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 times. 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 low. 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 a network to the use case 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 rule 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. Finally, it is assumed that there is a method to config the switching rules for each node.¶

1. Known 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 Impacts

The change of link status will change the topology of the network. Furthermore, the data routing may be affected which may result in packet disorder or packet loss. In order to solve these problems, the existing routing protocols may 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, and the overlay of mutiple groups of time-variant information (For example, the regularity of traffic in campus network is quite differern on weekdays and weekend) also should be considered.¶
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, so it is required that each node advertise its own time-variant information(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 already knows all of the time-variant information about the topology).¶
3. Routing algorithm based on time-variant information. When the routing calculator knows the time-variant information of each node, there is a need for a new algorithm to calculate the routing paths, it may be quite different from the existing algorithm.¶

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, and the traffic of the network at different time is shown in Figure 1.¶

T |
R |    ------                   ------
A |   /      \                 /      \
F |  /        \               /        \
F | /          \             /          \
I |/            ------------/
C +---++----++-----------------++------++---
     t1    t2                 t1+T    t2+T
                 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 during the period form t1+nT to t2+nT(n=0,1,2,...). For example, link L5 and L6 can be shut down when the traffic is low, 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 (form t1+T to t2+T)    Topology 2(form t2+T to t1+T)

In this example, The controller is required to deliver the time-variant information of link L5 and L6 to the related nodes, and then the controller or each node(Every node has already known the time-variant information of topology) needs to calculate the routing path with the time-variant information of L5 and L6. It should be noted that if there are some packets being transmitted over link L5 or L6 at time t1, the shutdown of L5 and L6 may cause packet loss until the source node computes a new routing path. The new routing mechanism may need solve these problems of tidal network.¶

5. Security Considerations

TBD¶

6. IANA Considerations

TBD¶

Authors' Addresses