ATM-cell format

In packet switching systems, data is often the data is divided into one group. In ATM, data packets used in what should be fixed length or variable length,http://www.planteea.ro/forum/index.php?action=profile;u=8780, the length of how to long for the good of these issues, CCITT study group made a thorough study and consultation, the ATM data Group taken as a fixed length,http://www.indiantvserial.org/index.php?action=profile;u=14764, and referred to as ATM cell. In addition, the length of the cell identified as 53 bytes. The number of bytes used not long ATM cell help to improve the processing speed, because the transmission of such a cell, in the 155Mb / s systems only 2.8us. The realization of the exchange terms from the use of fixed length cell to facilitate use of hardware. 5 byte header from the content of the composition, mainly in the asynchronous time division multiplexing is used to indicate the virtual channel belonging to the same cell, and complete the appropriate routing functions. Specifically, the letter header includes such elements: the general flow control (GFC); virtual channel identification (VPI); virtual channel identification (VCI); payload type identifier (PTI); cell loss priority (CLP ); header error control (HEC). The remaining 48 bytes of information is the payload data segment.

network equipment by checking the cell header to decide how to deal with this cell and this cell sent to the location. Network device does not check the cell carrier, only to be seen as a unit 384bit (48 bytes). So by the carrier data, voice or video bit in which the composition does not matter, bit is the bit. Therefore, in a single network support for all data transmission, which is the outstanding merits of ATM. On the other hand, the length of the cell is small, the network transmission and switching rate,http://www.rpguni-jka.com/forum/profile.php?mode=viewprofile&u=47044, and so the ATM can be a good voice, moving images and other delay-sensitive business.

Second, ATM procedures

As with frame relay and x.25, ATM is connection-oriented. ATM point of order is divided into three layers: The following is the physical layer, the middle is the ATM layer, ATM adaptation layer is above. ATM physical layer data stream and provides the interface between the physical media, including the two sub-layers: Physical Medium Dependent Sublayer and transmission convergence sublayer. Physical Medium Dependent Sublayer provides ATM data stream transmitted by the rate of a given medium. Convergence sublayer provides the physical media dependent sublayer through the transmission cell of the order. ATM layer is the core of ATM technology, although there are multiple ATM adaptation layer and multiple physical layer to choose from, but the description of the structure and control the header cell of the exchange is fixed, does not vary due to stratification difference. ATM cell layer is responsible for the routing, multiplexing, and repeated use.

ATM is the highest level of order ATM Adaptation Layer (AAL). It will rise to the users in the ATM business into the format and length of the payload to the destination station after it converted to the original user business. This layer consists of five sub-layer (AAL1-AAL5), different sub-ATM adaptation layer and ATM supports different business consistent. AAL1 supports constant bit rate (CBR) services such as digital sound and image signals, used for both cell delay and loss sensitive applications; AAL2 support time-sensitive variable bit rate (VBR) services; AAL3 / 4 sudden support for the business connection, and data services; AAL5 support sudden LAN data services. AAL layer can also be connection-oriented ATM connectionless oriented data integrated together, so that ATM users to broadcast and multipoint communication.

three, ATM Transmission Control

cell monitoring and management of the transmission in the network is called Transmission Control. It is essential to doing good or bad, especially for delay-sensitive video data. Different types of communication require different levels of service. An ATM network for different traffic types to provide different QOS (Quality of Service) level.

1. ATM traffic types

We can ATM network of the three characteristics: bandwidth, latency and cell delay variation to the communication type classification. Bandwidth to support a connected network size. Waiting time is the delay related to the amount of connection. If you need low latency means that the cell need to quickly from the network point to another point. Cell delay variation is that each group of related cell delay experienced by the scope. Low cell delay variation means that a cell must be not too far away from each other the way through the network.

ATM network, there are three types of communication: CRB (Constant bit rate constant orientation rate), VRB (Variable bit rate change bit rate) and ARB (Available bit rate available bit rate). CRB communications, including voice and video. To accomplish this communication, ATM provides a constant bandwidth, low latency and low cell delay variation. VRB different bandwidth requirements in addition to outside communications and CRB similar. ABR traffic does not need the bandwidth or delay parameters accepted by many data applications.

