A Guide to Designing and Implementing Local and Wide Area
Download
Report
Transcript A Guide to Designing and Implementing Local and Wide Area
LAN/WAN Interconnectivity
Learning Objectives
Explain the OSI reference model, which
sets standards for LAN and WAN
communications
Discuss communication between OSI
stacks when two computers are linked
through a network
Apply the OSI model to realistic
networking situations
continued…
Learning Objectives
Describe the types of networks as represented
through LAN topologies
Describe major LAN transmission methods,
including Ethernet, token ring, and FDDI
Explain basic WAN network communications
topologies and transmission methods, including
telecommunications, cable TV, and satellite
technologies
LAN/WAN Interconnectivity
Intense competition between three
sectors:
Telecommunications companies
Cable TV companies
Satellite communications companies
OSI Reference Model
Foundation that brings continuity to LAN
and WAN communications
Product of two standards organizations:
ISO
ANSI
Developed in 1974
Set of communication guidelines for
hardware and software design
OSI Guidelines Specify…
How network devices contact each other;
how devices using different protocols
communicate
How a network device knows when to
transmit and not transmit data
How physical network network devices are
arranged and connected
continued…
OSI Guidelines Specify…
Methods to ensure that network
transmissions are received correctly
How network devices maintain a
consistent rate of data flow
How electronic data is represented on
network media
OSI Layers
OSI Layers
Bottom layers
Middle layers
Support for physical connectivity, frame formation,
encoding, and signal transmission
Establish and maintain a communication session
between two network nodes
Monitor for error conditions
Uppermost layers
Application/software support for encrypting data and
assuring interpretation/presentation of data
Physical Layer Functions
Provides transfer medium (eg, cable)
Translates data into a transmission signal
Sends signal along the transfer medium
Includes physical layout of network
Monitors for transmission errors
Determines voltage levels for data signal
transmissions and to synchronize
transmissions
Determines signal type (eg, digital or analog)
Analog Signals
Digital Signals
Data Link Layer Functions
Constructs data frames
Creates CRC information; checks for
errors
Retransmits data if there is an error
Initiates communications link; makes sure
it is not interrupted (ensures node-to-node
physical reliability)
Examines device addresses
Acknowledges receipt of a frame
Data Link Layer
Data link frame contains fields consisting
of address and control information
Two important sublayers
Logical link control (LLC)
Media access control (MAC)
Connectionless service versus connectionoriented service
Network Layer Functions
Determines network path for routing
packets
Helps reduce network congestion
Establishes virtual circuits
Routes packets to other networks,
resequencing packet transmissions when
needed
Translates between protocols
Transport Layer Functions
Ensures reliability of packet transmissions
Ensures data is sent and received in the same
order
Sends acknowledgement when packet is
received
Monitors for packet transmission errors and
resends bad packets
Breaks large data units into smaller ones and
reconstructs them at the receiving end for
networks using different protocols
Session Layer Functions
Establishes and maintains
communications link
Determines which node transmits at any
point in time
Disconnects when communication session
is over
Translates node addresses
Presentation Layer Functions
Translates data to a format the receiving
node understands (eg, from EBCDIC to
ASCII)
Performs data encryption
Performs data compression
Application Layer Functions
Enables sharing remote drivers and
printers
Handles e-mail messages
Provides file transfer services
Provides file management services
Provides terminal emulation services
Communicating Between
Stacks
OSI model provides standards for:
Communicating on a LAN
Communicating between LANs
Internetworking between LANs and WANs
and between WANs and WANs
Peer Protocols
Primitives
Layered Communications
Applying the OSI Model
Types of Networks
Three main topologies
Bus
Ring
Star
Bus Topology
Built by running cable
from one PC or file
server to the next
Terminators signal the
