Transcript Χωρίς τίτλο διαφάνειας

TCP/IP Networks
Table of Contents
• Computer networks, layers, protocols, interfaces;
• OSI reference model;
• TCP/IP reference model;
• Internet Protocol (operations, addresses, classes);
• Routing;
• Transmission Control Protocol (TCP);
• User Datagram Protocol (UDP);
• Applications;
• Sockets.
Computer Networks
•Hosts;
•Routers - Gateways;
•Bridges - Repeaters;
•Data packets networks, ISDN, leased lines;
Computer networks classification
NETW ORK CHARACTERIS TICS
LAN's
C a m p u s O ffic e
S iz e
1 0 Mb p s -1 0 0 Mb p s
S pe e d
To p o lo g y S h a re d m e d ia
Shared media:
MAN's
C ity , To wn
1 0 0 Mb p s
S h a re d m e d ia
W AN's
C o u n ty , C o u n try
1 Mb p s , (4 5 Mb p s S MDS )
mes h
Workstation
Workstation
Workstation
Workstation
Workstation
Token-ring
Workstation
Workstation
Workstation
Bus
Ring
Backbone network Vs local access network
Switching Techniques
• Circuit switching;
• Message switching;
• Packet switching.
Protocol Hierarchies
Host A
Layer 5
Layer 4/5 interface
Layer 4
Layer 3/4 interface
Layer 3
Layer 2/3 interface
Layer 2
Layer 1/2 interface
Layer 1
Host A
Layer 5 protocol
Layer 4 protocol
Layer 3 protocol
Layer 2 protocol
Layer 1 protocol
Physical medium
Layer 5
Layer 4
Layer 3
Layer 2
Layer 1
Information Flow
Layer 5
Layer 4
Layer 3
Layer 5 protocol
M
Layer 4 protocol
H4 M
H3 H4 M1
Layer 2 H2 H3 H4 M1 T2
M
H3 M2
H2 H3 M2 T2
H4 M
H3 H4 M1
H2 H3 H4 M1 T2
H3 M2
H2 H3 M2 T2
Layer 1
Source machine
destination machine
OSI Reference Model
The OSI reference model based on a proposal developed by ISO has seven
layers. The principles that were applied to arrive at the seven layers are as
follows:
• A layer should be created where a different level of abstraction is needed;
• Each layer should perform a well defined function;
• The function of each layer should be chosen with an eye toward defining
internationally standardised protocols;
• The layer boundaries should be chosen to minimise the information flow across
the interfaces;
• The number of layers should be large enough that distinct functions need not be
thrown together in the same layer out of necessity, and small enough that the
architecture does not become unwieldy.
OSI Layers Functions
Application
Presentation
Session
Transport
Network
Data link
Physical
Application: provides user access to an OSI
environment.
Presentation:hides from the application layer
differences in representation of information.
Session:provides facilities for
synchronization.
Transport: enables QoS network facilities.
Network: establishes, maintains and
terminates connections.
Data Link: controls data transfer over
physical link, including error detection.
Physical: provides electrical and mechanical
control to transmit data bits onto
communication medium.
TCP/IP Reference Model
Application
• The protocols came first and model is just a
description of existing protocols;
• The TCP/IP reference model can not
Transport
describe non-TCP/IP networks;
•The layers 5 and 6 are not present in this
Internet
Host-toNetwork
model.
OSI vs TCP/IP
Application
Application
Presentation
Session
Transport
Network
TCP
UDP
IP
Data link
Physical
Host-toNetwork
TCP/IP Detailed View
FTP, WWW,CMOT
Telnet, rlogin, SMTP,
TFTP, DNS, SNMP
NFS, yp, etc.
TCP
UDP
ARP
RARP
PING
ICMP
IP
IEEE 802.2, 802.1
IEEE 802.3
MAC
IEEE 802.4
MAC
HDLC/X.25,
IEEE 802.5 IEEE 802.6 PPP, SLIP
MAC
MAC
Ethernet
Token bus
Token ring
MAN
WAN
Internet Protocol (IP)
• Connectionless (i.e., each packet it treated independently, with no
reference to packets that have long gone before);
•Cannot guarantee reliable, in-order delivery;
•PDU:
IP datagram, which contains user data, source-destination IP
addresses, other inf. (such as its length, time-to-live, etc.);
• IP main operations:
Fragmentation/Reassembly and Routing
Fragmentation/Reassembly
Reassembly
Two options: either in host B, or in router G2.
It is preferred the first option.
Gain: Simpler routers (no buffering of fragments)
Loss:decrement of network utilisation and increment of packet loss
probability.
IP Addresses







An IP address defines both the network and the host on the
particular network;
An IP address has 4 bytes, so there are 4 billion addresses;
There is one-to-one correspondence between IP and physical
addresses;
Example of an IP address : 147.102.7.1;
An IP address includes two parts: a network identifier (netid) and
a host identifier (hostid);
The netid defines the network, while the hostid differentiate a
host of the network from the others;
The length of netid depends on the address class: there are
three address classes, namely A,B and C;
Address Classes
Class Α:
Class B:
Class C:




