Physical Layer

OSI Model
7 Application Layer
6 Presentation Layer
5 Session Layer
4 Transport Layer
3 Network Layer
2 Data Link Layer
1 Physical Layer
OSI model
7. Application Layer
NNTP  · SIP  · SSI  · DNS  · FTP  · Gopher  · HTTP  · NFS  · NTP  · SMPP  · SMTP  · DHCP  · SNMP  · Telnet  · Netconf  · (more)
6. Presentation Layer
MIME  · XDR  · TLS  · SSL
5. Session Layer
Named Pipes  · NetBIOS  · SAP  · L2TP  · PPTP
4. Transport Layer
TCP  · UDP  · SCTP  · DCCP
3. Network Layer
IP (IPv4, IPv6)  · ICMP  · IPsec  · IGMP  · IPX  · AppleTalk
2. Data Link Layer
ATM  · SDLC  · HDLC  · ARP  · CSLIP  · SLIP  · PLIP  · IEEE 802.3  · Frame Relay  · ITU-T G.hn DLL  · PPP  · X.25
1. Physical Layer
EIA/TIA-232  · EIA/TIA-449  · ITU-T V-Series  · I.430  · I.431  · POTS  · PDH  · SONET/SDH  · PON  · OTN  · DSL  · IEEE 802.3  · IEEE 802.11  · IEEE 802.15  · IEEE 802.16  · IEEE 1394  · ITU-T G.hn PHY  · USB  · Bluetooth

The Physical Layer is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY.

The Physical Layer consists of the basic hardware transmission technologies of a network. It is a fundamental layer underlying the logical data structures of the higher level functions in a network. Due to the plethora of available hardware technologies with widely varying characteristics, this is perhaps the most complex layer in the OSI architecture.

The Physical Layer defines the means of transmitting raw bits rather than logical data packets over a physical link connecting network nodes. The bit stream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a hardware transmission medium. The Physical Layer provides an electrical, mechanical, and procedural interface to the transmission medium. The shapes and properties of the electrical connectors, the frequencies to broadcast on, the modulation scheme to use and similar low-level parameters, are specified here.

Within the semantics of the OSI network architecture, the Physical Layer translates logical communications requests from the Data Link Layer into hardware-specific operations to affect transmission or reception of electronic signals.

Contents

Physical signaling sublayer

In a local area network (LAN) or a metropolitan area network (MAN) using open systems interconnection (OSI) architecture, the physical signaling sublayer is the portion of the Physical Layer that:

List of services

The major functions and services performed by the Physical Layer are:

The Physical Layer is also concerned with

List of protocols

Hardware equipment (network node) examples

Relation to TCP/IP model

The TCP/IP model, defined in RFC 1122 and RFC 1123, is a high-level networking description used for the Internet and similar networks. It does not define an equivalent layer that deals exclusively with hardware-level specifications and interfaces, as this model does not concern itself directly with physical interfaces. Several RFC:s mention the physical layer and data link layer, but that is in context of IEEE protocols. RFC 1122 and 1123 does not mention any physical layer functionality or physical layer standards. A common interpretation occurring in the literature is that physical layer standards are not considered as protocols, but are dealt with at a hardware layer below the four conceptual protocol layers of the original TCP/IP model, resulting in a five-layer TCP/IP model. Another common interpretation is that physical layer issues are absorbed into the TCP/IP model Link Layer.

See also

References

  1. ↑  This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
  2. ↑ Bersekas, Dimitri; Gallager, Robert (1992). Data Networks. Prentice Hall. p. 61. ISBN 0-13-200916-1. 

External links