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59-397: A WWAN often differs from wireless local area network (WLAN) by using mobile telecommunication cellular network technologies such as 2G , 3G , 4G LTE , and 5G to transfer data. It is sometimes referred as Mobile Broadband . These technologies are offered regionally, nationwide, or even globally and are provided by a wireless service provider . WWAN connectivity allows a user with

118-547: A wireless access point (WAP) that also serves as a bridge to other networks such as a local area network or the Internet. Since wireless communication uses a more open medium for communication in comparison to wired LANs, the 802.11 designers also included encryption mechanisms: Wired Equivalent Privacy (WEP), no longer considered secure, Wi-Fi Protected Access (WPA, WPA2, WPA3), to secure wireless computer networks. Many access points will also offer Wi-Fi Protected Setup ,

177-543: A wireless network router , which links them to the internet. Hotspots provided by routers at restaurants, coffee shops, hotels, libraries, and airports allow consumers to access the internet with portable wireless devices. Norman Abramson , a professor at the University of Hawaii , developed the world's first wireless computer communication network, ALOHAnet . The system became operational in 1971 and included seven computers deployed over four islands to communicate with

236-608: A 5-byte header and a 48-byte payload. ATM defines two different cell formats: user–network interface (UNI) and network–network interface (NNI). Most ATM links use UNI cell format. Diagram of a UNI ATM cell Payload and padding if necessary (48 bytes) Diagram of an NNI ATM cell Payload and padding if necessary (48 bytes) ATM uses the PT field to designate various special kinds of cells for operations, administration and management (OAM) purposes, and to delineate packet boundaries in some ATM adaptation layers (AAL). If

295-407: A WDS must be configured to use the same radio channel and share WEP keys or WPA keys if they are used. They can be configured to different service set identifiers. WDS also requires that every base station be configured to forward to others in the system as mentioned above. There are two definitions for wireless LAN roaming: Asynchronous Transfer Mode Asynchronous Transfer Mode ( ATM )

354-586: A WDS over some other solutions is that it preserves the MAC addresses of client packets across links between access points. An access point can be either a main, relay, or remote base station. A main base station is typically connected to the wired Ethernet. A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them to relay or main stations. Because data

413-521: A WWAN. A WWAN may also be a low-power, low-bit-rate wireless WAN, ( LPWAN ), intended to carry small packets of information between things , often in the form of battery operated sensors. Since radio communications systems do not provide a physically secure connection path, WWANs typically incorporate encryption and authentication methods to make them more secure. Some of the early GSM encryption techniques were flawed, and security experts have issued warnings that cellular communication, including WWAN,

472-435: A cell-by-cell basis, but this is sub-optimal for encapsulated packet traffic as discarding a single cell will invalidate a packet's worth of cells. As a result, schemes such as partial packet discard (PPD) and early packet discard (EPD) have been developed to discard a whole packet's cells. This reduces the number of useless cells in the network, saving bandwidth for full packets. EPD and PPD work with AAL5 connections as they use

531-598: A dual leaky bucket controller to a PCR and CDVT and an SCR and maximum burst size (MBS). The MBS will normally be the packet ( SAR - SDU ) size for the VBR VC in cells. If the traffic on a virtual circuit exceeds its traffic contract, as determined by the GCRA, the network can either drop the cells or set the Cell Loss Priority (CLP) bit, allowing the cells to be dropped at a congestion point. Basic policing works on

590-440: A fixed length (53 octets ) called cells . This differs from approaches such as Internet Protocol (IP) (OSI layer 3) or Ethernet (also layer 2) that use variable-sized packets or frames. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the data exchange begins. These virtual circuits may be either permanent (dedicated connections that are usually preconfigured by

649-505: A group owner in the Wi-Fi Direct group. In one approach, the user sets up a P2P group owner manually. This method is also known as autonomous group owner ( autonomous GO ). In the second method, called negotiation-based group creation , two devices compete based on the group owner intent value. The device with higher intent value becomes a group owner and the second device becomes a client. Group owner intent value can depend on whether

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708-419: A laptop and a WWAN card to surf the web, check email, or connect to a virtual private network (VPN) from anywhere within the regional boundaries of cellular service. Various computers can have integrated WWAN capabilities. A WWAN may also be a closed network that covers a large geographic area. For example, a mesh network or MANET with nodes on buildings, towers, trucks, and planes could also be considered

