Disjoint Multipath Routing for Failure Recovery in IP ... · ways of routing. In a (virtual) circuit switched network a path for transporting is established, which is the basic object

@IJRTER-2016, All Rights Reserved 192

Disjoint Multipath Routing for Failure Recovery in IP Networks Using

Edged Spanning Tree with Wakeup

Mrs. K.Shobana1,Mrs. N.Tamilarasi

2

1Department of Computer Science,Sri Akilandeswari Women’s College.

2MCA., M.Phil., B.Ed., SET.,Department of Computer Science,Sri Akilandeswari Women’s College.

Abstract—Internet faces many challenges due to link failures. In most of the existing system the failure

recovery is made with the help of finding another path to reach the destination but this recovery path

may leads to loop formation. In-order to avoid the infinite loop formation we have selected the spanning

tree. The contribution of this paper is given as the first contribution of this paper is constructing disjoint

paths for failure recovery and multipath routing. The infrastructure necessary for reactive failure

recovery schemes is exploited to provide disjoint paths for multipath routing during link failure time.

The second contribution of this paper is about the overhead occurred in finding the multipath. The last

contribution of this paper is reducing energy usage by keeping the nodes to standby state and wakeup

the nodes whenever there is a necessary for the nodes to transmit the packets using the line cards. We

illustrate how the spanning trees rooted at a destination may be employed to achieve multipath routing

and IP fast recovery. In this method we keeps the host processor in a standby mode, which only

consumes a small fraction of power but will reduce the traffic by saving the wakeup time. The traffic

formed is considerably reduced during wakeup in standby to sleep mode when compared to sleep to

wakeup mode. We propose a new line card design with two major changes. A separate power supply is

dedicated to the CPU and its circuits related to it to keep them running during line card is at sleep state

and then the nodes on the selected path are made to wakeup.

Index Terms—Independent spanning tree, dual link failures, disjoint multipath routing, power

efficiency, wakeup time.

I. INTRODUCTION

In the last few decades, communication has changed the world. Thanks to the massive improvement of

both Internet and mobile telephony, now it takes almost no time to find the decent information or reach

somebody almost anywhere. Moreover, corporations have changed and nowadays the whole economy

depends more or less on communication networks.

Since communication networks mesh the world, they need to be quite huge in size. Naturally, in a

system huge enough, sooner or later a failure occurs. It is a natural desire that if after the failure of some

resources transporting information is still possible, network should remain operable. Mechanisms

providing this self-healing aspect are called recovery mechanisms.

There are two fundamentally different types of recovery. One approach, called restoration, reactively

deals with the failure after it occurred. Although some precomputation can take place, the way of

bypassing the failed resource is computed only after the failure. The main advantage of this approach is

its simplicity and robustness.

Since the failed resource is exactly known, it can well adapt to all the situations. Unfortunately, since

significant part of the operation is done only after the failure, this approach.

In order to overcome the problems of restoration, protection techniques are applied. Protection

techniques are proactive, since they find the way of bypassing some failures long before they happen.

Naturally, since preparing to arbitrary number of failures is next to impossible, these techniques prepare

to only a given number and given type of failures.

International Journal of Recent Trends in Engineering & Research (IJRTER)

Volume 02, Issue 08; August - 2016 [ISSN: 2455-1457]


Before further discussing recovery techniques, it is important to deal first with the two most common

ways of routing. In a (virtual) circuit switched network a path for transporting is established, which is

the basic object of routing. Therefore, this type of routing is called connection oriented. In these

networks, all the paths are managed separately and it is possible to establish two paths between the same

two endpoints, which were computed in fundamentally different ways. This approach provides quite

high control on forwarding, making it relatively easy to bypass a failed resource. In connection oriented

networks typically both protection and restoration techniques are applied.

On the other hand, it is possible to send data in a connectionless manner, without explicitly establishing

the paths. This scheme can be applied mostly in packet switched networks, where the transported

information is split into small pieces called packets. Each packet has a header with the information

needed for forwarding it to the proper destination. Typically, packets contain a destination address, and

they are forwarded based on this address. Therefore, the assumption in the sequential that the next hop is

determined by the destination.

A routing is the same problem as computing a proper partial order for each node as a destination. In the

common case, when links have lengths and packets are forwarded along the shortest path, this partial

order is a total order; packets are forwarded to a node with smaller distance to the destination. If a failure

occurs, closer nodes may become unavailable. Therefore, restoration in packet switched networks

typically means recomputing the partial orders. Protection in these networks is usually not used,

although it would mean to switch to another, precomputed order.

