Network layer in practice: IP and atm

1. Network layer in practice: IP and atm

2. The TCP/IP protocol suite • Transmission Control Protocol / Internet Protocol • Developed by DARPA to connect universities and research labs The Internet Layered model Telnet, FTP, email etc TCP, UDP IP, ICMP, IGMP Device drivers, interface cards TCP: Transmission Control Protocol UDP: User Datagram Protocol IP: Internet Protocol

3. Internet sub-layer • A sub-layer between the transport and network layers is required when various incompatible networks are joined together • This sub-layer is used at gateways between the different networks • In the internet this function is accomplished using the Internet Protocol (IP) On a gateway connecting different types of networks, IP is the protocol to realize inter-operability IP DLC Layer Link 1 DLC Layer Link 1 DLC Layer Link 1

4. Internetworking with TCP/IP FTP, HTTP, SMTP… application application TCP/UDP protocol transport transport IP protocol IP protocol IP IP IP Data link and lower layer Ethernet Token ring Data link and lower layer Ethernet Ethernet Token ring

5. The TCP/IP suite PING telnet & rlogin FTP SMTP X Trace route DNS TFTP BOOTP SNMP RPC TCP UDP ICMP IP IGMP ARP DATA LINK RARP

6. IP addresses • 32 bit address written as four decimal numbers • One per byte of address (202.120.39.134) • IP Address classes 8 32 Class A Address 16 32 Class B Address 16 32 Class C Address 16 32 Class D Address, (For multicast only)

7. IPv4 address classes

8. Routing a packet in the network 1 3 2 3 4 2 1 1 1 2 3 3 1 4 3 2 4 2 6 2 2 1 5 1 3

9. Host name • Each host has a unique name • Domain name system (DNS): a distributed database that provides a mapping between IP addresses and host names • E.g., 202.120.39.134  FRONT.SJTU.EDU.CN

10. Internet standards • Internet Engineering Task Force (IETF) • Development on near term internet standards • Open body • Meets 3 times a year • Request For Comments (RFCs) • Official internet standards • Available from IETF web page: http://www.ietf.org/

11. The Internet protocol (IP) • Routing packets across the network • Unreliable service • Best effort delivery • Recovery from lost packet must be done at higher layers • Connectionless • Packets are delivered independently • Can arrive out of order • Re-ordering must be done at higher layers • Current version V4, IPv4 • Future IPv6

12. IP header • Note that the minimum header size is 20 bytes, or 160 bits

13. IP header

14. Dynamic Host Configuration (DHCP) • Automated method for assigning network numbers • IP addresses, default routers • Computer contact DHCP server at Boot-up time • Server assigns IP address • Allows sharing of address space • More efficient use of address space • Adds scalability • Addresses are “leased” for some time • Not permanently assigned

15. Address Resolution Protocol (ARP) • The role of the IP routing is to deliver the packet to its destination subnet • To the last hop router • Addressing inside a subnet, or a LAN, is based on local addresses, such as Ethernet addresses • ARP provides a mapping between IP addresses and LAN addresses • RARP provides mapping from LAN addresses to IP addresses • Both accomplished by sending out a broadcast message • An ARP cache is maintained at each node with recent mappings to avoid frequent address resolution (for better performance)

16. ARP at source subnet (3) Hi all~ Where is my lovely router R1? (4) I am here at 00-01-21-32-32-32 R1 Computer S is configured to have a default router R1 S wants to send a message to D, and D is outside of the same LAN S sends an ARP request for Ethernet Address of R1 R1 sends ARP responds to S S sends the message to R1 with Ethernet addressing R1 routes the packet to the next hop in the internet and the message will be subsequently routed further toward D S

17. ARP at destination subnet (4) Hi R2~ I am here at 00-01-01-11-AB-ED (3) Hi all~ I got a message for 202.120.39.134. Where is he? R2 An IP packet is delivered by the network from its source subnet to router R2. Router R2 realizes that the packet has reached its destination subnet by comparing the destination address in the IP packet and its local interface configurations (subnet address and mask) Router R2 sends an ARP request on the interface to the subnet Destination node D responses to the request Packet is delivered to D with Ethernet addressing D

