Lecture Computer Networks
Prof. Dr. Hans Peter Großmann mit M. Rabel sowie
H. Hutschenreiter und T. Nau | Sommersemester 2012 |
Institut für Organisation und Management von
Informationssystemen
Asynchronous Transfer Mode (ATM)
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Computer Networks | ATM | Sommersemester 2012
ATM – The Idea
•
Provision of network capabilities for handling all current and
future applications independently of their bandwidth
requirements.
•
The main goal was a unification of telecommunication with
data communication.
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Computer Networks | ATM | Sommersemester 2012
ATM – The Idea (II)
Computer and
Application Software
Video
V ideo
Disks
Audio
Network
ATM
Interface
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Computer Networks | ATM | Sommersemester 2012
B-ISDN
Telecommunication
Radio and Television
Data Communication
Telecommunication
Data Communication
B-ISDN
ISDN
(Integrated Services
Digital Network)
(Broadband Integrated
Services Digital Network)
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Computer Networks | ATM | Sommersemester 2012
Todays Communication Infrastructure
TC
P u b lic
STN
M U X
TC
...
M U X
c o n n e c t io n o r ie n t e d
R o u te r
R o u te r
p a c k e t s w it c h e d
R o u te r
H U B
X .2 5
F ra m e -R e la y
R o u te r
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Computer Networks | ATM | Sommersemester 2012
B-ISDN / ATM Infrastructure
B-ISDN
IBCN
Services
Server
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Computer Networks | ATM | Sommersemester 2012
Asynchronous Transfer Mode (ATM)
•
Strategic B-ISDN direction since 1988
•
Standards of ITU and the ATM Forum
•
Technology
• Fast packet switching
• Variable bandwidth channel assignment
•
ATM can handle different bit rates and traffic parameters with data rates
155.52 Mbps / 622.08 Mbps at UNI
•
Transmission interface SONET / SDH up to 2.4 Gbps
•
Culmination of all developments in circuit and packet switching over the
past 20 years
•
ATM-Forum founded in 1991
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Computer Networks | ATM | Sommersemester 2012
ATM II
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Computer Networks | ATM | Sommersemester 2012
ATM Drafts
Packet switching
• no linkwise error protection
• connection-oriented
• small packet (cells) of fixed length
Time division multiplexing method
• time slot method
• time relations are not supported
• time slots are not marked by their position (asynchronous)
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Computer Networks | ATM | Sommersemester 2012
STM / ATM
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Computer Networks | ATM | Sommersemester 2012
Synchronous Transfer Mode (STM)
•
Based on time division multiplexing
•
Disadvantages
– Fixed data rates
– Fixed bandwidth for connection
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Computer Networks | ATM | Sommersemester 2012
ATM Transmission Efficiency
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Computer Networks | ATM | Sommersemester 2012
Cell Structure
5 Bytes
48 Bytes
Header
Payload
GFC:
Generic Flow Control
(used only with UNI)
GFC
VPI
GFC: Generic Flow Control
VPI: (used
Virtual
Identifier
only Path
with UNI)
VPI
VCI
VPI:
PathChannel
IdentifierIdentifier
VCI: Virtual
Virtual
VCI:
Channel
Identifier
PTI: Virtual
Payload
Type
Identifier
VCI
VCI
PTI
HEC
1 Byte
CLP
PT:
Type Priority
Identifier
CLP: Payload
Cell Loss
CLP:
Loss Priority
HEC: CellHeader
Error Control
HEC: Header Error Control
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Computer Networks | ATM | Sommersemester 2012
ATM Bandwidth
•
NNI (network-network interface)
155 Mb/s, 622 Mb/s, 2.4 Gb/s
•
UNI (user-network interface)
25 Mb/s ... 622 Mb/s
•
bandwidth allocation for an application on demand
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Computer Networks | ATM | Sommersemester 2012
Modes of Connection
Permanent Virtual Circuit (PVC)
• VCI/VPI tables are created manually by administrator
• PVCs exist permanent, even when there is no data traffic
Switched Virtual Circuits (SVC)
• connections are established and closed dynamically by ATM
signalling
• SVCs normally are closed when no data traffic occurs
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Computer Networks | ATM | Sommersemester 2012
ATM Switch Matrix
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Computer Networks | ATM | Sommersemester 2012
Page 18
Computer Networks | ATM | Sommersemester 2012
ATM - Classes of Services I
Class A
Time Reference
Bit rate
Class B
time-continuous
constant
Connection
Mode
Class C
Class D
not time-continuous
variable
connection-oriented
Services
Audio / Video
Audio / Video
Adaption Layer
AAL 1
AAL 2
connectionless
Services for
data
Services for
data
AAL 5, AAL 3/4
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Computer Networks | ATM | Sommersemester 2012
ATM - Classes of Services II
Class A
– Circuit emulation
– Intended for constant bitrate voice and video applications
– Timing relationship between source and destination
Class B
– Variable bit rate services
– Intended for isochronous voice and video traffic with variable
bitrate information
– Timing relationship between connection endpoints (connectionoriented)
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Computer Networks | ATM | Sommersemester 2012
ATM - Classes of Services III
Class C
– Connection-oriented data transfer
– Intended for traditional data traffic as known e.g. in X.25
– “message mode”: transfer of single frames
– “streaming mode”: transport for multiple fixed length frames
Class D
– Connectionless data transfer
– Intended to carry e.g. TCP/IP or LAN interconnection traffic
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Computer Networks | ATM | Sommersemester 2012
ATM Architecture
Management Plane
OSI Model
Higher
Layers
Control
Plane
Signalling &
Controlling
User Plane
Class 1
Class 2
Class 3
ATM Adaptation Layer (AAL)
Layer 2
ATM Layer
Layer 1
Physical Layer
Class 4
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Computer Networks | ATM | Sommersemester 2012
ATM Layers
Control
User
Higher
Layers
Signalling
Class
A
Class
B
ATM Adaptation
Layer
Sign. AAL
AAL1
AAL2
ATM Layer
Class
C
AAL3/4
or AAL5
Convergence Sublayer CS
Segmentation and Reassembly SAR
Physical Layer
Transmission Convergence TC
Physical Medium PM
Class
D
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Computer Networks | ATM | Sommersemester 2012
Encapsulation – the general scheme
Data from Application
Convergence Layer
Header
Trailer
CS
Data
CS
ATM
SAR
Data
CS
SAR
SAR
Data
CS
SAR
SAR
Data
SAR
Data
SAR
CS
SAR
SAR
SAR Sublayer
Data
ATM
SAR
CS
SAR
ATM
cells:
ATM
SAR
ATM Layer
Data
(Not each adaption layer uses CS and SAR header and trailer)