chapter6 - lan hardware
TRANSCRIPT
Chapter 6-Local Area Network Hardware
1
Necessary to connect LAN to LAN or WAN
LAN to LAN connections are often performed with bridge-like device.
LAN to WAN connections are usually performed with router.
Third device, switch, can be used to interconnect segments of LAN.
Introduction
Chapter 6-Local Area Network Hardware
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Local Area Network Hardware
Focus on hardware technologyTransition from shared media network architectures to hardware based switched network architectures
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To connect one division with another.
To connect two LANs with different protocols.
To connect LAN to Internet.
To break LAN into segments to relieve traffic congestion.
To provide security between different users.
Why Interconnect
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LAN Requirements
LAN requires following components Central wiring concentrator (Hub) Media - cable or wireless NIC - internal or external Other – switch, repeater, etc.
NIC drivers - programs that interface between NIC and NOS.
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Network interface card driver software bridges the hardware/software gap between the Network Interface Card (NIC) and the installed Network Operating System (NOS)
SERVER
WIRING CENTER of some type -
CLIENT PC
media
hub MAU LAN switch
Logical Diagram
NIC (network interface card)
NIC (network interface card)
NIC driver software
Network Operating System
GOLDMAN & RAWLES: ADC3e FIG. 06-01
LAN Architecture
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Implications of LAN Technology Choices
Choosing particular technology in one LAN technology category has significant implications/limitations on available technology choices in other LAN technology categories
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Architecture choices - Peer-to-Peer vs. Client/Server
Server Function choices
Network Operating System choices Network Operating System choices
Adapter Card Driver choices
Adapter Card Driver choices
Operating System choices
Operating System choices
Access Methodology choices
Logical and Physical Topology choices
Network Architecture choices
Wiring System choices
Wiring Center choices
Network Adapter Card choices
CPU choices
Media choices
BUS Type choices
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Representative Server PC Representative Client PC
Wiring System choices
Media choices Network Adapter
Card choicesCPU
choices
BUS Type choices
GOLDMAN & RAWLES: ADC3e FIG. 06-02
Implications of LAN Technology Choices
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Media Sharing vs. Switched
Client/server systems and distributed computing has put increasing demands on LAN infrastructure with demands for amount of data traffic to be transferred One solution to bandwidth problem is to offer higher speed shared media network architectures
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Media Sharing vs. Switched cont’d
LAN switches resolve one at time limitation of shared-media LAN architectures by offering attached workstations access to switching matrix that provided point-to-point connections between any two ports.Each port on LAN switch is dedicated LAN segment with dedicated bandwidth
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Media Sharing vs. Switched cont’d
Limiting factor in switch-based LAN architecture is number of simultaneous point-to-point connections that switch can support.Coming slide contrasts differences in wiring center functionality between media sharing and switch based LAN architecture.
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serversclient workstations
Shared Media Hubshared, single 10Mbps LAN
segment
only one 10Mbps connection at a
time
Shared Media LAN Architecture
10 Mbps
"10 Mbps for ALL"
Switching Hubmultiple dedicated
10Mbps LAN segments
Workgroup with shared connection
Workgroup with shared connection
servers with dedicated connections
shared media hub
shared media hub
Workstations with dedicated connections
Multiple, simultaneous
10Mbps connections
All connections at 10Mbps
switching matrix
Switch-Based LAN Architecture
"10 Mbps for EACH"
GOLDMAN & RAWLES: ADC3e FIG. 06-03
Switched LAN Architectures vs. Media-Sharing LAN Architectures Wiring Center
Functionality
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12GOLDMAN & RAWLES: ADC 3e FIG: 06-04
LAN Switch
1 Gigabit per second network
LAN Switch
LAN Switch
10 Mbps network10 Mbps network
100 Mbps network
Servers
workstations
workstations
Building Bandwidth Hierarchy with Switched LAN Architecture
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Workstation Connected to LAN
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ADVANTAGES of SWITCHED LAN
ARCHITECTURES
Switched LAN architecture only change wiring center technology and manner in which workstations set up point to point communication to each other.Installing LAN switch is often easiest alternative chosen when network bandwidth demands exceed current supply.