767-436: A low-jitter network interface. Cells were introduced to provide short queuing delays while continuing to support datagram traffic. ATM broke up all data packets and voice streams into 48-byte pieces, adding a 5-byte routing header to each one so that they could be reassembled later. Being 1/30th the size reduced cell contention jitter by the same factor of 30. The choice of 48 bytes was political rather than technical. When

826-425: A proposed route through a network in order to satisfy the service requirements of a VC or VP. Another key ATM concept involves the traffic contract . When an ATM circuit is set up each switch on the circuit is informed of the traffic class of the connection. ATM traffic contracts form part of the mechanism by which quality of service (QoS) is ensured. There are four basic types (and several variants) which each have

885-553: A quick, but no longer considered secure, method of joining a new device to an encrypted network. Most Wi-Fi networks are deployed in infrastructure mode . In infrastructure mode, wireless clients, such as laptops and smartphones, connect to the WAP to join the network. The WAP usually has a wired network connection and may have permanent wireless connections to other WAPs. WAPs are usually fixed and provide service to their client nodes within range. Some networks will have multiple WAPs using

944-452: A set of parameters describing the connection. VBR has real-time and non-real-time variants, and serves for bursty traffic. Non-real-time is sometimes abbreviated to vbr-nrt. Most traffic classes also introduce the concept of cell-delay variation tolerance (CDVT), which defines the clumping of cells in time. To maintain network performance, networks may apply traffic policing to virtual circuits to limit them to their traffic contracts at

1003-412: A useful ability to carry multiple logical circuits on a single physical or virtual medium, although other techniques exist, such as Multi-link PPP , Ethernet VLANs , VxLAN , MPLS , and multi-protocol support over SONET . An ATM network must establish a connection before two parties can send cells to each other. This is called a virtual circuit (VC). It can be a permanent virtual circuit (PVC), which

1062-597: A wireless medium in a network are referred to as stations. All stations are equipped with wireless network interface controllers . Wireless stations fall into two categories: wireless access points (WAPs) and clients. WAPs are base stations for the wireless network. They transmit and receive radio frequencies for wireless-enabled devices to communicate with. Wireless clients can be mobile devices such as laptops, personal digital assistants , VoIP phones and other smartphones , or non-portable devices such as desktop computers , printers, and workstations that are equipped with

1121-659: A wireless network interface. The basic service set (BSS) is a set of all stations that can communicate with each other at PHY layer. Every BSS has an identification (ID) called the BSSID, which is the MAC address of the access point servicing the BSS. There are two types of BSS: Independent BSS (also referred to as IBSS), and infrastructure BSS. An independent BSS (IBSS) is an ad hoc network that contains no access points, which means they cannot connect to any other basic service set. In an IBSS

1180-928: Is a telecommunications standard defined by the American National Standards Institute and International Telecommunication Union Telecommunication Standardization Sector (ITU-T, formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of the Broadband Integrated Services Digital Network as defined in the late 1980s, and designed to integrate telecommunication networks. It can handle both traditional high-throughput data traffic and real-time , low-latency content such as telephony (voice) and video. ATM provides functionality that uses features of circuit switching and packet switching networks by using asynchronous time-division multiplexing . ATM

1239-402: Is created administratively on the end points, or a switched virtual circuit (SVC), which is created as needed by the communicating parties. SVC creation is managed by signaling , in which the requesting party indicates the address of the receiving party, the type of service requested, and whatever traffic parameters may be applicable to the selected service. Call admission is then performed by

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1298-439: Is forwarded wirelessly, consuming wireless bandwidth, throughput in this method is halved for wireless clients not connected to a main base station. Connections between base stations are done at layer-2 and do not involve or require layer-3 IP addresses. WDS capability may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging). All base stations in

1357-551: Is going to dominate". However, in 2005 the ATM Forum , which had been the trade organization promoting the technology, merged with groups promoting other technologies, and eventually became the Broadband Forum . Wireless ATM, or mobile ATM, consists of an ATM core network with a wireless access network. ATM cells are transmitted from base stations to mobile terminals. Mobility functions are performed at an ATM switch in

