How do ATM switches differ from IP routers in B-ISDN? (original) (raw)

Broadband ISDN (B-ISDN) is a network architecture that uses asynchronous transfer mode (ATM) to deliver high-speed data, voice, and video services. ATM is a packet-switching technology that divides data into fixed-length cells and routes them through a network of ATM switches. IP routers, on the other hand, are devices that forward packets of variable length based on their destination addresses. How do ATM switches differ from IP routers in B-ISDN? In this article, we will explore some of the key differences and advantages of each technology.

ATM switch features

ATM switches are specialized hardware devices that can handle high volumes of traffic and provide quality of service (QoS) guarantees. They operate at the data link layer of the OSI model and use virtual circuits (VCs) to establish logical connections between end points. VCs are identified by a pair of numbers called virtual path identifier (VPI) and virtual channel identifier (VCI), which are carried in the cell header. ATM switches use these identifiers to look up the output port and forward the cells accordingly. ATM switches do not need to examine the payload of the cells, which reduces processing overhead and latency.

Designed to handle high volumes of small, fixed-size packets called cells (53 bytes). Ensure low latency and minimal jitter, critical for real-time applications like voice and video. Functions at the second layer of the OSI model, focusing on data transfer between directly connected nodes. Ensures the logical link control and error detection without delving into higher-layer protocols. Lookup routing tables to determine the correct output port. Forward cells to the next hop in the network. This switching process avoids the need to examine cell payloads, reducing overhead and processing time.

ATM/IP integration

ATM and IP are not mutually exclusive technologies, but can be integrated to leverage their respective strengths. For example, ATM can be used as a transport layer for IP, providing quality of service and efficiency for IP packets, while IP can be used as a control layer for ATM, providing routing and signaling functions for ATM VCs. There are several methods to achieve this integration, such as classical IP over ATM which assigns each IP host an ATM address and uses an address resolution protocol (ARP) server to map IP addresses to ATM addresses. Multiprotocol over ATM (MPOA) extends this method by allowing IP routers to establish VCs across multiple ATM switches, while IP switching combines ATM switching and IP routing in a single device.