Introduction
TDM transport networks are not sufficient for data communications
Low utilization TDM networks are being replaced by
packet/frame/cell based data communication systems
So the question is what are such communication systems and protocols?
Transport Protocol Classification
Any communication system provides its services in two basic ways
Dedicated lines (circuits) Shared lines (circuits)
In packet/frame based technologies, shared resources are categorized as
Connection oriented Multiple predefines virtual paths are established through the
same physical link (highway system) The virtual path can be
Permanent: logical circuit provisioned as the system us turned-up Switched: Logical circuit established upon request
Connectionless No predefined path exists; routing takes place based on the
source and destination nodes (airplane system)
Network Basics
The backbone or core networkConsists of switches, core routers,Gateway routers (maybe called Differently)
Edge routers are used to be connected to the core network
Data path
Ingress Edge node
Egress Edge node
Transport Layer
End-to-end delivery of the entire message. Differs from network layer that oversees end-to-end delivery of
individual packets without recognizing any relationship between them.
Addressing We have seen that in the Internet the top three OSI layers are
combined into the application layer. On the Internet, the transport layer interacts with applications. Because many applications (and application instances - -
windows) can be active at any one time, this requires an additional layer of addressing known as port addressing
Connectionless vs. Connection-Oriented
Connectionless Services There is no error control, so
incorrect frames are simply discarded.
This is called a best try service. Commonly used for low error
rate lines. The Internet model network
layer protocol, IP, is a connectionless service.
UDP is the Internet model transport layer protocol.
Connection-oriented Services Involves negotiating a ‘link’ between
the source and destination. This link will be a virtual
connection in a switched network.
Since a single pathway is established, the acknowledgement process for error control is facilitated.
These services are considered reliable and therefore are the most frequently used.
There is no connection-oriented network layer protocol in the Internet model.
TCP is the connection-oriented transport layer protocol in the Internet model.
Functions of a Connection-Oriented Transport Protocol
Connection establishment Reliable delivery:
error control (similar to data link) sequence control; loss control; duplication control (discard duplicated)
Flow control Connection termination
Functions of a Connection-Oriented Transport Protocol
Flow control Flow control similar to that used
by the data link layer, however, the flow control is from end-to-end.
Transmission Control Protocol (TCP)
Connection oriented transport protocol that provides all the functionality defined for the transport layer in the OSI model.
Packets are called segments:-16 bits are allowed for port addresses (numbers) in both protocols (allows for up to 65536 ports!)-TCP source and destination
User Datagram Protocol (UDP)
UDP provides a connectionless service with limited error control.
No sequence numbers implies that sequence, loss and duplication control are not supported.
Packets are called datagrams:
RTP (real-time protocol) header contains field used to assist UDP in transmitting real-time traffic such as VoIP
IP Protocol
IPv4 Addresses are 32 bits wide Its header is 20 bytes at minimum Uses doted-decimal notation (e.g. 43.23.43.56)
IPv6 Provides larger address domain; addresses are 128
bits wide Multiple separate headers are supported Handles audio and video; providing high quality
paths Supports unicast, multicast, anycast
IP Header
The IP datagram contains data and IP address
The IP datagram is encapsulated in a frame with physical address
The header changes as the frame goes from one network domain to the next IP Datagram
Frame
DataIP Address
FrameAddress
IP Packet Format
+ 0 - 3 4 - 7 8 - 15 16 - 18 19 - 31
0 Version Header length Type of Service Total Length
32 Identification Flags Fragment Offset
64 Time to Live Protocol Header Checksum
96 Source Address
128 Destination Address
160 Options
192 Data
All numbers are in bits
IP Packet Format
+ 0 - 3 4 - 7 8 - 15 16 - 18 19 - 31
0 Version Header length Type of Service Total Length
32 Identification Flags Fragment Offset
64 Time to Live Protocol Header Checksum
96 Source Address
128 Destination Address
160 Options
192 Data
All numbers are in bits Internet header Length
Reliability/TH/delay
How long in seconds pkt stays in Internet
Next higher level protocol after IP
IP Packet Format - TTL
TTL (time-to-live) refers to the number of router hops (or seconds) the IP packet is allowed before it must be discarded. Each router that receives a packet subtracts
one from the count in the TTL field. When the count reaches zero, the router
detecting it discards the packet and sends an Internet Control Message Protocol (ICMP) message back to the originating host.
Encapsulated IP Packet in Ethernet Frame
MAC and Associated IP address
Ethernet Frame Carrying IP Packet
Protocol Analyzer Display: 0000 00 00 C0 A0 51 24 00 C0 93 21 88 A7 08 00 45 080010 00 5A DC 28 00 00 FF 01 88 08 C0 99 B8 01 C0 990020 B8 03 2a B4 DD …..
Encapsulated IP Packet in Ethernet Frame
Ethernet Frame Carrying IP Packet
IP starting with 45 Hex indicates IPv4 with standard length of 20 bytes
IP starting with 4F Hex indicates IPv4 with standard length of 60 bytes
Remember: 24=16; 45= 0100 0101= One Byte
An Ethernet frame containing IP information has 08 00 in its type field
99 is one byte
1001 1001
Example:
IP Addressing
Two address types Physical address (the frame has the physical address)
Embedded in the hardware (NIC, e.g., 00 00 11 00 11 33) Also called the Media Address Control (MAC) address
Logical IP datagram contains the logical IP address
To transport IP packets both physical and IP addresses must be known
ARP (address resolution protocol) and RARP (reverse) address resolution protocol are used to convert MAC to IP address and vice versa
Static address resolution Dynamic address resolution
IP Addressing
Uses doted-decimal notation A network address is divided into Netid and
Hostid IP Address classification
(number of hosts per network)Class Leading bits NetworkAddress (Netid)
Host Address (Hostid)
Class A 0 7 bit (125)* 24 bit (16,777,151,750)
Class B 10 14 bit (16,368) 16 bit (65,534)
Class C 110 21 bit (2,096,896) 8 bit (254)
Class D (multicast) 1110
Class E (reserved) 1111
* Some values are reserved!
IP Addressing Classification
Network Address Host Address
Network Address
Host Address
Network Address
Host Address
Reserved for Internet research
Multicast Address
Example of IP Addressing
Q1: Determine the network address for the following IP addresses:
1- 84.42.58.11 (84 = 54 Hex = 0101 0100) Netid=84.0.0.0 Class A Hostid=0.42.58.11
2- 144.54.67.5 (144 = 90 Hex = 1001 0000) Netid=144.62.0.0 Class B Hostid=0.0.67.5
Q2: What type of IP address classificationwill a large organization with 1000individual users in 150 dispersed buildings use? Class B
IP Routing Protocols
Routing packets requires having knowledge about the network
Partial (know your own neighbors) Full (know the entire network elements)
Retrieving network information (network discovery protocols)
RIP (routing information protocol): routing based on the least number of hops
OSPF (open shortest path first): Routing based on number of hops, link speed, congestion
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