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DATA COMMUNICATION

&

NETWORKING

GLOBAL ROUTINGApoorv Kumar Sadh(06)

Debabrata Sahana(09)

Paramvir Ahlawat(16)

Shiwam Rai(22)

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Global Routing

a.  What is Global routing:

The Internet is one of the 20th century's greatest communications developments. It

allows people around the world to send e-mail to one another in a matter of seconds,

and it lets you read, among other things.

We're all used to seeing the various parts of the Internet that come into our homes and

offices -- the Web pages, e-mail

messages and downloaded files

that make the Internet a dynamic

and valuable medium. But none of 

these parts would ever make it to

your computer without a piece of 

the Internet that you've probably

never seen. In fact, most people

have never stood "face to machine"

with the technology most

responsible for allowing the

Internet to exist at all the

technology of routing.

One of the greatest things about

the Internet is that nobody really

owns it. It is a global collection of networks, both big and small. These networks connect

together in many different ways to form the single entity that we know as the Internet.

None of us have ever thought that how do we get all those information over internet.Thanks to the virtual world of web that makes it possible and the insight of it that is

global routing manages traffic over the internet.

In very simple words global routing can be compared with traffic control systems on

the roads. As efficient traffic control on road enables smooth traffic flow similarly global

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routing manages traffic of packets coming from different networks, transferring from

one network to other network and reaching their destinations following the routes

chosen by the routers over net this concept is called global routing.

What is incredible about this the process of global routing is that a message can leaveone computer and travel halfway across the world through several different networks

and arrive at another computer in a fraction of a second!

The routers in the global routing determine where to send information from one

computer to another.

Routers are specialized

computers that send

your messages andthose of every other

Internet user speeding

to their destinations

along thousands of 

pathways. A router has

two separate, but

related, jobs:

  It ensures that

information doesn't go

where it's not needed. This is crucial for keeping large volumes of data from

clogging the connections of "innocent bystanders."

  It makes sure that information does make it to the intended destination.

In performing these two jobs, a router is extremely useful in dealing with two separate

computer networks. It joins the two networks, passing information from one to the

other. It also protects the networks from one another, preventing the traffic on one

from unnecessarily spilling over to the other. Regardless of how many networks are

attached, the basic operation and function of the router remains the same. Since theInternet is one huge network made up of tens of thousands of smaller networks, its use

of routers is an absolute necessity.

Global routing works on a set of pre written algorithms Known as Border Gateway

Protocols.

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b.  Border Gateway Protocol:

The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. It

maintains a table of IP networks or 'prefixes' which designate network reachability

among autonomous systems (AS). It is described as a path vector protocol. BGP does not

use traditional Interior Gateway Protocol (IGP) metrics, but makes routing decisions

based on path, network policies and/or rulesets.

In other words BGP maintains a log that which packet is going on which path and

whether it has landed on its destination based on this log or table the protocol directs

the packets on the route which is available and have lesser traffic. BGP was created to

replace the Exterior Gateway Protocol (EGP) routing protocol to allow fully

decentralized routing.

Very large private IP networks use BGP internally. An example would be the joining of a

number of large Open Shortest Path First (OSPF) networks where OSPF by itself would

not scale to size. Another reason to use BGP is multihoming a network for better

redundancy either to multiple access points of a single ISP (RFC 1998) or to multiple

ISPs.

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The above diagram explains how a connection is established using a BGP session.

The BGP standard specifies a number of decision factors, more than are used by any

other common routing process.

c.  ISP and Global Routing:Let us take this situation for example you are using google talk on internet and

chatting with your friend sitting in another city. Now your internet service provider is

for example reliance and your friend is using a internet connection provided by Sify

have we ever thought that how does these two different ISPs communicate with

each other how the data sent over one ISP reaches the other the ISP. Here also the

concept of global routing comes into the picture. To be more precise it uses the

technology of BGP and Peering.

Above Diagram illustrates an example of peer to peer network

Let us understand what is Peering:

Peering is a voluntary interconnection of administratively separate Internet networks

for the purpose of exchanging traffic between the customers of each network. The

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pure definition of peering is settlement-free or "sender keeps all," meaning that

neither party pays the other for the exchanged traffic; instead, each derives revenue

from its own customers. Marketing and commercial pressures have led to the word

peering routinely being used when there is some settlement involved, even though

that is not the accurate technical use of the word. The phrase "settlement-freepeering" is sometimes used to reflect this reality and unambiguously describe the

pure cost-free peering situation.

Peering requires physical interconnection of the networks, an exchange of routing

information through the Border Gateway Protocol (BGP) routing protocol and is

often accompanied by peering agreements of varying formality, from "handshake" to

thick contracts.

The Internet is a collection of separate and distinct networks, each one operating

under a common framework of globally unique IP addressing and global BGP routing.

The relationships between these networks are generally described by one of the

following three categories:

  Transit (or pay )  – You pay money (or settlement ) to another network for Internet

access (or transit ).

  Peer (or swap)  – Two networks exchange traffic between each other's customers

freely, and for mutual benefit.

  Customer (or sell ) –

Another network pays you money to provide them with

Internet access.

Furthermore, in order for a network to reach any specific other network on the

Internet, it must either:

  Sell transit  (or Internet access) service to that network (making them a

'customer'),

  Peer directly with that network, or with a network who sells transit service to

that network, or

  Pay another network for transit service, where that other network must in turnalso sell, peer, or pay for access.

The Internet is based on the principle of  global reachability  (sometimes called end-

to-end reachability ), which means that any Internet user can reach any other

Internet user as though they were on the same network. Therefore, any Internet

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connected network must by definition either pay another network for transit, or

peer with every other network that also does not purchase transit.