Internet Protocols

1. Internet Protocols • Each host computer on the network must have a unique (logical) address • Scaled up very well to support more sophisticated distributed applications • IP Defines • A format for assigning addresses • An (unreliable) mechanism for transferring data (datagram)

2. IP Protocol • Provides an unreliable or best-effort delivery service • Only checksum is the header checksum. • IP layer • Puts IP datagrams into network packets suitable for transmission in the underlying network; • E.g., Ethernet. • When the datagram is longer than MTU of the underlying network, it is broken into smaller segments and reassembled at the destination. • Must insert “physical” network address of the message destination if necessary; • Depends on the underlying network technology, i.e., Ethernet requires and Ethernet address for the host on the local Ethernet.

3. Mobility and IP • Dynamic Host Configuration Protocol (DHCP) • Designed to support the ability of a mobile device to maintain simple access to services; • Assigns a temporary IP address to the device. • To provide permanent access by clients to a mobile computer it must maintain a permanent IP address. • Problem: IP routing is subnet-based. • Subnets are at fixed locations.

4. MobileIP • A transparent solution based on tunnelling. • When a mobile computer is connected to the Internet elsewhere, two agents take responsibility for routing. • Home agent (HA): • holds up-to-date knowledge of the mobile host’s current location; • The IP address at which it can be reached. • The mobile host informs HA upon leaving home • HA acts as a proxy to the clients communicating to the mobile host during this time.

5. MobileIP (cont’d) • Foreign agent (FA): • Allocates a temporary IP address to a mobile host upon its arrival to a new site; • Contact HA and supplies it with the contact address for the mobile host (FA’s address). • HA encapsulates original IP packets and sends them to FA. • FA unpacks the packets and delivers them to the mobile host. • HA sends the contact address for the mobile host o the original sender • If the sender is Mobile-enabled it communicates to the FA directly from now on; • If not, the HA continues to act as a proxy for it.

6. TCP and UDP • Provide communication capabilities to the application programs. • IPv6 will support TCP/UDP as well as other connection protocols (remember the Internet Model). • Enable interprocess communication through the use of ports attached to applications. • Port number is included in the header.

7. UDP • Almost transport-level replica of IP. • Offers no guarantee of delivery. • The header is short, but includes an optional checksum for the payload; • The packets that fail the check are dropped.

8. TCP • Provides reliable delivery of arbitrary long sequences of bytes via stream-based programming abstraction. • Connection-oriented; • The sending and the receiving processes establish a communication channel; • Use of ACK (acknowledgement) messages).

9. TCP Reliability Mechanisms • Sequencing: a sequence number is attached to every TCP segment; • Used for message re-assembly at the destination. • Flow control: overflow prevention; • The receiver send an ACK with the highest sequence number in its input stream (no segments before that one have been omitted) and a window size. • Window size specifies the amount of data the sender is permitted to send. • ACK are attached to the backward flow if there is any. • Burstiness of network traffic is smoothed through the use of local buffering an a configurable time-out on it. • Naggle’s algorithm.

10. TCP (cont’d) • Due to the unreliability of wireless networks these mechanisms are not efficient. • Solutions: WAP and modified TCP. • Modified TCP for wireless networks. • Implement a TCP support component at the base station (gateway between wired and wireless networks). • The support component snoops on TCP packets to and from the wireless network • re-transmitting segments that are not promptly acknowledged. • Requesting re-transmission of inbound segments when gaps in sequence numbers are noticed.

11. WAP • Wireless Application Protocol • “An open, global specification that empowers mobile users with wireless devices to easily access and interact with information and services instantly.” - WAP Forum • “The de facto worldwide standard for providing Internet communications and advanced telephony services on digital mobile phones, pagers, personal digital assistants and other wireless terminals.” - WAP Forum (www.wapforum.org)

12. Why is WAP needed? • Traditional internet protocols (HTML, HTTP, TCP, etc.) and their security mechanisms (TLS) are inefficient over mobile networks. • Handheld devices tend to have less powerful CPUs, less memory and more restrictions on power consumption than desktops, so require special considerations. • Handheld devices tend to use input devices other than keyboards (e.g. voice, keypad).

13. Bearer Limitations • Power consumption • increased bandwidth requires increased power. • Cellular network economics • Fixed bandwidth shared among many users, so efficient bandwidth use required. • Latency • wide range of network latencies common (< 1 second to 10s of seconds). • Bandwidth • Less bandwidth than found in wired environments.

14. WAP Forum: www.wapforum.org • WAP Forum founded in December 1997 by Nokia, Ericsson, Motorola and Phone.com (formerly Unwired Planet) • Currently contains over 200 members; • Carriers with more than 100 million subscribers; • Infrastructure providers; • Software developers, and others. • Represent over 95% of the global handset market. • WAP Protocol development • Current WAP Version: 1.2

15. How does WAP work? • Uses client-server model. • Phone incorporates a microbrowser, while the intelligence is in the WAP gateways. • Services and applications reside on servers. • Similar to Java – applications written for WAP, which then run on multiple bearers (e.g. GSM, SMS, USSD, etc.)

