TCP/IP and TCP
protocols
Internet 1
Ethernet
⚫ Data Link Layer protocol
⚫ Ethernet (IEEE 802.3) is widely used.
⚫ Supported by a variety of physical layer
implementations.
⚫ Multi-access (shared medium).
TCP/IP 2
CSMA/CD
⚫ Carrier Sense Multiple Access with Collision
Detection
⚫ Carrier Sense : can tell when another host is
transmitting
⚫ Multiple Access : many hosts on 1 wire
⚫ Collision Detection : can tell when another host
transmits at the same time.
TCP/IP 3
An Ethernet Frame
Destination Source
Preamble Len DATA CRC
Address Address
8 bytes 6 6 2 0-1500 4
⚫ The preamble is a sequence of alternating 1s and 0s
used for synchronization.
⚫ CRC is Cyclic Redundency Check
TCP/IP 4
Ethernet Addressing
⚫ Every Ethernet interface has a unique 48 bit address
(a.k.a. hardware address).
⚫ Example: C0:B3:44:17:21:17
⚫ The broadcast address is all 1’s.
⚫ Addresses are assigned to vendors by a central authority.
⚫ Each interface looks at every frame and inspects the
destination address. If the address does not match the
hardware address of the interface (or the broadcast
address), the frame is discarded.
TCP/IP 5
Internet Protocol
⚫ IP is the network layer
⚫ packet delivery service (host-to-host).
⚫ translation between different data-link protocols
⚫ IP provides connectionless, unreliable delivery of IP
datagrams.
⚫ Connectionless: each datagram is independent of all
others.
⚫ Unreliable: there is no guarantee that datagrams are
delivered correctly or even delivered at all.
TCP/IP 6
IP Addresses
⚫ IP addresses are not the same as the underlying
data-link (MAC) addresses.
⚫ IP is a network layer - it must be capable of providing
communication between hosts on different kinds of
networks (different data-link implementations).
⚫ The address must include information about what
network the receiving host is on. This is what makes
routing feasible.
TCP/IP 7
IP Addresses
⚫ IP addresses are logical addresses (not physical)
IPv4 (version 4)
⚫ 32 bits.
⚫ Includes a network ID and a host ID.
⚫ Every host must have a unique IP address.
⚫ IP addresses are assigned by a central authority (American
Registry for Internet Numbers for North America).
TCP/IP 8
Network and Host IDs
⚫ A Network ID is assigned to an organization by a global
authority.
⚫ Host IDs are assigned locally by a system administrator.
⚫ Both the Network ID and the Host ID are used for
routing.
TCP/IP 9
CLASSES
Internet 10
The
Class
four formats of IP Addresses
A 0 NetID HostID
128 possible network IDs, over 4 million host IDs per network ID
B 10 NetID HostID
16K possible network IDs, 64K host IDs per network ID
C 110 NetID HostID
Over 2 million possible network IDs, 256 host IDs per network ID
D 1110 Multicast Address
8 bits 8 bits 8 bits 8 bits
TCP/IP 11
CLASS IP ADDRESS RANGE
Internet 12
IP Addresses
⚫ IP Addresses are usually shown in dotted decimal
notation:
1.2.3.4
00000001 00000010 00000011 00000100
⚫ cse.unr.edu is 134.197.40.3
10000110 11000101 00101000 00000010
CSE has a class B network
TCP/IP 13
Host and Network Addresses
⚫ A single network interface is assigned a single IP address
called the host address.
⚫ A host may have multiple interfaces, and therefore
multiple host addresses.
⚫ Hosts that share a network all have the same IP network
address (the network ID).
⚫ An IP address that has a host ID of all 0s is called a
network address and refers to an entire network.
TCP/IP 14
Subnet Addresses
⚫ An organization can subdivide it’s host address space
into groups called subnets.
⚫ The subnet ID is generally used to group hosts based on
the physical network topology.
10 NetID SubnetID HostID
TCP/IP 15
Subnetting
router
Subnet 1 Subnet 2 Subnet 3
134.197.1.x 134.197.2.x 134.197.3.x
TCP/IP 16
Subnetting
⚫ Subnets can simplify routing.
