IP-OVER-ATM

The popularity of IP (Internet Protocol) applications contributes to implementation of IP overlays on top of multiservice ATM networks. IP-over-ATM solutions employ protocols such as MPOA (MultiProtocol-over-ATM) and MPLS (MultiProtocol Label Switching) for leveraging IP enhancements. Moreover, IP packets can be mapped to ATM service classes to transport, for instance, IP-based voice and video traffic via CRC and VBR-rt. Additionally, IP-over-ATM implementations support VPNs (Virtual Private Networks) and ATM emulated LAN (ELAN) protocols that work in concert with the Network Layer or Layer 3 and the Transport Layer or Layer 4 of the OSI (Open Systems Interconnection) Reference Model. Sponsored by the ATM Forum, the ATM-IP Collaborative Working Group (AIC) develops specifications for coordinating the provision of IP services with ATM technology. Approaches for mapping ATM QoS to the IP DiffServ (Differentiated Services) protocol are also in development.

In order to interoperate with IP packet-switched services, ATM defines a framing structure for carrying IP packets as sets of ATM cells. ATM PVCs (Permanent Virtual Circuits) support virtual connections within an IP network. In provisioning IP integrated services over an ATM infrastructure, a portion of the available bandwidth is reserved for specified CoS transmissions. By employing fixed capacity virtual connections for designated CoS transmissions, the ATM infrastructure guarantees the availability of reserved bandwidth on-demand.


CIP-OVER-ATM (CLASSICAL IP-OVER-ATM)

Protocols for preserving in-place infrastructure investments in ATM environments include Classical IP-over-ATM (CIP-over-ATM). A CIP-over-ATM solution employs Permanent Virtual Circuits (PVCs) or dynamic Switched Virtual Circuits (SVCs) for transporting IP packets to ATM addresses. Moreover, CIP-over-ATM deployments enable access to ATM services and connectivity to legacy IP applications. CIP-over- ATM implementations require modification of the IP Address Resolution Protocol (ARP) in order to establish ATM connections that correspond to IP addresses.


MULTIPROTOCOL-OVER-ATM (MPOA) PROTOCOL

Endorsed by the ATM Forum, the MPOA (MultiProtocol over ATM) protocol defines Network Layer or Layer 3 services for enabling ATM implementations. IMPOA employs Next Hop Resolution Protocol (NHRP) for mapping IP packets to ATM cells at AAL5 of the ATM protocol stack. In addition, MPOA routes ATM traffic directly between ELANs (Emulated LANs) and employs SVCs (Switched Virtual Circuits) to ensure reliable and dependable voice, video, and/or data delivery to destination addresses. Robust transmissions are achieved by reducing the number of nodes participating in the internetwork transmission process.

With MPOA, network stations or nodes on different subnetworks establish Permanent Virtual Connections (PVCs) or shortcuts, thereby eliminating the need for intermediate cell segmentation and cell reassembly. In contrast to MPOA, LANE (LAN Emulation) and CIP protocols use intermediate routers for enabling intercommunications between subnetwork nodes. This process limits ATM transmission rates and the amount of voice, video, and data throughput transported via the network by requiring intermediate cell segmentation and reassembly.


MULTIPROTOCOL LABEL SWITCHING (MPLS)

Developed by the IETF (Internet Engineering Task Force), the MPLS (MultiProtocol Label Switching) protocol enables the provision of merged IP and ATM services within the same networking environment. To accomplish this objective, the MPLS protocol interlinks the IP Layer and the ATM Layer and interconnects IP routers and ATM switches, thereby enabling IP transmissions to take advantage of ATM traffic management capabilities in provisioning CoS assurances. IP also benefits from ATM broadband transmission rates for enabling high-speed and dependable multimedia delivery.

MPLS technology enables operations at the Data-Link Layer or Layer 2 of the OSI Reference Model, supports connection-oriented switching based on IP routing and control protocols, and employs fixed-length labels for rapidly routing transmissions to destination addresses. The MPLS protocol works in concert with its own LDP (Label Distribution Protocol) in establishing links and shortcuts in accordance with IP addresses, ATM CoS requirements, and ATM QoS guarantees.

MPLS implementation requires development of a Label-Switching Path (LSP) for handling volume-intensive traffic that takes a specific destination route over the network and supporting identification of a communications channel with high capacity and minimal congestion to accommodate application bandwidth requirements. MPLS solutions optimize network performance, control network operating costs, minimize congestion, decrease the number of information packets dropped as a consequence of network instability, and provision preferential service for delivery of priority transmissions. The MPLS protocol works in concert with IPv4 (Internet Protocol version 4) and supports migration to IPv6 (Internet Protocol version 6) operations. In addition to ATM, the MPLS protocol optimizes performance of network configurations based on POS (Packet over SONET/SDH), Frame Relay, Ethernet, Fast Ethernet, and Gigabit Ethernet technologies.