What Is a Core Router?

The core router, also known as the "backbone router", is a router located at the center of the network. The router at the edge of the network is called an access router. Core routers and edge routers are relative concepts. They all belong to routers, but have different sizes and capacities.

As early as 40 years ago,

One of the indicators: Throughput

Throughput is the router's packet forwarding capability. Throughput is related to the number of router ports, port speed, packet length, packet type, routing calculation mode (distribution or concentration), and test methods. Generally, it refers to the processor's ability to process packets. The high-speed router's packet forwarding capability is at least 20Mpps. The throughput mainly includes two aspects:

Machine throughput

The whole machine refers to the packet forwarding capability of the whole machine, which is an important indicator of device performance. The router's job is to select a route based on the IP packet header or MPLS label. Therefore, the performance index refers to the number of forwarded packets per second. The overall throughput is usually less than the sum of the throughput of all the ports of the router.

Port throughput

Port throughput refers to the port packet forwarding capability, which is the packet forwarding capability of the router on a certain port. Two test interfaces at the same rate are usually used. The general test interface may be related to the interface position and relationship. For example, the test throughput between ports on the same card may be different from the throughput value between ports on different cards.

Indicator two: routing table capability

Routers usually rely on the routing tables established and maintained to determine packet forwarding. The routing table capability refers to the limit of the number of routing entries contained in the routing table. Because routers that implement the BGP protocol on the Internet usually have hundreds of thousands of routing entries, this item is also an important manifestation of router capabilities. Generally speaking, a high-speed router should be able to support at least 250,000 routes, and each destination address provides at least 2 paths. The system must support at least 25 BGP peers and at least 50 IGP neighbors.

Indicator three: backplane capability

The backplane refers to the physical path between the input and output ports. The backplane capability is an internal implementation of the router. Traditional routers use shared backplanes, but as high-performance routers will inevitably encounter congestion problems, and it is difficult to design high-speed shared buses. Therefore, existing high-speed routers generally use switchable Back plate design. The backplane capability can be reflected in the router throughput. The backplane capability is usually greater than the value calculated based on the throughput and test packet length. However, the backplane capability can only be reflected in the design and generally cannot be tested.

Indicator 4: Packet Loss Rate

The packet loss rate refers to the proportion of data packets that a router cannot forward due to lack of resources under a stable continuous load. The packet loss rate is usually used to measure the performance of the router when it is overloaded. The packet loss rate is related to the data packet length and packet sending frequency. In some environments, routing jitter or a large number of routes can be added for test simulation.

Indicator 5: Delay

Delay refers to the time interval between the first bit of a data packet entering the router and the last bit output from the router. This time interval is the processing time of the router that works in store-and-forward mode. Delay is related to both packet length and link rate, and is usually tested within the range of router port throughput. Delay has a large impact on performance. As a high-speed router, in the worst case, it is required that the delay for IP packets of 1518 bytes and below is less than 1ms.

Indicator number six: back-to-back frames

The number of back-to-back frames refers to the number of data packets when the most data packets are transmitted at the minimum frame interval without causing packet loss. This indicator is used to test the router's cache capability. For routers with wire-speed full-duplex forwarding capabilities, the value of this indicator is infinite.

Indicator 7: Delay Jitter

Delay jitter refers to delay variation. Data services are not sensitive to delay jitter, so this indicator is usually not an important indicator for measuring high-speed routers. For IP services other than data, such as voice and video services, this indicator is necessary for testing.

Indicator number eight: service quality capability

Queue management mechanism

The queue management control mechanism usually refers to the router congestion management mechanism and its queue scheduling algorithm. Common methods are RED, WRED, WRR, DRR, WFQ, WF2Q, etc.

Queuing strategy:

Support fair queuing algorithm.

Support weighted fair queuing algorithm. This algorithm gives each queue a weight, which determines the link bandwidth that the queue can enjoy. In this way, real-time services can indeed obtain the required performance, and inelastic service flows can be isolated from ordinary (Best-effort) service flows.

In the management of input / output queues, a virtual output queue method should be adopted.

Congestion control:

Must support congestion control mechanisms such as WFQ and RED.

Must support a mechanism that can mark a higher drop priority for traffic that does not meet its service level CIR / Burst contract, which should take precedence over drop of traffic that meets the contract and best-effort traffic Grade high.

In a switching environment where output queue contention may exist, effective methods must be provided to eliminate head congestion.

2. Number of port hardware queues

Usually the priority supported by the router is guaranteed by the port hardware queue. The priority in each queue is controlled by the queue scheduling algorithm.

Indicator 9: Network Management

Network management refers to operations where a network administrator centrally manages resources on a network through a network management program, including configuration management, accounting management, performance management, error management, and management. The degree of network management supported by the device reflects the manageability and maintainability of the device, and is usually managed using the SNMPv2 protocol. Network management granularity indicates the granularity of router management, such as the granularity of management to ports, network segments, IP addresses, and MAC addresses. Management granularity may affect router forwarding capabilities.

Indicator number ten: reliability and availability

1. Equipment redundancy

Redundancy can include interface redundancy, card redundancy, power supply redundancy, system board redundancy, clock board redundancy, and equipment redundancy. Redundancy is used to ensure the reliability and availability of the equipment. The design of the amount of redundancy should be a compromise between equipment reliability requirements and investment. The router can ensure the redundancy of the router through protocols such as VRRP.

2. Hot-swappable components

Because routers usually work 24 hours, replacing parts should not affect router operation. Hot plugging of components is the guarantee for the router to work 24 hours.

3. No trouble working time

This indicator indicates the time during which the equipment works without failure according to statistical methods. Generally cannot be tested, it can be calculated by the trouble-free working time of the main device or the working condition of a large number of the same equipment.

4.Internal clock accuracy

Routers with ATM ports for circuit simulation or POS ports usually need to be synchronized. When using the internal clock, its accuracy will affect the bit error rate.

In the technical specifications of high-speed routers, the reliability and reliability requirements of high-speed routers should meet the following requirements:

The system should reach or exceed 99.999% availability.

Continuous working time without failure: MTBF> 100,000 hours.

Failure recovery time: system failure recovery time <30 mins.

The system should have automatic protection switching function. The master-standby switchover time should be less than 50ms.

SDH and ATM interface should have automatic protection switching function, and the switching time should be less than 50ms.

The equipment is required to have high reliability and high stability. The main components of the system such as the main processor, main memory, switching matrix, power supply, bus arbiter, and management interface should have hot backup redundancy. Line cards require m + n backups and provide remote test diagnostic capabilities. A power failure keeps the connection valid.

The system must be free of single points of failure. ^[2]