The Internet

The present Internet is actually a collection of sub-networks, or a 'network of networks', interconnected through 'routers' by a high-speed mesh topology backbone. The networks of the Internet are managed by Network Service Providers (NSP) and Internet Service Providers (ISP). Large NSPs build national or global networks and sell bandwidth to regional NSPs, who in turn resell bandwidth to local ISPs, who in their turn provide services to the users. The sub-networks are connected to each other at Internet exchanges, known as network access points. A network access point is usually an Asynchronous Transfer Mode (ATM) or a gigabit Ethernet switch surrounded by routers. The switches are interconnected in a fully meshed fashion by permanent virtual circuits running over high-speed dense wavelength division multiplexed fiber links. The network access point facilities are hired by the NSPs to install their own routers to exchange traffic coming from the ISPs. Further, many NSPs may establish

Application layer

Host config BOOTP DHCP

Name server DNS

File sharing NFS

Signaling

Network management

SNMP RMON

File transfer FTP TFTP

Interactive real time voice video

Interactive non-real time

Telnet IRC

SIP H.323

Security

Diameter, RADIUS

Gopher

HTTP Gopher

HTTP Gopher

Transport layer

File sharing NFS

SNMP RMON

Telnet IRC

Transmission control protocol

TCP

UDP

IP support protocols

IP routing protocols

Address resolution protocol

Network layer

Internet protocol IPv4, IPv6

IPsec

IP NAT

mobileIP

IP support protocols

ICMPv4/ ICMPv6

Neighbor discovery (ND)

IP routing protocols

RIP OSPF BGP EGP

Address resolution protocol

ARP RARP

Link/ network interface layer

PPP SLIP SDLC IEEE 802.2 RLC X.25 ATM UMTS 3GPP LTE/SAE IEEE802.3X IEEE802.11 ISDN SMDS FDDI SONET/SDH T-carrier E-carrier XDSL DOCSIS UTP

Figure 3.3: The TCP/IP protocol architecture.

private peering arrangements as well, bypassing the switches. The users avail the services of the Internet by connecting through a variety of connections ranging from low bit rate dial-up connection, broadband DSL, LAN, wireless LAN, etc., provided by the ISPs, who also provide such services to the users as Internet transit, domain name, registration and hosting, etc. The ISPs provide the required customer premises equipment and often some additional functionality such as security software, etc. Through the access links, customer premises equipment attaches to the point of presence or to the 'edge of the ISP network', a physical location that houses servers, routers, switches, etc.

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