What is Network Protocols?
Network Protocols
In this chapter, you will find information on the history and working principles of several network protocols adopted in ATM network environment.
TCP/IP: TCP/IP is a protocol family created by the research group of National Defense in USA. Its purpose is to connect networks of different manufactures to one Internet for mutual access. Its success lies in that it provides some basic services (FTP, Email, HTTP, etc.) required by people on the network. People can use TCP/IP protocol to establish LAN, which can be connected with Internet via IP route. Considering the disaster recovery function required by the network on the battle field, US army designed it to be a powerful automatic disaster recovery system. This design permits big-scale network without too much management. However, this feature makes it impossible for the fault in a certain section of the network to be timely diagnosed, therefore it may stay in unavailable status for a long time.
Same as other network protocols, TCP/IP adopts a layer structure, as shown in Figure 4-1.
In TCP/IP protocol, different physical devices are labeled with IP addresses. The terminal application connects with the peer via SOCKET.
X.25: X.25 is a set of internationally recognized communication protocols defined by CCITT (now called ITU).
In the communication protocol standards defined by ITU,X series represents PSN (Packet Switching Network) protocol; V series represents PSTN (Public Switched Telephone Network) protocol; I series represents ISDN ( Integrated Services Digital Network) protocol.
X.25 protocol defines the interface with packet switching network at DTE (Data Terminal Equipment). DTE accesses X.25 network by connecting DCE (Data Communicational Equipment).Thus X.25 defines the interface between DTE and DCE. X.25 hasn't defined data transmission method in the packet switching network, which is fully accomplished by X.25 network.
One feature of X.25 is that it provides the reliable service, which means it ensures data is transmitted in sequence. This makes the application easy, for you do not need to consider errors in data transmission. On the other hand, it is just the reliable service that lowers the transmission performance (such as bandwidth and time), compared with those unreliable communication protocols that may discard the communication protocol of the data packet, such as Frame Relay.
X.25 is a network layer protocol, which only transfers data packets to X.25 network in the mode accepted by X.25 network.
The data link layer protocol under X.25 protocol layer is the LAPB ( Link Access Procedure Balanced) protocol of HDLC (High-Level Data Link Control). The variation of HDLC protocol not only includes LAPB, but also includes SDLC of IBM.LAPB is a very reliable data link layer protocol, which enhances data error recovery.
X.25 is also a layered protocol, whose network layers are shown in Figure 4-3.
SNA (System Network Architecture) /SDLC (Synchronized Data Link Control)
SNA is not a private product, but a network architecture for distributed processing of IBM. It defines a network easy to be established and modified. SNA supports the interconnection between different products with a set of standard network protocols. One important feature of SNA is the network data transmission is transparent to the terminal user or the terminal application.
As shown in Figure 4-4, the terminal user accesses SNA network via an LU (Logic Unit) port and a virtual link is established between LUs for data transmission.
For the terminal user, the connections between LUs seem to be the direct connection. In fact, data transmission between LUs is a complicated process. During the transmission, data must undergo the process of coding, routing and error tolerance before it can be sent to the peer correctly. To accomplish the complicated process, IBM defines a network layered structure:
In the above network structure, layer 2 is data link layer and the data link layer protocol in SNA is SDLC protocol, which defines the link control function in data transmission. In fact, SDLC is variation of HDLC.
In SNA network, each physical node is labeled with PU. Since the node has different types, PU’s types also differ, which include PU-T1, PU-T2, PU-T4 and PU-T5.
LU permits the end user to access SNA network resources and interact with other LU users. LU end users communicate via LU-LU protocol.
You can find many descriptions of LU-LU protocol, and deem LU-LU protocol a session. In SNA network, session refers to a temporary logic connection between two LU end users.
The session only starts after two LU end users are bound. LU binding process is a complicated protocol command interactive sequence, which almost involves all layers of SNA network. The disconnection of the binding of two LUs is just reverse.
LU is a general name. In fact, there are two kinds of LUs: PLU (master LU) and SLU (slave LU).Usually the Central has one PLU, which is responsible for responding the session establishment request from other LUs and then establishing the session. PLU is also responsible for error recovery. LU has several different forms of LU-T0, LU-T1, LU-T4, etc.
