Integrated Services An architecture for streaming multimedia Aimed at both unicast and multicast applications An example of unicast: a single user streaming a video clip from a news site An example of multicast: a collection of digital television stations broadcasting their programs as streams of IP packets to many receivers at various locations Unicast is a special case of multicast Integrated Services In multicast applications, groups can change membership dynamically (people enter a video conference and then get bored and switch to a soap opera or the croquet channel) Under these conditions, the approach of having the senders reserve bandwidth in advance does not work well, since it would require each sender to track all entries and exits of its audience For a system designed to transmit television with millions of subscribers, it would not work at all RSVP Resource reservation Protocol Allows multiple senders to transmit to multiple groups of receivers Permits individual receivers to switch channels freely Optimizes bandwidth use while at the same time eliminating congestion Expedited Forwarding Expedited packets experience a trafficfree network. Assured Forwarding A possible implementation of the data flow for assured forwarding. Internetworking How Networks Differ How Networks Can Be Connected Concatenated Virtual Circuits Connectionless Internetworking Tunneling Internetwork Routing Fragmentation
Connecting Networks A collection of interconnected networks. How Networks Differ Some of the many ways networks can differ. How Networks Can Be Connected In the physical layer, networks can be connected by repeaters or hubs, which just move the bits from one network to an identical network. These are mostly analog devices and do not understand anything about digital protocols (they just regenerate signals) In data link layer, bridges and switches can be used. They can accept frames, examine the MAC addresses, and forward the frames to a different network while doing minor protocol translation in the process How Networks Can Be Connected In network layer, routers can connect two networks. If two networks have dissimilar network layers, the router may be able to translate between the packet formats In transport layer, transport gateways can interface between two transport connections In the application layer, application gateways translate message semantics. As an example, gateways between Internet e-mail (RFC 822) and X.400 e-mail must parse the e-mail messages and change various header fields How Networks Can Be Connected (a) Two Ethernets connected by a switch. (b) Two Ethernets connected by routers. With a switch (or bridge), the entire frame is transported on the basis of its MAC address. With a router, the packet is extracted from the frame and the address in the packet is used for deciding where to send it. Switches do not have to understand the network layer protocol being used to switch packets. Routers do How Networks Can Be Connected Two styles of internetworking are possible a connection-oriented concatenation of virtualcircuit subnets: In the past, most (public) networks were connection oriented (and frame relay, SNA, 802.16, and ATM still are) a datagram internet style: with the rapid acceptance of the Internet, datagrams became fashionable
Concatenated Virtual Circuits A connection to a host in a distant network is set up in a way similar to the way connections are normally established The subnet sees that the destination is remote and builds a virtual circuit to the router nearest the destination network Then it constructs a virtual circuit from that router to an external gateway (multiprotocol router) This gateway records the existence of the virtual circuit in its tables and proceeds to build another virtual circuit to a router in the next subnet This process continues until the destination host has been reached Concatenated Virtual Circuits Once data packets begin flowing along the path, each gateway relays incoming packets, converting between packet formats and virtual-circuit numbers as needed. All data packets must traverse the same sequence of gateways. Packets in a flow are never reordered by the network. Best when all the networks have roughly the same properties Concatenated Virtual Circuits Internetworking using concatenated virtual circuits. Connectionless Internetworking Does not require all packets belonging to one connection to traverse the same sequence of gateways Datagrams from host to host take different routes through the internetwork A routing decision is made separately for each packet, possibly depending on the traffic at the moment the packet is sent can use multiple routes and thus achieve a higher bandwidth than the concatenated VC model There is no guarantee that the packets arrive at the destination in order (if they arrive at all) Connectionless Internetworking A connectionless internetwork Tunneling Tunneling a packet from Paris to London.
Tunneling (2) Internetwork Routing Tunneling a car from France to England. (a) An internetwork. (b) A graph of the internetwork. Internetwork Routing Two-level routing algorithm within each network an interior gateway protocol is used between the networks, an exterior gateway protocol is used Since each network is independent, they may all use different algorithms Because each network in an internetwork is independent of all the others, it is often referred to as an Autonomous System (AS) Differences between internetwork routing and intranetwork routing Boundary (international vs national) Charging (cost) Fragmentation Each network imposes some maximum size on its packets Network designers are not free to choose any maximum packet size they wish Maximum payloads range from 48 bytes (ATM cells) to 65,515 bytes (IP packets), although the payload size in higher layers is often larger The only solution is to allow gateways to break up packets into fragments, sending each fragment as a separate internet packet Fragmentation The Network Layer in the Internet The IP Protocol IP Addresses Internet Control Protocols OSPF & BGP Internet Multicasting Mobile IP IPv6 (a) Transparent fragmentation. (b) Nontransparent fragmentation.
