What is the significance of cir and mar in packet switched architectures

Computer servers power packet-switched networks. In modern circuit-switched networks, electronic signals pass through several switches before a connection is established. And during a call, no other network traffic can use those switches. In packet-based networks, however, the message gets broken into small data packets that seek out the most efficient route as circuits become available.

Each packet may go a different route; its header address tells it where to go and describes the sequence for reassembly at the destination computer, says Joel Maloff, president of consultancy Maloff Group International Inc. Formerly, packet-switched digital networks would connect to circuit-switched ports to gain access to computer networks in different locations.

But nowadays, remote dial-up access to corporate computers is usually over the Internet, using global Internet service providers ISP , says Ron Westfall, an analyst at Current Analysis Inc.

With the expanded use of the Internet for voice and video, analysts predict a gradual shift away from circuit-switched networks. If you're doing voice applications solely, it's great," says Maloff. Voice-over-IP vendors point out that IP-based calls are cheaper than circuit-based ones, but analysts say it will be a long time before corporations abandon proven PBX systems and use packet-based networks for data, voice and video.

A congested network can also drop packets. The other three hospitals, with lower data needs, ar connected to the data center via a set of T3 circuits in a star architecture. The data center also has a T3 connection into the Internet to enable its 3, or so doctors to access clinical data from their private practice offices or from home. Figure 9. So, for example, if computer C attempts to reach computer B, it will have to wait until the circuit is closed.

In contrast, packet-switched services enable multiple connections to exist simultaneously between computers over the same physical circuit, just like LANs and BNs. With packet-switched services , the user again buys a connection into the common carrier cloud Figure 9.

The user pays a fixed fee for the connection into the network depending on the type and capacity of the service and is charged for the number of packets transmitted. At the other end, another PAD reassembles the packets back into the network layer and data link layer protocols expected by the destination and delivers it to the appropriate computer.

One of the key advantages of packet-switched services is that different locations can have different connection speeds into the common carrier cloud. The PAD compensates for differences in transmission speed between sender and receiver; for example, the circuit at the sender might be 1. In contrast, a dial-up circuit or a dedicated circuit must have the same speed at both the sender and receiver. Packet-switched networks enable packets from separate messages with different destinations to be interleaved for transmission, unlike switched circuits and dedicated circuits.

Packet switching is popular because most data communications consist of short bursts of data with intervening spaces that usually last longer than the actual burst of data. Packet switching takes advantage of this characteristic by interleaving bursts of data from many users to maximize use of the shared communication network. The little boat-shaped figures shown on the communication circuits represent individual packets from separate messages.

Although the packets in one data stream may mix with several other data streams during their journey, it is unlikely that packets from two different data streams will travel together during the entire length of their transmission.

The two communicating computers do not need to know through which intermediate devices their data are routed because the packet network takes care of it by either of two methods. The first method, called datagram, is a connectionless service. It adds a destination address and sequence number to each packet, in addition to information about the data stream to which the packet belongs. In this case, a route is chosen for each packet as it is accepted into the packet network.

Each packet may follow a different route through the network. At the destination address, the sequence number tells the network how to reassemble the packets into a continuous message. The sequence number is necessary because different routes may deliver packets at different speeds, so data packets often arrive out of sequence.

Few networks today use datagrams for data transfer. The second and more common routing method is a connection-oriented approach called a virtual circuit. In this case, the packet-switched network establishes what appears to be one end-to-end circuit between the sender and receiver. All packets for that transmission take the same route over the virtual circuit that has been set up for that particular transmission. The two computers believe they have a dedicated point-to-point circuit, but in fact, they do not.

Virtual circuits are usually permanent virtual circuits PVCs , which means that they are defined for frequent and consistent use by the network. They do not change unless the network manager changes the network. Some common carriers also permit the use of switched virtual circuits SVCs although this is not usual.

It often takes days or weeks to create or take down PVCs although this is mostly due to poor management by common carriers rather than due to technology issues, so this may change.

Because most network managers build packet-switched networks using PVCs, most packet-switched networks behave like dedicated-circuit networks. At first glance, the basic architecture in Figure 9. However, because virtually all data-intensive networks use PVCs, this means that the network is actually built using virtual circuits that are the software equivalent of the hardware-based dedicated circuits.

Computer Network Fundamentals. Physical layer. Data Link layer. Network layer. Transport layer. Application layer. Network Security. Computer Network Quizes. Table of Contents. Save Article. Improve Article. Like Article. In Packet switching directly data transfer takes place. In circuit switching, each data unit know the entire path address which is provided by the source. In Packet switching, each data unit just know the final destination address intermediate path is decided by the routers.

In Circuit switching, data is processed at source system only In Packet switching, data is processed at all intermediate node including source system. Delay between data units in circuit switching is uniform.