Shocked! Is it possible to disguise yourself on the Internet?

The question of “a lot of money”

Boss Wang runs a company called PTN (Packet Transport Network), which mainly uses optical fiber as a medium to provide transmission technology for various voice and data services. With the advantages of high reliability and flexible scalability of its product technology, PTN has gradually replaced its rival SDH (Synchronous Digital Hierarchy) company and gained a place in the bearer network market. SDH is a company that mainly transmits voice services based on TDM (Time Division Multiplexing) technology. The commercial competition among companies in the bearer network market is very exciting, but this is another story. Please stay tuned. Here is a short story about PTN. One day, Boss Wang took the technical director to meet a big customer, Ms. "A Lot of Money".

In the negotiation room, Boss Wang explained to Ms. Qian that their PTN technology can perfectly solve problems such as network bandwidth bottlenecks. Later in the conversation, Boss Wang asked Ms. Qian whether she was willing to use their company's products.

Ms. Qian began to look embarrassed: "Mr. Wang, I am very interested in your company's products, but I have two questions:

• We established the SDH backbone network in the early years, and there are many users who use SDH company services. After the new PTN backbone network is established, the cost of maintaining these backbone networks and corresponding access networks at the same time will be very high. Is it possible to achieve the integration of the SDH network access method with the PTN network without the SDH backbone network?
• Our users still have many demands for TDM services, and they need TDM services to be transmitted between PTN and SDH networks. How can we realize the transmission of TDM services in PTN networks? "

Li Chenggong's trick

Technical Director Lao Li spoke up: "We already have solutions to these two problems. After the PTN backbone network is built, traditional networks such as SDH can be moved down to the access network. We can perform "disguise" on the received services and disguise them into the appearance recognized by PTN. When they are about to leave the PTN network and reach the user, we will remove the disguise. This can perfectly solve your problem. We call this "disguise" PWE3."

Ms. Qian gave a thumbs up and said, "Great! I am very interested in your PWE3 technology. I hope this solution can be implemented quickly."

PWE3: The Art of Disguise in Transmission Networks

What is PWE3?

PWE3 (Pseudo-Wire Emulation Edge-to-Edge) is a Layer 2 service bearer technology that simulates the basic behaviors and characteristics of ATM, frame relay, Ethernet, TDM/SDH and other services as realistically as possible in the PTN network. The core idea of ​​this technology is to establish an end-to-end virtual channel between the service sender and the receiver, and realize the transmission of different services in this channel. During the transmission process, it does not care about what service is transmitted, but is only responsible for encapsulation and transmission.

How does PWE3 disguise itself?

Before introducing PWE3 in detail, let me first briefly introduce the key components of PWE3.

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• CE1 and CE2 (Customer Edge): Customer-side edge devices, used to connect to edge devices of the PTN network.
• PE1, PE2 (Provider Edge): Network edge devices used for encapsulation and decapsulation.
• AC (Attachment Circuit): Access circuit, used to connect CE and PE.
• VC (Virtual Circuit): A virtual circuit used for a unidirectional logical connection between two PE devices.
• Tunnels: used to carry PWs and provide end-to-end connectivity.
• PW (Pseudo Wire): A pseudo wire consists of a pair of reverse virtual links and is used to carry customer services. Different customer services are carried by different pseudo wires.
• PW Signaling Protocol: PW is created and maintained by performing parameter negotiation through a signaling protocol. Generally, Label Distribution Protocol (LDP) is used as the signaling protocol for transmitting VC information.
• Inner label: used to identify the PW and contains VC information such as VC Type and VC ID.
• Outer label: used to identify PE2.

How do businesses manage to roam across the Internet in disguise?

What is the service transmission process of PWE3? Combining the above introduction of PWE3 components and the following picture, we can use the cross-city express delivery as an analogy. Comparing the service to an express package, CE is equivalent to the express delivery station in the area, PE is equivalent to the city-level transfer center, and PW is equivalent to air, water, land and other transportation methods.

1. Xiao Ming in City A wants to send a package to Xiao Hong in City B. Xiao Ming calls the courier to pick up the package.
2. The courier delivers the package to the nearest courier station CE1.
3. The staff at the express delivery station is responsible for loading all the parcels that arrive at the station and sending them to the transfer center PE1 in City A.
4. After the parcel arrives at the transfer center, the staff will affix an inner label to each parcel, and then sort them according to the parcel's weight, volume, receiving address, delivery service level and other attributes. Parcels with the same attributes are uniformly packaged into a large box dedicated to the express company and affixed with an outer label.
5. Large packages are transported to the municipal transfer center PE2 in City B by appropriate means of transportation such as trains and cars.
6. After receiving the large package, the express transfer center in City B unpacks it, tears off the two layers of labels, and distributes it to the regional express station CE2 according to the express information table in the logistics system.
7. The courier completed the package delivery, and Xiaohong successfully received the package sent by Xiaoming.

What is the secret to practicing the art of disguise?

The secret weapon of PWE3 is to use the PW signaling protocol to establish PW. After the PW is established, various services can be transmitted within their respective simulated virtual links. The following uses the mainstream LDP signaling protocol as an example to describe how to use the PW signaling protocol to establish and delete PW. We use two figures to introduce it.

Create a pw schematic

1. PE1 sends a Request message and a Mapping message (which contains information such as VC label, VC Type, VC ID, and interface parameters) to PE2.
2. After receiving the Request message, PE2 immediately sends a Mapping message to PE2, and compares the received Mapping message with the local VC information. If the information is consistent, PE2 accepts the label mapping message, and the unidirectional VC1 is successfully established. At the same time, PE2 knows the inner label added by PE1.
3. After receiving the Mapping message from PE2, PE1 performs the same check and successfully establishes VC2. At this point, two reverse VCs, namely PWs, are successfully established, and PE1 and PE2 notify each other of their status through Notification messages.

Delete pw schematic

1. When PE1 detects that the AC or tunnel status is Down, PE1 sends Withdraw and Release messages to notify PE2 to remove the label.
2. After receiving the message, PE2 removes the label from VC1 and dismantles VC1. After the dismantling is complete, it sends a Release message to PE1, informing PE1 that the label has been removed.
3. After receiving the Release message, PE2 removes the label of VC2 and dismantles VC2. At this point, the PW is deleted.

"Li Chenggong" work summary

The PWE3 disguise solution was successfully implemented, and PTN received a large order from Ms. Qian. At the project review meeting, Director Li sorted out and summarized the highlights of this solution:

• In some special scenarios, PWE3 can realize the transmission of different services and the interconnection of different networks. For example, an operator has established a national backbone network. The user has two branches in Shanghai and Beijing. The Beijing branch accesses the backbone network via ATM, and the Shanghai branch accesses the backbone network via FR. The operator only needs to establish a PWE3 connection between Beijing and Shanghai to provide users with point-to-point services across the WAN.
• The key to PWE3 technology is to establish PW. ​
• PWE3 workflow: encapsulation-transmission-decapsulation.
• PWE3 networking modes are divided into single-hop and multi-hop, and their transmission mechanisms are the same. ​