Introduction -
As a technology ATM has been around for many years with the first standards
having been with us for well in excess of 10 years. ATM has developed and
evolved dramatically over this time and is now regarded as an extremely robust
and well understood technology used extensively in carrier network environments
as well as a backbone technology for much of today's Internet traffic. It has
also found many other applications including use in the 3rd Generation mobile
(3G or UMTS) network environment as well as others such as wireless local loop
applications and DSL (Digital Subscriber Lines), to name a few.
Contrary to what many people will tell you, the use of ATM continues to grow at
a dramatic rate. There are alternative ways of achieving many of the
applications that ATM supports, but there is yet to be a technology that can
deliver everything that ATM offers in terms of variety, guarantees of operation
(e.g. Quality of Service - QoS) and standardisation.
What the Course
Delivers - This course provides
a solid understanding of ATM in terms of the technology as well as how it is
applied to real-life applications. We look at ATM in a real way, giving the
benefits to its use as well as highlighting some of the issues it creates. We
include a wide range of application coverage, although it is normal not to cover
all subjects to the same depth. We appreciate the areas that are of most (and of
least) importance today and focus on these in greater depth. If a specific
audience wishes to focus on specific areas, then we are very happy to do this.
Much emphasis is placed on ensuring the students leave the course with a
thorough understanding of ATM and, to that end, we make use of a lot of
exercises throughout the course.
Who should attend
the course? - Anyone wishing to
develop a solid understanding of ATM technology. A basic understanding of
datacommunications/telecommunications is helpful.
Course Length
- Three days.
ATM Technology
1. Introduction
to ATM
2. The ATM layer
3. The Physical layer
4. The ATM Adaptation Layer (AAL)
5. ATM Service
Categories and Traffic Management
6. Signalling for SVCs and Soft-PVCs
7. ILMI and OAM
8. Private
Network-Network (Network-Node) Interface - PNNI
Applications on ATM
9. Voice
over ATM
10. MPEG-2 Video over ATM
11. IP
over ATM (Layer 2 Support):
12. IP
over ATM (Layer 3 Support):
13. Frame
Relay/ATM Interworking
ATM Technology
1
Introduction to ATM
This section acts as an introduction to
ATM, defining what it is and why its use is so popular in many networking
environments. We look at some of the applications that are driving ATM's
deployment along with the nature of the types of traffic produced by them and
which ATM so successfully supports.
Also discussed are some of the fundamental points behind ATM, which lay the
ground for a more detailed understanding of the way in which ATM actually
operates.
- What is ATM?
- Why use ATM?
- What applications are suitable for
ATM?
- The nature of different traffic types
- An introduction to service categories
- CBR, VBR (rt and nrt), ABR, UBR, UBR+ and GFR
- Some fundamental points to ATM
- ATM network reference points
- A small bit on the standards for ATM -
ITU-T, ATM Forum, IETF, ETSI, ANSI etc…
2
The ATM Layer
One of the key factors behind ATM
offering high-speed networking along with the ability to deliver Quality of
Service guarantees, is the use of a small and fixed size cell. This section
looks at the ATM cell header in detail with a description of the various fields
within it and how the network and/or end-user equipment uses them.
-
- GFC (Generic Flow Control)
- VPI/VCI (Virtual Path Identifier,
Virtual Channel Identifier)
- PT (Payload Type)
- CLP (Cell Loss Priority)
- HEC (Header Error Control)
3
The Physical Layer
The original idea behind ATM was for
use on high speed transport mechanisms such as SDH and SONET. The original ITU-T
recommendations described only two transport speeds of 155Mbit/s and 622Mbit/s.
Today, many other physical interfaces
have also been defined for the support of ATM cells. This section will have a
brief look at how ATM cells are actually transported on some of the physical
interfaces. In addition, we also look at how ATM may be inverse multiplexed
across a number of low speed lines to give a virtual higher speed line.
-
A summary of the 'standardised'
physical interfaces
- Example of cell based interface for
clear channel operation
- Example of framed interface carrying ATM cells
-
Cell delineation using HEC field
-
IMA - Inverse Multiplexing over ATM
(Version 1 and 1.1)
4
The ATM Adaptation Layer (AAL)
This section looks at the various
different ATM Adaptation Layers in terms of how actual data from an application
is taken and fitted into ATM cells. The structure of each AAL is looked at along
with an explanation of which one is used for what type of application and why.
Some examples are also given of real traffic and how it is broken up and fitted
into the ATM cells.
-
- Synchronous Residual Time Stamp (SRTS)
- Adaptive Clock Recovery
5
ATM Service Categories and Traffic Management
Key to the successful operation of an
ATM network is traffic management. Basically, traffic management is necessary to
protect the users and the network to ensure that network performance objectives
are met. When a connection is established across an ATM network, we need to be
sure that this connection receives the required quality of service so long as it
stays within its traffic parameters. We also need to be sure that other,
existing, connections continue to receive their expected quality of service.
This section looks at the various
aspects associated with traffic management and some of the schemes that ATM
equipment uses to ensure that the network performance objectives are met.
-
CBR (Constant Bit Rate), VBR (Variable
Bit Rate) - rt and nrt, ABR (Available Bit Rate), UBR (Unspecificed Bit Rate),
UBR+ (UBR Plus) and GFR (Guaranteed Frame Rate)
-
Traffic parameters - SCR (Sustainable
Cell Rate), PCR (Peak Cell Rate), MBS (Maximum Burst Size), MCR (Minimum Cell
Rate) etc..
