Calculation of Cisco Router Processing Power for a Large Network with Thousands of Nodes

Alireza Sarikhani 1,*, Mehran Mahramian 2, Hamidreza Hoseini 3

*Corresponding author: 1Department of Computer, Arak Branch Islamic Azad University Arak, Iran ar.sarikhani@gmail.com 2 Informatics Services Corp. Tehran, Iran m_mahramian@isc.iranet.net

3 Department of Electronic, Arak Branch Islamic Azad University Arak, Iran Hr-hoseiny@iau-arak.ac.ir

Abstract—Router processing power in VSAT networks is a serious problem due to the huge amount of packets transferring between satellite links and terrestrial links. In this paper, we model power of core routers which are using OSPF and EIGRP protocols. The model can accurately predict the power consumption of the routers with a significant speedup. Also we determine the total number of routers required to support thousands of servers in the mentioned network. Simulations done with NS2 in a wide range of network configurations to support the proposed model. Results obtained from the simulations are in agreement with those obtained by the model.

Keywords- Power Processing; Satellite Link Simulation; Dynamic Routing; DVB-RCS, Large-Scale Network Simulation; OSPF; EIGRP

I. INTRODUCTION In the Internet model, smaller networks are connected to

bigger networks through routers. Originally, routers were implemented on general purpose workstations. These early routers had a single CPU, which had to do two main tasks: Routing and Forwarding. Routing refers to discovering the network topology. Forwarding refers to the look-up and transfer of packets to the matching outbound next-hop for a given packet. Routing, as defined here, mainly concerns signaling information and forwarding mainly concerns user information. As long as the general purpose processor has infinite processing power and memory, the union of both routing and forwarding functions in the same device does no harm. Practically speaking, processing power and memory are always finite resources and experience has shown that the two functions mutually influence each other in their competition for processing and storage resources. Unifying routing and forwarding may cause stability problems during transient conditions, for instance, when a large traffic trunk needs to be rerouted. The stress occurs because the routing subsystem has to calculate alternative paths for the broken traffic trunk and, at the same time, the forwarding process may be hit by a large wave of traffic being rerouted through this router by another router. And that is exactly the problem with the unified design combining routing and forwarding. For example, what happens when the central CPU is 100 percent utilized? Not all traffic can be routed and packets have to be dropped. If the signaling or control traffic generated by the routing protocols is part of the dropped

traffic, this may result in further topology changes and result in endless stress that propagates through the whole network [1].

Cisco corporation routers have huge proportion of network bargain in hand and using them in common and dedicated networks are developing them day in day out. Announced technical specifications for these products usually with the purpose of giving bargain in hand in the best conditions presented and it may not be appropriate for customers use in special conditions. Also these specifications usually are presented with this purpose in mind in order to clients choose more powerful product until meet their future needs. Something which happens in action is that clients usually have to change network configurations after occurring some problems which happen in special and critical conditions until reach appropriate functions that this issue can cause problems for network customers and server corporations. Also in these cases required amount of expertise for troubleshooting problems and moving framework better is high, that it may not be available for all servers.

The paper is organized as follows. Section II introduces the basic concepts utilized in the paper, as well as the objectives of the designed procedures. Section III presents the concepts in details. Section IV describes the proposed our simulation procedure. Finally, Section V concludes the paper.

II. BASIC CONCEPTS In this chapter an introduction is presented into the

interesting field of how router works. Knowledge of the internal workings of a router is important to get the full understanding of what goes on in a network, and to interpret the results from measurements. Especially it is important to understand when and why failure occurs, and what constitutes the failure.

A generic model of a router is developed, where the functionality and resources of a router are split into four different parts; Router processing power which is used for router forwarding table lookup and decisions regarding the correct output port. Internal bus capacity used for packet transmission from input buffers to the correct output buffer. And finally, the capacity on the outgoing links. Input and output buffering time however, is greatly influenced by the router load, with cross traffic causing buffer delay [2].

