How do ATM switches differ from IP routers in B-ISDN?

1 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.

2 IP router features

IP routers are general-purpose devices that can run various protocols and applications. They operate at the network layer of the OSI model and use IP addresses to route packets. IP routers need to analyze the packet header and perform a longest prefix match to find the best next hop for each packet. IP routers also need to handle fragmentation and reassembly of packets that exceed the maximum transmission unit (MTU) of the underlying link. IP routers do not provide QoS guarantees, but rely on congestion control and prioritization mechanisms to manage traffic.

3 ATM switch advantages

ATM switches have several advantages over IP routers in B-ISDN, such as higher bandwidth efficiency, lower latency and jitter, and better QoS support. ATM switches can utilize the full capacity of the link by multiplexing cells from different VCs, which is more efficient than IP routers that may waste bandwidth due to packet overhead and fragmentation. Furthermore, ATM switches can forward cells faster and more predictably than IP routers, which is important for real-time applications such as voice and video. Additionally, ATM switches can allocate bandwidth and buffer resources for each VC according to predefined QoS parameters, while IP routers only offer best-effort or differentiated services.

4 IP router advantages

IP routers have some advantages over ATM switches in B-ISDN, such as greater flexibility and scalability, as IP routers can support a wider range of protocols and applications than ATM switches. IP routers can also adapt to changes in the network topology and traffic patterns more easily than ATM switches, which require manual configuration of VCs. Additionally, IP routers are cheaper and simpler to deploy and maintain than ATM switches, due to the widespread adoption and standardization of IP as the universal network protocol.

6 Here’s what else to consider

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