Transcript Lecture 8 - cda college

ATM Technologies
Chapter 8
Learning Objectives
Explain the general characteristics of ATM
Describe ATM layered communications
Explain the ATM cell structure
Explain how ATM works
Discuss ATM design considerations
Describe ATM applications on LANs and WANs
Discuss virtual LANs and ATM
Discuss network management issues for ATM
LANs and WANs
Introduction to ATM
High-speed transport technology that
handles voice, video, data, and multimedia
transmissions
Transmits fixed-length cells rather than
packets over virtual circuits
Uses cell-switching
Has QoS capabilities
Advantages of ATM
Scalable
Solves congestion problems
Helps segment networks
Provides high-speed connectivity to desktop
Contributors to ATM
ATM Forum
Internet Engineering Task Force (IETF)
Frame Relay Forum
Switched Multimegabit Data Service
Special Interest Group (SMDS SIG)
Technologies Compatible
with ATM
B-ISDN
DSL
FDDI
Frame relay
Gigabit and 10 Gigabit Ethernet
SONET and SDH
SMDS
Wireless communication
ATM Characteristics
Transports wide range of information
transmissions at high speeds
Divides data into equal-sized cells
Attaches a header to ensure that each cell is routed to its
destination
Transports voice, video, and data equally well
Easily scalable; switch-based technology
Physical links operate over many cable types
Many possible ATM transmission speeds
ATM Layered
Communications
ATM Protocol Reference Model
Four-layer architecture
Enables multiple services to function at same
time on single network
ATM MAC equivalent sublayer operates
independently of upper layers
ATM layer and ATM Adaptation layer
(AAL) specifically perform ATM functions
ATM Layers
ATM Physical Layer
Converts cell stream into transportable bits
Handles functions at physical medium
(cable)
Defines electrical and physical interfaces,
line speeds, and transmission control
Two sublayers
Transmission Convergence (TC) sublayer
Physical Medium Dependent (PMD) sublayer
ATM Layer
Creates the ATM cell
Determines cell structure, how cell is
routed, and error-control techniques
Ensures QoS of virtual circuit or channel
Functions performed by:
ATM switch
ATM attached device
ATM QoS Service Attributes
ATM Adaptation Layer (AAL)
Responsible for segmentation and reassembly of
data into and out of ATM cell format
Ensures that different traffic types are assigned
correct QoS level
Provides support for four classes of service
Two sublayers
Convergence sublayer
Segmentation and Reassembly (SAR) sublayer
AAL Types
ATM Services and
Applications Layer
Determines class of service needed for a
transmission
Establishes link between node generating the data
stream and the ATM Adaptation layer
Four service classes
Constant bit-rate service (CBR)
Variable bit-rate service (VBR)
Unspecified bit-rate service (UBR)
Available bit-rate service (ABR)
ATM Services and Applications
Layer Service Types
ATM Cell Structure
Fixed-length cell
5-byte header
Provides each cell with channel and path
information
48-byte payload
Fields in ATM Cell Header
Generic Flow Control (GFC)
Virtual Path Identifier (VPI)
Virtual Channel Identifier (VCI)
Payload Type Indicator (PTI)
Cell Loss Priority (CLP)
Header Error Control (HEC)
ATM Cell Header
How ATM Works
Creates virtual circuits as pathways between
sending and receiving nodes
Permanent virtual circuit (PVC)
Switched virtual circuit (SVC)
Smart permanent virtual circuit (SPVC)
PVC
Dedicated between two endpoints
Preassigned path and fixed allocated
bandwidth between endpoints
SVC
Created on an as-needed basis only for as
long as devices are communicating
SPVC
Combines characteristics of PVCs and
SVCs
Must be manually configured (like PVC)
Each transmission has its own defined path
(like SVC)
ATM Transmission
Characteristics
Logical connection-oriented technology
Virtual circuits define logical channels
Virtual channels (VCs)
Virtual paths (VPs)
Advantages of
ATM Network Design
Cells arriving at incoming port can be easily
directed to appropriate outgoing port
Grouped/shared connections along a
common virtual path require only one set of
management services
Easy to add virtual circuits
Automatic adjustment of all channels in a