2. ATM connection

caused by issuing a consultation with the ATM network connection requests, ATM ATM network and request one end connected to the other end. This process is known as connection establishment process. Most need to be consulted by the ATM Forum UNI 3.0 specifies, including the type of communication, constant, and peak bandwidth, the signal sequence length and QOS levels. This process ensures that ATM network and endpoints to create a \Network committed to submit a QOS, ATM endpoint promise not to send the required than the connection process more traffic.

When obstruction occurs, the transmission control provides a mechanism to restore the network state. ATM network control technology using three transmission: transmission control, transmission shaping and congestion control:

(1) Transmission Control (Traffic Policing)

ATM network to ensure that each connection does not exceed the negotiated traffic parameters, ATM switch using a \Imagine the bottom of the wooden bucket has a hole, the water at a constant rate (consultation rate) from the bucket (buffer) outflow. When the information flow rate and buffer overflows more than consultation, the need for transmission control. Each ATM cell header has a CLP (Cell Loss Priority) bit, that is, the cell loss attribute bit that indicates whether the cell is consistent with the contract. For example, if the cell is inconsistent with the contract, which means there may be more than the contract allowed cell, ATM switches CLP bit set to 1. The cell only when there is sufficient network capacity can be transmitted through the network, if there is not enough bandwidth available, CLP bit inconsistent cell is lost, then need to re-transfer of these cells. CBR traffic requires a single \VBR traffic using a dual \If any one value over protocol parameters, ATM switches managed by controlling the CLP bit VBR traffic.

(2) transfer of Plastic (Traffic Shaping)

similar and transmission control, transmission shaping is done on the user network interface. Use double \Complete the transfer device is a typical plastic used in the PC or workstation, bridges, routers and DSUs (digital service unit) in the ATM network adapter.

(3) congestion control

obstruction occurs in any network, when a user sends data over the network throughput in the bandwidth available to blocking. The same network as more users to transfer data, for any bandwidth available to a user change over time. Most networks can not tell the user at any given moment how much bandwidth available. As a result, there is no basis for the user to control the amount of data sent. When the data sent over the network can handle the data, the network buffers fill and overflow, the data must be retransmitted, which will further increase the traffic makes the network more congested. ATM network to perform ABR traffic congestion control in order to effectively use bandwidth. Effective congestion control can reduce the block re-transmission of data needs.

ATM expansion of the network capacity to support a variety of applications and help network managers. Using ATM technology as a foundation to ensure a wide area network with (WAN) interface acceptable to meet the LAN broadband services in high demand. Traffic management designed to ensure users get the quality of service they need.

four, ATM LAN emulation networks

existing network running on a wide range of network layer protocols such as IP, IPX, Appletalk, DECnet, Banyan, Vines, etc., to achieve a variety of ATM networks with existing key LAN interconnection is to use the same network layer protocol, for example, using IP and IPX protocols uniform because the function is the network layer and application layer protocol to provide consistent network view.

ATM network is a key factor in the success of these techniques is to have the ability to interoperate. Running across the ATM network has two kinds of network layer protocol implementations. Called native mode operation, using the address network layer address changes in technology will be directly mapped into ATM addresses, so the network layer information package can be transmitted through the ATM network. Another network layer through the ATM network to transmit information package method is LAN emulation (LANELAN Em-ulation).

LANE is top of the ATM network simulation of a LAN. LANE agreement specifically defined for the IEEE802.3 Ethernet and IEEE 802.5 Token Ring LAN simulation. LANE LANE protocol is defined as the level the same business with the existing LAN interface, the data transmitted through the ATM network is still the appropriate LAN MAC packet of information format package. LANE makes all aspects of ATM, including the establishment of connections, cell segmentation and reassembly (SAR), completely transparent to the node.

