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Introduction to network architecture 1
Chapter 1Introduction to network architecture
Departamento deTecnología Electrónica
Some of these slides are copyrighted by:
Computer Networking: A Top Down Approach 5th edition. Jim Kurose, Keith RossAddison-Wesley, April 2009.
2
Chapter 1: Introduction to network architecture Chapter goals:
Remembering networking basic concepts that are key for the subject.
o OSI Model and TCP/IP architectureo Transport layer conceptso Network layer conceptso Data link layer concepts
Introducing Virtual Local Area Networks (VLAN)
Introduction to network architecture
3
Chapter 1: Introduction to network architecture 1.1 OSI Model. TCP/IP
Architecture 1.2. Transport layer 1.3. Network layer
1.4. Data link layer 1.5 Virtual Local Area
Network, VLANs
Introduction to network architecture
4Introduction to network architecture
Chapter 1: Introduction to network architecture 1.1 OSI Model. TCP/IP
Architecture 1.2. Transport layer 1.3. Network layer
1.4. Data link layer 1.5 Virtual Local Area
Network, VLANs
5
TCP/IP Architecture
application
transport
network
data link
physical
A_PDUmessage
T_PDUsegment
R_PDUDatagram/
packet
E_PDUframe
Introduction to network architecture
application: supporting network applications FTP, SMTP, HTTP
transport: process-process data transfer TCP, UDP
network: addressing and routing of datagrams from source to destination IP, routing protocols
data link: data transfer between neighboring network elements PPP, Ethernet
physical: bits “on the wire”
OSI Model
6Introduction to network architecture
presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
session: synchronization, checkpointing, recovery of data exchange
Internet stack “missing” these layers! these services, if needed, must
be implemented in application
application
presentation
session
transport
network
link
physical
(N+1)-PDU
(N)-DU (N)-PDU
(N)-SDU
(N)-PCI
Level N
Level N+1
En
cap
su
latio
n
TransmitterTransmitter
7
Encapsulation
Simplified encapsulation model
Introduction to network architecture
8
Decapsulation
(N+1)-PDU
(N)-DU (N)-PDU
(N)-SDU
(N)-PCI
Level N
Level N+1
Decap
su
latio
n
ReceiverReceiver
Introduction to network architecture
Example of layer architecture: Internet
Sourceapplicationtransportnetworkdata linkphysical
HtHn M
segment Ht
datagram
Destination
applicationtransportnetworkdata linkphysical
HtHrHe M
HtHr M
Ht M
M
networkdata linkphysical
router
message M
Ht M
Hrframe
HtHrHe M
HtHr M
HtHrHe M
Example: Two hosts connected by a router.
Nota
Phy medium
Hx = X_PCIM = A_PCI(Ha) + User data (UD)Example UD:e_mail subject/bodyText of a WhatsApp message
9Introduction to network architecture
Multiplexion
10
How do we identify the client protocol? TCP & UDP: Port field. IP: Protocol field Ethernet: Ethertype field (Type/length) IEEE 802.3 (MAC) uses LLC (IEEE 802.2) IEEE 802.2: DSAP y SSAPSNAP may be used together with IEEE 802.2 to identify with Ethertype
Introduction to network architecture
more than one transport protocol available to apps Internet: TCP and UDP
FTP HTTP SMTP DNS TFTP
TCP UDP
IP
Link layer (LLC & MAC)
Physical Layer
Application
Transport
Network
Multiplexion. Example (I)
11Introduction to network architecture
Multiplexion. Example (II)
12
Data link
Message
DataH C
Introduction to network architecture
Multiplexion. Example (III)
13
Data link
Network
Message
DataH E
DataH
Introduction to network architecture
Multiplexion. Example (IV)
14
Data link
Network
DataH
Transport
DataH
Introduction to network architecture
15Introduction to network architecture
Chapter 1: Introduction to network architecture 1.1 OSI Model. TCP/IP
Architecture 1.2. Transport layer 1.3. Network layer
1.4. Data link layer 1.5 Virtual Local Area
Network, VLANs
16Introduction to network architecture
Transport services and protocols
provide logical communication between app processes running on different hosts
transport protocols run in end systems breaks app messages into segments, passes to
network layer
NetworkHost A Host B
17Introduction to network architecture
Internet transport-layer protocols more than one
transport protocol available to apps Internet: TCP
and UDP
TCP UDP
Connection- oriented
Non-connection- oriented
Reliable Unreliable
Segment grouping Unfragmented messages
Rcv orders segments
User datagram
ACKs and timers No ACKs
Flow control No flow control
Congestion control No congestion control
18Introduction to network architecture
Internet transport-layer protocols Port: identifies application Port numbers:
http://www.iana.org/assignments/port-numbers
Application protocol
Port numbers Transport protocol
FTP 20, 21 TCP
Telnet 23 TCP
SMTP 25 TCP
DNS 53 UDP (TCP (*))
TFTP 69 UDP
HTTP 80 TCP
POP3 110 TCP
RIP 520 UDP
UDP_PDU32 bits
length checksum
Header (T_PCI) has only 4 fields. Lenght is in bytes
and deals with the whole T_PDU,
including the header.
