Chapter 5 Network and Transport Layers
Connectionless messaging
*-Each packet is treated separately and makes its own way through the network* -Sender sends packets as unrelated entities -Packets can take different routes depending on routing and traffic *What type of messaging is this...?*
Segmenting
*-To take one outgoing message from the app. layer and break it into a set of smaller segments for transmission through the network* -Take incoming set of segments and reassemble them -Can be delivered one at a time (web browser) or wait until all packets have arrived and message is complete (email) -ensures receiver got all the packets (continuous ARQ)
Static routing
-*Decentralized*-all computers/routers make own routing decisions following protocol -*Self adjusting*-adapt to changes in network configuration -routing *decisions made in fixed manner* -routing table developed by manager and only changed when computers are +/-
Dynamic routing (adaptive)
-*decentralized by individual comp*. -*multiple routes through network* and *important to select best route* -tries to route messages over best possible route -network manager makes routing table but computers cont. update it
Loopback range
-127 address -Reserved for a computer to communicate with itself -Mostly used by developers/system administrators
IPv6 address
-16 byte long-3.4x10^38 addresses -hexadecimal (eight sets of 2 byte numbers) -Compressed notation: eliminates leading 0's within each block and blocks that are all 0's
How many bits in a typical TCP segment
-192 bit header (24 bytes) of control information
User Datagram Protocol
-2nd type of transport layer protocol -PDUs called "datagrams" -Used when sender needs to send a single small packet to the reciever -Transport layer doesn't need to worry about segmenting-faster transmission -Datagram 4 fields-source port, destination port, length and CRC-16 -Does not check for lost messages
Addresses are divided up in Internet Address Classes (IPv4)
-3 classes: assigned by value of their first byte -Class A: 1-126 -Class B: 128-191 -Class C:192-223
Broadcast messages
-Addresses starting with 255
What does IP perform
-Addressing and routing -IP software is used at each intervening comp. through which the message passes -IP routes message to final destination
Application Layer Addresses (server names)
-Also assigned by software configuration -all servers have app. layer address but most client computers do not -important for users to access servers and info they contain but not important for someone to access someone else's client comp.
What happens if packets arrive out of order in connectionless messaging?
-Because they travel different routes can arrive out of order -Sender's network layer adds sequence # on each packet and info about the message stream to which the packet belongs
What do routers consist of?
-CPU -Memory -ports/interfaces that connect them to a network or other computers
PDU at the transport layer
-Called a "segment" -Network layer takes message from transport layer and routes them through the network selecting the best path from computer to computer and adds an IP packet
Operating system used by 90% of routers
-Cisco Internetwork Operating system -Uses command line interface -creat configuration file that define how router will operate -routing protocol, interfaces, encryption
TCP/IP can use connection oriented or connectionless
-Connection oriented used-TCP -Connectionless used- UDP packet (header much smaller)-usually used when message can fit in single message
Session
-Conversation between two computers
Link state dynamic routing
-Count # of hops, speed of circuits, how busy each route is -tries to determine how fast each route is -preferred in large networks
Distance vector dynamic routing
-Count the number of hops along route -hop=one circuit -comp share info on hop count/relative speeds of circuits
Replication
-DNS servers exchange information about new and changed addresses among themselves
Assigning Addresses
-Data link layer address encoded in each network card (physical/MAC address) -address is part of hardware never changed
What does IP protocol define
-Defines address space that can be used on Internet -Address space-total number of addresses available
Subnets
-Designed to logically subdivide the network into logical pieces -addressing hierarchy
TCP/IP
-Dominate transport/network layer protocol -Developed by US dept of defense advanced research project agency network (ARPANET) -Transport/network protocol used on internet -Compatible with a number data link protocols -Used by most BNs and WANS
Routing Information protocol
-Dynamic distance vector interior -smaller networks- 1 organization -counts # of computers in possible routes and selects route with the least -Used by TCP/IP and IPX/SPX
Four way Handshake
-Full-duplex connection so each side has to terminate session independently 1.Sender sends FIN so server 2. Server sends back ACK 3. Server sends FIN 4. connection successfully terminated when server receives ACK for FIN
How are network layer address assigned?
-Generally assigned by software -software package usually has configuration file that specifies the network layer address for that comp. -Important each comp. on network has unique network layer address so every network has standards group that defines what network layer address can be used by each organization
What does the application layer software use? TCP or UDP?
-HTTP/SMTP/FTP/Telnet=TCP -DHCP/RIP/SNMP=UDP
Network Layer Address
-IP protocol -web addresses translated into IP address -4 bytes long when using IPv4
What does TCP perform?