LANE higher level network protocol that does not require any modifications, you can run on the ATM network. LANE service because the driver for the network layer to provide the same service the existing MAC protocol interface (such as a network drive interface specification NDLS or ODI Open Data link interface driver interface). Therefore, these drivers do not need to make any changes.

LANE agreement provides for a single emulation LAN (ELAN) operation, an ATM can exist on the number of ELAN, ELAN each simulation is Ethernet or Token Ring network.

LANE protocol 2 ATM equipment will be used:

(1) ATM network interface cards by (NIC)

ATM NIC will implement the LANE protocol, and to achieve to hit port ATM network, the connection of the terminal system, ATM NIC will provide a higher level protocol current LAN service interface. Thus, in the end system's network layer protocol will continue to use the same process as communication with the LAN, but can use the extensive ATM network bandwidth.

(2) network interconnection, and LAN switching equipment

mainly refers to the connection of the LAN ATM switches and routers. these devices and their directly connected with the ATM used to provide the host with the virtual LAN service. Because ATM LAN emulation is essentially an agreement on a bridge, LANE protocol basic function is to change the MAC address of ATM addresses, so particularly suitable for fast simulation of multi-LAN port LAN switching equipment. If my school's campus computer network that uses IBM's LANE server for network interconnection and LAN switching.

LAN emulation specification model includes the LAN emulation client (LEC), LAN emulation server (LES), Broadcast and Unknown Server (BUS) and LAN Emulation Configuration Server (LECS).

LEC in the ELAN system to perform a single data transmission terminal, address analysis and other control functions, but also for their own organizations with any level of a standard service interface. ELAN interface with ATM NIC or LAN connection in each switch fabric to support a ELAN LEC,http://torrent.om.ua/forum/index.php?s=bfb35b0d12640bb087bc43770c346ab7&showuser=76751, each LEC ATM address by an independent to identify, but with one or more ATM addresses can be reached through the MAC address is connected. ELAN LES for a specific executive control. Each ELAN is only one logical LES, both the LES belonging to a particular ELAN. Each one has its own dedicated LES ATM address to identify it.

BUS is a multicast server, whose role is to expand the unknown destination address traffic to a specific client in the delivery ELAN multicast and broadcast traffic, each LEC and only on the ELAN A BUS is connected, but in a particular ELAN may have more than one BUS, the way they communicate with vendors to determine and coordination. A BUS LEC connected by their own proprietary ATM address of a logo. In LES, the broadcast MAC address of the address associated with this mapping is usually configured in the LES in.

LECS by assigned to each LANE client corresponding ELAN LES,http://www.pompahealthsolutions.com/forum/member.php?u=32924, the client is assigned to a particular ELAN. Each management domain has only one logical LECS, it is all the domain-based ELAN services. LANE protocol does not require LES, BUS and LECS specific location,http://wlansecurity.comze.com/forum/profile.php?mode=viewprofile&u=9374, most current network equipment vendors are (ATM switches and routers) rather than the implementation of the host and workstations, to ensure its high performance and reliability.

five, LAN simulation is running

LANE ATM connections with each other through a series of communications. Maintain their connection between the LEC in order to transmit data and control flow.

configuration control virtual channel connections, including direct connection (Virtual Channel Connection, VCC), direct control and distribution control VCC VCC. Direct VCC is a bi-directional point to point configuration VCC, is set by the LEC to the LECS in; direct control of the VCC is a bidirectional VCC, is set by the LEC to the LES's; distributed control VCC is a unidirectional VCC, from the LES back LEC, usually This is a multipoint connection.

data connections, including direct data VCC. Multicast Send VCC and Multicast pass VCC. VCC is a direct data exchange of data in the two hope to set a two-way point between LEC VCC. Usually two straight by using the same LEC VCC transfer data between them all the information package , rather than between them on the MAC address of each to establish a new VCC, this can save resources and connections set the connection waiting time; multicast send VCC is a bi-directional point to point VCC,http://theredocean.net/ROForum/index.php?action=profile;u=1605, is set by the LEC to the BUS's; multicast is a way to pass VCC VCC, is set to the LEC from the BUS, usually it is a multipoint connections, each LEC is its leaf nodes.

