Several of the most common Wan

Wan Example

1 X. Network

The common packet Switched Data network (Psdn-packet switched) is a communication network which is based on packet (Packet) as the basic data unit for data exchange. It uses packet switching (packet switching) transmission technology, leased line, is a packet-switched public data network. Since the common packet switched Data network uses the X. Protocol standard, it is often referred to as X. NET.

In the the 1970s, many European countries began to develop public data networks (networks that everyone who needs network services can use). The problems they face are different from those of the United States. In the United States, most regions can develop public data networks by renting out existing telephone lines. In Europe, it is not easy to do so because of the inherent problem of communication systems across borders. As a result, European countries have abandoned the development of independent incompatible standards, but have developed a unified standard with the support of I T U. The result is a public data network service interface called the X-series (x family) protocol. Includes a variety of general protocols: X., X.3, x.28, and x.29.

The X family (X series) protocol is an important protocol used by packet switching networks. This is just a definition of the protocol between D T E and D-C, which is connected to the public data network.

X. • Defines a synchronous transmission similar to the low three layer of O S I (Figure 6-18). The network layer receives the user data and puts it into the X. group. The X. Group is sent to the data link layer, where it is embedded in the L-A P-B frame. The physical layer then uses the X.21 protocol to transfer L-A P-B frames. X. Also may use x.21 b i s, which is a transition protocol that connects the V series M O D E m to the packet switching network. The X.21 protocol should replace it, but as with many other plans, this does not happen. In some cases, X. Even uses the E I A 2 3 2 protocol.

Complete all these needs to have the ability to create groupings and implement protocols for intelligent D T E. Sometimes the problem is that D T E is a synchronous terminal that is difficult to accomplish. This situation will be dealt with later. Due to the low-level discussion of the two tiers, the packet protocol for the network layer is discussed here.
X. and OSI Model

Physical protocol layer: the physical protocol layer is defined by the ITU-T x.21 Standard, which controls the physical connection to the communication adapter and the communication cable.

Data Link layer: The 2nd layer of X. A is equivalent to the MAC sub-layer of the data link layer of the OSI model. The 2nd layer deals with data transmission, addressing, error detection and correction, flow control, and X. Frame composition. This includes the Balanced Link Access Procedure (LAPB) protocol, which is used to establish or disconnect virtual connections on the WAN. There can be more than one virtual X. Connection in a physical connection or communication cable. LAPB can also ensure that frames are received in the order in which they are sent.

Group layer: The 3rd layer is similar to the network layer of O S i. This layer handles the exchange of information order and ensures the reliability of the virtual connection. It can simultaneously transfer up to 4 0 9 5 virtual connections on a virtual connection.

The 3rd tier provides the following basic services: Create two logical channels between DTE and DCE. One channel is used for the sending side and one for the receiving end. Create a virtual circuit outside the network device interface connected to the logical channel machine.

X. the shortcomings

The X.-based protocol provides only connection-oriented services. The other is that its network layer (layer 3rd) is incomplete. For example, the OSI layer 3rd provides routing capabilities, while the 3rd layer of X. In addition, X. I prepared some connection-oriented features for remote DTE. Because point-to-point connections appear more in the 4th tier, it is thought that this is a layer of two layers mixed. In this way, the differences between the layers defined by the OSI become blurred.

2 Frame Relay Network

Frame Relay (Relay) is a new public data exchange network which was developed in the 80 's, and it is a fast packet switching technology. The basic similarities between frame Relay and X. Zero are that they all use packet switching techniques, which are peer-to point-to-point communication. However, there are some differences between them, the main difference is that: the X. Protocol includes a low three-layer protocol, Frame relay only contains the physical layer and Data Link layer protocol.

From the viewpoint of design, Frame Relay and X. The difference is that the frame relay focus on fast transmission, and x. The emphasis on high reliability, so in X. NET, the transmission of data to verify, and have error handling mechanism, and frame relay omitted this function, therefore, Frame Relay transmission speed (64kbps-2.048mbps).

Frame Relay performance is higher than X., and is the best choice for long-range multi-node data transfer users.

Frame Relay in several ways with X. 2 5 same: Both use packet switching technology on virtual circuits (on Frame relay, called virtual connections). In addition, the virtual connection can have both Exchange type (SVC) and permanent type (PVC) in the same way as X.

With X. 2 5 different, by assuming that the new network technology in the directly connected node can have error detection function, Frame Relay can carry out high-speed data transmission, so it does not integrate a large number of error detection function, that is, this is a non-connected service. Frame relay is often used in conjunction with TCP/IP-based networks, both of which deal with end-to-end error checking.