16. What works with WAP? • Designed for use with: • All mobile phones; • Any service, e.g. SMS (Short Message Service), CSD (Circuit Switched Data), USSD (Unstructured Supplementary Services Data), GPRS (General Packet Radio Service); • Any network, e.g. CDMA (Code Division Multiple Access), GSM (Global System for Mobiles), UMTS (Universal Mobile Telephone System); • Any input device, e.g. keyboard, stylus, touch screen, keypad.

17. WAP Protocol Model (Stack) Wireless Application Other Services and Application Layer Applications Environment (WAE) Wireless Session Session Layer Protocol (WSP) Wireless Transaction Transaction Layer Protocol (WTP) Wireless Transport Security Layer Layer Security (WTLS) Transport Layer Datagrams (UDP/IP) Datagrams (WDP) Wireless Bearers: Network Layer SMS USSD CSD IS-136 CDMA CDPD Etc… * Source: the WAP White Paper, October 1999.

18. WAP Architecture WAP Gateway Web Server WAP Phone Internet Gateway Web Server Client Encoded request Request Response Encoded response

19. WDP Layer • Wireless Datagram Protocol. • Provides consistent service and common interface to upper layers of the protocol. • Supports: SMS, USSD, CSD, CDPD, IS-136 packet data, and GPRS.

20. WTLS Layer • Wireless Transport Layer Security (TLS). • Implements options for authentication and encryption. • Optimized for mobile environment. • Based on Transport Layer Security (TLS), which was formerly Secure Sockets Layer (SSL). • Optimized for use over narrow-band communication channels. • Ensures data integrity, privacy, authentication and denial-of-service protection.

21. WTP Layer • Wireless Transaction Protocol • Runs on top of datagram service. • Works over both secure and non-secure wireless services. • Features: • Three classes of transaction service • Class 0: for applications requiring an “unreliable push” service • Class 1: for applications requiring a “reliable push” service • Class 2: to provide the basic invoke/response transaction service • Optional user-to-user reliability. • Asynchronous transactions. • PDU (protocol data unit) concatenation and delayed acknowledgements to reduce number of messages sent.

22. WSP Layer • Wireless Session Protocol • Provides consistent interface for both connection-oriented and connectionless services. • Provides the following functionality: • HTTP 1.1 compliance; • Long-lived session state; • Session suspend and resume; • Facility for data “push”.

23. WAE • Wireless Application Environment • Interoperable environment for multiple wireless platforms. • Consists of: • Wireless Markup Language (WML); • WMLScript; • Wireless Telephony Application (WTA); • Content Formats.

24. WML • WAP Mark-up Language • WML is an XML application. • Also uses WMLScript, which is similar to JavaScript. • Optimized for use with handheld devices. • Minimal use of CPU and memory.

25. Benefits of WAP • Reduces amount of data to be transmitted (by translating HTTP headers from text into binary). • Allows sessions to be suspended and resumed. • Provides reliable datagram service without the unnecessary overhead of TCP. • TCP stack is not required on handheld device. • WAP protocol stack requires less packets for interaction than HTTP/TCP/IP. • Support for “push” functionality built into protocol. • WML developers can use standard web tools (e.g. CGI, Perl, ASP, etc.).

26. Drawbacks to WAP • Difficult to configure WAP phones for new WAP services. • Not yet widely supported. • Current services (e.g. SMS, USSD) not optimized for WAP. • Expected to be expensive. • WAP does not support cookies. • Premature encryption endpoint (gateway decrypts data, then forwards via https – see www.gsmworld.com/technology/wap_06.html).

27. Caches and proxy servers • Cache: a store of recently used data objects that is closer than the objects themselves. • When a new object is received it is placed in the cache possibly evicting another object. • When an object is requested, the cache is checked first for an up-to-date copy; • If it’s not available, a fresh copy is fetched. • A cache can be collocated with each client or located on a proxy server. • Proxy server: a machine/process performing tasks on behalf of its clients. • A web proxy server maintains a cache of web resources for its clients; all the requests go though it. • The actual client is transparent for outside servers.

28. DNS • A name service design whose principal database is used across the Internet to perform name resolution for web resources. • A name is resolved when it is translated into data about the named resource or object in order to invoke an action upon it.

29. The Internet Naming Scheme • The Internet support a scheme for the use of symbolic names for hosts and networks. • The named entities are organized into a hierarchy. • The named entities are called domains and the symbolic names are called domain names. • Domains are organized into a hierarchy that intends to reflect organizational structure. • Naming is entirely independent from the network physical layout. • Domain names must be translated into IP • Responsibility of DNS.

30. DNS Operation • Implemented as a server process that can run on host computers anywhere on the Internet. • There are at least 2 DNS servers in each domain. • Servers in each domain hold a partial map of the domain name tree below their domain. • Requests for the translation of domain names outside their portion of the domain tree are handled by issuing requests to DNS servers in the relevant domains; • Recursive procedure that follows from right to left resolving the name in segments. • The resulting translation is then cached at the server handling the original request.