This lack of protection is a growing problem nowadays due to the development of Internet. Current

Internet is based on Internet Protocol (IP), a typical connectionless, packet switched protocol, with

forwarding (typically) based on the destination address, and with extremely robust restoration but no

protection. Thus, the recovery provided by IP is quite slow, it can take several seconds even in the

simplest but very common case, when a single failure occurs. This slow recovery is acceptable for the

traditional elastic traffic, which IP was designed for.

Unfortunately, current IP networks are used to transport real-time traffic too, such as the traffic of

(video)telephoning (e.g., 3G, 4G mobile networks), on-line gaming, TV broadcasting or even business

critical stock exchange transactions. These types of traffic need to avoid seconds of service disruption.

Moreover, currently several companies use Virtual Private Networks (VPN) in order to interconnect

their geographically separated divisions. The quality of service of these VPNs is typically defined in a

contract called Service Level Agreement (SLA).

Since some of these companies use several real-time or delay sensitive applications (like continuous

database connection or remote desktop), these SLAs can be quite strict with serious consequences, if the

service provider fails to fulfill their requirements. In order to provide such VPN connections on pure IP,

a native protection scheme is indispensable.

The Internet takes an increasingly central role in the communication infrastructure. Traditional

application data were delivered in a manner of best efforts. However, the demands of delay-sensitive

applications, such as voice over IP (VoIP), video streaming, and gaming, have been increasing. These

applications require more continuous availability compared to data applications. Availability is not only

related to failure recovery, but also to QoS such as end-to-end delay or available bandwidth. Multipath

routing is one of the promising schemes to improve availability. Most currently deployed routing

protocols select only a single path for the traffic between a source-destination pair. However, single path

routing takes additional time to compute a new path after a failure and when congested, and may not

provide sufficient bandwidth to the application even when alternate paths exist between the source and

the destination. Multipath routing can overcome these problems by forwarding to alternate paths and

flexibly splitting traffic among multiple paths when the primary path does not meet availability. The




well-known benefits of multipath routing include flexibility in meeting application performance

requirements, improving end-to-end reliability, and avoiding congested paths [1].

Traditionally networks are built to handle peak traffic demands and varying traffic loads, the network

may have excess capacity beyond the current requirements. The excess capacity results in wasted energy

and there is a growing interest in reducing the energy consumption in networks. By providing increased

number of options for routing traffic, multipath is expected to enable increased energy savings in

networks. Multipath routing (MPR) is an effective strategy to achieve robustness, load balancing,

congestion reduction, and low power consumption. Disjoint multipath routing provides increased

security and bandwidth compared to non disjoint multipath routing as link- or node-disjoint paths are

employed.

Multipath routing in IP networks is mostly limited to equal-cost multi-paths (ECMP). Recently, some

sophisticated routers offer multipath routing [3], however they are limited to two kinds: The source-

based forwarding, which provides only single-path routing for a source; and the forwarding the packets

on the selected path must be made to standby to awake mode in-order to reduce the power consumed by

the node at idle state.

A. Previous work

The most commonly used method for finding the multipath in Internet is ECMP. Equal cost multipath

routing provides the path but it does not provide the path which is disjoint. The solutions applied during

failure for fast recovery are: ECMP, using MPLS tunnels or multihop repair paths for routing around

failed links, fast rerouting framework for IP networks, multiple routing configurations, failure

insensitive routing (FIR), and tunneling using not-via addresses. These solutions does not provide

protection and as well as it does not provide guaranteed recovery except in case of single link failure.

This paper shows how to construct the three independent trees for handling arbitrary dual link failures

and for finding the multipath routing. In addition, they listed three conjectures in their paper.

1) Vertex conjecture: Any -vertex-connected graph has vertex-independent spanning trees rooted at an

arbitrary vertex .

2) Edge conjecture: Any -edge-connected graph has edge independent spanning trees rooted at an

arbitrary vertex .

II. EDGED INDEPENDENT SPANNING TREE

A spanning tree is a subset of Graph G, which has all the vertices covered with minimum possible

number of edges. Hence, a spanning tree does not have cycles and it cannot be disconnected. By this

definition the conclusion is that every connected & undirected Graph G has at least one spanning tree. A

disconnected graph do not have any spanning tree, as it cannot spanned to all its vertices.