Frame Trunking Hierarchical Communication

Another difference between frame Relay and X. x is that frame relay uses only two communication layers: the physical layer and the frame mode Bearer Service link Access Protocol (LAPF). These layers correspond to the physical layer and data link layer in the OSI model, respectively.

Frame the predecessor of the relay was X.

It inherits the concept of VC from X. Technology. However, because X. 70-80 was developed in the year, the line rate is not high, the quality of the line is often problematic. Therefore, it is necessary to provide error detection and reliability mechanism on the basis of each hop (per-hop). While these technologies can ultimately enable data to be safely delivered to the destination, the cost of response time and network latency is high at two.

Error detection no longer important

With the advent of LANs and the increasing need for LANs to interconnect across the WAN, a new technology that can handle high-traffic operations is increasingly needed. Today's digital communications systems have already provided more than X. 2 5 much higher network capacity and no longer need to provide reliability and error detection mechanisms between two points in the network. In addition, a very important feature is the ability to allocate network bandwidth as needed so that the network can support the ever-increasing variability and randomness of the data stream.

New Technical Ideas

Frame Relay Technology leverages the latest high-quality, high-speed, and higher-performance communication link technologies, such as optical fiber communications. Error detection is still implemented on a per-hop basis, but the error recovery process is moved to the edge of the network. All kinds of intelligent functions, such as flow control and error recovery, are realized by connecting to the terminal system on the Frame relay network.

3 ATM (Asynchronous transfer mode) network

It can take advantage of the size of the fixed packet to achieve the transfer rate from 2 5 to 6 2 2 M b p S.

This fixed-size packet of at M is also called a cell, which consists of 4 8 bytes of data plus 5 bytes of header information. By using fixed-size packets, at M provides predictable communication patterns and better control over bandwidth usage.

At M is a virtual circuit mode. It can use a dedicated virtual circuit (P v c) or swap virtual circuits (S v c).

S V C is a logical point-to-point connection. It relies on the at M switch to select the optimal path between the sender and the recipient. The at M switch establishes this connection before the network transmits at M data. Instead, Ethernet transmits data first, and lets routers and switches take offline to determine how to direct data transfer.

At M relies on "clean" digital transmission media, such as fiber, to achieve high transmission rates. However, it can also be connected with other systems such as copper-axis or twisted-pair media, as well as other system uses such as Ethernet or Frame Relay transmission methods.

Time-delay-critical data such as video, audio, images, and other ultra-large file transfers are well suited for use with at M technology.

Because at M high-quality service, load-balancing capability, transfer rate, and interoperability, it may be an ideal way to communicate over long distances. As with other emerging technologies, at M's disadvantage is that it costs too much and lacks well-defined standards.

4 SONET (Synchronous fiber network) network

Bell Communications Laboratories in the 2 No. 0 century 8 0 years to open the S O N E T to connect the world's different telephone systems. If you say x. 2 5 is the originator of WAN transmission technology, that s O N E T can only be considered a new generation.

SONET defines a signal hierarchy, similar to the definition of T-media, but extends to higher bandwidths.

Capable of providing data transfer rates from 64kbps~2.4gbps, it uses the same T-D-M technology used with T media.

Since S O N E T standardizes fiber transmission, it can be directly compatible with different standards in different countries, and it has developed into the best choice for connecting the WAN between North America, Europe and Asia. Internationally, S O N E T is known as S D H (synchronous data layer, synchronous Digital Hierarchy). S O N E T and T Media, I S D N, and at M technology have good interoperability, making it a good choice for long distances (even in the same country) to connect Wan and LAN.

S O N E T relies on fiber-optic transmission media to achieve very high service quality and throughput. As with the T media, it is also connected using a multiplexer and terminal device on the client side. A typical s O N E T Network employs a ring topology similar to F D d I. In this network, there is one ring acting as the primary route for the data transfer, and the other as the backup. For example, if a ring is being maintained, the S O N E T Technology automatically transmits the data through the backup ring. This feature, known as the autonomous technology, makes the S O N E T highly reliable. Companies can rent the entire ring from local or long distance media companies, or they can rent part of s o n e t so that they can take advantage of the high reliability of S o n e t and provide equivalent throughput to T 1.

The data transfer rate of the S O N E T-ring is expressed using its optical fiber medium (OC, Optical Carrier) quality. This rate notation has been recognized by network experts and standardization organizations around the world. The fiber media quality of S O N E T is similar to the digital signal quality of T 1.

SONET Fiber Media Quality

Fiber Media mass Throughput (M b p s)

OC1 51. 8 4

OC3 155. 5 2

OC1 2622

OC2 41244

OC4 82480

Several of the most common Wan