Transcript TCP - Department of Computer Engineering

Transport Layer Protocols –
UDP and TCP
Asst. Prof. Chaiporn Jaikaeo, Ph.D.
[email protected]
http://www.cpe.ku.ac.th/~cpj
Computer Engineering Department
Kasetsart University, Bangkok, Thailand
Adapted from the notes by Lami Kaya and lecture slides from Anan Phonphoem
© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.
© The McGraw-Hill Companies, Inc.
Outline
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Transport Layer
User Datagram Protocol (UDP)
Transmission Control Protocol (TCP)
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TCP/IP protocol Suite
Application
Application
Transport
Transport
Network
Network
Network
Data Link
Data
Data
Data Link
Physical
Phy
Phy
Physical
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Issues in Network Layer
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No/Little error detection
No attempt to correct
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Retransmission
Point-to-point (connectionless)
No handshaking
No verification
No flow control
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Transport Protocol
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Set of rules
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for exchange control message / data
End-to-End
Application may by-pass Transport Layer
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build functions on top of IP
reduce overhead
application run on switch/router that has no
Transport Layer
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Transport Protocols
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User Datagram Protocol (UDP)
Transmission Control Protocol (TCP)
Stream Control Transmission Protocol (SCTP)
Real-Time Transport Protocol (RTP)
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Ports and Addresses
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IP address is the end point of identifier
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On same machine (same IP)
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source / destination
needs identifier for each application
multiple applications (e.g. 3 ftp sessions)
“Port”
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16-bit number (65,356 ports) for each IP
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Ports and Addresses
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Unique connection identifier
[source IP] + [source port]
+ [dest. IP] + [dest. port]
Web #1 [Src 3.5.10.7:3213, Dst 158.108.1.2:80]
Web #2 [Src 57.2.1.9:4121, Dst 158.108.1.2:80]
Ftp [Src 1.2.1.1:9785, Dst 158.108.1.2:21]
IP address: 158.108.1.2
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Ports and Addresses
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Known destination IP
Concern Issues
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destination port ?
listen port ?
IANA* divides ports into three ranges
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well-known ports
registered ports
dynamic / private ports
*IANA – The Internet Assigned Numbers Authority
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Well-known ports
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0 – 1023
Used by server applications
Use with restricted privileges (root)
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Registered Ports
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1024 – 49,151
Assigned by IANA
Used for server applications
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Allow client to make contact
Can be used by ordinary users
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Dynamic / Private ports
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49,152 – 65,535
Ephemeral (temporary) ports
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as-needed basis
freed up when done
Assigned by local machines
Cannot be registered with IANA
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Connection-Oriented Transport
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Advantages
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Disadvantages
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easy to communicate (if receiver is there!)
verify the real receiver
establish connection
agree on some protocols
transfer data
error correction
tear down connection
heavier-weight protocol
sophisticated implementation (keep state)
consume high bandwidth for management
TCP – Transmission Control Protocol
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Connectionless Transport
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Datagram approach
Advantages
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rapid data transfer
no connection setup
no need for connection maintenances
Disadvantages
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transfer data
not reliable (losses are expected)
out of order packets
application more complex (takes precautions)
UDP – User Datagram Protocol
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Outline
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Transport Layer
User Datagram Protocol (UDP)
Transmission Control Protocol (TCP)
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User Datagram Protocol (UDP)
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Characteristics
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No error detection/recovery
No flow control
No checking for existing of destination
Simple services
Very useful protocol
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UDP Basic Functions
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Provides basic functions above raw IP
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Port addressing – to specific application
Data integrity verification – checksum
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UDP Message Format
Total length = UDP header+ Payload ≤ 216 bytes
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UDP Message Fragmentation
UDP Header
DataData
Transport Layer
IP Layer
IP Header
Payload
IP Header
Data
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Protocols that use UDP
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TFTP (trivial FTP)
BOOTP (for diskless station)
Network Time Protocol (NTP)
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Network File System (NFS)
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need basic delivery and checksum
need low overhead
Many multimedia applications
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need low latency
losses are acceptable
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Outline
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Transport Layer
User Datagram Protocol (UDP)
Transmission Control Protocol (TCP)
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Transmission Control Protocol (TCP)
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Most popular/important in Internet
Reliable transport protocol
Connection-oriented
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need connection establishment
[IP+source port]  [IP+destination port]
guarantee error-free / in-order delivery
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TCP Messages (Segment)
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Making connection
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Application on server
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Client
Server
passive receive mode
listening by issue Listen request to socket
locally
Application on Client
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request to socket API locally with
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destination IP
destination port
(source port: if not specify, TCP assigns private
port)
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TCP Connection Establishment
Internet
Server
Application
Client
TCP stack
TCP stack
Passive Open
Application
Active Open
Open Req
Open Ready
Open Ready
3-way Handshake
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TCP Segments
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Segment size
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at source node = MTU local link
fit in IP packet
may be fragmented along the way
TCP Header
Data
Transport Layer
IP Layer
IP Header
Payload
IP Header
Data
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Data Transmission (I)
Internet
Server
Application
TCP stack
Client
TCP stack
Application
Send Req.
1500 bytes
Seq. 1 ; length 1000
Ack 1001
Seq. 1001 ; length 500 Push
Ack 1501
Rec. 1000 bytes
Rec. 500 bytes
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Flow Control
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A process of managing rate of data
transmission between two devices
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Make sure fast sender does not overwhelm slow
receiver
Take this
Take this
Take this
:
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I'm running
out of buffer!
TCP uses Windowing Flow Control
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TCP Window Control
Send Buffer
Recv. Buffer
Win
Win
Win
Win
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Closing Connection (By either end)
Internet
Server
Application
TCP stack
Data
Last Data Segment
Client
TCP stack
Ack
1 byte
Close req (Empty Data) Fin Flag; Seq.= n + 1
Close
Application
Data
Close
Fin Flag; Ack = n+2; Seq.= m + 1
Ack = m + 2
Close Resp
3-way Handshake
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Protocols that use TCP
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File Transfer Protocol (FTP)
Hypertext Transfer Protocol (HTTP)
Simple Mail Transfer Protocol (SMTP)
Post Office Protocol (POP3)
Telnet
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Choosing between TCP and UDP
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TCP
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reliable transport services
UDP
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non-reliable transport services
only delivery data to specific port
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Summary
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Transport Layer
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User Datagram Protocol (UDP)
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port & IP address
packet format (8-byte header)
functions
Transmission Control Protocol (TCP)
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packet format ( 20-byte header)
connection establishment / tear down
window control
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