⚫ IP subnet broadcasts have a hostID of all 1s.
⚫ It is possible to have a single wire network with multiple
subnets.
TCP/IP 17
Mapping IP Addresses to
Hardware Addresses
⚫ IP Addresses are not recognized by hardware.
⚫ If we know the IP address of a host, how do we find out
the hardware address ?
⚫ The process of finding the hardware address of a host
given the IP address is called
Address Resolution
TCP/IP 18
Arp Arp!
ARP
⚫ The Address Resolution Protocol is used by a
sending host when it knows the IP address of the
destination but needs the Ethernet (or whatever)
address.
⚫ ARP is a broadcast protocol - every host on the network
receives the request.
⚫ Each host checks the request against it’s IP address - the
right one responds.
⚫ hosts remember the hardware addresses of each other.
TCP/IP 19
ARP conversation
HEY - Everyone please listen!
Will 128.213.1.5 please send me
his/her Ethernet address?
not me
Hi Green! I’m 128.213.1.5, and
my Ethernet address is
87:A2:15:35:02:C3
TCP/IP 20
ICMP
Internet Control Message Protocol
⚫ ICMP is a protocol used for exchanging control
messages.
⚫ ICMP uses IP to deliver messages.
⚫ ICMP messages are usually generated and processed by
the IP software, not the user process.
TCP/IP 21
ICMP Message Types
⚫ Echo Request
⚫ Echo Response
⚫ Destination Unreachable
⚫ Redirect
⚫ Time Exceeded
⚫ Redirect (route change)
⚫ there are more ...
TCP/IP 22
Transport Layer & TCP/IP
Q: We know that IP is the network layer - so TCP must
be the transport layer, right ?
A: No… well, almost.
TCP is only part of the TCP/IP transport layer - the
other part is UDP (User Datagram Protocol).
TCP/IP 23
The Internet Hourglass
ICMP, ARP & RARP
802.3
TCP/IP 24
UDP User Datagram Protocol
⚫ UDP is a transport protocol
⚫ communication between processes
⚫ UDP uses IP to deliver datagrams to the right host.
⚫ UDP uses ports to provide communication services to
individual processes.
TCP/IP 25
Ports
⚫ TCP/IP uses an abstract destination point called a
protocol port.
⚫ Ports are identified by a positive integer.
⚫ Operating systems provide some mechanism that
processes use to specify a port.
Host A Host B
Proc Proce
ess ss
Proc Proce
ess ss
Proc Proce
ess ss
TCP/IP 26
UDP
⚫ Datagram Delivery
⚫ Connectionless
⚫ Unreliable
⚫ Minimal UDP Datagram Format
Source Port Destination Port
Length Checksum
Data
TCP/IP 27
TCP
Transmission Control Protocol
⚫ TCP is an alternative transport layer protocol
supported by TCP/IP.
⚫ TCP provides:
⚫ Connection-oriented
⚫ Reliable
⚫ Full-duplex
⚫ Byte-Stream
TCP/IP 28
Connection-Oriented
⚫ Connection oriented means that a virtual connection
is established before any user data is transferred.
⚫ If the connection cannot be established, the user
program is notified (finds out).
⚫ If the connection is ever interrupted, the user
program(s) is finds out there is a problem.
TCP/IP 29
Reliable
⚫ Reliable means that every transmission of data is
acknowledged by the receiver.
⚫ Reliable does not mean that things don't go wrong, it
means that we find out when things go wrong.
⚫ If the sender does not receive acknowledgement within
a specified amount of time, the sender retransmits the
data.
TCP/IP 30
Byte Stream
⚫ Stream means that the connection is treated as a
stream of bytes.
⚫ The user application does not need to package data in
individual datagrams (as with UDP).
TCP/IP 31
Buffering
⚫ TCP is responsible for buffering data and determining
when it is time to send a datagram.
⚫ It is possible for an application to tell TCP to send the
data it has buffered without waiting for a buffer to fill
up.
TCP/IP 32
Full Duplex
⚫ TCP provides transfer in both directions (over a single
virtual connection).