TCP/IP: TCP/IP is a protocol family created by the research group of National Defense in USA. Its purpose is to connect networks of different manufactures to one Internet for mutual access. Its success lies in that it provides some basic services (FTP, Email, HTTP, etc.) required by people on the network. People can use TCP/IP protocol to establish LAN, which can be connected with Internet via IP route. Considering the disaster recovery function required by the network on the battle field, US army designed it to be a powerful automatic disaster recovery system. This design permits big-scale network without too much management. However, this feature makes it impossible for the fault in a certain section of the network to be timely diagnosed, therefore it may stay in unavailable status for a long time.
Same as other network protocols, TCP/IP adopts a layer structure, as shown in Figure 4-1.
FIGURE 4-1: TCP/IP NETWORK LAYERS AND PROTOCOLS
In TCP/IP protocol, different physical devices are labeled with IP addresses. The terminal application connects with the peer via SOCKET.
FIGURE 4-2: SOCKET CONNECTION
X.25: X.25 is a set of internationally recognized communication protocols defined by CCITT (now called ITU).
In the communication protocol standards defined by ITU,X series represents PSN (Packet Switching Network) protocol; V series represents PSTN (Public Switched Telephone Network) protocol; I series represents ISDN ( Integrated Services Digital Network) protocol.
X.25 protocol defines the interface with packet switching network at DTE (Data Terminal Equipment). DTE accesses X.25 network by connecting DCE (Data Communicational Equipment).Thus X.25 defines the interface between DTE and DCE. X.25 hasn't defined data transmission method in the packet switching network, which is fully accomplished by X.25 network.
One feature of X.25 is that it provides the reliable service, which means it ensures data is transmitted in sequence. This makes the application easy, for you do not need to consider errors in data transmission. On the other hand, it is just the reliable service that lowers the transmission performance (such as bandwidth and time), compared with those unreliable communication protocols that may discard the communication protocol of the data packet, such as Frame Relay.
X.25 is a network layer protocol, which only transfers data packets to X.25 network in the mode accepted by X.25 network.
The data link layer protocol under X.25 protocol layer is the LAPB ( Link Access Procedure Balanced) protocol of HDLC (High-Level Data Link Control). The variation of HDLC protocol not only includes LAPB, but also includes SDLC of IBM.LAPB is a very reliable data link layer protocol, which enhances data error recovery.
X.25 is also a layered protocol, whose network layers are shown in Figure 4-3.
FIGURE 4-3: X.25 NETWORK LAYER
SNA (System Network Architecture) /SDLC (Synchronized Data Link Control)
SNA is not a private product, but a network architecture for distributed processing of IBM. It defines a network easy to be established and modified. SNA supports the interconnection between different products with a set of standard network protocols. One important feature of SNA is the network data transmission is transparent to the terminal user or the terminal application.
As shown in Figure 4-4, the terminal user accesses SNA network via an LU (Logic Unit) port and a virtual link is established between LUs for data transmission.
FIGURE 4-4: THE TERMINAL USER ACCESSES SNA NETWORK VIA LU
For the terminal user, the connections between LUs seem to be the direct connection. In fact, data transmission between LUs is a complicated process. During the transmission, data must undergo the process of coding, routing and error tolerance before it can be sent to the peer correctly. To accomplish the complicated process, IBM defines a network layered structure:
FIGURE 4-5: SNA NETWORK LAYERS
In SNA network, each physical node is labeled with PU. Since the node has different types, PU’s types also differ, which include PU-T1, PU-T2, PU-T4 and PU-T5.
LU permits the end user to access SNA network resources and interact with other LU users. LU end users communicate via LU-LU protocol.
You can find many descriptions of LU-LU protocol, and deem LU-LU protocol a session. In SNA network, session refers to a temporary logic connection between two LU end users.
The session only starts after two LU end users are bound. LU binding process is a complicated protocol command interactive sequence, which almost involves all layers of SNA network. The disconnection of the binding of two LUs is just reverse.
LU is a general name. In fact, there are two kinds of LUs: PLU (master LU) and SLU (slave LU).Usually the Central has one PLU, which is responsible for responding the session establishment request from other LUs and then establishing the session. PLU is also responsible for error recovery. LU has several different forms of LU-T0, LU-T1, LU-T4, etc.
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