RSVP (Resource Reservation Protocol)

There is no doubt that TCP/IP has transformed our computer networks and played a pivotal role in the expansion of the world wide web, however it is far from perfect.   RSVP is an Internet protocol designed to alleviate some of the issues with TCP/IP particularly regarding delivering data on time and in the right order.  This has been always one of TCP/IP’s biggest shortcomings – it’s ‘best effort’ IP delivery service has no guarantees.  Whereas TCP which is connection orientated does guarantee delivery but gives no assurances on the time it takes.

Guaranteed on time delivery is essential in many of the modern day applications particularly over the internet – especially those including voice and video delivery.  Indeed most web sites involve large amounts of video and voice data which require fast, reliable and timely delivery whenever possible.  If anyone has tried streaming or downloading from applications like the BBC iPlayer like this for example they will know how frustrating slow speeds and missing data packets can be.

The issues are well known and RSVP is an attempt to provide a suitable quality of service for video and voice delivery particularly across the internet and other large TCP/IP based networks.  The way RSVP works is to reserve bandwidth across router connected networks.   It does this by asking each router to keep some of it’s bandwidth allocated to particular traffic flow.  In some senses it is an attempt to add some of the quality features of ATM to TCP/IP in order to facilitate the changing requirements of modern day networks.

RSVP is one of the first attempts to introduce a quality service to TCP/IP but many vendors are looking at introducing many other options too.  Most of them focus like RSVP on reserving bandwidth however this isn’t always an ideal situation.  The obvious issue is that if you reserve network capacity for specific traffic or connection then the amount is reduced for all other users and applications. Some of this issue has been mitigated by  the increase in capacity of both corporate networks and the connections for individual users to the internet.

RSVP works by establishing and maintain bandwidth reservations on a specific network so it’s not a WAN or wide area solution normally. The protocol works from router to router setting up a reservation from each end of the system. It is primarily a signalling protocol not specifically a routing protocol.  If a specific router along the connection cannot provide the requested bandwidth then RSVP will look for an alternative route.  Obviously this only works if the routers have RSVP enabled which many currently do to support this process.   Applications can also use this feature by making similar requests.

Further Reading:

Watching UK TV in USA – a study in optimizing video streams using QoS enabled routers.

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