Design Principles for Internet RFC 1958 Make sure it works Keep it simple Make clear choices Exploit modularity Expect heterogeneity Avoid static options and parameters Look for a good design; it need not be perfect Be strict when sending and tolerant when receiving Think about scalability Consider performance and cost Collection of Subnetworks The Internet is an interconnected collection of many networks (autonomous systems-as). Internet Protocol The glue that holds the whole Internet together is the network layer protocol, IP (Internet Protocol) Unlike most older network layer protocols, it was designed from the beginning with internetworking in mind Its job is to provide a best-efforts (i.e., not guaranteed) way to transport datagrams from source to destination, without regard to whether these machines are on the same network or whether there are other networks in between them How it works? The transport layer takes data streams and breaks them up into datagrams in theory, can be up to 64 Kbytes each in practice usually not more than 1500 bytes (fit in one Ethernet frame) Each datagram is transmitted through the Internet, possibly being fragmented into smaller units When all the pieces finally get to the destination machine, they are reassembled by the network layer into the original datagram This datagram is then handed to the transport layer, which inserts it into the receiving process' input stream IP Datagram The IP Protocol (v4) header Format of the IP datagram consists a header part a text part The header has a 20-byte fixed part and a variable length optional part
The IP Protocol IP Addresses IP address formats - classful addressing (no longer used) Some of the IP options IP Addresses Class A formats allow for up to 128 networks with 16 million hosts each Class B: 16,384 networks - 64K hosts Class C: 2 million networks - 256 hosts Class D support for multicast, in which a datagram is directed to multiple hosts Class E: addresses beginning with 1111 are reserved for future use Network Numbers Network numbers are managed by a nonprofit corporation called ICANN (Internet Corporation for Assigned Names and Numbers) to avoid conflicts Network addresses, (32-bit numbers, written in dotted decimal. Each of the 4 bytes is written in decimal, from 0 to 255. E.g., the 32-bit hexadecimal address C0290614 is written as 192.41.6.20. The lowest IP address is 0.0.0.0 and the highest is 255.255.255.255 The values 0 and -1 (all 1s) have special meanings The value 0 means this network or this host The value of -1 is used as a broadcast address to mean all hosts on the indicated network 127.xx.yy.zz are reserved for loopback testing IP Addresses Special IP addresses Subnets In IP addressing, all the hosts in a network must have the same network number This can cause problems as networks grow Getting a second network address would be hard to do A small change was made to the addressing system to deal with it Allow a network to be split into several parts for internal use but still act like a single network to the outside world
Subnets A campus network consisting of LANs for various departments Subnets In the Internet literature, the parts of the network (in this case, Ethernets) are called subnets. This usage conflicts with ''subnet'' to mean the set of all routers and communication lines in a network Subnets When a packet comes into the main router, how does it know which subnet (Ethernet) to give it to? One way would be to have a table with 65,536 (class B) entries in the main router telling which router to use for each host on campus This idea would work, but it would require a very large table in the main router and a lot of manual maintenance as hosts were added, moved, or taken out of service Subnets Instead, a different scheme was invented Basically, instead of having a single class B address with 14 bits for the network number and 16 bits for the host number, some bits are taken away from the host number to create a subnet number For example, if the university has 35 departments, it could use a 6-bit subnet number and a 10-bit host number, allowing for up to 64 Ethernets, each with a maximum of 1022 hosts (0 and -1 are not available) This split could be changed later if it turns out to be the wrong one Subnet Mask To implement subnetting, the main router needs a subnet mask that indicates the split between network + subnet number and host Subnet masks are also written in dotted decimal notation, with the addition of a slash followed by the number of bits in the network + subnet part For the example, the subnet mask can be written as 255.255.252.0 (252 = 11111100) An alternative notation is /22 to indicate that the subnet mask is 22 bits long Subnet Mask A class B network subnetted into 64 subnets