A. General properties of spanning tree

The conclusion is that one graph can have more than one spanning trees. Below are few properties

is spanning tree of given connected graph G.

1. A connected graph G can have more than one spanning tree.

2. All possible spanning trees of graph G, have same number of edges and vertices.

3. Spanning tree does not have any cycle (loops)

4. Removing one edge from spanning tree will make the graph disconnected i.e. spanning tree is

minimally connected.

5. Adding one edge to a spanning tree will create a circuit or loop i.e. spanning tree is maximally

acyclic.




B. Mathematical properties of spanning tree

Spanning tree has n-1 edges, where n is number of nodes (vertices).From a complete graph, by

removing maximum e-n+1 edges, we can construct a spanning tree.A complete graph can have

maximum nn-2

number of spanning trees.

So the conclusion in that spanning trees are subset of a connected Graph G and disconnected

Graphs do not have spanning tree.

C. Computing a Spanning Tree

There are many algorithms to compute a spanning tree for a connected graph. The first is an example of

a vertex-centric algorithm.

1. Pick an arbitrary node and mark it as being in the tree.

2. Repeat until all nodes are marked as in the tree:

(a) Pick an arbitrary node u in the tree with an edge e to a node w not in the tree. Add e to the spanning

tree and mark w as in the tree.

The iteration is done for n−1 times in Step 2, because there are n−1 vertices that have to be added to

the tree. The efficiency of the algorithm is determined by how efficiently the qualifying path has been

found.

The second algorithm is edge-centric.

1. Start with the collection of singleton trees, each with exactly one node.

2. As long as there are more than one tree, connect two trees together with an edge in the graph.

This second algorithm also performs n steps, because it has to add n – 1 edges to the trees until we have

a spanning tree. Its efficiency is determined by how quickly an edge would connect two trees or would

connect two nodes already in the same tree.

D. Minimum Spanning Tree (MST)

In a weighted graph, a minimum spanning tree is a spanning tree that has minimum weight that all

other spanning trees of the same graph. In real world situations, this weight can be measured as distance,

congestion, traffic load or any arbitrary value denoted to the edges.

E. Cycle Property

Let C is a subset of E be a cycle, and e be an edge of maximal weight in C. The e does not need to be in

an MST. Assume we have a spanning tree, and edge e from the cycle property connects vertices u and

w. If e is not in the spanning tree, then, indeed, it is not necessary. If e is in the spanning tree, then

another MST is constructed without e. Edge e splits the spanning tree into two subtrees. There must be

another edge e’ from C connecting the two subtrees. Removing e and adding e’ instead yields another

spanning tree, and one which does not contain e. It has equal or lower weight to the first MST, since e’

must have less or equal weight than e.

The cycle property is the basis for Kruskal’s algorithm.

1. Sort all edges in increasing weight order.

2. Consider the edges in order. If the edge does not create a cycle, add it to the spanning tree. Otherwise

discard it. Stop, when n − 1 edges have been added, because then we must have spanning tree. It is a

straightforward application of the cycle property. Sorting the edges will take O(e * log(e)) steps with

most appropriate sorting algorithms. The complexity of the second part of the algorithm depends on how

efficiently we can check if adding an edge will create a cycle or not. This can be O(n * log(n)) or even

more efficient if we use a so-called union-find data structure.




F. Spanning Tree Protocol

The Spanning Tree Protocol was originally developed by Radia Perlman for the Digital Equipment

Corporation (DEC) in 1983 (Menga, 2004) and was first published in 1985 (Perlman, 1985) The IEEE

standard version of the protocol, 802.1D was published in 1990 and was superseded by RSTP 802.1W in

the 2004 version (Iveson, 2013). STP currently exists in the original Digital Equipment Corporation

(DEC) implementation and the Institute of Electrical and Electronic Engineers (IEEE) standard which

was developed from the latter and is almost exclusively used in networks today (Menga, 2004).

Prior to STP introduction any switch architecture which had a loop would end up with duplicate

frames flooding between switches causing an outage; this is commonly referred to as a "broadcast

storm". The Spanning Tree algorithm(STA) solved the problems associated with this physical loop by

creating a logical blocking solution by stopping normal switch forwarding (Bahethi, 2014). Once the

root bridge has been selected, each non-root bridge determines the best path to reach the root bridge

while blocking any other paths which introduce loops on the network.

