Transport Layer How TCP, UDP, and Ports fit into IP Layer 4: the - - PowerPoint PPT Presentation

Transport Layer

How TCP, UDP, and Ports fit into IP

Layer 4: the Transport Layer

Responsibilities and Services

Overall: message delivery “End-to-end" communications between

processes (i.e. running programs)‏

− Communicating processes may be on widely-

separated network hosts, or on the same computer

Connection-oriented or Connectionless

service

Reliable transport using checksums Flow control (so hosts aren't overwhelmed)‏

Identifying the End Processes

Processes run on hosts that have IP

addresses

Each (networking) process on the host is

assigned a port

Combination of IP address and Port is

called a network socket

− Processes on the Internet are uniquely

identified by their network sockets

Network sockets are an implementation of

OSI-model's Service Access Points

Well-Known and Other Ports

Some ports are assigned to specific

applications by common agreement

− Ports, Protocol numbers, IP addresses, etc.

were originally maintained by Jon Postel, and reported in "RFC" documents – RFC1700, October 1994, was the last

Goodbye, RFC 1700. Hello, IANA!

− The Internet Assigned Numbers Authority now

assigns and registers numbers in a database

Well-known ports: 1-1023 IANA Registered ports: 1024-49151

A Sampling of Port Numbers

• As of March 19, 2009
• IANA-assigned ("Well-Known") ports:

ftp-data 20/tcp File Transfer [Default Data] ftp-data 20/udp File Transfer [Default Data] ftp 21/tcp File Transfer [Control] ftp 21/udp File Transfer [Control] ssh 22/tcp SSH Remote Login Protocol ssh 22/udp SSH Remote Login Protocol smtp 25/tcp Simple Mail Transfer smtp 25/udp Simple Mail Transfer http 80/tcp World Wide Web HTTP http 80/udp World Wide Web HTTP newacct 100/tcp [unauthorized use] bgp 179/tcp Border Gateway Protocol bgp 179/udp Border Gateway Protocol netware-ip 396/tcp Novell Netware over IP netware-ip 396/udp Novell Netware over IP https 443/tcp http protocol over TLS/SSL https 443/udp http protocol over TLS/SSL philips-vc 583/tcp Philips Video-Conferencing philips-vc 583/udp Philips Video-Conferencing soap-beep 605/tcp SOAP over BEEP soap-beep 605/udp SOAP over BEEP rsync 873/tcp

rsync

rsync 873/udp

rsync

1023/tcp Reserved 1023/udp Reserved

• Registered ports:

– Over 9000 ports have been registered… remote-as 1053/tcp Remote Assistant (RA)‏ remote-as 1053/udp Remote Assistant (RA) estamp 1982/tcp Evidentiary Timestamp estamp 1982/udp Evidentiary Timestamp xbox 3074/tcp Xbox game port xbox 3074/udp Xbox game port ipfltbcst 4068/tcp IP Fleet Broadcast ipfltbcst 4068/udp IP Fleet Broadcast

# Trung Huu Tran <trung.tran&navy.mil> March 2007

freeciv 5556/tcp Freeciv gameplay freeciv 5556/udp Freeciv gameplay asr 7800/tcp Apple Software Restore asr 7800/udp Apple Software Restore gamesmith-port 31765/tcp GameSmith Port gamesmith-port 31765/udp GameSmith Port

• Dynamic and/or Private ports:

– The Dynamic and/or Private Ports are those from 49152 through 65535 – The registered ports can also be used as dynamic ports, as long as the communicating hosts aren't using a conflicting registered service

Transport-Protocol Data Units

TCP/IP: primary protocols are UDP, TCP

− SCTP, UDP-Lite are newer protocols − IP headers (layer 3) include information about

the TCP/UDP (layer-4) PDUs

User Datagram Protocol: individual

datagrams without guaranteed delivery

Transport Control Protocol: divides

application data streams into segments based on lower layer constraints

− E.g., no more than 1448 application-data bytes

per Ethernet frame

Transport Layer and Network Layer

Layer 3, the Network layer, routes the data

across the Internet

− IP is the most common layer-3 protocol − Novell's IPX is another

IP packets consist of header fields that do

the layer-3 work, and a payload

Payload can be

− a layer-3 management packet − a layer-4 packet

(Transport Protocol Data Unit or T-PDU)

the IP header

IHL field specifies header length

(in 32-bit words)‏

− Optional fields – 32 bits per field –

are seldom used

Total-Length field specifies

datagram's length

Protocol field specifies payload

type

Transport-layer Protocol Headers

IP's total length, minus IHL (IP header

length), determines payload (T-PDU) size

− UDP includes its own length field − TCP length depends on IP total length

UDP – User Datagram Protocol

Connectionless transport Four 2-byte fields in header

− Source port, Destination port; length and

checksum of header, payload, & some IP fields

0 – 65528 bytes of payload

Some Applications Using UDP

Source:

www.tcpipguide.com/free/t_UDPCommonA pplicationsandServerPortAssignments- 3.htm

TCP – Transport Control Protocol

Connection-oriented transport 3-way handshake uses SYN, ACK flags to

negotiate a comm's channel

Sequence, acknowledgment numbers

allow long payloads to be split into segments

TCP – the 3-way Handshake

• “SYN” and “ACK” flags

−

These flags are fields within the TCP header. A TCP packet may contain a payload as well as the flags, or may carry only the flags and no payload.

• First: SYN – Synchronize flag

−

The “caller” sends a packet that requests a connection.

−

Details such as maximum packet size are included.

−

No payload, header fields only.

• Second: SYN-ACK – SYN flag and Acknowledge flags, combined

−

The “recipient” (generally a server) sends a single packet containing an ACK of the SYN, along with a SYN of its own.

−

No payload in this packet either.

• Third: ACK – "caller" acknowledges the returned SYN

−

The “caller” acknowledges the server's SYN with an ACK. The handshake is completed.

−

There could be a payload in this packet, but often there isn't any.

Some Applications Using TCP

Source: www.tcpipguide.com/free/t_UDPCommonApplicationsandServerPortAssignments-3.htm

Some Protocols that Aren't Transport-Layer

• ICMP – Echo request, reply (Ping)‏
• ARP – request, reply

end of Network Layer Protocols