1. Asynchronous Transfer Mode (ATM) and QoS

2. ATM Era : Multiservice Networks Departure from Service Specialization
bulk
data
video
Multiservice
Network
voice
interactive
data

3. Why ATM Did Not Make it the Way it was Initially Envisioned
Advantages of ATM
Disadvantages of ATM
Commercial Factors
Single network optimized for everything (Data, phone, TV)
Same technology for WAN, MAN, LAN (Seamless integration)
QoS oriented and high-speed oriented
Fast Hardware
Tremendous amount of research has been done
Large overhead for packets
QoS is a bit complicated from the applications point of view and network management point of view
Not that great from web browsing (which is one killer application)
Millions of networks already installed
Lack of applications
Expensive at the LAN (where it really matters)
No strong business incentive for QoS (even up to now)
Can achieve similar speed with an IP router as compared to an ATM switch (May be)

4. Fixed length packet = cell
What is ATM?
ATM is packet switching!
Switched or permanent connections
Traffic type independent (voice, data, interactive video)
Fixed length packet - 53 bytes (cell)
header
payload
Fixed length packet = cell
Temorary or permenant connections
connection oriented or connectionless oriented
Traffic type independent - media independent - rate independent
Fixed length - easily implementable in silicon - predictiable
Typical LAN packets are several Kbytes

5. ATM Cell Relay: The Underlying Technology
Cell Features Benefit
Small Low latency to support real-time services like audio and video (What is an appropriate size?)
Fixed Length Fast hardware switching and scalability
Standardized Usable in all networks (LAN and WAN)
Cells
Voice
Data
Video
SMALL - other data doesn’t get stuck behind it
Fixed Length - predictable delays

6. Without Short Cells
A voice packet waits behind a large data packet

7. With Short Cells Voice packet can go immediately after data packet #1
Waiting for voice is reduced significantly

8. Virtual Paths & Virtual Channels
A Virtual Path (VP) describes the semi-permanent route between two end points.
A Virtual Channel (VC) describes a cell transmission channel inside a virtual path
Physical
Transmission
Link
VCs VP
Unique on a link-by-link basis
Virtual channels are contained within virtual paths
Interpreted at each switch to:
determine output link
determine outgoing VPI/VCI
Two-level structure:
allows “trunking” of virtual channels as one virtual path
virtual path can be switched
both used to route cells through network
Physical transmission link = cable/media (copper or fiber)
switched virtial channels within permanent virtual path
Key point: customers can have SVCs even though service providers (carriers) have only PVP services. Often referred to as SVC tunnelling.
Also, PVP’s can provide some firewalling capabilities
VCs associated to VPs are globally switched
VPs mostly between switches
reduce reroute time - upon failures

9. Connection Identifiers

10. ATM switch routing Virtual Paths ATM ATM Switch Switch ATM Switch ATM
Circuits

11. ATM Switches ATM switches translate VPI/VCI values
Input
Output 45
Port
VPI/VCI
Port
VPI/VCI 1 29 2 45 2 29 64 2 45 1 29 1 1 64 3 29 3 3 29 1 64 29
ATM switches translate VPI/VCI values
VPI/VCI value unique only per interface— eg: locally significant and may be re-used elsewhere in network

12. ATM Switching Connections (routes) set up by software
Routing (path through multiple-switch network) and resource allocation is performed once per connection by switch control CPU
Cells are switched by hardware
Hardware (table lookup + switching fabric) switches each incoming cell to appropriate output port
Once a connection is established, cells are not touched by software
• Resource allocation is by connection, not packet
• Better performance and price - with hardware switching
• Scalability
Hardware Switching = fast
ATM = scalable

13. VP and VC Switch Two types of ATM switch
VP switch does not look at VCIs, switching is based on VPIs only
VCI does not change when passing through a VP switch; VPI may change
VC switch looks at both VPI and VCI
VCI (as well as VPI) may change when passing through a VC switch

14. Routing with a VP Switch

15. A Conceptual View of a VP Switch

16. Routing with a VC Switch

17. A Conceptual View of a VC Switch

18. ATM Protocol Stack Upper Layers ATM Adaptation Layer ATM Layer
Reference Model
Analogous to Link and Physical layer of OSI, but w/ enhancement
• connection oriented
• integral routing
Transmission
• Cell muxing
• Cell headering generation
• UPI/VCI translation
Physical Layer

19. ATM Architecture Application Upper Layer Protocols Presentation
Session
ATM Adaptation Layer
Transport
Network
Data Link
ATM Layer
Transmission-convergence
physical medium dependent
Physical

20. Adaptation Layers: Service Classes

21. Service Classes and Capacity of Network

22. QUEUES and PRIORITY Classifier Output CBR Traffic Priority 1
VBR Traffic
Priority 2
Classifier
Output
ABR Traffic
Priority 3
Priority 4
UBR Traffic

23. ATM Adaptation Layer: Summary
Class
Service Categories
Bit Rate
Connection Mode
Timing Concern
Application Examples
ATM Adaptation Layer
(AAL) A
AAL1
CBR (Constant)
Connection- Oriented
Yes
Bandwidth and throughput guaranteed
Good for voice and video B
AAL2
VBR (Variable) VBR-RT and VBR-NRT
Connection- Oriented
Yes
Best effort bandwidth and throughput
Good for live video, multimedia, LAN-to-LAN
ATM Layer C
AAL5
ABR (Available)
Connection- Oriented No
Best effort with congestion feedback
Reliable delivery of bursty traffic if latency okay
Physical Layer D
AAL3/4
UBR (Un-specified)
Connection- less No
No guarantee
For SMDS/LAN

24. QUALITY OF SERVICE
Max CDT, Mean CTD, CDV, CLR, CER, SECBR, CMR

25. Application Requirements
Bandwidth
Peak Cell Rate (PCR)
Sustained Cell Rate (SCR)
Minimum Cell Rate (MCR)
Delay
Cell Transfer Delay (CTD)
Cell Delay Variation (CDV)
Reliability
Cell Loss Ratio (CLR)
Cost ($ or Admin)
Link Weighting