1. ATM Technologies
Chapter 8

2. 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

3. 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

4. Advantages of ATM Scalable Solves congestion problems
Helps segment networks
Provides high-speed connectivity to desktop

5. Contributors to ATM ATM Forum Internet Engineering Task Force (IETF)
Frame Relay Forum
Switched Multimegabit Data Service Special Interest Group (SMDS SIG)

6. Technologies Compatible with ATM
B-ISDN
DSL
FDDI
Frame relay
Gigabit and 10 Gigabit Ethernet
SONET and SDH
SMDS
Wireless communication

7. 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

8. 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

9. ATM Layers

10. 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

11. 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

12. ATM QoS Service Attributes

13. 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

14. AAL Types

15. 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)

16. ATM Services and Applications Layer Service Types

17. ATM Cell Structure Fixed-length cell 5-byte header 48-byte payload
Provides each cell with channel and path information
48-byte payload

18. 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)

19. ATM Cell Header

20. 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)

21. PVC Dedicated between two endpoints
Preassigned path and fixed allocated bandwidth between endpoints

22. SVC
Created on an as-needed basis only for as long as devices are communicating

23. SPVC Combines characteristics of PVCs and SVCs
Must be manually configured (like PVC)
Each transmission has its own defined path (like SVC)

24. ATM Transmission Characteristics
Logical connection-oriented technology
Virtual circuits define logical channels
Virtual channels (VCs)
Virtual paths (VPs)

25. 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

26. ATM Design Considerations
ATM components
ATM switch
ATM switch characteristics and types
ATM interface types

27. ATM Components

29. 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

30. ATM Switch Types ATM LAN switches
ATM modules for existing multiprotocol network hubs
Multiprotocol hubs

31. ATM Interface Types User-Network Interface (UNI)
End node-to-switch connection
Network Node Interface (NNI)
Connection between two ATM switches

32. Uses of ATM LAN backbone LAN design uses
High-speed LAN access to servers
Connections to desktop
WAN design uses

33. Uses of ATM

34. 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

35. ATM on a Legacy LAN

36. ATM on a Large Multi-LAN

37. 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

38. 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

39. 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)

40. 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

41. 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)

42. 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

43. 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

44. 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

45. Transporting Frame Relay over ATM

46. Transporting Frame Relay over ATM

47. 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

48. 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

49. 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