PACKET SWITCHING- The Big Picture
Tags: Packet Switching, Thebigpicture, Internet, Analysis

Packet switching

Packet Switching transmits data across digital networks by breaking it down into blocks or packets for more efficient transfer using various network devices. Each time one device sends a file to another, it breaks the file down into packets so that it can determine the most efficient route for sending the data across the network at that time. The network devices can then route the packets to the destination where the receiving device reassembles them for use.

Delays in Packet switching :

1.Transmission Delay

2.Propagation Delay

3.Queuing Delay

4.Processing Delay

Transmission Delay :

Time taken to put a packet onto link. In other words, it is simply time required to put data bits on the wire/communication medium. It depends on length of packet and bandwidth of network.

Transmission Delay = Data size / bandwidth = (L/B) second

Propagation delay :

Time taken by the first bit to travel from sender to receiver end of the link. In other words, it is simply the time required for bits to reach the destination from the start point. Factors on which Propagation delay depends are Distance and propagation speed.

Propagation delay = distance/transmission speed = d/s

Queuing delay :

Queuing delay is the time a job waits in a queue until it can be executed. It depends on congestion. It is the time difference between when the packet arrived Destination and when the packet data was processed or executed. It may be caused by mainly three reasons i.e. originating switches, intermediate switches or call receiver servicing switches.

Average Queuing delay = (N-1)L/(2*R)

where N = no. of packets

L=size of packet

R=bandwidth

Processing Delay :

Processing delay is the time it takes routers to process the packet header. Processing of packets helps in detecting bit-level errors that occur during transmission of a packet to the destination. Processing delays in high-speed routers are typically on the order of microseconds or less.

In simple words, it is just the time taken to process packets

Reliability:

The packet switching process is reliable in that the destination can identify any missing packets. However, circuit switched networks deliver packets in order along the same route and are therefore less likely to experience missing packets in the first place.

Data Transmission :

A packet switched network follows networking protocols that divide messages into packets before sending them. Packet-switching technologies are part of the basis for most modern Wide Area Network (WAN) protocols, including Frame Relay, X.25, and TCP/IP.

Compare this to standard telephone network landline service, which is based on circuit switching technology. Circuit switching networks are ideal for most real-time data, transmission, while packet switching networks are both effective and more efficient for data that can tolerate some transmission delays, such as site data and e-mail messages.

Network Performance

Improved efficiency means less network bandwidth wastage. No need to reserve the circuit even when it’s not in use means the system is more efficient. A constantly reserved circuit results in wasted network bandwidth, so network efficiency tends to increase with the use of packet switching.

Implementation :

Packet Switching is implemented using store and forward and pipeline concepts. Every node is independent of deciding next journey of packet. Packet has header unlike that in circuit switching, which contains source and destination IP along with sequential number. Packet Switching is implemented mostly for small data , because in case of large data delay increases significantly.

Error Handling :

Occasionally, packets might bounce from router to router many times before reaching their destination IP address. Enough of these kinds of “lost” data packets in the network can congest it, leading to poor performance. Data packets that bounce around in the network too many times may get lost.

The hop count addresses this problem, setting a maximum number of bounce times per packet. “Bouncing” simply refers to the inability to locate the final destination IP address, and the resulting transfer from one router to another instead. If a certain packet reaches its maximum hop count, or maximum number of hops it is permitted before reaching its destination, the router it is bouncing from deletes it. This causes packet loss.

Applications :

LTE technology in mobile phone

E-mail services used in daily life

Does INTERNET Is Using Packet Switching As a Default Transmission Technique?

The Commission has defined the Internet as “a global, packet switched network that enables interconnection between networks using the Internet Protocol.” While

this is true, it is only part of the story. The IP is not used just for interconnecting existing provider networks-it extends all the way to the end users of these networks. Put differently, end-user devices utilize the Internet as a packet-switched network directly-unless blocked by a firewall or similar device, every Internet-connected computer can send messages to every other Internet-connected computer in the same native IP format. More technically, the Internet is the packet-switched network that receives IP formatted packets from connected users and delivers them, immediately and unmodified, to the destination specified by the user in the corresponding field of the IP packet header. The genius of the IP, and the reason for its success, is that it enforces standardization only at a single, abstract network layer. This allows considerable flexibility in the lower transport layers and provides a consistent and transparent interface to higher application layers.79 Thus, an IP network can be built using any physical layer technologyso so long as that technology can accurately deliver IP packets to the next switch in the network. The advantage of this approach is that it allows the creation of a large, interconnected network using existing networks as transport. This flexibility greatly reduced adoption costs, which was crucial to initial adoption

New technique used by internet

Multiprotocol Label Switching (MPLS)

Multiprotocol Label Switching (MPLS) is data forwarding technology that increases the speed and controls the flow of network traffic. With MPLS, data is directed through a path via labels instead of requiring complex lookups in a routing table at every stop.

Scalable and protocol independent, this technique works with Internet Protocol (IP) and Asynchronous Transport Mode (ATM).

When data enters a traditional IP network, it moves among network nodes based on long network addresses. With this method, each router on which a data packet lands must make its own decision, based on routing tables, about the packet’s next stop on the network. MPLS, on the other hand, assigns a label to each packet to send it along a predetermined path.

How Does Multiprotocol Label Switching Work?

Label Switched Paths (LSPs) are predetermined, unidirectional paths between pairs of routers across an MPLS network.

1.When a packet enters the network through a Label Edge Router (also known as an “ingress node”), it is assigned to a Forwarding Equivalence Class (FEC), depending on the type of data and its intended destination. FECs are used to identify packets with similar or identical characteristics.

2.Based on the FEC, the ingress node will apply a label to the packet and encapsulate it inside an LSP.

3.As the packet moves through the network’s “transit nodes” (also known as Label Switch Routers), those routers continue to direct the data by the instructions in the packet label. These in-between stops are based on the packet label, not additional IP lookups.

4.At the “egress node,” or final router at the end of the LSP, the label is removed and the packet is delivered via normal IP routing.