Chapter 6 WAN Technologies X.25, Frame Relay, ATM PDF

EGEC4120 – TELECOMMUNICATION NETWORKS and SWITCHING CHAPTER 6 - WAN TECHNOLOGIES: X.25,FRAME RELAY & ATM NETWORKS Prepared by: Analene Montesines Nagayo and Mohamed Yousuf Hasan Outcom...

EGEC4120 – TELECOMMUNICATION NETWORKS and SWITCHING CHAPTER 6 - WAN TECHNOLOGIES: X.25,FRAME RELAY & ATM NETWORKS Prepared by: Analene Montesines Nagayo and Mohamed Yousuf Hasan Outcome Covered OC5: Understand and demonstrate Wide Area Packet data networks of Frame Relay and Cell Relay networks and their applications.  X.25 NETWORK  Internet is a widely connected back bone high speed network with the help of multiple WAN technologies such as X.25 frame relay and ATM networks.  X.25 is an ITU-T standard protocol suite for packet- switched data communication in wide area networks (WAN).  X.25 uses the old traditional packet switch originally designed for low-quality physical network and include data integrity checking at many protocol layers.  X.25 is a WAN technique that uses a virtual circuit identified by a logical channel number (LCN).  X.25 is working with higher layered protocol checking called as LAPB ( link access protocol balanced ).  X.25 NETWORK  Due to the multiple layer processing X.25 is safe and secure for data transmission , but the quality of service is not guaranteed.  X.25 is used only for the low-quality application networks.  The date rate of X.25 is very minimum when compared to frame relay and ATM network.  The transmission capacity for a DTE typically ranges from 75 Kbps to 192 kbps, up to 2 Mbps. packet-switching exchange (PSE) packet assembler/disassembler, abbreviated PAD  X.25 protocol suit with OSI model X.25 ITU-T Recommendation was defined in 1976 and based on the OSI protocol stack. Interface for synchronous transmissions between the user terminal (Data Terminal Equipment, DTE ) and the first network equipment (Data Circuit-terminating Equipment, DCE). *LAP-B (link access protocol – Balanced) X.21 DCE serial router Cable Applications of X.25 Typical applications include:  Automated teller machine (ATM)networks.  Credit card verification networks. Drill Problem: X.25 Example 1: Calculate the transmission time for 1.048 MBytes of data over an X.25 network with a packet size of 128 bytes and a transmission rate of 64 Kbps.  Transmission Time (T) per packet = Packet Size / Link Data Rate  Total transmission time = Time to transmit one packet * Number of packets  Frame Relay Network  Frame relay networks was designed over come the difficulties of X.25.  Frame relay technology is widely used by network operators that provides long distance communications service to companies.  Frame Relay is a packet-switched data communication technology that is used to connect LANs (Local Area Networks) and other network devices over a Wide Area Network (WAN).  Frame relay uses ordinary data applications and transmits data frames with variable length called frames.  These frames are identified by a virtual circuit identifier (VCI) and a virtual path identifier (VPI), which are used to route the frames through the network.  Frame Relay Network  The frame relay network remove one complete layer process such as data checking and acknowledgement procedure to the network users and the protocol is use are much simpler and can support a much higher date rate.  The frame relay supports data rates of 1.544 Mbps to 44.376 Mbps.  Frame Relay uses packet-switching, which allows multiple virtual circuits to share the same physical connection.  This results in more efficient use of network bandwidth and can lead to cost savings for network operators. Frame Relay Network  The frame relay uses link access protocol for frame mode barrier service is abbreviated as LAPF.  The frame relay virtual circuits can be identified as DLCI ( Data link connection identifier).  Frame relay is a connection-oriented protocol with virtual circuits (an end-to-end connection must be established before data can be transferred). Frame Relay Network Comparison of X.25 and Frame Relay Protocol Stacks *(Link Access protocol for frame mode barrier service) –LAPF *(Link Access protocol –Balanced –(LAP-B) Comparison of X.25 and Frame Relay Layers Frame Format of Frame Relay protocol  Frame relay Congestion control refers to the mechanisms and techniques to control the congestion and keep the load below the capacity. Backward Explicit Congestion Notification (BECN) notifies upstream (source) nodes of congestion The Forward Explicit Congestion Notification (FECN) notifies downstream (destination) nodes of congestion. Applications of Frame Relay  Frame relay can be applied to banks, securities and other financial and large enterprises, government departments and local branches of the local network between the interconnection.  LAN and WAN connection. Frame relay composed of high-speed LAN and WAN connection, can improve the leased line bandwidth utilization. Drill Problem: Frame Relay Example 2: Calculate the transmission time for a Frame Relay frame with the following parameters: Frame Size (F): 1000 bytes Link Data Rate (R): 2 Mbps  Transmission Time (T) = Frame Size (F) / Link Data Rate (R) Asynchronous Transfer Mode (ATM) – Cell Relay Protocol  Most packet-switched techniques make use of variable-sized packets, and this leads to significant variations in the arrival times of the packets of a particular data stream.  Because each physical connection may carry traffic from many individual data streams, it occurs every now and then that a specific packet is queued behind several large packets from other data streams that are waiting to be sent out on the physical connection.  