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OSI layer

Layer	Name	Description
7	Application	e.g. HTTP, SMTP, SNMP, FTP, Telnet, SSH and Scp, NFS, RTSP etc.
6	Presentation	e.g. XDR, ASN.1, SMB, AFP etc
5	Session	e.g. TLS, SSH, ISO 8327 / CCITT X.225, RPC, NetBIOS, ASP etc.
4	Transport	e.g. TCP, UDP, RTP, SCTP, SPX, ATP etc.
3	Network	e.g. IP/IPv6, ICMP, IGMP, X.25, CLNP, ARP, RARP, BGP, OSPF, RIP, IPX, DDP etc
2	Data Link	e.g. Ethernet, Token ring, PPP, HDLC, Frame relay, ISDN, ATM, 802.11 Wi-Fi, FDDI etc
1	Physical	e.g. wire, radio, fiber optic etc.

TCP Performance measurement

Linux Kernel Networking	Linux Kernel Network Data Flow	Writing Netfilter modules
Network Advanced Socket Example