1416-462: Is in contrast to Ethernet which uses carrier-sense multiple access with collision detection (CSMA/CD). The 802.11 specification includes provisions designed to minimize collisions because mobile units have to contend with the hidden node problem where two mobile units may both be in range of a common access point, but out of range of each other. A bridge can be used to connect networks, typically of different types. A wireless Ethernet bridge allows

1475-508: Is in use for a given cell is not encoded in the cell. Instead, it is negotiated by or configured at the endpoints on a per-virtual-connection basis. Following the initial design of ATM, networks have become much faster. A 1500 byte (12000-bit) full-size Ethernet frame takes only 1.2 μs to transmit on a 10 Gbit/s network, reducing the motivation for small cells to reduce jitter due to contention. The increased link speeds by themselves do not eliminate jitter due to queuing. ATM provides

1534-401: Is no longer secure. UMTS (3G) encryption was developed later and has yet to be broken. Wireless local area network A wireless LAN ( WLAN ) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building. This gives users

1593-650: The CCITT (now ITU-T) was standardizing ATM, parties from the United States wanted a 64-byte payload because this was felt to be a good compromise between larger payloads optimized for data transmission and shorter payloads optimized for real-time applications like voice. Parties from Europe wanted 32-byte payloads because the small size (4 ms of voice data) would avoid the need for echo cancellation on domestic voice calls. The United States, due to its larger size, already had echo cancellers widely deployed. Most of

1652-525: The Independent Basic Service Set (IBSS). A Wi-Fi Direct network is a different type of wireless network where stations communicate peer-to-peer. In a peer-to-peer network wireless devices within range of each other can discover and communicate directly without involving central access points. In a Wi-Fi P2P group, the group owner operates as an access point and all other devices are clients. There are two main methods to establish

1711-528: The Private Network-to-Network Interface (PNNI) protocol to share topology information between switches and select a route through a network. PNNI is a link-state routing protocol like OSPF and IS-IS . PNNI also includes a very powerful route summarization mechanism to allow construction of very large networks, as well as a call admission control (CAC) algorithm which determines the availability of sufficient bandwidth on

1770-558: The Wi-Fi brand name). Beginning in 1991, a European alternative known as HiperLAN/1 was pursued by the European Telecommunications Standards Institute (ETSI) with a first version approved in 1996. This was followed by a HiperLAN/2 functional specification with ATM influences accomplished February 2000. Neither European standard achieved the commercial success of 802.11, although much of

1829-493: The most significant bit (MSB) of the PT field is 0, this is a user data cell, and the other two bits are used to indicate network congestion and as a general-purpose header bit available for ATM adaptation layers. If the MSB is 1, this is a management cell, and the other two bits indicate the type: network management segment, network management end-to-end, resource management, and reserved for future use. Several ATM link protocols use

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1888-532: The public switched telephone network and in the Integrated Services Digital Network (ISDN) but has largely been superseded in favor of next-generation networks based on IP technology. Wireless and mobile ATM never established a significant foothold. To minimize queuing delay and packet delay variation (PDV), all ATM cells are the same small size. Reduction of PDV is particularly important when carrying voice traffic, because

1947-422: The 1990s. However, even by the end of the decade, the better price–performance ratio of Internet Protocol -based products was competing with ATM technology for integrating real-time and bursty network traffic. Companies such as FORE Systems focused on ATM products, while other large vendors such as Cisco Systems provided ATM as an option. After the burst of the dot-com bubble , some still predicted that "ATM

2006-582: The European parties eventually came around to the arguments made by the Americans, but France and a few others held out for a shorter cell length. 48 bytes was chosen as a compromise, despite having all the disadvantages of both proposals and the additional inconvenience of not being a power of two in size. 5-byte headers were chosen because it was thought that 10% of the payload was the maximum price to pay for routing information. An ATM cell consists of

2065-505: The GFC field for a local flow control and sub-multiplexing system between users. This was intended to allow several terminals to share a single network connection in the same way that two ISDN phones can share a single basic rate ISDN connection. All four GFC bits must be zero by default. The NNI cell format replicates the UNI format almost exactly, except that the 4-bit GFC field is re-allocated to

2124-510: The HEC field to drive a CRC-based framing algorithm, which allows locating the ATM cells with no overhead beyond what is otherwise needed for header protection. The 8-bit CRC is used to correct single-bit header errors and detect multi-bit header errors. When multi-bit header errors are detected, the current and subsequent cells are dropped until a cell with no header errors is found. A UNI cell reserves

