overview

TELE202 Lecture 9 Internet Protocols (1) 1 Lecturer Dr Z. Huang

Overview

Last Lecture» Congestion control

» Source: chapter 12

This Lecture» Internet Protocols (1)


Next Lecture» Internet Protocols (2)



TCP/IP

Transmission Control ProtocolInternet ProtocolTCP/IP refers to an entire suite of

networking protocols, developed for use on the Internet

» TCP and IP are two of the most important

TCP/IP reference model

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OSI

Application

Presentation

Session

Transport

Network

Data link

Physical

Application

Transport

Internet

Host-to-network

TCP/IP

Not presentin the model


TCP/IP and Internet

Internet is different from ‘internet’A brief history

» 1969 ARPA funded ARPANET

» 1973 Ethernet (Bob Metcalfe’s PhD Thesis)

» 1977 packet switching funded by ARPA

» 1979 Internet Research Group for TCP/IP

» 1982/1983 TCP/IP as a core protocol

» 1983 BSD4.2 Unix with TCP/IP from UCB

» 1986 BSD4.3, performance improvements

» 1988 BSD4.3, slow start, congestion avoidance

» 1993 BSD4.4, multicasting

Size» 1969 - 4 sites

» 1981 - 200 sites

» 1996 - 100,000th network added in Internet

» 1997 - 16M computers



» How many computers in Internet today?

Internet Activities Board» Internet Engineering Task Force

» Internet Research Task Force

» Network Information Center

» RFC: technical reports on protocols


IP - Internet Protocol

Unreliable connectionless protocol» A datagram service

» Not guaranteed delivery

– best effort delivery

» Packets are not guaranteed to arrive in order or via the same route

– Packets may be duplicated

» Routing decisions may be made for each packet

» Reliability is the responsibility of next layer up (e.g. TCP)

Uses the packet-switching techniqueIP takes care of network differences

» Make sure IP packets can be transferred through different networks

» Use data link layer protocols, e.g. Ethernet, or other network layer protocols, e.g. X.25, as vehicles to transfer IP packets

» IP packets are encapsulated into data link layer frames or other network packets

Ethernet hdr IP packet


IP operation

The following figure illustrates how an IP packet is transferred from one LAN to another LAN through X.25


Interface with higher layer

Interface with higher layer, e.g. TCP» Functions to be performed

» Form of primitive implementation dependent

– e.g. subroutine call

» Send

– Request transmission of data unit

» Deliver

– Notify user of arrival of data unit

Parameters for send and deliver» Source address

» Destination address

» Protocol

» Type of service indicators

» Identification

» Don’t fragment identifier

» Time to live

» Data length

» Option data

» Data


IP packet format

Version (4 bits)» version of IP that created the packet

» Currently IPv4, shortly IPv6

Header length (4 bits)» number of 32-bit words in the packet header

» Minimum 5, maximum 15

Service type (3 bits)» allows the host to tell the subnet what kind of

service it desires (reliability and speed)

Total datagram length (16 bits)» length of the entire IP packet. Max 64KB.


IP packet fields

Identification, flags, fragment offset» used for breaking up a packet received from

the next higher layer protocol and reassembling it if the packet is too big

Time to live (8 bits)» Decremented by routers to prevent looping.

» Normally set to 30

» Packet is discarded when it reaches 0.

Protocol (8 bits)» Specifies the next higher protocol. Used at

destination to give data to appropriate entity.

» 6, to TCP; 17, to UDP; 1, to ICMP

Header checksum (16 bits)» Error correction for the packet header. IP

only worries about errors at its level.

Source and destination IP addresses » 32 bit fields for the addresses

Options» record route, timestamp, packet routing,

security

Padding» makes header end at a 32 bit boundary


IP packet fields

Data» data provided by higher layer.

» Integer multiple of 8 bits long (octet)

» Max length of an IP datagram (header plus data) 65,535 octets

Type of services» Precedence: 3 bits, 8 levels

» Reliability: 1 bit, normal or high

» Delay: 1 bit, normal or low

» Throughput: 1 bit, normal or high

Options» Security

– Attach a security label

» Source routing

– A sequence of router addresses specifying the route

» Route recording

– Record the sequence of routers visited

» Stream identification: reserve resources for real-time applications

» Timestamping:add a timestamp when goes by


Fragmentation

Different networks allow different maximum frame sizes.

» Maximum Transfer Unit (MTU).

» If IP receives a packet larger than the MTU of an underlying network, IP must break up the packet into fragments to transmit it.

The identification, flags, and fragment offset fields are used in this process

» Identification: packet’s identification value

» Flag field contains a more-fragments bit (mfb), indicating there are more fragments following

» Fragment offset field: offset of the fragment in the packet’s data field


Re-assembly

When to re-assemble» At destination

– Results in packets getting smaller as data traverses internet

» Intermediate re-assembly

– Need large buffers at routers

– Buffers may fill with fragments

– All fragments must go through same router, which inhibits dynamic routing

IP re-assembles at destination onlyDealing with failure

» Re-assembly may fail if some fragments get lost

» Need to detect failure

Re-assembly time out» Assigned to first fragment to arrive

» If timeout expires before all fragments arrive, discard partial data

Use time-to-live field of the first fragment as the packet life time

» Let the time-to-live field continue to decrement per second

» If time-to-live runs out, discard partial data


IP Addresses

An IP address has four bytes» Dotted decimal notion e.g.139.80.32.92

IP addresses are divided into classesClass A

» 0nnnnnnn xxxxxxxx xxxxxxxx xxxxxxxx

» 8-bit network address

» 24-bit node ID address

» 126 networks of 16 million hosts

Class B» 10nnnnnn nnnnnnnn xxxxxxxx xxxxxxxx



» 16,384 networks of 64K hosts

Class C» 110nnnnn nnnnnnnn nnnnnnnn xxxxxxxx



» 2 million networks of 254 hosts


IP Addresses

Class D is multicast address» 1110xxxx xxxxxxxx xxxxxxxx xxxxxxxx

Class E is reserved for future use» 11110xxx xxxxxxxx xxxxxxxx xxxxxxxx

Example: 139.80.32.92» Which class? Convert it into binary code:

– 10001101.01010000.00100000.01011100


Internet Domains and Names

IP domain» Hierarchical

» Domains are not geographical

» Domains can have subdomains

» Example: edu, com, org, gov, nz, co.nz

IP name» ws1.cs.mit.edu

» vax2.dunedin.xyz.co.nz

IP name is different from IP address!Examples

» mary.otago.ac.nz - 139.80.32.92

» microsoft.co.nz - 202.37.145.231

There is a mapping between IP name and IP address

Domain Name System (DNS)» Provide DNS servers to map an IP Name into

an IP address

» A distributed database for name-address pairs - no DNS server knows everything

» A hierarchical system distributed among DNS servers

Try ‘nslookup’ to get the IP address for a text name

» Example: nslookup atlas.otago.ac.nz


Summary

TCP/IP reference modelTCP/IP protocol suiteInternet Protocol

» Datagram service

» Packet switching

» Interface with higher layer

» IP packet format

» Fragmentation and re-assembly

» IP addresses and classes

» Internet domains and names

overview

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