WHAT IS ROUTING?

Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone network, and computer networks, such as the Internet

Network routing is the process of selecting a path across one or more networks. The principles of routing can apply to any type of network, from telephone networks to public transportation. In packet-switching networks, such as the Internet, routing selects the paths for internet protocol (IP) packets to travel from their origin to their destination. These Internet routing decisions are made by specialized pieces of network hardware called routers.

Consider the image below. For a data packet to get from Computer A to Computer B, should it pass through networks 1, 3, and 5 or networks 2 and 4? The packet will take a shorter path through networks 2 and 4, but networks 1, 3, and 5 might be faster at forwarding packets than 2 and 4. These are the kinds of choices network routers constantly make.

How does routing work?

Routers refer to internal routing tables to make decisions about how to route packets along network paths. A routing table records the paths that packets should take to reach every destination that the router is responsible for. Think of train timetables, which train passengers consult to decide which train to catch. Routing tables are like that, but for network paths rather than trains.

Routers work in the following way: when a router receives a packet, it reads the headers* of the packet to see its intended destination, like the way a train conductor may check a passenger’s tickets to determine which train they should go on. It then determines where to route the packet based on information in its routing tables.

Routers do this millions of times a second with millions of packets. As a packet travels to its destination, it may be routed several times by different routers.

Routing tables can either be static or dynamic. Static routing tables do not change. A network administrator manually sets up static routing tables. This essentially sets in stone the routes data packets take across the network, unless the administrator manually updates the tables.

Dynamic routing tables update automatically. Dynamic routers use various routing protocols (see below) to determine the shortest and fastest paths. They also make this determination based on how long it takes packets to reach their destination — similar to the way Google Maps, Waze, and other GPS services determine the best driving routes based on past driving performance and current driving conditions.

Dynamic routing requires more computing power, which is why smaller networks may rely on static routing. But for medium-sized and large networks, dynamic routing is much more efficient.

*Packet headers are small bundles of data attached to packets that provide useful information, including where the packet is coming from and where it is headed, like the packing slip stamped on the outside of a mail parcel.

What are the actual routing protocols?

In networking, a protocol is a standardized way of formatting data so that any connected computer can understand the data. A routing protocol is a protocol used for identifying or announcing network paths.

The following protocols help data packets find their way across the Internet:

IP: The Internet Protocol (IP) specifies the origin and destination for each data packet. Routers inspect each packet’s IP header to identify where to send them.

BGP: The Border Gateway protocol (BGP) routing protocol is used to announce which networks control which IP Addresses, and which networks connect to each other. (The large networks that make these BGP announcements are called autonomous systems) BGP is a dynamic routing protocol.

The below protocols route packets within an AS:

OSPF: The Open Shortest Path First (OSPF) protocol is commonly used by network routers to dynamically identify the fastest and shortest available routes for sending packets to their destination.

RIP: The Routing Information Protocol (RIP) uses “hop count” to find the shortest path from one network to another, where “hop count” means number of routers a packet must pass through on the way. (When a packet goes from one network to another, this is known as a “hop.”)

Other interior routing protocols include EIGRP (the Enhanced Interior Gateway Routing Protocol, mainly for use with Cisco routers) and IS-IS (Intermediate System to Intermediate System).

WHAT IS ADAPTIVE ROUTING?

Dynamic routing is, also called adaptive routing, is a process where a router can forward data via a different route or given destination based on the current conditions of the communication circuits within a system. 

 Adaptive routing is a process for determining the optimal path a data packet should follow through a network to arrive at a specific destination. Adaptive routing can be compared to a commuter taking a different route to work after learning that traffic on his usual route is backed up.

Adaptive routing uses algorithms  and routing protocols that read and respond to changes in network topology In addition to Open Shortest Path First (OSPF), other routing protocols that facilitate adaptive routing include Intermediate System to Intermediate System (IS-IS) protocol for large networks such as the internet and routing information protocol (RIP) for short-distance transport.

What is adaptive and non adaptive routing?

Adaptive Routing algorithm is an algorithm that constructs the routing table based on the network conditions. The Non–Adaptive Routing algorithm is an algorithm that constructs the static table to determine which node to send the packet. … Routing decisions are made based on topology and network traffic.

What are the advantages and disadvantages of adaptive routing?

Advantages

(1) An adaptive routing strategy can improve performance, as seen by the network user. (2) An adaptive routing strategy can aid in congestion control. Because an adaptive routing strategy tends to balance loads, it can delay the onset of severe congestion.

Disadvantages

(1) The routing decision is more complex; therefore, the processing burden on network nodes increases. (2) In most cases, adaptive strategies depend on status information that is collected at one place but used at another. There is a tradeoff here between the quality of the information and the amount of overhead. The more information that is exchanged, and the more frequently it is exchanged, the better will be the routing decisions that each node makes. On the other hand, this information is itself a load on the constituent networks, causing a performance degradation. (3) An adaptive strategy may react too quickly, causing congestion-producing oscillation, or too slowly, being irrelevant.”

Difference between Adaptive and Non-Adaptive Routing algorithms :

S.NO	Adaptive Routing algorithm	Non-Adaptive Routing algorithm
1.	This algorithm creates a routing table based on network conditions.	Whereas this algorithm creates a static table in order to determine when to send packets and which node.
2.	This algorithm is used by dynamic routing.	Whereas this algorithm is used by static routing.
3.	In adaptive routing algorithm, the routing decisions are made based on network traffic and topology.	Whereas in a non-adaptive routing algorithm, the routing decisions are not made based on network traffic and topology.
4.	Adaptive routing algorithms are more complex as compared to non-adaptive routing algorithms in terms of complexity.	While non-adaptive routing algorithms are simple in terms of complexity.
5.	In adaptive routing algorithm, the routing decisions are not static tables.	While in non-adaptive routing algorithm, the routing decisions are static tables.
6.	Adaptive routing algorithm is categorized into distributed, centralized and isolation algorithm.	Whereas non-adaptive routing algorithm is categorized into random walks and flooding.
7.	Adaptive routing algorithm is more used as compared to non-adaptive.	Whereas non-adaptive routing algorithm is comparatively less used.

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