Source port Dest port
App level data(message)
UDP T_PDU format
T_PCI
T_UD
Introduction to network architecture 19
20
socketdoor
T C Psend buffer
T C Preceive buffer
socketdoor
segm ent
applicationwrites data
applicationreads data
Introduction to network architecture
TCP: Overview RFCs: 793, 1122, 1323, 2018, 2581
full duplex data: bi-directional data flow
in same connection MSS: maximum
segment size
connection-oriented: handshaking (exchange
of control msgs) init’s sender, receiver state before data exchange
flow controlled: sender will not
overwhelm receiver
point-to-point: one sender, one
receiver
reliable, in-order byte stream: no “message
boundaries”
pipelined: TCP congestion and flow
control set window size
send & receive buffers
21Introduction to network architecture
TCP segment structure
source port # dest port #
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG: urgent data (generally not used)
ACK: ACK #valid
PSH: push data now(generally not used)
RST, SYN, FIN:connection estab(setup, teardown
commands)
# bytes rcvr willingto accept
countingby bytes of data(not segments!)
Internetchecksum
(as in UDP)
22Introduction to network architecture
TCP seq. #’s and ACKsHost A Host B
Seq=M, SYN=1
Seq=N, ACK=M+1, SYN=1
Seq=M+1, ACK=N+1
Client starts active open
Client confirms
server open
Server is in passive open, starts connection
and confirms client open
timeConnection established
23Introduction to network architecture
Chapter 1: Introduction to network architecture 1.1 OSI Model. TCP/IP
Architecture 1.2. Transport layer 1.3. Network layer
1.4. Data link layer 1.5 Virtual Local Area
Network, VLANs
24
Network layerNetwork layer functions:
•Packet routing•Logical addressing•Multiplexion•Packet segmentation (fragmentation)
Introduction to network architecture
Which route?
Adressing: Network & HostNetwork Host
-Network address: Used by the router
-Host address: used by a determined host
25
IPv4 protocol
Most used network layer protocol
32-bit address Network part Host part
Network and host parts are determined by the subnet mask. First x bits are set to 1
and define the number of bits of the network part.
Last 32-x bits are set to 0 and define the number of bits of the host part
Introduction to network architecture
Network Host
IP addressing
IPv4 special addresses
Addresses Meaning Use
0.0.0.0/32The own host inside the own
networkAs source address if a host does not know
its IP address
10.0.0.0/8172.16.0.0/12
192.168.0.0/16Private addresses
IP connectivity, but no access to the Internet
127.0.0.0/8 Loopback intefaceIp use without access to the physical
medium.
169.254.0.0/16 AutoconfigurationA host does not have an IP address,
neither manually nor by means of a DHCP server
224.0.0.0/4 Multicast IP Multicast (D class)
240.0.0.0/4 Reserved For the use of IANA (E class)
255.255.255.255 Limited broadcast Broadcast destination for the network
26Introduction to network architecture
27
IP_PDU format (datagram/packet)
Introduction to network architecture
ver length
32 bits
data (variable length,typically a TCP
or UDP segment)
16-bit identifier
header checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
forfragmentation/reassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
head.len
type ofservice
“type” of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) E.g. timestamp,record routetaken, specifylist of routers to visit.
how much overhead with TCP?
20 bytes of TCP 20 bytes of IP = 40 bytes + app
layer overhead
Routing table (host)
Host IP addr? Subnet mask? Network Id.? MAC address? Default gateway? Gateway for 10.10.63.20? Gateway for 150.214.141.120? MAC for 10.10.63.255?
28Introduction to network architecture
Routing table (router)
NETWORK 2
NETWORK 2
Router 1192.1.1.2
192.1.2.1
192.1.2.2
192.1.1.1
192.1.1.3
…
192.1.2.3 192.1.2.63
…192.1.1.31
E0 E1
NETWORK 1NETWORK 1
NETWORK 3
NETWORK 3
…
192.1.3.2 192.1.3.127
192.1.3.1
Router 2
E2
E0 E1
192.1.4.2
192.1.4.1
When receiving a packet, the router makes the AND operation between IP dest addr and the different subnet masks in the routing table. Finally, it sends the packet for the interface pointed out by the routing table.
29
RT Router 1
Network Subnet mask Next hop Interface
192.1.1.0 255.255.255.224 - E0
192.1.2.0 255.255.255.192 192.1.4.1 E1
192.1.3.0 255.255.255.128 - E2
192.1.4.0 255.255.255.0 - E1
RT Router 2
Network Subnet mask Next hop Interface
192.1.1.0 255.255.255.224 192.1.4.2 E0
192.1.2.0 255.255.255.192 - E1
192.1.3.0 255.255.255.128 192.1.4.2 E0
192.1.4.0 255.255.255.0 - E0
Introduction to network architecture
Difference between logical addresses (IP) and physical addresses (MAC)
Router142.128.1.1 150.214.141.1
Source IP addr
Host A142.128.1.11
00:1C:27:56:34:AA
Host Y150.214.141.19
00:1C:27:18:00:01
IP packet
Source MAC addrDest IP addr Dest MAC addr
IP packet
12:34:56:78:90:AB
142.128.1.11 150.214.141.19 00:1C:27:56:34:AA 12:34:56:78:90:AB
Source IP addr Source MAC addrDest IP addr Dest MAC addr
142.128.1.11 150.214.141.19 12:34:56:78:90:AB 00:1C:27:18:00:01
30Introduction to network architecture
Socket
A process sends/recieves messages by/from its socket
A socket is identified by: IP address. Port number.