-It performs segmenting: breaking the data into smaller PDUs called segments -Numbers them -Ensures each segment is reliably delivered -puts them in proper order at destination -TCP software only needs to be active @ sender/receiver because TCP only involved when data goes/comes from app. layer
Network layer determines best route through network to final destination
-Network layer identifies data link layer address of next computer message should be sent -Running Ethernet- IP address translated to Ethernet address
Address resolution
-Process where the sender *translates the application layer address* of the destination *into a network layer address* and *in turn translate it into a data link layer address*
Interior routing protocol
-Protocols *used within an autonomous system* -*provide detailed routing* info about all comps inside system
Classes of Service
-QoS routing provides different priorities for different types of messages -Transport layer establishes connection, specifies class of service that connection requires -Each path through network designed to support different # and mix of service classes -When connection established, network makes sure no connection exceeds max # of that class on given circuit
ICANN (Internet Corporation for assigned names and numbers)
-Responsible for managing the assignment of network layer addresses -Set rules by which new domain names are created and IP addresses are assigned -Directly manages Internet domains and authorizes companies to become domain name registrars
SYN and ACK
-SYN= Synchronize- usually a randomly generated number that identifies a packet -ACK- acknowledgment
Connectionless messaging
-Sender only wants to send on short info message or request -don't start a session and just send the one quick message
Dynamic addressing
-Server is designated to supply a network layer address to a computer each time the computer connect to the network -Common for client but not servers
Application layer address
-Server name -www.indiana.com -type address into browser, request is passed to netowrk layer as part of app layer packet formatted with HTTP protocol
Why are IP addresses often assigned in groups?
-So that one organization receives a set of numerically similar addresses -application layer addresses and network layer addresses can be assigned at the same time
DHCP
-Special software installed on client that instructs it to contract a DHCP server to obtain an address -Can assign the same network address each time -Can "lease" the address by picking next available network layer address from list
Quality of service routing
-Special type of connection oriented messaging in which different connections are assigned different priorities -Video conferencing needs fast delivery of packets while 10 sec delay doesn't matter with email
Reserved address
-Start with 224 -Should not be used on IP network
RSVP and RTSP are used to create a connection and request certain minimum guaranteed data rate
-They use Real-Time Transport protocol to send packets -RTP has info about sending application, packet sequence #, and a time stamp so data in RTP packet can by synchronized with other RTP packets
Data link layer address
-To send message to another computer in subnet, comp must know the correct*...* -TCP/IP sends broadcast message to all computers in subnet
Server name resolution
-Translation of application layer addresses into network layer addresses -Done using domain name service -Throughout internet series of comp. called name servers that provide DNS service -Dont know IP #-send request to name server requesting IP #
Classless addressing (slash notation)
-Uses a slash to indicate address range
Root servers
-When resolving name server doesn't know, asks root server and root server will respond with the DNS server it should ask -Includes IP address for top level domain server (.edu) -TLD then would send back a response telling it to ask that websites authoritative name server who in turn would send the IP address -Once you receive address stored in your DNS cache
Private IPv4 address space
-Within each class, address space that can only be used internally by organizations -Routers on Internet do not route packets that use private addresses -Used to increase security (hackers can't send messages to them)
Multicasting
-addresses from 224-239 -Class D -*sending messages to group of computers* rather than to one computer (normal) or every computer on a network (broadcast)
Centralized routing
-all routing decisions are made by *one central* computer or router -host based networks -routing decisions are simple
Subnet mask
-any portion of the IP address can be designated as a subnet -Every comp. in TCP/IP network is given a subnet mask so it can determine which other comps. are on the same subnet and which are outside the subnet -Partial bytes can be used as subnets as well
Routers
-devices that enable routing -found at the edge of subnets b/c connect subnets together and enable messages to flow from one subnet to another -Connection called an "interface"
Border Gateway protocol
-dynamic distance vector exterior routing protocol -*exchange routing info between large sections of the internet* -no businesses use it b/c hard to administer
Enhanced Interior gateway routing protocol
-dynamic hybrid interior developed by Cisco -commonly used inside organizations -better version of IGRP -store own routing tables and routing tables of their neighbors
Open shortest path first
-dynamic hybrid interior on Internet -*Uses # of comp, network traffic, error rates to select best route* -selectively sends status updates directly to selected computers -Preferred Interior routing protocol of TCP/IP
Port address
-how transport layer decides which application layer program it should deliver the message too -Source port: own port address of application layer sending message -Destination port: port address of the receiving application program -Can be any 16 bit (2 byte) number
Intermediate systems to intermediate systems
-link state interior routing -large networks -ISO protocol added to many TCP/IP networks
Internet Protocol (IP)
-network layer protocol -PDUs called "packets" -2 forms of IP: 1. IPv4 (192 bit header-source/destination addresses, packet length, packet number) 2.IPv6-320 bit header-increase in address size from 32-128 bits-simpler packet structure easier for routing
Autonomous system
-network operated by one organization -organization that runs one part of the Internet
Access control list
-network security -defines what types of packets should be routed and what type should be discarded
Unicast message
-one computer sends a message to another computer
Routing protocols
-protocol that is used to exchange information among computers to enable them to build/maintain routing tables
Exterior routing protocols
-protocols used between autonomous systems -only provide info about the best routes
Broadcast message
-received and processed *by all computers on LAN* -specially formatted in Address Resolution Protocol -asks computers whoever's IP address this is, send me your data link layer address
Multicast message
-send the same message to a group of computers -Special type of packet called Internet group management protocol -each group special IP -Comp. know to route any messages with this IP address to the subnet that contains the requesting comp.