LAN simulation run, including initialization. Three stages of connection and data transfer.

1. Initialization

initialization, LEC received by address register their ATM addresses, and then, LEC set the configuration of a direct connection to the LECS, LEC LECS can find the location of three ways: using a fixed ANI process to determine the address of LECS; using a known LECS address; use of a known permanent connection to the LECS (VPI: 0,http://www.exotically.com/travelforum/profile.php?mode=viewprofile&u=134667, VCI = 17).

After determining the location of LECS, LEC will establish a direct allocation to the LECS VCC, once connected, LECS using a configuration protocol to notify the LEC, ELAN connect it to the target, including the ATM address of LES . The type of emulated LAN. ELAN's largest information package the size of the ELAN name.

2. Connection

LEC been a LES address, that is the direct removal LECS configuration VCC, and set to the LES of the direct control of the VCC, at the same time, LES for the LEC LEC specifies a unique identifier (LECID), and LEC LES registered on their own in the MAC and ATM addresses.

Subsequently, LES set up a return to the distribution of control LEC VCC. This can in LEC LAN emulation ARP (LE-ARP) process using distributed control, directly or VCC to a specific MAC address corresponding to the ATM address. This process, LEC form a LEARP, and sends it to the LES. If the LES can identify the map (because some of the LEC MAC address on the registration), can be directly answered by directly controlling the VCC, while the request is passed to the distributed control of the VCC, to seek to know the MAC address of the LEC requests a response.

If a LEC to respond to the LE-ARP, it will respond by directly controlling the VCC LES. Then, LES can only return this response to the request of the LEC, distributed control can also be passed to all of the LEC, the LEC so that all can obtain and cache the address of this particular mapping.

for the completion of initialization, LEC using the LE ARP mechanism to determine a BUS's ATM address. It is sent through the MAC broadcast address to the LES's LEARP to complete,http://jtechapps.com/whatsupdon/forum_live/profile.php?mode=viewprofile&u=67323, with the BUS's ATM address of the latter response. Then, LEC set to BUS multi-point radio transmission VCC. Next, set the BUS multi-point broadcasting, the VCC back to LEC, is usually connected to the LEC as a multipoint leaf nodes. This LEC to prepare for data transmission.

3. Data transfer

in the data transmission process, LEC, or receive a high-level protocol is sent from the network layer information package , or receive a pass through the LAN port MAC information package . The former data source will not target LEC LEC's ATM address. At this point, LEC to the LES sends a first component of a LE ARP response.

ARP waiting for a response when LE, LEC also information package with the provisions of the package is passed to the BUS, BUS will package information Diffusion to all of the LEC. LEC Upon receipt of a LE-ARP response to the destination node to set up a direct data VCC, and use it for data transmission, instead of using the BUS path. But before the original LEC must ensure that all information sent to the BUS package in the use of direct data VCC has been sent to the destination before. In this mechanism, a control cell will vary on an information package sent to the first transmission path, the destination cell before receiving this reply, do not send a message using the second path package .

tag through if a data connection already exists in the LEC, which you can reach a specific MAC address, the source LEC can re-use the data directly.

If you have not received a response to the LEARP, LEC will continue to send information to the BUS packets , while periodically re-send LEARP, until you receive a response. Typically, an information packet by BUS proliferation, and the target response to the source, a number of LEC will know the destination location, and then respond to subsequent LEARP.

LEC will get through LEARP from the local cache of all MAC addresses to ATM address mapping, if the LEC receive an information packet to sent to the same MAC address requirements, it will refer to this local cache and use the cached mapping table, and not to issue another LE-ARP.

LEC also packets of information using the BUS broadcast and multicast. Information after the packet is passed to the BUS, BUS or redirect them all LEC, LEC for all data frames received from the BUS prefix LECID filter according to the relevant fields to ensure the frame will not receive their issue.

six. ATM existing problems and prospects

While the ATM-related technology and research developed rapidly, but