In-depth explanation of the multi-layer exchange technology in the Communication Network

At present, multi-layer switching has become an indispensable part of the exchange technology, here we analyze the comprehensive application of multi-layer switching technology in the communication network, the International Standardization Organization ISO) Proposed Open System Interconnection Reference Model OSI-RM) the bottom layer, data link layer, network layer, and transmission layer are communication layers. Therefore, the bottom layer can be analyzed one by one:

1) Layer 1

For the physical layer, the traditional circuit switching belongs to this layer.

2) Layer 2

For the data link layer, in the traditional sense, the real exchange belongs to this layer. A hardware-based forwarding mechanism is adopted in this layer to forward various data link layer protocols, including Ethernet and high-speed ring network FD-DI in LAN) and WAN) and asynchronous transfer mode ATM), classic LAN multi-port bridge also belongs to this layer. This layer supports simple network segments and significantly improves network performance. The popularity of layer-2 Exchange has supported the development of layer-3 and layer-4 Exchange.

3) Layer 3

Is the network layer. The main task is to find a suitable route for the group. Because traditional routers use software and general CPUs to forward data packets, the latency is large and the forwarding speed is slow. The layer-3 Exchange is designed for this problem. The so-called layer-3 switching does not only use the layer-3 function, but integrates the layer-3 routing selection with the layer-2 switching function to implement fast Network grouping. Correspondingly, the third-tier switch aims to have two features, and usually uses the dedicated Integrated Circuit ASIC: Supplication Specific Integrated Circuit) to solidify common software functions in hardware, form a complete subset of vrouters. In the future, layer-3 switches will have more features and become more fully functional routers. For example, in addition to the forwarding function, it will also have the function of Automatically dividing the data stream level and service level, as well as providing some form of QoS, etc, this will be another important feature of layer-3 switches.

Since the middle of 1990s, the world's major companies have studied the third-tier exchange and proposed many different solutions and launched many products. Such as Cisco label exchange TAG Swiching, Ipsilon IP address exchange, and Toshiba Cell Exchange Router CSR: Cell Switching Router) and IBM's ARISAggregate Route based IP Switching), and IETF's Multi-Protocol Label Switching MPLS: Multi-Protocol Label Switching.

TAG Switching is a vro at the edge of the switch. It maps the layer-3 address of each input frame to a simple TAG, converts the tagged frame to an ATM cell, and maps it to the VC, in the core ATM switch of the network, the router saves the route table of the tag information table) to find the layer-3 route. Finally, the labeled cells are sent to the destination router. The destination router removes the Information Mark, converts the cells into frames, and sends them to the destination. In this process, the performance of Frame Forwarding can be improved by exchanging small data units and performing only one simple tag query.
Multi-layer IP address switching is a technology that combines layer-2 switching and layer-3 routing. It is another type of multi-layer switching, similar to CSR, it is an application that data streams drive IP address exchange. That is to say, they can arrange switch resources based on the arrival of independent business flows, and map the data streams to the signaling information IFMP and FANP on VC through tag allocation to realize the exchange process. These operations are independent of a single IP data stream, which maintains the scalability of the Internet model and forwards all services on the third layer in a step-by-step manner, A specific control protocol is introduced to transfer IP data streams to an end-to-end direct path.

ARIS is a multi-layer IP address exchange technology based on the aggregation path. Its basic function is to establish and maintain the exchange path based on the destination end of the aggregation IP data stream. ARIS utilizes the information of the routing protocol and associates the information with the exchange path from the network entry to the egress. Specifically, ARIS is a control protocol running on the integrated switch/router device network, because ISR supports Layer 2 switches such as ATM for IP routing ), therefore, ARIS can use the information in the routing protocol from OSPF and BGP) to map IP groups to Layer 2 exchange channels, through ISR devices and networks, it becomes the first IP exchange mechanism to introduce aggregation and switching channels. Between multiple different sources and the same destination, ARIS can establish a multi-point-to-point exchange path, thus reducing the consumption of switch resources. Multi-layer exchange technology is difficult to communicate with each other because companies adopt their own standards. Therefore, IETF is developing MPLS standards to unify the layer-3 Exchange Technology Standards of various companies.

MPLS is a layer-2 switching technology that perfectly integrates layer-2 switching functions with layer-3 routing functions. Based on the IP routing and control protocols, MPLS provides connection-oriented switching. MPLS supports various protocols at the network layer, such as IPv4, IPv6, IPX, and CLNP. MPLS also supports Layer 2 protocols, supports any layer-2 media that can transmit network-Layer groups between network-layer entities, rather than a link technology. MPLS implements information transmission in a very simple way. Similar to TAG and ATM switching, a fixed-length short Label is introduced as the basis for data forwarding in the mpl s network.

MPLS networks are composed of label exchange router LSR and Label Edge Router LER. LDP is used to distribute tags between LER and LSR. That is to say, when each MPLS device runs a layer-3 routing protocol such as OSPF and BGP, it uses the Label Distribution Protocol based on the calculated route to allocate tags to information flows, and establish a data transmission channel, that is, the label exchange path LSP). Therefore, when the business data IP group, Frame Relay frame, or ATM Cell) reaches the LER at the edge of the MPLS network, LER first maps the data stream to a fixed-length tag based on certain principles. The corresponding principle not only takes into account the destination address information of the data stream, but also QoS information before adding tags for the data. In this way, in the future forwarding process, the LSR will only forward data based on the Label carried by the data stream in the form of Table query and exchange. After the data arrives at the egress LER, the LER will remove the Label, restore the original data stream and transmit the data in the original way.

In short, multi-service, stream classification, traffic planning, routing display, services of different levels and IP QoS based on ATM are all key features of MPLS. The goal is to solve the problem of network expansion and provide a variety of network services on the same infrastructure. With the emergence of MPLS, Virtual Private Network VPN that supports real-time communication on the Internet will also become a reality in a short period of time.

4) Layer 4

It is a transport layer that extends the second and third layers of exchange and supports fine-grained network adjustment and division of the Communication stream priority. The layer-4 information is used, for example, the port number of a TCP/UDP application is used to determine the forwarding mode of the traffic.

Layer-4 Switching Allows you to prioritize communication data based on applications. Therefore, administrators can restrict certain applications to use a certain amount of bandwidth for important application communications. In essence, layer-4 Switching provides methods for implementing the Open Systems Federation COS in the network.