Learn DLSW routing technology in three minutes

Today we have a comprehensive understanding of DLSW technology.

DLSw (Data Link Switching) is developed by APPN (Advanced Peer-to-Peer Networking) and Implementers Workshop (AIW) to implement a method of carrying SNA (System Network Architecture) through TCP/IP. 

SNA is a network architecture corresponding to the OSI reference model launched by IBM in the 1970s. To realize the SNA protocol across the WAN transmission, one of the solutions is DLSw technology.

Using DLSw technology, it is also possible to realize SDLC (Synchronous Data Link Control) link protocol across TCP/IP transmission. First convert the SDLC format message to LLC2 format message, and then interconnect with the remote end through DLSw. In this way, DLSw also supports the interconnection of different media between LAN and SDLC.

DLSw currently has two versions: DLSw1.0 and DLSw2.0.

The DLSw implemented based on RFC 1795 is version DLSw1.0; in order to improve product maintainability and reduce network overhead, the system implements DLSw2.0 version based on RFC 2166.

In DLSw2.0, the function of supporting sending UDP inquiry messages in multicast and unicast mode is added. When the communication peer is also DLSw2.0, the two can use UDP packets to inquire about reachability information, and only establish a TCP connection when there is a data transmission demand.

There were many problems in version 1.0, so DLSW2.0 version came later:

Let's see what are the problems:

1. The problem of TCP connection: All messages (including inquiry messages, circuit establishment request messages, and data messages) are transmitted using TCP connections. First establish two TCP connections. After the performance exchange is completed, disconnect one TCP connection. This caused a waste of network resources to a certain extent.

2. Flooding of broadcast messages: When there is no reachable path information in the reachable information list of DLSw or there is too little reachable path information, the inquiry messages will flood the WAN through the established TCP connections.

3. Poor maintainability: When the link is interrupted, DLSw1.0 uses two types of messages to notify the opposite end, but it cannot tell the opposite end what caused the link interruption. It is difficult to determine the problem.

DLSw2.0 improvements:

1. Use UDP packets to query peer addresses: In order to avoid establishing unnecessary TCP connections, DLSw2.0 generally does not use TCP connections to send inquiry packets, but uses UDP packets instead.

2. Establish a single TCP channel: When there is a need to establish a link, a TCP connection is established between the source DLSw2.0 router and the target DLSw2.0 router.

3. Enhanced maintainability: Five reasons for circuit interruption are defined: unknown error detected, DISC frame received by DLSw from the terminal, DLC error detected by the terminal, circuit standard protocol error and system initialization.

DLSW+: Data linkswitching Plus --- DLSw+ is a method of transmitting SNA and NetBIOS data in a wide area network or campus network. The terminal system can be connected via Token Ring, Ethernet, synchronous SDLC protocol or FDDI Go online.

DLSw+ can convert data between different media, terminate the data link locally, keep the response, keepalive and close the polling information of the WAN. The data link layer terminates locally and also eliminates control timeouts caused by network congestion or re-routing. Finally, DLSw+ also provides a dynamic search for SNA or NetBIOS resource mechanism and high-number algorithms to minimize broadcast transmission.

In the document, DLSw+ routers can be regarded as peerrouters, peers and partners. The connection between two DLSw+ routers is called a peer connection. A DLSw circuit includes the data link control connection between the initial terminal system and the initial router, the connection between the two routers (usually a TCP connection), and the data link control connection between the destination terminal system and the destination router. A single peer connection can support multiple circuits.

DLSW+ comparison DLSW standard adds four new points:

①Scalability-a method to build IBM network to reduce the amount of broadcast transmission and enhance network scalability.

② Practicality-quickly and dynamically find related paths and optionally use multiple active peers and ports for load balancing.

③Transmission flexibility-high-performance transmission avoids network interruption caused by timeout.

④Operation mode-dynamically detect the performance of peer routers and detect them according to their performance.

DLSW+ link establishment:

The establishment of a link for a group of end systems includes searching for target resources and setting up the data link connection of the end system. In the local area network, the SNA device sends a detection frame with the destination MAC address to look for other SNA devices. When a DLSw router receives the detection frame, it sends a canureach frame to every partner router it can reach. If one of the DLSw partners can reach the specified MAC address, it responds with an icanreach frame.

Each router and the local SNA designate the data link connection between the system and the TCP connection between DLSwpartner. This link is uniquely identified by the source and destination link numbers. Each link number is in turn composed of source and destination MAC addresses, source and destination chains Road service access point and a data link control number to define. Once the link is established, the information frame can be transmitted.

The above is the news sharing from the PASSHOT. I hope it can be inspired you. If you think today' s content is not too bad, you are welcome to share it with other friends. There are more latest Linux dumps, CCNA 200-301 dumps, CCNP Written dumps and CCIE Written dumps waiting for you.