physical end to the
segment
Advantages of Bus Topology
Works well for small networks
Relatively inexpensive to implement
Easy to add to it
Disadvantages of
Bus Topology
Management
costs can be high
Potential for congestion with network
traffic
Ring Topology
Continuous path for
data with no logical
beginning or ending
point, and thus no
terminators
Advantages of Ring Topology
Easier to manage; easier to locate a
defective node or cable problem
Well-suited for transmitting signals over
long distances on a LAN
Handles high-volume network traffic
Enables reliable communication
Disadvantages of
Ring Topology
Expensive
Requires more cable and network
equipment at the start
Not used as widely as bus topology
Fewer equipment options
Fewer options for expansion to high-speed
communication
Star Topology
Oldest and most
common network
design
Multiple nodes
attached to a central
hub
Advantages of Star Topology
Good option for modern networks
Low startup costs
Easy to manage
Offers opportunities for expansion
Most popular topology in use; wide variety
of equipment available
Disadvantages of
Star Topology
Hub is a single point of failure
Requires more cable than the bus
Bus Networks in a Physical Star
Layout
No exposed terminators
Capability for connecting multiple hubs to
expand network in many directions
Expansion opportunities for implementing
high-speed networking
Popular design; wide range of equipment
available
LAN Transmission Methods
Ethernet
IEEE 802.3 specifications
Broadest options for expansion and highspeed networking
Token ring
IEEE 802.5 specifications
FDDI (Fiber Distributed Data Interface)
High-speed variation of token ring
Ethernet
Uses CSMA/CD access method for data
transmission on a network
Typically implemented in a bus or bus-star
topology
Carrier sense
Collision
Ethernet Communications
Ethernet II
Ethernet Standards
Token Ring
Developed by IBM in the 1970s; remains a
primary LAN technology
Employs physical star topology with logic
of ring topology
Each node connects to a central hub, but
the frame travels from node to node as
though there were no starting or ending
point
Token Ring Frame
Token Ring Terms
Multistation access unit (MAU)
Beaconing
Broadcast storms
FDDI
Fiber-optic data transport method capable of a
100-Mbps transfer rate using a dual ring
topology
Synchronous versus asynchronous
communications
Nodes monitor network for error conditions
Long periods of no activity
Long periods where the token is not present
Class A and Class B nodes
WAN Network Communications
Typical providers of WAN network services
Newer sources of WAN connectivity
Telecommunications companies
Cable TV companies
Satellite providers
Cable television networks
Satellite TV companies
Wireless WANs
Wide use of star topology
Telecommunications WANs
Earliest source of WAN connectivity
Regional telephone companies, also
called:
Telcos
Regional bell operating companies (RBOCs)
Long-distance telecommunications
companies
Plain old telephone service (POTS) or
public switched telephone network (PSTN)
General Topology Linking LATA
and IXC Lines
Connecting LANs through
a T-Carrier Line
T-Carrier Services and Data
Rates
Cable TV WANs
Also called cablecos or multiple system
operators (MSOs)
Use a distributed architecture that consists
of several star-shaped centralized
locations
Headend is the main focal point in the star
Wireless WANs
Use radio, microware, and satellite
communications
Packet radio communications
Topology of a Radio Wave WAN
Joining Two LANs
WAN Transmission Methods
Use different switching techniques to
create data paths (channels) for
transmitting data
Switching
Enables multiple nodes to simultaneously
transmit and receive data, or
Enables data to be transmitted over different
routes to achieve maximum efficiency in terms
of speed and cost
Switching Techniques
Time division multiple access
(TDMA)
Divides channels into distinct time
slots
Frequency division multiple
access (FDMA)
Divides channels into frequencies
Statistical multiple access
Dynamically allocates bandwidth
based on application need
Circuit switching
Uses a dedicated physical circuit
Message switching
Uses store-and-forward method of
data transmission
Packet switching
Combines circuit and message
switching
Chapter Summary
Open Systems Interconnection (OSI)
model
Basic network topologies
Key LAN transmission methods
WAN communications options
WAN transmission methods