2183-893: The STAs are configured in ad hoc (peer-to-peer) mode. An extended service set (ESS) is a set of connected BSSs. Access points in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte (maximum) character string. A distribution system (DS) connects access points in an extended service set. The concept of a DS can be used to increase network coverage through roaming between cells. DS can be wired or wireless. Current wireless distribution systems are mostly based on WDS or Mesh protocols , though other systems are in use. The IEEE 802.11 has two basic modes of operation: infrastructure and ad hoc mode. In ad hoc mode, mobile units communicate directly peer-to-peer. In infrastructure mode, mobile units communicate through

2242-547: The US, and 2 to 34 Mbit/s in Europe. At 155 Mbit/s, a typical full-length 1,500 byte Ethernet frame would take 77.42  μs to transmit. On a lower-speed 1.544 Mbit/s T1 line , the same packet would take up to 7.8 milliseconds. A queuing delay induced by several such data packets might exceed the figure of 7.8 ms several times over. This was considered unacceptable for speech traffic. The design of ATM aimed for

2301-743: The VCI is similar to that of the data link connection identifier (DLCI) in Frame Relay and the logical channel number and logical channel group number in X.25 . Another advantage of the use of virtual circuits comes with the ability to use them as a multiplexing layer, allowing different services (such as voice, Frame Relay, IP). The VPI is useful for reducing the switching table of some virtual circuits which have common paths. ATM can build virtual circuits and virtual paths either statically or dynamically. Static circuits (permanent virtual circuits or PVCs) or paths (permanent virtual paths or PVPs) require that

2360-550: The VPI field, extending the VPI to 12 bits. Thus, a single NNI ATM interconnection is capable of addressing almost 2 VPs of up to almost 2 VCs each. ATM supports different types of services via AALs. Standardized AALs include AAL1, AAL2, and AAL5, and the rarely used AAL3 and AAL4. AAL1 is used for constant bit rate (CBR) services and circuit emulation. Synchronization is also maintained at AAL1. AAL2 through AAL4 are used for variable bitrate (VBR) services, and AAL5 for data. Which AAL

2419-407: The VPI, is used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. The length of the VPI varies according to whether the cell is sent on a user-network interface (at the edge of the network), or if it is sent on a network-network interface (inside the network). As these cells traverse an ATM network, switching takes place by changing

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2478-521: The VPI/VCI values (label swapping). Although the VPI/VCI values are not necessarily consistent from one end of the connection to the other, the concept of a circuit is consistent (unlike IP, where any given packet could get to its destination by a different route than the others). ATM switches use the VPI/VCI fields to identify the virtual channel link (VCL) of the next network that a cell needs to transit on its way to its final destination. The function of

2537-625: The ability to move around within the area and remain connected to the network. Through a gateway , a WLAN can also provide a connection to the wider Internet . Wireless LANs based on the IEEE 802.11 standards are the most widely used computer networks in the world. These are commonly called Wi-Fi , which is a trademark belonging to the Wi-Fi Alliance . They are used for home and small office networks that link together laptop computers , printers , smartphones , Web TVs and gaming devices with

2596-494: The central computer on the Oahu island without using phone lines. Wireless LAN hardware initially cost so much that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by technical standards , primarily the various versions of IEEE 802.11 (in products using

2655-435: The circuit (the service contract ) and the two endpoints. ATM networks create and remove switched virtual circuits (SVCs) on demand when requested by an end station . One application for SVCs is to carry individual telephone calls when a network of telephone switches are interconnected using ATM. SVCs were also used in attempts to replace local area networks with ATM. Most ATM networks supporting SPVPs, SPVCs, and SVCs use

2714-409: The circuit is composed of a series of segments, one for each pair of interfaces through which it passes. PVPs and PVCs, though conceptually simple, require significant effort in large networks. They also do not support the re-routing of service in the event of a failure. Dynamically built PVPs (soft PVPs or SPVPs) and PVCs (soft PVCs or SPVCs), in contrast, are built by specifying the characteristics of

2773-439: The connection of devices on a wired Ethernet network to a wireless network. The bridge acts as the connection point to the wireless LAN. A wireless distribution system (WDS) enables the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required. The notable advantage of

