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Enabling PHP’s mail command to work with Kerio Connect on Mac OS X? Transport Protocol - An internet standard used for email transmission across IP. SCP Containment Breach for Mac OS X, download best alternative solutions carefully chosen by our editors and user community. Scp Containment Breach Access Codes List. I havent used my nintendo 3ds xl in such a long time but today. Hacks 3 IdiotBox. How to update Microsoft Defender for Endpoint on Mac. Microsoft regularly publishes software updates to improve performance, security, and to deliver new features. To update Microsoft Defender for Endpoint on Mac, a program named Microsoft AutoUpdate (MAU) is used. To learn more, see Deploy updates for Microsoft Defender for Endpoint on Mac. The Media Access Control (MAC) data communication Networks protocol sub-layer, also known as the Medium Access Control, is a sub-layer of the data link layer specified in the seven-layer OSI model. The medium access layer was made necessary by systems that share a common communications medium. Typically these are local area networks. The MAC layer is the 'low' part of the second OSI layer, the.

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In IEEE 802 LAN/MAN standards, the medium access control (MAC, also called media access control) sublayer is the layer that controls the hardware responsible for interaction with the wired, optical or wireless transmission medium. The MAC sublayer and the logical link control (LLC) sublayer together make up the data link layer. Within the data link layer, the LLC provides flow control and multiplexing for the logical link (i.e. EtherType, 802.1Q VLAN tag etc), while the MAC provides flow control and multiplexing for the transmission medium.

These two sublayers together correspond to layer 2 of the OSI model. For compatibility reasons, LLC is optional for implementations of IEEE 802.3 (the frames are then 'raw'), but compulsory for implementations of other IEEE 802 physical layer standards. Within the hierarchy of the OSI model and IEEE 802 standards, the MAC sublayer provides a control abstraction of the physical layer such that the complexities of physical link control are invisible to the LLC and upper layers of the network stack. Thus any LLC sublayer (and higher layers) may be used with any MAC. In turn, the medium access control block is formally connected to the PHY via a media-independent interface. Although the MAC block is today typically integrated with the PHY within the same device package, historically any MAC could be used with any PHY, independent of the transmission medium.

When sending data to another device on the network, the MAC sublayer encapsulates higher-level frames into frames appropriate for the transmission medium (i.e. the MAC adds a syncword preamble and also padding if necessary), adds a frame check sequence to identify transmission errors, and then forwards the data to the physical layer as soon as the appropriate channel access method permits it. For topologies with a collision domain (bus, ring, mesh, point-to-multipoint topologies), controlling when data is sent and when to wait is necessary to avoid collisions. Additionally, the MAC is also responsible for compensating for collisions by initiating retransmission if a jam signal is detected. When receiving data from the physical layer, the MAC block ensures data integrity by verifying the sender's frame check sequences, and strips off the sender's preamble and padding before passing the data up to the higher layers.

Functions performed in the MAC sublayer[edit]

According to IEEE Std 802-2001 section 6.2.3 'MAC sublayer', the primary functions performed by the MAC layer are:^[1]

Frame delimiting and recognition
Addressing of destination stations (both as individual stations and as groups of stations)
Conveyance of source-station addressing information
Transparent data transfer of LLC PDUs, or of equivalent information in the Ethernet sublayer
Protection against errors, generally by means of generating and checking frame check sequences
Control of access to the physical transmission medium

In the case of Ethernet, the functions required of a MAC are:^[2]

receive/transmit normal frames
half-duplex retransmission and backoff functions
append/check FCS (frame check sequence)
interframe gap enforcement
discard malformed frames
prepend(tx)/remove(rx) preamble, SFD (start frame delimiter), and padding
half-duplex compatibility: append(tx)/remove(rx) MAC address

Addressing mechanism[edit]

The local network addresses used in IEEE 802 networks and FDDI networks are called media access control addresses; they are based on the addressing scheme that was used in early Ethernet implementations. A MAC address is intended as a unique serial number. MAC addresses are typically assigned to network interface hardware at the time of manufacture. The most significant part of the address identifies the manufacturer, who assigns the remainder of the address, thus provide a potentially unique address. This makes it possible for frames to be delivered on a network link that interconnects hosts by some combination of repeaters, hubs, bridges and switches, but not by network layerrouters. Thus, for example, when an IP packet reaches its destination (sub)network, the destination IP address (a layer 3 or network layer concept) is resolved with the Address Resolution Protocol for IPv4, or by Neighbor Discovery Protocol (IPv6) into the MAC address (a layer 2 concept) of the destination host.

