1. ATM service types CBR (Constant Bit Rate)
rt-VBR (Real-time Variable Bit Rate)
nrt-VBR (Non real-time Variable Bit Rate)
ABR (Available Bit Rate)
UBR (Unspecified Bit Rate) 9 22

2. ATM service classes Four Specified QoS classes are defined:
Class 1: (CBR) Suitable for Circuit Emulation.
Class 2: (VBR) packetized video/audio -- eg. motion JPEG
Class 3: (nrt VBR) CONS -- eg. frame relay, X.25
Class 4: (ABR) CLNS -- eg. IP
Class 0: (UBR) Best Effort Service. 10 23

3. Constant Bit Rate (CBR)
Has defined rate (cells per second)
Peak Cell Rate (PCR) equals Sustainable Cell Rate (SCR): no burstiness
Cells are carried at high priority
Emulates fixed-bandwidth channel 24

4. The Issue of the CBR CDV accumulation problem
But it is a very important service:
DiffServ defined virtual leased line service

5. Variable Bit Rate (VBR)
Has Peak Cell Rate (PCR) that is higher than the Sustainable Cell Rate (SCR)
Conforming cells get high priority; excessive cells are given lower cell loss priority
ITU divides by use:
Class B: VBR audio and video
Class C: Connection-oriented data (e.g., Frame Relay or X.25 over ATM)
Class D: Connectionless data (e.g., IP over ATM) 25

6. The Issues of VBR Advantages:
Statistically multiplexed, more efficient use of bandwidth
Disadvantages:
non-zero cell loss
currently no parameter to specify the source type,
it is difficult to engineer the traffic so that the QoS
is guaranteed while multiplexing is achieved

7. Available Bit Rate (ABR)
Use unused bandwidth by CBR and VBR
User can exceed PCR and SCR: well-suited for bursty data traffic
Flow control required to make efficient use 27

8. The Issues of ABR
The share of available bandwidth for each ABR connection
is dynamic and may be down to a specified minimum cell
rate.
The ABR service is appropriate only for application which
adapt their rates to the time-varying available bandwidth
and tolerate unpredictable cell delays. ABR guaranteed a
minimum cell loss for those application

9. Impact of Cell loss in ATM networks
What we can do for the issue ? 5 29

10. Flow control Rate based (ATM Forum)
Explicit forward congestion indication (EFCI)
Explicit rate (ER)
Both are end to end types of flow control
Credit based
- hop by hop
Generic flow control (end-station only)
Hybrid

11. The issues of the EFCI ABR
When ATM switch activates EFCI in a connection.
What is the problem ?
Can only indicate the existence of congestion
somewhere along the connection,but not the location
or severity.
How about some cell carry these type of info ?

12. The issues of the EFCI ABR
Actually it is a delayed report for network status.
How to improve it ? What are disadvantages ?
Ideas: (1) backward
(2) Congestion flag in backward RM cells
(3) Breaks the feedback loop into separate segments

13. The Issues For The ER ABR
Advantages:
How about If the RM cell is lost due to congestion ?
Source rate transitions is explicit and immediately
to proper rate.
Congestion relieved faster
How about RM cell direction ?
When the RM cells should be sent back by the dst ?

14. The Issues For the ABR Service
Policing issue
Policing complexity issue for EFCI ABR

15. Traffic parameter mapping13 62