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Some analytical models of the router may also be given for different regimes. In the limiting case for these regimes some of the resources in the router may be viewed as unlimited. Three different regimes are therefore identified for analyzing the router analytically; Output link capacity limited, memory size limited or processing time limited. First, by introducing a very big buffer and a fast enough processor such that no input queuing is experienced, the output links are the only restriction. Second, letting the buffer size be the limited resource, the packet loss is of great interest. This issue is complicated by the fact that packets are of different sizes. At last, the capacity on the outgoing links and the buffer capacity may be large, causing the processing power to restrict the throughput of the router [2].

A. Network Resources To understand these issues, one needs to determine 1-

what network resources are, 2- how these resources are consumed, and 3- how network performance is defined. These terms are defined below. First, there are two types of network resources, router and link resources: router resources refer to router CPU cycles and memory, and link resources refer to link bandwidth. Second, these network resources are consumed by two types of messages: data messages and routing messages. Both types of messages consume link resources as they traverse the network and router resources because routers receiving these messages have to process and/or forward them. Third, network performance is determined by application network demands. In general, performance the faster data messages are delivered from their sources to their destinations, the higher the network performance can be characterized by the speed in which data messages are delivered to their destinations [3].

B. Routers The Internet can be described as a collection of networks

interconnected by routers using a set of communications standards known as the Transmission Control Protocol/Internet Protocol (TCP/IP) suite [4].

Once a router receives a packet at an input link, it must determine the appropriate output link by looking at the destination address of the packet. The packet is transferred router by router so that it eventually ends up at its destination. Therefore, the primary functionality of the router is to transfer packets from a set of input links to a set of output links [4].

A router has three fundamental jobs. The first is to compute the best path that a packet should take through the network to its destination. The second job of the router is to actually forward packets received on an input interface to the appropriate output interface for transmission across the network. The third major router function is to temporarily store packets in large buffer memories to absorb the bursts and temporary congestion that frequently occur and to queue the packets using a priority-weighted scheme for transmission [5].

Therefore, the key components of a router are the forwarding engine to lookup IP address, the switch fabric to

exchange packets between line cards, and the scheduler to manage the buffer [4].

C. Routing Routing is more strictly associated with the procedure of

determining network layer reach ability, identifying the most suitable link on which to send packets. The result is a Routing Information Base (RIB), which contains the routes for each destination. This information could be used directly to process packets, but is generally compiled to a more readily used format (the Forwarding Information Base, FIB) [6].

Routing is a background process, which creates and regularly updates a RIB via signaling messages exchanged between neighboring IP nodes [6].

The FIB contains associations between destination IP addresses and next-hop IP addresses. In addition, an address resolution cache lists link-layer addresses of nodes for next hop IP addresses having an interface on a link. If a link layer address is not found in this table, an address resolution process is called to create such an entry through a signaling exchange on the link [6].

There are two types of routing: static routing and dynamic routing. Static routing refers to routes to destinations being listed manually, or statically, as the name implies, in the router. Network reach ability in this case is not dependent on the existence and state of the network itself. Whether a destination is active or not, the static routes remain in the routing table, and traffic is still sent toward the specified destination. Dynamic routing refers to routes being learned via an interior or exterior routing protocol. Network reach ability is dependent on the existence and state of the network. If a destination is down, the route disappears from the routing table, and traffic is not sent toward that destination [7].

Routing protocols in the Internet could be classified into two main groups: link-state routing and distance-vector routing. Typically in the current Internet, distance-vector routing protocols (e.g., BGP, and EIGRP) are used for inter-domain routing (i.e., routing among Autonomous Systems (ASs)), while link-state routing protocols (e.g., OSPF, and IS-IS) are used for intra-domain routing [7]. In this paper we study two common routing protocols: OSPF and EIGRP.

• OSPF Overview OSPF is a link-state routing protocol, OSPF maintains a

map of the network at all routers. Each router collects their local link information and floods the network with that information so that all the routers have a global map of the network [8].

In OSPF, routers send HELLO packets to their neighbors to check whether they are up or down. HELLO packets are sent periodically at every Hello Interval. If the neighbor does not respond after some period of time, then it is assumed dead. This period of time is called the Router Dead Interval, and is typically four times the Hello Interval. Each router maintains link status announcements (LSAs) received from other routers. Collection of these LSAs is called a Link-State Database (LS-Database), which in fact shows the global map

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of the network. The routers run Dijkstra’s or some other shortest path algorithm to find the routes in the network. When a link goes down or comes up, the router detects the change via HELLO messages [8].

