ATM QoS

1
ATM QoS
2
Overview

• ATM introduction
• ATM architecture
• ATM QoS
• IP-ATM integration
• IP-ATM QoS Mapping

3
Pre-ATM EraService Specialization
POTS (Plain Old Telephone Service) VOICE Circuit
Switching Delay Guarantee QoS Limited Speed
Data No Video
Computer Network (LAN, MAN, WAN) DATA Packet
Switching No Delay Guarantee No QoS (best
effort) Not suitable for Voice and Video
TV Network (CATV, Satellite, etc.) VIDEO Circuit
Switching Delay Guarantee QoS No data or voice
4
Consequence of Service Specialization

• Several Independent networks, each has its own
• design
• manufacturing
• implementation
• maintenance
• Low utilization Free resources in one network
  cannot be utilized by another network
• Inflexible cannot benefit from technological
  advances that change service requirements (e.g.
  NISDN switches cannot handle 32Kbps ADPCM voice)

5
ATM Era Multiservice NetworksDeparture from
Service Specialization
bulk data
video
Multiservice Network
voice
interactive data
6
ATM Convergence
POTS
Voice
N-ISDN
ATM Network
10 Mbps Ethernet
FastEthernet FDDI
Digital TV VOD
Analog TV Video Cass
Video
Data LAN
Frame Relay
Data WAN
X.25
7
ATM Protocol Architecture
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
8
End-to-End ATM Architecture
ATM terminal
ATM terminal
ATM switch
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
9
Virtual Channels

• ATM is connection oriented
• AN ATM connection is called virtual
  channel/connection/circuit (VC)
• A VC must be established between two end points
  before data can be transmitted
• Tens of thousands of VCs per fiber
• Different VC, different bandwidth, QoS
• User data and signaling on different VCs

10
Virtual Paths

• Virtual Private Network over public ATM
• many individual VCs between two sites
• switches need to switch VCs individually even if
  they start and end at the same points
• VCs starting and ending at the same points can be
  bundled in virtual paths or VPs
• Switches may switch only VPs, not aware of
  individual VCs inside the VP

11
Virtual Paths Virtual Channels
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
VC
VC
VP
VC
VC
VC
VC
VP
VC
VC
Physical Channel
VC
VP
VC
VC
VC
VC
VP
VC
VC
VC
12
Virtual Path Connection (VPC)
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
13
Virtual Channel Connection (VCC)
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
14
Permanent Virtual Circuit

• VPIs and VCIs for the end-to-end connection are
  preconfigured in hardware
• Semi-PVC VPIs and VCIs are preconfigured, but
  can be erased and reconfigured later
• PVC is good for Virtual Leased Line for VPN
• PVC does not scale well for an ATM LAN/WAN with
  many stations too many PVCs required

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Switched Virtual Circuit

• Circuit on demand
• Scalable solution to ATM connectivity
• Different VPIs and VCIs at successive call setups
  for the same source-destination.

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ATM Interfaces

• User-Network Interface (UNI)
• public
• private
• Network-Network Interface (NNI)

Copy figure 9.3 from text
17
ATM Cells

• 53-byte long
• 5-byte header
• 48-byte payload
• Slightly different format for User-Network and
  Network-Network communications

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Advantages of Short, Fixed Size Cells

• Minimise delay for voice/video traffic
• minimise delay variance (jitter)
• Easier to process (fast switching)

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UNI Cell Structure
8 7 6 5 4 3 2
1
GFC
VPI
VPI
VCI
VCI
VCI
PT
CLP
HEC
Cell Payload (48 octets)
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
20
NNI Cell Structure
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
8 7 6 5 4 3 2
1
VPI
VPI
VCI
VCI
VCI
PT
CLP
HEC
Cell Payload (48 octets)
21
ATM Adaptation Layer 5
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
22
AAL5 Format
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
23
QoS Support

• Traffic contract
• Traffic descriptions
• QoS parameters
• Service classes

24
ATM Traffic Contract
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
25
Traffic Descriptors

• Peak cell rate
• Sustainable cell rate
• Minimum cell rate
• Maximum burst size
• Maximum frame size
• Cell delay variation tolerance

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QoS Parameters

• Maximum cell transfer delay
• Cell delay variation
• Cell loss ratio

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Service Classes

• Constant bit rate
• Variable bit rate
• Available bit rate
• Unspecified bit rate
• Guaranteed frame rate

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IP-ATM Integration

• ATM to the desk-top
• ATM in the backbone

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ATM to the Desktop
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
30
ATM in the Backbone
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
31
Encapsulation IP into ATM

• Encapsulating IP packets into Ethernet or Token
  Ring frames were trivial
• IP into ATM is not that trivial as ATM is
  connection-oriented (VC-Based) and ATM has high
  protocol overhead

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LLC/SNAP Encapsulation

• Traditional encapsulation technique
• Multiprotocol support (same VC, many protocols)
• 8-byte additional overhead

IP Datagram
IP, IPX, Netbeui
LLC/SNAP Header
VC 1
8
AAL5 Trailer
8
AAL5 packet
Source
Destination
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com
33
VC-Based Multiplexing
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com

• Each VC is configured and dedicated for a given
  protocol
• LLC/SNAP header is not required

IP
VC 1
IP Datagram
AAL5 Trailer
Netbeui
8
VC 2
IPX
AAL5 packet
VC 3
Source
Destination
34
IP-ATM QoS Mapping
Reprinted with Permission from Engineering
Internet QoS - Jha Hassan, Artech House
Publishing, Norwood, MA, USA. www.artechhouse.com

• Intserv over ATM
• Diffserv over ATM
• Performance implications of QoS mapping

35
Intserv over ATM
Show Tables 9.2, 9.3 and 9.4
36
Diffserv over ATM
Figure 9.17
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Performance of QoS Mapping

• Mapping provides approximate solution
• ATM has two drop precedences, Diffserv AF has
  three
• ATM uses cells/sec, IP uses bytes/sec
• not the same due to padding
• Experiments show problems with QoS mapping
• Over provision may be needed to account for QoS
  mapping inaccuracies