Port number examples:
HTTP: port 80 DNS: port 53
31Introduction to network architecture
32Introduction to network architecture
Chapter 1: Introduction to network architecture 1.1 OSI Model. TCP/IP
Architecture 1.2. Transport layer 1.3. Network layer
1.4. Data link layer 1.5 Virtual Local Area
Network, VLANs
LAN (Local Area Network) Local Area Networks are the most used network
technology. They allow the connection between hosts and routers
inside a broadcast domain. Most used LAN standards are:
802.3, Ethernet. 802.11, WI-FI (WLAN, Wireless LAN).
Data link layer is divided into two sublevels: o LLC (Link Layer Control). Its functions are flow control and error correction.o MAC (Medium Access Control). Foer frame synchronism, error detection, medium access control, and physical addressing.
Implmented in NIC (Network Interface Card) up to MAC sublevel.
OSI LAN
Data link LLC
MAC
Physical
33Introduction to network architecture
MAC addresses Size -> 48 bits.
Example: 1B:03:F2:45:78:25
There are three types of MAC addresses: Unicast: To send DL_PDUs to an only destination.
All the network interfaces have a default factory MAC address. Broadcast: As a destination, it is used to send DL_PDUs to ALL
the hosts in a broadcast domain (FF:FF:FF:FF:FF:FF). Multicast: As a destination, it is used to send DL_PDUs to SOME
of the hosts in a broadcast domain . Configurable. The least significant bit in the first byte of the MAC
address is set to 1. IEEE manages unicast factory MAC addresses.
Every manufacturer has a range of MAC addresses (to assure MAC addresses are unique)
It is possible to change them.
34Introduction to network architecture
35
Standards
LAN/MAN standards
Introduction to network architecture
MAC_PDU (frame)
Preamble (8 bytes)
Dest MAC address(6 bytes)
Source MAC address(6 bytes)
Length/Type(2 bytes)
MAC_UD(46-1500 bytes)
Trailer
CRC(4 bytes)
1 byte7 bytes with 10101010.1 byte (the last one) con 10101011.
MTU for Ethernet is 1500 bytesNote
•<=1500 meaning length:
- number of bytes for MAC_UD- Sublevel LLC is present.
•>=1536 meaning type:
Multiplexion and demultiplexion
Data corresponding to the upper layer, generally IP, ARP o rLLC.If MAC_UD size is below 46 bytes, there is a trailer of bytes set to 0.
36Introduction to network architecture
37Introduction to network architecture
Chapter 1: Introduction to network architecture 1.1 OSI Model. TCP/IP
Architecture 1.2. Transport layer 1.3. Network layer
1.4. Data link layer 1.5 Virtual Local Area
Network, VLANs
VLAN
38Introduction to network architecture
Introduction: Hierarchic topology for institutional modern LANs Every working gruup has its own switched LAN Switched LANs may be interconnected by a
hierarchy of switches.
A
B
S1
C D
E
FS2
S4
S3
H
I
G
VLAN
Disadvantages: Traffic is not isolated
Broadcast traffic Traffic must be limited for security and confidentiality
reasons
Inefficient use of switches User management
39Introduction to network architecture
VLAN
VLAN: Port-based VLAN
Switch ports are divided into groups Every group constitutes a VLAN Every VLAN is a broadcast domain User management -> Change in switch configuration
A B C D E F G H I 40Introduction to network architecture
VLAN
VLAN: How is information between groups sent?
Connect switch port to an external router Configure that port as a member of both groups Logical configuration -> Separate switches connected by a
router Habitually, manufacturers include VLAN and router in an only
device
A B C D E F G H I 41Introduction to network architecture
VLAN
VLAN: Different location
Members of the same group in different buildings Several switches needed Connecting group ports between switches -> Non scalable
A BC
D E FG HI 42Introduction to network architecture
VLAN
VLAN: Different location
VLAN Trunking Trunk port belongs to all VLANs Destination VLAN? 802.1Q frame format
A BC
D E FG HI
Trunk link
43Introduction to network architecture
VLAN
IEEE 802.1Q: IEEE 802.3 (Ethernet)
IEEE 802.1Q
Dest addr
DataPreambleSourceaddr
Type CRC
Destaddr
DataPreambleSource
addr
TypeNewCRC
TPID TCI
Tag Control Information
Tag Protocol Identifier
44Introduction to network architecture
VLAN
VLAN: MAC-based VLAN
The network administrator creates VLAN groups based on MAC address ranges.
Switch port is connected to the VLAN that corresponds to the associated host’s MAC address.
IP-based VLAN Based on IPv4 or IPv6 addresses Based on network protocols (Appletalk, IPX, TCP/IP)
45Introduction to network architecture