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Implementation Scenarios for Switched LAN
Architectures
Stand-alone workgroup/departmental LAN switches Backbone attached workgroup/departmental LAN switches Backbone/data center switches Switches offer switched connectivity to
other workgroup switches, media sharing hubs, and corporate servers that must be accessed by multiple departments/groups
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GOLDMAN & RAWLES: ADC 3e FIG: 06-05
shared media hub
Stand-Alone Workgroup/Departmental LAN Switches
Dedicated switched connections for all clients and servers.
Dedicated switched connections for servers, shared switched connections for clients.
Standard Server front-end variation
LAN Switch
Backbone-Attached Workgroup/Departmental LAN Switches
100Mbps backbone connection to backbone network.
10Mbps local switched connections
Backbone/Data Center Switches
Corporate shared servers
Corporate backbone network
Backbone/data center switch
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Backbone attached workgroup/departmental LAN switches with locally attached clients and servers.
LAN Switch
LAN Switch
shared media hub
Implementation Scenarios for Switched LAN Architectures
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Network Interface Card
NIC - Physical link between client and server PC and media of network NIC have ability to adhere to access methodology (CSMA/CD or token passing) of network architectureSoftware rules, implemented by NIC, control access to shared network media and are known as media access control (MAC) protocols
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Network Interface Card, cont’d
NIC cards determine network architecture and constituent protocols more than any other componentNIC act like mediator or translator Has demands of client/server PC Has network architecture with rules
for accessing network media or LAN switch.
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Technology Analysis
Bus into which network adapter card allows different types of cards to be attached in pathway leading to CPU and RAM memory.PCI bus offers clocking signaling and low CPU utilization and seems to be bus of choice for high performance NICs.
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Technology Analysis, cont’d
Important choice related to bus architecture is that network adapter card chosen is compatible with installed bus and takes advantage of data transfer capability bus may offer.Key job of NIC is to transfer data between local PC and shared network media.
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Technology Analysis, cont’d
Hardware related network adapter characteristics that bare on data transfer efficiency are Amount of on board memory Processing power of onboard CPU
contained on network adapter card
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Technology Analysis, cont’d
Coming figure summarizes NIC to PC memory data transfer techniques.Techniques are: Programmed I/O Direct Memory Access (DMA) Shared memory Bus mastering DMA
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CPU
RAM
RAMCPU
network interface card
Motherboard
BUS
Shared I/O address
NIC connector
network media (cable)
Programmed I/OSteps
Data enters network interface card through the network media and connector. Adapter card CPU loads network data into a specific I/O address on the motherboard. Main CPU checks I/O area for data If data exists, it is transferred to main memory, RAM, by main CPU.
Keynote The motherboard's CPU has the ultimate responsibility of data transfer into RAM.
1. 2. 3. 4.
CPU
RAM
CPU
network interface card
Motherboard
BUS
NIC connector
network media (cable)
DMA (Direct Memory Access)Steps
Data enters network interface card through the network media and connector. Adapter card CPU interrupts the motherboard CPU. Main CPU stops other processing and transfers the data to RAM.
Keynote The motherboard's CPU has the ultimate responsibility of data transfer into RAM.
1. 2. 3.
CPU
RAM
RAMCPU
network interface card
Motherboard
BUS
NIC connector
network media (cable)
Shared MemorySteps
Data enters network interface card through the network media and connector. Adapter card CPU stores data on its RAM. Adapter card CPU interrupts the motherboard CPU. Main CPU stops other processing and transfers data into RAM.
Keynote The motherboard's CPU has the ultimate responsibility of data transfer into RAM.
1. 2. 3. 4.
RAM
RAMCPU
network interface card
Motherboard
BUS
NIC connector
network media (cable)
Bus Mastering DMASteps
Data enters network interface card through the network media and connector. Adapter card CPU temporarily stores data on its RAM. Adapter card CPU sends data directly to motherboard RAM when network transmission completes (it does NOT interrupt the main CPU.)
Keynote The adapter card's CPU has the ultimate responsibility of data transfer into RAM.
1. 2. 3.
