2. Networks: ATM
Networks: ATM 2
2
Issues Driving LAN Changes
Issues Driving LAN Changes
• Traffic Integration
– Voice, video and data traffic
– Multimedia became the ‘buzz word’
• One-way batch Web traffic
• Two-way batch voice messages
• One-way interactive Mbone broadcasts
• Two-way interactive video conferencing
• Quality of Service guarantees (e.g. limited jitter,
non-blocking streams)
• LAN Interoperability
• Mobile and Wireless nodes
8. Networks: ATM
Networks: ATM 8
8
ATM
ATM Conceptual Model
Conceptual Model
Four
Four Assumptions
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.
12. Networks: ATM
Networks: ATM 12
12
ATM
ATM Conceptual Model
Conceptual Model
Assumptions (cont.)
Assumptions (cont.)
3. Vast majority of ATM networks will run on
optical fiber networks with extremely low
error rates.
4. ATM must support low cost attachments.
• This decision lead to a significant decision – to
prohibit cell reordering in ATM networks.
ATM switch design is more difficult.
16. Networks: ATM
Networks: ATM 16
16
ATM
ATM Protocol Architecture
Protocol Architecture
• ATM Adaptation Layer (AAL) – the protocol
for packaging data into cells is collectively
referred to as AAL.
• Must efficiently package higher level data
such as voice samples, video frames and
datagram packets into a series of cells.
Design Issue: How many adaptation layers
should there be?
19. Networks: ATM
Networks: ATM 19
19
Original
Original ATM
ATM Architecture
Architecture
• CCITT envisioned four classes of
applications (A-D) requiring four distinct
adaptation layers (1-4) which would be
optimized for an application class:
A. Constant bit-rate applications CBR
B. Variable bit-rate applications VBR
C. Connection-oriented data applications
D. Connectionless data application
20. Networks: ATM
Networks: ATM 20
20
ATM Architecture
ATM Architecture
An AAL is further divided into:
The Convergence Sublayer (CS)
manages the flow of data to and from SAR sublayer.
The Segmentation and Reassembly Sublayer
(SAR)
breaks data into cells at the sender and reassembles
cells into larger data units at the receiver.
23. Networks: ATM
Networks: ATM 23
23
• The AAL interface was initially defined as classes A-D
with SAP (service access points) for AAL1-4.
• AAL3 and AAL4 were so similar that they were
merged into AAL3/4.
• The data communications community concluded that
AAL3/4 was not suitable for data communications
applications. They pushed for standardization of AAL5
(also referred to as SEAL – the Simple and Efficient
Adaptation Layer).
• AAL2 was not initially deployed.
Original
Original ATM
ATM Architecture
Architecture
25. Networks: ATM
Networks: ATM 25
25
Revised
Revised ATM
ATM Service Categories
Service Categories
Class Description Example
CBR Constant Bit Rate T1 circuit
RT-VBR Real Time Variable Bit
Rate
Real-time
videoconferencing
NRT-VBR Non-real-time Variable Bit
Rate
Multimedia email
ABR Available Bit Rate Browsing the Web
UBR Unspecified Bit Rate Background file
transfer
26. Networks: ATM
Networks: ATM 26
26
QoS
QoS,
, PVC
PVC, and
, and SVC
SVC
• Quality of Service (QoS) requirements are
handled at connection time and viewed as
part of signaling.
• ATM provides permanent virtual connections
and switched virtual connections.
– Permanent Virtual Connections (PVC)
permanent connections set up manually
by network manager.
– Switched Virtual Connections (SVC)
set up and released on demand by the end user
via signaling procedures.