In a converged STP, each port is either in a forwarding or blocking state. Ports which are considered

the best path to the root bridge are placed into a forwarding state while all other ports are placed into a

blocking state. On their first initialization, each switch generates a unique bridge ID used by spanning

tree to uniquely identify the bridge. The bridge ID is a combination of the bridge MAC address plus a 2-

byte bridge priority field, where the priority field can be altered by a network administrator to directly

affect whether or not a bridge becomes the root bridge. The switch with the lowest bridge ID is the root

bridge. When the bridge ID has been determined, this bridge begins to generate configuration Bridge

Protocol Data Units (BPDUs) assuming that is the root bridge.

There are two types of BPDUs used in spanning tree, configuration BPDUs and Topology Change

Notification (TCN) BPDUs. Configuration BPDUs are originated by the Root Bridge and flow outward

along the active paths that radiate from the root bridge. TCN BPDUs flow upstream (towards the root

bridge) to alert the root bridge that the active topology has changed (Rossi, 2000).

G. Configuration BPDUs

This type of BPDU is the main communication mechanism for STP and is used to determine the root

bridge and whether or not a port should be forwarding or blocking state. The configuration BPDU has

various fields which are used to indicate important parameters for the generation of the final STP by the

Spanning Tree Algorithm (STA).

On receiving a configuration BPDU containing a lower root bridge ID, the bridge immediately considers

this lower root bridge ID as the new root bridge and begins propagating the configuration BPDUs

received from this bridge. Therefore in a network with multiple bridges, the bridge with the lowest

bridge ID will eventually become the root bridge to all bridges.

Configuration BPDUs are generated by the root bridge only. Configuration BPDUs for nonroot bridges

are generated only when a configuration BPDU originated by the root bridge are received via the root

port of the non-root bridge. The non-root bridge updates fields, such as root path cost, bridge ID and

port ID in the received configuration BPDU and then propagates the updated configuration BPDU out

all forwarding ports, except the root port upon which the BPDU was generated. This ensures that

configuration BPDUs are propagated throughout the entire network. After the root bridge has been

selected each non-root bridge attempts to build a topology that forms the lowest-cost path to the root

bridge. The lower this cost the more preferable the link. Depending on bandwidth each logical port has a

default cost associated with it, as defined in the IEEE standard. This cost can be modified to influence

root port selection.




Table 1 Default STP Costs

Bandwidth(Mbps) Cost

4 250

10 100

16 62

100 19

155 14

622 6

1000 4

10000 2

Every port within STP transitions through several states upon port initialization. Data from the user is

only forwarded when a port is in the forwarding state. This approach is taken to prevent any loops from

forming even for a short period, as a broadcast storm can bring down a network in seconds. There are

five spanning tree port states, which are as follows:

1. Disabled State

A port is disabled when the port is down. This may be because the port has been

administratively shut down or because of some issue with processing BPDUs. A port

transitions from this state to the blocking state moving immediately to a listening state after

it is initialised at the Layer 2 level.

2. Listening State

This is the phase where most of the important groundwork of generating a loop-free

topology is carried out. Within this phase, spanning tree goes through the following

processes:

i. Root Bridge Election

The bridge with the lowest bridge ID is selected as the root bridge.

ii. Root Port Selection

A single root port is selected from every non-root bridge providing the closest path to the root bridge.

iii. Designated bridge (port) selection for each segment

Each switch determines whether or not it represents the shortest path to the root bridge for each

network segment attached to the non-root switch this excludes the network segment attached to the

root port. If this is the case, it configures itself as the designated bridge for the segment and configures

the port as a designated port. Designated ports are placed into a forwarding state, while all other non-

designated ports are placed into a blocking state. An exception to this configuration is if a non-

designated port represents the root port on another switch. If this is the case, the root port on the other

switch remains in a forwarding state, as well as remaining the designated port on the local switch.

Whether root bridge election or a root port selection, the same STA selection process is used for all

decisions. Priority criteria are processed one by one, by comparing the configuration BPDUs received

on a port with the configuration BPDUs that are sent out a port.

3. Learning State

The bridge is accepting user data without forwarding it during the learning phase. The local MAC

address table is populated on each bridge, so that once traffic is forwarded, the bridge does not need to

flood a lot of traffic.

4. Forwarding State

Depending on whether a port has been selected as either a root port or designated port, it is placed

into the forwarding state. A port will remain in a forwarding state until a topology change occurs, where

the port transitions to the listening phase and performs the appropriate selection processes.




