high speed networks lecture 3
DESCRIPTION
ATM motivations and featuresTRANSCRIPT
Content to be covered
• Motivation for ATM• Definition of ATM• Genesis of ATM
Motivations for ATM
• There exist too many networks already.• But each one tailored (designed) for a specific
service requirement.• It is desired to have a single platform capable of
handling all the requirements.• single platform– Better network management– Reduced operational costs– Greater flexibility to network infrastructure
Motivations for ATM
• ATM is developed to fulfill this need.• So, for its realization, it deserves– Single Platform To provide end to end connectivity.
– Universal Platform that integrates different network services.
• Provisioning of Single Platform is called Seamless Networking
Seamless Networking
• Geographical distance between communicating entities must be hidden from end users (including time taken to fetch data from remote server, propagation time,..).
• This response time is different for LANs and WANs.
• ATM answers this problem by providing a common medium of transmission in both LAN and WAN environments.
Seamless Networking
• Generally, WANs provide lower data rates than LANs
• ATM overcome this problem as it is a point-to-point based technology. It has common LAN/WAN transmission medium.
Universal Platform
• Requirement to have a universal platform that can support different types of applications.
• Before ATM, networking fraternity was divided into two factions:1. Telecommunication world
backed by ITU-T.2. Data communication world
backed by IEEE, ISO and IETF
Universal Platform
Telecommunication world• ITU-T• Priority: voice transmission• ISDN paved a digital pipe
for Integrated (Multimedia) services.
• Failure of ISDN to provide Universal Platform, lead to the invention of B-ISDN
Data communication world
• ISO, IETF, IEEE• Priority: Data
transmission• VOIP made voice
transmission comfortable
• ATM was developed to provide a synergy between these two worlds.
Network Failures Vs Successes
Requirements for Success
• Low cost• High Performance Killer Applications• Timely Completion • Management• Interoperability• Coexistence with legacy LANs• Existing Infrastructure is more important than
new technology
ATM-definition
• Asynchronous Transfer Mode• It is the transfer mode in which information is
organized into cells, it is asynchronous in the sense that the recurrence of cells containing information is not periodic.
• Standardized as ITU-T I.113
MUX
`
Wasted bandwidth
ATM
TDM
4 3 2 1 4 3 2 1 4 3 2 1
4 3 1 3 2 2 1
Voice
Data packets
Images
Asynchronous Transfer Mode (ATM)
What in ATM?
ATM • ATM standard (defined by CCITT) is widely accepted
by common carriers as mode of operation for communication – particularly BISDN.
• ATM is a form of cell switching using small fixed-sized packets.
Header Payload
5 Bytes 48 Bytes
Basic ATM Cell Format
Leon-Garcia & Widjaja: Communication Networks
ATM Conceptual ModelFour Assumptions
1. ATM network will be organized as a hierarchy.User’s equipment connects to networks via a UNI (User-
Network Interface).Connections between provided networks are made through
NNI (Network-Network Interface).
2. ATM will be connection-oriented.A connection (an ATM channel) must be established before any cells are sent.
X
X
X
X
X
X
X
X
X
Private UNI
Public UNI
NNI
Private NNI
Private ATM network
Public UNI
B-ICI
Public UNIPublic ATM network A
Public ATM network B
Figure 9.5Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
ATM Connections
• two levels of ATM connections:virtual path connectionsvirtual channel connections
• indicated by two fields in the cell header: virtual path identifier VPI virtual channel identifier VCI
Physical Link
Virtual Paths
Virtual Channels
Figure 7.40
ATM Virtual Connections
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
ATM Conceptual Model Assumptions (cont.)
3. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates.
4. ATM must supports low cost attachments• This decision lead to a significant decision – to
prohibit cell reordering in ATM networks. ATM switch design is more difficult.
GFC (4 bits) VPI (4 bits)
VPI (4 bits) VCI (4 bits)
VCI (8 bits)
VCI (4 bits) PT (3 bits) CLP (1 bit)
HEC (8 bits)
ATM cell header
Payload (48 bytes)
Figure 9.7
UNI Cell Format
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
2
3
N
1Switch
N
1…
5
6
video 25
video
voice
data
32
32 61
2532
3261
75
67
3967
N1
32
video 75
voice 67
data 39
video 67
Figure 7.38
…
…
ATM Cell Switching
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
c ATMSw1
ATMSw4
ATMSw2
ATMSw3
ATMDCC
ab
de
VP3 VP5
VP2
VP1
a
bc
deSw = switch
Figure 7.39
Digital Cross ConnectOnly switches virtual paths
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
25
Plane managem
entManagement plane
Control plane User plane
Physical layer
ATM layer
ATM adaptation layer
Higher layers Higher layers
Layer managem
ent
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
ATM-layers
Cell Switching and Jitter
References
• Sumit Kasera, “ATM Networks-concepts and Protocols”, 2e, Tata McGraw Hill publications, ISBN-10: 0-07-058353-6.
• Harry Perros, “ATM Networks”.• Leon-Garcia & Widjaja, “ Communication
Networks”.• ATM network Simulatorhttp://w3.antd.nist.gov/Hsntg/req_atm-sim.html.