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GOLDMAN & RAWLES: ADC3e FIG. 06-07
Network Interface Cards Data Transfer Methods
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Technology Analysis, cont’d
Only bus mastering DMA data transfer technique leaves system CPU alone to process other applicationsIn bus mastering DMA, CPU on network adapter card manages movement of data directly into PC’s RAM without interrupting system CPU by taking control of PC’s expansion bus
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Technology Analysis, cont’d
Bus mastering DMA on adapter cards requires expansion bus in PC to support being “mastered” by CPU on network adapter card.CPU and operating system must have capability to relinquish control of expansion bus for bus mastering network adapter cards to function correctly
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Technology Analysis, cont’d
NIC must be properly configured to interact successfully with that computerNIC configuration issues: IRQ (Interrupt request) – IRQ must not
be used by other device and must be supported by NIC
Base I/O port address – defines memory location through which data will flow between NIC and CPU
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Technology Analysis, cont’d
Base Memory Address – Some NICs require base memory address to indicate starting location in computer’s memory to be used by NIC as buffer memory
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Technology Analysis, cont’d
NIC must worry about hardware compatibility in two directions NIC must be compatible with expansion
bus into which it will be inserted NIC must be compatible with media of
network architecture
Some NICs come with interfaces for more than one media type.Jumpers on NIC enable one media type or another
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8 pin RJ-45 jack for 10Base-T
BNC connector for 10Base-2 (thin coax Ethernet)
DB-15 AUI connector for 10Base-5 (thick coax Ethernet)
Jumpers to enable/disable media interfaces
Transceiverthick coax Ethernet
DB-15 AUI
AUI or transceiver cable
DB-15 AUI
GOLDMAN & RAWLES: ADC3e FIG. 06-09
Ethernet Media Interfaces
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Technology Analysis, cont’d
Possible for NIC to be connected externally to PC via PC’s parallel port USB NICs communicate with PC at speeds greater than 12 Mbps Actual USB performance depends
on number of devices sharing bus
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Network Interface Card Trends
Dual speed cards – 10/100 Ethernet cards feature auto sensing, automatically determine whether traffic is being transmitted and received at 10 or 100 Mbps through single media interface card.Integrated or on board NICs – Build Ethernet NIC onto motherboardMultiport NICS – Ability of PCI bus allows multiport NICs to be manufactured on single card.
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Network Interface Card Trends, cont’d
On-NIC virus protection and security – Some NICS now offer encryption, virus protection, or both
Integrated repeater modules – allow up to seven additional devices to be cascaded from NIC and attached to network via single 10BaseT hub port.
Full duplex mode – Some Ethernet NICs have full duplex capability that can be enabled.
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Network Interface Card Trends, cont’d
Performance improvements – Mfg of Ethernet NICs implemented fast packet forwarding technologyNext packet of information is forwarded as soon as start of frame is detected rather than waiting for previous frame to be totally on network media before beginning transmission of next packet.
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NIC Drivers
Interoperability depends on compatibility between NIC and NOS installed in given computer, and is delivered by network interface card driversIt was to an adapter card vendor ‘s advantage to ship drivers for as many operating systems as possible.
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Approaches for NIC Drivers
Supply drivers that could interact successfully with either NetBIOS or TCP/IP.Emulate adapter interface specifications of market leading network interface cards for which drivers are most commonly available.
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Multiprotocol NIC Drivers
By allowing adapter card vendors to develop one file called IPX.COM which was linked with Novell file called IPX.OBJ through process known as WSGEN, unique drivers could be more easily created and updated.
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Network Driver Interface Specification (NDIS)
NDIS - driver specification offering standard commands for communication between NDIS compliant NOS protocol stacks (NDIS protected driver) and NDIS compliant network adapter card drivers (NDIS MAC drivers).NDIS specifies binding operation managed by protocol managerNDIS specifies standard commands for communication between protocol manager program and protocol or MAC drivers.
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Open Datalink Interface (ODI)
ODI allows users to load several protocol stacks simultaneously for operation with single network adapter card and supports independent development with subsequent linking of protocol drivers and adapter drivers.
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PCMCIA Drivers
When NICs are PCMCIA based, two levels of driver software are required: Drivers to interface to OS and
NOS. Drivers to interface PCMCIA
controller to PCMCIA card and on client software drivers.
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PCMCIA Drivers, cont’d
PCMCIA version 2.1 has Card and Socket Service (CSS) driver specifications.CSS is split into two logical sub layers:1. Card services sub layer is hardware independent and interfaces to NOS driver software.2. Socket services sub layer is written specifically for type of PCMCIA controller included in laptop.