5. Blocking

Where a port is found not to represent the shortest path to the root bridge it is placed in the blocking

state. This is where the port is being blocked from sending or receiving any user data while still sending

and receiving configuration BPDUs.

Timers determine how quickly or slowly a spanning-tree topology can react to a link or bridge

failure converging to a new topology. There are three spanning-tree timers which are as follows:

1. Hello timer

The Interval between the generation of each configuration BPDU. The default is two seconds.

2. Max age timer

This timer controls the validity of a configuration BPDU after being received. The default is 20 seconds,

meaning that if a configuration BPDU is not received within 20 seconds of the previous configuration

BPDU, the previous configuration BPDU is no longer valid and a new root bridge must be selected.

3. Forward delay

This timer controls the amount of time spent by a bridge port in each of the listening and learning states

before transitioning into a blocking to a forwarding state.

A majority of BPDUs on a healthy network should be configuration BPDUs, although all bridged

networks see at least a few of the second type of BPDU, the Topology Change Notification (TCN)

BPDU. TCN BPDUs play a key role in handling changes in the active topology.

The TCN BPDU is much simpler than the configuration BPDU consisting of only three fields. TCN

Fig 1 Topology Change Notification working towards the root bridge

BPDUs are identical to the first three fields of a configuration BPDU with the exception of a single bit

in the type field, with the type field containing one of two hexadecimal values 0x00 (Binary: 0000 0000)

indicating a configuration BPDU or 0x80 (Binary: 1000 0000) indicating a TCN BPDU. Configuration

BPDUs are only originated by the root bridge, but a TCN BPDU will be

generated by any switch in the network when either of two things happens: A port has gone into

forwarding state and a port has gone from forwarding or learning state into blocking state

While the TCN BPDU is important, it doesn't give the other switches a lot of detail. The TCN

doesn't say exactly what happened, just that something happened".

When a bridge receives the topology TCN it will send a Topology Change

Acknowledgement(TCA) on its designated port towards the downstream switch. It will create a TCN

itself and send it on its root port as well.(Molenaarin, 2014)

When the root bridge receives the TCN, the root will also respond with an acknowledgement, taking

the form of a configuration BPDU with the topology change bit/flag set. This indicates to all receiving

bridges that the aging time for their MAC address tables should be changed from the default of 300

seconds/5 minutes to the forward delay spanning tree timer value (default 15 seconds).

A Portfast enabled port changing STP state cannot result in the generation of a TCN BPDU. The

most common usage of Portfast is when a single PC is connected directly to the bridge port, and since




such a port going into forwarding state (or leaving it) doesn't impact STP operation, there's no need to

alert the entire network about it.(Bryant, 2015)

H. Recent Spanning Tree Developments

The IEEE has published a number of new specifications relating to STP, which include both Rapid

Spanning Tree Protocol (RSTP) 802.1W and Multiple Spanning Tree (MST) 802.1S specifications.

The RSTP specification is the most significant development for spanning tree in recent times. RSTP

has depreciated the 802.1D standard and redefines the states that bridge ports can be in, as well as how

bridges detect failure and the associated convergence time. RSTP aims to reduce convergence times and

also includes standards-based implementations of PortFast, UplinkFast, and BackboneFast.

Fig 2 Topology Change Acknowledgement from Root Bridge

The MST specification relates to how spanning tree interacts with topologies that include multiple

Virtual Local Area Networks (VLANs). Modes of operation can be defined on Cisco Catalyst switches,

which determine how the switch maintains STP for multiple VLANs.

The following lists the common STP modes of operation:

1. Common Spanning Tree (CST)

This standard dictated that a single spanning-tree instance should be used for multiple VLANs. The

reason for defining CST is to ensure interoperability with non-802.1Q bridges, as all STP

communication is sent untagged on the native VLAN. By having only one spanning tree instance each

switch CPU needs to deal only with a single STP instance, although this has the drawback of being

unable to use implement load sharing.

2. Cisco Per-VLAN spanning tree (PVST+)

This is a proprietary standard developed by Cisco, which allows multiple STP instances to operate in a

Layer 2 network, while also allowing load sharing. This standard operates a unique STP instance per

VLAN. Although allowing the load sharing, the implementation is flawed as a single STP instance is

required for each VLAN, even if VLANs share the same STP topology. This has a detrimental effect on

CPUs in network environments which could support hundreds or thousands of VLANs.