A further consequence is that switching is carried out by software that will eventually constrain the speed and performance of the network.  To overcome this delay, ITU decided to develop ATM.  ATM is a cell-relay technology, which uses small fixed-size frames called cells. Asynchronous Transfer Mode (ATM) – Cell Relay Protocol  ATM is a switching technique that uses time division multiplexing (TDM) for data communications.  ATM networks are connection-oriented networks for cell relay that supports voice, video and data communications.  It encodes data into small fixed - size cells so that they are suitable for TDM and transmits them over a physical medium.  The size of an ATM cell is 53 bytes: 5-byte header and 48-byte payload.  Cell relay transmits frames with constant length, 53 octets, and provides both variable-bit-rate (VBR) service that is optimum for data transmission and constant-bit-rate (CBR) service for voice and video applications.  CBR is not available in frame-relay technology. Asynchronous Transfer Mode (ATM) – Cell Relay Protocol  ATM uses virtual channels (VCs) and virtual paths (VPs) to route cells through a network.  In essence, a virtual channel is merely a connection between a source and a destination, which may entail establishing several ATM links between local switching centers.  With ATM, all communications occur on the virtual channel, which preserves cell sequence.  On the other hand, a virtual path is a group of virtual channels connected between two points that could compromise several ATM links.  The data rate of ATM Networks are 1.544 Mbps to 622 Mbps.  Protocol Layers of ATM  ATM networks can be considered as several layers providing different functions.  The ATM stack consists of a physical layer, ATM cell layer, and ATM adaptation layer.  ATM networks are connection-oriented, which means that there is a connection establishment phase followed by a data transfer phase.  During the connection establishment phase, a path (virtual circuit) through the network is built up and all cells of this call then use this path.  This principle was already in Virtual circuit approach. Protocol Architecture Protocol Layers of ATM ATM Adaptation Layer (AAL)  ALL is meant for isolating higher-layer protocols from details of ATM processes and prepares for conversion of user data into cells and segments it into 48-byte cell payloads.  AAL protocol excepts transmission from upper-layer services and helps them in mapping applications, e.g., voice, data to ATM cells.  AAL is sub divided into two sublayers:  The Convergence Sublayer (CS) Manages the flow of data to and from SAR sublayer.  The Segmentation and Reassembly Sublayer (SAR) breaks data into cells at the sender and reassembles cells into larger data units at Protocol Layers of ATM Physical Layer It manages the medium-dependent transmission and is divided into two parts physical medium-dependent sublayer and transmission convergence sublayer. The main functions are as follows: It converts cells into a bitstream. It controls the transmission and receipt of bits in the physical medium. It can track the ATM cell boundaries. Protocol Layers of ATM ATM Layer  It handles transmission, switching, congestion control, cell header processing, sequential delivery, etc.  It is responsible for simultaneously sharing the virtual circuits over the physical link known as cell multiplexing and passing cells through an ATM network known as cell relay making use of the VPI and VCI information in the cell header.  ATM Protocol Architecture The protocol reference model involves three separate planes: User plane: Provides for user information transfer, along with associated controls (e.g., flow control, error control) Control plane: Performs call control and connection control functions Management plane: Includes plane management, which performs management functions related to a system as a whole and provides coordination between all the planes, and layer management, which performs management functions relating to resources and parameters residing in its protocol entities ATM Virtual Path Connection ATM virtual Circuit can be identified as VPI / VCI – Virtual Path Identifier / Virtual Circuit Identifier Advantages of Virtual Paths  simplified network architecture  increased network performance and reliability  reduced processing  short connection setup time  enhanced network services Basic ATM Cell Format  ATM Cells  The ATM cell is 53 bytes long with 48 bytes reserved for carrying the pay-load and 5 bytes for the header.  UNI Header: This is used within private networks of ATMs for communication between ATM endpoints and ATM switches. It includes the Generic Flow Control (GFC) field.  NNI Header: is used for communication between ATM switches, and it does not include the Generic Flow Control(GFC) instead it includes a Virtual Path Identifier (VPI) which occupies the first 12 bits.  ATM Cells  The asynchronous transfer mode makes use of fixed-size cells, consisting of a 5- octet header and a 48-octet information field.  The use of small cells may reduce queuing delay for a high-priority cell, because it waits less if it arrives slightly behind a lower-priority cell that has gained access to a resource (e.g., the transmitter).  Fixed-size cells can be switched more efficiently, which is important for the very high data rates of ATM.  