Subnet Mask Outside the network, the subnetting is not visible In this example, the first subnet might use IP addresses starting at 130.50.4.1; second subnet might start at 130.50.8.1; third subnet might start at 130.50.12.1; etc. To see why the subnets are counting by fours, note that the corresponding binary addresses are as follows: Subnet 1: 10000010 00110010 000001 00 00000001 Subnet 2: 10000010 00110010 000010 00 00000001 Subnet 3: 10000010 00110010 000011 00 00000001 Here the vertical bar ( ) shows the boundary between the subnet number and the host number. To its left is the 6-bit subnet number; to its right is the 10-bit host number Subnet Mask Using subnet, the routing tables are changed, adding entries of the form (this-network, subnet, 0) and (this-network, this-subnet, host) A router on subnet k knows how to get to all the other subnets and also how to get to all the hosts on subnet k It does not have to know the details about hosts on other subnets All that needs to be changed is to have each router do a Boolean AND with the network's subnet mask to get rid of the host number and look up the resulting address in its tables Subnet Mask For example, a packet addressed to 130.50.15.6 and arriving at the main router is ANDed with the subnet mask 255.255.252.0/22 to give the address 130.50.12.0. This address is looked up in the routing tables to find out which output line to use to get to the router for subnet 3 Subnetting thus reduces router table space by creating a three-level hierarchy consisting of network, subnet, and host (instead of only two: network and host) CIDR Classless InterDomain Routing IP is running out of addresses CIDR (RFC 1519): to allocate the remaining IP addresses in variable-sized blocks, without regard to the classes If a site needs, say, 2000 addresses, it is given a block of 2048 addresses on a 2048-byte boundary The routing tables all over the world are now updated with local assigned entries, each entry contains a base address and a subnet mask Local entries can be combined into a single aggregate entry NAT Network Address Translation IP is running out of addresses NAT (RFC 3022): assign each company a single IP address (or at most, a small number of them) for Internet traffic within the company, every computer gets a unique IP address, which is used for routing internal traffic when a packet exits the company and goes to the ISP, an address translation takes place when a packet leaves the company premises, it passes through a NAT box that converts the internal IP source address (e.g. 10.0.0.1) to the company's true IP address (e.g. 198.60.42.12) Internet Control Protocols In addition to IP, which is used for data transfer, the Internet has several control protocols used in the network layer: ICMP: Internet Control Message Protocol ARP(Address Resolution Protocol): mapping IP address into other (Ethernet) address RARP (Reverse Address Resolution Protocol): mapping other (Ethernet) address into IP address BOOTP (Bootstrap Protocol): static mapping table DHCP: Dynamic Host Configuration Protocol : dynamic address assignment using special server.
ICMP Operation of Internet is monitored by the routers When something unexpected occurs, the event is reported by the ICMP (Internet Control Message Protocol), which is also used to test the Internet About a dozen types of ICMP messages are defined Each ICMP message type is encapsulated in an IP packet www.iana.org/assignments/icmp-parameters ICMP The principal ICMP message types Routing in the Internet Gateway Routing Protocols: Interior Gateway Routing Protocol: OSPF (Open Shortest Path First) The Exterior Gateway Routing Protocol: BGP (Border Gateway Protocol) Internet Multicasting Typical internet connection is one-to-one Multicasting is supported: Usage: Updating replicated Distributed database Digital conferences How: Using class D address Permanent Temporary Mobile IP Problems: Moving new IP address? Complete IP address on router? IP address must belong to LAN which it is currently attached? Probing periodically? Registration? Security? IPv6 GOAL: Support billions of hosts, even with inefficient address space allocation. Reduce the size of the routing tables. Simplify the protocol, to allow routers to process packets faster. Provide better security (authentication and privacy) than current IP. Pay more attention to type of service, particularly for real-time data. Aid multicasting by allowing scopes to be specified. Make it possible for a host to roam without changing its address. Allow the protocol to evolve in the future. Permit the old and new protocols to coexist for years
IPv6 IPv6 has longer addresses than IPv4. They are 16 bytes Simplification of the header It contains only seven fields (versus 13 in IPv4) This allows routers to process packets faster and thus improve throughput and delay Better support for options and the way options are represented Speeds up packet processing time Security Authentication and privacy are key features