After updating its local LS-Database, the router sends an LS-Update message which conveys the change to other routers. Normally, LS Update messages are sent when a change in the LS-Database occurs. Such a change can happen either because of a local link, or because of an LS-Update message received from elsewhere. There is also LS-Refresh messages sent across the OSPF routers. Each OSPF router floods its LS-Database to other routers at every LS Refresh Interval, which is typically 45 minutes [8].

• EIGRP Overview EIGRP (Enhanced Interior Gateway Routing Protocol) is

a distance-vector routing protocol developed by Cisco Systems to reduce routing protocol overhead in steady state, and to provide fast convergence in case of topology changes. In well-designed networks, EIGRP scales well and converges quickly with minimal network traffic. To minimize its load on the network, EIGRP propagates only routing table changes instead of the entire routing table when a change occurs [9].

EIGRP activities start at EIGRP start time by sending initial hello messages through the active interfaces of the underlying router node. The EIGRP node discovers neighbor EIGRP modules when they send hello messages, and the module begins to build its topology and routing tables accordingly. In an effort to discover the entire network, the EIGRP nodes then exchange topology and update messages with their new-found neighbors. When all update messages have been processed and there are no triggered update messages left, the EIGRP network has converged (that is, all routers have discovered all of the IP sub-networks in the entire network). At this point, the EIGRP process enters into steady state [9].

In steady state, periodic hello messages are used by EIGRP nodes to detect changes in neighbor node status. If an EIGRP node does not receive a hello message from a neighbor for a specific amount of time, the EIGRP process considers that neighbor to be down or unreachable. If the failed node recovers, then its EIGRP process will start sending periodic hello messages again, and these hello messages alert its neighbors that it has recovered. In case of topology changes, the EIGRP process tries to recover quickly by using its topology table to find an alternate route. [9].

D. DVB-RCS Systems Digital Video Broadcasting with Return Channel via

Satellite (DVB-RCS) has emerged as the platform to integrate the satellite broadcasting capabilities with the Internet infrastructure. The IP/DVB architecture defines the basic set of functionalities required for users interactivity across a satellite DVB-S distribution system. Basically, IP packets are firstly encapsulated into an MPE (Multi Protocol Encapsulation) structure containing the source/destination MAC addresses of the traffic stations involved in the data

transfer. Then, MPE packets are delivered using a transport stream of 188 bytes MPEG-2 cells [10].

Figure 1 shows the main elements of our DVB-RCS network. The NCC is the core of the network: it provides control and monitoring functions and it manages network resources. RCSTs are fixed with Return Channel via Satellite (RCS) that allows transmitting data or control signaling, using an MF-TDMA access scheme. Resources are time slots on different available carrier frequencies. DVB-RCS return link resources are divided in super-frames that are characterized by suitable portions of time and frequency bands; each super-frame is divided in frames that are composed of several time-slots. RCSTs send their resource requests to the NCC. The NCC looks at the available return link resources and sends a broadcast response to the RCSTs (forward channel) through the Terminal Burst Time Plan (TBTP), a message belonging to the Service Information (SI) tables, that allows the RCSTs to transmit data in allocated time slots, in some carrier frequencies and with a given power level [11].

Figure 1. DVB-RCS Network Architecture.

The DVB-RCS standard envisages 4 different types of resource allocation schemes:

1. Constant Rate Assignment (CRA). The link resources are negotiated at the beginning of the transmission and are maintained for all the duration of the connection. Thus, this scheme does not require bandwidth consuming dynamic signaling from satellite terminals to NCC.

2. Rate Based Dynamic Capacity (RBDC). In this DAMA scheme, a ST periodically submits to the RNCC a capacity request message based on measurement of the local incoming traffic. Every explicit request overrides the previously submitted one and new requests are submitted only if needed.

3. Volume Based Dynamic Capacity (VBDC). In this scheme, the TT dynamically signals the data volume required to empty its buffer. New requests are sent any time more traffic is queued. The scheduler assigns the capacity according to these requests, while taking the constraints remaining after CRA and RBDC into account.