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PCMCIA Drivers, cont’d
If compatible card and socket service (CSS) drivers are not available for particular PC card/controller combination or if amount of memory CSS drivers requires is unacceptable, then lower level drivers known as direct enablers must be configured and installed.
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LAN Wiring Centers
Most common network physical topology employed today is star topology Token ring wiring centers are known as MAUs (Multistation Access Units)Wiring centers for other networks are known as hubs. Hubs and MAUs are multiport digital signal repeaters
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Hubs
Active central element of star layout.When single station transmits, hub repeats signal on outgoing line to each station.Physically star; logically bus.Hubs can be cascaded in hierarchical configuration.
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Types of Wiring Center Categories
Repeaters Hubs
Stackable Hubs
Multistation Access Units
Enterprise Hubs
Management Hubs
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Wiring Center Categories
Wiring centers can be separated into three broad categories.1. Stand-alone hubs - Offers limited number of ports of particular type of network architecture and media.2. Stackable hubs - add expandability and manageability. Stackable hubs can be linked together to form one larger virtual hub of single type of network architecture and media.
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Wiring Center Categories, cont’d
3. Enterprise hubs - modular by design and offer chassis based architecture to which variety of different modules can be inserted.
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10 Base-T
Stand-alone hubs
all RJ-45 connections for UTP
Network Interface Card in
workstation Fixed number of ports Single network architecture Hubs are cascadable Single media type
Stackable hubsserial
connection into management
console
management console port(s)
Each hub has a fixed number of ports Hubs are stackable Single network architecture and media Provides management software and link to network management console Logically one large hub/switch
management console
Enterprise hubs
10Base-T
Token Ring
FDDI
multiple redundant cooling fans
management module
multiple redundant power supplies
Modular chassis-based design Supports multiple network architectures and media types Integrated management module May include internetworking or WAN modules
stacking port(s)
Major Categories of Hubs
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Repeaters
Stand-alone hubs
Stackable hubs
MAUsstand-alone
stackable
Enterprise hubs
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GOLDMAN & RAWLES: ADC3e FIG. 06-15
Wiring Center Functional Comparison
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Repeater
Repeater - repeats each bit of digital data that it receives. Repeating action cleans up digital signal by retiming and regenerating signal before passing this repeated data from one attached device or LAN segment to next.
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Hub
Hubs - are subnet of repeaters that allow attachment of single devices rather than LAN segments to each hub port.Terms hub and concentrator or intelligent concentrator are often used interchangeably.
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Hub interconnects two or more workstations into local area network.
When workstation transmits, hub resends data frame out all connecting links.
Hub can be managed or unmanaged. managed hub possesses enough processing power that it can be managed from remote location.
Hubs, cont’d
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Multistation Access Unit (MAU)
MAU (Multistation Access Unit) is IBM’s name for token ring hub.MAUs offer varying degrees of management capability.Active management MAUs – send alerts to management consoles regarding malfunctioning token ring adapters and forcibly remove misbehaving adapters from ring.
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Enterprise Hubs
Hub allows concentrator to mix cards Cards could be added for connections with Ethernet modules, Token ring adapters, PCs, workstations with FDDI adapters, or dumb asynchronous terminalsAdditional modules available for some concentrators may allow data traffic to travel to other local LANs via bridge or router add-on modules
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Enterprise Hubs, cont’d
Local network traffic travels through single enterprise hub; ideal location for security modules to be added for either encryption or authorization functionality
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Hub Management Hub - ideal place for installation of management software to monitor and manage network trafficIn stackable and enterprise hubs, two layers of management software may be found 1. Software is supplied by hub vendor.
Allows monitoring and management of hub.