31. DNS and caching • Caching is a key to a name service performance; • Assists in maintaining availability and masking server crashes. • Caching is successful because naming data are changed relatively rarely. • The possibility exists of a name service returning out-of-date attributes during resolution. • DNS allows naming data to become inconsistent; • Stale data might be provided for periods in order of days.

32. Internet and Network Security • Types of Attacks on Internet • Break-ins: Unauthorized attempts to gain access to a secure system • Denial of service: A legitimate user is denied access to a service (e.g. Flooding a WWW server with requests) • Bombs: Large email messages or other large data intended to overwhelm and possibly weaken a system. • Eavesdropping - Listening in on an electronic conversation. Perhaps with intent to gather information for a future break-in. • Viruses.

33. Firewall • Monitors and controls all the traffic into and out of an intranet. • Firewall security policy • Service control: determine which services are available for external access and reject all other requests; • Levels of filtering: IP, TCP. • Example: reject HTTP request unless they are directed to the official website. • Behavioral control: prevent behavior that infringes organization policies; • Levels of filtering: IP, TCP, application; • Example: filtering of ‘spam’ e-mail. • User control: discriminate between users’ privileges; • Example: management of dial-up provided for off-site users.

34. Filtering levels • IP packet filtering • Decisions made based on the destination and the source IP addresses, the service type field in the IP header, port numbers in TCP/UDP headers. • Example: prohibition of external access to NFS servers. • Performed by a process within the operating system kernel of a router. • TCP Gateway • A TCP Gateway process checks TCP connection requests and segment transmission for correctness. • Example: Denial-of-service attack prevention.

35. Filtering levels (cont’d) • Application-level gateway • An application-level gateway process acts as a proxy for an application process. • Example: a Telnet proxy. All telnet requests are routed through the proxy process for approval. • A firewall is a combination of several processes working at different protocol levels running on more than one machine (for fault-tolerance). • Two overall (mutually exclusive) policies: • Anything not explicitly denied is allowed. • Anything not explicitly allowed is denied.

36. Basic Internet Firewalls • A basic firewall is a router (a host with at least 2 network interfaces). • One interface is connected to the Internet - the Host side. • The other(s) is(are) connected to the company's internal network. • Performs IP packet filtering.

37. Advanced Internet Firewalls • When TCP and application-level gateway processes are required, they usually run on another computer: Bastion. • A host located inside the intranet and protected by an IP router/filter, to which it is attached by a Stub LAN. • Stub LAN only has 1 or 2 hosts on it. Not connected to any other company LANs. • A bastion host is connected to both the stub LAN and to the company network

38. Advanced Internet Firewalls (cont’d) • Further protection can be insured by placing another router/filter between the bastion and the company intranet. • Note that for performance reasons company web/ftp severs are placed on the Stub LAN.

39. Virtual Private Networks • Suppose a company wants to connect the intranets of its 5 offices. • One option is to lease a private line. • Another is to connect through the internet. • But then everything is open. • The solution is to use encryption schemes to establish secure tunnels through the internet. • Such a set-up is called a virtual private network.

40. Directory and Discovery Services • Directory service: A service that stores collections of bindings between names and attributes and that looks up entries that match attribute-based specifications. • Example: MS Active Directory Service, UNIX X.500, etc. • Discovery service: a directory service that registers the services in a spontaneous networking environment. • Provides an interface for automatically registering and de-registering services (fax machines, printers, etc.). • Provides a lookup interface for mobile devices • Example: Jini

41. Jini • A system designed for spontaneous networking. • Java-based: assumes that JVMs run on all of the computers, allowing them to communicate through RMI (remote method invocation, a flavor of interprocess communication in an object-oriented environment). • Provides facilities for service discovery, transactions and shared data spaces called JavaSpaces.

42. Jini Directory-Related Component • Lookup service, Jini services and Jini clients. • The lookup service implements what we have termed a discovery service; • Jini uses discovery only for discovering the lookup service itself. • Allows Jini services to register the services they offer and Jini clients to request services that match their requirements. • A Jini service provides an object that provides the service as well as the attributes of the service. • May be registered with several lookup services that store the objects. • Example: printing service.

43. Jini Directory-Related Component (cont’d) • Jini clients query lookup service to find Jini services that match their requirements. • If a match is found they download an object that provides the service from the lookup service. • Bootstrap connectivity: how to find the lookup service upon entering a network. • Solutions: • A priory knowledge of lookup services IP addresses. • Doesn’t scale up. • Use a multicast IP address that is known to all instances of Jini software.

44. Jini Directory-Related Component (cont’d) • When a Jini client or service starts up it sends a request stamped with time-to-live value to a well-known multicast address. • Lookup services listen on a socket bound to this address and replies to a unicast address from which it received the request. • The client can then perform RMI to query the lookup service. • Lookup services sometimes broadcast datagrams announcing their existence to the same multicast address, and client and services listen on it.