On slower or congested links ( 622 Mbit / s and below ), ATM does make sense, and for this reason most asymmetric digital subscriber line ( ADSL ) systems use ATM as an intermediate layer between the physical link layer and a Layer 2 protocol like PPP or Ethernet.

Layer 2 Timeslot 16, 64Kbs operates as HDLC LAPB, to support up to 60 PVCs or DLCs ( data link connections ) ( 30 directly associated with the bearer channels and 30 for unrelated messages ) as the specification describes them.

The standard defines both the physical ( Layer 1 ) and data-link ( Layer 2 ) layers of the OSI model.

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* low bitrate encoding with halved sampling rate ( MPEG-1 Layer 1 / 2 / 3 LSF-a. k. a.

Once a match is found, the packet is encapsulated in the Layer 2 data link frame for that outgoing interface.

The most prominent example of a Layer 2 Meta-Object Facility model is the UML metamodel, the model that describes the UML itself.

* MPEG Layer 1, 2 and 3 ( Also known as MP3 ), using the mpg123 library

This distinction stems from the fact that common LAN technologies operating at Layer 1 / 2 ( such as the forms of Ethernet or Wifi ) are often geared towards physically localised networks, and thus cannot transmit data over tens, hundreds or even thousands of miles or kilometres.

As a WAN protocol, Frame Relay is most commonly implemented at Layer 2 ( data link layer ) of the Open Systems Interconnection ( OSI ) seven layer model.

CSMA / CA is a protocol that operates in the Data Link Layer ( Layer 2 ) of the OSI model.

* At the Data Link Layer: The IEEE 802. 2 protocol at the Logical Link Control sublayer of the data link layer may provide both connectionless and connection-oriented services.

In computer networking, a frame is a data packet on the Layer 2 of the OSI model.

Multicast addressing can be used in the Link Layer ( Layer 2 in the OSI model ), such as Ethernet multicast, and at the Internet Layer ( Layer 3 for OSI ) for Internet Protocol Version 4 ( IPv4 ) or Version 6 ( IPv6 ) multicast.

# The Layer 2 ( Data Link Layer ) PDU is the frame

* Layer 2, the data link layer:

Layer 2 switching is hardware based, which means switches use application-specific integrated circuit ( ASICs ) to build and maintain filter tables ( also known as MAC address tables ).

Layer 2 switching provides the following

While SDH is considered to be a transmission protocol ( Layer 1 in the OSI Reference Model ), it also performs some switching functions, as stated in the third bullet point requirement listed above.

Layer 2 switching is highly efficient because there is no modification to the data packet, only to the frame encapsulation of the packet, and only when the data packet is passing through dissimilar media ( such as from Ethernet to FDDI ).

Layer 2 switching is used for workgroup connectivity and network segmentation ( breaking up collision domains ).

Layer 2 switching has helped develop new components in the network infrastructure

Layer 3 switching is all hardware-based packet forwarding, and all packet forwarding is handled by hardware ASICs.

Layer 4 switching is considered a hardware-based layer 3 switching technology that can also consider the application used ( for example, Telnet or FTP ).

Layer 4 switching provides additional routing above layer 3 by using the port numbers found in the Transport layer header to make routing decisions.

Layer II can use a method called bit rate switching.

The major difference between the packet switching operation of a router and that of a Layer 3 switch is the physical implementation.

In general-purpose routers, packet switching takes place using software that runs on a microprocessor, whereas a Layer 3 switch performs this using dedicated application-specific integrated circuit ( ASIC ) hardware.

According to Cisco, Layer 3 switches are basically routers that switch based on Layer 3 information, the basic difference being processing speed and / or the way they do the switching ; Layer 3 switches use ASICs / hardware instead of the CPU / software that a router would.

Layer 7 switching is the base technology of a content delivery network.

The service being carried over the " wire " may be Asynchronous Transfer Mode ( ATM ), Frame Relay, Ethernet or Time-division multiplexing ( TDM ) while the packet network may be Multi-protocol label switching ( MPLS ), Internet Protocol ( IPv4 or IPv6 ), or Layer 2 Tunneling Protocol Version 3 ( L2TPv3 ).

VTP uses Layer 2 trunk frames to manage the addition, deletion, and renaming of VLANs on a network-wide basis from a centralized switch in the VTP server mode.

The DAB standard uses the MPEG-1 Audio Layer II ( ISO / IEC 11172-3 ) for 48 kHz sampling frequency and the MPEG-2 Audio Layer II ( ISO / IEC 13818-3 ) for 24 kHz sampling frequency.

The Layer III ( MP3 ) component uses a lossy compression algorithm that was designed to greatly reduce the amount of data required to represent an audio recording and sound like a decent reproduction of the original uncompressed audio for most listeners.

Any application that supports the Secure Socket Layer ( SSL ) can make use of certificates signed by CAcert, as can any application that uses X. 509 certificates, e. g. for encryption or code signing and document signatures.

Included with the eCos distribution is RedBoot, an open source application that uses the eCos Hardware Abstraction Layer to provide bootstrap firmware for embedded systems.

The original Frozen Bubble was written in Perl by Guillaume Cottenceau, and uses the Simple DirectMedia Layer ( SDL ) library.

The first generation DAB uses the MPEG-1 Audio Layer II ( MP2 ) audio codec which has less efficient compression than newer codecs.

EAP-Transport Layer Security ( EAP-TLS ), defined in RFC 5216, is an IETF open standard that uses the Transport Layer Security ( TLS ) protocol, and is well-supported among wireless vendors.

Secure Sockets Layer ( SSL ) uses Diffie-Hellman key exchange if the client does not have a public-private key pair and a published certificate in the Public Key Infrastructure, and Public Key Cryptography if the user does have both the keys and the credential.

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It is written in the C programming language and uses various free and open source helper libraries, including the Simple DirectMedia Layer ( SDL ), and has since been made available for Microsoft Windows, Apple Mac OS X, BeOS and other platforms.

RedBoot ( an acronym for Red Hat Embedded Debug and Bootstrap firmware ) is an open source application that uses the eCos real-time operating system Hardware Abstraction Layer to provide bootstrap firmware for embedded systems.