2. Hubs - capable of sharing MIS with enterprise network management systems.
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Hub Management, cont’d
Standards that govern network management communication is part of TCP/IP family of protocols, more correctly known as Internet suite of protocols.Network management information is formatted according to simple network management protocol (SNMP)
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58GOLDMAN & RAWLES: ADC 3e FIG: 06-16
Agent
Management Information Base
Enterprise Network Management System
Enterprise Hub
Stackable Hubs
SNMP protocol
Stackable HubsAgentAgent
Standards-Based Network Management Communications
Protocols
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LAN Switches
LAN switch - seeks to overcome this “one at time” broadcast scheme, which can lead to data collisions, retransmissions, and reduced throughput between high bandwidth demanding devicesSwitched LAN Architectures vs. Media-Sharing LAN Architectures Wiring Center Functionality
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LAN Switches, cont’d
Many high-end LAN switches support ATM (Asynchronous Transfer Mode), which is type of switching that not only allow previously mentioned LAN architectures to be switched extremely quickly, but also allows similarly quick switching of voice, video, and image traffic
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Switch is combination of hub and bridge.
It can interconnect two or more workstations, but like bridge, it observes traffic flow and learns.
When frame arrives at switch, switch examines destination address and forwards frame out one necessary connection.
Switches, cont’d
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Switches, cont’d
Workstations that connect to hub are on shared segment.
Workstations that connect to switch are on switched segment.
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Backplane of switch is fast enough to support multiple data transfers at one time.
Switch that employs cut-through architecture is passing on frame before entire frame has arrived at switch.
Switches, cont’d
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Switches, cont’d
Multiple workstations connected to switch use dedicated segments. Very efficient way to isolate heavy users from network.
Switch can allow simultaneous access to multiple servers, or multiple simultaneous connections to single server.
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Full duplex switch allows for simultaneous transmission and reception of data to and from workstation.
Full duplex connection helps to eliminate collisions.
To support full duplex connection to switch, two sets of wires are necessary - one for receive operation and one for transmit operation.
Full Duplex Switches
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Types of Switches – Cut Through Switch
Cut through switches - read only address information in MAC layer head before beginning processing. After reading destination address, switch consults an address look up table to determine which port on switch this frame should be forwarded to. Once address look up is completed, point-to-point connection is created and frame is immediately forwarded.
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Types of Switches- Store and Forward
Store and Forward switches – read entire frame into shared memory area in switch. Contents of transmitted Frame Check Sequence (FCS) field is read and compared to locally recalculated frame check sequence. If results match, switch consults address look up table, builds appropriate point-to-point connection, and forwards frame.
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Types of Switches- Error free cut through
switches Error free cut through switches – read both addresses and frame check sequences for every frame. Frames are forwarded immediately to destination nodes in an identical fashion to cut through switches.
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Types of Switches - Error free cut through switches,
cont’d
Should bad frames be forwarded, error free cut through switch is able to reconfigure those individual ports producing bad frames to use store and forward switching. As errors diminish to preset thresholds, port is set back to cut through switching for higher performance throughput.
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Ethernet Hubs and Switches
Shared medium hubs
Switched LAN hubs
x
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Advantages of Switched Hubs
No modifications needed to workstations when replacing shared-medium hubEach device has dedicated capacity equivalent to entire LANEasy to attach additional devices to network
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Types of Switched Hubs
Store and forward switch Accepts frame on input line Buffers it briefly Routes it to appropriate output line
Cut-through switch Begins repeating frame as soon as it
recognizes destination MAC address Higher throughput, increased chance
of error
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Layer 3 Switches
Problems With Layer 2 Switches Broadcast overload Lack of multiple links Can be solved with subnetworks
connected by routers
Layer 3 switches implement packet-forwarding logic of router in hardware.
