Ports and Their Multiplexing
 


Multiplexing and Demultiplexing using port numbers
Transport Layer protocols (TCP and UDP) are responsible for supporting multiple network applications at the same instance and these applications can send and receive network data simultaneously. Transport Layer Protocols are capable of doing this by making use of application level addressing, known as port numbers. The data from different applications operating on a network device are multiplexed at the sending device using port numbers and demultiplexed at the receiving device, again using port numbers.

TCP UDP Port Numbers
The two 16 bit fields in the TCP Header, Source port and Destination port identifies the port number which the application is listening at the sending device and receiving device. Since port number is a 16 bit number, the maximum possible value is 65535 ((2^16)-1).

The port numbers are divided into three ranges.

  • The Well Known Ports are those in the range 0 - 1023. The Well Known Ports are assigned by the IANA for major protocols.
  • The Registered Ports are those in the range 1024 - 49151.
  • The Private Ports are those in the range 49152 - 65535.

Port Number

Description

1

TCP Port Service Multiplexer (TCPMUX)

5

Remote Job Entry (RJE)

7

ECHO

18

Message Send Protocol (MSP)

20

FTP - Data

21

FTP - Control

22

SSH Remote Login Protocol

23

Telnet

25

Simple Mail Transfer Protocol (SMTP)

29

MSG ICP

37

Time

42

Host Name Server (Nameserv)

43

WhoIs

49

Login Host Protocol (Login)

53

Domain Name System (DNS)

69

Trivial File Transfer Protocol (TFTP)

70

Gopher Services

79

Finger

80

HTTP

103

X.400 Standard

108

SNA Gateway Access Server

109

POP2

110

POP3

115

Simple File Transfer Protocol (SFTP)

118

SQL Services

119

Newsgroup (NNTP)

137

NetBIOS Name Service

139

NetBIOS Datagram Service

143

Interim Mail Access Protocol (IMAP)

150

NetBIOS Session Service

156

SQL Server

161

SNMP

179

Border Gateway Protocol (BGP)

190

Gateway Access Control Protocol (GACP)

194

Internet Relay Chat (IRC)

197

Directory Location Service (DLS)

389

Lightweight Directory Access Protocol (LDAP)

396

Novell Netware over IP

443

HTTPS

444

Simple Network Paging Protocol (SNPP)

445

Microsoft-DS

458

Apple QuickTime

546

DHCP Client

547

DHCP Server

563

SNEWS

569

MSN

1080

Socks