Examples of physical networks are Ethernet networks and Wi-Fi networks, both of which are IEEE 802 networks and use IEEE 802 48-bit MAC addresses.

A MAC layer is not required in full-duplexpoint-to-point communication, but address fields are included in some point-to-point protocols for compatibility reasons.

Channel access control mechanism[edit]

The channel access control mechanisms provided by the MAC layer are also known as a multiple access method. This makes it possible for several stations connected to the same physical medium to share it. Examples of shared physical media are bus networks, ring networks, hub networks, wireless networks and half-duplex point-to-point links. The multiple access method may detect or avoid data packet collisions if a packet mode contention based channel access method is used, or reserve resources to establish a logical channel if a circuit-switched or channelization-based channel access method is used. The channel access control mechanism relies on a physical layer multiplex scheme.

The most widespread multiple access method is the contention-based CSMA/CD used in Ethernet networks. This mechanism is only utilized within a network collision domain, for example an Ethernet bus network or a hub-based star topology network. An Ethernet network may be divided into several collision domains, interconnected by bridges and switches.

A multiple access method is not required in a switched full-duplex network, such as today's switched Ethernet networks, but is often available in the equipment for compatibility reasons.

Channel access control mechanism for concurrent transmission[edit]

Use of directional antennas and millimeter-wave communication in a wireless personal area network increases the probability of concurrent scheduling of non‐interfering transmissions in a localized area, which results in an immense increase in network throughput. However, the optimum scheduling of concurrent transmission is an NP-hard problem.^[3]

Cellular networks[edit]

Cellular networks, such as GSM, UMTS or LTE networks, also use a MAC layer. The MAC protocol in cellular networks is designed to maximize the utilization of the expensive licensed spectrum.^[4] The air interface of a cellular network is at layers 1 and 2 of the OSI model; at layer 2, it is divided into multiple protocol layers. In UMTS and LTE, those protocols are the Packet Data Convergence Protocol (PDCP), the Radio Link Control (RLC) protocol, and the MAC protocol. The base station has absolute control over the air interface and schedules the downlink access as well as the uplink access of all devices. The MAC protocol is specified by 3GPP in TS 25.321^[5] for UMTS, TS 36.321^[6] for LTE and TS 38.321^[7] for 5G New Radio (NR).

Containment Protocol Mac Os Download

References[edit]

^'IEEE 802-2001 (R2007) IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture'(PDF). IEEE.
^'4.1.4', IEEE 802.3-2002, IEEE
^Bilal, Muhammad; et al. (2014). 'Time‐Slotted Scheduling Schemes for Multi‐hop Concurrent Transmission in WPANs with Directional Antenna'. ETRI Journal. 36 (3): 374–384. arXiv:1801.06018. doi:10.4218/etrij.14.0113.0703.
^Guowang Miao; Jens Zander; Ki Won Sung; Ben Slimane (2016). Fundamentals of Mobile Data Networks. Cambridge University Press. ISBN978-1107143210.
^3GPP TS 25.321 Medium Access Control (MAC) protocol specification
^3GPP TS 36.321 Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification
^3GPP TS 38.321 NR; Medium Access Control (MAC) protocol specification

Retrieved from 'https://en.wikipedia.org/w/index.php?title=Medium_access_control&oldid=1001405903'

App Sandbox is an access control technology provided in macOS, enforced at the kernel level. It is designed to contain damage to the system and the user’s data if an app becomes compromised. Apps distributed through the Mac App Store must adopt App Sandbox. Apps signed and distributed outside of the Mac App Store with Developer ID can (and in most cases should) use App Sandbox as well.

