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Internet Protocol. ECS 152B. Ref: slides by J. Kurose and K. Ross. Road Map. I. Introduction Computer Networks Overview Layered architecture II. IP Protocols Internet Protocol Routing protocols ICMP and IGMP III. Transport Layer UDP TCP. Goals.
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Internet Protocol ECS 152B Ref: slides by J. Kurose and K. Ross
Road Map I. Introduction • Computer Networks Overview • Layered architecture II. IP Protocols • Internet Protocol • Routing protocols • ICMP and IGMP III. Transport Layer • UDP • TCP
Goals • Principles of network layer services • Internet Protocol • Addressing • Routing • ARP • ICMP
Overview Encapsulation application message User process User process HTTP SNMP TCP UDP transport segment network datagram IGMP ICMP IP Hardware interface link frame ARP RARP Demultiplexing
transport packet from sending to receiving hosts network layer protocols in every host, router network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical application transport network data link physical application transport network data link physical Network layer functions
Functions • path determination: route taken by packets from source to dest. Routing algorithms • forwarding: move packets from router’s input to appropriate router output • call setup: some network architectures require router call setup along path before data flows (not Internet)
Q:What service model for transporting packets from sender to receiver? guaranteed bandwidth? preservation of inter-packet timing (no jitter)? loss-free delivery? in-order delivery? congestion feedback to sender? Network service model The most important abstraction provided by network layer: ? ? virtual circuit or datagram? service abstraction ?
call setup, teardown for each call before data can flow each packet carries VC identifier (not destination host ID) every router on source-dest path maintains “state” for each passing connection link, router resources (bandwidth, buffers) may be allocated to VC to get circuit-like perf. “source-to-dest path behaves much like telephone circuit” Virtual circuits
used to setup, maintain teardown VC used in ATM, frame-relay, X.25 not used in today’s Internet application transport network data link physical application transport network data link physical Virtual circuits: signaling protocols 6. Receive data 5. Data flow begins 4. Call connected 3. Accept call 1. Initiate call 2. incoming call
no call setup at network layer routers: no state about end-to-end connections no network-level concept of “connection” packets forwarded using destination host address packets between same source-dest pair may take different paths application transport network data link physical application transport network data link physical Datagram networks: the Internet model 1. Send data 2. Receive data
Network layer service models: Guarantees ? Network Architecture Internet ATM ATM ATM ATM Service Model best effort CBR VBR ABR UBR Congestion feedback no (inferred via loss) no congestion no congestion yes no Bandwidth none constant rate guaranteed rate guaranteed minimum none Loss no yes yes no no Order no yes yes yes yes Timing no yes yes no no • Internet model being extended: Intserv, Diffserv
VC vs. Datagram • VC • Guaranteed service • Complexity • Datagram • Simple • Best effort
Internet data exchange among computers “elastic” service, no strict timing req. “smart” end systems (computers) can adapt, perform control, error recovery simple inside network, complexity at “edge” many link types different characteristics uniform service difficult application at the end system, easy to define new services ATM evolved from telephony human conversation: strict timing, reliability requirements need for guaranteed service “dumb” end systems telephones complexity inside network Datagram or VC network: why?
Internet Protocol • Functionality: • Determine how to route packets from source to destination • Hide the details of the physical network • Unreliable, connectionless, datagram delivery • To be studied: • Addressing • Routing • ARP • ICMP and IGMP
Encapsulation source destination original message Application Application Transport Transport Network Network Link Link
IP protocol version number 32 bits total datagram length (bytes) header length (bytes) type of service head. len ver length for fragmentation/ reassembly fragment offset “type” of data flgs 16-bit identifier max number remaining hops (decremented at each router) upper layer time to live Internet checksum 32 bit source IP address 32 bit destination IP address upper layer protocol to deliver payload to E.g. timestamp, record route taken, specify list of routers to visit. Options (if any) data (variable length, typically a TCP or UDP segment) IP header 20 bytes overhead
IP Header • Version: 4 • Header length: 4 bits, max 15x4=60 bytes • TOS: 0 for normal service, • Total length: 16 bits, max 65535 bytes • TTL: 32/64, decrease by one in each hop • Protocol field: TCP,UCP,ICMP,IGMP,etc. • Checksum: header only
class 1.0.0.0 to 127.255.255.255 A network 0 host 128.0.0.0 to 191.255.255.255 B network 10 host 192.0.0.0 to 223.255.255.255 C network host 110 224.0.0.0 to 239.255.255.255 D multicast address 1110 32 bits IP Address Class-based address: 7 bits 14 bits 21 bits 28 bits
host part network part 11001000 0001011100010000 00000000 200.23.16.0/23 IP addressing: CIDR • Classful addressing: • inefficient use of address space, address space exhaustion • e.g., class B net allocated enough addresses for 65K hosts, even if only 2K hosts in that network • CIDR:Classless InterDomain Routing • network portion of address of arbitrary length • address format: a.b.c.d/x, where x is # bits in network portion of address
