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Electronic Commerce (WS-02/03) 3-
Sockets (1)
Several distributed systems are based on sockets, e.g.,
- Network File System (NFS),
- X-Window System,
- Remote Procedure Calls (RPC),
- DCE (Distributed Computing Environment),
- CORBA (Common Object Request Broker Architecture) Middleware Definition A socket is a network communication endpoint. It abstracts from the IP address, the protocol and the port number. There are active sockets and passive sockets:
- An active socket is connected to a remote active socket via an open data connection. Closing the connection closes and removes the active sockets at each endpoint.
- A passive socket is not connected, but rather waits for incoming connection, which will establish a new active connection (create an active socket to the socket from which requested the connection). A socket is associated with a port. Each port can have a single passive socket, awaiting incoming connections, and multiple active sockets, each corresponding to an open connection on the port.
Electronic Commerce (WS-02/03) 3-
Sockets (2)
o Sockets can be realized using different protocols.
- The common socket types use TCP or UDP (User Datagram Protocol) as Transport Protocol.
- Sender and receiver must use the same protocol. TCP IP Network
TCP
IP
virtual communication channel real communication channel Process A (Web Browser) Process B (Web Server) Socket Socket
Electronic Commerce (WS-02/03) 3-
Future of the Internet Protocol (v6)
o Expansion of address space to 128 Bit (2^128 addresses)
- 15% utilization fi Hundreds of IP addresses per human o Unification of addressing o Improved Support for Quality-of-Service (QoS) Parameters:
- Real-time data transmission support via prioritization (0-15)
- Security mechanisms at the protocol level: Encapsulating Security Payload (ESP)
- Selected Routing to commit packets to fixed paths fi uniform latency time o Packet size > 64KB fi performance increase
Electronic Commerce (WS-02/03) 3-
Web Technologies (1)
HTTP: Hypertext Transfer Protocol. Purpose: Accessing resources on the internet (web documents). Clients (browsers) issue requests for resources to a server, the server sends the requested document back to the client as a response. Current version is HTTP/1.1. Purpose Purpose Purpose
**1. Infrastructure
- Target Identification** 3. Service Messaging Proxies, Gateways, Tunnels, Mirrors, Firewalls: Important additional client- and server-side resources on the web used to enhance performance, availability, accessibility and to protect servers, etc. URL: Uniform Resource Locator. Defines the location of a resource on the internet. Example: http://www.sts.tu-harburg.de/teaching/ is a URL. Requests, Responses, Headers, Extensions, Negotiation, etc. regulate the format of messages which communicate service details HTTP Requirements:
Electronic Commerce (WS-02/03) 3-
HTTP Protocol
Simplest form of interaction: Connections may use intermediate stations. We take a deeper look at the following types of intermediate station: o Proxies, Gateways, Tunnels o Mirrors, Firewalls HTTP is a simple request/response protocol that is built on top of a reliable, connection-oriented transport service. It makes use of computers in two roles: client and server. Client sends requests to the server, the server then sends responses to the client. Definition Client Server
- send request to the server
- answer with response
Electronic Commerce (WS-02/03) 3- Proxies can act both as a client proxy and server proxy.
HTTP: Proxies (1)
Proxies act as an intermediate station between client and server. They primarily cache requests in order to increase performance. Definition Client Proxy
- issue request
- send response Server Cache
- [cache hit] lookup
- [cache miss] issue request
- send response
- generate and send response
Electronic Commerce (WS-02/03) 3-
HTTP: Tunnels
Tunnels are “blind” intermediate stations, i.e., they do not cache requests or responses but only forward them. They may consist of several intermediate stations. They can be used to send requests/responses of one protocol over another protocol at the same level. In contrast to protocol layering, protocol tunneling is transparent (Examples: RAS tunneling, NetBEUI over TCP/IP). Reasons for tunneling: Speed, availability, security, etc. Client
- issue request
- send response Server
- issue request
- send response Tunnel Definition
