Download Local Area Network (LAN)

Local Area Network
(LAN)
LAN
About 80% of the data traffic originated within the business
Advantages of LAN
◦ Timely access to data for customer service and product development
◦ Centralized management of shared applications
◦ Economic and cost saving due to sharing resources
Separating network nodes
Sharing the resources
LAN Components
Network nodes – an addressable entity where a communication line interfaces (e.g., a server with
multiple MAC to work as multiple nodes)
NIC – Network interface card which connects to the physical medium of LAN interface
Transmission system – a wired or wireless medium to carry actual data/connection
Software and data – protocol data unit (PDU) handling control, packaging and addressing as per
standard
User interface – a interface to receive user input to initiate, manage and terminate the
communication
Operating system – serves the user requirement for data, file or resources
LAN characteristics
Four key characteristics of a LAN
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Type of transmission Medium
Transmission technique
Network accessing
Network topology
LAN transmission media
o Bandwidth requirement
o How much do you need per client?
o How much do you need per server?
o Application specific, peak/off-pick load, up gradation/commissioning/relocation
o Cost and easy of connection
o Wired or wireless
o Bandwidth
o Easy up gradation/relocation
o Interference and noise sensitivity
o Type of business (office or power plant)
o Security
o Encryption
LAN transport techniques and standards
o Broadband
o Cable TV – through FDM different channels carry analog and digital information
o A set-top-box is used to extract information on a particular channel frequency band from a multichannel
coaxial cable
o Baseband
o A single channel digital system carrying packets of frames of data
o Ethernet
o Token ring
o FDDI/CDDI – later replaced by 1Gbps Ethernet
LAN standards
Characteristics
Ethernet
Token Ring
FDDI
Standard
IEEE 802.3
IEEE 802.5
IEEE 802.6
Logical topology
Bus
Ring
Bus
Physical topology
Bus, star
Ring, star
Dual ring, dual bus
Media
Coax, UTP, STP, fiber
Coax, UTP, STP
Fiber
Transmission mode
Baseband
Baseband
Baseband
BW
10Mbps, 100Mbps, 1Gbps, 10Gbps
4Mbps, 16Mbps, 100Mbps, 1Gbps
100Mbps
Media access
Nondeterministic
Deterministic
Deterministic
Control
CSMA/CD, CSMA/CA
Token passing
Token passing
LAN access method: Token Passing
o Used in token ring and FDDI
o MSAU- Multistation access unit
o The process
o A token is inserted into the ring
o Token circulates around the ring
o Grab the token to send data and release when finished
o Token hold time - a timer for sender to finish and release token
o Receiver grab the data, send acknowledgement
o Sender get notified and generates a new token
o Pros and cons
o Deterministic – maximum delay can be estimated
o Unidirectional ring - wait for the token
o Broken ring – needs to reinitiate the ring
LAN access method: CSMA/CD
o Carrier sense multiple access/ collision detection (CSMA/CD)
o Nondeterministic
o Needs to scan the network for collision
o Process
o Listen
o If clear, send the data
o If collide, produce a jam signal
and stop sending
o Wait random amount of time and retransmit
o If collide again, back off, wait and try again
o If frequent collision, break the LAN into sub segments
LAN topologies
o Common topologies are
o Tree
o All transmission must pass through head end
o Transmission and reception may use different frequencies
o Translation from transmit to receive frequency is called re-modulation
o Bus
o Each station is connected to the trunk or backbone
o A terminator is used to absorb the free signal and clear the cable
o Ring
o Nodes are connected to a unbroken loop
o Each node receives and boosts the signal and sends to the next node
o Star
o All stations are connected to the central hub
o Easy of by passing, fault isolation and centralized resource management
LAN interconnection: Hubs
o Hubs are used to expand the network
o Easy of connectivity and suitable for centralized monitoring
o Commonly known as concentrator or multi-station access unit (MSAU)
o Intelligent hub – can accommodate Ethernet, token ring or FDDI
oActive
o Regenerates and retransmits data
o Requires electrical power to run and can serve 8-12 nodes
o Passive
o Do not regenerate, signals just pass through the point
o Requires no electrical power to run
LAN interconnection: LAN switches
o To meet the demand for increased bandwidth
o Each port offers a dedicated channel with high speed
connectivity
o full duplex mode provides great scalability to the backbone
network
LAN interconnection: VLANs
o Does not restrict to a limited geographical location
o A single switch serving multiple LAN allowing
users to share the same broadcast domain
o Restricts the broadcast and collision within each
virtual LAN
o Managed and controlled by software application
LAN interconnection: Bridges
o Used for connecting network segments
o To avoid traffic bottleneck and to control the traffic flow
o Cannot translate between Layer 2 protocols (e.g., Ethernet, FDDI)
o Faster and less expensive, but subject to broadcast storm
o Functions include
o Learning
o Builds a MAC address table that controls the access of each NIC to the shared
transmission media
o Only determines whether a destination is within a network segment
o Packet transfer
o Filter, ignore or forward packets
o Using STP (Spanning Tree Protocol)
o Provides a loop-free topology to ensure that no two alternate routes are active
simultaneously
What would have happened?
