Download Chapter 11

CIS 212
Microcomputer
Architecture
Day 22
Rhys Eric Rosholt
Office:
Office Phone:
Web Site:
Email Address:
Gillet Hall - Room 304
718-960-8663
http://comet.lehman.cuny.edu/rosholt/
rhys.rosholt @ lehman.cuny.edu
Chapter 9
Computer Networks
Chapter 9
Computer Networks
Chapter Outline
Network Topology
Addressing and Routing
Media Access Control
Network Hardware
OSI Network Layers
TCP/IP
Focus – Voice over IP
Network Standards
Focus - Ethernet
Focus - Upgrading Network Capacity (Part II)
Chapter Goals
• Compare and contrast bus, ring, and star
network topologies
• Describe packet routing across local and
wide area networks
• Describe the CSMA/CD media access control
protocol
• Describe network hardware devices, including
network interface units, routers, and
switches
• Describe the OSI network model, the
TCP/IP protocol suite, and IEEE network
standards
Chapter 9
Computer Networks
Network Topology
• Spatial organization of network devices,
physical routing of network cabling, and flow
of messages from one network node to
another
• Can be physical or logical
• Three types – star, bus, ring –
differentiated by
– Length and routing of network cable
– Type of node connections
– Data transfer performance
– Susceptibility of network to failure
Point-to-Point Network Topology
Impractical for all but very small networks
Point-to-Point Network Topology
Impractical for all but very small networks
Point-to-Point Network Topology
Impractical for all but very small networks
Advanced Network Topologies
Improve practicality for most networks
Store and Forward System
Centralizes the work of networking
Network Topologies
• Uses a central node to which all end nodes
Star
are connected
• Relatively simple wiring
• Connects each end node to a common
transmission line
Bus
• Relatively simple wiring
• Low susceptibility to failure
• Connects each end node to two other end
nodes
• Long maximum network length
Ring • Low susceptibility to noise and distortion
• Susceptible to failure and difficulty in
adding, removing, or moving nodes
Star Topology
Uses a central node
to which all end nodes
are connected
Relatively
simple
wiring
Bus Topology
Connects each
end node
to a common
transmission
line
Low
susceptibility
to failure
Relatively
simple
wiring
Ring Topology
Connects each
end node
to two other
end nodes
Low susceptibility
to noise
and distortion
Long maximum
network length
Susceptible to failure
and difficulty in
adding, removing, or
moving nodes
Physical Star / Logical Bus
Topology
The strengths of two different topologies can be combined
by using one topology for physical layout
and another for message routing.
Addressing and Routing
• How messages sent by end nodes find their
way through transmission lines and central
nodes to their ultimate destination
• Local area networks (LANs)
– Interconnected to form WANs
• Wide area networks (WANs)
Local Area Network Routing
• Each central node maintains and uses a
routing table to make routing decisions
• LAN hub or switch usually handles packet
routing
• Logical network topology determines exact
procedure for routing a message between
two end nodes in the same LAN
Example
of a
WAN
Includes
• end nodes
• LANs
• zone
networks
• backbone
network
• central
nodes
LAN Central Node
Routing Decisions
Wide Area Network Routing
• Packet routing uses a store and forward
approach
• Forwarding stations can be implemented using
– Bridges
– Routers
– Switches
Media Access Control
• Uses a protocol that specifies rules for
accessing a shared transmission medium
– Carrier Sense Multiple Access/Collision
Detection (CSMA/CD)
• Commonly used in bus networks to
detect and recover from collisions
– Token passing MAC protocol
• Used by ring network topologies
CSMA/CD Protocol
• Process
– Listen and wait for an idle state
– Transmit a packet
– Listen for a collision
– If a collision is detected
• First wait for a random period of time
• Then retransmit the same packet
• Primary Advantage
– Simplicity
• Primary Disadvantage
– Potentially inefficient use of data transfer
capacity
Token Passing MAC Protocol
• Token passes from node to node
– in a predetermined order
• includes all nodes on network
– in a specified time interval
• Only the node that “possesses” the token is
allowed to transmit messages
– All others can only receive and repeat
messages
• No longer used in LANs; rarely in WANs
Effect of CSMA/CD Protocol
on Network Throughput
Network Hardware Devices
Network Interface Units
(NIUs)
• Interface between network node and network
transmission medium
• Scan destination address of all packets
– In bus network
• ignores packets not addressed to it
– In ring network
• retransmits all packets not addressed to it
• Implement media access control functions
Hubs
• Connect nodes to form a LAN
• Most are Ethernet devices
• Combine separate point-to-point connections
between nodes and the hub into a single
shared transmission medium by repeating all
incoming packets to every connection point
• Low-cost alternative for home and small
office networks
Bridges
• Connect two networks or network segments
and copy packets between them
• Look at source addresses and update internal
tables of node addresses on each network
segment
• Common uses
– Construct a virtual LAN from two separate
LANs
– Divide a network into segments in order to
minimize congestion
Routers
• Intelligently route and forward packets
among two or more networks
• Forward packets based on information other
than destination address
• Build internal “map” of the network
– constantly scan the netework to monitor
traffic patterns and network node
changes
Switches
• High-speed devices that create virtual LANs
on a per-packet basis
• Each input connection is treated as a
separate LAN
• Dramatically increase network performance
– Connection decisions made by hardware
are based only on destination address
– Each virtual LAN has only one sending and