3. Multiple Spanning Tree (MST)

MST is a combination of both 802.1Q and PVST+. It allows the user to map a configurable number of

VLANs to a single STP instance, meaning that all VLANs that share the same STP topology can be

supported by just one STP instance. Load sharing is achieved by having multiple STP instances, but the

number of STP instances that must be maintained on each switch can be matched to the number of

different logical topologies required for the network to implement load sharing (Menga, 2004).

Where a port is found not to represent the shortest path to the root bridge it is placed in the blocking

state. This is where the port is being blocked from sending or receiving any user data while still sending

and receiving configuration BPDUs.


@IJRTER-2016, All Rights Reserved

III.

As three-edge connectivity is required to tolerate any dual link failures, the network will be three

connected.

Fig 3 Example of a Edged Spanning Tree

Fig 4 (a) Red tree. (b) Blue tree. (c) Green tree.

The assumption is that the network employs the link

aware of the network topology. The following terms

vertex, link and edge.

IV. DISJOINT

A. Routing through multiple paths

Instead of using single path to reach the destination the

same destination over multiple consecutive ports

B. Failure Recovery

In any approaches the decisions for selecting the node for forwarding the packet is based on the

destination address in the packet header and the incoming interface over which the packet was received.

The assumption is that all packets will be routed on t

overhead bit (SF) that indicates if the packet has seen a second failure or not. Thus, if a packet is

received on an incoming edge that is present in the red tree, it is assumed that the packet

failures. The SF bit is ignored and route the packet

C. Findings of Overhead bit

1) One Link Failure:

If a link is failed in the red tree then the packet will be rerouted

tree on which the packet is rerouted is dete

packet will be rerouted on the blue tree. If

In both these situations, when the packet is rerouted from the


Volume 02, Issue 08; August - 2016

III. MODEL OF THE NETWORK

edge connectivity is required to tolerate any dual link failures, the network will be three

Fig 3 Example of a Edged Spanning Tree

Fig 4 (a) Red tree. (b) Blue tree. (c) Green tree.

assumption is that the network employs the link-state protocol, hence all nodes in the network are

he following terms are used such as network and graph, node and

DISJOINT MULTIPATH ROUTING

rough multiple paths

path to reach the destination the multiple subflows are established to reach the

same destination over multiple consecutive ports.



that all packets will be routed on the red tree by default. Every packet carries a one


received on an incoming edge that is present in the red tree, it is assumed that the packet

and route the packet on the red tree.

If a link is failed in the red tree then the packet will be rerouted either on the blue or the green tree. The

is rerouted is determined by the color of the edge. Thus, if

packet will be rerouted on the blue tree. If the link is green, the packet will be rerouted on the green tree.

, when the packet is rerouted from the red to blue/green tree, the SF bit is set to 0.


2016 [ISSN: 2455-1457]

200

edge connectivity is required to tolerate any dual link failures, the network will be three-edge

state protocol, hence all nodes in the network are

such as network and graph, node and

are established to reach the



he red tree by default. Every packet carries a one


received on an incoming edge that is present in the red tree, it is assumed that the packet has seen no

the blue or the green tree. The

if the link is blue, the

is green, the packet will be rerouted on the green tree.

to blue/green tree, the SF bit is set to 0.




2) Two Link Failures:

A node that receives a packet over the blue (green) incoming interface would forward the packet over

the blue (green) tree. If the blue (green) forwarding link is not available and the SF bit in the packet is

set to 0, this implies thatthe packet has seen one failure. Hence, the packet is rerouted to

the green (blue) tree with the SF bit set to 1. If the blue (green)

forwarding link is not available and the SF bit in the packet is

set to 1, then the packet is dropped.

V. CONSTRUCTING THE SPANNING TREE

Given a graph that is three-edge-connected and a destination Vertex d , the outline of our approach to

compute the three edge independent spanning trees rooted at a destination is as follows:

1) a) Given a graph, prune edges to consider a minimally three-edge-connected graph.

b) Divide the resultant graph into two-vertex-connected components. Thus, every component is

three-edge and two-vertex-connected (3E-2V, for short). For a given destination, identify a root vertex

in each component. This root vertex is the vertex through which every path from a vertex in the

component to the destination must traverse. For the rest of the paper, the assumption is that a two-

vertex- and minimally three-edge-connected graph.

