Overview Of The SPP Architecture

This section gives an overview of the SPP architecture. It describes the key hardware and software features that make it possible to support the main abstractions provided to an SPP user:

• Slice
• Fastpath
• Meta-Interface
• Packet queue and scheduling
• Filter

Coupled with these abstractions are the following system features:

• Resource virtualization
• Traffic isolation
• High performance
• Protocol extensibility

These features allow the SPP to support the concurrent operation of multiple high-speed, virtual routers and allows the user to add support for new protocols. For example, one PlanetLab user could be forwarding IPv4 traffic while a second one could be forwarding I3 traffic. Meanwhile a third user could be programming the SPP to support MPLS.

We begin with a very simple example of an IPv4 router to illustrate the SPP concepts. Then, we describe the architectural features in three parts. Part I describes how packets travel through the SPP assuming that it has already been configured with a fastpath for an IPv4 router. Part II describes what happens when we create and configure the SPP abstractions (e.g., create a meta-interface and bind it to a queue) for the router in Part I. Part III sketches how the example would be different if the router handled a simple virtual circuit protocol instead of IPv4.

IPv4 Example

File:Example-two-slices-one-spp.png

Two Slices Sharing One SPP

We begin with a simple example of two users (A and B) concurrently using the same SPP as an IPv4 transit router (R3) between the same two routers (R1 and R2) that are attached to ports 1 and 2 of the SPP (see figure to the right). Furthermore, both users need 100 Mb/s bandwidth in each direction (R1 to R2 and R2 to R1) and no special treatment of traffic.

File:Example-two-slices-one-spp-logical.png

Logical Configuration of Each Slice

From a logical point of view, each user of R3 needs a configuration (right) which includes one fastpath consisting of three meta-interfaces (m0-m2), four queues (q0-q3), and six filters (f0-f5). Meta-interface m0 goes to R3 itself; m1 to R1; and m2 to R2.

The configuration of R3 for both users is identical except for UDP port numbers of their meta-interfaces. Both user A and B will have the logical views shown in the tables (right). Note the following:

• The total bandwidth of the meta-interfaces (202 Mb/s) can not exceed the bandwidth of the fastpath (FP).
• There should be atleast one queue bound to each meta-interface (MI).
• The highest numbered queues are associated with meta-interface 0 which are for local delivery and exception traffic.
• The only difference between the two tables is that UDP port number of the MI sockets are 22000 for user A and 33000 for user B.

User A	MI Socket	BW (Mb/s)	Queues
FP	na	202
m0	(10.1.16.3, 22000)	2	q2, q3
m1	(10.1.32.2, 22000)	100	q0
m2	(10.1.17.1, 22000)	100	q1

User B	MI Socket	BW (Mb/s)	Queues
FP	na	202
m0	(10.1.16.3, 33000)	2	q2, q3
m1	(10.1.32.2, 33000)	100	q0
m2	(10.1.17.1, 33000)	100	q1

There are six filters. Each meta-interface has two filters, one for each possible meta-interface destination. For example, traffic from m1 can go to m0 or m2.

	MIout
MIin	m0	m1	m2
m0		f0	f1
m1	f2		f3
m2	f4	f5

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Part I: IPv4 Packet Forwarding

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Part II: Configuring the SPP

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Part III: A Virtual Circuit Router

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