Illustrated TCP/IP Illustrated TCP/IP
by Matthew G. Naugle
Wiley Computer Publishing, John Wiley & Sons, Inc.
ISBN: 0471196568   Pub Date: 11/01/98  

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Chapter 325
Alternatives

Alternatives

•  Ethernet allows us some scaling with three speeds.
•  ToS offers different paths based on an application request.
•  RSVP is a protocol useful where improved Quality of Service (QoS) would enhance transmission of an application’s datastream and create higher reliability of its reception at the receiving endstation(s).
•  An example where RSVP would be appropriate would be an application for streaming video to the desktop, in a multicast environment, in a routed infrastructure.

Since its inception, IP has had a field known as Type of Service (ToS). The ToS is for internet service quality selection and is specified along the abstract parameters of precedence, delay, throughput, reliability, and cost. These abstract parameters are mapped into the actual service parameters of the particular networks the datagram traverses. File transfers could take a high-delay network while terminal access could take one with low delay (refer to Part III, the IP Protocol). In order to provide for this, router vendors have to provide for ToS in their routers, and application vendors have to build this into their applications. For routers, this can require the maintenance of multiple routing tables for each ToS. The application program is the program that sets these bits and in the past, most application programs moved data and there really was no demand for ToS. Over the years, we simply came up with faster networks to compensate for the millions of new users and bandwidth-hungry applications—the easy way to support QoS is to manipulate the bandwidth.

Gigabit Ethernet now allows us three choices for Ethernet: 10, 100, or 1000 Mbps. This allows for scaling but not for data QoS. Bandwidth is simply one factor in the equation. Also, what comes after gigabit Ethernet (the current Proposal is 10 gigabit Ethernet)? After this we are finally moving into the capabilities of ATM; however, we still run into customer resistance to ATM conversion. They will place ATM on the backbone and possibly use it for the WAN, but not to the desktop. We cannot keep producing more bandwidth without giving some consideration to taming the applications.

RSVP is the first widely known protocol to allow for some type of QoS on an existing broadcast-oriented network. As of this writing, it is still an RFC draft, with the latest version being the functional specification of May 1997. It can be used with IPv6 or IPv4. RSVP covers the QoS portion of protocols optimized for real-time, streaming, multimedia issues. It operates directly on top of IP and supports both unicast and multicast protocols. The operation of RSVP appears to have far greater advantages when used in a multicast network. It is not a transport protocol, but a control protocol like ICMP or IGMP. With IPv4, RSVP operates with UDP, but with IPv6, it will operate on top of IP using the extension header concept.


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