At a Glance

Complex systems will always have vulnerabilities, and software complexity only increases over time. No matter how carefully you adopt secure coding practices and guard against bugs, attackers only need to get through your defenses once to succeed. While App Sandbox doesn’t prevent attacks against your app, it does minimize the harm a successful one can cause.

A non-sandboxed app has the full rights of the user who is running that app, and can access any resources that the user can access. If that app or any framework it is linked against contain security holes, an attacker can potentially exploit those holes to take control of that app, and in doing so, the attacker gains the ability to do anything that the user can do.

Designed to mitigate this problem, the App Sandbox strategy is twofold:

App Sandbox enables you to describe how your app interacts with the system. The system then grants your app the access it needs to get its job done, and no more.
App Sandbox allows the user to transparently grant your app additional access by way of Open and Save dialogs, drag and drop, and other familiar user interactions.

App Sandbox is not a silver bullet. Apps can still be compromised, and a compromised app can still do damage. But the scope of potential damage is severely limited when an app is restricted to the minimum set of privileges it needs to get its job done.

App Sandbox is Based on a Few Straightforward Principles

By limiting access to sensitive resources on a per-app basis, App Sandbox provides a last line of defense against the theft, corruption, or deletion of user data, or the hijacking of system hardware, if an attacker successfully exploits security holes in your app. For example, a sandboxed app must explicitly state its intent to use any of the following resources using entitlements:

Hardware (Camera, Microphone, USB, Printer)
Network Connections (Inbound or Outbound)
App Data (Calendar, Location, Contacts)
User Files (Downloads, Pictures, Music, Movies, User Selected Files)

Access to any resource not explicitly requested in the project definition is rejected by the system at run time. If you are writing a sketch app, for example, and you know your app will never need access to the microphone, you simply don’t ask for access, and the system knows to reject any attempt your (perhaps compromised) app makes to use it.

On the other hand, a sandboxed app has access to the specific resources you request, allows users to expand the sandbox by performing typical actions in the usual way (such as drag and drop), and can automatically perform many additional actions deemed safe, including:

Invoking Services from the Services menu
Reading most world readable system files
Opening files chosen by the user

The elements of App Sandbox are entitlements, container directories, user-determined permissions, privilege separation, and kernel enforcement. Working together, these prevent an app from accessing more of the system than is necessary to get its job done.

Relevant chapters:App Sandbox Quick Start, App Sandbox in Depth

Design Your Apps with App Sandbox in Mind

After you understand the basics, look at your app in light of this security technology. First, determine if your app is suitable for sandboxing. (Most apps are.) Then resolve any API incompatibilities and determine which entitlements you need. Finally, consider applying privilege separation to maximize the defensive value of App Sandbox.

Xcode Helps You Migrate an Existing App to App Sandbox

Some file system locations that your app uses are different when you adopt App Sandbox. In particular, you gain a container directory to be used for app support files, databases, caches, and other files apart from user documents. Xcode and macOS support migration of files from their legacy locations to your container.

Relevant chapter:Migrating an App to a Sandbox

Preflight Your App Before Distribution

After you have adopted App Sandbox in your app, as a last step each time you distribute it, double check that you are following best practices.

How to Use This Document

To get up and running with App Sandbox, perform the tutorial in App Sandbox Quick Start. Before sandboxing an app you intend to distribute, be sure you understand App Sandbox in Depth. When you’re ready to start sandboxing a new app, or to convert an existing app to adopt App Sandbox, read Designing for App Sandbox. If you’re providing a new, sandboxed version of your app to users already running a version that is not sandboxed, read Migrating an App to a Sandbox. Finally, before distributing your app, work through the App Sandbox Checklist to verify that you are following best practices for App Sandbox.

Prerequisites

Before you read this document, make sure you understand the overall macOS development process by reading Mac App Programming Guide.

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