LAN interconnection: Routers
o To expand smaller networks into a larger one or to segment
larger network into smaller ones
o Limits broadcast storm by
o Reading network addresses and forwarding the packet to target or
destination address
o Acting as a traffic filtering, isolation and forwarding
o Can make linking and rerouting decisions
o Selection depends on cost, speed, priority and so on
o Often applied as firewalls to separate network segments
o Functions
o Learning
o Filtering
o Routing and switching
o Adapting to network conditions
Wide Area Network
(WAN)
WAN
o A group of computers connected over
long distances by communication link
o Circuit switched
o Leased line
o ISDN
o Packet switched
o X.25
o Frame relay
o ATM
o IP
Circuit switched network: Leased Line
o Connectivity options
o Telco Network Leased Line (DLC)
o Services
o Installation and maintenance
o IP number allocation
o Domain Name Service (DNS)
o Usage Reporting
o Static & Dynamic Routing Protocol
o 24x7 Support
o Connection type
o Single point
o Multipoint
Leased line: Single point
o A dedicated connection between two nodes
o Challenges
o Cost per mile
o Not economic for network expansion or relocation
CSU – Channel services equipment
DSU – Data services equipment
Leased line: Multipoint
o A shared communication link to reduce mileage
cost
o Shared link is
o Cost effective
o But increases control and services overhead
CSU – Channel services equipment
DSU – Data services equipment
Leased line: Connectivity
o Digital Data services (DDS) - 56Kbps or 64Kbps
o T, E or J carrier
o SDH/SONET
o Dark fiber
Leased line: DDS
o A lease line at either 56Kbps or 64Kbps serviced by a T, E or
J carrier backbone
o Uses RS232 or V.35 for physical connectivity between DTE
and DCE
o The access line from DCE connects to the digital circuit
switch which is known as DDS hub
o DDS hub or DSU converts the binary data to line coding and
synchronization
o A one for positive voltage
o A zero for negative voltage
o If >15zeros, network may loose synchronization
o Hence, DSU performs bipolar variation by alternating one as positive or negative
voltages
o A switched DDS can support 56, 64, 384 or 1536 Kbps
Switched 56 – 56Kbps full duplex dial up connection for serial interface
V.35 – High speed serial interface between DTE and DCE
Data set - A digital device connecting V.35 to 56Kbps access link of Telecom company
Leased line: T, E or J carrier
o Connectivity between cities are
supported by both p2p and multipoint
leased lines
o It requires a single backbone to replace
all the different infrastructures
o A private network to replace existing
o Dynamic bandwidth
o Dynamic routing
o
Leased line: Private network backbone
Dynamic routing
Static and dynamic bandwidth
Leased line: SDH/SONET and Dark fiber
o SDH/SONET
o An infrastructure based on fiber optics
o High speed digital access of multimedia and visualization requiring high bandwidth applications for
enterprises
o
o
o
o
o
OC-1 (51 Mbps)
OC-3 (155 Mbps)
.
.
OC- 192 (10 Gbps)
o Customers of SDH/SONET are airports, universities, large government agencies
o Dark fiber
o Requires equipment to activate fiber at customer premises
o Possible to get extra bps or wavelength out of fiber
o Reduce costs for bandwidth
Circuit switched network: ISDN
o An alternate to leased lines that support both
voiced and non-voiced services
o Reduces overhead costs for individual aces to
circuit-switched, leased-line or packetswitched network
o Requires –
o Digital local exchange and software
o SS7 (signaling system 7) network
o CPE (customer premises equipment)
Circuit switched network: N-ISDN
o 2 interfaces
o Basic rate interface (BRI)
o Primarily for residential services and small businesses offered by
Telcos
o Can be configured as 1B, 2B, 1B+D or 2B+D
o An ISDN modem at customer premises can be of 2B for 128kbps
access to ISP
o Primary rate interface (PRI)
o Primarily used for business applications
o A key data application is LAN/WAN integration
Circuit switched network: ISDN applications
o Internet Access – Other than DSL or broadband availability, N-ISDN can provide speed
o Remote access – Teleworkers or telecommuters can access to corporate resources
o LAN/WAN connections – Multiple LANS across a WAN can be connected over N-ISDN
o High capacity access – Increased capacity access for file transfer, graphics, video and multimedia
o Private-line backup – N-ISDN can be a backup for DDS services recovery period
o BRI 0B+D packet data – One 16Kbps can be shared by 8 devices. 0B+D can support 9.6kbps low
speed terminals such as credit card readers and automatic teller machines
o ISDN DSL (IDSL) – Full duplex dedicated data services only. Operates either at 1B or 2B (64kbps or
128kbps)
Packet switched network
o Designed to support burst data traffic
o Longer connection of low volume data
o May include statistical multiplexing
o Packet formats may vary depending on
o Number of bits/packet
o Sensitivity to delay/loss
o Addressing rules for forwarding to destination
o 2 types of network
o Connection oriented (X.25, Frame relay, ATM)
o Only one packet is required to set up the connection between source to destination.
o Rest of the packets are routed to the established connection
o Error detection and corrections are handled by destination devices
o Connectionless (X.25, IP)
o Each packet carries source and destination route information
o Sensitive to delay for real-time applications as each packet is subjective to inspection for routing and error control
Packet switched network: X.25
o X.25 evolved to support
o Low volume and bursty nature of data shared among multiple
users
o High integrity against high error rate of analog transmission
o Delay due to error control at each transmission nodes
o Small packet size (128 bytes or 256 bytes) to support
retransmission for error control
PSE – Packet switching equipment
PAD – Packet assembler/disassembler