2) Construct three edge-independent spanning trees in each 3E-2V component rooted at r.

3) Merge the trees constructed in each 3E-2V component to get the final three edge-independent

spanning trees for destination vertex d .

VI. POWER CONSUMPTION THROUGH WAKEUP MECHANISM

A. Line Cards

A line card or digital line card is a modular electronic circuit designed to fit on a separate printed

circuit board (PCB) and interface with a telecommunications access network. A line card typically

interfaces the twisted pair cable of a plain old telephone service (POTS) local loop to the public

switched telephone network (PSTN). Telephone line cards perform multiple tasks, such as analog-to-

digital and digital-to-analog conversion of voice, off-hook detection, ring supervision, line integrity

tests, and other BORSCHT functions. In some telephone exchange designs, the line cards generate

ringing current and decode DTMF signals. The line card in a subscriber loop carrier is called a

subscriber line interface card (SLIC).

B. FPGA

A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a

customer or a designer after manufacturing – hence "field-programmable". The FPGA configuration is

generally specified using a hardware description language (HDL), similar to that used for an application-

specific integrated circuit (ASIC). (Circuit diagrams were previously used to specify the configuration,

as they were for ASICs, but this is increasingly rare. FPGAs contain an array of programmable logic

blocks, and a hierarchy of reconfigurable interconnects that allow the blocks to be "wired together", like

many logic gates that can be inter-wired in different configurations. Logic blocks can be configured to

perform complex combinational functions, or merely simple logic gates like AND and XOR. In most

FPGAs, logic blocks also include memory elements, which may be simple flip-flops or more complete

blocks of memory.

C. Sleep/Wakeup Mechanism for Power Saving

Power-saving schemes for network devices can be divided into two categories, namely, uncoordinated

sleeping and coordinated sleeping. In uncoordinated sleeping, link interfaces sleep based on local

decisions alone. A straightforward strategy is opportunistically putting interfaces to sleep when links are

idle. While this might be reasonable for low-speed LANs with large packet inter-arrival time, it does not




apply to high speed links effectively. To improve this, Buffer-and-burst is proposed to deliberately

buffer traffic in the upstream router to create more idle time between traffic bursts for the downstream

router to sleep. Indeed, for low-level CMOS circuits, the power mode transition can be made in very

short time via techniques such as clock gating and power gating. However, it is not that easy for a high-

end router to change its power state globally in such short period, since a high-end router usually

consists of numerous heterogeneous sub modules and needs extra driver software to achieve global

synchronization with additional delay.

Unlike uncoordinated sleeping, in coordinated sleeping, the sleep/wakeup decisions are made

collaboratively at network level. Power is conserved by aggregating traffic into fewer links and putting

idle links to sleep. Coordinated sleeping relies on a centralized controller to collect the link status from

distributed network nodes, and make corresponding sleep/wakeup decisions periodically. The figure

exemplifies how coordinated sleeping works.

VIII. EVALUATION OF A MULTIPATH

A. No Failures

The average path lengths is computed in the network when there are no failures. This default path length

from node to the destination under the specific routing approach. Then, the average path length under no

failures in the network is computed in all four approaches.

B. One-Link Failures We are only interested in computing the average path length when a link failure affects the default path.

All other single-link failure scenarios do not affect the routing schemes.

C. Two-Link Failures

The tunneling approach and our approach handle failures differently; the former is a link-level recovery,

while the trees directly reroute toward the destination. Hence, it is not possible to compare a particular

two-link failure scenario across the schemes as a two-link failure encountered when tunneling may not

be seen when the trees are employed, and vice versa.

VII. CONCLUSION

We have provided an algorithm to construct three edge-independent spanning trees. We show how the

three edge-independent trees can be used for routing in an IP network. We develop a routing scheme that

is capable of providing the disjoint multipath routing using only the destination address in the packet

header. We also develop three routing approaches using the trees which provides very minimal packet

overhead. All of the routing schemes developed are guaranteed to withstand any arbitrary dual link

failures in the network. To support fast line card wakeup, we made penetrating measurement on the boot

procedure of line cards. We propose corresponding designs including separating the on-board CPU

power supply from the other parts of a line card, setting up a minimized hardware configurations. In

future we can provide multiple link failure solutions and also low power image and video

compression techniques are need to be design aiming to increase the battery life and strong

cryptographic algorithm need to be implement.

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