatted to be transmitted through the
network.
How the layers fit together in practice
Message Transmission Using Layers
Network model layers use protocols, i.e., sets of rules to
define how to communicate at each layer and how to
interface with adjacent layers.
Generally, outgoing messages travel down all network
layers.
Before sending a message to the next layer, each layer
places it in an envelope of overhead information related
to that layer (encapsulation).
At the receiving end, messages travels up through the
network layers, each layer removing the envelopes
added when the message was sent.
Message transmission using layers
Why Standards?
Standards provide a fixed way for hardware
and/or software systems to communicate.
For example, USB enables two pieces of
equipment to interface even though they are
manufactured by different companies.
By allowing hardware and software from
different companies to interconnect,
standards help promote competition.
Some Major Standards Making Bodies
ISO: International Organization for
Standardization (http://www.iso.ch)
ITU-T: International Telecommunications Union
—Telecom Group (http://www.itu.int)
ANSI: American National Standards Institute
(http://www.ansi.org)
IEEE: Institute of Electrical and Electronic
Engineers (http://standards.ieee.org)
IETF: Internet Engineering Task Force
(http://www.ietf.org)
Layers & Standards
Layer
Common Standards
5. Application layer
HTTP, HTML (Web)
MPEG, H.323 (audio/video)
IMAP, POP (e-mail)
4. Transport layer
TCP (Internet)
SPX (Novell LANs)
3. Network layer
IP (Internet)
IPX (Novell LANs)
2. Data link layer
Ethernet (LAN)
PPP (dial-up via modem)
1. Physical layer
RS-232c cable (LAN)
Category 5 twisted pair (LAN)
V.92 (56 kbps modem)
Topology
Topology refers to the geometric layout of
the network.
A logical topology is how the network
works conceptually
Physical topology refers to how the
network is physically connected.
Topology
Topology determines type of equipment to
purchase and how to manage network
When designing a network, you must
understand different topologies
Consider growth and security requirements
Good design grows and adapts as needs
change
Standard Topologies
Today’s network designs are based on three
topologies:



Bus consists of series of computers
connected along a single cable segment
Ring connects computers to form a loop
Star connects computers via central
connection point
Terminated Bus Network
Cable Break
Ring Network
Star Topology
Ethernet
Ethernet’s two forms, shared and switched
Ethernet, use bus and star logical topologies,
respectively.
Hub Operation
Ethernet Hub
Station A1-44-D5-1F-AA-4C
transmits a bit.
D4-47-55-C4-B6-9F
C3-2D-55-3B-A9-4F
A1-44-D5-1F-AA-4C
B2-CD-13-5B-E4-65
Hub Operation
Ethernet Hub
Hub broadcasts the bit
out all ports.
D4-47-55-C4-B6-9F
C3-2D-55-3B-A9-4F
A1-44-D5-1F-AA-4C
B2-CD-13-5B-E4-65
Switches
Networking devices that manage network
connections between any pair of star-wired
devices on a network
Does not broadcast; forwards the message
to the intended computer
Offer greater bandwidth (not shared)
Switch Operation
Ethernet Switch
Station A1-44-D5-1F-AA-4C
transmits a bit.
D4-47-55-C4-B6-9F
On Switch Port 13
A1-44-D5-1F-AA-4C
On Switch Port 10
C3-2D-55-3B-A9-4F
On Switch Port 13
B2-CD-13-5B-E4-65
On Switch Port 11
Switch Operation
Ethernet Switch
A switch sends a frame
out a single port—
the one to the receiver
D4-47-55-C4-B6-9F
On Switch Port 13
A1-44-D5-1F-AA-4C
On Switch Port 10
C3-2D-55-3B-A9-4F
On Switch Port 13
B2-CD-13-5B-E4-65
On Switch Port 11
Switch Operation with Multiple Simultaneous
Conversations
Ethernet Switch
Multiple simultaneous
conversations are
possible
D4-47-55-C4-B6-9F
On Switch Port 13
A1-44-D5-1F-AA-4C
On Switch Port 10
C3-2D-55-3B-A9-4F
On Switch Port 13
B2-CD-13-5B-E4-65
On Switch Port 11
Star Topology
Star (Modern Ethernet)
Switch
Only one possible
path between two
stations
Extended Star or Hierarchy
(Modern Ethernet)
Root
Switch
Switch
Switch
Mesh Topology
A
Path
ABD
B
C
D
Multiple alternative
paths between two
stations
Path
ACD
Network Interface Cards
Network interface cards, also called network
adapters
NICs are part of both the physical and data
link layer and include a unique data link layer
address (MAC address), placed in them by
their manufacturer.
Before sending data onto the network, the
network card also organizes data into frames
and then sends them out on the network.
Notebook computers often use NICs that are
plugged into the PCMCIA port.
NIC Allows the Computer and the
Network Cable to Communicate
Note: Gigabit Ethernet uses parallel transmission
Ethernet NIC
Cables
Each computer is physically connected to the
network using a cable.
The cables used on Ethernet LANs are either
twisted-pair or optical fiber cables.
Data can flow through cables in one of three
modes:
 One way only (simplex)
 Both ways, one way at a time (half-duplex)
 Both ways at the same time (full-duplex)
Simplex, half-duplex, and full-duplex transmissions
General Cable Characteristics
Bandwidth rating (Mbps)
Maximum segment length
Interference susceptibility: EMI
(electromagnetic interference), RFI (radio
frequency interference)
Connection hardware
Cable grade: cabling requirements for building
and fire codes
Bend radius
Material costs
Installation costs
Twisted-Pair Cable
TP is two or more pairs of insulated copper
wires twisted around each other



