Data Link Layer

WAN is a network that covers a broad geographic area, which often uses service providers’ (SP) transmission facilities and operates on Physical Layer#, Data Link Layer# and Network Layer# to connect several #Local-Area Network (LAN). Several network devices could operate within WAN such as Switch# (at data link layer) and Router#.

In VLAN Trunking, a tag will assign to the frame to indicate their #Virtual LAN (VLAN) belonging which is handled by either a switch or a router. After the frame passed through a trunk link, the tag will be removed from the packet when it reaches the destination node or non-trunk link, usually a switch.

SONET is a #Physical Layer #optical technology that supports from 155 Mbps up to 10 Gbps high transmission rates for Metropolitan Area Network (MAN) using #Time-Division Multiplexing (TDM) multiplexing scheme. It provides means of transportation to Data Link Layer# protocols and of conversion using Fibre-Optic Transmission Systems (FOTS), which is a Modulator. It has extensive OAMP (operation, administrative, maintenance and provisioning) capabilities. This allows precise fault detection and a rapid (50 ms) failover (switching to a redundant or standby computer server, system, hardware component or network upon the failure or abnormal termination of the previously active application). Its speed is range from 51.84 Mbps (OC-1) to 9953.28 Mbps (OC-192).

Switch is a #Network Device that can operates in either Data Link Layer# or Network Layer# (modern implementation). It is an intelligence Bridge, which provide superior throughput performance, more ports (lower per-port cost), high-speed connections, segmentation using Virtual LAN (VLAN)# or Broadcast Domain# (modern), and even routing (in the case of Multilayer Switch). This makes large-scale segmentation possible within the [Local-Area Network (LAN)](202207051554)❌.

STP is a #202206131651 protocol designed to run on 202207051851# and 202207051907# in order to prevent #202207081644 inside the network. It has been standardised by the Institute of Electrical and Electronic Engineers (IEEE) with 802.1d.

Physical layer is the first in #Open Systems Interconnection (OSI) Model. In #Internet Protocol Suite (TCP/IP), it is treated as Link Layer together with Data Link Layer. It is responsible to convert a frame into bits, which is its Protocol Data Units (PDU)#, to be transmitted over the networks. It has a mean to validate whether a data is corrupted.

The following devices operate at Data Link Layer# :

Network Access Protocols are the Protocol# that have two primary functions: communication over Data Link Layer# and transmission of data on the network media over Physical Layer#.

MPLS is a Data Link Layer# #Wide Area Network (WAN) backbone technology that delivers WAN and MAN services. It is one of the alternative to replace the legacy Frame Relay, Asynchronous Transfer Mode (ATM) and Point-to-Point/Leased Line as it can provide their functionalities in a multiservice form. Though it can be used to aggregate and transport Frame Relay, ATM, and IP-based traffic, the former two could be done using Any Transport over MPLS (AToM) technology. It also provides the Virtual Private Network (VPN)# technology.

Link Encryption occurs independently on every link, which could be done at Physical Layer# or Data Link Layer#. This means that the devices should encrypt and decrypt the traffic using paired keys. It encrypts not only the user data but also the header, routing information and destination address, which harden the internal communication channel from monitoring and eavesdropping. Thus, it is recommended as a solution to traffic flow protection#

ISDN is a set of technologies developed to carry voice, video and data across Public Switched Telephone Network (PSTN) by existing telephone lines. It utilises #Circuit Switching and primarily operates at Physical Layer#, Data Link Layer# and Network Layer#. ISDN offers bandwidth from 128kbps up to 384kbps. It was the first #broadband service deployed in the home but nowadays, it has been outshone by Digital Subscriber Line (DSL) and Cable Modem.

The integrity checking of IPv6 is done by checksum and High-Level Data Link Control protocol (HDLC, which operate at Data Link Layer).

IEEE 802.1Q is an efficient #VLAN Trunking technique introduced by Institute of Electrical and Electronic Engineers (IEEE)#. It only inserts 4 bytes to the Ethernet# frame.

Frame Relay is a #packet-switched Wide Area Network (WAN) service that operate at the Physical Layer# (EIA/TIA-232 specification is the standard) and Data Link Layer#. Its speed usually ranges from 56 kbps to 2Mbps, and it provides connection-oriented services using virtual circuits. Recently, it’s been viewed as obsolete because of the wide adoption of Dense Leased Line (DLL).

Ethernet is a system that links the computers within a local area which consists of #hardware (e.g. network interface card), software, and cabling for the connections. Computers are attached to the Ethernet with a shared #data link. It supports network speed ranging from 10Mbps to 10Gbps. It is the most dominated protocol for the #Local-Area Network (LAN) communication.

DLPI is a SRV4 Unix interface that provides access to the Data Link Layer#.

CDP is a #Data Link Layer Cisco proprietary tool used to gather information about other directly connected Cisco network devices. However, it is recommended to disable CDP by no cdp run for the entire device or no cdp enable for one particular interface.

CSMA/CD is an #202207051550 protocol aimed to resolve collisions between computers when sharing the #data link. It defines how a computer should listen to the network before transmitting. The computer can transmit the data if the network is quiet. Otherwise, the computer will back off from the collisions (they will be detected by the protocol) and try to retransmit that data with a random timer.

Bridge is a #202207051821 operates at 202206131651# which provides the ability to split the #202207051805 into smaller ones, controls data flow, handles transmission error and enables access to physical device.

BPF is a BSD Unix interface that provides access to the Data Link Layer#

ATM is a Wide Area Network (WAN) technology that support both #Packet Switching and #Circuit Switching functionalities. It operates at #Data Link Layer. The basic components in an ATM network are ATM switches#, which is responsible for moving cells through the network, and ATM endpoints, such as workstations, Router, data service units (DSU) etc.