⚫ To the application program these appear as 2 unrelated
data streams, although TCP can piggyback control and
data communication by providing control information
(such as an ACK) along with user data.
TCP/IP 33
TCP Ports
⚫ Interprocess communication via TCP is achieved with
the use of ports (just like UDP).
⚫ UDP ports have no relation to TCP ports (different
name spaces).
TCP/IP 34
TCP Segments
⚫ The chunk of data that TCP asks IP to deliver is called a
TCP segment.
⚫ Each segment contains:
⚫ data bytes from the byte stream
⚫ control information that identifies the data bytes
TCP/IP 35
TCP Segment Format
1 byte 1 byte 1 byte 1 byte
Source Port Destination Port
Sequence Number
Request Number
offset Reser. Control Window
Checksum Urgent Pointer
Options (if any)
Data
TCP/IP 36
TCP process
⚫ When a client requests a connection, it sends a “SYN”
segment (a special TCP segment) to the server port.
⚫ SYN stands for synchronize. The SYN message includes
the client’s ISN.
⚫ ISN is Initial Sequence Number.
TCP/IP 37
More...
⚫ Every TCP segment includes a Sequence Number
that refers to the first byte of data included in the
segment.
⚫ Every TCP segment includes a Request Number
(Acknowledgement Number) that indicates the byte
number of the next data that is expected to be
received.
⚫ All bytes up through this number have already been
received.
TCP/IP 38
And more...
⚫ There are a bunch of control flags:
⚫ URG: urgent data included.
⚫ ACK: this segment is (among other things) an
acknowledgement.
⚫ RST: error - abort the session.
⚫ SYN: synchronize Sequence Numbers (setup)
⚫ FIN: polite connection termination.
TCP/IP 39
And more...
⚫ MSS: Maximum segment size (A TCP option)
⚫ Window: Every ACK includes a Window field that tells
the sender how many bytes it can send before the
receiver will have to toss it away (due to fixed buffer
size).
TCP/IP 40
Addressing in TCP/IP
⚫ Each TCP/IP address includes:
⚫ Internet Address
⚫ Protocol (UDP or TCP)
⚫ Port Number
NOTE: TCP/IP is a protocol suite that includes IP, TCP and UDP
TCP/IP 41
TCP vs. UDP
Q: Which protocol is better ?
A: It depends on the application.
TCP provides a connection-oriented, reliable, byte
stream service (lots of overhead).
UDP offers minimal datagram delivery service (as little
overhead as possible).
TCP/IP 42
TCP Connection Creation
⚫ A server accepts a connection.
⚫ Must be looking for new connections!
⚫ A client requests a connection.
⚫ Must know where the server is!
TCP/IP 43
Client Server
SYN 1
ISN=X
time
SYN 2
ISN=Y ACK=X+1
ACK=Y+1 3
TCP/IP 44
TCP Data and ACK
⚫ Once the connection is established, data can be sent.
⚫ Each data segment includes a sequence number
identifying the first byte in the segment.
⚫ Each segment (data or empty) includes a request
number indicating what data has been received.
TCP/IP 45
TCP Buffers
⚫ The TCP layer doesn’t know when the application will
ask for any received data.
⚫ TCP buffers incoming data so it’s ready when we ask for
it.
⚫ Both the client and server allocate buffers to hold
incoming and outgoing data
⚫ The TCP layer does this.
⚫ Both the client and server announce with every ACK
how much buffer space remains (the Window field in a
TCP segment).
TCP/IP 46
Send Buffers
⚫ The application gives the TCP layer some data to send.
⚫ The data is put in a send buffer, where it stays until the
data is ACK’d.
⚫ it has to stay, as it might need to be sent again!
⚫ The TCP layer won’t accept data from the application
unless (or until) there is buffer space.
TCP/IP 47
ACKs
⚫ A receiver doesn’t have to ACK every segment (it can
ACK many segments with a single ACK segment).
⚫ Each ACK can also contain outgoing data
(piggybacking).
⚫ If a sender doesn’t get an ACK after some time limit
(MSL) it resends the data.
TCP/IP 48
