tcp/ip networks. table of contents computer networks, layers, protocols, interfaces; osi reference...
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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
NETWORK CHARACTERIS TICS
LAN's MAN's WAN's
S iz e Ca m pus Offic e City, Town County, Country
S pe e d 10Mbps -100Mbps 100Mbps 1Mbps , (45Mbps S MDS )
To po lo g y S ha re d m e dia S ha re d m e dia m e s h
Token-r ing
Works tation
Works tation
W ork station
W orkstati on
Works tation
Works tationW orkstati on
W orkstation
Shared media:
Bus
RingBackbone network Vs local access network
Switching Techniques
• Circuit switching;
• Message switching;
• Packet switching.
Protocol Hierarchies
Physical medium
Layer 5 protocol
Layer 4 protocolLayer 4/5 interface
Layer 3/4 interface
Layer 2/3 interface
Layer 1/2 interface
Layer 5
Layer 1
Layer 2
Layer 3
Layer 4
Host A
Layer 3 protocol
Layer 2 protocol
Layer 1 protocol
Layer 5
Layer 1
Layer 2
Layer 3
Layer 4
Host A
Information Flow
Layer 5 Layer 5 protocolM
Layer 4 protocolH4 M
H3 H4 M1 H3 M2
H2 H3 H4 M1 T2 H2 H3 M2 T2
M
H4 M
Source machine destination machine
H3 H4 M1 H3 M2
H2 H3 H4 M1 T2 H2 H3 M2 T2Layer 2
Layer 1
Layer 4
Layer 3
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: 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.
Application
Presentation
Session
Transport
Network
Data link
Physical
TCP/IP Reference Model
• The protocols came first and model is just a
description of existing protocols;
• The TCP/IP reference model can not
describe non-TCP/IP networks;
•The layers 5 and 6 are not present in this
model.
Application
Transport
Internet
Host-to-Network
OSI vs TCP/IP
Application
Presentation
Session
Transport
Network
Data link
Physical
Application
TCP
IP
Host-to-Network
UDP
TCP/IP Detailed View
IEEE 802.3MAC
PING
TCP
IP
UDP
ARPRARP
ICMP
FTP, WWW,CMOTTelnet, rlogin, SMTP,
TFTP, DNS, SNMPNFS, yp, etc.
IEEE 802.4MAC
IEEE 802.5MAC
IEEE 802.6MAC
Ethernet Token bus Token ring MAN WAN
IEEE 802.2, 802.1HDLC/X.25,
PPP, SLIP
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: 0 + 7bits (netid=1byte) + 3bytes (hostid);Class B: 10 + 14bits (netid=2byte) + 2bytes (hostid);Class C: 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
ΒΑ
Γ
2 1
3
ii i
iii
A B
C1 2
3I II
III
3 separate physical networks, with their own addresses, packet size and pattern.
Indirect Routing Example
ΒΑ
Γ
2 1
3
ii i
iii
A B
C1 2
3I II
III
D4
4IV
The networks are connected via two routers. The routers can send/receive packets to/from both
networks.
Indirect Routing Example
Introduction of the unique IP address for each host and the IP datagram as common transfer unit.
ΒΑ
Γ
2 1
3
ii i
iii
A B
C1 2
3I II
III
D4
5IV
1.1 1.2
1.31.4
2.4
2.1 2.22.3
2.5
3.4
3.1 3.23.3
Indirect Routing Example
ΒΑ
Γ
2 1
3
ii i
iii
A B
C1 2
3I II
III
D4
5IV
1.1 1.2
1.31.4
2.4
2.1 2.22.3
2.5
3.4
3.1 3.23.3
• 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.
3.3 dataD
3.3 data5
3.3 dataiii
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
1.x2.x3.x
N R
Computation of the physical address1.41.4
Router 1.4/2.4
1.x2.x3.x
N R
direct connection
2.5direct connection
1.21.31.3
1.1 A
B
DC
Physical Addresses Table:
Transmission Control Protocol (TCP)• Connection-oriented (i.e., a connection is established before the data transmission);
• Can guarantee reliable stream delivery services;
• reserved TCP port numbers (16 bits): FTP 21
Telnet 23
Finger 79
HTTP 80
A
B
1500
1501
128.10.0.3
FTP21
23
128.10.0.7
Telnet
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 53
TFTP 69
SNMP 161
• Mainly, broadcasting applications use UDP.
Applications
FTP; SMTP; WWW; Telnet; Many others
Sockets
A
B
1500
1501
128.10.0.3
FTP21
23
128.10.0.7
Telnet
The combination of an IP address with a port number identifies a socket;
A socket defines an application service;