18. Routing in the multi-AS Internet • The Internet is divided into sub-networks, each under the control of a single authority known as an Autonomous Systems (AS) • Routing algorithms are divided into two categories • Interior protocols (within an AS) • Exterior protocols (between ASs) • Interior protocols use shortest path algorithms • Distance vector proto. Based on Bellman-Ford • Link state proto. Based on Dijkstra’s algorithm • Exterior protocols route packets across ASs • Issue: no single cost metric, policy routing, etc • Hierarchical routing based on “peering” agreements • Example: Exterior Gateway Protocol (EGP) and Border Gateway Protocols (BGP)

19. Border Gateway Protocol (BGP) • Routing between Autonomous systems • Find a path (no optimality) to destination (AS) • Path must satisfy policy criteria AS corporation AS Large service provider AS Large service provider Transit AS AS Small ISP AS Small ISP Multi-homed AS (No transit traffic) AS Small ISP AS corporation AS corporation Stub AS

20. BGP overview • BGP speaker – one per AS • Establishes (TCP) sessions with other “speakers” to exchange reachability information • Border “gateways” – routers that interface between AS’s • BGP advertises complete paths to destination AS • Avoid loop problems • Enable policy decisions (e.g. avoid certain ASs) • AS numbers – centrally assigned 16 bit numbers for transit ASs AS - 367 • 128.64.3 • 128.61.2 AS - 12 AS - 144 AS - 298 • 192.12.2 • Path to 128.64.2: (AS-144, AS-367)

21. Relationship between ASs • ISP “tiers” • Tier-1 ISPs – provide global reachability • Tier-2 ISPs – regional/country • Tier-3 ISPs – local • Provider-customer relationship (transit) • Smaller ASs purchase internet access from larger ones • Peering • ISPs of similar size are “peers” and forward each other’s traffic at no charge • Paid peering: a small ISP may purchase the right to peer with a larger provider • Policy issue • Which route would an ISP advertise? Tier-1 ISP Tier-2 ISP Tier-1 ISP Tier-2 ISP Tier-3 ISP

22. IPv6 • Effort started in 1991 as IPng • Motivation • Need to increase IP address space • Support for real-time applications – QoS • Security, mobility and auto-configuration • Major changes • Increased address space (128bit) • Support for QoS via Flow Label field • Simplified header • Transition to IPv6 • Cannot be done at once; must support co-existance • Dual-stack: routers run both IPv4 and IPv6 • Tunneling: IPv6 packets carried in payload of IPv4 packets, or vice versa

23. QoS in the Internet • Quality of Service parameters • Dropped packets • Delay • Jitter • Out-of-order delivery • Error • Applications that require QoS • Multimedia streaming • IPTV • IP telephony, or VoIP • Video conferencing • Online game • Remote control • …

24. QoS mechanisms • IntServ: integrated services • best-effort service, real-time service, and controlled link sharing • Resource reserved prior to data transfer • Resource released after transfer completes request grant

25. QoS mechanisms (cont.) • DiffServ: differentiated services • Tagging on ingress edge node • Un-tagging on egress edge node • Routed/processed in network according to the tag/label • Realizes service differentiation through per-hop behavior (PHB)

26. DiffServ and MPLS • MPLS: Multi-ProtocolLabel Switching

27. ATM - Asynchronous Transfer Mode • 1980’s effort by the phone companies to develop an integrated network standard (B-ISDN) that can support voice, data, video, etc. • ATM uses small (53 Bytes) fixed size packets called “cells” • Why cells? Cell switching has properties of both packet and circuit switching Easier to implement high speed switches • Why 53 bytes? • Small cells are good for voice traffic (limit sampling delays) For 64Kbps voice it takes 6 ms to fill a cell with data • ATM networks are connection oriented • Virtual circuits

28. ATM Reference Architecture • Upper layers • Applications • TCP/IP • ATM adaptation layer • Similar to transport layer • Provides interface between upper layers and ATM • Break messages into cells and reassemble • ATM layer • Cell switching • Congestion control • Physical layer • ATM designed for SONET • Synchronous optical network • TDMA transmission scheme with 125 μs frames

29. ATM Cell format

30. VPI/VCI

31. ATM cell switches

32. ATM summary • ATM is mostly used as a “core” network technology • ATM Advantages • Ability to provide QoS • Ability to do traffic management • Fast cell switching using relatively short VC numbers • ATM disadvantages • It not IP -most everything was design for TCP/IP • It’s not naturally an end-to-end protocol • Does not work well in heterogeneous environment • Was not design to inter-operate with other protocols • Not a good match for certain physical media (e.g., wireless) • Many of the benefits of ATM can be “borrowed” by IP • Cell switching core routers • Label switching mechanisms