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More on Switches
Circuit-switched Packet-switched
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Circuit-SwitchingDefinition: Communication in which dedicated communications path is established between two devices through one or more intermediate switching nodesDominant in both voice and data communications today e.g. PSTN is circuit-switched network
Relatively inefficient (100% dedication even without 100% utilization)
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Circuit-Switching Stages
Circuit establishmentTransfer of information point-to-point from endpoints to node internal switching/multiplexing among
nodes
Circuit disconnect
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Circuit Establishment
Station requests connection from nodeNode determines best route, sends message to next linkEach subsequent node continues establishment of pathOnce nodes have established connection, test message is sent to determine if receiver is ready/able to accept message
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Information Transfer
Point-to-point transfer from source to nodeInternal switching and multiplexed transfer from node to nodePoint-to-point transfer from node to receiverUsually full-duplex connection throughout
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Circuit Disconnect
When transfer is complete, one station initiates terminationSignals must be propagated to all nodes used in transit in order to free up resources
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Public Switched Telephone Network
(PSTN)
SubscribersLocal loop Connects
subscriber to local telco exchange
Exchanges Telco switching
centers Also known as end
office
Trunks Connections
between exchanges
Carry multiple voice circuits using FDM or synchronous TDM
Managed by IXCs (inter-exchange carriers)
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Digital Circuit-Switching Node
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Circuit Switching Node:Digital Switch
Provides transparent signal path between any pair of attached devicesTypically full-duplex
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Circuit-Switching Node:Network Interface
Provides hardware and functions to connect digital devices to switchAnalog devices can be connected if interface includes CODEC functionsTypically full-duplex
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Circuit-Switching Node:Control Unit
Establishes on-demand connectionsMaintains connection while neededBreaks down connection on completion
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Blocking/Nonblocking Networks
Blocking: network is unable to connect two stations because all possible paths are already in useNonblocking: permits all possible connection requests because any two stations can be connected
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Switching Techniques
Space-Division Switching Developed for analog
environment, but has been carried over into digital communication
Requires separate physical paths for each signal connection
Time-Division Switching Used in digital
transmission Utilizes multiplexing
to place all signals onto common transmission path
Bus must have higher data rate than individual I/O lines
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Routing in Circuit-Switched Networks
Requires balancing efficiency and resiliencyTraditional circuit-switched model is hierarchical, sometimes supplemented with peer-to-peer trunksNewer circuit-switched networks are dynamically routed: all nodes are peer-to-peer, making routing more complex
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Alternate Routing
Possible routes between two end offices are predefinedOriginating switch selects best route for each callRouting paths can be fixed (1 route) or dynamic (multiple routes, selected based on current and historical traffic)
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Control Signaling
Manage establishment, maintenance, and termination of signal pathsIncludes signaling from subscriber to network, and signals within networkIn-channel signaling uses same channel for control signals and callsCommon-channel signaling uses independent channels for controls (SS7)
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ISDN1st generation: narrowband ISDN Basic Rate Interface (BRI) Two 64Kbps bearer channels + 16Kbps data
channel (2B+D) = 144 Kbps Circuit-switched
2nd generation: broadband ISDN (B-ISDN) Primary Rate Interface (PRI) Twenty-three 64Kbps bearer channels + 64
data channel (23B+D) = 1.536 Mbps Packet-switched network Development effort led to ATM/cell relay
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Packet-Switching Networks
Includes X.25, ISDN, ATM and frame-relay technologiesData is broken into packets, each of which can be routed separatelyAdvantages: better line efficiency, signals can always be routed, prioritization optionDisadvantages: transmission delay in nodes, variable delays can cause jitter, extra overhead for packet addresses
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Packet-Switching Techniques
Datagram each packet treated independently and
referred to as datagram packets may take different routes, arrive
out of sequence
Virtual Circuit preplanned route established for all packets similar to circuit switching, but circuit is not
dedicated
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Packet-Switched Routing
Adaptive routing changes based on network conditionsFactors influencing routing are failure and congestionNodes must exchange information on network statusTradeoff between quality and amount of overhead
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Packet-Switched Congestion Control
When line utilization is >80%, queue length grows too quicklyCongestion control limits queue length to avoid throughput problemsStatus information exchanged among nodesControl signals regulate data flow using interface protocols (usually X.25)
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X.25 Interface Standard
ITU-T standard for interface between host and packet-switched networkPhysical level handles physical connection between host and link to node Technically X.21, but other standards can be
substituted, including RS-232
Link level provides for reliable data transfer Uses LAPB, which is subset of HDLC
Packet level provides virtual circuits between subscribers
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Virtual-Circuit Service
External virtual circuit: logical connection between two stations on networkInternal virtual circuit: specific preplanned route through networkX.25 usually has 1:1 relationship between external and internal circuitsIn some cases, X.25 can be implemented as packet-switched network
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Bridges
Allow connections between LANs and WANsOperates at Layer 2 (Data Link Layer) of OSIUsed between networks using identical physical and link layer protocolsProvide number of advantages Reliability: Creates self-contained units Performance: Less contention Security: Not all data broadcast to all users Geography: Allows long-distance links
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Bridge Functions
Read all frames from each networkAccept frames from sender on one network that are addressed to receiver on other networkRetransmit frames from sender using MAC protocol for receiverMust have some routing information stored in order to know which frames to pass
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Bridge (or bridge-like device) can be used to connect two similar LANs, such as two CSMA/CD LANs.
