Physical transmission medium lies in which layer of OSI reference model?

Open Systems Interconnection model - OSI model defines a networking framework to implement protocols in seven layers. OSI MODEL is conceptual model and it doesn't perform any functions in the networking process.
   

OSI Model Layer
Layer		Data unit	Function	Examples
Host layers	7.  Application	Data	High-level APIs , including resource sharing, remote file access, directory services and virtual terminals	HTTP , FTP , SMTP , SSH , TELNET
	6.  Presentation		Translation of data between a networking service and an application; including character encoding , data compression and encryption/decryption	HTML , CSS , GIF
	5. Session		Managing communication sessions, i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes	RPC,PAP,SSL,SQL
	4. Transport	Segments/Datagram	Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing	TCP, UDP, NETBEUI
Media layers	3. Network	Packet	Structuring and managing a multi-node network, including addressing, routing and traffic control	IPv4, IPv6, IPsec,AppleTalk, ICMP
	2. Data link	Frame	Reliable transmission of data frames between two nodes connected by a physical layer	PPP , IEEE 802.2 , L2TP , MAC , LLDP
	1. Physical	Bit	Transmission and reception of raw bit streams over a physical medium	Ethernet physical layer , DSL , USB , ISDN , DOCSIS

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