Communications

Link Layer

Network Layer

Transport Layer

Application Layer

For transporting Protocol Data Units (PDUs) inside local networks

Important protocols: Ethernet, 802.3, 802.11 (WLAN), PPP

For transporting PDUs between local networks

Important protocols: IP, ARP, ICMP, IGMP

Provides end-to-end transfer of PDUs between applications residing on end systems, possibly in a reliable way

Important protocols: TCP, UDP, SCTP

Contains protocols for providing network services to applications/users and for managing network communication through applications

Important protocols: HTTP, DNS, DHCP, SMTP, SNMP, SIP, RTP, …

each network device is responsible for own implementation

network services are independent from end system

A network device implements only a subset of the TCP/IP stack and specific protocols necessary for forwarding PDUs

End systems (hosts) implement the complete TCP/IP stack, but only those protocols that are necessary for end-to-end data transpor

Implement link layer only, forward frames between end systems in the same network

implement link and network layer, forward packets in the direction of the destination network, employ routing protocols to find the “best” way

Send or Receive possible, but not at the same time

Typically due to usage of shared medium

Medium access protocol necessary

Send and Receive possible, at the same time

Requires dedicated bidirectional links between devices

Requires switches for linking more than two systems