Frame relay is a high-performance WAN protocol that operates at the physical and data link layers of the OSI model, designed for connection-oriented communication across integrated services digital networks. It utilizes virtual circuits for data transmission, which can either be switched or permanent, allowing for flexible and efficient connection management. Additionally, ATM technology supports various data rates and includes a unique protocol architecture consisting of user, control, and management planes, aimed at improving network performance and reliability.

1. FRAME RELAY
 Frame Relay - high-performance WAN protocol
 Operates at the physical and data link layers
of the OSI reference model.
 Frame Relay originally was designed for use across
Integrated Services Digital Network (ISDN) interfaces
 Based on packet-switched technology
 Frame relay provides connection-oriented data link layer
communication.

2. FRAME RELAY NETWORK

3.  This service is implemented by using a Frame Relay
virtual circuit, which is a logical connection created
between two data terminal equipment (DTE) devices
across a Frame Relay packet-switched network (PSN).
 Virtual circuits provide a bidirectional communication
path from one DTE device to another and are uniquely
identified by a Data-Link Connection Identifier (DLCI).
 A number of virtual circuits can be multiplexed into a
single physical circuit for transmission across the
network.
 Frame Relay uses virtual circuits to carry packets from
one DTE to another.

4. FR FRAME
 Flags indicate the beginning and end of the frame.
 Address area, which is 2 bytes in length, is
comprised of 10 bits representing the actual circuit
identifier and 6 bits of fields related to congestion
management.
 This identifier commonly is referred to as the data-
link connection identifier (DLCI).

5. Frame Relay Virtual Circuits
 A virtual circuit can pass through any number of
intermediate DCE devices (switches) located within the
Frame Relay Packet Switched Network (PSN).
 Frame Relay virtual circuits fall into two categories:
1.Switched virtual circuits (SVCs)
2.Permanent virtual circuits (PVCs).

6. Switched virtual circuits
 Temporary connections used in situations requiring only
interrupted data transfer between DTE devices across
the Frame Relay network.
 Call setup- VC between two Frame Relay DTE devices
is established.
 Data transfer- Data is transmitted between the DTE
devices over the VC.
 Idle- The connection between DTE devices is still active,
but no data is transferred.
 If an SVC remains in an idle state for a defined period of
time, the call can be terminated.
 Call termination- The virtual circuit between DTE devices
is terminated.

7. Permanent virtual circuits
 Permanently established connections that are used for
frequent and consistent data transfers between DTE
devices across the Frame Relay network.
 DTE devices can begin transferring data whenever they
are ready because the circuit is permanently established.
 Communication across a PVC does not require the call
setup and termination states that are used with SVCs,
but data transfer and idle state are available

8. ATM- Protocol Architecture

9.  ATM has its own reference model different from OSI or
TCP/IP model.
 If ATM is viewed as a Network Layer protocol, then the
corresponding Transport Layer protocol is the ATM
Adaptation Layer (AAL).

10. Physical Layer
 Responsible for transmission of ATM cells as a bit-
stream across physical medium.
 Divided into Physical Medium Dependent (PMD) sub-
layer and Transmission Convergence (TC) sub-layer.
 Data rates specified include 155 and 622 Mbps with
other data rates possible

11. PMD sub-layer
 Interfaces the actual cable.
 provides width of bit and line coding depending (NRZ,
RZ, Manchester etc.) on particular physical medium.
TC sub-layer
 It consists of transmission functions independent of
physical medium.
 It converts the ATM cell (from ATM layer) into normal bit
string (like TTL).
 TC sub-layer also converts the ATM cell into frame

12. ATM Adaptation Layer
 Supports transfer protocols not based on ATM.
 It maps higher layer information into ATM cells to be
transported over an ATM network.
 collects information from ATM cells for delivery to higher
layers (e.g. a IP packet can be mapped to ATM cells).

13. ATM Planes
There are 3 planes in the protocol architecture:
 User plane - for user traffic including flow and error
control
 Control plane - for connection control
 Management plane - manages the system as a whole
and coordinates the planes and layers.

14. Advantages of Virtual Path
 Simplified network architecture
 Increased network performance and reliability
 Reduced processing and short connection setup time
 Enhanced network services

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