4. Free Capacity Assignment (FCA). In this scheme, the capacity is assigned from the BoD controller to the TTs. Since capacity allocation does not involve any explicit demand from the TTs to the controller, FCA is designed to satisfy utilization and fairness criteria. “Bandwidth on demand” can be employed to support the largest number of users possible [10].

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E. TCP Mechanism The Transmission Control Protocol (TCP) is a transport

protocol that provides a reliable, byte stream-based and connection-oriented service to the application layer. Three functions can be identified in the TCP protocol: flow control, congestion control and error recovery. The flow control scheme allows an efficient exchange of data not exceeding the capacity of the receiver buffer [12].

TCP is efficient on wired networks, but provides poor performance on satellite networks due to the specific characteristics of satellite links [13].

In [14] Dennis Roddy presented the factors that can adversely affect TCP performance over satellite links are as follows:

Bit error rate (BER). Satellite links have a higher bit error rate than the terrestrial links.

Round-trip time (RTT).With GEO satellites, the round-trip propagation path is ground station to satellite to ground station and back again. The send TCP layer must wait this length of time to receive the ACKs.

F. Network Processor Systems The general idea of a network processor is that it will

receive a flow of packets. The packets will then be processed. This might involve changing, removing or adding data to a packet. When the processing is finished the packet is sent out again. Network processor used because network processors are programmed to perform computer communication tasks and algorithms [15].

In this section, a model for a network processor system is presented. The major building blocks of the model are line cards using network processors, a switch fabric and a route processor. The basic building blocks of a network processor line card are processing blocks, engines, queues and channels. Such a line card can be logically separated into an ingress and an egress part. Figure 2 shows a network processor system that represents a router with four ingress and four egress line cards [16].

Figure 2. Network Processor System overview

Assumed that there is only one port on each line card, and packets arriving at this port are first processed at the ingress line card, and are then transmitted through the switch fabric to the egress line cards. Moreover, there is a route processor whose main task is to handle routing and management protocols [16].

Typical functions performed by network processors are summarized below:

Lookup and pattern matching: This function compares packet header fields with specific patterns to classify the type of packets, for example perform a table lookup to return the relevant table entry or determining type of incoming packets are an IPv4 or an IPv6 packet [17].

Forwarding: This function is defined as determining the output path for incoming packets. It is implemented using hardware prefix tree structure and special hardware [17].

Access control and queue management: Once packets have been identified, they are placed in appropriate queues for further processing. Packets are also checked against security access policy rules to see if they should be forwarded or discarded [17].

Traffic shaping and control: Some protocols or applications require that, as traffic is released to the outgoing wire or fiber, it is shaped to ensure that it meets delay or delay variation requirements. Other requirements specify the priority of traffic between different channels or message types [17].

Data Manipulation: This is where the packet is modified in some way; this could be decrementing the Time to Live (TTL) field in an IP packet, recalculating the CRC check, performing packet segmentation and reassembly and encryption or decryption of packets [17].

III. OUR PROPOSED SIMULATION Our test bed is an IP-based network with thousands of

nodes. Each of these nodes is in a star topology and is connected to the core router via an edge router. Connection of any edge router with core router can be done with two paths. The first one is a terrestrial link with low delay and second is a geostationary satellite link with higher delay. The terrestrial link is the default path and the satellite link works as the backup path. Also connection between each edge router with core at any time is via VPN and IPSec used. Figure 3 shows one of nodes in our network topology.

Our work includes two stages. In stage one, we must find the number of packets that are generated when a failure occurs in network topology and in the other stage we need to find amount of time required for processing a packet in the core router network processor. When we have amounts of these two sections, can determine extra required processing power for handling packets that generate due to a network failure.

A. Finding generated packets Absolute simulations of satellite network require

modeling of microwaves frequency capabilities details and operations of different protocols. In other hand we need special information about satellite network capabilities.

We must first define nodes in topologies. In NS2 a node has two key actions. Act as a router and forward packets into communication links base on routing tables. When act as a

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host, deliver packets to transport layer that specified in packet header. We create different terminals in different locations and connect all of them with uplink and downlink satellite channels. Also we model propagation delays in system. In addition, for implementation of DVB-RCS we define transmit and receive channels separately.

