Use Case of Tidal Network

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Table of Contents

1. Introduction

The tidal effect of traffic is very typical on our network, and the traffic volume varies greatly at different time. For example, in the Chinese New Year, there are 200 million people move from their work town to home town, and these people generate huge traffic on our network. For the campus network, there are thousands of people go to the Teaching buildings, libraries and labs in the daytime and go to dormitory in the night. Therefore, the traffic of different places in the campus fluctuate obviously and regularly.¶

In the previous scenarios, If the network maintains all the devices up to guarantee the maximum throughput all the time, a lot of power will be wasted. Therefore, it is an effective energy-saving method to shut down some devices when the traffic is at a low level. Thus, a scenario in which the network connection status can be predicted is formed in the tidal network.¶

This document introduces the time variant routing scenario in the tidal network, and then describes the assumptions and routing impacts based on the use case. Finally, an exemplar of tidal network is provided.¶

2. Assumptions

In order to reduuce energy consumption based on the regularity of tidal traffic, the controller or other control device needs to know the regularity of traffic changing. It is assumed that there is a algorithm that can calculates which nodes and links should be disabled or enabled under different traffic scales.¶

1. Knowing the regularity of tidal traffic, It is assumed that the controller or other control device knows the regularity of tidal traffic, and the change of traffic in the future can be predicated. The regularity information may come from the manual input or the results of computer's calculation.¶
2. An algorithm to calculate which nodes or links can be disabled or enabled under different traffic scales. It is assumed that the controller or other control device supports a algorithm to calculate the minimal topology that satisfies the requirements of traffic at different time. Based on that, it is known which nodes or link should be disabled or enabled under different traffic scales.¶

3. Routing Requirements

The change of link status will change the topology of network. Furthermore, the data forwarding may be affected and result in packet disorder or packet loss. In order to solve these problems, the existing routing protocols need to provide the following capabilities.¶

1. Data model with time-variant information. There is a need for the nodes or controllers to deliver the predicated time-variant information by specific data model or structure. For the tidal network, the change of network topology usually has a regular period but may has multiple regularities (For example, the regularity of traffic in campus network is quite different on weekdays and weekend).¶
2. Collection and advertisement for the time-variant information of each node and link. For the distributed routing protocols, each node needs to calculate the routing table by itself, so each node needs to advertise its own time-variant information to other nodes (This step is not necessary when every node knows all of the time-variant information about the topology). For the centralized routing protocols, the controller is responsible for the calculation of routing path, so the controller may need to collect the time-variant information of all the nodes (It is also not necessary when the controller knows all of the time-variant information about the topology by other means).¶
3. Routing algorithm based on time-variant information. When the routing calculator knows the time-variant information of each node, a new algorithm is needed to calculate the routing paths based on the time-variant information, it may be quite different from the existing algorithms.¶
4. Routing path with time-variant information. The routing path is calculated based on the time-variant topology, so the change of topology will also affect the routing path. Therefore, the routing path may need be expressed with a time-variant information which is associated with the change of the topology so that the node can schedule paths according to their time-variant information.¶

4. Exemplar

One example of a network with tidal traffic is the campus network, the traffic in the dormitory will raise in the evening and drop in the morning. In contrast, the traffic in the library will raise in the morning and almost drop to zero at night. the traffic of campus changes with a significant period.¶

Consider a four nodes network for the dormitory, the traffic of the network will raise at 12 o'clock and drop to the low level at 14 o'clock, then it will raise at 21 o'clock and drop to the low level at 2 o'clock. The traffic at different time is shown in Figure 1.¶

T |
R |                             ------
A |   ----                     /      \
F |  /    \                   /        \
F | /      \                 /          \
I |/        -----------------            ----
C +---------++--------------++-----------++---
  12        16              21           2
                 Time

The topology of network is shown in Figure 2¶

    N1---------L1---------N2
    |  \                / |
    |    \            /   |
    |      \        /     |
    |       L6    L5      |
    L2         \/         L3
    |         /  \        |
    |       /      \      |
    |     /          \    |
    |   /              \  |
    N3--------L4----------N4

In order to reduce the power consumption, some of the links may be shut down when the traffic is at a low level. For example, link L5 and L6 can be shut down from 16:00 to 21:00 and from 2:00 to 12:00, so the possible time-variant topology is as shown in Figure 3¶

        N1---------L1---------N2                 N1---------L1---------N2
        |  \                / |                  |                     |
        |    \            /   |                  |                     |
        |      \        /     |                  |                     |
        |        L6    L5     |                  |                     |
       L2          \/        L3                  L2                   L3
        |         /  \        |                  |                     |
        |       /      \      |                  |                     |
        |     /          \    |                  |                     |
        |   /              \  |                  |                     |
        N3---------L4---------N4                 N3---------L4---------N4
   Topology1 (12:00-16:00 and 21:00-2:00)  Topology 2(16:00-21:00 and 2:00-12:00)

5. Security Considerations

TBD¶

6. IANA Considerations

TBD¶

Authors' Addresses