one receiving node
• eliminates congestion
OSI Network Layers
Open System Interconnection (OSI) model
• ISO conceptual model that divides network
architecture into seven layers
• Each layer uses services of layer below and
is unaware of other layer’s implementations
• Uses:
– General model of networks
– Framework for comparing networks
– Architectural roadmap that enhances
interoperability among network
architectures and products
OSI Network Model
Application Layer
• Network service request and response
• Contains programs that make and respond to
high-level requests for network services
– End-user network utilities
– Network services embedded in the OS
– Network service providers
Presentation Layer
• Converts and formats data
• Ensures correct interpretation of
transmitted data
– Encryption and decryption
– Compression and decompression
– Converting data between EBCDIC and
ASCII
– Font substitution
• Primarily used by applications that format
data for user display
Session Layer
• Negotiates and implements high-level
protocol parameters
–
–
–
–
timeout
half or full duplex
synchronization
quality of service
• Establishes and manages communication
sessions
• Monitors communication to detect and
resolve problems that arise once protocol has
been established
Transport Layer
• Formats messages into packets suitable for
transmission over the network
• Places messages within a packet data area
and adds header/trailer information (network
addresses, error detection data, packet
sequencing data)
• Gives packets to network layer for delivery
• Examines packets for errors; requests
retransmission if necessary (when receiving
packets)
Network Layer
• Routes packets to their proper destination
• Those within central node interact with one
another to exchange routing information and
update internal routing tables
Data Link Layer
• Transmits packets and bits
• Interface between network software and
hardware
Physical Layer
• Transmits bit streams
• Where communication between devices
actually takes place
• Includes hardware devices that encode and
decode bit streams and the transmission
lines that transport them
OSI Network Model
OSI Network Model
TCP/IP
• The core Internet protocol suite
• Delivers most services associated with the
Internet
–
–
–
–
File transfer via FTP
Remote login via Telnet protocol
Electronic mail distribution via SMTP
Access to Web pages via HTTP
• Predates and corresponds poorly to OSI
model
IP
Internet Protocol
• Provides connectionless packet transport
across LANs and WANs
• Translates datagrams into format suitable
for transport by physical network
• IP layer can divide datagram into smaller
units and transmit them individually
– Attaches header information to each unit,
including its sequence in the datagram
IP
Internet Protocol
• Assumes datagram will traverse multiple
networks via nodes called gateways
• Determines transmission routes via related
protocols (ICMP, RIP)
• IP nodes
– Identified by unique 32-bit address
(nnn.nnn.nnn.nnn)
– Periodically exchange routing information
to keep tables current
Only the IP layer is
implemented within the gateways
TCP
Transmission Control Protocol
• Provides connection-oriented packet
transport to higher-level Internet service
protocols, including HTTP, FTP, and Telnet
– Provides framework to check for lost
messages; explicitly establishes connection
with intended recipient before
transmitting messages
• Performs connection management functions
(verifying receipt, verifying data integrity,
controlling message flow, securing message
content)
TCP
Transmission Control Protocol
• Sender and recipient TCP layers maintain
information about one another (message
routes, errors encountered, transmission
delays, status of ongoing data transfers)
• Uses positive acknowledgment protocol to
ensure data delivery
• Establishes connections through a port and
an socket
VoIP
Voice over IP
• Technologies/standards that carry voice
messages and data over single packetswitched network
• Lower cost than traditional public switched
telephone network (PSTN)
• Complex and competing standards
• Transmission quality problems
– packet loss
– latency
– jitter
H.323 is an umbrella
for many component protocols
Network Standards
• IEEE 802 standards
– Describe network hardware, transmission
media, transmission methods, and
protocols
– Help ensure compatibility among products
from competing vendors
– Developed by committees whose
membership is drawn from industry,
government, and academia
• Ethernet standard (802.3) - very successful
IEEE 802
Network
Standards
Ethernet
No provision for packet priorities
or guarantees of quality of service
10 Gigabit Ethernet
Business Focus – Upgrading
Network and Storage Capacity
•
•
•
•
Bradley Advertising Agency
The trade-off between short and long-range
benefits of copper and fiber optic wiring
Copper is installed in most buildings, works
well for current needs, and can be upgraded
– Current technology pushes copper to its
maximum
Fiber optic cable has far greater theoretical
capacity than copper
– Current optical products are expensive
and not yet perfected
Fiber optic cable is the future
– But when is it cost effective for a
particular organization or need?
Summary
• Network topology
• Addressing and routing
• Media access control
• Network hardware
• OSI network layers
• Network standards
Chapter Goals
• Compare and contrast bus, ring, and star
network topologies
• Describe packet routing across local and
wide area networks
• Describe the CSMA/CD media access control
protocol
• Describe network hardware devices, including
network interface units, routers, and
switches
• Describe the OSI network model, the
TCP/IP protocol suite, and IEEE network
standards
Next Class
Thursday
April 26, 2012
Rhys Eric Rosholt
Office:
Office Phone:
Web Site:
Email Address:
Gillet Hall - Room 304
718-960-8663
http://comet.lehman.cuny.edu/rosholt/
rhys.rosholt @ lehman.cuny.edu