NS2 in its routing modules does not have a topology that can support satellite and terrestrial nodes at the same time. A new module is added for routing to support satellite and terrestrial nodes in topology. This capability allows us to have a hybrid network that terrestrial clients via terminals on satellite link connected to satellite hub.

Because we used DVB-RCS in return channel (uplink), must use DAMA algorithms for dynamic bandwidth allocation. Satellite link is shared with MF/TDMA scheme. In this design, uplink divided into time slots. Terminals that located in different geographical positions periodically synchronize with signals that send via hub and this guaranty that in presence of different propagation delays, all terminals are aware at same time from allocated time slots. Our system uses a combination of the CRA and RBDC resource allocation algorithms: for each satellite terminal (ST) connected to the network an amount of bandwidth equal to one time-slot per MF-TDMA multi-frame is reserved. Such slot can be used both to transmit signaling (as the terminal configuration information and allocation requests messages) as well as data messages. However, signaling packets have always higher priority than data packets. At this point, we need to set DAMA parameters such as slots per frame, frame per super-frame, super-frame duration in milliseconds.

Traffic that sends from users is transaction formal. In other hand, user sends required data to edge router and then to core router. After processing information, forward response to user and send acknowledge from user to center for purpose of successive transaction.

Figure 3. Network Topology

What we study in this paper is calculation of power processing for core routers, especially focusing on when all terrestrial links from STs to NCC goes down. At this time, routing algorithms start to work and exchange all routing tables. Using static routing, when a link fails, alternate path is replaced if it is possible. In dynamic routing, routing tables are being calculated continuously. When a link fails, the adjacent node should advertise the failure to other nodes. This may put a high workload to links because in addition to data messages, also routing messages must be carried from these links and this might limit our processing power.

We calculate the amount of traffic goes to NCC for dynamic routing. Sometimes this is a bottleneck itself. In this paper we focus on number of nodes that we can attach to a core router. We implement this by simulating at node level. For example, for each node we must calculate the maximum number of packets that can be routed in each second.

B. Finding process time required for a packet When a packet incomes/outcomes to/from router CPU, in

average 4 tasks execute on it: 1- moving to buffer, 2- check with IP Address, 3- moving to next buffer and 4- send packet. For each task we calculated the number of instructions that execute in CPU. For this reason we used NEPSim simulator. When we want to receive or transmit a packet from/to network, CPU executes a set of instruction on it. From sum of these numbers we can determine total number of instructions that executed on a packet. For each instruction it is clear the number of clock per instruction and the percentage amount of CPU that an instruction can consume.

IV. EXPREMENTAL RESAULTS We can categories our result as the following: At the first step of the simulation, we calculate the

number of routing packets in several conditions. At first, when the network have worked properly and was in idle state, both terrestrial links and satellite links are connected and working properly.

The second state is when all terrestrial links fail at the same time and all packets must reroute to satellite links. Based on result that we obtain from simulation, we tried to analyze data that are in output trace file and make generate functions from any types of routing packets. Following tables shows generate functions and amount of function's reliability in OSPF and EIGRP routing protocol.

Also, data traffic is variable base on our request from network. Total traffic on the network obtains from sum of data traffic and routing traffic. In Tables III and VI, total number of packets field's shows that when a failure occurs in topology, this value of packets must be added to the number of packets in idle time. Then we need more routing processor power to handle this (In all of tables, x represents the total number of RCSTs).

As we can see in Table III, when a failure occurs in the network, there is no change in some OSPF packet types and generation function for them is 0. In Tables IV, V and VI, generation function for EIGRP_message packet type represents total number of packets that generate in NCC and Total EIGRP Packets represents total number of EIGRP message than generate in entire of network.

TABLE I. THE NUMBER OF ROUTING PACKETS IN EIGRP ROUTING PROTOCOL IDLE STATE.

Packet types Generation Function Reliability Hello Y = 0.041x - 0.956 R² = 0.999

Database Description y = 0.150x1.358 R² = 0.998Link-State

A k l dy = -0.008x2 + 0.607x - 1.756 R² = 0.968

Link Statement y = 1.073x1.089 R² = 0.875Link-State Update y = 0.305x0.598 R² = 0.995

Total OSPF packets y = -7E-06x2 + 0.020x - 0.221 R² = 0.991

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TABLE II. THE NUMBER OF ROUTING PACKET IN OSPF ROUTING PROTOCOL CRITICAL STATE.