path to compensate for a problem
ATM Design Considerations
ATM components
ATM switch
ATM switch characteristics and types
ATM interface types
ATM Components
ATM Switch Characteristics
Number and size of cell buffers
Port contention and management of port
parameters
Connection management
Latency
Types of physical and internetworking
interfaces
Traffic and congestion control options
ATM Switch Types
ATM LAN switches
ATM modules for existing multiprotocol
network hubs
Multiprotocol hubs
ATM Interface Types
User-Network Interface (UNI)
End node-to-switch connection
Network Node Interface (NNI)
Connection between two ATM switches
Uses of ATM
LAN backbone
LAN design uses
High-speed LAN access to servers
Connections to desktop
WAN design uses
Uses of ATM
ATM as a LAN Backbone
Simplifies network management by reducing
complexity of internetworking environments
Able to increase backbone speeds incrementally
Allows “future-proofing” of network
Common in campus environment
Works well for:
Small to medium-sized legacy backbones
As a backbone for large multi-LAN designs
ATM on a Legacy LAN
ATM on a Large Multi-LAN
ATM LAN Design Uses
LAN Emulation (LANE)
Technique used to adapt ATM to Ethernet network by
creating a multicast network to enable preassigned
groups of Ethernet nodes to receive transmissions
Vital for integrating ATM with non-ATM networks
Uses ATM’s connection-oriented technology without
requiring hardware or software changes within legacy
LAN
Benefits of LANE
Compatible with legacy LAN equipment
Application software and upper-layer
protocols can communicate over LANE
Client can be anywhere; not bound by
distance limitations of legacy LAN
Network traffic congestion not a problem
LANE Components
LAN Emulation Client (LEC) software
LAN emulation software; implemented on
three logical servers
LAN Emulation Server (LES)
Broadcast and Unknown Server (BUS)
LAN Emulation Configuration Server (LECS)
Classical IP over ATM
Transport of IP over ATM; focuses strictly
on IP support
Each subnet must have its own ARP server
Simpler implementation than LANE;
generates less network overhead
Any device with a legacy LAN connection
must pass through a router to reach
destination device
Multiprotocol over ATM
(MPOA)
Communications technique that enables
multiprotocol traffic to be routed over ATM
Network layer protocols use routers to
communicate across subnet boundaries
Can produce performance problems
Integrates LANE and the Next Hop
Resolution Protocol (NHRP)
ATM High-Speed LAN Access
to Servers
Alternative when Fast Ethernet no longer able to
handle traffic to heavily used LAN servers
Benefits of a “server farm”
Easy to connect to ATM switches on network backbone
Cheaper and easier bandwidth upgrades
Easier for administrator to control access to servers
Enables servers to be secured
Easier to place servers on conditioned power and UPS
Multiple servers can share one display monitor
ATM for Connections
to the Desktop
To relieve congestion caused by more
demanding software applications
To achieve full QoS
Each end device must be equipped with an
ATM adapter o NIC
ATM WAN Design Uses
Connecting two or more LANs using an
ATM WAN
Transporting ATM over SONET
Connecting frame relay WANs using an
ATM WAN
Connecting SMDS WANs using an ATM
WAN
Transporting Frame Relay
over ATM
Transporting Frame Relay
over ATM
Virtual LANs
Benefits of VLANs over ATM networks
Enable logical segmentation of a network
regardless of physical network constraints
Enhanced network performance
Advanced network management features
Capability for reducing number of router hops
and amount of required bandwidth
Network Management Issues
for ATM LANs and WANs
Monitoring and controlling all virtual
circuits (PVCs and SVCs)
Network topology
Status of ATM network devices
Overall goal
Monitor network congestion and flow control
for optimal traffic patterns
Chapter Summary
Characteristics of ATM networks
ATM layered communications
ATM’s use of cells instead of packets
How ATM works
ATM design elements
How ATM is applied to LANs and WANs
Link between ATM and virtual LAN
configurations
Basic ATM network management considerations