ISYS 310 Chapter 5 (Network and transport layers)

IPv6 Packet

-Fixed header -320 bits (40 bytes) of overhead Optional Headers Hop-by hop options Destination options (with routing options) Routing Fragment Authentication Encapsulation Security Payload Destination options Mobility

Internet Protocol (IP) v4 (IPv4)

-Most common version of IP used -32-bit addresses (2^32 or ~4.29 billion possible) -Exhaustion of address space

IP version 6 (IPv6)

128-bit addresses (2^128 or ~3.4 X 10^38 possible) -Slowly being adopted due to IPv4 exhaustion

IPv4 Packet

160-192 bits (20-24byest) of overhead -Options field rarely used

Typical TCP Segment

192-bit header (24 bytes) of control information; contains the source and destination port identifier

Session Management (3)

A session can be thought of as a conversation between two computers or creating a virtual circuit; sessions provide reliable end-to-end connections

Segmenting (2)

Breaking up large files into smaller segments (and putting them back together) Segments may be passed individually to application layer or after reassembly

Does HTTP use UDP connections because they are often very short?

False. HTTP ALWAYS uses TCP connection-oriented messaging.

Common Port Standards

HTTP: TCP port 80 HTTPS: TCP port 443 FTP: TCP ports 20 and 21 SMTP: TCP port 25 IMAP: TCP port 143 POP3: TCP port 110 (more commonly TCP port 995 secure version) DNS: TCP or UDP port 53 (most commonly UDP)

Addressing

IPv4 addresses are 32 bits Most common way to write is using dot-decimal notation (breaks the address into four bytes and writes each byte in decimal notation instead of binary)

What layer is the Network Layer in the Internet Model?

Layer 3

What layer is the Transport Layer in the Internet Model?

Layer 4

Transmission Control Protocol (TCP)

Most common transport layer protocol; PDU called a segment; used for reliable transmission of data; 160-192 bits (20-24 bytes) of overhead; options field is not required

User Datagram Protocol (UDP)

Operates at the transport layer - PDU called a segment - used in time-sensitive situations, for control messages, or when reliability is handled by the application layer -32-64 bits (4-8 bytes) of overhead -Source port is optional in IPv4 and IPv6, Checksum is option in IPv4

What are network layer PDU's called?

Packets

Connectionless Messaging (UDP)

Sending messages without establishing a session

How large are the segments?

Size depends on the network and data link layer protocols Maximum Segment Size (MSS) is negotiated during TCP handshake e.g., if the maximum size of the data in an Ethernet frame is 1,500 bytes and TCP and IP use 20 byte headers, the maximum segment size is 1460 bytes

SYN

Synchronize; usually a randomly generated number that identifies a packet

What is the most common protocols of the Internet, LANs, WANs, and backbone networks?

TCP/IP

Linking to the Application Layer (1)

TCP/UDP may serve multiple application layer protocols Ports used to identify application (2-byte numbers) Many source/destination ports follow standards Common port standards

TCP/IP

Transmission Control Protocol/Internet Protocol

TCP

Transport layer protocol that links the application layer to the network layer; performs segmenting: breaking the data into smaller PDUs called segments, numbering them, ensuring each segment is reliably delivered, and putting them in the proper order at the destination

Addressing (4)

Used to direct messages from source to destination Addresses are assigned in various ways (i.e. by system administrators, ICANN, hardware vendors, etc.) Addresses exist at different layers Addresses may be translated (resolved) from one layer to another

Connection-Oriented Messaging (TCP)

Using a session to send data

Quality of Service (QoS)

a special type of connection-oriented messaging in which different connections are assigned different priorities

Session

can be thought of as a conversation between two computers; when the sending computer wants to send a message to the receiver, it usually starts by establishing a session with that computer

TCP/IP Development

developed for the US Department of Defense's Advanced Research Project Agency network (ARPANET) by Vinton Cerf and Bob Kahn in 1974

Transport Layer

links application and network layers; responsible for segmentation and reassembly; session management; responsible for end-to-end delivery of messages

Connectionless Messaging

means each packet is treated separately and makes its own way through the network;

TCP/IP

originally developed as a single internetworking protocol by Vint Cerf and Bob Kahn in 1972; later divided into the TCP and IP Protocols; most common protocols of the Internet and in LANs, WANs, and backbone networks

Network Layer

responsible for addressing and routing of messages

User Datagram Protocol (UDP)

second type of transport layer protocol; used when the sender needs to send a single small packet to the receiver

Three-way Handshake

sending of a SYN, response of a ACK, then sending of a SYN

Connection-oriented Messaging

sets up a TCP connection (also called a session) between the sender and the receiver; to establish a connection, the transport layer on both the sender and receiver must send a SYN and receive a ACK segment

IP

the network layer protocol and performs addressing and routing. IP Software is used at each of the intervening computers through which the message passes; it is IP that routes the message to the final destination

Connectionless messaging

the sender only wants to send one short information message or a request. in this case, the sender may choose not to start a session but just send the one quick message and move on

Segmenting

to take one outgoing message from the application layer and break it into a set of smaller segments for transmission through the network; it also means to take the incoming set of smaller segments from the network layer and reassemble them into one message for the application layer

TCP Connections are opened by...

using a 3 way handshake -SYN -SYN-ACK -ACK

Connection-oriented messaging

when the sending computer wants to send a message to the receiver, it usually starts by establishing a session with that computer. the sender transmits the segments in sequence until the conversation is done, and then the sender ends the session

Four-way Handshake

when the transmission is complete, the session is terminated using a four-way handshake