Improves resistance to interference
Limits crosstalk (EMI generated by wire pairs)
The more twists, the better
Two primary types of TP cable


Unshielded twisted-pair (UTP)
Shielded twisted pair (STP)
STP and UTP Cable
Ethernet Standards
Standardization

Institute of Electrical and Electronics
Engineering (IEEE)
 802 LAN/MAN Standards Committee (802
Committee) creates LAN standards
 802.3 Working Group creates Ethernet
standards
 So Ethernet standards are also known as
802.3 standards.
Ethernet Standards
Physical Layer Ethernet Standards Using UTP

802.3 10Base-T
 10 Mbps

802.3 100Base-TX
 100 Mbps
 10/100 operation thanks to auto-sensing

802.3 1000Base-T
 Gigabit Ethernet
Purchasing and Installing UTP
Wiring Quality Categories






Governed by the TIA/EIA-568 standard
Categories 3, 4, 5, 5e (enhanced), and 6
 Higher numbers indicate better quality
CAT 5e is recommended for new buildings
CAT 5—for 100Base-TX
CAT 5e—for 1000Base-TX (Gigabit Ethernet)
CAT 6—for 10 Gbs networks
Fiber-Optic Cable
Uses pulses of light rather than electrical
signals
Immune to interference; very secure;
eliminates electronic eavesdropping
Excellent for high-bandwidth, high-speed,
long-distance data transmissions
Slender cylinder of glass fiber called core
surrounded by cladding and outer sheath
Fiber-Optic Cable
Fiber-Optic Cable
Each core passes signals in only one
direction
Most fiber-optic cable has two strands in
separate cladding

May be enclosed within single sheath or
jacket or may be separate cables
More difficult to install and more expensive
than copper media
Fiber-Optic Cables
Two primary types:
 Single-mode cables: cost more; span longer

distances; work with laser-based emitters
Multimode cables: cost less; span shorter
distances; work with light-emitting diodes
(LEDs)
Used for network backbone connections and
with long-haul communications carrying large
amounts of voice and data traffic
Full-Duplex Optical Fiber Cord
Fiber Cord
Switch
Fiber Cord
Router
A pair of fibers is needed for
full-duplex (simultaneous 2-way) transmission.
Each fiber carries a signal in only one direction.
Optical Fiber Cabling
Two fiber cords for
full-duplex (twoway) transmission
ST
Connectors
(Popular)
SC
Connectors
(Recommended)
Summary
Layered communication: OSI model
LAN topologies
Network interface cards
Cable characteristics
Ethernet standard: 802.3
Twisted pair
Fiber optic