Matakuliah
Tahun
Versi
: H0174/Jaringan Komputer
: 2006
: 1/0
Pertemuan 23
Layer Transport
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan fungsi Transport Layer
2
Outline Materi
• TCP
• UDP
3
Transport layer duties
4
Addressing
• TCP uses the concept of source and destination port
numbers which uniquely identify a particular
communicating process on a host.
• Port numbers
• Well known port numbers (defined by IANA)
• Server applications run by privileged users to
communicate on these ports (0 – 1023)
 Registered ports (1024 - 49151)
 Administratively assigned to some specific
applications.
 Private ports/Ephemereal (49152 - 65535)
 application associated with them. Used by
applications that are ephemeral in nature
5
Well-Known Port Addresses
•
•
•
•
•
Port 80 – HTTP (web server)
Port 25 – SMTP (mail server)
Port 23 – Telnet
Port 22 – SSH
Port 110 – POP3
6
IP Addresses vs Port Numbers
7
Application Addressing
• Target user specified by User identification called
socket in TCP/IP
• Consist of usually IP address (host), port
• Port represents a particular transport service
(TS) user
– Transport entity identification
• Generally only one per host
• If more than one, then usually one of each
type
– Specify transport protocol (TCP, UDP)
– Host address
• An attached network device
• In an internet, a global internet address
8
Socket address
9
Multiplexing
• Multiple users employ same transport
protocol
• User identified by port number or service
access point (SAP)
• May also multiplex with respect to network
services used
10
Transport Layer Protocol
• Transmission Control Protocol
– Connection oriented
– RFC 793
• User Datagram Protocol (UDP)
– Connectionless
– RFC 768
11
Types of data deliveries
The transport layer is responsible for processto-process delivery
12
TCP segment format
13
TCP Services
• Reliable communication between pairs of processes
• Across variety of reliable and unreliable networks
and internets
• Two labeling facilities
– Data stream push
• TCP user can require transmission of all data
up to push flag
• Receiver will deliver in same manner
• Avoids waiting for full buffers
– Urgent data signal
• Indicates urgent data is upcoming in stream
• User decides how to handle it
14
TCP Mechanisms
• Connection establishment
– Three way handshake
– Between pairs of ports
– One port can connect to multiple
destinations
15
Connection Establishment
16
TCP Mechanisms
• The bytes of data being transferred in each connection
are numbered by TCP. The numbering starts with a
randomly generated number
• The value of the sequence number field in a segment
defines the number of the first data byte contained in
that segment
• The value of the acknowledgment field in a segment
defines the number of the next byte a party expects to
receive
• The acknowledgment number is cumulative.
• Data transfer
– Logical stream of octets, Octets numbered modulo
223
– Flow control by credit allocation of number of octets
– Data buffered at transmitter and receiver
17
UDP
• UDP is a connectionless, unreliable protocol that
has no flow and error control
• It uses port numbers to multiplex data from the
application layer (e.g. network management)
• Delivery and duplication control not guaranteed
• Reduced overhead
• UDP is a convenient transport-layer protocol for
applications that provide flow and error control. It
is also used by multimedia applications
18
User datagram format
The calculation of checksum and its inclusion in the user
datagram are optional
19
Matakuliah
Tahun
Versi
: H0174/Jaringan Komputer
: 2006
: 1/0
Pertemuan 24
Layer Application
20
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan peran Application Layer
21
Outline Materi
• SMTP
• HTTP
22
Electronic Mail
• Most heavily used application on any network
• Simple Mail Transfer Protocol (SMTP)
– TCP/IP
– Delivery of simple text messages
• Multi-purpose Internet Mail Extension (MIME)
– Delivery of other types of data
– Voice, images, video clips
23
SMTP
• RFC 821
• Not concerned with format of messages or data
– Covered in RFC 822 (see later)
• SMTP uses info written on envelope of mail
– Message header
• Does not look at contents
– Message body
• Except:
– Standardize message character set to 7 bit ASCII
– Add log info to start of message
• Shows path taken
24
Basic Operation
• Mail created by user agent program (mail client)
– Message consists of:
• Header containing recipient’s address and
other info
• Body containing user data
• Messages queued and sent as input to SMTP sender
program
– Typically a server process (daemon on UNIX)
25
SMTP Sender
• Takes message from queue
• Transmits to proper destination host
– Via SMTP transaction
– Over one or more TCP connections to port 25
• Host may have multiple senders active
• Host should be able to create receivers on demand
• When delivery complete, sender deletes destination
from list for that message
• When all destinations processed, message is deleted
26
SMTP Receiver
• Accepts arriving message
• Places in user mailbox or copies to outgoing queue
for forwarding
• Receiver must:
– Verify local mail destinations
– Deal with errors
• Transmission
• Lack of disk space
• Sender responsible for message until receiver
confirm complete transfer
– Indicates mail has arrived at host, not user
27
SMTP Mail Flow
28
Text Messages RFC 882
• Message viewed as having envelope and contents
• Envelope contains information required to transmit
and deliver message
• Message is sequence of lines of text
– Uses general memo framework
– Header usually keyword followed by colon
followed by arguments
29
MIME
• Multipurpose Internet Mail Extension (MIME) Extension to
RFC822
• SMTP can not transmit executables
• Can not transmit text including international characters
(e.g. â, å, ä, è, é, ê, ë)
– Need 8 bit ASCII
• Servers may reject mail over certain size
• Translation between ASCII and EBCDIC not standard
• SMTP gateways to X.400 can not handle none text data in
X.400 messages
• Some SMTP implementations do not adhere to standard
– CRLF, truncate or wrap long lines, removal of white
space, etc.
30
Overview of MIME
• Five new message header fields
– MIME version
– Content type
– Content transfer encoding
– Content Id
– Content Description
• Number of content formats defines
• Transfer encoding defined
31
HTTP
• Hypertext Transfer Protocol
• Underlying protocol of the World Wide Web
• Not a protocol for transferring hypertext
– For transmitting information with efficiency
necessary for hypertext jumps
• Can transfer plain text, hypertext, audio,
images, and Internet accessible information
32
HTTP Overview
• Transaction oriented client/server protocol
• Usually between Web browser (clinet) and Web
server
• Uses TCP connections
• Stateless
– Each transaction treated independently
– Each new TCP connection for each transaction
– Terminate connection when transaction complete
33
Headers
HTTP uses the services of TCP on well-known port 80
34
Retrieve Image
35
Distributed services
36
Browser architecture
37
Categories of Web documents
38
Static document
39
Dynamic document
40
Active document
41