Packet types Generation Function Reliability Hello y = 0.042x - 1.002 R² = 0.998

Database Description y = 0.333x - 1 R² = 1Link-State y = -0.002x2 + 0.333x - 1.908 R² = 0.987

Link Statement y = 1.142x1.016 R² = 0.864Link-State Update y = 0.260x0.572 R² = 0.995

Total OSPF packets y = -8E-06x2 + 0.017x - 0.203 R² = 0.997

TABLE III. THE NUMBER OF ROUTING PACKET GENERATED IN OSPF ROUTING PROTOCOL WHEN ALL TERRESTRIAL LINKS FAILED.

Packet types Generation Function Reliability Hello y = 0.066x + 0.062 R² = 0.999

Database Description y=0 R2=1Link-State y=2 R2=1

Link Statement y=0 R2=1Link-State Update y=x-1 R2=1

Total OSPF packets y = -2E-05x2 + 0.073x + 0.238 R² = 0.999

TABLE IV. THE NUMBER OF ROUTING PACKETS IN EIGRP ROUTING PROTOCOL IDLE STATE.

Packet types Generation Function Reliability Eigrp_message y = 1.142x2 + 73.34x + 74 R² = 1

Total EIGRP Packets y = 1.857x2 + 299.0x + 146.2 R² = 1

TABLE V. THE NUMBER OF ROUTING PACKET IN EIGRP ROUTING PROTOCOL IN CRITICAL STATE.

Packet types Generation Function Reliability EIGRP_message y = 2.357x2 + 69.95x + 80.8 R² = 0.999

Total EIGRP Packets y = 7.714x2 + 297.5x + 153.4 R² = 1

TABLE VI. THE NUMBER OF ROUTING PACKET GENERATED IN EIGRP ROUTING PROTOCOL WHEN ALL TERRESTRIAL LINKS FAILED.

Packet types Generation Function Reliability EIGRP_message y = 1.357x2 - 4.042x + 6.8 R² = 0.963

Total EIGRP Packets y = 5.857x2-1.542x + 7.2 R² = 0.996 In stage two from our simulation, the total numbers of

simulated cycles per each packet is 101 and total numbers of instructions that executed on one packet is 83. In simulation we consider that our router is Cisco 7206 with 700MHz processor speed. Simplicity with reversing router's frequency, obtain duration of one clock. Thus, clock=1/700*106=1.429*10-9 seconds. Times that network processor consume for processing of a packet is multiplication of CPU clock cycles for a program in clock cycle time. Thus, CPU Time=101*1.429* 10-9=0.1443*10-6. Each packet in network processor needs 0.1443*10-6 second for process. With a simple coordination we can determine the number of packets that a router processor can process in one second. For our router 873896 packets obtained. But in Cisco router's specifications announced that performance of this router is processing up to 1 million packets per second. This differential came from this fact that Cisco consider all packets are equal size. But in real networks packets are in different size length. Thus, processing time for packets is not equal and depends on packet size.

From sum of above issues, we can calculate the percentage of CPU that consume in critical times.

V. CONCLUSION This paper introduces a method for calculating routers

power processing in networks. Based on our proposed technique, we can summarize our findings to 1) If we use static routing instead of dynamic protocol, when a failure occurs in network, there is no extra power required for handling this. 2) If we use EIGRP as routing protocol, we must have more powerful router at NCC in coordination to OSPF routing protocol. Results show that in a network topology failure, total number of routing packets in OSPF routing protocol decreases. However, in EIGRP routing protocol the number of routing packets increases in the same condition. Following researches could be done to confirm the effectiveness of the proposed technique.

For reducing the time of simulation, we use a limit number of nodes. In real DVB-RCS networks thousands of nodes works together at same time.

In addition users must be able to use variety of applications.

For simplicity we consider BER of forward channels and return channel is zero. A model must define a non zero BER on both forward link and return link and present the results.

In scheduling allocation of bandwidth, other scheduling mechanisms must be used.

For simplicity, data that travel in the network consider normal data. In other hand, there is no encryption on it. In networks that security is important for them, data must be encrypted. This means more time required for processing data.

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