0 + 7bits (netid=1byte) + 3bytes (hostid);
10 + 14bits (netid=2byte) + 2bytes (hostid);
110 + 21bits (netid=3byte) + 1bytes (hostid);
When a network is separated into subnetworks, the hostid
defines both the host and the subnetwork of the host.
<IP address>=<netid><subnetid><hostid>
A subnet mask (32-bit) indicates the split of hostid to subnetid
and new hostid;
A subnet mask contains 1 for bits of netid and subnetid and 0 for
bits of hostid;
Example: The mask 255.255.255.0 defines 14 subnetorks and
4094 hosts for each subnetwork.
Domain Name Service (DNS)



The DNS servers correspond names such as
“swpc94.telecom.ece.ntua.gr” in IP addresses like
“147.102.7.94”;
However, the traffic of TCP/IP packets uses IP addresses and not
names;
Before an Internet process, there is a dialogue (approx. 1/10 sec)
between the source host and the local DNS server for finding the
IP address of the target host.
Routing
• Direct routing: In the same network, usage of the Address Resolution
Protocol (ARP) and Reserve Address Resolution Protocol (RARP)
• Indirect routing: Between different networks, usage of the routers
Routers
• They can manipulate packets from all the interconnected networks;
• They communicate with all the interconnected networks;
• They are “multihomed”, i.e., they have multiple IP addresses referring to all
the interconnected networks;
• They perform routing algorithms using the netid of the IP datagrams.
Indirect Routing Example
A

Α
B

Β

Γ
1

1
C
2

2

3
3
I

i
II

ii

iii
III
3 separate physical networks,
with their own addresses, packet
size and pattern.
Indirect Routing Example
A
B


Β
Α

Γ
D
4
1
C
2


2
1

3
4
IV
I

i
3
II

ii

iii
III
The networks are connected via
two routers. The routers can
send/receive packets to/from both
networks.
Indirect Routing Example
A
B
 1.2

Β
Α
1.1

Γ
1.4
2.4
1
D
4
1.3
C
2


2
1
2.1
2.2
2.3

3
2.5
I
3.4

i
3.1
5
IV
3
II

ii
3.2

iii
III
3.3
Introduction of the unique IP
address for each host and the IP
datagram as common transfer unit.
Indirect Routing Example
A
B
 1.2

Β
Α
1.1
D
3.3
data
1.4
D
4 2.4
1
C
2
2
2.1
2.2
3.3
2.3

data
3
5 2.5
IV 3.4
I
3
II


ii
i
3.2
3.1

iii
iii
1.3


1
5

Γ
3.3
data
III
3.3
• Each host or router forwards the
datagram per one hop towards its
destination. For each hop, the
datagram is encapsulated into a
specific physical layer packet with a
local physical address. The datagram
keeps the IP address of its
destination.
• The routers firstly exams the netid.
• Only at the last hop of routing, the
hostid is mapped to the physical
address.
• In case of fragmentation, the
destination takes over the
reassembly.
Indirect Routing Example
• Both hosts and routers keep routing tables for leading the IP datagrams to
destinations and physical addresses tables for mapping the IP addresses to
corresponding physical addresses.
• Routing Table: It contains pairs of the form (N,R), where N is the IP address
of the destination network and R is the IP address of the next router towards
the destination.
• Examples: Host 1.1
Router 1.4/2.4
N
1.x
2.x
3.x
R
N
Computation of the physical address
1.4
1.4
Physical Addresses Table:
1.x
2.x
3.x
1.1
A
1.2
1.3
1.3
B
C
D
R
direct connection
direct connection
2.5
Transmission Control Protocol (TCP)
• Connection-oriented (i.e., a connection is established before the data
transmission);
• Can guarantee reliable stream delivery services;
A
1500
FTP
21
B
1501
Telnet
23
128.10.0.3
128.10.0.7
• reserved TCP port numbers (16 bits):
FTP
21
Telnet
23
Finger 79
HTTP
80
Transmission Control Protocol (TCP)



Sliding Window Technique;
Multiplicative Decrease Congestion Avoidance;
Slow Start Recovery;
Allowed_window = min (Receiver_Advertisement, Congestion_Window)
User Datagram Protocol (UDP)
• Connectionless;
• No confirmations, packets numbering, flow control;
• No error detection/recovery;
•Cannot guarantee reliable in order delivery services;
• reserved UDP port numbers (16 bits): DNS
TFTP
53
69
SNMP 161
• Mainly, broadcasting applications use UDP.
Applications





FTP;
SMTP;
WWW;
Telnet;
Many others
Sockets


A
1500
FTP
21
B
1501
Telnet
23
128.10.0.3
128.10.0.7
The combination of an IP address with a port number
identifies a socket;
A socket defines an application service;