-
CDVT - Cell Delay Variation Tolerance
-
Traffic management defined
-
Quality of Service (QoS) defined
-
How an ATM network actually deliver a
range of different qualities of service
-
The Traffic Contract
-
Connection/Call Admission Control (CAC)
-
Usage Parameter Control (UPC)
-
Generic Cell Rate Algorithm (GCRA)
-
- The "leaky bucket"
-
- Frame Discard (PPD - Partial Packet
Discard and EPD - Early packet Discard)
- Explicit Forward Congestion Indication (EFCI)
6
Signalling for SVCs and Soft-PVCs
ATM as a technology was designed from
the ground up to provide ‘dial-up’ bandwidth on demand regardless of the
type of application in use, i.e. voice, video, data or a combination of these.
To achieve this, signalling messages need to be passed between the end user
equipment and the ATM network and between ATM switches within the network. This
section looks at how this signalling is implemented at the UNI (User Network
Interface) as defined in UNI 3.1 and UNI 4 specifications.
-
Definition of SVCs and Soft-PVCs
-
Signalling functions
-
ATM addressing
-
Point-to-point and Point-to-multipoint
-
Signalling AAL (SAAL)
-
Q.2931 vs. UNI 3.1 / 4
-
A description of and examples of
signalling messages
7
ILMI and OAM
This section provides a look at the
subjects of ILMI (Integrated Local Management Interface) and OAM (Operations,
Administration and Maintenance). ILMI is used for the exchange of information
between two attached devices on a UNI, NNI or PNNI. OAM primarily provides
various facilities for fault and performance management of an ATM network.
-
Integrated Local Management Interface (ILMI)
- Management Information Database (MIB)
-
Operations, Administration and
Maintenance (OAM)
- Loopback cells, AIS (Alarm Indication
Signal) and RDI (Remote Defect Indication) cells etc…
8
Private Network-Network (Network-Node) Interface (PNNI)
This section looks at PNNI, which
defines a standard for signalling and routing protocols to be used in a large
and scalable network environment.
Applications on ATM
9
Voice Over ATM
ATM was always cited and, indeed
designed, as a suitable technology for the communication of multimedia traffic
including voice. There are many ways in which voice can be carried over ATM, and
this fact is reflected in the many standards that have been developed by the ATM
Forum and the ITU-T. We shall look at the various standard methods available,
but concentrate on the support of voice over ATM Adaptation Layer 2 (AAL2).
-
Circuit emulation using both the
unstructured and structured modes of AAL1
-
DBCES - Dynamic Bandwidth Circuit
Emulation Service using AAL1
-
An in-depth look at the support of
voice using AAL2
- ATM in the 3rd generation - 3G - UMTS
mobile environment
- Voice over DSL (Digital
Subscriber Line)
10
MPEG-2 Video over ATM
As the demand for the support of
multimedia traffic in today’s networks grows, the need for a standardised
means of supporting video on ATM also grows. The ATM Forum has defined a
standard that describes how MPEG-2 video is carried in ATM.
-
Overview of MPEG-2
-
Carrying MPEG-2 in AAL1
-
Carrying MPEG-2 in AAL5
11
IP over ATM (Layer 2 Support)
A number of key specifications have
been defined for the support of LANs and LAN interworking via ATM.
Specifications have been produced by both the ATM Forum and the IETF - Internet
Engineering Task Force.
-
RFC1483:
Multiprotocol Encapsulation over AAL5
- LLC Encapsulation and VC Based
Multiplexing
-
RFC1577
and RFC2225: Classical IP and ATP over ATM
- SVC Operation
- PVC Operation
LANE
Emulation (LANE)
-
LAN Emulation defined
-
LANE Components:
-
- LAN Emulation Client (LEC)
- LAN Emulation Server (LES)
- Broadcast and Unknown Server (BUS)
- LAN Emulation Configuration Server (LECS)
12
IP over ATM (Layer 3 Support)
It is well understood in networks today
that a routing function is required in order to make most efficient use of
bandwidth within the wide area while not wasting bandwidth unnecessarily.
However, traditional routed networks are inherently slow and cannot deliver
quality of service due to the connectionless and laborious packet-by-packet
decisions that need to be made by routers on the path between the source and the
destination.
Two main initiatives have been made in
order to provide a high-speed routing capability sometimes also referred to as
layer 3 switching.
Multi Protocol Over ATM (MPOA) and
Multi Protocol Label Switching (MPLS) are both specifications that offer this
layer 3 switching capability. MPOA was developed by the ATM Forum, while MPLS is
developed by the Internet Engineering Task Force (IETF).
Multiprotocol
Over ATM (MPOA)
-
MPOA defined
-
MPOA Components:
-
- MPOA clients (MPCs)
- MPOA Servers (MPSs)
Multiprotocol
Label Switching (MPLS)
- MPLS defined
- Routing protocol overview
- Label Distribution Protocol (LDP)
- MPLS on an ATM architecture
13
Frame Relay/ATM Interworking
Many of today's wide area networks are
based upon the Frame Relay protocol. It is very efficient for the transport of
data orientated traffic and is scaleable from low speeds to reasonably high
speeds. Today, there is a growing demand to be able to inter-operate between
Frame Relay and ATM and standards have been produced to that end.
- FRF.5: Network Interworking
- FRF.8: Service Interworking
- Mapping of ATM to Frame Relay and vice
versa - VPI & VCI/DLCI, CLP/DE, EFCI/FECN, Traffic parameters etc...
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