2832-454: The conversion of digitized voice into an analog audio signal is an inherently real-time process. The decoder needs an evenly spaced stream of data items. At the time of the design of ATM, 155 Mbit/s synchronous digital hierarchy with 135 Mbit/s payload was considered a fast optical network link, and many plesiochronous digital hierarchy links in the digital network were considerably slower, ranging from 1.544 to 45 Mbit/s in

2891-401: The core network, known as a crossover switch , which is similar to the mobile switching center of GSM networks. The advantage of wireless ATM is its high bandwidth and high-speed handoffs done at layer 2. In the early 1990s, Bell Labs and NEC research labs worked actively in this field. Andy Hopper from the University of Cambridge Computer Laboratory also worked in this area. There

2950-498: The crowded 2.4 GHz band , which is also shared with Bluetooth devices and microwave ovens . The 5 GHz band also has more channels than the 2.4 GHz band, permitting a greater number of devices to share the space. Not all WLAN channels are available in all regions. A HomeRF group formed in 1997 to promote a technology aimed at residential use, but it disbanded in January 2003. All components that can connect into

3009-413: The end of packet marker: the ATM user-to-ATM user (AUU) indication bit in the payload-type field of the header, which is set in the last cell of a SAR-SDU. Traffic shaping usually takes place in the network interface controller (NIC) in user equipment, and attempts to ensure that the cell flow on a VC will meet its traffic contract, i.e. cells will not be dropped or reduced in priority at the UNI. Since

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3068-506: The entry points to the network, i.e. the user–network interfaces (UNIs) and network-to-network interfaces (NNIs) using usage/network parameter control (UPC and NPC). The reference model given by the ITU-T and ATM Forum for UPC and NPC is the generic cell rate algorithm (GCRA), which is a version of the leaky bucket algorithm . CBR traffic will normally be policed to a PCR and CDVT alone, whereas VBR traffic will normally be policed using

3127-415: The network to confirm that the requested resources are available and that a route exists for the connection. ATM operates as a channel-based transport layer, using VCs. This is encompassed in the concept of the virtual paths (VP) and virtual channels. Every ATM cell has an 8- or 12-bit virtual path identifier (VPI) and 16-bit virtual channel identifier (VCI) pair defined in its header. The VCI, together with

3186-474: The reference model given for traffic policing in the network is the GCRA, this algorithm is normally used for shaping as well, and single and dual leaky bucket implementations may be used as appropriate. The ATM network reference model approximately maps to the three lowest layers of the OSI reference model . It specifies the following layers: ATM became popular with telephone companies and many computer makers in

3245-417: The same SSID and security arrangement. In that case, connecting to any WAP on that network joins the client to the network, and the client software will try to choose the WAP that gives the best service, such as the WAP with the strongest signal. An ad hoc network is a network where stations communicate only peer-to-peer (P2P). There is no base and no one gives permission to talk. This is accomplished using

3304-457: The service provider), or switched (set up on a per-call basis using signaling and disconnected when the call is terminated). The ATM network reference model approximately maps to the three lowest layers of the OSI model: physical layer , data link layer, and network layer . ATM is a core protocol used in the synchronous optical networking and synchronous digital hierarchy (SONET/SDH) backbone of

3363-477: The wireless device performs a cross-connection between an infrastructure WLAN service and a P2P group, available power in the wireless device, whether the wireless device is already a group owner in another group or a received signal strength of the first wireless device. IEEE 802.11 defines the PHY and medium access control (MAC) layers based on carrier-sense multiple access with collision avoidance (CSMA/CA). This

3422-414: The work on HiperLAN/2 has survived in the physical specification ( PHY ) for IEEE 802.11a , which is nearly identical to the PHY of HiperLAN/2. In 2009, 802.11n was added to 802.11. It operates in both the 2.4 GHz and 5 GHz bands at a maximum data transfer rate of 600 Mbit/s. Most newer routers are dual-band and able to utilize both wireless bands. This allows data communications to avoid

3481-494: Was seen in the 1990s as a competitor to Ethernet and networks carrying IP traffic as, unlike Ethernet, it was faster and designed with quality-of-service in mind, but it fell out of favor once Ethernet reached speeds of 1 gigabits per second. In the Open Systems Interconnection (OSI) reference model data link layer (layer 2), the basic transfer units are called frames . In ATM these frames are of

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