Internet control message protocol
-simplest interior routing protocol on Internet -enables comps. to report routing errors to message senders -limited ability to update tables
NAT firewalls
-special devices that translate private addresses on messages into valid public addresses so can send messages to other computers on the Internet
Routing table
-table that specifies how messages will travel through the network -1st column: every network/comp. that router knows -2 column lists the interface that connects to it -decides where to send messages it receives
Resolving name server
-the DNS server that the client computer is connected to
Parts of a TCP segment
1. Destination port: tells the TCP software at the destination to which app. layer program the application layer packet should be sent 2.Source port: tells the receiver which application layer program the packet is from 3. Sequence number: TCP software at destination can assemble the segments into the correct order and make sure no segments have been lost 4.Options field: optional and rarely used 5. Header length field: used to tell receiver how long the TCP packet is (whether or not option field included)
Three way handshake (connection oriented messaging)
1. Establish TCP connection (session) between sender and reciever 2. Sender (client) sends SYN to reciever (server) 3. Server sends back an ACK and then its on SYN 4. Client sends ACK for server's SYN 5. segments flow and TCP uses continuous ARQ to provide flow control
3 unique functions performed by the Transport layer
1. Linking the application layer to network layer 2. Segmentation/reassembly 3. Session management
2 drawback to dynamic routing
1. Requires more processing by each computer 2. transmission of routing info wastes network capacity
Internet provides several QoS protocols that can work in a TCP/IP environment (2)
1. Resource Reservation Protocol (RSVP) (more general purpose) 2. Real-Time streaming protocol (RTSP) (audio/video streaming) -both permit app. layer software to request connections that have minimum data transfer capabilities
TCP/IP 2 parts
1. TCP: transport layer protocol that links application layer to network layer 2. IP: network layer protocol
Types of routing 3
1. centralized routing 2. static routing 3. dynamic routing
3 ways network manager can connect to a router and configure/maintain it
1. console port 2. network interface port 3. auxiliary port
3 functions of a router
1. determine the path for the packet to travel 2. transmit the packet across the path 3. supports communication between wide variety of devices and protocols
What does the transport layer do?
1. links application software in app. layer with network 2. Responsible for end to end delivery of message 3. Accepts outgoing messages from application layer and segments them for transmission 4. accept incoming messages from data link layer and organize them into coherent message that are passed to application layer
TCP/IP allows....
1. reasonably effiecient and error-free transmission 2. performs error checking
Translating App. layer address to IP address
1.Sends a special DNS request packet to DNS server 2. Asks DNS server for IP address that matches Internet app. layer address provided 3. Sends back packet with IP address 4. If it doesn't have it-sends packet to another DNS server
-Server name resolution -Data link layer address resolution
2 types of address resolution
-routers connect two or more subnets -Without routers the subnets would not be able to communicate
What do routers do in terms of subnets?
-Data link layer protocol used -TCP/IP commonly combined with ethernet -Ethernet 1492 bytes so max size of TCP message field if IPv4 is used is 1492-24(TCP header)-24(IPv4 header)=1444
What does the size of the message field depend on?
Connection-oriented messaging
When a computer sends a message it starts a session with the other computer, transmits the message, and then ends the session at the end
Dynamic Host Configuration Protocol
most common standard of Dynamic addressing
Routing
process of determining the route or path through the network that a message will travel