Bridge can connect two closely similar LANs, such as CSMA/CD LAN and token ring LAN.
Bridges
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Bridges, cont’d
Bridge examines destination address in frame and either forwards this frame onto next LAN or does not.
Bridge examines source address in frame and places this address in routing table, to be used for future routing decisions.
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Bridge Interconnecting
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Bridge – Similar LANs
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Bridge Operation
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Transparent bridge does not need programming but observes all traffic and builds routing tables from this observation.
This observation is called backward learning.
Each bridge has two connections (ports) and there is routing table associated with each port.
Transparent Bridges
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Transparent Bridges, cont’d
Bridge observes each frame that arrives at port, extracts source address from frame, and places that address in port’s routing table.
Transparent bridge is CSMA/CD LANs.
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Bridge – CSMA/CD LANs
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Transparent bridge can also convert one frame format to another.
Note that some people/manufacturers call bridge such as this gateway or sometimes router.
Bridge removes headers and trailers from one frame format and inserts (encapsulates) headers and trailers for second frame format.
Transparent Bridge
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Data Frame – CSMA/CD to Token
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Source-routing bridge used with token ring networks.
Source-routing bridges do not learn from watching tables.
When workstation wants to send frame, it must know exact path of network / bridge …
Source-Routing Bridge
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Source-Routing Bridge, cont’d
If workstation does not know exact path, it sends out discovery frame.
Discovery frame makes its way to final destination, as it returns, it records path.
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Remote bridge is capable of passing data frame from LAN to LAN when LANs are separated by long distance and there is WAN connecting two LANs.
Remote bridge takes frame before it leaves first LAN and encapsulates WAN headers and trailers.
When packet arrives at destination remote bridge, bridge removes WAN headers and trailers leaving original frame.
Remote Bridge
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LAN with Frame Relay Network
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Device that connects LAN to WAN or WAN to WAN.
Router accepts an outgoing packet, removes any LAN headers and trailers, and encapsulates necessary WAN headers and trailers.
Routers
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Because router has to make WAN routing decisions, router has to dig down into network layer of packet to retrieve network destination address.
Routers operate at third layer, or OSI network layer, of packet.
Routers often incorporate firewall functions.
Routers, cont’d
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Asynchronous Transfer Mode
Connection oriented switched transmission methodology ATM characteristics is capability of delivering variety of traffic over both local and wide area networksATM has fixed length 53-byte cellUniform length allows timed, dependable delivery for streaming traffic (voice, video), and simplifies troubleshooting, administration, setup, and design
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Migration Strategies to ATM
IP over ATM – Known as classical IP, adapts CP/IP protocol stack to employ ATM services as native transport protocol directlyLAN emulation - allows all current upper layer LAN protocols to be transported by ATM services in an unmodified fashion. Provides translation between ATM addressing scheme and scheme native to particular emulated LAN.
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Migration Strategies to ATM, cont’d
Multi-Protocol Over ATM (MPOA), provides support for multiple local area network protocols running on top of ATM cell switched network
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ATM switch
ATM switch connections running at 155Mbps, upgradeable to 2.4 Gbps or higher.
ATM Backbone Network
Bridge or Router with ATM module - also known as an
ATM Access Switch
10 Mbps 16 Mbps
100 or 155 Mbps
155 Mbps
155 Mbps
Corporate Servers or High Speed Workstations with
155 Mbps NICs
25 Mbps ATM workgroup
concentrator
Local Clients and Servers with 25Mbps ATM NICs
25 Mbps
100 Mbps or 155 Mbps connection from workgroup concentrator to
ATM switch.
ATM WAN
Services
10Mbps Token Ring
MAU
Token Ring LAN (16Mbps)
10Base-T hub
Ethernet LAN (10Mbps)
ATM switch
ATM switch
155 Mbps
155 Mbps
GOLDMAN & RAWLES: ADC3e FIG. 06-20
ATM Implementation