With fixed-size cells, it is easier to implement the switching mechanism in hardware. ATM Cells  The GFC field is used at a user interface only to control the data flow between the first ATM switch and the user node. Inside the network (i.e., in the NNI), this field is used for virtual path identification together with the other VPI fields. This is the only difference in the cell structure between UNI and NNI.  The majority of the header is taken up by VPI and VCI. Together they identify an individual circuit. They are used in the same way as the logical channel number in X.25 or the data link connection identifier of frame-relay technology.  Payload type specifies whether the cell contains user information or information to be used by the network itself, for example, for O&M. The network can use these maintenance cells between nodes to perform operations in, for example, a congestion situation. ATM Cells  The cell loss priority bit carries information between an ATM user system and the network. For example, in a congestion situation the network may use this field to define the priority of cells in the queues or to decide which cells are discarded first in the case of overload.  HEC is a checksum for the first 4 bytes. It makes possible the detection of multiple errors and the correction of a single error. ATM cells with more than one error will be discarded by the network. It is up to the end systems to detect and recover from such losses. The end systems also must detect errors in the user data. When an ATM switch updates the virtual circuit and path identifications of a cell, it calculates a new HEC for the following hop to the next switch. Service Classes and Adaptation Layer Four service classes supported by ATM for Different Application. Class A: Constant-bit-rate service for voice and video applications. Class B: Variable-bit-rate service with timing information for variable-bit-rate voice and video applications. Class C: Variable-bit-rate service for ordinary data applications. Class D: Variable-bit-rate service for connectionless transmission of very short data messages (no connection establishment). Class A/AAL1  AAL1 provides the support for traffic, which requires CBR service, and it is mainly used for voice and video applications.  This AAL is quite simple because there is no requirement for error detection and recovery for this type of traffic. Class B/AAL2  AAL2 provides the support for VBR traffic that requires maintenance of timing information during the call.  Timing information is transmitted in the adaptation layer header.  Examples of this type of traffic are variable-bit-rate voice and video applications in a LAN environment. Class C/AAL5, AAL3/4  AAL3/4 is a complicated protocol and it provides both connection-oriented service of class C and connectionless service of class D.  AAL3/4 was found to be too complex and inefficient for ordinary LAN traffic.  AAL5 it was designed to be simple and efficient. It supports only variable-bit-rate traffic, like burst data of LANs, with no timing relationships.  AAL5 does not provide enhanced services and thus consequently it does not require much overhead for protocol information.  It is the primary AAL used to provide LAN interconnections over ATM networks. Class D/AAL3/4  This class supports variable-bit-rate traffic that requires no timing information.  It supports connectionless service that does not require connection establishment.  Class D is suitable for datagram transmission in which only a small amount of data is transmitted during one connection. Application of ATM  ATM is used as a technology for high-data-rate backbone networks of some telecommunications network operators.  ATM was expected to be a major backbone technology and some access technologies, such as ADSL, were specified to transmit ATM cells. However, because LAN and IP switching technology has developed to manage higher data rates, the importance of ATM is decreasing.  ATM was also defined to be the initial network technology for UMTS(Universal Mobile Telecommunications System)  It will be replaced by evolving IP technology later in Drill Problem: ATM Cell Relay Example 3: Calculate the transmission time for an ATM cell with the following parameters: Cell Size (C): 53 bytes Link Data Rate (R): 155 Mbps (155,000,000 bits per second)  Transmission Time (T) = Cell Size (C) / Link Data Rate (R) Drill Problem: ATM Cell Relay Example 4: Given an ATM relay network with three nodes connected via fiber optic cable: Node A, Node B, and Node C. Node A wants to transmit an ATM cell to Node C through Node B. with the following operating conditions: Link Data Rate between Node A and Node B (R_AB): 100 Mbps Link Data Rate between Node B and Node C (R_BC): 155 Mbps ATM cell size (C): 53 bytes Calculate the transmission time, propagation time, and total delay between these nodes. Transmission Time (T) = Cell Size (C) / Link Data Rate (R) Propagation time=Distance / Propagation Speed​ Total Delay = Transmission time + Propagation time Comparison between Frame Relay and ATM  References Anttalainen, Tarmo. Introduction to telecommunications network engineering. Artech House, 2003. https://www.masader.om/eds/detail?db=e000xww&an=87734&isbn=97815805 36165 Tomasi, W., Electronic Communication System: Fundamentals Through Advanced, 5th Ed. Prentice Hall Int’l., N.J., 2004 Gnanasivam, P. Telecommunication switching and networks. New Age International, 2005 Principles of voice and data communications by Regis J. Bates / Marcus Bates. ] Frenzel, L., Principles of Electronic Communication Systems, 3 rd Ed. McGrawHill, 2008